@phdthesis{Sieker2015,
  author    = {Sieker, Jakob Tobias},
  title     = {Direkter adenoviraler Gentransfer von Bone morphogenetic protein-2 und Indian Hedgehog zur Knorpelregeneration im Kaninchenmodell},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-142622},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2015},
  abstract  = {Einleitung Fokale Gelenkknorpeldefekte treten in der Deutschen Bev{\"o}lkerung mit einer gesch{\"a}tzten Inzidenz von {\"u}ber 300 000 j{\"a}hrlichen F{\"a}llen auf. In der US-amerikanischen Bev{\"o}lkerung wird j{\"a}hrlich von {\"u}ber 600 000 F{\"a}llen ausgegangen. Aufgrund der Insuffizienz k{\"o}rpereigener Heilungskapazit{\"a}ten und verf{\"u}gbarer Therapieverfahren, schreitet die Erkrankung regelhaft zur post-traumatischen Arthrose fort. Neben der individuellen Lebensqualit{\"a}tseinschr{\"a}nkung besteht eine sozio{\"o}konomische Bedeutung mit gesch{\"a}tzten Krankheitskosten von j{\"a}hrlich {\"u}ber 10 Milliarden US Dollar in den Vereinigten Staaten. Das Versagen zellbasierter Therapieverfahren beruht unter anderem auf einer Insuffizienz der chondrogenen Differenzierung, sowie der hypertrophen Differenzierung der Chondrozyten mit nachfolgender Osteogenese analog den Vorg{\"a}ngen in der Wachstumsfuge. F{\"u}r die Induktion der chondrogenen Differenzierung stehen insbesondere Mitglieder der TGF-β Superfamilie, wie BMP-2, zur Verf{\"u}gung. Diese sind jedoch ebenso durch eine Induktion der hypertrophen Differenzierung gekennzeichnet. Zur Induktion der Chondrogenese unter Umgehung der TGF-β-Signalwege wurde IHH in-vitro als vielversprechend beschrieben. Bislang besteht jedoch kein Nachweis der in-vivo Effektivit{\"a}t von IHH zur Knorpelreparation. Die Schaffung eines Wachstumsfaktor-Milieus in der Gelenkknorpell{\"a}sion in-vivo stellt ebenso eine Herausforderung dar. Diesbez{\"u}glich wurde ein vereinfachtes Verfahren zum lokalisierten in-vivo Gentransfer mittels adenoviraler Vektoren und autologen Knochenmarkskoagulaten anhand von Markergenen beschrieben. Die Effektivit{\"a}t jenes Verfahrens zur in-vivo Knorpelreparation wurde noch nicht gezeigt. Zweck dieses kontrollierten in-vivo Experimentes ist es, mittels des oben genannten Gentransferverfahrens die Wirksamkeit von BMP-2 und IHH zur Reparation von osteochondralen Defekten in New Zealand White Rabbits nachzuweisen. Die zentrale Hypothese lautete, dass BMP2 beziehungsweise IHH Gentransfer in einer h{\"o}heren langzeit-histologischen Qualit{\"a}t des Reparationsgewebes resultiert. Explorativ sollten dabei Unterschiede in den einzelnen Dimensionen der Gewebequalit{\"a}t anhand des ICRS-II Histology Scoring Systems, sowie der Grad der Typ I (als Faserknorpelmarker), Typ II (als Marker hyalinen Gelenkknorpels) und Typ X Kollagen Deposition (als Marker hypertropher Chondrozyten) beschrieben werden. Material und Methoden Als Tiermodel wurden bilaterale 3,2 mm durchmessende osteochondrale Bohrlochdefekte in der Trochlea von New Zealand White Rabbits verwendet (n=10 unabh{\"a}ngige Tiere, 20 Gelenke). Die Defekte wurden mit autologen Knochenmarkkoageln gef{\"u}llt, die nach vorheriger Beckenkammaspiration gewonnen wurden. In den experimentellen Gruppen wurden die Knochenmarkkoagel beladen mit jeweils 1 x 1011 infekti{\"o}sen Partikeln adenoviraler Vektoren, die cDNA codierend f{\"u}r BMP2 (n=3 Tiere, entsprechend 6 Gelenken) oder IHH (n=4; 8) enthielten. In der Kontrollgruppe wurde das nicht-chondrogene Markergen GFP (n=3; 6) transferiert. Beide Gelenke eines Tieres wurden der gleichen Gruppe zugeordnet. Die histologische Gewebequalit{\"a}t wurde nach 13 Wochen anhand des ICRS-II Scoringsystems durch 3 unabh{\"a}ngige, verblindete Untersucher bewertet. Als prim{\"a}re Outcomes wurden der ICRS-II Parameter „Generelles Assessment", sowie die Typ II Kollagen positive Fl{\"a}che designiert. Als explorative Outcomes wurden die verbleibenden ICRS-II Parameter, sowie die Typ I und Typ X Kollagen