@phdthesis{Link2020, author = {Link, Yasmin}, title = {3D-Druck mikrofluidischer Systeme mittels Stereolithografie}, doi = {10.25972/OPUS-21152}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-211529}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2020}, abstract = {Der 3D-Druck ist ein elementarer Bestandteil der Biofabrikation. Beispielsweise wird mittels Biotinten und einem geeigneten 3D-Druckverfahren Schicht f{\"u}r Schicht eine Geometrie aufgebaut. Durch die Gestaltung von mikrofluidischen Druckk{\"o}pfen wird eine M{\"o}glichkeit geschaffen multiple Materialans{\"a}tze im Druckkopf zu vermischen und so in einem bestimmten Mischungsverh{\"a}ltnis zu drucken. Mit dem DLP-SLA-Drucker Vida HD Crown and Bridge (EnvisionTEC) und dem Harz E-Shell 600 (EnvisionTEC) wurden zun{\"a}chst die Aufl{\"o}sungsgrenzen des Druckers ermittelt sowie Komponenten f{\"u}r die Realisierung eines mikrofluidischen Druckkopfes prozessiert. Bei den Komponenten handelt es sich zum einen um Geometrien, die beispielsweise als Mischeinheit im Kanal dienen k{\"o}nnen und des Weiteren um senkrechte Kan{\"a}le die Biotinten f{\"u}hren k{\"o}nnen, sowie um Kan{\"a}le, die als Zul{\"a}ufe f{\"u}r den Hauptkanal des mikrofluidischen Druckkopfs dienen k{\"o}nnen. Die Eigenschaften und die technische Realisierbarkeit der gedruckten Objekte wurden eruiert. Dabei wurden die jeweiligen Geometrien und Kanal{\"o}ffnungen vermessen, große Aspektverh{\"a}ltnisse der Geometrien untersucht und die Durchg{\"a}ngigkeit der Kan{\"a}le gepr{\"u}ft. Zuk{\"u}nftig k{\"o}nnen die prozessierten Komponenten f{\"u}r einen mikrofluidischen Druckkopf variabel kombiniert werden und auf dieser Basis weiterf{\"u}hrende Experimente stattfinden.}, subject = {3D-Druck}, language = {de} } @phdthesis{Kreczy2020, author = {Kreczy, Dorothea}, title = {Untersuchung des in vivo Einwachsverhaltens von Zementgranulaten und -pasten aus resorbierbaren Calcium-dotierten Magnesiumphosphat-Phasen}, doi = {10.25972/OPUS-20551}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-205510}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2020}, abstract = {In der vorliegenden Arbeit wurden unterschiedliche zementbasierte Knochenersatzmaterialien hinsichtlich ihres Potentials zur Behandlung kn{\"o}cherner Defekte in vivo untersucht. Zwei verschiedene Calcium-dotierten Magnesiumphosphat Zementformulierungen (CMPC) wurden mit einem Referenzmaterial aus Calciumphosphat Zement (CPC) verglichen. Dazu wurden auf Basis von CMPC pr{\"a}fabrizierte, injizierbare Pasten bzw. sph{\"a}rische Granulate hergestellt und anhand von orthotopen, potenziell kraftbelasteten Defekten in Kaninchenfemora getestet. Zentrales Ziel hierbei war es, herauszufinden, wie sich die Materialien in Defektsituationen mit Hartgewebekontakt biologisch verhalten und degradieren bzw. in Knochen umbauen. Nach einer Liegedauer von 6 bzw. 12 Wochen wurden die Knochenneubildung und die Degradation der Materialien mittels Histomorphometrie analysiert. Alle Materialien waren biokompatibel und f{\"u}hrten zur Bildung von neuem Knochen. Der CMPC-Zement zeigte im Vergleich zu CPC einen beschleunigten Abbau, w{\"a}hrend sich am Referenzmaterial mehr mineralisierter Knochen bildete. Die untersuchten Calcium-dotierten Struvit-bildenden Magnesiumphosphatzemente erwiesen sich als biokompatibel, gut resorbierbar und stellen mit ihrer F{\"a}higkeit zur Knochenbildung ein vielversprechendes Knochenersatzmaterial dar.}, subject = {Knochenzement}, language = {de} } @phdthesis{MeiningergebChrist2018, author = {Meininger [geb. Christ], Susanne}, title = {Processing of calcium and magnesium phosphate cements for bone substitution}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-169126}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2018}, abstract = {The main focus of this thesis was the processing of different calcium and magnesium phosphate cements together with an optimization of mechanical and biological properties. Therefore, different manufacturing techniques like 3D powder printing and centrifugally casting were employed for the fabrication of reinforced or biomedically improved implants. One of the main problems during 3D powder printing is the low green strength of many materials, especially when they are only physically bonded and do not undergo a setting reaction. Such materials need post-treatments like sintering to exhibit their full mechanical performance. However, the green bodies have to be removed from the printer requiring a certain stability. With the help of fiber reinforcement, the green strength of printed gypsum samples could be increased by the addition of polymeric and glass fibers within the printing process. The results showed that fiber reinforcement during 3D powder printing is possible and opens up diverse opportunities to enhance the damage tolerance of green bodies as well as directly printed samples. The transfer to biomedically relevant materials like calcium and magnesium phosphate cements and biocompatible fibers would be the next step towards reinforced patient-specific implants. In a second approach, centrifugally casting derived from construction industries was established for the fabrication of hollow bioceramic cylinders. The aim was the replacement of the diaphysis of long bones, which exhibit a tubular structure with a high density of cortical bone on the fringe. By centrifugation, cement slurries with and without additives could be fabricated to tubes. As a first establishment, the processing parameters regarding the material (e.g. cement composition) as well as the set-up (e.g. rotation times) had to be optimized for each system. In respect of mechanics, such tubes can keep up with 3D powder printed tubes, although the mechanical performance of 3D printed tubes is strongly dependent on printing directions. Additionally, some material compositions like dual setting systems cannot be fabricated by 3D powder printing. Therefore, a transfer of such techniques to centrifugally casting enabled the fabrication of tubular structures with an extremely high damage tolerance due to high deformation ability. A similar effect was achieved by fiber (mesh) addition, as already shown for 3D powder printing. Another possibility of centrifugally casting is the combination of different materials resulting in graded structures to adjust implant degradation or bone formation. This became especially apparent for the incorporation of the antibiotic vancomycin, which is used for the treatment of bacterial implant infections. A long-term release could be achieved by the entrapment of the drug between magnesium phosphate cement layers. Therefore, the release of the drug could be regulated by the degradation of the outer shell, which supports the release into an acidic bacterial environment. The centrifugally casting technique exhibited to be a versatile tool for numerous materials and applications including the fabrication of non-centrosymmetric patient-specific implants for the reconstruction of human long bones. The third project aimed to manufacture strontium-substituted magnesium phosphate implants with improved biological behavior by 3D powder printing. As the promoting effect of strontium on bone formation and the inhibitory impact on bone resorption is already well investigated, the incorporation of strontium into a degradable magnesium phosphate cement promised a fast integration and replacement of the implant. Porous structures were obtained with a high pore interconnectivity that is favorable for cell invasion and bone ingrowth. Despite the porosity, the mechanical performance was comparable to pure magnesium phosphate cement with a high reliability of the printed samples as quantitatively determined by Weibull statistics. However, the biological testing was impeded by the high degradation rate and the relating ion release. The high release of phosphate ions into surrounding media and the detachment of cement particles from the surface inhibited osteoblast growth and activity. To distinguish those two effects, a direct and indirect cell seeding is always required for degradable materials. Furthermore, the high phosphate release compared to the strontium release has to be managed during degradation such that the adverse effect of phosphate ions does not overwhelm the bone promoting effect of the strontium ions. The manufacturing techniques presented in this thesis together with the material property improvement offer a diverse tool box for the fabrication of patient-specific implants. This includes not just the individual implant shape but also the application like bone growth promotion, damage tolerance and local drug delivery. Therefore, this can act as the basis for further research on specific medical indications.}, subject = {Calciumphosphate}, language = {en} } @phdthesis{Ruecker2017, author = {R{\"u}cker, Anja}, title = {Entwicklung eines photochemisch vernetzbaren, methacrylat- und isocyanathaltigen Knochenklebers mit degradierbaren keramischen F{\"u}llstoffen}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-154473}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2017}, abstract = {Bisher getestete Knochenkleber zeigen h{\"a}ufig geringe Klebeeigenschaften auf Knochen bei Zutritt von Feuchtigkeit. Gegenstand dieser Arbeit war es, die Haftf{\"a}higkeit im feuchten Milieu zu verbessern. Hierf{\"u}r wurde der Einfluss sternf{\"o}rmiger, mit Isocyanaten funktionalisierter Poly(ethylenglykol) Molek{\"u}le (NCO-sP(EO-stat-PO)) auf die Klebefestigkeit und Alterungsbest{\"a}ndigkeit einer photopolymerisierbaren Poly(ethylenglykol)dimethacrylat-Basis (PEGDMA) untersucht. Die Polymerisation mittels energiereicher Strahlung erlaubt hohe Reaktionsraten bei K{\"o}rpertemperatur sowie zeitliche und {\"o}rtliche Kontrolle {\"u}ber die Polymerisationsreaktion. Durch den Zusatz degradierbarer, keramischer F{\"u}llstoffe auf Calciumsulfat- und Magnesiumphosphat-Basis in die Matrix sollten durch L{\"o}sungsprozesse Poren geschaffen werden. Diese k{\"o}nnten das Einwachsen neuer Knochensubstanz in das ausgeh{\"a}rtete Material erm{\"o}glichen. Die Ver{\"a}nderungen der kristallinen Strukturen wurden mittels R{\"o}ntgendiffraktometrie beobachtet. Zudem wurden die Proben infrarotspektroskopisch und mikroskopisch untersucht. Die Klebefestigkeit auf kortikalem Rinderknochen im Abscherversuch ebenso wie die Biegefestigkeit vor und nach Lagerung in feuchter Umgebung wurde unter Variation des NCO-sP(EO-stat-PO)-Gehaltes ermittelt. Anschließend sollten die mikroskopische Analyse und energiedispersive R{\"o}ntgenspektrometrie (EDX) Aufschluss {\"u}ber das Bruchverhalten des Materials beim Klebeversuch geben. Es konnte gezeigt werden, dass durch die Zugabe von 20 bis 40 Gew.-\% NCO sP(EO-stat-PO) zur Matrix die Klebefestigkeit auf Knochen von initial etwa 0,15 bis 0,2 MPa auf etwa 0,3 bis 0,5 MPa gesteigert werden kann. W{\"a}hrend alle Referenzproben ihre Haftung an Knochen innerhalb von weniger als 24 Stunden verloren, zeigten Proben mit NCO sP(EO-stat-PO) auch nach 7-t{\"a}giger Lagerung noch Festigkeiten von 0,18 bis 0,25 MPa. Die h{\"o}chste Festigkeit nach 7 Tagen war bei Proben mit dem F{\"u}llstoff Newberyit und einem NCO-sP(EO-stat-PO)-Anteil von 40 Gew.-\% zu verzeichnen. Diese Proben wiesen auch in der mikroskopischen Analyse und im EDX eindeutig ein rein koh{\"a}sives Versagen auf. 20\%-ige Proben zeigten zumindest in geringem Maße auch adh{\"a}sives Versagen. Die 3-Punkt Biegefestigkeit lag initial bei 3,5 bis 5,5 MPa. Durch die Lagerung in PBS sank die Festigkeit auf ~1 MPa. Die Zugabe von NCO-sP(EO-stat-PO) und die Art des eingesetzten F{\"u}llstoffes hatten kaum einen Einfluss auf diese.}, subject = {Isocyanate}, language = {de} } @phdthesis{Stengele2017, author = {Stengele, Anja}, title = {Systematische Analyse der Abbindereaktion von Magnesiumphosphat mit Polyacryls{\"a}ure im Vergleich zu klassischen w{\"a}ssrigen Zementsystemen}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-153871}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2017}, abstract = {Gegenstand der vorliegenden Arbeit war eine systematische Analyse der Ver-arbeitbarkeit, Abbindedauer, pH Wert- und Temperatur-Verl{\"a}ufe w{\"a}hrend des Abbindens und der Eigenschaften der ausgeh{\"a}rteten Zementpaste, welche je-weils aus Farringtonit (Mg3(PO4)2) unterschiedlicher Reaktivit{\"a}t bestand und mit Diammoniumhydrogenphosphat und Polyacryls{\"a}ure zur Reaktion gebracht und konventionellen w{\"a}ssrigen Zementsystemen gegen{\"u}bergestellt wurde. Ein besonderer Fokus wurde hierbei auf die Beurteilbarkeit der Eignung dieser Zementsysteme als injizierbare Zementpasten in m{\"o}glicherweise lasttragenden Bereichen gelegt. Eine Reaktivierung von Farringtonit und anschließendes Ab-binden mit Wasser konnte durch Hochenergiemahlung f{\"u}r 2 h bis 24 h erzielt werden. Mechanisch aktiviertes Farringtonit mit Polyacryls{\"a}ure (100.000 g/mol) bzw. kurzzeitig gemahlenes Farringtonit mit h{\"o}her molekulargewichtiger Polyac-ryls{\"a}ure f{\"u}hrte auf Grund der zum Teil summierten Reaktivit{\"a}t in der sauren Umgebung der Polyacryls{\"a}ure zu einer schlechten Verarbeitbarkeit und unzu-reichenden Druckfestigkeiten. Um chelatisiertes Farringtonit mit angemessenen Festigkeiten zu erhalten, zeigte sich die Anwesenheit von Ammoniumionen als vielversprechende Strategie. Als hydratisierte Produkte wurden je nach Formu-lierung Struvit (MgNH4PO4·6H2O), Newberyit (MgHPO4·3H2O) oder Mag-nesiumphosphathydrat (Mg3(PO4)2·22H2O) gewonnen. Besonders die Kombina-tion von kurzzeitig gemahlenem Farringtonit mit 17,5 Gew.\%iger Poly-acryls{\"a}ure L{\"o}sung und 23,1 Gew.\%iger Diammoniumhydrogenphos-phat L{\"o}sung mit einem Pulver-zu-Fl{\"u}ssigkeitsverh{\"a}ltnis von 1,5 g/ml f{\"u}hrte zu Zementpasten, die hinsichtlich ihres Abbindeverhaltens und der mechanischen Eigenschaften denen der Einzelbestandteile {\"u}berlegen waren. Die entwickelten Zementsysteme zeigten 60 min nach Beginn des Abbindevor-gangs einen pH-Wert von 4,7 bis 6,4 und Temperaturmaxima von 28,5 °C bis 52 °C je nach Zusammensetzung. Der Mischzement, f{\"u}r welchen maximale Druckfestigkeiten von 15,0±4,1 MPa gemessen wurden, zeigte ein deutlich we-niger spr{\"o}des Bruchverhalten im Vergleich zu den reinen Verd{\"u}nnungen. Da der spr{\"o}de Charakter klassischer mineralische Knochenzemente einen limitie-renden Faktor f{\"u}r die Anwendung in lasttragenden Bereichen darstellt, kann dies als deutliche Verbesserung der mechanischen Eigenschaften beurteilt wer-den. Immerhin lagen die erzielten Festigkeitswerte in der Gr{\"o}ßenordnung der humanen Spongiosa. Besonders hervorzuheben ist außerdem der synergisti-sche Effekt, welcher bei Zementformulierungen aus kurzzeitig gemahlenem Farringtonit mit 17,5 Gew.\%iger Polyacryls{\"a}ure L{\"o}sung und 23,1 Gew.\%iger Diammoniumhydrogenphosphat L{\"o}sung mit einem Pulver-zu-Fl{\"u}ssigkeitsver-h{\"a}ltnis von 1,5 g/ml beobachtet werden konnte. Diese Formulierung wies bis zu vierfach h{\"o}here Festigkeitswerte als die Einzelbestandteile auf. Somit bildet das entwickelte Mischzement-System eine gute Basis f{\"u}r weitere Entwicklungen hin zu mechanisch lasttragenden Defekten.}, subject = {Magnesiumphosphate}, language = {de} } @phdthesis{Zipplies2018, author = {Zipplies, Theresa Leonora}, title = {Fluoreszenzmarkierte Nanogele auf Poly(glycidol)-Basis - Herstellung, Charakterisierung und deren Interaktion in vitro}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-162645}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2018}, abstract = {Ziel dieser Arbeit war die Herstellung fluoreszent markierter Pr{\"a}polymere sowie deren Optimierung, die kontrollierte und reproduzierbare Synthese von redox-sensitiven und nicht redox-sensitiven NG mit und ohne Fluoreszenzmarkierung in einem durchschnittlichen Partikelgr{\"o}ßenbereich von 150 - 300 nm und mit einer Konzentration > 10*10 Partikel/ml, die Charakterisierung der NG, ihre Untersuchung bez{\"u}glich ihrer Stabilit{\"a}t und des Assoziationsverhaltens zu BSA sowie die Erlangung von Erkenntnissen bez{\"u}glich des Aufnahmemechanismus der NG in Abh{\"a}ngigkeit vom Transportpeptid Tat. Abschließend kann zusammenfassend gesagt werden: 1. Das große Potential von PG-basierten NG f{\"u}r biologische bzw. medizinische Einsatzgebiete konnte weiter untermauert werden. 2. Das mit Cy5-Alkin markierte PG PG-SH-Cy5 erscheint aufgrund des relativ hohen erreichten Markierungsgrades bei der Herstellung als aussichtsreichster Kandidat f{\"u}r weitere Untersuchungen. Diese Umsetzung besitzt noch Optimierungspotentiale bez{\"u}glich einer Verringerung des Polymerverlusts bei der Aufarbeitung, des erreichbaren Markierungsgrades und der Markierungsausbeute. M{\"o}glichkeiten, dies zu erreichen, wurden diskutiert. 3. Klare Aussagen {\"u}ber den Einfluss des esterhaltigen bzw. esterfreien Ausgangspolymers PG-SH auf die Konzentration und die Partikelgr{\"o}ße konnten aufgrund einer nicht ausreichenden Datenlage nicht getroffen werden. 4. Die esterhaltigen PG-SH-Molek{\"u}le erscheinen aufgrund ihrer Labilit{\"a}t gegen{\"u}ber Hydrolyse f{\"u}r die NP-Synthese weniger geeignet (geringere Stabilit{\"a}t). 5. Die Charakterisierung der aus den markierten und unmarkierten Ausgangspolymeren hergestellten NG, welche teilweise zus{\"a}tzlich mit dem Transportpeptid Tat funktionalisiert wurden, erfolgte mittels NTA und zeigt f{\"u}r die meisten Spezies relativ schmale, gut definierte, monomodale Gr{\"o}ßenverteilungen mit einem Maximum um 100-200 nm im Bereich von ca. 40 - max. 400 nm mit Partikelkonzentrationen im Bereich von 1010 - 1011 Partikeln/ml. 6. Insgesamt konnte gezeigt werden, dass der untersuchte, von PG-SH abgeleitete NP-Typ (z. B. NG_3, redox-sensitiv unmarkiert) aufgrund seiner Einheitlichkeit, Partikelgr{\"o}ße und der Reproduzierbarkeit der Herstellung als gut geeignet f{\"u}r den geplanten Einsatz in biologischen Systemen erscheint. Von den weiter derivatisierten NG erscheinen die folgenden aufgrund der oben geschilderten Kriterien als besonders geeignet f{\"u}r den geplanten Einsatz in biologischen Systemen und weiterer Untersuchungen wert: NG680_(TAT)_1-4 (redox-sensitiv, markiert), NGCy5_(TAT)_1 (redox-sensitiv, markiert), NG_MA_2 (nicht redox-sensitiv, unmarkiert), NGCy7_MA_1 (nicht redox-sensitiv, markiert). Aufgrund des relativ hohen erreichbaren Markierungsgrades bei der Markierung der Ausgangspolymere erscheinen die mit Cy5-markierten Verbindungen als besonders vorteilhaft. 7. Die esterfreien, redox-sensitiven NP erwiesen sich bei 14-t{\"a}giger Lagerung unter physiologischen Bedingungen als stabil. Ihre Konzentration nahm {\"u}ber 14 Tage um ca. 60 \% vom Ausgangswert ab. Gleichzeitig nahm der Teilchendurchmesser w{\"a}hrend des Beobachtungszeitraums um ca. 25 \% zu. Die Abnahme der Teilchenzahl ist - zumindest teilweise - durch eine Vergr{\"o}ßerung des mittleren Teilchendurchmessers und m{\"o}gliche Adsorptionseffekte an die Gef{\"a}ßw{\"a}nde des Versuchsaufbaus zu erkl{\"a}ren. 8. Die Konzentration der esterfreien, nicht redox-sensitiven NP verringert sich bei 14-t{\"a}giger Inkubation unter physiologischen Bedingungen deutlich auf ca. 10 \% des Ausgangswerts. Der mittlere Durchmesser der Partikel bleibt innerhalb des Untersuchungszeitraums innerhalb der Fehlergrenzen konstant. Die starke Abnahme der Partikelkonzentration ist wahrscheinlich auf die Hydrolyse des verwendeten esterhaltigen Crosslinkers PEGDA zur{\"u}ckzuf{\"u}hren. Desweiteren sind Adsorptionsph{\"a}nomene an Oberfl{\"a}chen des Versuchsaufbaus nicht auszuschließen. Insgesamt hervorzuheben ist die wesentlich h{\"o}here Stabili{\"a}t der redox-sensitiven NP unter den Versuchsbedingungen. Diese Substanzklasse sollte daher weiter verfolgt werden. 9. Es wurde gezeigt, dass sowohl die NG, die das Aufnahmeprotein Tat enthalten, als auch die NG ohne Tat mit Fluoreszenz-markiertem BSA (8,3 µg/ml) wechselwirken und zusammen mit diesem bei der Zentrifugation abgeschieden werden. {\"U}ber die Art der Wechselwirkung kann keine Aussage getroffen werden. 10. Durch in vitro Zellaufnahmeuntersuchungen an Hela-Zellen konnte gezeigt werden, dass die mit Tat funktionalisierten, redox-sensitiven, Fluoreszenz-markierten NP von den Zellen aufgenommen werden. Die Aufnahme erfolgt {\"u}ber eine deutlich erkennbare Vesikelbildung, die an der Plasmamembran verst{\"a}rkt beobachtet werden kann. Im Gegensatz hierzu konnte bei den nicht mit Tat funktionalisierten NP keine vergleichbare in vitro Zellaufnahme beobachtet werden. Die Ergebnisse dieser Arbeit best{\"a}tigen insgesamt das große Potential der von Thiol-funktionalisierten PG abgeleiteten NG f{\"u}r die medizinische Forschung und zuk{\"u}nftige Anwendungen in der Diagnostik und Therapie. Es wird eine Reihe von Ansatzpunkten aufgezeigt, auf deren Basis weitere vertiefende Untersuchungen zur Charakterisierung und Optimierung sowie zu zuk{\"u}nftigen nutzbringenden Anwendungen vorgenommen werden sollten.