The inability to accurately reproduce the complexities of the in vivo tumor microenvironment with reductionist-based two-dimensional in vitro cell culture models has been a notable deterrent in identifying therapeutic agents that reliably translate to in vivo animal and human clinical trials. In an effort to address this, a growing number of three-dimensional (3D) in vitro tumor models capable of mimicking specific tumorigenic processes have emerged within the last decade. This concept stems from the understanding that cells cultured within 3D in vitro matrices have the ability to acquire phenotypes representative of the in vivo microenvironment. The objective of this project was to apply a tissue engineering approach towards developing a 3D in vitro tumor angiogenesis model. Initially, different scaffolds were investigated for supporting 3D tumor growth, including bacterial cellulose, electrospun polycaprolactone/collagen I, and highly porous electrospun poly(L-lactic acid). However, cancer cells cultured on these scaffolds demonstrated poor adhesion, sufficient adhesion with poor infiltration, and increased but still inadequate infiltration, respectively. Collagen I hydrogels were chosen as an appropriate scaffold for facilitating 3D in vitro tumor growth for two reasons -- cell-mediated degradation and immediate 3D cell growth. It was hypothesized that cancer cells cultured within collagen I hydrogels could be encouraged to recapitulate key characteristics of in vivo tumor progression. MDA-MB-231 human breast cancer cells were shown to experience hypoxia and undergo necrosis in response to limitations in oxygen diffusion and competition for nutrients. Upregulation of hypoxia-inducible factor-1" resulted in a significant increase in vascular endothelial growth factor gene expression. To capitalize on this endogenous angiogenic potential, microvascular endothelial cells were cultured on the surface of the designated "bioengineered tumors." It was hypothesized that paracrine signaling between tumor and endothelial cells co-cultured within this system would be sufficient for inducing an angiogenic response in the absence of exogenous pro-angiogenic growth factors. Endothelial cells in the co-culture group were shown to invasively sprout into the underlying collagen matrix, forming a capillary-like tubule network. This project culminated with the establishment of an improved in vitro tumor model that can be used as a tool for accurate evaluation and refinement of cancer therapies. / Ph. D.

<p dir="ltr">Depression affects over 20 million adults in the US every year. It has been shown that depression is correlated with dysregulation of the hypothalamic-pituitary-adrenal axis, resulting in elevated cortisol levels which return to normal following successful treatment. Tracking cortisol as a physiological biomarker of depression could be used to complement traditional diagnosis and treatment monitoring. In this work, I aim to develop a minimally invasive method of measuring cortisol concentrations at the point of care.</p><p dir="ltr">The two main goals of this research are to implement a simple, painless sample collection method via hydrogel microneedles, and develop an electrochemical biosensor to measure and track cortisol concentrations at the point of care. Interstitial fluid is a rich source of biomarkers, including cortisol, found just beneath the surface of the skin. Hydrogel microneedles are used to painlessly sample interstitial fluid, but typically require sample processing to isolate the biomarker for measurement. Here, a rapid swelling methacrylated hyaluronic acid hydrogel microneedle platform is used to passively sample interstitial fluid from skin. Single-use gold leaf electrodes are functionalized with an aptamer to measure cortisol concentration directly from the hydrogel matrix without the need for sample processing.</p><p dir="ltr">Together, these platforms for interstitial fluid sampling and cortisol measurement will provide a minimally invasive, user friendly tool for monitoring depression throughout the course of treatment that can benefit the millions of people affected by depression.</p>

