TY - THES A1 - Bakirci, Ezgi T1 - Development of \(In\) \(vitro\) Models for Tissue Engineering Applications Using a High-Resolution 3D Printing Technology T1 - Entwicklung von \(In\) \(vitro\)-Modellen für Tissue-Engineering-Anwendungen mithilfe einer hochauflösenden 3D-Drucktechnologie N2 - In vitro models mimic the tissue-specific anatomy and play essential roles in personalized medicine and disease treatments. As a sophisticated manufacturing technology, 3D printing overcomes the limitations of traditional technologies and provides an excellent potential for developing in vitro models to mimic native tissue. This thesis aims to investigate the potential of a high-resolution 3D printing technology, melt electrowriting (MEW), for fabricating in vitro models. MEW has a distinct capacity for depositing micron size fibers with a defined design. In this thesis, three approaches were used, including 1) extending the MEW polymer library for different biomedical applications, 2) developing in vitro models for evaluation of cell growth and migration toward the different matrices, and 3) studying the effect of scaffold designs and biochemical cues of microenvironments on cells. First, we introduce the MEW processability of (AB)n and (ABAC)n segmented copolymers, which have thermally reversible network formulation based on physical crosslinks. Bisurea segments are combined with hydrophobic poly(dimethylsiloxane) (PDMS) or hydrophilic poly(propylene oxide)-poly(ethylene oxide)-poly(propylene oxide) (PPO-PEG-PPO) segments to form the (AB)n segmented copolymers. (ABAC)n segmented copolymers contain all three segments: in addition to bisurea, both hydrophobic and hydrophilic segments are available in the same polymer chain, resulting in tunable mechanical and biological behaviors. MEW copolymers either support cells attachment or dissolve without cytotoxic side effects when in contact with the polymers at lower concentrations, indicating that this copolymer class has potential in biological applications. The unique biological and surface properties, transparency, adjustable hydrophilicity of these copolymers could be beneficial in several in vitro models. The second manuscript addresses the design and development of a melt electrowritten competitive 3D radial migration device. The approach differs from most of the previous literature, as MEW is not used here to produce cell invasive scaffolds but to fabricate an in vitro device. The device is utilized to systematically determine the matrix which promotes cell migration and growth of glioblastoma cells. The glioblastoma cell migration is tested on four different Matrigel concentrations using a melt electrowritten radial device. The glioblastoma U87 cell growth and migration increase at Matrigel concentrations 6 and 8 mg mL-1 In the development of this radial device, the accuracy, and precision of melt electrowritten circular shapes were investigated. The results show that the printing speed and design diameter are essential parameters for the accuracy of printed constructs. It is the first instance where MEW is used for the production of in vitro devices. The influence of biochemical cues and scaffold designs on astrocytes and glioblastoma is investigated in the last manuscript. A fiber comprising the box and triangle-shaped pores within MEW scaffolds are modified with biochemical cues, including RGD and IKVAV peptides using a reactive NCO-sP(EO-stat-PO) macromer. The results show that astrocytes and glioblastoma cells exhibit different phenotypes on scaffold designs and peptide-coated scaffolds. N2 - In-vitro-Modelle sind Werkzeuge, die die gewebespezifische Anatomie nachbilden und eine wesentliche Rolle in der personalisierten Medizin und bei der Behandlung von Krankheiten spielen. Als hochentwickelte, multifunktionale Fertigungstechnologie überwindet der 3D-Druck die Grenzen herkömmlicher Technologien und bietet ein hervorragendes