}, subject = {Nanoparticles}, language = {de} } @phdthesis{Hochleitner2018, author = {Hochleitner, Gernot}, title = {Advancing melt electrospinning writing for fabrication of biomimetic structures}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-162197}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2018}, abstract = {In order to mimic the extracellular matrix for tissue engineering, recent research approaches often involve 3D printing or electrospinning of fibres to scaffolds as cell carrier material. Within this thesis, a micron fibre printing process, called melt electrospinning writing (MEW), combining both additive manufacturing and electrospinning, has been investigated and improved. Thus, a unique device was developed for accurate process control and manufacturing of high quality constructs. Thereby, different studies could be conducted in order to understand the electrohydrodynamic printing behaviour of different medically relevant thermoplastics as well as to characterise the influence of MEW on the resulting scaffold performance. For reproducible scaffold printing, a commonly occurring processing instability was investigated and defined as pulsing, or in extreme cases as long beading. Here, processing analysis could be performed with the aim to overcome those instabilities and prevent the resulting manufacturing issues. Two different biocompatible polymers were utilised for this study: poly(ε-caprolactone) (PCL) as the only material available for MEW until then and poly(2-ethyl-2-oxazoline) for the first time. A hypothesis including the dependency of pulsing regarding involved mass flows regulated by the feeding pressure and the electrical field strength could be presented. Further, a guide via fibre diameter quantification was established to assess and accomplish high quality printing of scaffolds for subsequent research tasks. By following a combined approach including small sized spinnerets, small flow rates and high field strengths, PCL fibres with submicron-sized fibre diameters (f{\O} = 817 ± 165 nm) were deposited to defined scaffolds. The resulting material characteristics could be investigated regarding molecular orientation and morphological aspects. Thereby, an alignment and isotropic crystallinity was observed that can be attributed to the distinct acceleration of the solidifying jet in the electrical field and by the collector uptake. Resulting submicron fibres formed accurate but mechanically sensitive structures requiring further preparation for a suitable use in cell biology. To overcome this handling issue, a coating procedure, by using hydrophilic and cross-linkable star-shaped molecules for preparing fibre adhesive but cell repellent collector surfaces, was used. Printing PCL fibre patterns below the critical translation speed (CTS) revealed the opportunity to manufacture sinusoidal shaped fibres analogously to those observed using purely viscous fluids falling on a moving belt. No significant influence of the high voltage field during MEW processing could be observed on the buckling phenomenon. A study on the sinusoidal geometry revealed increasing peak-to-peak values and decreasing wavelengths as a function of decreasing collector speeds sc between CTS > sc ≥ 2/3 CTS independent of feeding pressures. Resulting scaffolds printed at 100 \%, 90 \%, 80 \% and 70 \% of CTS exhibited significantly different tensile properties, foremost regarding Young's moduli (E = 42 ± 7 MPa to 173 ± 22 MPa at 1 - 3 \% strain). As known from literature, a changed morphology and mechanical environment can impact cell performance substantially leading to a new opportunity of tailoring TE scaffolds. Further, poly(L-lactide-co-ε-caprolactone-co-acryloyl carbonate) as well as poly(ε-caprolactone-co-acryloyl carbonate) (PCLAC) copolymers could be used for MEW printing. Those exhibit the opportunity for UV-initiated radical cross-linking in a post-processing step leading to significantly increased mechanical characteristics. Here, single fibres of the polymer composed of 90 mol.\% CL and 10 mol.\% AC showed a considerable maximum tensile strength of σmax = 53 ± 16 MPa. Furthermore, sinusoidal meanders made of PCLAC yielded a specific tensile stress-strain characteristic mimicking the qualitative behaviour of tendons or ligaments. Cell viability by L929 murine fibroblasts and live/dead staining with human mesenchymal stem cells revealed a promising biomaterial behaviour pointing out MEW printed PCLAC scaffolds as promising choice for medical repair of load-bearing soft tissue. Indeed, one apparent drawback, the small throughput similar to other AM methods, may still prevent MEW's industrial application yet. However, ongoing research focusses on enlargement of manufacturing speed with the clear perspective of relevant improvement. Thereby, the utilisation of large spinneret sizes may enable printing of high volume rates, while downsizing the resulting fibre diameter via electrical field and mechanical stretching by the collector uptake. Using this approach, limitations of FDM by small nozzle sizes could be overcome. Thinking visionary, such printing devices could be placed in hospitals for patient-specific printing-on-demand therapies one day. Taking the evolved high deposition precision combined with the unique small fibre diameter sizes into account, technical processing of high performance membranes, filters or functional surface finishes also stands to reason.}, subject = {scaffold}, language = {en} } @phdthesis{Renner2018, author = {Renner, Tobias}, title = {In vitro Testverfahren zur Qualifizierung von Knochenklebstoffen}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-161546}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2018}, abstract = {Knochenklebstoffe, welche eine unkonventionelle M{\"o}glichkeit im Bereich der chirurgischen Frakturversorgung darstellen, m{\"u}ssen bereits in vitro eine Reihe an klinischen Anforderungen erf{\"u}llen. Hinsichtlich entsprechender Pr{\"u}fverfahren wurde noch keine Normierungsarbeit geleistet, weswegen Ergebnisse verschiedener Arbeiten schwierig vergleichbar sind. Ziel der Arbeit war es daher Pr{\"u}fverfahren vorzustellen, welche die Besonderheiten des „Werkstoffes Knochen" ber{\"u}cksichtigen. In diesem Rahmen werden zwei neuartigen Klebstoffsysteme, ein in situ h{\"a}rtender Knochenzement aus Trimagnesiumphosphat, Magnesiumoxid und organischer Phytins{\"a}ure und ein lichth{\"a}rtender Knochenklebstoff aus Polyethylenglycoldimethacrylat, NCO-sP(EO-stat-PO), Campherchinon und anorganischen Newberyit-F{\"u}llern, vorgestellt. Neben diesen sind drei kommerziell erh{\"a}ltliche Klebstoffe Gegenstand der Untersuchung. Dies sind zum einen Histoacryl® und TruGlue® Gewebekleber, zwei Klebstoffe auf Cyanoacrylat-Basis mit unterschiedlich langer Alkyl-Seitenkette, zum anderen Bioglue®, ein Gewebekleber aus Albumin und Glutaraldehyd. Bei den Klebstoffen wurde die Zug- und Scherfestigkeit unter Einfluss der physiologischen Klebstoffalterung, der Variation der Klebefugenbreite, der Variation von komplement{\"a}ren F{\"u}geteilen, sowie F{\"u}geteiloberfl{\"a}chen inspiziert. Makro- und mikroskopische, sowie elektronenmikroskopischen Untersuchung der Bruchfl{\"a}chen auf mikrostrukturelle Besonderheiten und Versagemechanismus wurden angestellt. Die neuartigen Klebstoffsysteme unterliegen zwar den konventionellen Cyanoacrylaten hinsichtlich mechanischer Parameter, weisen aber dennoch ad{\"a}quate Klebefestigkeiten auf bei zugleich zahlreichen Vorteilen gegen{\"u}ber konventionellen Systemen im Umgang mit Knochen. Gerade der Magnesiumphosphatzement scheint auf Grund mechanischer Parameter und Vorz{\"u}gen wie der guten Biokompatibilit{\"a}t und biologischen Abbaubarkeit, Osteoinduktivit{\"a}t, Osteokonduktivit{\"a}t, der einfachen Applizierbarkeit, einem hohen Kosten-Nutzen-Faktor oder dem g{\"u}nstigen Verhalten in w{\"a}ssrigen Milieu vielversprechend.}, subject = {bone}, language = {de} } @phdthesis{Saratsis2018, author = {Saratsis, Vasileios}, title = {Untersuchungen zum Abbindeverhalten und der Injizierbarkeit von Magnesiumphosphat-Knochenzementen}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-158902}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2018}, abstract = {Ziel dieser Arbeit war die experimentelle Untersuchung von selbsth{\"a}rtenden Magnesiumphosphat Zementen als Knochenersatzmaterial bez{\"u}glich der Verarbeitungsqualit{\"a}t, der Temperaturentwicklung beim Abbinden, der Injizierbarkeit und der mechanischen Eigenschaften. Der Schwerpunkt wurde dabei auf die Anpassung der rheologischen Eigenschaften der Zementpaste f{\"u}r eine minimal-invasive Applikation gelegt. Durch eine elektrische Aufladung der Partikeloberfl{\"a}che von Farringtonit nach Adsorption von Citrat-Ionen und Zusatz der biokompatiblen F{\"u}llstoffe Struvit oder TiO2 f{\"u}r die Einstellung einer bimodalen Partikelgr{\"o}ßenverteilung, war es m{\"o}glich, die Viskosit{\"a}t der Pasten zu erniedrigen und den filter-pressing-Effekt w{\"a}hrend der Injektion zu unterdr{\"u}cken. Die Modifikation des Mg3(PO4)2 Pulvers und der fl{\"u}ssigen Phase erlaubte bei einer Verarbeitungszeit von ca. 10 min die nahezu quantitative Injektion des Zements durch eine 40 mm lange Kan{\"u}le mit einem inneren Durchmesser von ca. 800 μm. Zemente mit dem P/L-Verh{\"a}ltnis von 2,0 g/ml erreichten so eine Festigkeit von {\"u}ber 50 MPa nach 24 h Aush{\"a}rtung. Obwohl die exotherme Abbindereaktion der Zemente teilweise zu einer Erw{\"a}rmung auf bis zu 67 °C f{\"u}hrte, geben literaturbekannte in vivo Studien keinen Hinweis auf Nebenwirkungen innerhalb des umliegenden Hart- bzw. Weichgewebes, was den Verdacht einer m{\"o}glichen thermischen Nekrose aufgrund der exothermen Abbindereaktion ausschließt. Dies liegt eventuell auch darin begr{\"u}ndet, dass die Temperaturmessungen in dieser Arbeit mit einer verh{\"a}ltnism{\"a}ßig großen Menge an Zementpaste (∼15 g) durchgef{\"u}hrt wurden, w{\"a}hrend in vivo doch eher geringere Mengen (< 5 g) appliziert werden.}, subject = {Knochenzement}, language = {de} } @phdthesis{Schmitz2016, author = {Schmitz, Tobias}, title = {Functional coatings by physical vapor deposition (PVD) for biomedical applications}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-144825}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2016}, abstract = {Metals are the most used materials for implant devices, especially in orthopedics, but despite their long history of application issues such as material failure through wear and corrosion remain unsolved leading to a certain number of revision surgeries. Apart from the problems associated with insufficient material properties, another serious issue is an implant associated infection due to the formation of a biofilm on the surface of the material after implantation. Thus, improvements in implant technology are demanded, especially since there is a projected rise of implants needed in the future. Surface modification methods such as physical vapour deposition (PVD), oxygen diffusion hardening and electrochemical anodization have shown to be efficient methods to improve the surfaces of metallic bulk materials regarding biomedical issues. This thesis was focused on the development of functional PVD coatings that are suitable for further treatment with surface modification techniques originally developed for bulk metals. The aim was to precisely adjust the surface properties of the implant according to the targeted application to prevent possible failure mechanisms such as coating delamination, wear or the occurrence of post-operative infections. Initially,  tantalum layers with approx 5 µm thickness were deposited at elevated substrate temperatures on cp Ti by RF magnetron sputtering. Due to the high affinity of tantalum to oxygen, these coatings are known to provide a self healing capacity since the rapid oxide formation is known to close surface cracks. Here, the work aimed to reduce the abrupt change of mechanical properties between the hard and brittle coating and the ductile substrate by creating an oxygen diffusion zone. It was found that the hardness and adhesion could be significantly increased when the coatings were treated afterwards by oxygen diffusion hardening in a two step process. Firstly, the surface was oxidized at a pressure of 6.7•10-3 mbar at 350 450 °C, followed by 1-2 h annealing in oxygen-free atmosphere at the same temperature leading to a diffusion of oxygen atoms into deeper parts of the substrate as proved by X-ray diffraction (XRD) analysis. The hereby caused mechanical stress in the crystal lattice led to an increase in Vickers hardness of the Ta layers from 570 HV to over 900 HV. Investigations into the adhesion of oxygen diffusion treated samples by Rockwell measurements demonstrated an increase of critical force for coating delamination from 12 N for untreated samples up to 25 N for diffusion treated samples. In a second approach, the development of modular targets aimed to produce functional coatings by metallic doping of titanium with biologically active agents. This was demonstrated by the fabrication of antimicrobial Ti(Ag) coatings using a single magnetron sputtering source equipped with a titanium target containing implemented silver modules under variation of bias voltage and substrate temperature. The deposition of both Ti and Ag was confirmed by X-ray diffraction and a clear correlation between the applied sputtering parameters and the silver content of the coatings was demonstrated by ICP-MS and EDX. Surface-sensitive XPS measurements revealed that higher substrate temperatures led to an accumulation of Ag in the near-surface region, while the application of a bias voltage had the opposite effect. SEM and AFM microscopy revealed that substrate heating during film deposition supported the formation of even and dense surface layers with small roughness values, which could even be enforced by applying a substrate bias voltage. Additional elution measurements using ICP-MS showed that the release kinetics depended on the amount of silver located at the film surface and hence could be tailored by variation of the sputter parameters. In a final step, the applied Ti and Ti(Ag) coatings deposited on cp Ti, stainless steel (316L) and glass substrates were subsequently nanostructured using a self-ordering process induced by electrochemical anodization in aqueous fluoride containing electrolytes. SEM analysis showed that nanotube arrays could be grown from the Ti and Ti(Ag) coatings deposited at elevated temperatures on any substrate, whereby no influence of the substrate on nanotube morphology could be observed. EDX measurements indicated that the anodization process led to the selective etching of Ti from Ti(Ag) coating. Further experiments on coatings deposited on glass surfaces revealed that moderate substrate temperatures during deposition resulting in smooth Ti layers as determined by AFM measurements, are favorable for the generation of highly ordered nanotube arrays. Such arrays exhibited superhydrophilic behavior as proved by contact angle measurements. XRD analysis revealed that the nanostructured coatings were amorphous after anodization but could be crystallized to anatase structure by thermal treatment at temperatures of 450°C.}, subject = {PVD-Verfahren}, language = {en} } @article{SinnEichlerMuelleretal.2011, author = {Sinn, Stefan and Eichler, Mirjam and M{\"u}ller, Lothar and B{\"u}nger, Daniel and Groll, J{\"u}ergen and Ziemer, Gerhard and Rupp, Frank and Northoff, Hinnak and Geis-Gerstorfer, J{\"u}rgen and Gehring, Frank K. and Wendel, Hans P.}, title = {NCO-sP(EO-stat-PO) Coatings on Gold Sensors-a QCM Study of Hemocompatibility}, series = {Sensors}, volume = {11}, journal = {Sensors}, number = {5}, doi = {10.3390/s110505253}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-141110}, pages = {5253-5269}, year = {2011}, abstract = {The reliability of implantable blood sensors is often hampered by unspecific adsorption of plasma proteins and blood cells. This not only leads to a loss of sensor signal over time, but can also result in undesired host vs. graft reactions. Within this study we evaluated the hemocompatibility of isocyanate conjugated star shaped polytheylene oxide-polypropylene oxide co-polymers NCO-sP(EO-stat-PO) when applied to gold surfaces as an auspicious coating material for gold sputtered blood contacting sensors. Quartz crystal microbalance (QCM) sensors were coated with ultrathin NCO-sP(EO-stat-PO) films and compared with uncoated gold sensors. Protein resistance was assessed by QCM measurements with fibrinogen solution and platelet poor plasma (PPP), followed by quantification of fibrinogen adsorption. Hemocompatibility was tested by incubation with human platelet rich plasma (PRP). Thrombin antithrombin-III complex (TAT), beta-thromboglobulin (beta-TG) and platelet factor 4 (PF4) were used as coagulation activation markers. Furthermore, scanning electron microscopy (SEM) was used to visualize platelet adhesion to the sensor surfaces. Compared to uncoated gold sensors, NCO-sP(EO-stat-PO) coated sensors revealed significant better resistance against protein adsorption, lower TAT generation and a lower amount of adherent platelets. Moreover, coating with ultrathin NCO-sP(EO-stat-PO) films creates a cell resistant hemocompatible surface on gold that increases the chance of prolonged sensor functionality and can easily be modified with specific receptor molecules.}, language = {en} } @phdthesis{Carrera2015, author = {Carrera, Eva-Maria}, title = {Modifikation von Calciumphosphat-Biokeramiken mit biologisch aktiven Metallionen}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-141338}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2015}, abstract = {Das Ziel dieser Arbeit war es, die Modifizierung von por{\"o}sem, calciumdefizit{\"a}rem, nanokristallinem Hydroxylapatit mit verschiedenen Metallionen zu testen. Es wurden α‑TCP‑basierende Zementproben hergestellt, die durch zwei verschiedene Dotierungsmethoden mit bestimmten Metallionen (Cu2+, Co2+, Mn2+, Ni2+, V3+, Zn2+) modifiziert wurden. Die eine Methode bestand in der Zusinterung der entsprechenden Metallionen zum α‑TCP‑Pulver. Bei der anderen Methode waren die Ionen in unterschiedlicher Konzentration (1 mmolar, 100 μmolar, 10 μmolar) in der Binderl{\"o}sung enthalten. Die hergestellten Zementproben wurden hinsichtlich bestimmter Eigenschaften wie der initialen Abbindezeit und Druckfestigkeit untersucht und zus{\"a}tzlich rasterelektronenmikroskopischen, r{\"o}ntgen-diffraktometrischen und massenspektrometrischen Analysen unterzogen. Als Referenz diente ein bereits am Menschen erfolgreich als Knochenersatzmaterial eingesetzter nanokristalliner, calciumarmer Hydroxylapatit-Zement. Da Hydroxylapatit nahezu nur durch Osteoklasten mittels einer lokalen pH‑Wert-Absenkung resorbiert werden kann, wurden in‑vitro‑Versuche mit einer immortalisierten Makrophagen-Zelllinie durchgef{\"u}hrt. {\"U}ber einen 15‑t{\"a}gigen Versuchszeitraum wurde die Zytokompatibilit{\"a}t mittels bestimmter Zellproliferations- und Zellaktivit{\"a}tsmessungen {\"u}berpr{\"u}ft. Zus{\"a}tzlich wurden die mit Zellen besiedelten Proben unter dem Rasterelektronenmikroskop betrachtet und eine TRAP‑F{\"a}rbung durchgef{\"u}hrt, um die Differenzierung zu osteoklasten{\"a}hnlichen Zellen beurteilen zu k{\"o}nnen. Bei der Auswertung der Versuche wurde deutlich, dass nicht das Metall alleine maßgeblich f{\"u}r Ver{\"a}nderungen der physikalischen Eigenschaften im Vergleich zum metallfreien Referenzzement war. Auch die Art der Metallionendotierung, ob durch Zugabe mit der Binderl{\"o}sung oder durch Zusinterung, hatte bei den Metallen unterschiedliche Auswirkungen auf die Zementeigenschaften. W{\"a}hrend der Versuche wurden Abbindezeiten von 18 Minuten bis {\"u}ber 60 Minuten gemessen und Druckfestigkeiten zwischen 9,3 MPa und 30,5 MPa festgestellt. Bei der Auswertung der Zellversuchsreihe wurde festgestellt, dass die Zellen auf den mit Metallionen modifizierten Zementpl{\"a}ttchen tendenziell eine niedrigere Aktivit{\"a}t bei gleich bleibender Proliferation aufwiesen als auf den metallfreien Referenzproben. Dieses Ergebnis konnte mikroskopisch best{\"a}tigt werden.}, subject = {Knochenzement}, language = {de} } @article{GeffersGrollGbureck2015, author = {Geffers, Martha and Groll, J{\"u}rgen and Gbureck, Uwe}, title = {Reinforcement strategies for load-bearing calcium phosphate biocements}, series = {Materials}, volume = {8}, journal = {Materials}, doi = {10.3390/ma8052700}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-148636}, pages = {2700-2717}, year = {2015}, abstract = {Calcium phosphate biocements based on calcium phosphate chemistry are well-established biomaterials for the repair of non-load bearing bone defects due to the brittle nature and low flexural strength of such cements. This article features reinforcement strategies of biocements based on various intrinsic or extrinsic material modifications to improve their strength and toughness. Altering particle size distribution in conjunction with using liquefiers reduces the amount of cement liquid necessary for cement paste preparation. This in turn decreases cement porosity and increases the mechanical performance, but does not change the brittle nature of the cements. The use of fibers may lead to a reinforcement of the matrix with a toughness increase of up to two orders of magnitude, but restricts at the same time cement injection for minimal invasive application techniques. A novel promising approach is the concept of dual-setting cements, in which a second hydrogel phase is simultaneously formed during setting, leading to more ductile cement-hydrogel composites with largely unaffected application properties.}, language = {en} } @phdthesis{Meier2020, author = {Meier, Nadine Karola}, title = {Das kn{\"o}cherne Einwachsen von TiAgN - beschichteten Titanimplantaten im Kaninchenknochen. Eine histologische Analyse.