There is a constant search for new sustainable materials. A material that has become increasingly more interesting is cellulose, since it is both renewable and biodegradable. By combining cellulose nanofibrils (CNF) and the polymer complex poly(3,4-ethylenedioxythiophene) polystyrene sulfonate (PEDOT:PSS), a conductive hydrogel can be made. The hydrogel can subsequently be used to 3D-print various structures, which further can be used in multiple applications such as microrobots, sensors and smart devices. The aim of this bachelor thesis was to develop a 3D-printable hydrogel composed of PEDOT:PSS and CNF was made. The goal was to print and crosslink a conductive structure, and subsequently induce electrical current through the structure to facilitate movement (i.e. artificial muscles). Several hydrogel inks composed of CNF and PEDOT:PSS were prepared across a range of concentrations. Homogenisation of the hydrogels was achieved through various mixing techniques. Both freeze-drying and evaporation were tested to concentrate the hydrogels. Furthermore, crosslinking tests were performed using iron(III)chloride hexahydrate and citric acid, followed by a conductivity measurement. Lastly, rheology tests were performed on four of the inks. The optimal concentration of solid material was determined to be 4.8 wt% and the most favourable way of concentrating the hydrogels was by freeze drying. Furthermore, iron(III)chloride hexahydrate was found to be more favourable when crosslinking the hydrogels. The conductivity measurements showed that crosslinking with iron(III)chloride hexahydrate resulted in a notable increase in conductivity in the material. Lastly, the rheology measurements showed that the 4.8 wt% hydrogel ink had high elasticity, viscosity and exhibited shear thinning behaviour. / Det söks konstant efter nya hållbara material. Ett material som har blivit alltmer intressant är cellulosa, eftersom det både är förnybart och bionedbrytbart. Genom att kombinera cellulosa nanofibriller (CNF) och polymer komplexet poly(3,4-etylendioxitiofen) polystyrensulfonat (PEDOT:PSS), kan en konduktiv hydrogel framställas. Denna hydrogel kan sedan användas för att 3D-printa en mängd olika strukturer, vilka senare kan används i olika tillämpningar så som mikrorobotar, sensorer och smarta enheter. Målet med detta kandidatarbete var att utveckla en hydrogel av PEDOT:PSS och CNF för användning i 3D-skrivare. Målet var att printa och korslänka en struktur med konduktiva egenskaper, vilken senare skulle induceras med elektricitet för att främja rörelse, med andra ord artificiella muskler. Ett flertal hydrogeler av CNF och PEDOT:PSS förbereddes i en rad olika koncentrationer. Homogenisering av hydrogelerna uppnåddes genom att testa olika metoder för omrörning. Både frystorkning och avdunstning testades för att koncentrera hydrogelerna. Dessutom undersöktes tvärbindning genom järn(III)kloridhexahydrat och citronsyra, följt av en konduktivitetsmätning. Slutligen utfördes reologimätningar på fyra av de framställda hydrogelerna. Den optimala koncentrationen av fast material i en hydrogel bestämdes till 4,8 vikt% och det mest gynnsamma sättet att koncentrera hydrogeler var genom frystorkning. Vidare, var järn(III)kloridhexahydrat ett mer fördelaktigt alternativ vad gällde tvärbindning av hydrogelerna. Konduktivitetsmätningarna visade att tvärbindning med hjälp av järn(III)kloridhexahydrat ökade konduktiviteten märkbart hos materialet. Slutligen visade reologimätningarna att hydrogelen med 4,8 vikt% hade hög elasticitet, viskositet och den uppvisade även skjuvningstunnande beteende.

Over the years, hydrogels have been developed and used for a huge variety of different applications ranging from drug delivery devices to medical products. In this thesis, a poly(2-methyl-2-oxazoline) (POx) / poly(2-n-propyl-2-oxazine) (POzi) bioink was modified and analyzed for the use in biofabrication and targeted drug delivery. In addition, the protein fibrinogen (Fbg) was genetically modified for an increased stability towards plasmin degradation for its use as wound sealant. In Chapter 1, a thermogelling, printable POx/POzi-based hydrogel was modified with furan and maleimide moieties in the hydrophilic polymer backbone facilitating post-printing maturation of the constructs via Diels-Alder chemistry. The modification enabled long-term stability of the hydrogel scaffolds in aqueous solutions which is necessary for applications in biofabrication or tissue engineering. Furthermore, we incorporated RGD-peptides into the hydrogel which led to cell adhesion and elongated morphology of fibroblast cells seeded on top of the scaffolds. Additional printing experiments demonstrate that the presented POx/POzi system is a promising platform for the use as a bioink in biofabrication. Chapter 2 highlights the versatility of the POx/POzi hydrogels by adapting the system to a use in targeted drug delivery. We used a bioinspired approach for a bioorthogonal conjugation of insulin-like growth factor I (IGF-I) to the polymer using an omega-chain-end