Potenzial für die Herstellung von In-vitro-Modellen. Der 3D-Druck ist eine der vielversprechendsten Techniken, um biologische Materialien in einer komplexen Anordnung zusammenzusetzen, die das natürliche Gewebe nachahmt. In dieser Arbeit soll das Potenzial der hochauflösenden 3D-Drucktechnologie melt electrowriting (MEW), für die Herstellung von In-vitro-Modellen untersucht werden. Wir konzentrieren uns auf drei Ansätze: 1) die Erweiterung der MEW-Polymerbibliothek für verschiedene biomedizinische Anwendungen, 2) die Entwicklung von In-vitro-Modellen zur Bewertung des Zellwachstums und der Zellmigration in Richtung der verschiedenen Matrizes und 3) die Untersuchung der Auswirkungen von MEW-Gerüstdesigns und biochemischen Faktoren der Mikroumgebung auf Zellen. Zunächst haben wir die MEW-Verarbeitbarkeit von segmentierten (AB)n- und (ABAC)n-Copolymeren vorgestellt, die eine thermisch reversible Netzwerkformulierung auf der Grundlage physikalischer Vernetzungen aufweisen. Bisurea-Segmente werden mit hydrophoben hydrophobic poly(dimethyl siloxane) (PDMS) oder hydrophilen poly(propylene oxide)-poly(ethylene oxide)-poly(propylene oxide) (PPO-PEG-PPO) Segmenten kombiniert, um die (AB)n segmentierten Copolymere zu bilden. Segmentierte (ABAC)n-Copolymere enthalten alle drei Segmente: Zusätzlich zu den Bisurea-Segmenten sind sowohl hydrophobe als auch hydrophile Segmente in derselben Polymerkette vorhanden, was den segmentierten (ABAC)n-Copolymeren abstimmbare mechanische und biologische Eigenschaften verleiht. MEW-Copolymere unterstützten entweder die Anhaftung an Zellen oder lösten sich ohne zytotoxische Nebenwirkungen auf, wenn sie in niedrigeren Konzentrationen mit ihnen in Berührung kamen, was darauf hindeutet, dass diese Copolymerklasse über umfassende biologische Eigenschaften verfügt. Die einzigartigen biologischen Eigenschaften und Oberflächeneigenschaften, die Transparenz und die einstellbare Hydrophilie dieser Copolymere könnten in verschiedenen In-vitro-Modellen von Vorteil sein. Das zweite Manuskript befasst sich mit einem durch MEW hergestellten wettbewerbsfähigen 3D-Radialmigrationsdesign. Der Ansatz unterscheidet sich vom Großteil der MEW-Literatur, da MEW nicht zur Herstellung von invasiven Zellgerüsten verwendet wurde, sondern zur Herstellung eines In-vitro-Designs diente. Das Design wurde verwendet, um systematisch die Matrix zu bestimmen, die die Zellmigration und das Wachstum von Glioblastomzellen fördert. Die Migration der Glioblastomzellen wurde auf vier verschiedenen Matrigel-Konzentrationen unter Verwendung einer durch MEW hergestellten Radialvorrichtung getestet. Das Wachstum und die Migration der Glioblastomzellen U87 nahmen bei Matrigelkonzentrationen von 6 und 8 mg mL-1 zu. Wir untersuchten auch die Genauigkeit und Präzision der durch MEW erzeugten Kreisformen. Die Ergebnisse zeigten, dass die Druckgeschwindigkeit und der Designdurchmesser wesentliche Parameter für die Genauigkeit der gedruckten Konstrukte sind. Die Arbeit ist die erste Studie, die MEW für die Herstellung von In-vitro-Modellen verwendet. Im letzten Manuskript wurde der Einfluss von biochemische Funktionalisierung in Kombination mit Gerüstdesigns auf Astrozyten und Glioblastome untersucht. Die kastenförmigen und achteckigen MEW-Gerüste wurden mit biochemischen Wirkstoffen modifiziert, darunter RGD- und IKVAV-Peptide unter Verwendung von reaktivem NCO-sP(EO-stat-PO). Wir fanden heraus, dass Astrozyten und Glioblastomzellen unterschiedliche Phänotypen auf den verschiedenen Designs und mit Peptiden beschichteten Gerüsten aufweisen. KW - Melt electrowriting KW - 3D-Druck KW - 3D printing KW - In vitro model Y1 - 2024 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-251645 ER - TY - JOUR A1 - Bakirci, Ezgi A1 - Frank, Andreas A1 - Gumbel, Simon A1 - Otto, Paul F. A1 - Fürsattel, Eva A1 - Tessmer, Ingrid A1 - Schmidt, Hans‐Werner A1 - Dalton, Paul D. T1 - Melt Electrowriting of Amphiphilic