Deposition bewertet. Die Korrelation zwischen den Untersuchern wurde nach Pearson ermittelt. Zum Test auf Signifikanz der Gruppenunterschiede wurde ein lineares gemischtes Modell verwendet, welches einer m{\"o}gliche Abh{\"a}ngigkeit beider Gelenke eines Tieres Rechnung tr{\"a}gt. Ergebnisse Qualitative Bewertung des Reparationsknorpels. Dreizehn Wochen nach der Intervention zeigten die meisten der BMP-2 behandelten Gelenke (4 von 6) und alle der IHH behandelten Gelenke (8 von 8) hyalin-artigen Reparationsknorpel, w{\"a}hrend alle GFP behandelten Kontrollgelenke (6 von 6) faserknorpel-artiges Reparationsgewebe zeigten. Zwei BMP-2 behandelten Gelenke zeigten eine ausgepr{\"a}gte intral{\"a}sionale Knochenformation. Prim{\"a}re Outcomes - ICRS-II „Generelles Assessment" und Typ II Kollagen positive Fl{\"a}che. IHH und BMP-2 behandelte Gelenke zeigten im Vergleich zu GFP h{\"o}here Punktzahlen in dem ICRS-II „Generelles Assessment" Parameter: +33.0 (95\% Konfidenzintervall: -0.4, +66.4) Punkte f{\"u}r IHH und +8.5 (-26.6, +43.7) Punkte f{\"u}r BMP-2. Beide Effekte erreichten nicht das Level statistischer Signifikanz (p=0.052 und 0.537). IHH erh{\"o}hte die Typ II Kollagen Deposition in der Defektregion, w{\"a}hrend BMP-2 Gelenke keinen Unterschied zu GFP Kontrollen zeigten: +18.7 (-4.5, +42.0) Punkte f{\"u}r IHH und +0.0 (-29.7, +29.8) Punkte f{\"u}r BMP-2. Die erh{\"o}hte Typ II Kollagendeposition erreichte nicht das konventionelle Level statistischer Signifikanz (p=0.093). Sekund{\"a}re Outcomes - ICRS-II Parameter. In dem Vergleich von BMP-2 mit GFP Kontrollen wurde in keinem der 12 untersuchten Parameter ein signifikanter Unterschied festgestellt. IHH Gentransfer resultierte hingegen in h{\"o}heren Punktzahlen in allen untersuchten Parametern, wobei der Unterschied in 5 der 12 Parameter das Niveau statistischer Signifikanz erreichte. Ein um 21.5 Punkte (+3.6, +39.4) erh{\"o}hter Score wurde f{\"u}r den Parameter „Gewebemorphologie" beobachtet, sowie +21.0 (+6.4, +35.7) f{\"u}r „Chondrozyt{\"a}res Clustering", +31.2 (+0.8, +61.5) f{\"u}r „Formation der Tidemark", +17.3 (+0.2, +34.5) f{\"u}r „Abnorme Kalzifikation/Ossifikation" und +35.0 (+4.6, +65.2) f{\"u}r das „Assessment der mittleren und tiefen Zone". Sekund{\"a}re Outcomes - Marker chondrozyt{\"a}rer Hypertrophie. Eine perizellul{\"a}re Deposition von Typ X Kollagen wurde in allen Gruppen beobachtet. Eine deutlich gesteigerte Deposition wurde nur in den Gelenken beobachtet, die nach BMP2 Gentransfer eine ausgepr{\"a}gte intral{\"a}sionale Knochenformation zeigten. Diskussion Das hier beschriebene Experiment stellt die erste Ver{\"o}ffentlichung der Wirksamkeit von IHH zur Verbesserung der histologischen Knorpelqualit{\"a}t von in-vivo therapierten Gelenkknorpeldefekten dar [175]. Die Hypothese, dass IHH zu einer verbesserten histologischen Knorpelqualit{\"a}t f{\"u}hrt wurde best{\"a}tigt, w{\"a}hrend die Hypothese zu den positiven Effekten von BMP-2 wiederlegt wurde. IHH f{\"u}hrte zu besseren Ergebnissen in allen Untersuchten Parametern, das Niveau statistischer Signifikanz wurde dabei in den Parametern „Gewebemorphologie", „Chondrozyt{\"a}res Clustering", „Formation der Tidemark", „Abnorme Kalzifikation/Ossifikation" und „Assessment der mittleren und tiefen Zone" erreicht. Das prim{\"a}re Ziel dieses Experimentes war es, den „Proof of concept" zu liefern, dass IHH auch in-vivo ein attraktiver Faktor f{\"u}r die Induktion der Chondrogenese darstellt. Das langfristige Ziel ist die Induktion der Chondrogenese unter Umgehung des TGF-β Signalweges zu erzielen, um eine folgende hypertrophe Differenzierung der Chondrozyten und die folgende Ossifikation des reparierten Defektes zu verhindern. Die Limitationen der Studie umfassen die ausschließlich histologische und immunhistochemische durchgef{\"u}hrte Bewertung der Knorpelqualit{\"a}t und eine eingeschr{\"a}nkte statistische Power. Ob IHH es vermag die hypertrophe Differenzierung zu umgehen und somit eine langfristige hyaline Knorpelreparation zu erm{\"o}glichen, ist in weiteren pr{\"a}klinischen Studien mit biochemischer und molekulargenetischer Analyse der Hypertrophie-Marker zu untersuchen. In Bezug auf den klinischen Einsatz zur Knorpelreparation erscheint der Einsatz der Wachstumsfaktoren als Protein auf funktionalisierten Matrices vielversprechend. BMP-2 wird aufgrund der hier beobachteten intral{\"a}sionalen Knochenformation nach BMP2 Gentransfer als nicht geeignet zur Unterst{\"u}tzung der Knorpelreparation in-vivo bewertet.},