}, doi = {10.25972/OPUS-20741}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-207413}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2020}, abstract = {Infektionen von Endoprothesen sind auch heute noch, obgleich aufgrund aktueller Hygienestandards seltener, eine schwerwiegende Komplikation. Die Folgen k{\"o}nnen risikoreiche Revisionsoperationen bis hin zum kompletten Prothesenverlust sein. Um die Gefahr bakterieller Protheseninfektionen zu minimieren, r{\"u}ckten unter anderem Oberfl{\"a}chenbeschichtungen mit antimikrobieller Wirkung in den Fokus der Forscher. Eine Kombination aus dem antimikrobiell wirksamen Metall Silber und dem die H{\"a}rte verbessernden Stickstoff - als TiAgN - Beschichtung - zeigte bereits gute in vitro Ergebnisse (Moseke et al. 2011). Auf Grundlage dieser positiven in vitro Studie wurde die TiAgN - Beschichtung in der hier vorliegenden Arbeit in vivo im Tiermodell untersucht. Ziel der Studie war es das Einwachsen TiAgN - beschichteter Titanimplantate im Kaninchenknochen mit unbeschichteten Titanimplantaten zu vergleichen. Hierzu wurden bei insgesamt drei Kaninchen jeweils zwei TiAgN - beschichtete Proben und eine unbeschichtete Kontrolle in beide Femora implantiert. Der Einheilzeitraum betrug drei Monate. Nach der Entnahme der Femora wurde zun{\"a}chst durch R{\"o}ntgenaufnahmen die genaue Lage der Implantate festgesellt. Nach der Anfertigung von D{\"u}nnschliffen nach Donath und der Trichrom - F{\"a}rbung nach Masson - Goldner wurden f{\"u}r die histologische Auswertung lichtmikroskopische Bilder in 40 - facher Vergr{\"o}ßerung angefertigt. Um den gesamten Umfang der Implantatanschnitte vermessen zu k{\"o}nnen, wurden die aufgenommen Einzelbilder zu den urspr{\"u}nglichen Gesamtbildern zusammengesetzt. Die Vermessung der Implantatumf{\"a}nge erfolgte hinsichtlich der Untersuchungsparameter Knochen - Implantat - Kontakt (KIK), nicht mineralisierter Knochen (Osteoid), Bindegewebe und Spalten - Implantatoberfl{\"a}chenbereiche an denen kein Gewebe angewachsen ist. F{\"u}r die drei beobachteten Kaninchen ergab sich f{\"u}r die TiAgN - beschichteten Probeimplantate ein KIK von 94,87 \%, ein Osteoidanteil am KIK von 45,15 \% und ein Spaltanteil von 2,82 \% verglichen mit den unbeschichteten Kontrollen von 97,31 \% f{\"u}r den KIK, 60,12 \% f{\"u}r den Osteoid - sowie 2,69 \% f{\"u}r den Spaltanteil. Somit zeigt sich f{\"u}r TiAgN - beschichtete Titanimplantate kein signifikant schlechteres Einwachsen im Vergleich zu unbeschichteten Titanimplantaten. Ausgehend von der guten antimikrobiellen Wirksamkeit und Zytokompatibilit{\"a}t in vitro (Moseke et al. 2011) sowie der guten Osseointegration in vivo pr{\"a}sentiert sich diese Beschichtung sehr vielversprechend. Dennoch sind weitere Untersuchungen erforderlich, wie beispielsweise die {\"U}berpr{\"u}fung der Haftfestigkeit zwischen Beschichtung und Implantat sowie die antimikrobielle Wirksamkeit in vivo. Ergeben sich f{\"u}r diese Beschichtung weiterhin gute Ergebnisse, kann eine Studie am Menschen in Erw{\"a}gung gezogen werden.}, subject = {Beschichtung}, language = {de} } @phdthesis{Wiesbeck2019, author = {Wiesbeck, Christina}, title = {Fabrication and characterization of NCO-sP(EO-stat-PO)- crosslinked and functionalized electrospun gelatin scaffolds for tissue engineering applications}, doi = {10.25972/OPUS-19098}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-190988}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2019}, abstract = {In Tissue Engineering, scaffolds composed of natural polymers often show a distinct lack in stability. The natural polymer gelatin is highly fragile under physiological conditions, nevertheless displaying a broad variety of favorable properties. The aim of this study was to fabricate electrospun gelatin nanofibers, in situ functionalized and stabilized during the spinning process with highly reactive star polymer NCO-sP(EO-stat-PO) ("sPEG"). A spinning protocol for homogenous, non-beaded, 500 to 1000 nm thick nanofibers from different ratios of gelatin and sPEG was successfully established. Fibers were subsequently characterized and tested with SEM imaging, tensile tests, water incubation, FTIR, EDX, and cell culture. It was shown that adding sPEG during the spinning process leads to an increase in visible fiber crosslinking, mechanical stability, and stability in water. The nanofibers were further shown to be biocompatible in cell culture with RAW 264.7 macrophages.}, subject = {Tissue Engineering}, language = {en} } @phdthesis{Bengel2019, author = {Bengel, Melanie}, title = {In vitro Testung neuer Anwendungsformen kalth{\"a}rtender Knochenzemente aus resorbierbaren Orthophosphaten}, doi = {10.25972/OPUS-18643}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-186435}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2019}, abstract = {Ziel der vorliegenden Arbeit war die Herstellung und Erprobung von innovativen Anwendungsformen kalth{\"a}rtender Knochenersatzmaterialien aus Calcium-, und Magnesiumphosphaten, die nach dem Abbindevorgang vorzugsweise aus dem Mineral Struvit (MgNH4PO4·6H2O) bestehen. Diese neuartigen Knochenzemente versprechen im Vergleich zu den herk{\"o}mmlichen Knochenersatzmaterialien eine deutlich schnellere kn{\"o}cherne Regeneration und Abbaubarkeit. Damit wird das Ziel verfolgt schneller Implantate setzen zu k{\"o}nnen und dem Patienten somit eine lange Wartezeit und dementsprechenden Leidensdruck ersparen zu k{\"o}nnen. Ebenso m{\"u}ssen konventionelle Produkte erst im OP anger{\"u}hrt und hiernach in einem schmalen Zeitfenser verarbeitet werden. Die pr{\"a}fabrizierten Zement-Pasten sind dagegen direkt applikationsbereit und h{\"a}rten erst nach Kontakt mit dem feuchten Milieu aus. In vorangegangenen Projekten wurden sowohl pr{\"a}fabrizierte Pasten als auch Granulate auf Basis Struvit-bildender Calcium-Magnesiumphosphate erfolgreich entwickelt. Vorteil dieser Granulate ist ihre sph{\"a}rische Form. Im Hinblick auf die klinische Anwendbarkeit sollten in der vorliegenden Studie beide Anwendungsformen vorgreifend auf eine tierexperimentelle Studie hinsichtlich ihrer Materialeigenschaften in vitro getestet werden.}, subject = {Knochenzemente}, language = {de} } @phdthesis{Wistlich2019, author = {Wistlich, Laura}, title = {NCO-sP(EO-stat-PO) as functional additive for biomaterials' development}, doi = {10.25972/OPUS-17836}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-178365}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2019}, abstract = {The aim of this thesis was the application of the functional prepolymer NCO-sP(EO-stat-PO) for the development of new biomaterials. First, the influence of the star-shaped polymers on the mechanical properties of biocements and bone adhesives was investigated. 3-armed star-shaped macromers were used as an additive for a mineral bone cement, and the influence on the mechanical properties was studied. Additionally, a previously developed bone adhesive was examined regarding cytocompatibility. The second topic was the examination of novel functionalization steps which were performed on the surface of electrospun fibers modified with NCO-sP(EO-stat-PO). This established method of functionalizing electrospun meshes was advanced regarding the modification with proteins which was then demonstrated in a biological application. Two different kinds of antibodies were immobilized on the fiber surface in a consecutive manner and the influence of these proteins on the cell behavior was investigated. The final topic involved the quantification of surface-bound peptide sequences. By functionalization of the peptides with the UV-reactive molecule 2-mercaptopyridine it was possible to quantify this compound via UV measurements by cleavage of disulfide bridges and indirectly draw conclusions about the number of immobilized peptides. In the field of mineral biocements and bone adhesives, NCO-sP(EO-stat-PO) was able to influence the setting behavior and mechanical performance of mineral bone cements based on calcium phosphate chemistry. The addition of NCO-sP(EO-stat-PO) resulted in a pseudo-ductile fracture behavior due to the formation of a hydrogel network in the cement, which was then mineralized by nanosized hydroxyapatite crystals following cement setting. Accordingly, a commercially available aluminum silicate cement from civil engineering could be modified. In addition, it could be shown that the use of NCO-sP(EO-stat-PO) is beneficial for adjusting specific material properties of bone adhesives. Here, the crosslinking behavior of the prepolymer in an aqueous medium was exploited to form an interpenetrating network (IPN) together with a photochemically curing poly(ethylene glycol) dimethacrylate (PEGDMA) matrix. This could be used for the development of a bone adhesive with an improved adhesion to bone in a wet environment. The developed bone adhesive was further investigated in terms of possible influences of the initiator systems. In addition, the material system was tested for cytocompatibility by using different cell lines. Moreover, the preparation of electrospun fiber meshes via solution electrospinning consisting of poly(lactide-co-glycolide) (PLGA) as a backbone polymer and NCO-sP(EO-stat-PO) as functional additive is an established method for the application of the meshes as a replacement of the native extracellular matrix (ECM). In general, these fibers reveal diameters in the nanometer range, are protein and cell repellent due to the hydrophilic properties of the prepolymer and show a specific biofunctionalization by immobilization of peptide sequences. Here, the isocyanate groups presented on the fiber surface after electrospinning were used to carry out various functionalization steps, while retaining the properties of protein and cell repellency. The modification of the electrospun fibers involved the immobilization of analogs or antagonists of tumor necrosis factor (TNF) and the indirect detection of these by interaction with a light-producing enzyme. Here, a multimodal modification of the fiber surface with RGD to mediate cell adhesion and two different antibodies could be achieved. After culturing the cell line HT1080, the pro- or anti-inflammatory response of cells could be detected by IL-8 specific ELISA measurements. Furthermore, the quantification of molecules on the surface of electrospun fibers was investigated. It was tested whether the detection by means of super-resolution microscopy would be possible. Therefore, experiments were performed with short amino acid sequences such as RGD for quantification by fluorescence microscopy. Based on earlier results, in which a UV-spectrometrically active molecule was used to detect the quantification of RGD, it was shown that short peptides can also be quantified in a small scale on flat functional substrates (2D) such as NCO-sP(EO-stat-PO) hydrogel coatings, and modified electrospun fibers produced from PLGA and NCO-sP(EO-stat-PO) (3D). In addition, a collagen sequence was used to prove that a successful quantification can be carried out as well for longer peptide chains. These studies have revealed that NCO-sP(EO-stat-PO) can serve as a functional additive for many applications and should be considered for further studies on the development of novel biomaterials. The rapid crosslinking reaction, the resulting hydrogel formation and the biocompatibility are to be mentioned as positive properties, which makes the prepolymer interesting for future applications.}, subject = {Sternpolymere}, language = {en} } @phdthesis{SchaefergebStichler2019, author = {Sch{\"a}fer [geb. Stichler], Simone}, title = {Thiol-ene Cross-linked Poly(glycidol) / Hyaluronic Acid Based Hydrogels for 3D Bioprinting}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-174713}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2019}, abstract = {The aim of the work was the development of thiol-ene cross-linked hydrogels based on functionalized poly(glycidol)s (PG) and hyaluronic acid (HA) for extrusion based 3D bioprinting. Additionally, the functionalization of the synthesized PG with peptides and the suitability of these polymers for physically cross-linked gels were investigated, in a proof of principle study in order to demonstrate the versatile use of PG polymers in hydrogel development. First, the precursor polymers of the different hydrogel systems were synthesized. For thiol-ene cross-linked hydogels, linear allyl-functionalized PG (P(AGE-co-G)) and three different thiol-(SH-)functionalized polymers, ester-containing PG-SH (PG SHec), ester-free PG-SH (PG-SHef) and HA-SH were synthesized and analysed, The degree of functionalization of these polymers was adjustable. For physically cross-linked hydrogels, peptide-functionalized PG (P(peptide-co-G)), was synthesized through polymer analogue thiol-ene modification of P(AGE-co-G). Subsequently, thiol-ene cross-linked hydrogels were prepared with the synthesized thiol- and allyl-functionalized polymers. Depending on the origin of the used polymers, two different systems were obtained: on the one hand synthetic hydrogels consisting of PG-SHec/ef and P(AGE-co-G) and on the other hand hybrid gels, consisting of HA-SH and P(AGE-co-G). In synthetic gels, the degradability of the gels was determined by the applied PG-SH. The use of PG-SHec resulted in hydrolytically degradable hydrogels, whereas the cross-linking with PG-SHef resulted in non-degradable gels. The physical properties of these different hydrogel systems were determined by swelling, mechanical and diffusion studies and subsequently compared among each other. In swelling studies the differences of degradable and non-degradable synthetic hydrogels as well as the differences of synthetic compared to hybrid hydrogels were demonstrated. Next, the stiffness and the swelling ratios (SR) of the established hydrogel systems were examined in dependency of different parameters, such as incubation time, polymer concentration and UV irradiation. In general, these measurements revealed the same trends for synthetic and hybrid hydrogels: an increased polymer concentration as well as prolonged UV irradiation led to an increased network density. Moreover, it was demonstrated that the incorporation of additional non-bound HMW HA hampered the hydrogel cross-linking resulting in gels with decreased stiffness and increased SR. This effect was strongly dependent on the amount of additional HMW HA. The diffusion of different molecular weight fluorescein isothiocyanate-dextran (FITC-dextran) through hybrid hydrogels (with/without HMW HA) gave information about the mesh size of these gels. The smallest FITC-dextran (4 kDa) completely diffused through both hydrogel systems within the first week, whereas only 55 \% of 40 kDa and 5-10 \% HMW FITC-dextrans (500 kDa and 2 MDa) could diffuse through the networks. The applicability of synthetic and hybrid hydrogels for cartilage regeneration purpose was investigated through by biological examinations. It was proven that both gels support the survival of embedded human mesenchymal stromal cells (hMSCs) (21/28 d in vitro culture), however, the chondrogenic differentiation was significantly improved in hybrid hydrogels compared to synthetic gels. The addition of non-bound HMW HA resulted in a slightly less distinct chondrogenesis. Lastly the printability of the established hydrogel systems was examined. Therefore, the viscoelastic properties of the hydrogel solutions were adjusted by incorporation of non-bound HMW HA. Both systems could be successfully printed with high resolution and high shape fidelity. The introduction of the double printing approach with reinforcing PCL allowed printing of hydrogel solutions with lower viscosities. As a consequence, the amount of additional HMW HA necessary for printing could be reduced allowing successful printing of hybrid hydrogel solutions with embedded cells. It was demonstrated that the integrated cells survived the printing process with high viability measured after 21 d. Moreover, by this reinforcing technique, robust hydrogel-containing constructs were fabricated. In addition to thiol-ene cross-linked hydrogels, hydrogel cross-linking via ionic interactions was investigated with a hybrid hydrogel based on HMW HA and peptide-functionalized PG. Rheological measurements revealed an increase in the viscosity of a 2 wt.\% HMW HA solution by the addition of peptide-functionalized PG. The increase in viscosity could be attributed to the ionic interactions between the positively charge PG and the negatively charge HMW HA. In conclusion, throughout this thesis thiol-ene chemistry and PG were introduced as promising cross-linking reaction and polymer precursor for the field of biofabrication. Furthermore, the differences of hybrid and synthetic hydrogels as well as chemically and physically cross-linked hydrogels were demonstrated. Moreover, the double printing approach was demonstrated to be a promising tool for the fabrication of robust hydrogel-containing constructs. It opens the possibility of printing hydrogels that were not printable yet, due to too low viscosities.}, subject = {Hyalurons{\"a}ure}, language = {en} } @phdthesis{Behets2018, author = {Behets, Jean Nicolas}, title = {Biomimetic calcium phosphate modification of 3D-printed tissue engineering scaffolds using reactive star-shaped macromers}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-171728}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2018}, abstract = {Biomimetic calcium phosphate (CaP) coatings imitate the trabecular bones surface structure and have shown to promote osteogenic differentiation in multipotent cells. The work of this thesis focused on the problem of former CaP coatings cracking and flaking off when being put on a bendable core structure like a 3D-printed poly (ε-caprolactone) (PCL) scaffold. The aim was to provide a chemical linkage between PCL and CaP using a star-shaped polymer (sPEG) and a phosphonate, 2-aminoethylphosphonic acid (2-AEP). First, a published CaP coating protocol was revised and investigated in terms of etching parameters for the PCL scaffold. Results presented reproducible thick coatings for all groups. The protocol was then broadened to include subsequent scaffold incubation in sPEG and 2-AEP solutions. Homogenous CaP coatings of decreased thickness presented themselves, proving feasibility. However, as is often found with physical CaP coating depositions, there were some irregular outcomes even during the same experimental group. A lower consumption of the chemical 2-AEP, for economic reasons, meant that the protocol was altered to simultaneously incubate scaffolds with sPEG and 2-AEP including preceding calculations for molar ratios. For ratios 1:1, 1:2 and 1:3, again a homogenous CaP coating was produced on most of the samples, although reproducibility issues maintained. However, the mechanical bending to induce surface cracking showed that the CaP did strongly bond to the sPEG/2-AEP, while the control CaP coating flaked off the surface in large pieces. This research demonstrates that chemically-bound CaP coatings resist flaking off the fiber surface. Future investigations should focus on the mechanisms of CaP crystallization, to improve reproducibility.}, subject = {Tissue engineering}, language = {en} } @phdthesis{Juengst2019, author = {J{\"u}ngst, Tomasz}, title = {Establishing and Improving Methods for Biofabrication}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-173444}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2019}, abstract = {Die Biofabrikation ist ein junges und sehr dynamisches Forschungsgebiet mit viel Potential. Dieses Potential spiegelt sich unter anderem in den ambitionierten Zielen wieder, die man sich hier gesetzt hat. Wissenschaftler in diesem Gebiet wollen eines Tages beispielsweise funktionale menschliche Gewebe nachbilden, die aus patienteneigenen Zellen bestehen. Diese Gewebe sollen entweder f{\"u}r die Testung neuer Arzneimittel und Therapien oder sogar als Implantate einsetzt werden. Der Schl{\"u}ssel zum Erfolg soll hier die Verwendung automatisierter Prozesse in Verbindung mit innovativen Materialien sein, die es erm{\"o}glichen, die Hierarchie und Funktion des zu ersetzenden nat{\"u}rlichen Gewebes nachbilden. Obwohl in den letzten Jahren große Fortschritte gemacht worden sind, gibt es immer noch H{\"u}rden, die {\"u}berwunden werden m{\"u}ssen. Ziel dieser Arbeit war es deshalb, die derzeit eingeschr{\"a}nkte Auswahl kompatibler Materialien f{\"u}r die Biofabrikation zu erweitern und bereits etablierte Verfahren wie den extrusionsbasierten Biodruck noch besser verstehen zu lernen. Auch neue Verfahren, wie etwa das Melt Electrospinning Writing (MEW) sollten etabliert werden. In Kapitel 3 dieser Arbeit wurde das MEW dazu verwendet, tubul{\"a}re Strukturen zu fertigen, die sich aus Polymerfasern mit einem durchschnittlichen Durchmesser von nur etwa 12 μm zusammensetzen. Die mit Hilfe von Druckluft in Verbindung mit einer hohen elektrischen Spannung aus einer Nadelspitze austretende Polymerschmelze wurde hierbei auf zylinderf{\"o}rmigen Kollektoren mit Durchmessern zwischen 0.5 und 4.8mm gesammelt. Auf diese Weise wurden r{\"o}hrenf{\"o}rmige Faserkonstrukte generiert. Das Hauptaugenmerk lag auf dem Einfluss des Durchmessers, der Rotations- und Translationsbewegung des Kollektors auf die Morphologie der Faserkonstrukte. Hierzu wurden die Fasern erst auf unbewegten Kollektoren mit unterschiedlichen Durchmessern gesammelt und die entstehenden Muster analysiert. Es zeigte sich, dass das Fasermuster mit zunehmendem Durchmesser des Kollektors mehr den symmetrischen Konstrukten mit runder Grundfl{\"a}che glich, die auch von flachen Kollektoren bekannt sind. Je kleiner der Kollektordurchmesser wurde, desto ovaler wurde die Grundfl{\"a}che der Muster, was den Einfluss der Kr{\"u}mmung deutlich machte. In weiteren Experimenten wurden die zylindrischen Kollektoren mit Geschwindigkeiten von 4,2 bis 42 Umdrehungen pro Minute um ihre L{\"a}ngsachse gedreht. Die von flachen Kollektoren bekannten {\"U}berg{\"a}nge der Fasermorphologie konnten auch f{\"u}r runde Kollektoren best{\"a}tigt werden. So {\"a}nderte sich die Morphologie mit zunehmender Geschwindigkeit der Oberfl{\"a}che von einer achterf{\"o}rmigen Gestalt {\"u}ber eine sinusf{\"o}rmige Ausrichtung der Fasern hin zu einer geraden Linie. Der Einfluss des Kollektordurchmessers wurde auch hier deutlich, da sich etwa die Amplitude der bei Rotationsgeschwindigkeiten im Bereich sinusf{\"o}rmiger Ausrichtung abgelegten Fasern mit abnehmendem Radius erh{\"o}hte. Im n{\"a}chsten Schritt wurde neben der Rotation der Kollektoren auch eine Translation induziert. Durch geeignete Kombination von Rotation und Translation konnten Konstrukte mit definiertem Wickelwinkel hergestellt werden. Es zeigte sich, dass die Wiedergabe des vorher kalkulierten Winkels unter Verwendung von Oberfl{\"a}chengeschwindigkeiten, die nahe am {\"U}bergang zur geraden Faserausrichtung waren, am besten war. Im Rahmen dieser Arbeit konnten Winkel zwischen 5 und 60° mit hoher Pr{\"a}zision wiedergegeben werden. Im Falle von sich wiederholenden Mustern konnte auch in Bezug auf die Stapelbarkeit der Fasern aufeinander eine hohe Pr{\"a}zision erreicht werden. Kapitel 4 dieser Arbeit befasste sich mit dem extrusionsbasierten 3D-Druck. Das etabliere Verfahren wurde auf eine bisher wenig untersuchte Materialzusammensetzung von Nanopartikeln-beladenen Hydrogeltinten