Physically Crosslinked Segmented Copolymers JF - Macromolecular Chemistry and Physics N2 - Various (AB)\(_{n}\) and (ABAC)\(_{n}\) segmented copolymers with hydrophilic and hydrophobic segments are processed via melt electrowriting (MEW). Two different (AB)\(_{n}\) segmented copolymers composed of bisurea segments and hydrophobic poly(dimethyl siloxane) (PDMS) or hydrophilic poly(propylene oxide)-poly(ethylene oxide)-poly(propylene oxide) (PPO-PEG-PPO) segments, while the amphiphilic (ABAC)\(_{n}\) segmented copolymers consist of bisurea segments in the combination of hydrophobic PDMS segments and hydrophilic PPO-PEG-PPO segments with different ratios, are explored. All copolymer compositions are processed using the same conditions, including nozzle temperature, applied voltage, and collector distance, while changes in applied pressure and collector speed altered the fiber diameter in the range of 7 and 60 µm. All copolymers showed excellent processability with MEW, well-controlled fiber stacking, and inter-layer bonding. Notably, the surfaces of all four copolymer fibers are very smooth when visualized using scanning electron microscopy. However, the fibers show different roughness demonstrated with atomic force microscopy. The non-cytotoxic copolymers increased L929 fibroblast attachment with increasing PDMS content while the different copolymer compositions result in a spectrum of physical properties. KW - melt electrowriting KW - 3D printing KW - additive manufacturing KW - electrohydrodynamics Y1 - 2021 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-257572 VL - 222 IS - 22 ER - TY - JOUR A1 - Bernhard, Lukas A1 - Krumpholz, Roman A1 - Krieger, Yannick A1 - Czempiel, Tobias A1 - Meining, Alexander A1 - Navab, Nassir A1 - Lüth, Tim A1 - Wilhelm, Dirk T1 - PLAFOKON: a new concept for a patient-individual and intervention-specific flexible surgical platform JF - Surgical Endoscopy N2 - Background Research in the field of surgery is mainly driven by aiming for trauma reduction as well as for personalized treatment concepts. Beyond laparoscopy, other proposed approaches for further reduction of the therapeutic trauma have failed to achieve clinical translation, with few notable exceptions. We believe that this is mainly due to a lack of flexibility and high associated costs. We aimed at addressing these issues by developing a novel minimally invasive operating platform and a preoperative design workflow for patient-individual adaptation and cost-effective rapid manufacturing of surgical manipulators. In this article, we report on the first in-vitro cholecystectomy performed with our operating platform. Methods The single-port overtube (SPOT) is a snake-like surgical manipulator for minimally invasive interventions. The system layout is highly flexible and can be adapted in design and dimensions for different kinds of surgery, based on patient- and disease-specific parameters. For collecting and analyzing this data, we developed a graphical user interface, which assists clinicians during the preoperative planning phase. Other major components of our operating platform include an instrument management system and a non-sterile user interface. For the trial surgery, we used a validated phantom which was further equipped with a porcine liver including the gallbladder. Results Following our envisioned preoperative design workflow, a suitable geometry of the surgical manipulator was determined for our trial surgery and rapidly manufactured by means of 3D printing. With this setup, we successfully performed a first in-vitro cholecystectomy, which was completed in 78 min. Conclusions By conducting the trial surgery, we demonstrated the effectiveness of our PLAFOKON operating platform. While some aspects – especially regarding usability and ergonomics – can be further optimized, the overall performance of the system is highly promising, with sufficient flexibility and