  subject      = {Bone morphogenetic protein-2},
  language  = {de}
}
@phdthesis{Rothaug2021,
  author    = {Rothaug, Johanna},
  title     = {Vergleich des Redifferenzierungspotenzials von zonalen Chondrozyten-Subpopulationen im 3D-Hydrogelmodell},
  doi       = {10.25972/OPUS-24922},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-249226},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2021},
  abstract  = {Im Rahmen neuer Therapieans{\"a}tze der Arthrose versucht man mittels Tissue Engineering transplantationsf{\"a}hige, hochwertige Knorpelkonstrukte zu z{\"u}chten. Dabei kommen h{\"a}ufig auch expandierte und redifferenzierte zonenspezifische Chondrozyten-Subpopulationen zum Einsatz. Wenige Studien besch{\"a}ftigten sich bisher mit dem Redifferenzierungspotential dieser Zellen und dem Effekt einer zonalen Schichtung unter verschiedenen Kulturbedingungen. In dieser Arbeit konnten {\"A}hnlichkeiten im Ph{\"a}notyp sowie der Chondrogenese der redifferenzierten Zellen zu den jeweiligen Subpopulationen in nativem Knorpel nachgewiesen werden. Sowohl die zonale Schichtung als auch Ver{\"a}nderungen im Studienprotokoll zeigten sich als entscheidende Einflussfaktoren auf das Zellverhalten. Die Frage nach den optimalen Kulturbedingungen stellt die Forschung jedoch weiterhin vor eine große Herausforderung.},
  subject      = {Osteoarthritis},
  language  = {de}
}
@phdthesis{Noeth2010,
  author    = {N{\"o}th, Alexia Irmgard},
  title     = {Rekonstruktion von Gelenkknorpeldefekten mit einer Kollagen I Hydrogel Matrix - klinische Ergebnisse einer Fallseriestudie},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-52630},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2010},
  abstract  = {F{\"u}r die Rekonstruktion von Gelenkknorpeldefekten des Kniegelenkes in Folge eines Traumas oder einer Osteochondrosis dissecans (OD) stehen verschiedene operative Verfahren zur Verf{\"u}gung. Die Autologe Chondrozytentransplantation (ACT) hat sich als zuverl{\"a}ssiges Rekonstruktionsverfahren erwiesen. In der vorliegenden Arbeit wurde eine prospektive Fallseriestudie f{\"u}r eine neue Form der ACT mit einem Kollagen I Hydrogel (CaReS-Technologie) durchgef{\"u}hrt. Die Vorteile der Technologie liegen zum Einen darin, dass sich die Zellen homogen im Gel verteilen und zum Anderen, dass die Zellen unmittelbar nach dem Herausl{\"o}sen aus dem Gelenkknorpel in das Gel eingebracht werden und dadurch eine geringere Dedifferenzierung der Chondrozyten stattfindet. Von M{\"a}rz 2003 bis Ende 2006 wurden 29 Patienten in die Studie eingeschlossen. Die Ein- und Ausschlusskriterien erf{\"u}llten die Kriterien der Arbeitsgruppe ACT und Tissue Engineering der Deutschen Gesellschaft f{\"u}r Orthop{\"a}die und Unfallchirurgie. Die Eingangs- und Nachuntersuchungsb{\"o}gen wurden an die IKDC Form 2000 angelehnt. Insgesamt zeigte sich ein signifikanter Anstieg des IKDC Scores im mittleren follow-up von 30,7 Monaten von 47,3 auf 74,9 bei den 29 Patienten. Bei Aufschl{\"u}sselung der Patienten bzgl. Diagnose, Defektgr{\"o}ße, Lokalisation und Defektanzahl zeigte sich bei den Behandlungsgruppen OD, Trauma/degenerativ, > 4 cm2, mediale Femurkondyle und Einzeldefekte eine signifikante Zunahme des IKDC Scores im zeitlichen Verlauf. Der postoperative Schmerz zeigte einhergehend mit dem Anstieg des IKDC Scores eine signifikante Abnahme der Schmerzintensit{\"a}t