dibenzocyclooctyne (DBCO) modification and a matrix metalloprotease-sensitive peptide linker. This approach enabled a bioresponsive release of IGF-I from hydrogels as well as spatial control over the protein distribution in 3D printed constructs which makes the system a candidate for the use in personalized medicine. Chapter 3 gives a general overview over the necessity of wound sealants and the current generations of fibrin sealants on the market including advantages and challenges. Furthermore, it highlights trends and potential new strategies to tackle current problems and broadens the toolbox for future generations of fibrin sealants. Chapter 4 applies the concepts of recombinant protein expression and molecular engineering to a novel generation of fibrin sealants. In a proof-of-concept study, we developed a new recombinant fibrinogen (rFbg) expression protocol and a Fbg mutant that is less susceptible to plasmin degradation. Targeted lysine of plasmin cleavage sites in Fbg were exchanged with alanine or histidine in different parts of the molecule. The protein was recombinantly produced and restricted plasmin digest was analyzed using high resolution mass spectrometry. In addition to that, we developed a novel time resolved screening protocol for the detection of new potential plasmin cleavage sites for further amino acid exchanges in the fibrin sealant. / Hydrogele wurden im Laufe der Jahre für eine Vielzahl von Anwendungen, von der Verabreichung von Medikamenten bis hin zu medizinischen Produkten, entwickelt und eingesetzt. In dieser Arbeit wurde eine Poly(2-methyl-2-oxazolin) POx) / Poly(2-n-propyl-2- oxazin) (POzi) Biotinte modifiziert und für den Einsatz in der Biofabrikation und für die gezielte Verabreichung von Medikamenten analysiert. Außerdem wurde das Protein Fibrinogen (Fbg) gentechnisch verändert, um seine Stabilität gegenüber dem Plasminabbau in seiner Funktion als Wundkleber zu erhöhen In Kapitel 1 wurde ein thermogelierendes, druckbares Hydrogel auf POx/POzi-Basis mit Furan- und Maleimid-Funktionen im hydrophilen Polymerrückgrat modifiziert, was die Reifung der Konstrukte nach dem Druck durch Diels-Alder-Chemie bewirkt. Die Modifizierung ermöglichte eine langfristige Stabilität der Hydrogele in wässrigen Lösungen, was für Anwendungen im Bereich der Biofabrikation oder im Tissue Engineering erforderlich ist. Darüber hinaus haben wir RGD-Peptide in das Hydrogel integriert, was zur Zelladhäsion und einer verlängerten Morphologie von Fibroblasten, die auf den Gelen ausgesät wurden, führte. Weitere Druckexperimente zeigen außerdem, dass das POx/POzi-System eine vielversprechende Plattform für den Einsatz als Biotinte in der Biofabrikation ist. Kapitel 2 unterstreicht die Vielseitigkeit der POx/POzi-Hydrogele, indem das System für die gezielte Abgabe von Medikamenten angepasst wird. Wir verwendeten einen von der Natur inspirierten Ansatz für eine biorthogonale Konjugation vom Insuline-like Growth Factor I (IGF- I) an das Polymer unter Verwendung einer Dibenzocyclooctin-Modifikation des Polymers am Ende der Omega-Kette und eines Matrix-Metalloproteasen-empfindlichen Peptid-Linkers. Dieser Ansatz ermöglichte eine bioresponsive Freisetzung von IGF-I aus Hydrogelen sowie eine räumliche Kontrolle über die Proteinverteilung in 3D-gedruckten Konstrukten, was das System zu einem Kandidaten für den Einsatz in der personalisierten Medizin macht. Kapitel 3 gibt einen allgemeinen Überblick über die Notwendigkeit von Wundversiegelungsmitteln und die derzeit auf dem Markt befindlichen Generationen von Fibrinklebern einschließlich der Vorteile und Herausforderungen. Darüber hinaus werden Trends und potenzielle neue Strategien zur Lösung aktueller Probleme und zur Erweiterung der Toolbox für künftige Generationen von Fibrinklebern aufgezeigt. In Kapitel 4 werden die Konzepte der rekombinanten Proteinexpression und des Molecular Engineering auf eine neue Generation von Fibrin Wundklebern angewandt. In einer Proof-of- Concept-Studie haben wir ein neues rekombinantes Fbg Expressionsprotokoll und eine Fbg Mutante entwickelt, die weniger anfällig für einen Abbau durch Plasmin ist. Gezielte Lysine in Plasmin-Schnittstellen in Fbg wurde entweder durch Alanin oder Histidin in unterschiedlichen Teilen des Moleküls ausgetauscht. Das Protein wurde rekombinant hergestellt und eine verminderte Schnittrate wurde mittels hochauflösender Massenspektrometrie gezeigt. Zusätzlich haben wir ein neues zeitaufgelöstes Screening-Protokoll entwickelt, mit dem sich neue potenzielle Plasmin-Spaltstellen für weitere Aminosäurenaustausche in Fibrin-Klebern auflösen lassen.