strength for conducting the necessary tissue manipulations. KW - individualized surgery KW - surgical manipulator KW - operating platform KW - preoperative planning KW - 3D printing Y1 - 2022 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-307490 SN - 0930-2794 SN - 1432-2218 VL - 36 IS - 7 ER - TY - JOUR A1 - Böhm, Christoph A1 - Stahlhut, Philipp A1 - Weichhold, Jan A1 - Hrynevich, Andrei A1 - Teßmar, Jörg A1 - Dalton, Paul D. T1 - The Multiweek Thermal Stability of Medical-Grade Poly(ε-caprolactone) During Melt Electrowriting JF - Small N2 - Melt electrowriting (MEW) is a high-resolution additive manufacturing technology that places unique constraints on the processing of thermally degradable polymers. With a single nozzle, MEW operates at low throughput and in this study, medical-grade poly(ε-caprolactone) (PCL) is heated for 25 d at three different temperatures (75, 85, and 95 °C), collecting daily samples. There is an initial increase in the fiber diameter and decrease in the jet speed over the first 5 d, then the MEW process remains stable for the 75 and 85 °C groups. When the collector speed is fixed to a value at least 10% above the jet speed, the diameter remains constant for 25 d at 75 °C and only increases with time for 85 and 95 °C. Fiber fusion at increased layer height is observed for 85 and 95 °C, while the surface morphology of single fibers remain similar for all temperatures. The properties of the prints are assessed with no observable changes in the degree of crystallinity or the Young's modulus, while the yield strength decreases in later phases only for 95 °C. After the initial 5-d period, the MEW processing of PCL at 75 °C is extraordinarily stable with overall fiber diameters averaging 13.5 ± 1.0 µm over the entire 25-d period. KW - polycaprolactone KW - 3D printing KW - additive manufacturing KW - electrohydrodynamic KW - melt electrospinning writing Y1 - 2022 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-257741 VL - 18 IS - 3 ER - TY - JOUR A1 - Böhm, Christoph A1 - Tandon, Biranche A1 - Hrynevich, Andrei A1 - Teßmar, Jörg A1 - Dalton, Paul D. T1 - Processing of Poly(lactic–co–glycolic acid) Microfibers via Melt Electrowriting JF - Macromolecular Chemistry and Physics N2 - Polymers sensitive to thermal degradation include poly(lactic-co-glycolic acid) (PLGA), which is not yet processed via melt electrowriting (MEW). After an initial period of instability where mean fiber diameters increase from 20.56 to 27.37 µm in 3.5 h, processing stabilizes through to 24 h. The jet speed, determined using critical translation speed measurements, also reduces slightly in this 3.5 h period from 500 to 433 mm min\(^{−1}\) but generally remains constant. Acetyl triethyl citrate (ATEC) as an additive decreases the glass transition temperature of PLGA from 49 to 4 °C, and the printed ATEC/PLGA fibers exhibits elastomeric behavior upon handling. Fiber bundles tested in cyclic mechanical testing display increased elasticity with increasing ATEC concentration. The processing temperature of PLGA also reduces from 165 to 143 °C with increase in ATEC concentration. This initial window of unstable direct writing seen with neat PLGA can also be impacted through the addition of 10-wt% ATEC, producing fiber diameters of 14.13 ± 1.69 µm for the first 3.5 h of heating. The investigation shows that the initial changes to the PLGA direct-writing outcomes seen in the first 3.5 h are temporary and that longer times result in a more stable MEW process. KW - poly(lactide-co-glycolide) KW - 3D printing KW - additive manufacturing KW - electrohydrodynamics KW - melt electrospinning writing KW - plasticizers Y1 - 2022 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-318444 VL - 223 IS - 5 ER - TY - JOUR A1 - Herz, Stefan A1 - Stefanescu, Maria R. A1 - Lohr, David A1 - Vogel, Patrick A1 - Kosmala, Aleksander A1 - Terekhov, Maxim A1 - Weng, Andreas M. A1 - Grunz, Jan-Peter