in den Behandlungsgruppen OD, Trauma/degenerativ, > 4 cm2, mediale Femurkondyle und Einzeldefekte. Nachgewiesen wurde ebenfalls ein Anstieg des SF36 Scores, der den gegenw{\"a}rtigen Gesundheitszustand sowohl k{\"o}rperlich als auch psychisch beurteilt. Zusammen mit einer globalen Patientenzufriedenheit von 80\% und einem IKDC Funktionsstatus von I und II bei 77\% der Patienten spiegeln die gewonnenen Daten die Ergebnisse der klassischen ACT bzw. anderer matrixgekoppelten Verfahren wieder. Die CaReS-Technologie stellt somit ein gleichwertiges Verfahren zu den bisher auf dem Markt befindlichen Techniken der ACT dar.},
  subject      = {Gelenkknorpel},
  language  = {de}
}
@phdthesis{Heymer2008,
  author    = {Heymer, Andrea},
  title     = {Chondrogenic differentiation of human mesenchymal stem cells and articular cartilage reconstruction},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-29448},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2008},
  abstract  = {Articular cartilage defects are still one of the major challenges in orthopedic and trauma surgery. Today, autologous chondrocyte transplantation (ACT), as a cell-based therapy, is an established procedure. However, one major limitation of this technique is the loss of the chondrogenic phenotype during expansion. Human mesenchymal stem cells (hMSCs) have an extensive proliferation potential and the capacity to differentiate into chondrocytes when maintained under specific conditions. They are therefore considered as candidate cells for tissue engineering approaches of functional cartilage tissue substitutes. First in this study, hMSCs were embedded in a collagen type I hydrogel to evaluate the cartilaginous construct in vitro. HMSC collagen hydrogels cultivated in different culture media showed always a marked contraction, most pronounced in chondrogenic differentiation medium supplemented with TGF-ß1. After stimulation with chondrogenic factors (dexamethasone and TGF-ß1) hMSCs were able to undergo chondrogenesis when embedded in the collagen type I hydrogel, as evaluated by the temporal induction of cartilage-specific gene expression. Furthermore, the cells showed a chondrocyte-like appearance and were homogeneously distributed within a proteoglycan- and collagen type II-rich extracellular matrix, except a small area in the center of the constructs. In this study, chondrogenic differentiation could not be realized with every hMSC preparation. With the improvement of the culture conditions, e.g. the use of a different FBS lot in the gel fabrication process, a higher amount of cartilage-specific matrix deposition could be achieved. Nevertheless, the large variations in the differentiation capacity display the high donor-to-donor variability influencing the development of a cartilaginous construct. Taken together, the results demonstrate that the collagen type I hydrogel is a suitable carrier matrix for hMSC-based cartilage regeneration therapies which present a promising future alternative to ACT. Second, to further improve the quality of tissue-engineered cartilaginous constructs, mechanical stimulation in specific bioreactor systems are often employed. In this study, the effects of mechanical loading on hMSC differentiation have been examined. HMSC collagen hydrogels were cultured in a defined chondrogenic differentiation medium without TGF-ß1 and subjected to a combined mechanical stimulation protocol, consisting of perfusion and cyclic uniaxial compression. Bioreactor cultivation neither affected overall cell viability nor the cell number in collagen hydrogels. Compared with non-loaded controls, mechanical loading promoted the gene expression of COMP and biglycan and induced an up-regulation of matrix metalloproteinase 3. These results circumstantiate that hMSCs are sensitive to mechanical forces, but their differentiation to chondrocytes could not be induced. Further studies are needed to identify