ausgeweitet. Die Tinte bestand aus einer Kombination von funktionalisierten Polyglyzidolen und einer unmodifizierten langkettingen Hyalurons{\"a}ure. Dieser wurden mesopor{\"o}se Silika-Nanopartikel mit unterschiedlicher Ladung zugesetzt und deren Freisetzung aus gedruckten Konstrukten mit einstellbarer Geometrien untersucht. Da die Hyalurons{\"a}ure selbst negativ geladen ist, wurde erwartet und auch gezeigt, dass aminofunktionalisierte Partikel mit positiver Ladung langsamer freigesetzt werden als carboxylfunktionalisierte Partikel mit negativer Ladung. Interessanterweise {\"a}nderten die Partikel nicht die rheologischen Eigenschaften der Tinte und es konnten Hydrogele, die mit positiv geladenen Partikeln beladen waren, bei den gleichen Druckparametern verdruckt werden, wie Hydrogele, die mit negativ geladenen Partikeln beladen waren. Die guten Druckeigenschaften der Tinten erm{\"o}glichten die pr{\"a}zise Fertigung von Konstrukten mit einer Gr{\"o}ße von 12x12x3mm^3, also von Konstrukten mit bis zu 16 aufeinanderfolgenden Lagen. Die Strangdurchmesser betrugen hierbei 627±31μm und die Verteilung der Partikel innerhalb der Str{\"a}nge war sehr homogen. Zudem konnten auch Strukturen gedruckt werden, bei denen beide Tintenarten, mit positiven und mit negativen Partikeln beladene Hydrogele, in einem Konstrukt kombiniert wurden. Hierbei zeigte sich, dass die Freisetzung der Partikel, die {\"u}ber 6 Wochen hinweg untersucht wurde, auch stark von der Geometrie der zwei-Komponenten-Konstrukte abhing. Insbesondere die Auswirkung des direkten Kontakts zwischen den Komponenten innerhalb eines Konstruktes war hier sehr deutlich. Wurden die Str{\"a}nge {\"u}ber Kreuz aufeinander abgelegt und hatten direkten Kontakt an den Kreuzungspunkten, konnte beobachtet werden, dass die positiv geladenen Partikel aus ihrem System in das mit den negativ geladenen Partikeln wanderten. Wurden die Str{\"a}nge ohne direkten Kontakt parallel nebeneinander abgelegt, wurden die positiv geladenen Partikel in umgebendes Medium freigesetzt, konnten aber selbst nach 6 Wochen nicht in den Str{\"a}ngen mit den negativ geladenen Partikeln nachgewiesen werden. Dies verdeutlicht, dass Geometrie und Ladung der Partikel einen Einfluss auf die Freisetzung der Partikel hatten und sich die Freisetzung der Partikel durch eine geschickte Kombination beider Parameter steuern l{\"a}sst. In Kapitel 5 dieser Arbeit wurde eine neue Materialklasse als Biotinte f{\"u}r den extrusionsbasierten Biodruck untersucht. Bei dem Material handelte es sich um Hydrogele auf Basis rekombinanter Spinnenseidenproteine. Diese konnten ab einer Proteinkonzentration von 3 \%Gew./Vol. ohne die Verwendung von Verdickungsmittel oder anderen Additiven und auch ohne eine nachtr{\"a}gliche Vernetzung verdruckt werden. Sowohl Hydrogele auf Basis des rekombinanten Proteins eADF4(C16) als auch eine mit einer RGD-Sequenz versehene Modifikation (eADF4(C16)-RGD) konnten mit einer hohen Formtreue verdruckt werden. Die RGD-Sequenz zeigte einen positiven Effekt auf das Anhaften von humanen Fibroblasten, die auf gedruckte Konstrukte ausges{\"a}t wurden. Zudem konnten mit Hilfe der Hydrogele auch zellbeladene Konstrukte gefertigt werden. Hierzu wurden die Hydrogele mit einer Zellsuspension so vermengt, dass eine finale Konzentration von 1,2 Millionen Zellen/ml erreicht wurde. Die beladenen Gele wurden verdruckt und es konnte eine {\"U}berlebensrate von 70,1±7,6\% nachgewiesen werden. Das in diesem Kapitel etablierte Materialsystem erm{\"o}glichte zum ersten Mal das Verdrucken lebender Zellen in einer neuen Klasse von Tinten, die weder die Beimengung von Verdickungsmittel noch einen zus{\"a}tzlichen Nachh{\"a}rtungsschritt f{\"u}r die Herstellung zellbeladener stabiler Konstrukte ben{\"o}tigt.}, subject = {3D-Druck}, language = {en} } @phdthesis{Feineis2018, author = {Feineis, Susanne}, title = {Thioether-poly(glycidol) as multifunctional coating system for gold nanoparticles}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-172902}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2018}, abstract = {The aim of this thesis was the development of a multifunctional coating system for AuNPs based on thioether polymers, providing both excellent colloidal stability and a variable possibility to introduce functionalities for biological applications. First, two thioether-polymer systems were synthesised as a systematic investigation into colloidal stabilisation efficacy. Besides commonly used monovalent poly(ethylene glycol) (PEG-SR), its structural analogue linear poly(glycidol) (PG-SR) bearing multiple statistically distributed thioether moieties along the backbone was synthesised. Additionally, respective thiol analogues (PEG-SH and PG-SH) were produced and applied as reference. Successive modification of varyingly large AuNPs with aforementioned thiol- and thioether-polymers was performed via ligand exchange reaction on citrate stabilised AuNPs. An increased stabilisation efficacy of both thioether-polymers against biological and physiological conditions, as well as against freeze-drying compared to thiol analogues was determined. Based on the excellent colloidal stabilisation efficacy and multi-functionalisability of thioether-PG, a plethora of functional groups, such as charged groups, hydrophilic/hydrophobic chains, as well as bio-active moieties namely diazirine and biotin was introduced to the AuNP surface. Moreover, the generic and covalent binding of diazirine-modified PG-SR with biomolecules including peptides and proteins was thoroughly demonstrated. Lastly, diverse applicability and bioactivity of aforementioned modified particles in various studies was displayed, once more verifying the introduction of functionalities. On the one hand the electrostatic interaction of charged AuNPs with hydrogels based on hyaluronic acid was applied to tune the release kinetics of particles from three-dimensional scaffolds. On the other hand the strong complexation of siRNA onto two positively charged AuNPs was proven. The amount of siRNA payload was tuneable by varying the surface charge, ionic strength of the surrounding medium and the N/P ratio. Moreover, the biological activity and selectivity of the biotin-streptavidin conjugation was verified with respectively functionalised particles in controlled agglomeration test and in laser-triggered cell elimination experiments. In the latter, streptavidin-functionalised AuNPs resulted in excellent depletion of biotinylated cells whereas unfunctionalised control particles failed, excluding unspecific binding of these particles to the cell surface.}, subject = {Nanopartikel}, language = {en} } @phdthesis{Stuckensen2016, author = {Stuckensen, Kai}, title = {Fabrication of hierarchical cell carrier matrices for tissue regeneration by directional solidification}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-145510}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2016}, abstract = {The key hypothesis of this work represented the question, if mimicking the zonal composition and structural porosity of musculoskeletal tissues influences invading cells positively and leads to advantageous results for tissue engineering. Conventional approaches in tissue engineering are limited in producing monolithic "scaffolds" that provide locally variating biological key signals and pore architectures, imitating the alignment of collagenous fibres in bone and cartilage tissues, respectively. In order to fill this gap in available tissue engineering strategies, a new fabrication technique was evolved for the production of scaffolds to validate the hypothesis. Therefore, a new solidification based platform procedure was developed. This process comprises the directional solidification of multiple flowable precursors that are "cryostructured" to prepare a controlled anisotropic pore structure. Porous scaffolds are attained through ice crystal removal by lyophilisation. Optionally, electrostatic spinning of polymers may be applied to provide an external mesh on top or around the scaffolds. A consolidation step generates monolithic matrices from multi zonal structures. To serve as matrix for tissue engineering approaches or direct implantation as medical device, the scaffold is sterilized. An Adjustable Cryostructuring Device (ACD) was successively developed; individual parts were conceptualized by computer aided design (CAD) and assembled. During optimisation, a significant performance improvement of the ACDs accessible external temperature gradient was achieved, from (1.3 ± 0.1) K/mm to (9.0 ± 0.1) K/mm. Additionally, four different configurations of the device were made available that enabled the directional solidification of collagenous precursors in a highly controlled manner with various sample sizes and shapes. By using alginate as a model substance the process was systematically evaluated. Cryostructuring diagraphs were analysed yielding solidification parameters, which were associated to pore sizes and alignments that were determined by image processing. Thereby, a precise control over pore size and alignment through electrical regulation of the ACD could be demonstrated. To obtain tissue mimetic scaffolds for the musculoskeletal system, collagens and calcium phosphates had to be prepared to serve as raw materials. Extraction and purification protocols were established to generate collagen I and collagen II, while the calcium phosphates brushite and hydroxyapatite were produced by precipitation reactions. Besides the successive augmentation of the ACD also an optimization of the processing steps was crucial. Firstly, the concentrations and the individual behaviour of respective precursor components had to be screened. Together with the insights gained by videographic examination of solidifying collagen solutions, essential knowledge was gained that facilitated the production of more complex scaffolds. Phenomena of ice crystal growth during cryostructuring were discussed. By evolutionary steps, a cryostructuring of multi-layered precursors with consecutive anisotropic pores could be achieved and successfully transferred from alginate to collagenous precursors. Finally, very smooth interfaces that were hardly detectable by scanning electron microscopy (SEM) could be attained. For the used collagenous systems, a dependency relation between adjustable processing parameters and different resulting solidification morphologies was created. Dehydrothermal-, diisocyanate-, and carbodiimide- based cross linking methods were evaluated, whereby the "zero length" cross linking by carbodiimide was found to be most suitable. Afterwards, a formulation for the cross linking solution was elaborated, which generated favourable outcomes by application inside a reduced pressure apparatus. As a consequence, a pore collapse during wet chemical cross linking could be avoided. Complex monolithic scaffolds featuring continuous pores were fabricated that mimicked structure and respective composition of different areas of native tissues by the presence of biochemical key stimulants. At first, three types of bone scaffolds were produced from collagen I and hydroxyapatite with appropriate sizes to fit critical sized defects in rat femurs. They either featured an isotropic or anisotropic porosity and partly also contained glycosaminoglycans (GAGs). Furthermore, meniscus scaffolds were prepared by processing two precursors with biomimetic contents of collagen I, collagen II and GAGs. Here, the pore structures were created under boundary conditions, which allowed an ice crystal growth that was nearly orthogonal to the external temperature gradient. Thereby, the preferential alignment of collagen fibres in the natural meniscus tissue could be mimicked. Those scaffolds owned appropriate sizes for cell culture in well plates or even an authentic meniscus shape and size. Finally, osteochondral scaffolds, sized to either fit well plates or perfusion reactors for cell culture, were fabricated to mimic the composition of subchondral bone and different cartilage zones. Collagen I and the resorbable calcium phosphate brushite were used for the subchondral zone, whereas the cartilage zones were composed out of collagen I, collagen II and tissue mimetic contents of GAGs. The pore structure corresponded to the one that is dominating the volume of natural osteochondral tissue. Energy dispersive X-ray spectroscopy (EDX) and SEM were used to analyse the composition and pore structure of the individual scaffold zones, respectively. The cross section pore diameters were determined to (65 ± 25) µm, (88 ± 35) µm and(93 ± 42) µm for the anisotropic, the isotropic and GAG containing isotropic bone scaffolds. Furthermore, the meniscus scaffolds showed pore diameters of (93 ± 21) µm in the inner meniscus zone and (248 ± 63) µm inside the outer meniscus zone. Pore sizes of (82 ± 25) µm, (83 ± 29) µm and (85 ± 39) µm were present inside the subchondral, the lower chondral and the upper chondral zone of osteochondral scaffolds. Depending on the fabrication parameters, the respective scaffold zones were also found to feature a specific micro- and nanostructure at their inner surfaces. Degradation studies were carried out under physiological conditions and resulted in a mean mass loss of (0.52 ± 0.13) \%, (1.56 ± 0.10) \% and (0.80 ± 0.10) \% per day for bone, meniscus and osteochondral scaffolds, respectively. Rheological measurements were used to determine the viscosity changes upon cooling of different precursors. Micro computer tomography (µ-CT) investigations were applied to characterize the 3D microstructure of osteochondral scaffolds. To obtain an osteochondral scaffold with four zones of tissue mimetic microstructure alignment, a poly (D, L-lactide-co-glycolide) mesh was deposited on the upper chondral zone by electrostatic spinning. In case of the bone scaffolds, the retention / release capacity of bone morphogenetic protein 2 (BMP-2) was evaluated by an enzyme linked immunosorbent assay (ELISA). Due to the high presence of attractive BMP binding sites, only less than 0.1 \% of the initially loaded cytokine was released. The suitability of combining the cryostructuring process with 3D powder printed calcium phosphate substrates was evaluated with osteochondral scaffolds, but did not appear to yield more preferable results than the non-combined approach. A new custom build confined compression setup was elaborated together with a suitable evaluation procedure for the mechanical characterisation under physiological conditions. For bone and cartilage scaffolds, apparent elastic moduli of (37.6 ± 6.9) kPa and (3.14 ± 0.85) kPa were measured. A similar behaviour of the scaffolds to natural cartilage and bone tissue was demonstrated in terms of elastic energy storage. Under physiological frequencies, less than 1.0 \% and 0.8 \% of the exerted energy was lost for bone and cartilage scaffolds, respectively. With average relaxation times of (0.613 ± 0.040) sec and (0.815 ± 0.077) sec, measured for the cartilage and bone scaffolds, they respond four orders of magnitude faster than the native tissues. Additionally, all kinds of produced scaffolds were able to withstand cyclic compression at un-physiological frequencies as high as 20 Hz without a loss in structural integrity. With the presented new method, scaffolds could be fabricated whose extent in mimicking of native tissues exceeded the one of scaffolds producible by state of the art methods. This allowed a testing of the key hypothesis: The biological evaluation of an anisotropic pore structure in vivo revealed a higher functionality of immigrated cells and led finally to advantageous healing outcomes. Moreover, the mimicking of local compositions in combination with a consecutive anisotropic porosity that approaches native tissue structures could be demonstrated to induce zone specific matrix remodelling in stem cells in vitro. Additionally, clues for a zone specific chondrogenic stem cell differentiation were attained without the supplementation of growth factors. Thereby, the hypothesis that an increased approximation of the hierarchically compositional and structurally anisotropic properties of musculoskeletal tissues would lead to an improved cellular response and a better healing quality, could be confirmed. With a special focus on cell free in situ tissue engineering approaches, the insights gained within this thesis may be directly transferred to clinical regenerative therapies.}, subject = {Tissue Engineering}, language = {en} } @phdthesis{Schmitz2016, author = {Schmitz, Michael}, title = {Functional hydrophilic polymers for chemoselective coupling}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-145629}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2016}, abstract = {Chemoselective poly(oxazolines) (POx) and poly[(oligo ethylene glycol) acrylates] were synthesized. An initiator was produced for the preparation of poly(oxazoline)s capable of participating in click chemistry reactions which allows the functionalization of the polymer at the α terminus which was confirmed by 1H NMR spectroscopy. The initiator was used for the polymerization of hydrophilic 2 methyl 2 oxazoline (MeOx), whereby chemoselective, alkyne functionalized polymers could be prepared for Cu-catalyzed azide-alkyne cycloaddition. The desired molecular weight could be achieved through the living, ring opening cationic polymerization and was confirmed by 1H NMR, SEC and MALDI ToF measurements. Polymers were terminated with piperidine if no further functionalization was needed, or with an ester derivate for enabling amine attachment in a subsequent step. In addition, polymers were functionalized by termination with NaN3 in order to provide the counterpart to the azide-alkyne reaction. IR spectroscopy was suitable for the azide detection. The coupling of polymers showed the reactivity and could be confirmed by SEC, 1H NMR and IR spectroscopy. The composition of cysteine functionalized POx was completed by thiol-ene chemistry. Since the commercially available iso 2 propyl 2 oxazoline is not available for the cationic polymerization, 2 butenyl and 2 decenyl 2 oxazoline (ButenOx and DecenOx) were first prepared. The synthesis of both copolymers, based on MeOx could be confirmed by 1H NMR as well as with SEC, whereby narrow distributions with dispersities of 1.06 could be achieved. The cysteine functionalization of the copolymers was enabled by the creation of a thiazolidine component which could be synthesized by acetal and formyl protection of cysteine and subsequent functionalization with a thiol. The component enabled the reaction with a polymer by thiol-ene reaction which was started by the addition of dimethoxyphenyl-acetophenone and was catalyzed by irradiation with UV light. Both copolymers, with a shorter (polymers with BuenOx) and longer (polymers with DecenOx) hydrophobic sidechain could be functionalized. 1H NMR spectroscopic analysis showed a quantitative reaction with the thiazolidine derivate. After deprotection by acidic workup the desired, cysteine functionalized polymer could be isolated. Quantification of cysteine functions was ensured by a modified TNBSA assay, whereby the thiols were first oxidized in order to confirm an independent measurement of amine functions. Both, the TNBSA assay as well as the NMR measurement showed the desired number of cysteine residues. The cytotoxicity of functionalized polymers with different compositions was tested by a luminescent cell viability assay (LCVA). Both, the amount of cysteine functions (5-10\%) in the copolymers as well as the length of the hydrophobic side chain were varied. All polymers did not show cytotoxicity up to concentrations of 10 mg∙mL-1. The cell activity and cell numbers only decreased below 50\% and 20\% respectively, when copolymers with 5\% cysteine and longer sidechains were measured, which was attributed to a contamination of the sample itself. The cooperation partner performed Native Chemical Ligation (NCL) with model peptides and purified the products by HPLC. A sterically non demanding peptide was synthesized, consisting of an aromatic amino acid and four glycine units. The aromatic unit was used for the quantification of the polymer-peptide conjugate in the 1H NMR spectroscopy. A polymer having five cysteine side chains has been fully implemented by NCL to a conjugate of one polymer with five peptides. A sterically more demanding peptide was additionally used and MALDI ToF measurements confirmed the successful conjugation. Furthermore the cysteine functionalized polymer was used for nanogel synthesis. The thiol of the cysteine function was oxidized in an inverse mini-emulsion by H2O2, resulting in nanogels (~500 nm) which could be confirmed by SEM, AFM, DLS and NTA measurements. Besides POx, oligo (ethylene glycol)acrylates (OEGA) were polymerized; by copolymerization with the reactive pentafluorophenyl acrylate (PFPA) reactive and amphiphilic polymers were obtained. The synthesis of PFPA could be confirmed spectroscopically by 1H , 19F NMR, and by FT IR. Copolymers were synthesized by RAFT polymerization with narrow dispersities. Functionalization with an amine functionalized thiazolidine led to a hydrophilic cysteine functionalized polymer after acidic deprotection. Apart from this polymer, a thioester functionalization was successfully performed by reaction of the active polymer with a cyclic amine functionalized thioester which does not release a toxic by product (such as the resulting thiol) during NCL and thus features a very high potential to replace former thioester.