A1 - Bley, Thorsten A. A1 - Schreiber, Laura M. T1 - Effects of image homogeneity on stenosis visualization at 7 T in a coronary artery phantom study: With and without B1-shimming and parallel transmission JF - PloS One N2 - Background To investigate the effects of B\(_1\)-shimming and radiofrequency (RF) parallel transmission (pTX) on the visualization and quantification of the degree of stenosis in a coronary artery phantom using 7 Tesla (7 T) magnetic resonance imaging (MRI). Methods Stenosis phantoms with different grades of stenosis (0%, 20%, 40%, 60%, 80%, and 100%; 5 mm inner vessel diameter) were produced using 3D printing (clear resin). Phantoms were imaged with four different concentrations of diluted Gd-DOTA representing established arterial concentrations after intravenous injection in humans. Samples were centrally positioned in a thorax phantom of 30 cm diameter filled with a custom-made liquid featuring dielectric properties of muscle tissue. MRI was performed on a 7 T whole-body system. 2D-gradient-echo sequences were acquired with an 8-channel transmit 16-channel receive (8 Tx / 16 Rx) cardiac array prototype coil with and without pTX mode. Measurements were compared to those obtained with identical scan parameters using a commercially available 1 Tx / 16 Rx single transmit coil (sTX). To assess reproducibility, measurements (n = 15) were repeated at different horizontal angles with respect to the B0-field. Results B\(_1\)-shimming and pTX markedly improved flip angle homogeneity across the thorax phantom yielding a distinctly increased signal-to-noise ratio (SNR) averaged over a whole slice relative to non-manipulated RF fields. Images without B\(_1\)-shimming showed shading artifacts due to local B\(_1\)\(^+\)-field inhomogeneities, which hampered stenosis quantification in severe cases. In contrast, B\(_1\)-shimming and pTX provided superior image homogeneity. Compared with a conventional sTX coil higher grade stenoses (60% and 80%) were graded significantly (p<0.01) more precise. Mild to moderate grade stenoses did not show significant differences. Overall, SNR was distinctly higher with B\(_1\)-shimming and pTX than with the conventional sTX coil (inside the stenosis phantoms 14%, outside the phantoms 32%). Both full and half concentration (10.2 mM and 5.1 mM) of a conventional Gd-DOTA dose for humans were equally suitable for stenosis evaluation in this phantom study. Conclusions B\(_1\)-shimming and pTX at 7 T can distinctly improve image homogeneity and therefore provide considerably more accurate MR image analysis, which is beneficial for imaging of small vessel structures. KW - stenosis KW - magnetic resonance imaging KW - thorax KW - in vivo imaging KW - coronary arteries KW - image processing KW - 3D printing KW - signal to noise ratio Y1 - 2022 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-300129 VL - 17 IS - 6 ER - TY - THES A1 - Hochleitner, Gernot T1 - Advancing melt electrospinning writing for fabrication of biomimetic structures T1 - Entwicklung des Melt Electrospinning Writing zur Erzeugung biomimetischer Strukturen N2 - 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 (fØ = 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. N2 - Um biomimetische extrazelluläre Matrices für das Tissue Engineering herzustellen, bedienen sich aktuelle Forschungsansätze oftmals der Produktion von Faser-Konstrukten durch additive Fertigung oder Elektrospinn-Verfahren. Das sogenannte Melt Electrospinning Writing (MEW) kombiniert Vorteile beider Techniken und weist dadurch ein hohes Applikationspotential auf. Daher bestand das Ziel der vorliegenden Arbeit in der Weiterentwicklung und Erforschung des MEW. Für diesen Zweck wurde eine neuartige Forschungsanlage konzipiert und gebaut, welche mit einzigartiger Verfahrenspräzision und Prozesskontrolle die Fertigung von hochqualitativen Konstrukten ermöglichte. Auf Basis dessen konnten die