Yes / In this work we report a facile method to prepare a fluorescence active self-healable hydrogel via incorporation of fluorescence responsive ionic block copolymers (BCPs). Ionic block copolymers were prepared via a combined effect of ring opening polymerization (ROP) of ε-caprolactone and xanthate mediated reversible addition–fragmentation chain transfer (RAFT) polymerization. Here polycaprolactone (PCL) was modified with xanthate to prepare a PCL based macro-RAFT agent and then it was utilized to prepare block copolymers with cationic poly(2-(methacryloyloxy)ethyltrimethyl ammonium chloride) (PCL-b-PMTAC) and anionic poly(sodium 4-vinylbenzenesulfonate) (PCL-b-PSS). During the block formation, the cationic segments were randomly copolymerized with a trace amount of fluorescein O-acrylate (FA) (acceptor) whereas the anionic segments were randomly copolymerized with a trace amount of 9-anthryl methylmethacrylate (AMMA) (donor) to make both the segments fluorescent. The block copolymers form micelles in a DMF : water mixture (1 : 4 volume ratio). The ionic interaction of two BCPs was monitored via Förster resonance energy transfer (FRET) and zeta potential measurements. The oppositely charged BCPs were incorporated into a polyacrylamide (PAAm) based hydrogel that demonstrated self-healing behavior and is also highly fluorescent. / IIT Kharagpur and MRC (MR/N501888/2)

Yes / Functional crosslinked hydrogels were prepared from 2-hydroxyethyl methacrylate (HEMA) and acrylic acid (AA). The acid monomer was incorporated both via copolymerization and chain extension of a branching, reversible addition–fragmentation chain-transfer agent incorporated into the crosslinked polymer gel. The hydrogels were intolerant to high levels of acidic copolymerization as the acrylic acid weakened the ethylene glycol dimethacrylate (EGDMA) crosslinked network. Hydrogels made from HEMA, EGDMA and a branching RAFT agent provide the network with loose-chain end functionality that can be retained for subsequent chain extension. Traditional methods of surface functionalization have the downside of potentially creating a high volume of homopolymerization in the solution. Branching RAFT comonomers act as versatile anchor sites by which additional polymerization chain extension reactions can be carried out. Acrylic acid grafted onto HEMA–EGDMA hydrogels showed higher mechanical strength than the equivalent statistical copolymer networks and was shown to have functionality as an electrostatic binder of cationic flocculants.