}, subject = {Konjugate}, language = {en} } @phdthesis{Bertlein2019, author = {Bertlein, Sarah}, title = {Hydrogels as Biofunctional Coatings and Thiol-Ene Clickable Bioinks for Biofabrication}, doi = {10.25972/OPUS-17422}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-174225}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2019}, abstract = {Ziel dieser Arbeit war die Entwicklung von funktionalisierbaren Hydrogel Beschichtungen f{\"u}r Schmelz-elektrogeschriebene PCL Ger{\"u}ste und von Bio-druckbaren Hydrogelen f{\"u}r die Biofabrikation. Hydrogel Beschichtungen von Schmelz-elektrogeschriebenen Konstrukten erm{\"o}glichten die Kontrolle der Oberfl{\"a}chen-Hydrophilie und damit Zell-Material Interaktionsstudien in minimal Protein-adh{\"a}siven Umgebungen. Zu diesem Zweck wurde ein hydrophiles sternf{\"o}rmiges vernetzbares Polymer verwendet und eine Optimierung der Beschichtungsbedingungen durchgef{\"u}hrt. Außerdem boten neu entwickelte photosensitive Konstrukte eine Zeit- und pH-unabh{\"a}ngige Biofunktionalisierung. Bio-druckbare Hydrogele f{\"u}r die Biofabrikation basierten auf der Allyl-Funktionalisierung von Gelatine (GelAGE) und modifizierten Hyalurons{\"a}ure-Produkten, die das Hydrogel-Vernetzen mittels Thiol-En Click Chemie erm{\"o}glichen. Die Optimierung der GelAGE Hydrogel-Eigenschaften wurde durch eine detaillierte Analyse der Syntheseparameter, variierender En:SH Verh{\"a}ltnisse, unterschiedlicher Vernetzungsmolek{\"u}le und Photoinitiatoren erreicht. Die Homogenit{\"a}t der Thiol-En Netzwerke wurde mit denen der freien radikalischen Polymerisation verglichen und die Verwendbarkeit von GelAGE als Bio-Tinte f{\"u}r den Extrusions-basierten Bio-Druck wurde untersucht. Es wurde angenommen, dass reine Hyalurons{\"a}ure-basierte Bio-Tinten eine Beibehaltung der mechanischen und rheologischen Eigenschaften, der Zellviabilit{\"a}t und der Prozessierbarkeit erm{\"o}glichen trotz geringerem Polymer- und Thiol-Anteil der Hydrogele. Hydrogel-Beschichtungen: Hoch definierte PCL Ger{\"u}ste wurden mittels MEW hergestellt und anschließend mit sechs armigen sternf{\"o}rmigen vernetzbaren Polymeren (sP(EO-stat-PO)) beschichtet. Die Vernetzung wird durch die w{\"a}ssrig-induzierte Hydrolyse reaktiver Isocyanatgruppen (NCO) von sP(EO-stat-PO) bedingt. Diese Beschichtung erh{\"o}hte die Oberfl{\"a}chen-Hydrophilie und stellte eine Plattform f{\"u}r weitere Biofunktionalisierungen, in minimal Protein-adh{\"a}siven Umgebungen, dar. Nicht nur das Beschichtungsprotokoll wurde hinsichtlich der sP(EO-stat-PO) Konzentrationen und der Beschichtungsdauern optimiert, sondern auch Vorbehandlungen der Ger{\"u}ste wurden entwickelt. Diese waren essentiell um die finale Hydrophilie von sP(EO-stat-PO) beschichteten Ger{\"u}ste so zu erh{\"o}hen, dass unspezifische Protein-Adh{\"a}sionen vollst{\"a}ndig unterbunden wurden. Die sP(EO-stat-PO) Schichtdicke, von ungef{\"a}hr 100 nm, erm{\"o}glicht generell in vitro Studien nicht nur in Abh{\"a}ngigkeit der Ger{\"u}st-Biofunktionalisierung, sondern auch in Abh{\"a}ngigkeit der Ger{\"u}st-Architektur durchzuf{\"u}hren. Das Ausmaß der Hydrogel-Beschichtung wurde mittels einer indirekten Quantifizierung der NCO-Hydrolyse-Produkte ermittelt. Kenntnis {\"u}ber die NCO-Hydrolyse-Kinetik erm{\"o}glichte ein Gleichgewicht zwischen ausreichend beschichteten Ger{\"u}sten und der Pr{\"a}senz der NCO-Gruppen herzustellen, welche f{\"u}r die anschließenden Biofunktionalisierungen genutzt wurden. Diese Zeit- und pH-abh{\"a}ngige Biofunktionalisierung war jedoch nur f{\"u}r kleine Biomolek{\"u}le m{\"o}glich. Um diese Beschr{\"a}nkung zu umgehen und auch hochmolekulare Biomolek{\"u}le kovalent anzubinden, wurde ein anderer Reaktionsweg entwickelt. Dieser basierte auf der Photolyse von Diazirin-Gruppen und erm{\"o}glichte eine Zeit- und pH-unabh{\"a}ngige Biofunktionalisierung der Ger{\"u}ste mit Streptavidin und Kollagen Typ I. Die Fibrillen bildende Eigenschaft von Kollagen wurde genutzt um auf den Ger{\"u}sten verschiedene Kollagen-Konformationen zu erhalten und eine erste in vitro Studie best{\"a}tigte die Anwendbarkeit f{\"u}r Zell-Material Interaktionsstudien. Die hier entwickelten Ger{\"u}ste k{\"o}nnten verwendet werden um tiefere Einblicke in die Grundlagen der zellul{\"a}ren Wahrnehmung zu erhalten. Insbesondere die Komplexit{\"a}t mit der Zellen z.B. Kollagen wahrnehmen bleibt weiterhin kl{\"a}rungsbed{\"u}rftig. Hierf{\"u}r k{\"o}nnten diverse Hierarchien von Kollagen-{\"a}hnlichen Konformationen an die Ger{\"u}ste gebunden werden, z.B. Gelatine oder Kollagen-abgeleitete Peptidsequenzen. Dann k{\"o}nnte die Aktivierung der DDR-Rezeptoren in Abh{\"a}ngigkeit der Komplexit{\"a}t der angebundenen Substanzen bestimmt werden. Aufgrund der starken Streptavidin-Biotin Bindung k{\"o}nnten Streptavidin funktionalisierte Ger{\"u}ste eine vielseitige Plattform f{\"u}r die Immobilisierung von jeglichen biotinylierten Molek{\"u}len darstellen. Gelatine-basierte Bio-Tinten: Zuerst wurden die GelAGE-Produkte hinsichtlich der Molekulargewichts-Verteilung und der Integrit{\"a}t der Aminos{\"a}uren-Zusammensetzung synthetisiert. Eine detailliert Studie, mit variierenden molaren Edukt-Verh{\"a}ltnissen und Synthese-Zeitspannen, wurde durchgef{\"u}hrt und implizierte, dass der Gelatine Abbau am deutlichsten f{\"u}r stark alkalische Synthesebedingungen mit langen Reaktionszeiten war. Gelatine beinhaltet mehrere funktionalisierbare Gruppen und anhand diverser Model-Substanzen und Analysen wurde die vorrangige Amingruppen-Funktionalisierung ermittelt. Die Homogenit{\"a}t des GelAGE-Polymernetzwerkes, im Vergleich zu frei radikalisch polymerisierten GelMA-Hydrogelen, wurde best{\"a}tigt. Eine ausf{\"u}hrliche Analyse der Hydrogel-Zusammensetzungen mit variierenden funktionellen Gruppen Verh{\"a}ltnissen und UV- oder Vis-Licht induzierbaren Photoinitiatoren wurde durchgef{\"u}hrt. Die UV-Initiator Konzentration ist aufgrund der Zell-Toxizit{\"a}t und der potenziellen zellul{\"a}ren DNA-Besch{\"a}digung durch UV-Bestrahlung eingeschr{\"a}nkt. Das Zell-kompatiblere Vis-Initiator System hingegen erm{\"o}glichte, durch die kontrollierte Photoinitiator-Konzentration bei konstanten En:SH Verh{\"a}ltnissen und Polymeranteilen, die Einstellung der mechanischen Eigenschaften {\"u}ber eine große Spanne hinweg. Die Flexibilit{\"a}t der GelAGE Bio-Tinte f{\"u}r unterschiedliche additive Fertigungstechniken konnte, durch Ausnutzung des temperaturabh{\"a}ngigen Gelierungsverhaltens unterschiedlich stark degradierter GelAGE Produkte, f{\"u}r Stereolithographie und Extrusions-basiertem Druck bewiesen werden. Außerdem wurde die Viabilit{\"a}t zellbeladener GelAGE Konstrukte bewiesen, die mittels Extrusions-basiertem Bio-Druck erhalten wurden. Die Verwendung diverser multifunktioneller und makromolekularer Thiol-Vernetzungsmolek{\"u}le erm{\"o}glichte eine Verbesserung der mechanischen und rheologischen Eigenschaften und ebenso der Prozessierbarkeit. Verglichen mit dem kleinen bis-Thiol-funktionellen Vernetzungsmolek{\"u}l waren geringere Thiol-Vernetzer-Konzentrationen notwendig um bessere mechanische Festigkeiten und physikochemische Eigenschaften der Hydrogele zu erhalten. Der Extrusions-basierte Bio-Druck unterschiedlicher eingekapselter Zellen verdeutlichte die Notwendigkeit der individuellen Optimierung von Zell-beladenen Hydrogel-Formulierungen. Nicht nur die Zellviabilit{\"a}t von eingekapselten Zellen in Extrusions-basierten biogedruckten Konstrukten sollte bewertet werden, sondern auch andere Parameter wie die Zellmorphologie oder die Kollagen- oder Glykosaminoglykan-Produktion, da diese einige der essentiellen Voraussetzungen f{\"u}r die Verwendung in Knorpel Tissue Engineering Konzepten darstellen. Außerdem sollten diese Studien auf die stereolithographischen Ans{\"a}tze erweitert werden und letztlich w{\"a}re die Flexibilit{\"a}t und Zellkompatibilit{\"a}t der Formulierungen mit makromolekularen Vernetzern von Interesse. Makromolekulare Vernetzer erm{\"o}glichten die Reduktion des Polymeranteils und des Thiol-Gehalts und k{\"o}nnen, insbesondere in Kombination mit dem Zell-kompatibleren Vis-Initiator-System, voraussichtlich zu einer gesteigerten Zellkompatibilit{\"a}t beitragen, was zu kl{\"a}ren bleibt. Hyalurons{\"a}ure-basierte Bio-Tinten: Unterschiedliche Hyalurons{\"a}ure-Produkte (HA) wurden synthetisiert, sodass diese En- (HAPA) oder Thiol-Funktionalit{\"a}ten (LHASH) beinhalteten, um reine HA Thiol-En vernetzte Hydrogele zu erhalten. In Abh{\"a}ngigkeit des Molekulargewichts der HA-Produkte, der Polymeranteile und des En:SH Verh{\"a}ltnisses, konnte eine große Spanne an mechanischen Festigkeiten abgedeckt werden. Aufgrund der hohen Viskosit{\"a}t war allerdings im Falle von hochmolekularen HA (HHAPA) Produkt-L{\"o}sungen (HHAPA + LHASH) die Handhabbarkeit auf 5.0 wt.-\% beschr{\"a}nkt. Die Verwendung der gleichen HA Thiol-Komponenten (LHASH) erm{\"o}glichte Hybrid-Hydrogele, mit HA und GelAGE, mit reinen HA-Hydrogelen zu vergleichen. Obwohl der Polymeranteil von HHAPA + LHASH Hydrogelen signifikant geringer war, als im Vergleich zu Hybrid-Hydrogelen (GelAGE + LHASH), wurden f{\"u}r gleiche En:SH Verh{\"a}ltnisse {\"a}hnliche mechanische und physikochemische Eigenschaften reiner HA-Hydrogele bestimmt. Aufgrund der geringen Viskosit{\"a}t niedermolekularer HA L{\"o}sungen (LHAPA + LHASH) konnten diese nicht f{\"u}r den Extrusions-basierten Druck verwendet werden. Das nicht temperaturabh{\"a}ngige HHAPA + LHASH System hingegen konnte mit nur einem Viertel des Polymeranteils der Hybrid Formulierungen gedruckt werden. Im Vergleich zu der Hybrid Bio-Tinte wurde angenommen, dass das hoch viskose Verhalten von HHAPA + LHASH L{\"o}sungen, der geringere Polymeranteil, der geringere Druck f{\"u}r das Drucken und eine demzufolge geringere Scherspannung, maßgeblich zu der hohen Zellviabilit{\"a}t in Extrusions-basiert-biogedruckten Konstrukten beisteuerten. Die niedrigmolekulare HA Formulierung (LHAPA + LHASH) konnte zwar nicht f{\"u}r den Extrusions-basierten Druck verwendet werden, allerdings besitzt dieses System Potential f{\"u}r andere additive Fertigungstechniken wie z.B. der Stereolithographie. Um dieses System weiterzuentwickeln w{\"a}re, analog zu dem GelAGE System, eine detailliertere Studie zu den Funktionen eingekapselter Zellen hilfreich. Außerdem sollte die Initiierung dieses Systems mit dem Vis-Initiator untersucht werden.}, subject = {Biomaterial}, language = {en} } @phdthesis{LiebschergebBloehbaum2020, author = {Liebscher [geb. Bl{\"o}hbaum], Julia}, title = {Side chain functional poly(2-oxazoline)s for biomedical applications}, doi = {10.25972/OPUS-20396}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-203960}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2020}, abstract = {The aim of the thesis was to develop water soluble poly(2-oxazoline) (POx) copolymers with new side group functionalities, which can be used for the formation of hydrogels in biomedical applications and for the development of peptide-polymer conjugates. First, random copolymers of the monomer MeOx or EtOx with ButEnOx and EtOx with DecEnOx were synthesized and characterized. The vinyl functionality brought into the copolymer by the monomers ButEnOx and DecEnOx would later serve for post-polymerization functionalization. The synthesized copolymers were further functionalized with thiols via post-polymerization functionalization using a newly developed synthesis protocol or with a protected catechol molecule for hydrogel formation. For the formation of peptide-polymer conjugates, a cyclic thioester, namely thiolactone acrylamide and an azlactone precursor, whose synthesis was newly developed, were attached to the side chain of P(EtOx-co-ButEnOx) copolymers. The application of the functionalized thiol copolymers as hydrogels using thiol-ene chemistry for cross-linking was demonstrated. The swelling behavior and mechanical properties were characterized. The hydrophilicity of the network as well as the cross-linking density strongly influenced the swelling behavior and the mechanical strength of the hydrogels. All hydrogels showed good cell viability results. The hydrogel networks based on MeOx and EtOx were loaded with two dyes, fluorescein and methylene blue. It was observed that the uptake of the more hydrophilic dye fluorescein depended more on the ability of the hydrogel to swell. In contrast, the uptake of the more hydrophobic dye methylene blue was less dependent on the swelling degree, but much more on the hydrophilicity of the network. For the potential application as cartilage glue, (biohybrid) hydrogels were synthesized based on the catechol-functionalized copolymers, with and without additional fibrinogen, using sodium periodate as the oxidizing agent. The system allowed for degradation due to the incorporated ester linkages at the cross-linking points. The swelling behavior as well as the mechanical properties were characterized. As expected, hydrogels with higher degrees of cross-linking showed less swelling and higher elastic modulus. The addition of fibrinogen however increased the elasticity of the network, which can be favorable for the intended application as a cartilage glue. Biological evaluation clearly demonstrated the advantage of degradable ester links in the hydrogel network, where chondrocytes were able to bridge the artificial gap in contrast to hydrogels without any ester motifs. Lastly, different ways to form peptide-polymer conjugates were presented. Peptides were attached with the thiol of the terminal cysteine group to the vinyl side chain of P(EtOx-co-ButEnOx) copolymers by radical thiol-ene chemistry. Another approach was to use a cyclic thioester, thiolactone, or an azlactone functionality to bind a model peptide via native chemical ligation. The two latter named strategies to bind peptides to POx side chains are especially interesting as one and in the case of thiolactone two free thiols are still present at the binding site after the reaction, which can, for example, be used for further thiol-ene cross-linking to form POx hydrogels. In summary, side functional poly(oxazoline) copolymers show great potential for numerous biomedical applications. The various side chain functionalities can be introduced by an appropriate monomer or by post-polymerization functionalization, as demonstrated. By their multi-functionality, hydrogel characteristics, such as cross-linking degree and mechanical strength, can be fine-tuned and adjusted depending on the application in the human body. In addition, the presented chemoselective and orthogonal reaction strategies can be used in the future to synthesize polymer conjugates, which can, for example, be used in drug delivery or in tissue regeneration.}, subject = {Polymere}, language = {en} } @phdthesis{Heffels2012, author = {Heffels, Karl-Heinz}, title = {Functional nanofibres for regenerative medicine}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-75684}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2012}, abstract = {This thesis concerned the design and examination of a scaffold for tissue engineering applications. The template for the presented scaffold came from nature itself: the intercellular space in tissues that provides structure and support to the cells of the respective tissue, known as extracellular matrix (ECM). Fibres are a predominant characteristic feature of ECM, providing adhesion sites for cell-matrix interactions. In this dissertation a fibrous mesh was generated using the electrospinning technique to mimic the fibrous structure of the ECM. Two base polymers were explored: a biodegradable polyester, poly(D,L-lactide-co-glycolide); and a functional PEG-based star polymer, NCO-sP(EO-stat-PO). This topic was described in three major parts: the first part was materials based, concerning the chemical design and characterisation of the polymer scaffolds; the focus was then shifted to the cellular response to this fibrous scaffold; and finally the in vivo performance of the material was preliminarily assessed. The first steps towards an electrospun mesh started with adjusting the spinning parameters for the generation of homogeneous fibres. As reported in Chapter 3 a suitable setup configuration was on the one hand comprised of a spinning solution that consisted of 28.5 w/v\% PLGA RG 504 and 6 w/v\% NCO-sP(EO-stat-PO) in 450 µL acetone, 50 µL DMSO and 10 µL of an aqueous trifluoroacetic acid solution. On the other hand an ideal spinning behaviour was achieved at process parameters such as a flow rate of 0.5 mL/h, spinneret to collector distance of 12-16 cm and a voltage of 13 kV. The NCO-sP(EO-stat-PO) containing fibres proved to be highly hydrophilic as the functional additive was present on the fibre surface. Furthermore, the fibres featured a bulk degradation pattern as a consequence of the proportion of PLGA. Besides the morphologic similarity to ECM fibres, the functionality of the electrospun fibres is also decisive for a successful ECM mimicry. In Chapter 4, the passive as well as active functionality of the fibres was investigated. The fibres were required to be protein repellent to prevent an unspecific cell adhesion. This was proven as even 6.5 \% sP(EO-stat-PO) in the PLGA fibres reduced any unspecific protein adsorption of bovine serum albumin and foetal calf serum to less than 1 \%. However, avidin based proteins attached to the fibres. This adhesion process was avoided by an additional fibre surface treatment with glycidol. The active functionalisation of NCO-sP(EO-stat-PO)/PLGA fibres was investigated with two fluorescent dyes and biocytin. A threefold, chemically orthogonal, fibre modification was achieved with these dyes. The chapters about the chemical and mechanical properties laid the basis for the in vitro chapters where a specific fibre functionalisation with peptides was conducted to analyse the cell adhesion and biochemical expressions. Beginning with fibroblasts in Chapter 5 the focus was on the specific cell adhesion on the electrospun fibres. While NCO-sP(EO-stat-PO)/PLGA fibres without peptides did not allow any adhesion of fibroblasts, a fibre modification with GRGDS (an adhesion mediating peptide sequence) induced the adhesion and spreading of human dermal fibroblasts on the fibrous scaffolds. The control sequence GRGES that has no adhesion mediating qualities did not lead to any cell adhesion as observed on fibres without modifications. While the experiments of Chapter 5 were a proof-of-concept, in Chapter 6 a possible application in cartilage tissue engineering was examined. Therefore, primary human chondrocytes were seeded on fibrous scaffolds with various peptide sequences. Though the chondrocytes exhibited high viability on all scaffolds, an active interaction of cells and fibres was only found for the decorin derived sequence CGKLER. Live-cell-imaging revealed both cell attachment and migration within CGKLER-modified meshes. As chondrocytes undergo a de-differentiation towards a fibroblast-like phenotype, the chondrogenic re-differentiation on these scaffolds was investigated in a long term cell culture experiment of 28 days. Therefore, the glycosaminoglycan production was analysed as well as the mRNA expression of genes coding for collagen I and II, aggrecan and proteoglycan 4. In general only low amounts of the chondrogenic markers were measured, suggesting no chondrogenic differentiation. For conclusive evidence follow-up experiments are required that support or reject the findings. The success of an implant for tissue engineering relies not only on the response of the targeted cell type but also on the immune reaction caused by leukocytes. Hence, Chapter 7 dealt with primary human macrophages and their behaviour and phenotype on two-dimensional (2D) surfaces compared to three-dimensional (3D) fibrous substrates. It was found that the general non-adhesiveness of NCO-sP(EO-stat-PO) surfaces and fibres does not apply to macrophages. The cells aligned along the fibres on surfaces or resided in the pores of the meshes. On flat surfaces without 3D structure the macrophages showed a retarded adhesion kinetic accompanied with a high migratory activity indicating their search for a topographical feature to adhere to. Moreover, a detailed investigation of cell surface markers and chemokine signalling revealed that macrophages on 2D surfaces exhibited surface markers indicating a healing phenotype while the chemokine release suggested a pro-inflammatory phenotype. Interestingly, the opposite situation was found on 3D fibrous substrates with pro-inflammatory surface markers and pro-angiogenic cytokine release. As the immune response largely depends on cellular communication, it was concluded that the NCO-sP(EO-stat-PO)/PLGA fibres induce an adequate immune response with promising prospects to be used in a scaffold for tissue engineering. The final chapter of this thesis reports on a first in vivo study conducted with the presented electrospun fibres. Here, the fibres were combined with a polypropylene mesh for the treatment of diaphragmatic hernias in a rabbit model. Two scaffold series were described that differed in the overall surface morphology: while the fibres of Series A were incorporated into a thick gel of NCO-sP(EO-stat-PO), the scaffolds of Series B featured only a thin hydrogel layer so that the overall fibrous structure could be retained. After four months in vivo the treated defects of the diaphragm were significantly smaller and filled mainly with scar tissue. Thick granulomas occurred on scaffolds of Series A while the implants of Series B did not induce any granuloma formation. As a consequence of the generally positive outcome of this study, the constructs were enhanced with a drug release system in a follow-up project. The incorporated drug was the MMP-inhibitor Ilomastat which is intended to reduce the formation of scar tissue. In conclusion, the simple and straight forward fabrication, the threefold functionalisation possibility and general versatile applicability makes the meshes of NCO-sP(EO-stat-PO)/PLGA fibres a promising candidate to be applied in tissue engineering scaffolds in the future.