durchgeführten Studien das Verständnis des elektrohydrodynamischen Druckvorgangs und der untersuchten Prozessparameter vertiefen und letztendlich zur Ausweitung des Verfahrens auf neue medizinisch relevante Thermoplaste beitragen. Um eine reproduzierbare Herstellung von Scaffolds zu ermöglichen, wurde eine häufig auftretende Prozessinstabilität erforscht und als pulsing, oder in stark ausgeprägten Fällen als long beading, klassifiziert. Durch Prozessanalyse konnte zudem eine Methode zur Vermeidung dieser Instabilität entwickelt werden. Dafür wurden zwei unterschiedliche biokompatible Polymere verwendet: Poly(ε-Caprolacton) (PCL) als bis dahin einziger verfügbarer MEW Werkstoff, sowie erstmalig Poly(2-Ethyl-2-Oxazolin). Die aufgestellte Hypothese umfasst eine universelle Abhängigkeit der pulsing Instabilität zu involvierten Massenströmen, welche durch Anpassung des angelegten Prozessdruckes und der elektrischen Feldstärke reguliert werden kann. Um ein optimales Prozessergebnis für nachfolgende Forschungsarbeiten zu erzielen, wurde zusätzlich ein Leitfaden zur quantitativen Bewertung des Grades der Instabilität bereitgestellt. Durch Kombination kleiner Spinndüsen, kleiner Schmelze-Flussraten und hoher elektrischen Feldstärken, konnten erstmalig PCL Fasern mit sub-mikron Durchmessern (fØ = 817 ± 165 nm) zu präzisen Scaffolds verarbeitet werden. Diese wurden anschließend durch materialwissenschaftliche Analytik charakterisiert. Dabei wurde eine molekulare Vorzugsorientierung und isotrope Kristallausrichtung entlang der Faser beobachtet, welche durch den hohen Verstreckungsgrad des erstarrenden Polymerstrahls erklärt werden konnte. Resultierende sub-mikron Fasern konnten zwar für einen akkuraten Druckvorgang verwendet werden, jedoch erwiesen sich die Strukturen als instabil und daher nicht geeignet für die Handhabung bei Zellkulturstudien. Aus diesem Grund wurde ein Beschichtungsansatz mittels hydrophilen und vernetzbaren Sternmolekülen für Substratflächen herangezogen. Während solche modifizierten Oberflächen bekanntermaßen Zelladhäsion verhindern, konnten gedruckte sub-mikron Scaffolds auf der Oberfläche haften und so für biologische Studien verwendet werden. Durch das gezielte Ablegen von Fasern unterhalb der kritischen Translationsgeschwindigkeit (CTS) des Kollektors, konnten sinusförmige Faserstrukturen erzeugt werden. Analog zu rein viskosen Fluiden, welche durch ein bewegliches Band aufgesammelt werden, schien dieser Vorgang dem sogenannten buckling zu unterliegen und daher phänomenologisch nicht oder nur geringfügig vom elektrischen Feld abhängig zu sein. Zudem konnte eine durchgeführte Studie die direkte Abhängigkeit der Fasergeometrie mit der Kollektorbewegung belegen. Unabhängig vom Prozessdruck, führte eine verminderte Kollektorgeschwindigkeit sc in den Grenzen CTS > sc ≥ 2/3 CTS zu erhöhten Amplituden bzw. Spitze-zu-Spitze Werten und verkürzten Wellenlängen. Durch das kontrollierte Ablegen der Fasern bei Geschwindigkeiten von 100 %, 90 % 80 % und 70 % CTS konnten zudem Scaffolds mit unterschiedlichen mechanischen Eigenschaften hergestellt werden. Speziell der Zugmodul wurde dadurch etwa um eine halbe Größenordnung moduliert (Es = 42 ± 7 MPa bis 173 ± 22 MPa bei 1 – 3 % Dehnung). Dies ist in Kombination mit der Strukturierung für maßgeschneiderte TE Scaffolds von großem Interesse, da zelluläre Systeme sensibel auf ihre Umgebung reagieren können. Des Weiteren wurden Poly(L-Lactid-co-ε-Caprolacton-co-Acryloylcarbonat) und Poly(ε-Caprolacton-co-Acryloylcarbonat) (PCLAC) Copolymere hinsichtlich deren MEW Verarbeitbarkeit untersucht. Solche Kunststoffe können nach dem Druckvorgang mit UV-Strahlung radikalisch vernetzt werden und dadurch deutlich erhöhte mechanische Eigenschaften ausbilden. Für Fasern aus 90 mol.% CL und 10 mol.