Die Entwicklung und Erforschung von Materialien, die biologische Gewebefunktionen erfüllen und geschädigtes Gewebe ersetzen können, steht im Fokus der Biofabrikation. Die steigenden Anforderungen und somit ein Mangel an geeigneten Biotinten erschweren jedoch den Fortschritt in diesem Bereich. Durch die Nachbildung einer natürlichen extrazellulären Matrix soll den Zellen in einem Hydrogel eine mechanisch unterstützende 3D-Umgebung geboten werden, um ein Zellüberleben und eine Zellproliferation zu erreichen. Mittels additiver Fertigungstechniken können so 3DKonstrukte hergestellt werden. Das Ziel dieser Arbeit war die zellbiologische Evaluation verschiedener Hydrogelsysteme und das Austesten dieser in einem volumetrischen 3D-Biodrucker. Dabei wurden die Hydrogelsysteme Alg-Gel, GelMA und GelAGE miteinander verglichen. Anhand von eingebetteten Mausfibroblasten L929 und NIH-3T3 wurde das Zellüberleben nach einer in-vitro Kultivierung von 7 Tagen mit verschiedenen Testverfahren evaluiert. Mittels CCK-8-Kit konnte die Zellaktivität und Zellproliferation untersucht werden, während der PicoGreen-Assay den absoluten DNA-Gehalt einer Probe bestimmen konnte. Zusätzlich wurde mittels Live/Dead-Assay das Zellüberleben an den verschiedenen Versuchstagen analysiert und die Zellverteilung und Morphologie anhand der Phalloidinfärbung genauer untersucht. In den Vorversuchen wurde das Zellüberleben von L929 und NIH-3T3- Zellen in gegossenen Alg-Gel-Hydrogelen getestet. Dabei konnte eine gute Zytokompatibilität des etablierten Hydrogelsystems festgestellt werden. Es wurden außerdem reproduzierbare Ergebnisse am FMZ in Würzburg erreicht. Um die beiden Hydrogelsysteme GelMA und GelAGE zu vergleichen, wurden diese zum einen in Förmchen gegossen und zum anderen mit einem 3D-Biodrucker hergestellt. Die Ergebnisse der metabolischen Stoffwechselaktivität waren gut. Es konnte zudem herausgefunden werden, dass sich die Zellen vor allem auf der Hydrogeloberfläche in einem gestreckten Zellnetzwerk ansiedelten, während im Gelinneren nur wenige Zellen diese Morphologie erreichten. Insgesamt stellt das Hydrogelsystem GelAGE eine neue und vielversprechende Bioplattform dar, das eine kosteneffiziente und reproduzierbare Herstellung von Hydrogelen ermöglicht und noch weiter erforscht werden sollte. / The development and research of materials that can fulfill biological tissue functions and replace damaged tissue is the focus of biofabrication. However, increasing requirements and the resulting lack of suitable bioinks are hampering progress in this area. By replicating a natural extracellular matrix, the aim is to provide the cells in a hydrogel with a mechanically supportive 3D environment in order to achieve cell survival and proliferation. Using additive manufacturing techniques, 3D constructs can be produced in this way. The aim of this work was the cell biological evaluation of different hydrogel systems and the testing of these in a volumetric 3D bioprinter. The hydrogel systems Alg-Gel, GelMA and GelAGE were compared with each other. Using embedded mouse fibroblasts L929 and NIH-3T3, cell survival was evaluated after 7 days of in vitro cultivation using various test methods. The CCK-8 kit was used to examine cell activity and proliferation, while the PicoGreen assay was used to determine the absolute DNA content of a sample. In addition, the cell survival on the different test days was analyzed using a live/dead assay and the cell distribution and morphology were examined in more detail using phalloidin staining. In the preliminary experiments, the cell survival of L929 and NIH-3T3 cells was tested in cast Alg-gel hydrogels. Good cytocompatibility of the established hydrogel system was found. Reproducible results were also achieved at the FMZ in Würzburg. In order to compare the two hydrogel systems GelMA and GelAGE, they were cast into molds and produced using a 3D bioprinter. The results of the metabolic activity were good. It was also found that the cells mainly colonized the hydrogel surface in an elongated cell network, while only a few cells achieved this morphology in the gel interior. Overall, the GelAGE hydrogel system represents a new and promising bioplatform that enables the cost-efficient and reproducible production of hydrogels and should be investigated further.