}, subject = {Nanofaser}, language = {en} } @phdthesis{Blum2021, author = {Blum, Carina}, title = {A first step to an integral biointerface design for the early phase of regeneration}, doi = {10.25972/OPUS-21211}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-212117}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2021}, abstract = {The implantation of any foreign material into the body automatically starts an immune reaction that serves as the first, mandatory step to regenerate tissue. The course of this initial immune reaction decides on the fate of the implant: either the biomaterial will be integrated into the host tissue to subsequently fulfill its intended function (e.g., tissue regeneration), or it will be repelled by fibrous encapsulation that determines the implant failure. Especially neutrophils and macrophages play major roles during this inflammatory response and hence mainly decide on the biomaterial's fate. For clinically relevant tissue engineering approaches, biomaterials may be designed in shape and morphology as well as in their surface functionality to improve the healing outcome, but also to trigger stem cell responses during the subsequent tissue regeneration phase. The main focus of this thesis was to unravel the influence of scaffold characteristics, including scaffold morphology and surface functionality, on primary human innate immune cells (neutrophils and macrophages) and human mesenchymal stromal cells (hMSCs) to assess their in vitro immune response and tissue regeneration capacity, respectively. The fiber-based constructs were produced either via melt electrowriting (MEW), when the precise control over scaffold morphology was required, or via solution electrospinning (ES), when the scaffold design could be neglected. All the fiber-based scaffolds used throughout this thesis were composed of the polymer poly(ε caprolactone) (PCL). A novel strategy to model and alleviate the first direct cell contact of the immune system with a peptide-bioactived fibrous material was presented in chapter 3 by treating the material with human neutrophil elastase (HNE) to imitate the neutrophil attack. The main focus of this study was put on the effect of HNE towards an RGDS-based peptide that was immobilized on the surface of a fibrous material to improve subsequent L929 cell adhesion. The elastase efficiently degraded the peptide-functionality, as evidenced by a decreased L929 cell adhesion, since the peptide integrated a specific HNE-cleavage site (AAPV-motif). A sacrificial hydrogel coating based on primary oxidized hyaluronic acid (proxHA), which dissolved within a few days after the neutrophil attack, provided an optimal protection of the peptide-bioactivated fibrous mesh, i.e, the hydrogel alleviated the neutrophil attack and largely ensured the biomaterial's integrity. Thus, according to these results, a means to protect the biomaterial is required to overcome the neutrophil attack. Chapter 4 was based on the advancement of melt electrowriting (MEW) to improve the printing resolution of MEW scaffolds in terms of minimal inter-fiber distances and a concomitant high stacking precision. Initially, to gain a better MEW understanding, the influence of several parameters, including spinneret diameter, applied pressure, and collector velocity on mechanical properties, crystallinity, fiber diameter and fiber surface morphology was analyzed. Afterward, innovative MEW designs (e.g., box-, triangle-, round , and wall-shaped scaffolds) have been established by pushing the printing parameters to their physical limits. Further, the inter-fiber distance within a standardized box-structured scaffold was successfully reduced to 40 µm, while simultaneously a high stacking precision was maintained. In collaboration with a co-worker of my department (Tina Tylek, who performed all cell-based experiments in this study), these novel MEW scaffolds have been proven to facilitate human monocyte-derived macrophage polarization towards the regenerative M2 type in an elongation-driven manner with a more pronounced effect with decreasing pore sizes. Finally, a pro-adipogenic platform for hMSCs was developed in chapter 5 using MEW scaffolds with immobilized, complex ECM proteins (e.g., human decellularized adipose tissue (DAT), laminin (LN), and fibronectin (FN)) to test for the adipogenic differentiation potential in vitro. Within this thesis, a special short-term adipogenic induction regime enabled to more thoroughly assess the intrinsic pro-adipogenic capacity of the composite biomaterials and prevented any possible masking by the commonly used long-term application of adipogenic differentiation reagents. The scaffolds with incorporated DAT consistently showed the highest adipogenic outcome and hence provided an adipo-inductive microenvironment for hMSCs, which holds great promise for applications in soft tissue regeneration. Future studies should combine all three addressed projects in a more in vivo-related manner, comprising a co-cultivation setup of neutrophils, macrophages, and MSCs. The MEW-scaffold, particularly due to its ability to combine surface functionality and adjustable morphology, has been proven to be a successful approach for wound healing and paves the way for subsequent tissue regeneration.}, subject = {Scaffold }, language = {en} } @phdthesis{Roedel2019, author = {R{\"o}del, Michaela}, title = {Development of Dual Setting Cement Systems as Composite Biomaterials with Ductile Properties}, doi = {10.25972/OPUS-18277}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-182776}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2019}, abstract = {Synthetic bone replacement materials have their application in non-load bearing defects with the function of (re-)construction or substitution of bone. This tissue itself represents a biological composite material based on mineralized collagen fibrils and combines the mechanical strength of the mineral with the ductility of the organic matrix. By mimicking these outstanding properties with polymer-cement-composites, an imitation of bone is feasible. A promising approach for such replacement materials are dual setting systems, which are generated by dissolution-precipitation reaction with cement setting in parallel to polymerization and gelation of the organic phase forming a coherent hydrogel network. Hereby, the high brittleness of the pure inorganic network was shifted to a more ductile and elastic behavior. The aim of this thesis was focused on the development of different dual setting systems to modify pure calcium phosphate cements' (CPCs') mechanical performance by incorporation of a hydrogel matrix. A dual setting system based on hydroxyapatite (HA) and cross-linked 2-hydroxyethyl methacrylate (HEMA) via radical polymerization was advanced by homogenous incorporation of a degradable cross-linker composed of poly(ethylene glycol) (PEG) as well as poly(lactic acid) (PLA) with reactive terminal methacrylate functionalities (PEG-PLLA-DMA). By integration of this high molecular weight structure in the HEMA-hydrogel network, a significant increase in energy absorption (toughness) under 4-point bending testing was observed. An addition of only 10 wt\% hydrogel precursor (referred to the liquid phase) resulted in a duplication of stress over a period of 8 days. Additionally, the calculated elasticity was positively affected and up to six times higher compared to pure HA. With a constantly applied force during compressive strength testing, a deformation and thus strain levels of about 10 \% were reached immediately after preparation. For higher degradability, the system was modified in a second approach regarding organic as well as inorganic phase. The latter component was changed by brushite forming cement that is resorbable in vivo due to solubility processes. This CPC was combined with a hydrogel based on PEG-PLLA-DMA and other dimethacrylated PEGs with different molecular weights and concentrations. Hereby, new reaction conditions were created including a shift to acidic conditions. On this ground, the challenge was to find a new radical initiator system. Suitable candidates were ascorbic acid and hydrogen peroxide. that started the polymerization and successful gelation in this environment. These highly flexible dual set composites showed a very high ductility with an overall low strength compared to HA-based models. After removal of the applied force during compressive strength testing, a complete shape recovery was observed for the samples containing the highest polymeric amount (50 wt\%) of PEG-PLLA-DMA. Regarding phase distribution in the constructs, a homogenously incorporated hydrogel network was demonstrated in a decalcifying study with ethylenediaminetetraacetic acid. Intact, coherent hydrogels remained after dissolution of the inorganic phase via calcium ion complexation. In a third approach, the synthetic hydrogel matrix of the previously described system was replaced by the natural biopolymer gelatin. Simultaneously to brushite formation, physical as well as chemical cross-linking by the compound genipin was performed in the dual setting materials. Thanks to the incorporation of gelatin, elasticity increased significantly, in which concentrations up to 10.0 w/v\% resulted in a certain cohesion of samples after compressive strength testing. They did not dissociate in little pieces but remained intact cuboid specimens though having cracks or fissures. Furthermore, the drug release of two active pharmaceutical ingredients (vancomycin and rifampicin) was investigated over a time frame of 5 weeks. The release exponent was determined according to Korsmeyer-Peppas with n = 0.5 which corresponds to the drug liberation model of Higuchi. A sustained release was observed for the antibiotic vancomycin encapsulated in composites with a gelatin concentration of 10.0 w/v\% and a powder-to-liquid ratio of 2.5 g/mL. With respect to these developments of different dual setting systems, three novel approaches were successfully established by polymerization of monomers and cross-linking of precursors forming an incorporated, homogenous hydrogel matrix in a calcium phosphate network. All studies showed an essential transfer of mechanical performance in direction of flexibility and bendability.}, subject = {Calciumphosphate}, language = {en} } @phdthesis{Wittmann2014, author = {Wittmann, Katharina}, title = {Adipose Tissue Engineering - Development of Volume-Stable 3-Dimensional Constructs and Approaches Towards Effective Vascularization}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-107196}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2014}, abstract = {Adipose tissue defects and related pathologies still represent major challenges in reconstructive surgery. Based on to the paradigm 'replace with alike', adipose tissue is considered the ideal substitute material for damaged soft tissue [1-3]. Yet the transfer of autologous fat, particularly larger volumes, is confined by deficient and unpredictable long term results, as well as considerable operative morbidity at the donor and recipient site [4-6], calling for innovative treatment options to improve patient care. With the aim to achieve complete regeneration of soft tissue defects, adipose tissue engineering holds great promise to provide functional, biologically active adipose tissue equivalents. Here, especially long-term maintenance of volume and shape, as well as sufficient vascularization of engineered adipose tissue represent critical and unresolved challenges [7-9]. For adipose tissue engineering approaches to be successful, it is thus essential to generate constructs that retain their initial volume in vivo, as well as to ensure their rapid vascularization to support cell survival and differentiation for full tissue regeneration [9,10]. Therefore, it was the ultimate goal of this thesis to develop volume-stable 3D adipose tissue constructs and to identify applicable strategies for sufficient vascularization of engineered constructs. The feasibility of the investigated approaches was verified by translation from in vitro to in vivo as a critical step for the advancement of potential regenerative therapies. For the development of volume-stable constructs, the combination of two biomaterials with complementary properties was successfully implemented. In contrast to previous approaches in the field using mainly non-degradable solid structures for mechanical protection of developing adipose tissue [11-13], the combination of a cell-instructive hydrogel component with a biodegradable porous support structure of adequate texture was shown advantageous for the generation of volume-stable adipose tissue. Specifically, stable fibrin hydrogels previously developed in our group [14] served as cell carrier and supported the adipogenic development of adipose-derived stem cells (ASCs) as reflected by lipid accumulation and leptin secretion. Stable fibrin gels were thereby shown to be equally supportive of adipogenesis compared to commercial TissuCol hydrogels in vitro. Using ASCs as a safe source of autologous cells [15,16] added substantial practicability to the approach. To enhance the mechanical strength of the engineered constructs, porous biodegradable poly(ε caprolactone)-based polyurethane (PU) scaffolds were introduced as support structures and shown to exhibit adequately sized pores to host adipocytes as well as interconnectivity to allow coherent tissue formation and vascularization. Low wettability and impaired cell attachment indicated that PU scaffolds alone were insufficient in retaining cells within the pores, yet cytocompatibility and differentiation of ASCs were adequately demonstrated, rendering the PU scaffolds suitable as support structures for the generation of stable fibrin/PU composite constructs (Chapter 3). Volume-stable adipose tissue constructs were generated by seeding the pre-established stable fibrin/PU composites with ASCs. Investigation of size and weight in vitro revealed that composite constructs featured enhanced stability relative to stable fibrin gels alone. Comparing stable fibrin gels and TissuCol as hydrogel components, it was found that TissuCol gels were less resilient to degradation and contraction. Composite constructs were fully characterized, showing good cell viability of ASCs and strong adipogenic development as indicated by functional analysis via histological Oil Red O staining of lipid vacuoles, qRT-PCR analysis of prominent adipogenic markers (PPARγ, C/EBPα, GLUT4, aP2) and quantification of leptin secretion. In a pilot study in vivo, investigating the suitability of the constructs for transplantation, stable fibrin/PU composites provided with a vascular pedicle gave rise to areas of well-vascularized adipose tissue, contrasted by insufficient capillary formation and adipogenesis in constructs implanted without pedicle. The biomaterial combination of stable fibrin gels and porous biodegradable PU scaffolds was thereby shown highly suitable for the generation of volume-stable adipose tissue constructs in vivo, and in addition, the effectiveness of immediate vascularization upon implantation to support adipose tissue formation was demonstrated (Chapter 4). Further pursuing the objective to investigate adequate vascularization strategies for engineered adipose tissue, hypoxic preconditioning was conducted as a possible approach for in vitro prevascularization. In 2D culture experiments, analysis on the cellular level illustrated that the adipogenic potential of ASCs was reduced under hypoxic conditions when applied in the differentiation phase, irrespective of the oxygen tension encountered by the cells during expansion. Hypoxic treatment of ASCs in 3D constructs prepared from stable fibrin gels similarly resulted in reduced adipogenesis, whereas endothelial CD31 expression as well as enhanced leptin and vascular endothelial growth factor (VEGF) secretion indicated that hypoxic treatment indeed resulted in a pro-angiogenic response of ASCs. Especially the observed profound regulation of leptin production by hypoxia and the dual role of leptin as adipokine and angiogenic modulator were considered an interesting connection advocating further study. Having confirmed the hypothesis that hypoxia may generate a pro-angiogenic milieu inside ASC-seeded constructs, faster vessel ingrowth and improved vascularization as well as an enhanced tolerance of hypoxia-treated ASCs towards ischemic conditions upon implanatation may be expected, but remain to be verified in rodent models in vivo (Chapter 5). Having previously been utilized for bone and cartilage engineering [17-19], as well as for revascularization and wound healing applications [20-22], stromal-vascular fraction (SVF) cells were investigated as a novel cell source for adipose tissue engineering. Providing cells with adipogenic differentiation as well as vascularization potential, the SVF was applied with the specific aim to promote adipogenesis and vascularization in engineered constructs in vivo. With only basic in vitro investigations by Lin et al. addressing the SVF for adipose repair to date [23], the present work thoroughly investigated SVF cells for adipose tissue construct generation in vitro, and in particular, pioneered the application of these cells for adipose tissue engineering in vivo. Initial in vitro experiments compared SVF- and ASC-seeded stable fibrin constructs in different medium compositions employing preadipocyte (PGM-2) and endothelial cell culture medium (EGM-2). It was found that a 1:1 mixture of PGM-2 and EGM-2, as previously established for co-culture models of adipogenesis [24], efficiently maintained cells with adipogenic and endothelial potential in SVF-seeded constructs in short and long-term culture setups. Observations on the cellular level were supported by analysis of mRNA expression of characteristic adipogenic and endothelial markers. In preparation of the evaluation of SVF-seeded constructs under in vivo conditions, a whole mount staining (WMS) method, facilitating the 3D visualization of adipocytes and blood vessels, was successfully established and optimized using native adipose tissue as template (Chapter 6). In a subcutaneous nude mouse model, SVF cells were, for the first time in vivo, elucidated for their potential to support the functional assembly of vascularized adipose tissue. Investigating the effect of adipogenic precultivation of SVF-seeded stable fibrin constructs in vitro prior to implantation on the in vivo outcome, hormonal induction was shown beneficial in terms of adipocyte development, whereas a strong vascularization potential was observed when no adipogenic inducers were added. Via histological analysis, it was proven that the developed structures were of human origin and derived from the implanted cells. Applying SVF cells without precultivation in vitro but comparing two different fibrin carriers, namely stable fibrin and TissuCol gels, revealed that TissuCol profoundly supported adipose formation by SVF cells in vivo. This was contrasted by only minor SVF cell development and a strong reduction of cell numbers in stable fibrin gels implanted without precultivation. Histomorphometric analysis of adipocytes and capillary structures was conducted to verify the qualitative results, concluding that particularly SVF cells in TissuCol were highly suited for adipose regeneration in vivo. Employing the established WMS technique, the close interaction of mature adipocytes and blood vessels in TissuCol constructs was impressively shown and via species-specific human vimentin staining, the expected strong involvement of implanted SVF cells in the formation of coherent adipose tissue was confirmed (Chapter 7). With the development of biodegradable volume-stable adipose tissue constructs, the application of ASCs and SVF cells as two promising cell sources for functional adipose regeneration, as well as the thorough evaluation of strategies for construct vascularization in vitro and in vivo, this thesis provides valuable solutions to current challenges in adipose tissue engineering. The presented findings further open up new perspectives for innovative treatments to cure soft tissue defects and serve as a basis for directed approaches towards the generation of clinically applicable soft tissue substitutes.}, subject = {Tissue Engineering}, language = {en} } @phdthesis{Spatz2013, author = {Spatz, Kerstin}, title = {Mechanische und rheologische Eigenschaften von Calciumphosphat-Zementen}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-124860}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2013}, abstract = {Zur Erh{\"o}hung der mechanischen Stabilit{\"a}t mineralischer Knochenzemente aus Calciumorthophosphaten (CPC) wurde in einem TTCP/DCPA-System das Zementedukt TTCP mit verschiedenen biokompatiblen Oxiden (SiO2, TiO2, ZrO2) w{\"a}hrend des Herstellungsprozesses dotiert. Dies f{\"u}hrte zur Bildung von Calciummetallaten und einer Herabsetzung der L{\"o}slichkeit der TTCP-Komponente des Zements. Gegen{\"u}ber einem oxidfreien Zement konnte die Druckfestigkeit von 65 MPa auf 80 MPa (SiO2) bzw. 100 MPa (TiO2) gesteigert werden. In einem zweiten Ansatz zur Verbesserung der Injizierbarkeit wurden die Wechselwirkungen der Partikeloberfl{\"a}chen mit der fl{\"u}ssigen Zementphase betrachtet. Durch biokompatible Additive sollte eine repulsive elektrostatische Wechselwirkung eingestellt werden, um Partikelagglomerate effektiv zu dispergieren und eine verfl{\"u}ssigende Wirkung zu erreichen. Die Injizierbarkeit eines TTCP/DCPA-Zements durch eine Kan{\"u}le mit 800 µm Durchmesser konnte durch die Verwendung von 500 mM tri-Natriumzitrat-L{\"o}sung aufgrund einer deutlichen Herabsetzung der Viskosit{\"a}t der Zementpaste signifikant gesteigert werden (>95\%, P/L 3,3/1, Kraftaufwand 20 N). Abschließend wurde der Einfluss der Partikelgr{\"o}ßenverteilung auf die Festigkeit und Injizierbarkeit einer auf monomodaler Partikelgr{\"o}ßenverteilung basierten Zementmatrix untersucht. Hierzu wurden einem mechanisch aktivierten a-TCP-System unreaktive, feink{\"o}rnige F{\"u}llstoffpopulationen (TiO2, CaHPO4, CaCO3) zugesetzt und systematisch deren Effekt in Verbindung mit einer Partikelaufladung durch tri-Natriumzitrat auf die rheologischen und mechanischen Eigenschaften untersucht. Erst die Kombination einer bimodalen Partikelgr{\"o}ßenverteilung mit tri-Natriumzitrat-L{\"o}sung f{\"u}hrte zu einer starken Erniedrigung der Viskosit{\"a}t, damit zur nahezu vollst{\"a}ndigen Injizierbarkeit der Zemente und einer teilweise signifikanten Steigerung der mechanischen Festigkeiten (z.B. 72 MPa reiner a-TCP-Zement auf 142 MPa mit Zusatz von CaHPO4).