% AC wurden beispielsweise maximale Zugfestigkeiten von σmax = 53 ± 16 MPa ermittelt. MEW gedruckte sinusförmige Faserstrukturen aus PCLAC wiesen darüber hinaus ein biomimetisches Spannungs-Dehnung-Verhalten auf, vergleichbar zu Sehnen- und Ligamentgewebe. Eine Untersuchung der Zellviabilität von L929 murinen Fibroblasten im Eluattest, sowie eine lebend/tot-Färbung von humanen mesenchymalen Stammzellen auf den Scaffolds, ergab vielversprechende Resultate und damit ein relevantes Anwendungspotential solcher Strukturen als Implantat. Neben genannten Vorteilen, weist MEW als Verfahren bislang allerdings geringe Produktionsgeschwindigkeiten auf. Diese sind daher in den Fokus aktueller Forschungsvorhaben gerückt. Einen Ansatz hierfür bieten Spinndüsen mit hohem Innendurchmesser und erhöhter Austragsrate, wobei die optimierte elektrische Feldstärke, sowie ein Verstrecken durch die Kollektorbewegung, zu den erwünschten dünnen Fasern führen können. Dadurch kann die abwärtslimitierte Düsengröße des FDM Verfahrens überwunden werden. Visionär gedacht, könnte eine solche Anlage direkt in Krankenhäusern zur Fertigung von patienten- und defektspezifischen Implantaten eingesetzt werden. Darüber hinaus ermöglicht die hohe Präzision, zusammen mit dem Drucken von Mikro-Fasern, einen technischen Einsatz zur Herstellung von Membranen, Filtern oder funktionalen Oberflächenbeschichtungen. KW - scaffold KW - polymer KW - 3D printing KW - additive manufacturing KW - melt electrospinning KW - melt electrowriting KW - tissue engineering KW - polymer processing Y1 - 2018 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-162197 ER - TY - JOUR A1 - Hochleitner, Gernot A1 - Jüngst, Tomasz A1 - Brown, Toby D A1 - Hahn, Kathrin A1 - Moseke, Claus A1 - Jakob, Franz A1 - Dalton, Paul D A1 - Groll, Jürgen T1 - Additive manufacturing of scaffolds with sub-micron filaments via melt electrospinning writing JF - Biofabrication N2 - The aim of this study was to explore the lower resolution limits of an electrohydrodynamic process combined with direct writing technology of polymer melts. Termed melt electrospinning writing, filaments are deposited layer-by-layer to produce discrete three-dimensional scaffolds for in vitro research. Through optimization of the parameters (flow rate, spinneret diameter, voltage, collector distance) for poly-ϵ-caprolactone, we could direct-write coherent scaffolds with ultrafine filaments, the smallest being 817 ± 165 nm. These low diameter filaments were deposited to form box-structures with a periodicity of 100.6 ± 5.1 μm and a height of 80 μm (50 stacked filaments; 100 overlap at intersections). We also observed oriented crystalline regions within such ultrafine filaments after annealing at 55 °C. The scaffolds were printed upon NCO-sP(EO-stat-PO)-coated glass slide surfaces and withstood frequent liquid exchanges with negligible scaffold detachment for at least 10 days in vitro. KW - additive manufacturing KW - 3D printing KW - biodegradable polymers KW - microstructures KW - nanostructures Y1 - 2015 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-254053 VL - 7 IS - 3 ER - TY - JOUR A1 - Höhne, Christian A1 - Dickhaut, Nora A1 - Schmitter, Marc T1 - Introduction of a new teaching concept for dentin post preparation with 3D printed teeth JF - European Journal of Dental Education N2 - Introduction The preparation for dentin posts is difficult and hard to learn. There are currently no reproducible simulation models to train this clinical procedure. The purpose of this study was the design, feasibility and evaluation of a three‐dimensional (3D) printed tooth model for the pre‐clinical teaching of students. Materials and methods A printable tooth was designed and printed by a stereolithographic printer. A total of 48 fourth‐year dental students in the first clinical course in prosthodontics were trained in a voluntary hands‐on course on 4 similar printed teeth. The students used standard model teeth and real‐teeth models during their education. They had experience in caries removement and root canal treatment on