the specific metabolic pathways which are altered by mechanical stimulation. Third, for the development of new cell-based therapies for articular cartilage repair, a reliable cell monitoring technique is required to track the cells in vivo non-invasively and repeatedly. This study aimed at analyzing systematically the performance and biological impact of a simple and efficient labeling protocol for hMSCs. Very small superparamagnetic iron oxide particles (VSOPs) were used as magnetic resonance (MR) contrast agent. Iron uptake was confirmed histologically with prussian blue staining and quantified by mass spectrometry. Compared with unlabeled cells, VSOP-labeling did neither influence significantly the viability nor the proliferation potential of hMSCs. Furthermore, iron incorporation did not affect the differentiation capacity of hMSCs. The efficiency of the labeling protocol was assessed with high resolution MR imaging at 11.7 Tesla. VSOP-labeled hMSCs were visualized in a collagen type I hydrogel indicated by distinct hypointense spots in the MR images, resulting from an iron specific loss of signal intensity. This was confirmed by prussian blue staining. In summary, this labeling technique has great potential to visualize hMSCs and track their migration after transplantation for articular cartilage repair with MR imaging.},
  subject      = {Gelenkknorpel},
  language  = {en}
}
@phdthesis{Hauptstein2022,
  author    = {Hauptstein, Julia},
  title     = {Hyaluronic Acid-based Multifunctional Bioinks for 3D Bioprinting of Mesenchymal Stromal Cells for Cartilage Regeneration},
  doi       = {10.25972/OPUS-26068},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-260681},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2022},
  abstract  = {Articular cartilage is a highly specialized tissue which provides a lubricated gliding surface in joints and thereby enables low-friction movement. If damaged once it has a very low intrinsic healing capacity and there is still no treatment in the clinic which can restore healthy cartilage tissue. 3D biofabrication presents a promising perspective in the field by combining healthy cells and bioactive ink materials. Thereby, the composition of the applied bioink is crucial for defect restoration, as it needs to have the physical properties for the fabrication process and also suitable chemical cues to provide a supportive environment for embedded cells. In the last years, ink compositions with high polymer contents and crosslink densities were frequently used to provide 3D printability and construct stability. But these dense polymeric networks were often associated with restricted bioactivity and impaired cell processes like differentiation and the distribution of newly produced extracellular matrix (ECM), which is especially important in the field of cartilage engineering. Therefore, the aim of this thesis was the development of hyaluronic acid (HA)-based bioinks with a reduced polymer content which are 3D printable and additionally facilitate chondrogenic differentiation of mesenchymal stromal cells (MSCs) and the homogeneous distribution of newly produced ECM. Starting from not-printable hydrogels with high polymer contents and restricted bioactivity, distinct stepwise improvements were achieved regarding stand-alone 3D printability as well as MSC differentiation and homogeneous ECM distribution. All newly developed inks in this thesis made a valuable contribution in the field of cartilage regeneration and represent promising approaches for potential clinical applications. The underlying mechanisms and established ink design criteria can further be applied to other biofabricated tissues, emphasizing their importance also in a more general research setting.},
  subject      = {Hyalurons{\"a}ure},
  language  = {en}
}
@phdthesis{Frischholz2021,
  author    = {Frischholz, Sebastian},