}, subject = {Biomaterial}, language = {de} } @article{HuettenDhanasinghHessleretal.2014, author = {H{\"u}tten, Mareike and Dhanasingh, Anandhan and Hessler, Roland and St{\"o}ver, Timo and Esser, Karl-Heinz and M{\"o}ller, Martin and Lenarz, Thomas and Jolly, Claude and Groll, J{\"u}rgen and Scheper, Verena}, title = {In Vitro and In Vivo Evaluation of a Hydrogel Reservoir as a Continuous Drug Delivery System for Inner Ear Treatment}, series = {PLoS ONE}, volume = {9}, journal = {PLoS ONE}, number = {8}, doi = {10.1371/journal.pone.0104564}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-119375}, pages = {e104564}, year = {2014}, abstract = {Fibrous tissue growth and loss of residual hearing after cochlear implantation can be reduced by application of the glucocorticoid dexamethasone-21-phosphate-disodium-salt (DEX). To date, sustained delivery of this agent to the cochlea using a number of pharmaceutical technologies has not been entirely successful. In this study we examine a novel way of continuous local drug application into the inner ear using a refillable hydrogel functionalized silicone reservoir. A PEG-based hydrogel made of reactive NCO-sP(EO-stat-PO) prepolymers was evaluated as a drug conveying and delivery system in vitro and in vivo. Encapsulating the free form hydrogel into a silicone tube with a small opening for the drug diffusion resulted in delayed drug release but unaffected diffusion of DEX through the gel compared to the free form hydrogel. Additionally, controlled DEX release over several weeks could be demonstrated using the hydrogel filled reservoir. Using a guinea-pig cochlear trauma model the reservoir delivery of DEX significantly protected residual hearing and reduced fibrosis. As well as being used as a device in its own right or in combination with cochlear implants, the hydrogel-filled reservoir represents a new drug delivery system that feasibly could be replenished with therapeutic agents to provide sustained treatment of the inner ear.}, language = {en} } @phdthesis{Heise2020, author = {Heise, Kathrin Leonie}, title = {Charakterisierung eines 3D-Mikrotumormodells zur Untersuchung von Tumor-Stroma-Interaktionen}, doi = {10.25972/OPUS-21534}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-215347}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2020}, abstract = {Tumorzellen, Stromazellen, Extrazellul{\"a}rmatrix (EZM) und l{\"o}sliche Faktoren in der Tumormikroumgebung beeinflussen und verst{\"a}rken sich gegenseitig in der Ausbildung eines malignen Ph{\"a}notyps. Sowohl die fibrotische EZM als auch eine kleine Subpopulation von pluripotenten Tumorstammzellen sind bekanntermaßen f{\"u}r die Steigerung der Tumoraggressivit{\"a}t verantwortlich. Inwiefern diese beiden unabh{\"a}ngigen Faktoren im Kontext von Brustkrebs miteinander in Beziehung stehen, ist jedoch bis heute unklar. Um untersuchen zu k{\"o}nnen, welchen Beitrag Tumorzellen, Stromazellen, EZM und l{\"o}sliche Faktoren einzeln und im Zusammenspiel zur Malignit{\"a}t eines Tumors leisten, ist die Entwicklung geeigneter in-vitro-Modelle unabdingbar. Daher war es das Ziel dieser Arbeit, ein 3D-Mikrotumormodell zu generieren, in dem eine Analyse dieser genannten Faktoren stattfinden k{\"o}nnte. An diesem Modell wurden dar{\"u}ber hinaus erste Untersuchungen von im Tumorkontext bekannten EZM-Proteinen durchgef{\"u}hrt. Um die dreidimensionale Anordnung von Tumorzellen und ihrer Gewebeumgebung ad{\"a}quat wiedergeben zu k{\"o}nnen, beinhalteten die 3D-Tumorsph{\"a}roide sowohl Brustkrebszellen (MDA-MB-231) als auch Stromazellen (hASCs). Die EZM als wichtiger Bestandteil der (Tumor-) Mikroumgebung sollte {\"u}bersichtshalber durch H{\"a}matoxylin-Eosin-F{\"a}rbung und detaillierter durch immunhistochemische Analyse nach zwei verschiedenen Kulturzeitpunkten charakterisiert werden, um EZM-Ver{\"a}nderungen im zeitlichen Verlauf darzustellen. Im Fokus der Analyse standen die beiden wichtigsten profibrotischen EZM-Proteine Fibronektin und Kollagen I, die maßgeblich an der Pathogenese von Brustkrebs beteiligt sind. Zudem wurde das Vorkommen des Myofibroblastenmarkers α-SMA untersucht. An den Sph{\"a}roiden einer Kontrollgruppe, die lediglich hASCs beinhaltete, sollte vergleichend eine Analyse der genannten EZM-Proteine sowie α-SMA durchgef{\"u}hrt werden. Um schließlich den Einfluss der von Tumorzellen sezernierten l{\"o}slichen Faktoren in der Tumormikroumgebung herauszustellen, wurden Sph{\"a}roide aus hASCs in tumorkonditioniertem Medium gez{\"u}chtet und darin ebenfalls Matrixproteine und α-SMA untersucht. Abschließend erfolgte eine Korrelation der EZM-Analyse mit dem Vorhandensein von Tumorstammzellen in den 3D-Tumorsph{\"a}roiden. Daf{\"u}r wurden die Tumorstammzellen mithilfe eines GFP-basierten Reporters f{\"u}r den Stammzellmarker NANOG (NANOG-GFP-Reporterzelllinie) in mikroskopischen Aufnahmen der 3D-Tumorsph{\"a}roide nachgewiesen und im Kontext mit der EZM lokalisiert.}, subject = {Brustkrebs}, language = {de} } @phdthesis{Ryma2022, author = {Ryma, Matthias}, title = {Exploiting the Thermoresponsive Properties of Poly(2-oxazoline)s for Biofabrication}, doi = {10.25972/OPUS-24746}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-247462}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2022}, abstract = {In this thesis, non-modified POx, namely PnPrOx and PcycloPrOx, with an LCST in the physiological range between 20 and 37°C have been utilized as materials for three different biofabrication approaches. Their thermoresponsive behavior and processability were exploited to establish an easy-to-apply coating for cell sheet engineering, a novel method to create biomimetic scaffolds based on aligned fibrils via Melt Electrowriting (MEW) and the application of melt electrowritten sacrificial scaffolds for microchannel creation for hydrogels. Chapter 3 describes the establishment of a thermoresponsive coating for tissue culture plates. Here, PnPrOx was simply dissolved in water and dried in well plates and petri dishes in an oven. PnPrOx adsorbed to the surface, and the addition of warm media generated a cell culture compatible coating. It was shown that different cell types were able to attach and proliferate. After confluency, temperature reduction led to the detachment of cell sheets. Compared to standard procedures for surface coating, the thermoresponsive polymer is not bound covalently to the surface and therefore does not require specialized equipment and chemical knowledge. However, it should be noted that the detachment of the cell layer requires the dissolution of the PnPrOx-coating, leading to possible polymer contamination. Although it is only a small amount of polymer dissolved in the media, the detached cell sheets need to be washed by media exchange for further processing if required. ...}, subject = {Thermoresponsive Polymere}, language = {en} } @phdthesis{Haschke2021, author = {Haschke, Sebastian}, title = {Untersuchung Thiol-En vernetzter Gelatine Hydrogele und Vergleich mit Alginat-Gelatine in Bezug auf das in vitro Zellverhalten von Fibroblasten}, doi = {10.25972/OPUS-24872}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-248727}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2021}, abstract = {Hydrogele stehen als Material f{\"u}r den 3D-Biodruck zunehmend im Fokus aktueller Forschung, da sie aufgrund ihrer wasserhaltigen Struktur optimale Voraussetzungen f{\"u}r Anwendungen der Zellkultur aufweisen. Durch die Verarbeitung solcher Biotinten mittels additiver Fertigungstechniken der Biofabrikation erhofft man sich besch{\"a}digtes oder krankes Gewebe zu heilen oder zu ersetzen. Allerdings wird der Fortschritt in diesem Bereich durch einen Mangel an geeigneten Materialien gebremst, weshalb die Entwicklung neuer Biotinten von zentraler Bedeutung ist. Das Polymer GelAGE ist ein am Lehrstuhl f{\"u}r Funktionswerkstoffe der Medizin und Zahnheilkunde der Universit{\"a}t W{\"u}rzburg synthetisiertes Hydrogelsystem. Zu diesem {\"u}ber eine Thiol-En Reaktion vernetzenden Material stehen systematische Untersuchungen der f{\"u}r die in vitro Zellkultur relevanten Eigenschaften noch aus. Das Ziel dieser Arbeit war daher die biologische Evaluation von GelAGE und der Vergleich mit der Biotinte Alginat-Gelatine. Zu diesem Zweck wurden L929-Zellen f{\"u}r 7 Tage in verschiedenen Hydrogelzusammensetzungen in vitro kultiviert. Um die zytokompatiblen Eigenschaften in den verschiedenen Versuchsgruppen zu untersuchen, wurden die Proben mittels der in vitro Testverfahren Live/Dead F{\"a}rbung, DNA-Assay, CCK-8-Assay und Phalloidin-F{\"a}rbung analysiert. Im Rahmen dieser Arbeit konnte ein Herstellungsprotokoll f{\"u}r das Material GelAGE etabliert werden, welches eine Grundlage f{\"u}r die Durchf{\"u}hrung weiterer biologischer Experimente bietet. Das Resultat der biologischen Untersuchungen war, dass das Polymer GelAGE als zytokompatibel bewertet werden kann, es jedoch nicht die Qualit{\"a}t des Alginat-Gelatine Hydrogelsystems aufweist. Allerdings konnten die Eigenschaften der GelAGE Proben teilweise durch eine Modifikation mit Humanem Pl{\"a}ttchenlysat verbessert werden. Des Weiteren konnten deutliche Unterschiede in der Zell-Material- Interaktion zwischen den verschiedenen GelAGE Varianten nachgewiesen werden.}, subject = {Hydrogel}, language = {de} } @article{ShanBoeckKelleretal.2021, author = {Shan, Junwen and B{\"o}ck, Thomas and Keller, Thorsten and Forster, Leonard and Blunk, Torsten and Groll, J{\"u}rgen and Teßmar, J{\"o}rg}, title = {TEMPO/TCC as a Chemo Selective Alternative for the Oxidation of Hyaluronic Acid}, series = {Molecules}, volume = {26}, journal = {Molecules}, number = {19}, issn = {1420-3049}, doi = {10.3390/molecules26195963}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-248362}, year = {2021}, abstract = {Hyaluronic acid (HA)-based hydrogels are very commonly applied as cell carriers for different approaches in regenerative medicine. HA itself is a well-studied biomolecule that originates from the physiological extracellular matrix (ECM) of mammalians and, due to its acidic polysaccharide structure, offers many different possibilities for suitable chemical modifications which are necessary to control, for example, network formation. Most of these chemical modifications are performed using the free acid function of the polymer and, additionally, lead to an undesirable breakdown of the biopolymer's backbone. An alternative modification of the vicinal diol of the glucuronic acid is oxidation with sodium periodate to generate dialdehydes via a ring opening mechanism that can subsequently be further modified or crosslinked via Schiff base chemistry. Since this oxidation causes a structural destruction of the polysaccharide backbone, it was our intention to study a novel synthesis protocol frequently applied to selectively oxidize the C6 hydroxyl group of saccharides. On the basis of this TEMPO/TCC oxidation, we studied an alternative hydrogel platform based on oxidized HA crosslinked using adipic acid dihydrazide as the crosslinker.}, language = {en} } @unpublished{SchaeferJanzenBakircietal.2019, author = {Schaefer, Natascha and Janzen, Dieter and Bakirci, Ezgi and Hrynevich, Andrei and Dalton, Paul D. and Villmann, Carmen}, title = {3D Electrophysiological Measurements on Cells Embedded within Fiber-Reinforced Matrigel}, series = {Advanced Healthcare Materials}, journal = {Advanced Healthcare Materials}, doi = {10.1002/adhm.201801226}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-244194}, year = {2019}, abstract = {2D electrophysiology is often used to determine the electrical properties of neurons, while in the brain, neurons form extensive 3D networks. Thus, performing electrophysiology in a 3D environment provides a closer situation to the physiological condition and serves as a useful tool for various applications in the field of neuroscience. In this study, we established 3D electrophysiology within a fiber-reinforced matrix to enable fast readouts from transfected cells, which are often used as model systems for 2D electrophysiology. Using melt electrowriting (MEW) of scaffolds to reinforce Matrigel, we performed 3D electrophysiology on a glycine receptor-transfected Ltk-11 mouse fibroblast cell line. The glycine receptor is an inhibitory ion channel associated when mutated with impaired neuromotor behaviour. The average thickness of the MEW scaffold was 141.4 ± 5.7µm, using 9.7 ± 0.2µm diameter fibers, and square pore spacings of 100 µm, 200 µm and 400 µm. We demonstrate, for the first time, the electrophysiological characterization of glycine receptor-transfected cells with respect to agonist efficacy and potency in a 3D matrix. With the MEW scaffold reinforcement not interfering with the electrophysiology measurement, this approach can now be further adapted and developed for different kinds of neuronal cultures to study and understand pathological mechanisms under disease conditions.}, language = {en} } @phdthesis{Bruns2015, author = {Bruns, Constanze}, title = {Der Einfluss von Laktobazillen auf Oberfl{\"a}che und Eigenschaften von verschiedenen Nahtmaterialien}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-132982}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2015}, abstract = {Hintergrund: Nach oralchirurgischen Eingriffen empfiehlt der Operateur allgemein die Vermeidung von Milchprodukten in Hinblick auf eine bessere Heilung im Wundgebiet. Dies st{\"u}tzt sich u.a. auf die Annahme, dass Laktobazillen und ihre Stoffwechselprodukte (z.B. Milchs{\"a}ure) Nahtmaterial angreifen k{\"o}nnen. Der Aufbau dieser Studie zielte darauf ab, diesen Sachverhalt in Frage zu stellen und Funktionsverluste bei Milchs{\"a}ureexposition sowie Besieldungsverhalten der Bakterien zu charakterisieren. Material und Methoden: Polyamid (PA), Polyester/Polyethylenterephtalat (PET), Polypropylen (PP), Polyvinylidenfluorid (PVDF), Seide, Polyglycols{\"a}ure (PGA bzw. PGACL), teilweise mit Polylactid (PLA), Polydioxanon (PDO) und Polytetrafluorethylen (PTFE) kamen zur Anwendung. Die F{\"a}den wurden mit L.acidophilus (LAC) beimpft, inkubiert und anschließen im Tensiometer mit verschiedenen Knotenvarianten getestet. F{\"u}r die Keimbesiedlung (CFU) wurden die F{\"a}den beimpft, inkubiert und das Keimmaterial anschließend mit Ultraschall- Vortex- Verfahren vom Faden abgel{\"o}st und ausgez{\"a}hlt. Dieses Verfahren wurde durch REM- Aufnahmen zus{\"a}tzlich bewertet. Ergebnisse: Reißfestigkeiten waren stets im Rahmen der Herstellerangaben bzw. dar{\"u}ber zu verzeichnen. Alle resorbierbaren F{\"a}den hatten h{\"o}here Ausgangsreißkr{\"a}fte als die nichtresorbierbaren Produkte. Die Applikation eines Knotens minderte ausschlaggebend f{\"u}r alle Produkte die maximale Reißfestigkeit eines Materials. Die Knotenhaltbarkeiten konnten sich w{\"a}hrend der Liegezeit im sauren w{\"a}ssrigen Milieu ver{\"a}ndern. Die f{\"u}r klinische Anwendungen besten Ergebnisse verzeichneten PA als nichtresorbierbare, monofiles PDO und polyfiles PGA/PLA + CHX als resorbierbare Vertreter. Eine erh{\"o}hte CFU-Zahl auf polyfilen F{\"a}den im Vergleich zu monofilen F{\"a}den wurde best{\"a}tigt. Seide (polyfil, nicht resorbierbar) hatte mit Abstand die h{\"o}chsten CFU, gefolgt von PGACL (polyfil, resorbierbar). PVDF (monofil, nichtresorbierbar) hatte die niedrigsten CFU- Werte. Im Schnitt war die CFU-Zahl von PGA/PLA+CHX (polyfil, resorbierbar) {\"a}hnlich hoch wie die von monofilen Produkten. Diskussion: Die Annahme, dass eine Kontamination mit LAC den Heilungserfolg beeinflussen kann, wurde im Hinblick auf Materialerm{\"u}dung durch S{\"a}ureexposition aus Stoffwechselprodukten des Bakteriums entkr{\"a}ftet. Die f{\"u}r klinische Anwendungen besten Ergebnisse verzeichneten PA als nichtresorbierbare, polyfiles PGA/PLA + CHX als resorbierbare Vertreter. Alle getesteten Produkte entsprachen trotz LAC- Einwirkungen den Herstellerangaben und haben somit die materiellen Voraussetzungen einer vorhersagbaren Nahthaltbarkeit erbracht.}, subject = {Lactobacillus acidophilus}, language = {de} } @phdthesis{Kessler2015, author = {Keßler, Martina}, title = {Biodegradable solvent cast films and solution electrospun meshes for the prevention of postsurgical adhesions}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-129358}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2015}, abstract = {Intraperitoneal adhesions are fibrous bands that connect tissues in the peritoneal cavity that are usually separated. These adhesions form as a consequence of trauma, inflammation or surgical interventions and often result in severe consequences such as chronic pain, small bowel obstructions or female infertility. The aim of this thesis was to develop a synthetic barrier device for adhesion prevention made of modified poly(lactide) [PLA]. Solid PLA films (SurgiWrap®) are already successfully in clinical use due to the good biocompatibility and the biodegradability of the material resulting in non-toxic degradation products since lactic acid is naturally part of the metabolic circles of the human body. Considering the brittleness and stiffness of the films, the long degradation time of several months as well as the need for suturing, there is potential for optimization. Through a copolymerization with the hydrophilic poly(ethylene glycol) [PEG], a reduction of the degradation time was intendend. Moreover, the copolymerization should also lead to an improvement of the mechanical properties of the films since PEG acts as plasticizer for PLA. Linear PLA-PEG-PLA triblock copolymers as well as star-shaped PEG-PLA copolymers were synthesized via standard ring opening polymerization to tailor the barrier properties. Besides solid films, solution electrospun meshes from PLA and the synthesized PEG-PLA copolymers were investigated for a potential application as well. Since suturing of a barrier additionally induces adhesion formation, alginate coated membranes were prepared in order to achieve self-adhesiveness. With the intention to reduce infections and consequently inflammation, electrospun meshes and solvent cast films were loaded with the antibacterial drug triclosan and drug release as well as antibacterial efficacy was investigated. Mechanical tests confirmed that through the variation of the PEG content and branching the mechanical properties can be tailored and are in good accordance with the glass transition temperatures [Tg] of the polymers. Consequently, potentially adequate mechanical properties for surgical handling as well as for the performance within the patient's body were successfully achieved. Degradation studies revealed that the degradation time was significantly shorter for PEG-PLA membranes than for PLA films and with an appropriate PEG content could be adjusted to the intended time frame. Cell adhesion and viability tests confirmed the non-toxicity of the clinically used PLA films as well as of PEG-PLA films and meshes. With a bioadhesion test the benefit of an alginate coated side towards the pure PLA film concerning self-adhesiveness was successfully demonstrated. Moreover, optical evaluations and a T-peel test of different alginate coated PLA films showed that the cohesion between the chemically different layers was distinctly enhanced by the use of an appropriate PEG-PLA mesh as intermediate cohesion promoting layer. In in vitro release studies with triclosan loaded films a higher release was determined for PEG-PLA than for PLA films. In agar diffusion tests a higher and longer inhibition of staphylococcus aureus growth was observed confirming the release results. Moreover, drug loaded meshes (especially drug loaded after electrospinning) showed enhanced and elongated bacterial inhibition in comparison to films.}, subject = {Polymere}, language = {en} } @article{ProjahnSimsekyilmazSinghetal.2014, author = {Projahn, Delia and Simsekyilmaz, Sakine and Singh, Smriti and Kanzler, Isabella and Kramp, Birgit K. and Langer, Marcella and Burlacu, Alexandrina and Bernhagen, J{\"u}rgen and Klee, Doris and Zernecke, Alma and Hackeng, Tilman M. and Groll, J{\"u}rgen and Weber, Christian and Liehn, Elisa A. and Koenen, Roy R.}, title = {Controlled intramyocardial release of engineered chemokines by biodegradable hydrogels as a treatment approach of myocardial infarction}, series = {Journal of Cellular and Molecular Medicine}, volume = {18}, journal = {Journal of Cellular and Molecular Medicine}, number = {5}, issn = {1582-4934}, doi = {10.1111/jcmm.12225}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-116597}, pages = {790-800}, year = {2014}, abstract = {Myocardial infarction (MI) induces a complex inflammatory immune response, followed by the remodelling of the heart muscle and scar formation. The rapid regeneration of the blood vessel network system by the attraction of hematopoietic stem cells is beneficial for heart function. Despite the important role of chemokines in these processes, their use in clinical practice has so far been limited by their limited availability over a long time-span in vivo. Here, a method is presented to increase physiological availability of chemokines at the site of injury over a defined time-span and simultaneously control their release using biodegradable hydrogels. Two different biodegradable hydrogels were implemented, a fast degradable hydrogel (FDH) for delivering Met-CCL5 over 24hrs and a slow degradable hydrogel (SDH) for a gradual release of protease-resistant CXCL12 (S4V) over 4weeks. We demonstrate that the time-controlled release using Met-CCL5-FDH and CXCL12 (S4V)-SDH suppressed initial neutrophil infiltration, promoted neovascularization and reduced apoptosis in the infarcted myocardium. Thus, we were able to significantly preserve the cardiac function after MI. This study demonstrates that time-controlled, biopolymer-mediated delivery of chemokines represents a novel and feasible strategy to support the endogenous reparatory mechanisms after MI and may compliment cell-based therapies.