real patients. Root perforations were counted for every attempt. The different benefits of the 3D printed tooth were evaluated by a questionnaire using German school grades from 1 (best) to 6 (worst). Results The overall rating of the printed tooth was Ø1.9 ± 0.3. The item “suitable exercise option” was rated Ø2.0 ± 0.8, and the teeth were “easy to use” Ø1.9 ± 0.9. The item “realistic approach to dentin post preparation” was rated Ø2.1 ± 0.8, and the teeth showed the “shortcomings at a root perforation” Ø1.5 ± 0.6. The students reported to have much more motivation and enthusiasm to improve their skills with the printed teeth Ø2.1 ± 0.9. They had a strong desire to include these teeth in their pre‐clinical education before the first patient treatment Ø1.6 ± 0.8. The success rate of the dentin post preparation was significantly better for the second 25% (P = .047) and fourth 48% (P = .04) attempt. Conclusions The feasibility of this teaching concept was confirmed. The students had the possibility to learn a correct dentin post preparation on a printed tooth model. The learning effect with this tooth model was rated as good to very good by the questionnaire. KW - 3D printing KW - additive manufacturing KW - CAD KW - CAM KW - clinical practice KW - dental education KW - dentin post KW - printed tooth KW - rapid prototyping KW - stereolithography KW - student training Y1 - 2020 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-215586 VL - 24 IS - 3 SP - 499 EP - 506 ER - TY - JOUR A1 - Höhne, Christian A1 - Schwarzbauer, Raphael A1 - Schmitter, Marc T1 - Introduction of a new teaching concept for crown preparation with 3D printed teeth JF - European Journal of Dental Education N2 - Introduction For both students and teachers, it is challenging to learn and teach a correct crown preparation. The purpose of this study was the design, feasibility and evaluation of a 3D printed tooth model with internal preparation for dental education in crown preparation and to analyse the quality of the prepared printed teeth in comparison with prepared standard model teeth. Materials and methods A printable tooth was designed and printed by a stereolithographic printer. 38 fourth‐year dental students in the first clinical course in prosthodontics were trained in a voluntary course using printed teeth. Different aspects of the printed tooth were evaluated by a questionnaire using German school grades (1 best to 5 worst). The quality of the preparation with the printed teeth and standard training teeth was also rated in an evaluation form done by an expert group consisting of five experienced dentists. Results The workflow was feasible and cost‐effective for the production of the teeth. The overall rating of the printed tooth was Ø 2.0 ± 0.34 in the questionnaire completed by the students. The students rated the printed tooth model (Ø 2.1 ± 0.85) as significantly better than the standard model tooth (Ø 3.3 ± 0.77; P = .000). The students reported great benefits in the use of this model tooth, for example valuable replacement of a standard model and real teeth, direct control of material loss. The quality of the preparation was evaluated by the expert group as significantly better with an overall mean grade of Ø 2.6 ± 0.37 for the printed teeth compared to Ø 2.9 ± 0.42 for the standard model teeth (P = .000). Conclusions The feasibility of this teaching concept was confirmed. The students favoured to work on the innovative 3D‐teeth with internal preparation, emphasising the usefulness of this technique in dental education. The expert group confirmed also the significant training effect of this tooth model in contrast to a standard model tooth. KW - 3D printing KW - additive manufacturing KW - clinical practice KW - dental education KW - printed tooth KW - student training Y1 - 2020 U6 - http://nbn-resolving.de/urn/resolver.pl?urn:nbn:de:bvb:20-opus-218133 VL - 24 IS - 3 SP - 526 EP - 534 ER -