  title     = {Resveratrol Counteracts IL-1β-mediated Impairment of Extracellular Matrix Deposition in 3D Articular Chondrocyte Constructs},
  doi       = {10.25972/OPUS-23745},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-237453},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2021},
  abstract  = {Articular cartilage is an exceptional connective tissue which by a network of fibrillar collagen and glycosaminoglycan (GAG) molecules allows both low- friction articulation and distribution of loads to the subchondral bone (Armiento et al., 2018, Ulrich-Vinther et al., 2003). Because of its very limited ability to self-repair, chondral defects following traumatic injury increase the risk for secondary osteoarthritis (OA) (Muthuri et al., 2011). Still, current OA treatments such as common nonsteroidal anti-inflammatory drugs (NSAIDs) and joint replacement primarily address end-stage symptoms (Tonge et al., 2014). As low-grade inflammation plays a pivotal role in the pathogenesis of OA (Robinson et al., 2016), there is a strong demand for novel therapeutic concepts, such as integrating application of anti-inflammatory agents into cartilage cell- based therapies in order to effectively treat OA affected joints in early disease stages. The polyphenolic phytoalexin resveratrol (RSV), found in the skin of red grapes, berries, and peanuts, has been shown to have effective anti-inflammatory properties (Shen et al., 2012). However, its long-term effects on 3D chondrocyte constructs cultured in an inflammatory environment with regard to tissue quality have remained unexplored so far. Therefore, in this study, pellets made from expanded porcine articular chondrocytes were cultured for 14 days with either the pro-inflammatory cytokine interleukin-1β (IL-1β) (1 - 10 ng/ml) or RSV (50 μM) alone, or a co-treatment with both agents. Constructs treated with chondrocyte medium only served as control. Treatment with IL-1β at 10 ng/ml resulted in a significantly smaller pellet size and reduced DNA content. However, RSV counteracted the IL-1β-induced decrease and significantly enhanced diameter and DNA content. Also, in terms of GAG deposition, treatment with IL-1β at 10 ng/ml resulted in a tremendous depletion of absolute GAG content and GAG/DNA. Again, RSV co-treatment counteracted the inflammatory stimulus and led to a partial recovery of GAG content. Histological analysis utilizing safranin-O staining confirmed these findings. Marked expression of the cartilage-degrading enzyme matrix metalloproteinase 13 (MMP13) was detected in IL-1β-treated pellets, but none upon RSV co- treatment. Moreover, co-treatment of IL-1β-challenged constructs with RSV significantly increased absolute collagen content. However, under non- inflammatory conditions, RSV induced gene expression and protein accumulation of collagen type X, a marker for undesirable hypertrophy. Taken together, in the present thesis, RSV was demonstrated to elicit marked beneficial effects on the extracellular matrix composition of 3D cartilaginous constructs in long-term inflammatory culture in vitro, but also induced hypertrophy under non-inflammatory conditions. Based on these findings, further experiments examining multiple concentrations of RSV under various inflammatory conditions appear desirable concerning potential therapeutic applicability in OA.},
  subject      = {Resveratrol},
  language  = {en}
}
@phdthesis{Berberich2024,
  author    = {Berberich, Oliver},
  title     = {Lateral Cartilage Tissue Integration - Evaluation of Bonding Strength and Tissue Integration \(in\) \(vitro\) Utilizing Biomaterials and Adhesives},
  doi       = {10.25972/OPUS-34602},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-346028},
  school      = {Universit{\"a}t W{\"u}rzburg},
  year      = {2024},