}, language = {en} } @article{KastenNaserBruellhoffetal.2014, author = {Kasten, Annika and Naser, Tamara and Br{\"u}llhoff, Kristina and Fiedler, J{\"o}rg and M{\"u}ller, Petra and M{\"o}ller, Martin and Rychly, Joachim and Groll, J{\"u}rgen and Brenner, Rolf E.}, title = {Guidance of Mesenchymal Stem Cells on Fibronectin Structured Hydrogel Films}, series = {PLOS ONE}, volume = {9}, journal = {PLOS ONE}, number = {10}, doi = {10.1371/journal.pone.0109411}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-114897}, pages = {e109411}, year = {2014}, abstract = {Designing of implant surfaces using a suitable ligand for cell adhesion to stimulate specific biological responses of stem cells will boost the application of regenerative implants. For example, materials that facilitate rapid and guided migration of stem cells would promote tissue regeneration. When seeded on fibronectin (FN) that was homogeneously immmobilized to NCO-sP(EO-stat-PO), which otherwise prevents protein binding and cell adhesion, human mesenchymal stem cells (MSC) revealed a faster migration, increased spreading and a more rapid organization of different cellular components for cell adhesion on fibronectin than on a glass surface. To further explore, how a structural organization of FN controls the behavior of MSC, adhesive lines of FN with varying width between 10 mu m and 80 mu m and spacings between 5 mu m and 20 mu m that did not allow cell adhesion were generated. In dependance on both line width and gaps, cells formed adjacent cell contacts, were individually organized in lines, or bridged the lines. With decreasing sizes of FN lines, speed and directionality of cell migration increased, which correlated with organization of the actin cytoskeleton, size and shape of the nuclei as well as of focal adhesions. Together, defined FN lines and gaps enabled a fine tuning of the structural organization of cellular components and migration. Microstructured adhesive substrates can mimic the extracellular matrix in vivo and stimulate cellular mechanisms which play a role in tissue regeneration.}, language = {en} } @article{RathBrandlHilleretal.2014, author = {Rath, Subha N. and Brandl, Andreas and Hiller, Daniel and Hoppe, Alexander and Gbureck, Uwe and Horch, Raymund E. and Boccaccini, Aldo R. and Kneser, Ulrich}, title = {Bioactive Copper-Doped Glass Scaffolds Can Stimulate Endothelial Cells in Co-Culture in Combination with Mesenchymal Stem Cells}, series = {PLOS ONE}, volume = {9}, journal = {PLOS ONE}, number = {12}, issn = {1932-6203}, doi = {10.1371/journal.pone.0113319}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-114339}, year = {2014}, abstract = {Bioactive glass (BG) scaffolds are being investigated for bone tissue engineering applications because of their osteoconductive and angiogenic nature. However, to increase the in vivo performance of the scaffold, including enhancing the angiogenetic growth into the scaffolds, some researchers use different modifications of the scaffold including addition of inorganic ionic components to the basic BG composition. In this study, we investigated the in vitro biocompatibility and bioactivity of Cu2+-doped BG derived scaffolds in either BMSC (bone-marrow derived mesenchymal stem cells)-only culture or co-culture of BMSC and human dermal microvascular endothelial cells (HDMEC). In BMSC-only culture, cells were seeded either directly on the scaffolds (3D or direct culture) or were exposed to ionic dissolution products of the BG scaffolds, kept in permeable cell culture inserts (2D or indirect culture). Though we did not observe any direct osteoinduction of BMSCs by alkaline phosphatase (ALP) assay or by PCR, there was increased vascular endothelial growth factor (VEGF) expression, observed by PCR and ELISA assays. Additionally, the scaffolds showed no toxicity to BMSCs and there were healthy live cells found throughout the scaffold. To analyze further the reasons behind the increased VEGF expression and to exploit the benefits of the finding, we used the indirect method with HDMECs in culture plastic and Cu2+-doped BG scaffolds with or without BMSCs in cell culture inserts. There was clear observation of increased endothelial markers by both FACS analysis and acetylated LDL (acLDL) uptake assay. Only in presence of Cu2+-doped BG scaffolds with BMSCs, a high VEGF secretion was demonstrated by ELISA; and typical tubular structures were observed in culture plastics. We conclude that Cu2+-doped BG scaffolds release Cu2+, which in turn act on BMSCs to secrete VEGF. This result is of significance for the application of BG scaffolds in bone tissue engineering approaches.}, language = {en} } @phdthesis{Zimmermann2014, author = {Zimmermann, Sabine Annette}, title = {Mechanisch stabile Magnesiumphosphatsch{\"a}ume und deren Zytokompatibilit{\"a}t}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-114055}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2014}, abstract = {Magnesiumphosphatsch{\"a}ume nehmen auf Grund ihrer guten Resorbierbarkeit, unter physiologischen Bedingungen, einen immer gr{\"o}ßeren Stellenwert als Knochenersatzmaterial ein. Ein weiterer Vorteil ist der neutrale pH-Wert den das entstehende Material besitzt. Magnesiumphosphatsch{\"a}ume besitzen eine hochpor{\"o}se offenporige Struktur um zum einen den Knochen nachzuahmen und zum anderen die Steuerung und Bildung von Knochengewebe zu erm{\"o}glichen. In der vorliegenden Arbeit wurden die mechanischen Eigenschaften als auch die Zytokompatibilit{\"a}t der hergestellten Sch{\"a}ume untersucht. Es wurden unterschiedliche Herstellungsverfahren genutzt um Magnesiumphosphatsch{\"a}ume zu erhalten. Zum einen das Replika- Verfahren, die dabei entstandenen Farringtonit Sch{\"a}ume (Mg3(PO4)2, Farringtonit) wurden zu Struvit ((NH4)Mg(PO4)•6H2O) umgewandelt bzw. mit PLGA infiltriert und auf ihre mechanische Eigenschaften hin untersucht. Zum anderen wurde ein proteinbasierter Schaumbildner verwendet. Die Zytokompatibilit{\"a}tspr{\"u}fung wurde mit der Osteosarkomzelllinie MG-63 durchgef{\"u}hrt. Es erfolgte die Untersuchung der Zellproliferation und der Zellaktivit{\"a}t (WST). Zudem wurden Proben mittels Licht- und Elektronenmikroskopie analysiert. Die Feststellung der Proteinexpression erfolgte nach gelelektrophoretischer Auftrennung mittels Western Blot und PCR Analyse.}, subject = {Magnesiumphosphate}, language = {de} } @phdthesis{Hinderer2021, author = {Hinderer, Sandra}, title = {Charakterisierung der Freisetzung verschiedener Antibiotika aus resorbierbaren anorganischen Knochenersatzmaterialien sowie die Untersuchung des Einflusses auf materialcharakteristische Eigenschaften}, doi = {10.25972/OPUS-23083}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-230836}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2021}, abstract = {Synthetische anorganische Knochenersatzmaterialien auf Calcium-Phosphat- und Magnesium-Phosphat-Basis wurden in der hier vorliegenden Dissertation mit verschiedenen handels{\"u}blichen Antibiotika versetzt und deren Freisetzungsverhalten charakterisiert. Zudem wurde der Einfluss des Antibiotikazusatzes auf bestimmte materialcharakteristische Eigenschaften untersucht, hierbei fanden die Quecksilberporosimetrie, die R{\"o}ntgendiffraktometrie und die Rasterelektronenmikroskopie ihre Anwendung. Insbesondere f{\"u}r die Knochenersatzmaterialien auf Calcium-Phosphat-Basis sollte eine klinisch praktikable und demnach m{\"o}glichst einfache Methode etabliert werden, um die Kombination mit einem Antibiotikum durchzuf{\"u}hren. Die Detektion der Antibiotika erfolgte mit Hilfe eines UV/VIS-Spektrophotometers. Zudem wurde f{\"u}r einige ausgew{\"a}hlte Kombinationen aus Antibiotikum und Knochenersatzmaterial durch einen Agardiffusionstest die antibakterielle Wirkung nach der Freisetzung aus dem jeweiligen Tr{\"a}germaterial best{\"a}tigt.}, subject = {Wirkstofffreisetzung}, language = {de} } @phdthesis{Jung2021, author = {Jung, Melissa}, title = {Entwicklung und Charakterisierung vorgemischter lagerstabiler Zementpasten f{\"u}r den 3D-Druck}, doi = {10.25972/OPUS-23018}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-230189}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2021}, abstract = {Ziel dieser Arbeit war die Entwicklung und Charakterisierung vorgemischter Calciumphosphatzementpasten sowie die {\"U}bertragung des Konzepts dieser Pasten auf den 3D-Druck. Es wurden drei verschiedene Zementformulierungen untersucht, basierend auf Pulvermischungen aus α-TCP/DCPA/CaCO3 (Biozement D), TTCP/DCPA und β-TCP/MCPA, die auf verschiedene Materialeigenschaften gepr{\"u}ft und einem 3D-Druckversuch unterzogen wurden. Die Biozement D Paste wurde mit drei Pulver-Fl{\"u}ssigkeits-Verh{\"a}ltnissen (PLR) (80/20, 85/15, 87/13), die TTCP/DCPA Paste mit zwei PLR (83/17, 85/15), und die β-TCP/MCPA Paste ebenfalls mit zwei PLR (67/33, 70/30) getestet. Alle Pasten konnten mit dem 3D-Drucker erfolgreich verdruckt werden. Die Biozement D Paste mit dem PLR 85/15 stellte sich in ihrer Gruppe als die geeignetste Paste heraus. Bessere Ergebnisse bez{\"u}glich der Injizierbarkeit und Druckbarkeit erreichte die TTCP/DCPA Paste. Hier wurden mit beiden PLR formstabile Scaffolds erzielt. Feine Wabenmuster konnten mit dem PLR von 83/17 in Kombination mit einer hohen Druckgeschwindigkeit hergestellt werden. Mit dem h{\"o}heren PLR (85/15) und einer niedrigeren Druckgeschwindigkeit stieg die Formstabilit{\"a}t weiter an, wodurch die hexagonale Struktur exakter gedruckt werden konnte. Ein gutes Druckergebnis konnte auch mit der β-TCP/MCPA Paste und dem PLR 70/30 erreicht werden.}, subject = {Knochenzemente}, language = {de} } @article{LorsonRuoppNadernezhadetal.2020, author = {Lorson, Thomas and Ruopp, Matthias and Nadernezhad, Ali and Eiber, Julia and Vogel, Ulrich and Jungst, Tomasz and L{\"u}hmann, Tessa}, title = {Sterilization Methods and Their Influence on Physicochemical Properties and Bioprinting of Alginate as a Bioink Component}, series = {ACS Omega}, volume = {5}, journal = {ACS Omega}, number = {12}, doi = {10.1021/acsomega.9b04096}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-229460}, pages = {6481-6486}, year = {2020}, abstract = {Bioprinting has emerged as a valuable threedimensional (3D) biomanufacturing method to fabricate complex hierarchical cell-containing constructs. Spanning from basic research to clinical translation, sterile starting materials are crucial. In this study, we present pharmacopeia compendial sterilization methods for the commonly used bioink component alginate. Autoclaving (sterilization in saturated steam) and sterile filtration followed by lyophilization as well as the pharmacopeia non-compendial method, ultraviolet (UV)-irradiation for disinfection, were assessed. The impact of the sterilization methods and their effects on physicochemical and rheological properties, bioprinting outcome, and sterilization efficiency of alginate were detailed. Only sterile filtration followed by lyophilization as the sterilization method retained alginate's physicochemical properties and bioprinting behavior while resulting in a sterile outcome. This set of methods provides a blueprint for the analysis of sterilization effects on the rheological and physicochemical pattern of bioink components and is easily adjustable for other polymers used in the field of biofabrication in the future.}, language = {en} } @article{HauptsteinForsterNadernezhadetal.2022, author = {Hauptstein, Julia and Forster, Leonard and Nadernezhad, Ali and Horder, Hannes and Stahlhut, Philipp and Groll, J{\"u}rgen and Blunk, Torsten and Teßmar, J{\"o}rg}, title = {Bioink Platform Utilizing Dual-Stage Crosslinking of Hyaluronic Acid Tailored for Chondrogenic Differentiation of Mesenchymal Stromal Cells}, series = {Macromolecular Bioscience}, volume = {22}, journal = {Macromolecular Bioscience}, number = {2}, doi = {10.1002/mabi.202100331}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-257556}, pages = {2100331}, year = {2022}, abstract = {3D bioprinting often involves application of highly concentrated polymeric bioinks to enable fabrication of stable cell-hydrogel constructs, although poor cell survival, compromised stem cell differentiation, and an inhomogeneous distribution of newly produced extracellular matrix (ECM) are frequently observed. Therefore, this study presents a bioink platform using a new versatile dual-stage crosslinking approach based on thiolated hyaluronic acid (HA-SH), which not only provides stand-alone 3D printability but also facilitates effective chondrogenic differentiation of mesenchymal stromal cells. A range of HA-SH with different molecular weights is synthesized and crosslinked with acrylated (PEG-diacryl) and allylated (PEG-diallyl) polyethylene glycol in a two-step reaction scheme. The initial Michael addition is used to achieve ink printability, followed by UV-mediated thiol-ene reaction to stabilize the printed bioink for long-term cell culture. Bioinks with high molecular weight HA-SH (>200 kDa) require comparably low polymer content to facilitate bioprinting. This leads to superior quality of cartilaginous constructs which possess a coherent ECM and a strongly increased stiffness of long-term cultured constructs. The dual-stage system may serve as an example to design platforms using two independent crosslinking reactions at one functional group, which allows adjusting printability as well as material and biological properties of bioinks.}, language = {en} } @article{WeissenbergerWeissenbergerGilbertetal.2020, author = {Weissenberger, M. and Weissenberger, M. H. and Gilbert, F. and Groll, J. and Evans, C. H. and Steinert, A. F.}, title = {Reduced hypertrophy in vitro after chondrogenic differentiation of adult human mesenchymal stem cells following adenoviral SOX9 gene delivery}, series = {BMC Musculoskeletal Disorders}, volume = {20}, journal = {BMC Musculoskeletal Disorders}, doi = {10.1186/s12891-020-3137-4}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-229232}, year = {2020}, abstract = {Background Mesenchymal stem cell (MSC) based-treatments of cartilage injury are promising but impaired by high levels of hypertrophy after chondrogenic induction with several bone morphogenetic protein superfamily members (BMPs). As an alternative, this study investigates the chondrogenic induction of MSCs via adenoviral gene-delivery of the transcription factor SOX9 alone or in combination with other inducers, and comparatively explores the levels of hypertrophy and end stage differentiation in a pellet culture system in vitro. Methods First generation adenoviral vectors encoding SOX9, TGFB1 or IGF1 were used alone or in combination to transduce human bone marrow-derived MSCs at 5 x 10\(^2\) infectious particles/cell. Thereafter cells were placed in aggregates and maintained for three weeks in chondrogenic medium. Transgene expression was determined at the protein level (ELISA/Western blot), and aggregates were analysed histologically, immunohistochemically, biochemically and by RT-PCR for chondrogenesis and hypertrophy. Results SOX9 cDNA was superior to that encoding TGFB1, the typical gold standard, as an inducer of chondrogenesis in primary MSCs as evidenced by improved lacuna formation, proteoglycan and collagen type II staining, increased levels of GAG synthesis, and expression of mRNAs associated with chondrogenesis. Moreover, SOX9 modified aggregates showed a markedly lower tendency to progress towards hypertrophy, as judged by expression of the hypertrophy markers alkaline phosphatase, and collagen type X at the mRNA and protein levels. Conclusion Adenoviral SOX9 gene transfer induces chondrogenic differentiation of human primary MSCs in pellet culture more effectively than TGFB1 gene transfer with lower levels of chondrocyte hypertrophy after 3 weeks of in vitro culture. Such technology might enable the formation of more stable hyaline cartilage repair tissues in vivo.}, language = {en} } @phdthesis{Wettstein2020, author = {Wettstein, Lars}, title = {Elektrochemische Abscheidung von Bruschitschichten auf Titan in Gegenwart von Kristallisationsinhibitoren zur Steuerung von Kristallitgr{\"o}ße und biologischer Reaktion}, doi = {10.25972/OPUS-21750}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-217502}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2020}, abstract = {Es erfolgte eine elektrochemische Abscheidung von Bruschitschichten auf Titan in Gegenwart von Kristallisationsinhibitoren. Dabei wurden die Kristallisationsinhibitoren Zitronens{\"a}ure, treta-Natriumdiphosphat-Decahydrat und Phytins{\"a}ure verwendet und die entstandenen Schichten mit denen ohne Inhibitorzugabe verglichen. Um das Ausmaß der Inhibierung zu verifizieren, wurde die Masse aller Schichten gemessen, welche f{\"u}r die Inhibition mit Zitronens{\"a}ure und Phytins{\"a}ure abnahm und f{\"u}r Natriumdiphosphat zunahm. Die kristallographische Zusammensetzung der mit und ohne Inhibierung abgeschiedenen Schichten wurde mit Hilfe der R{\"o}ntgendiffraktometrie bestimmt und zeigte, dass sich reine Bruschitschichten mit unterschiedlichem amorphem Anteil abschieden. Die daraus entstandenen Werte lieferten zugleich die Informationen {\"u}ber die einzelnen Kristallitgr{\"o}ßen innerhalb der Schichten. {\"U}ber den Einfluss der Inhibitoren auf die Schichtmorphologie gaben rasterelektronenmikroskopische Aufnahmen weiteren Aufschluss. Die Inhibition verursachte teils mit Rissen durchzogene Schichten, deren Kristallformationen sich von Standardelektrolyt unterschieden. Ausgew{\"a}hlte Proben wurden unter verschiedenen Bedingungen desinfiziert bzw. sterilisiert und nachfolgend erneut gewogen und mittels R{\"o}ntgendiffraktogrammetrie und Rasterelektronenmikroskopie analysiert. Nach der Desinfektion entstanden reine Bruschitschichten, die an Masse verloren aber trotzdem die typischen Kristallformationen zeigten. Die Sterilisation f{\"u}hrte zur Umwandlung von Bruschit in Monetit und Hydroxylapatit. Des Weiteren wurde die biologische Reaktion der Schichten auf humane f{\"o}tale Osteoblasten-Zelllinien zur {\"U}berpr{\"u}fung der Zellvertr{\"a}glichkeit ermittelt. Die entstandenen Ergebnisse waren nicht verwertbar und enthielt sehr hohe Standardabweichungen.}, subject = {Elektrochemische Abscheidung}, language = {de} } @phdthesis{Meininger2022, author = {Meininger, Markus}, title = {Calcium hydroxide as antibacterial implant coating}, doi = {10.25972/OPUS-26112}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-261122}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2022}, abstract = {In modern medicine hip and knee joint replacement are common surgical procedures. However, about 11 \% of hip implants and about 7 \% of knee implants need re-operations. The comparison of implant registers revealed two major indications for re-operations: aseptic loosening and implant infections, that both severely impact the patients' health and are an economic burden for the health care system. To address these problems, a calcium hydroxide coating on titanium was investigated in this thesis. Calcium hydroxide is a well-known antibacterial agent and used with success in dentistry. The coatings were applied with electrochemically assisted deposition, a versatile tool that combines easiness of process with the ability to coat complex geometries homogeneously. The pH-gradient during coating was investigated and showed the surface confinement of the coating process. Surface pre-treatment altered the surface morphology and chemistry of the titanium substrates and was shown to affect the morphology of the calcium hydroxide coatings. The influence of the coating parameters stirring speed and current pulsing were examined in various configurations and combinations and could also affect the surface morphology. A change in surface morphology results in a changed adhesion and behavior of cells and bacteria. Thus, the parameters surface pre-treatment, stirring speed and current pulsing presented a toolset for tailoring cellular response and antibacterial properties. Microbiological tests with S. aureus and S. epidermidis were performed to test the time-dependent antibacterial activity of the calcium hydroxide coatings. A reduction of both strains could be achieved for 13 h, which makes calcium hydroxide a promising antibacterial coating. To give insight into biofilm growth, a protocol for biofilm staining was investigated on titanium disks with S. aureus and S. epidermidis. Biofilm growth could be detected after 5 days of bacterial incubation, which was much earlier than the 3 weeks that are currently assumed in medical treatment. Thus, it should be considered to treat infections as if a biofilm were present from day 5 on. The ephemeral antibacterial properties of calcium hydroxide were further enhanced and prolonged with the addition of silver and copper ions. Both ionic modifications significantly enhanced the bactericidal potential. The copper modification showed higher antibacterial effects than the silver modification and had a higher cytocompatibility which was comparable to the pure calcium hydroxide coating. Thus, copper ions are an auspicious option to enhance the antibacterial properties. Calcium hydroxide coatings presented in this thesis have promising antibacterial properties and can easily be applied to complex geometries, thus they are a step in fighting aseptic loosening and implant infections.}, subject = {Calciumhydroxid}, language = {en} } @phdthesis{Kade2023, author = {Kade, Juliane Carolin}, title = {Expanding the Processability of Polymers for a High-Resolution 3D Printing Technology}, doi = {10.25972/OPUS-27005}, url = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-270057}, school = {Universit{\"a}t W{\"u}rzburg}, year = {2023}, abstract = {This thesis identifies how the printing conditions for a high-resolution additive manufacturing technique, melt electrowriting (MEW), needs to be adjusted to process electroactive polymers (EAPs) into microfibers. Using EAPs based on poly(vinylidene difluoride) (PVDF), their ability to be MEW-processed is studied and expands the list of processable materials for this technology.}, subject = {Polymere}, language = {en} }