  abstract  = {Articular cartilage defects represent one of the most challenging clinical problem for orthopedic surgeons and cartilage damage after trauma can result in debilitating joint pain, functional impairment and in the long-term development of osteoarthritis. The lateral cartilage-cartilage integration is crucial for the long-term success and to prevent further tissue degeneration. Tissue adhesives and sealants are becoming increasingly more popular and can be a beneficial approach in fostering tissue integration, particularly in tissues like cartilage where alternative techniques, such as suturing, would instead introduce further damage. However, adhesive materials still require optimization regarding the maximization of adhesion strength on the one hand and long-term tissue integration on the other hand. In vitro models can be a valuable support in the investigation of potential candidates and their functional mechanisms. For the conducted experiments within this work, an in vitro disc/ring model obtained from porcine articular cartilage tissue was established. In addition to qualitative evaluation of regeneration, this model facilitates the implementation of biomechanical tests to quantify cartilage integration strength. Construct harvesting for histology and other evaluation methods could be standardized and is ethically less questionable compared to in vivo testing. The opportunity of cell culture technique application for the in vitro model allowed a better understanding of cartilage integration processes. Tissue bonding requires chemical or physical interaction of the adhesive material and the substrate. Adhesive hydrogels can bind to the defect interface and simultaneously fill the gap of irregularly shaped defect voids. Fibrin gels are derived from the physiological blood-clot formation and are clinically applied for wound closure. Within this work, comparisons of different fibrin glue formulations with the commercial BioGlue® were assessed, which highlighted the need for good biocompatibility when applied on cartilage tissue in order to achieve satisfying long-term integration. Fibrin gel formulations can be adapted with regard to their long-term stability and when applied on cartilage disc/ring constructs improved integrative repair is observable. The kinetic of repairing processes was investigated in fibrin-treated cartilage composites as part of this work. After three days in vitro cultivation, deposited extracellular matrix (ECM) was obvious at the glued interface that increased further over time. Interfacial cell invasion from the surrounding native cartilage was detected from day ten of tissue culture. The ECM formation relies on molecular factors, e.g., as was shown representatively for ascorbic acid, and contributes to increasing integration strengths over time. The experiments performed with fibrin revealed that the treatment with a biocompatible adhesive that allows cartilage neosynthesis favors lateral cartilage integration in the long term. However, fibrin has limited immediate bonding strength, which is disadvantageous for use on articular cartilage that is subject to high mechanical stress. The continuing aim of this thesis was to further develop adhesive mechanisms and new adhesive hydrogels that retain the positive properties of fibrin but have an increased immediate bonding strength. Two different photochemical approaches with the advantage of on-demand bonding were tested. Such treatment potentially eases the application for the professional user. First, an UV light induced crosslinking mechanism was transferred to fibrin glue to provide additional bonding strength. For this, the cartilage surface was functionalized with highly reactive light-sensitive diazirine groups, which allowed additional covalent bonds to the fibrin matrix and thus increased the adhesive strength. However, the disadvantages of this approach were the multi-step bonding reactions, the need for enzymatic pretreatment of the cartilage, expensive reagents, potential UV-light damage, and potential toxicity hazards. Due to the mentioned disadvantages, no further experiments, including long-term culture, were carried out. A second photosensitive approach focused on blue light induced crosslinking of fibrinogen (RuFib) via a photoinitiator molecule instead of using thrombin as a crosslinking mediator like in normal fibrin glue. The used ruthenium complex allowed inter- and intramolecular dityrosine binding of fibrinogen molecules. The advantage of this method is a one-step curing of fibrinogen via visible light that further achieved higher adhesive strengths than fibrin. In contrast to diazirine functionalization of cartilage, the ruthenium complex is of less toxicological concern. However, after in vitro cultivation of the disc/ring constructs, there was a decrease in integration strength. Compared to fibrin, a reduced cartilage synthesis was observed at the defect. It is also disadvantageous that a direct adjustment of the adhesive can only be made via protein concentration, since fibrinogen is a natural protein that has a fixed number of tyrosine binding sites without chemical modification. An additional cartilage adhesive was developed that is based on a mussel-inspired adhesive mechanism in which reactivity to a variety of substrates is enabled via free DOPA amino acids. DOPA-based adhesion is known to function in moist environments, a major advantage for application on water-rich cartilage tissue surrounded by synovial liquid. Reactive DOPA groups were synthetically attached to a polymer, here POx, to allow easy chemical modifiability, e.g. insertion of hydrolyzable ester motifs for tunable degradation. The possibility of preparing an adhesive hybrid hydrogel of POx in combination with fibrinogen led to good cell compatibility as was similarly observed with fibrin, but with increased immediate adhesive strength. Degradation could be adjusted by the amount of ester linkages on the POx and a direct influence of degradation rates on the development of integration in the in vitro model could be shown. Hydrogels are well suited to fill defect gaps and immediate integration can be achieved via adhesive properties. The results obtained show that for the success of long-term integration, a good ability of the adhesive to take up synthesized ECM components and cells to enable regeneration is required. The degradation kinetics of the adhesive must match the remodeling process to avoid intermediate loss of integration power and to allow long-term firm adhesion to the native tissue. Hydrogels are not only important as adhesives for smaller lesions, but also for filling large defect volumes and populating them with cells to produce tissue engineered cartilage. Many different hydrogel types suitable for cartilage synthesis are reported in the literature. A long-term stable fibrin formulation was tested in this work not only as an adhesive but also as a bulk hydrogel construct. Agarose is also a material widely used in cartilage tissue engineering that has shown good cartilage neosynthesis and was included in integration assessment. In addition, a synthetic hyaluronic acid-based hydrogel (HA SH/P(AGE/G)) was used. The disc/ring construct was adapted for such experiments and the inner lumen of the cartilage ring was filled with the respective hydrogel. In contrast to agarose, fibrin and HA-SH/P(AGE/G) gels have a crosslink mechanism that led to immediate bonding upon contact with cartilage during curing. The enhanced cartilage neosynthesis in agarose compared to the other hydrogel types resulted in improved integration during in vitro culture. This shows that for the long-term success of a treatment, remodeling of the hydrogel into functional cartilage tissue is a very high priority. In order to successfully treat larger cartilage defects with hydrogels, new materials with these properties in combination with chemical modifiability and a direct adhesion mechanism are one of the most promising approaches.},
  subject      = {Knorpel},
  language  = {en}
}