Yes / A set of water-swollen core−shell particles was synthesized by emulsion polymerization of a 1,3-dioxolane functional monomer in water. After removal of the 1,3- dioxolane group, the particles’ shells were shown to swell in aqueous media. Upon hydrolysis, the particles increased in size from around 70 to 100−130 nm. A bicinchoninic acid assay and ζ-potential measurements were used to investigate the adsorption of lysozyme, albumin, or fibrinogen. Each of the core−shell particles adsorbed significantly less protein than the noncoated core (polystyrene) particles. Differences were observed as both the amount of difunctional, cross-linking monomer and the amount of shell monomer in the feed were changed. The core−shell particles were shown to be resistant to protein adsorption, and the degree to which the three proteins adsorbed was dependent on the formulation of the shell. / EPSRC and MRC

La peau est un organe à l'architecture complexe qui assure plusieurs rôles essentiels dont celui de barrière contre les agressions extérieures. De plus, il est capable de se régénérer grâce un processus hautement régulé: la cicatrisation. Des biomatériaux, synthétisés à partir de macromolécules d'origine naturelle et/ou synthétique, ont été développés pour servir de pansements, de support de culture cutanée ou de substitut cutané.L'originalité de notre étude a été de mimer, non pas la matrice extracellulaire dermique, mais le réseau de fibrine, temporaire, qui apparait lors de la cicatrisation. Au cours de travaux précédents, il a été démontré qu'il était possible de renforcer mécaniquement un réseau de fibrine, à concentration physiologique, en l'associant, dans une architecture de réseaux interpénétrés de polymères (RIP), avec un réseau de polyoxyde d'éthylène (POE). Durant mes travaux, la non toxicité de ces matériaux envers des cellules modèles a été démontrée. Puis, la composition du matériau a été optimisée pour augmenter son module de stockage jusqu'à un facteur 100 par rapport à celui du gel de fibrine. Ensuite, grâce à la synthèse d'alcool polyvinylique méthacrylate (PVAm) pour le remplacement du POE, un matériau présentant mêmes qualités, mais plus facilement stockable à l'état déshydraté et complètement réhydratable, a pu être obtenu. Nous nous sommes ensuite attachés à rendre ce nouveau matériau biodégradable. L'introduction de sérum albumine bovine méthacrylate (BSAm) copolymérisée avec le PVAm (co-réseau) dans une architecture RIP avec un réseau de fibrine a permis de synthétiser un matériau hydride présentant l'ensemble des propriétés précédemment décrites et dégradable par des enzymes. Ce matériau a été testé en contact avec des populations cellulaires fibroblastiques. Il a pu être démontré, qu'en plus d'être non cytotoxique, ce matériau pouvait être totalement colonisé par ces cellules. Pour finir, l'encapsulation de cellules à l'intérieur de cette matrice et leur prolifération ont pu être observées. En conclusion, les matériaux synthétisés lors de ces travaux, c'est-à-dire des RIPs associant un réseau de fibrine à la concentration physiologique et un réseau de polymère synthétique, possèdent les propriétés nécessaires pour être utilisés en tant que pansements et supports de culture pour la régénération cutanée. De plus, la possibilité d'encapsuler des fibroblastes dans le RIP à base de coréseaux de PVAm et BSAm en fait un substitut cutané potentiel.Mots clefs : hydrogel, réseaux interpénétrés de polymères, fibrine, POE, PVA, BSA, encapsulation cellulaire, fibroblaste, médecine régénérative, peau. / The skin is an organ with a complex architecture that provides several key roles including barrier against external aggressions. In addition, it has the ability to regenerate itself by following a highly regulated process,: the wound healing. Biomaterials, synthesized by using macromolecules from natural and/or synthetic origin, have been developed to serve as wound dressing, cell culture support or skin substitute.The originality of our study was to not mimic the dermal extracellular matrix, but mimic the the fibrin scaffold, the temporary matrix who appears during the healing process. In previous work, it was shown that it was possible to mechanically reinforce a fibrin scaffold at physiological concentration by associating into interpenetrating polymer network (IPN) architecture with a polyethylene oxide (PEO) network. In my work, the non-toxicity of these materials was proved with model cells. Then, the material composition has been optimized to increase the storage modulus by 100 in comparison of the fibrin scaffold. Then, through the synthesis of polyvinyl alcohol methacrylate (PVAm) to replace the POE, a material with the same properties, but more easily stored in a dehydrated state (more ductile) and completely rehydratable could be obtained. We then attached to make this new biodegradable material. The use of bovin serum albumin methacrylate (BSAm) copolymerized with PVAm(conetwork) into IPN architecture with a fibrin scaffold performs to synthesize a hybrid material with all the properties described above and degradable by enzymes. This material has been tested in contact with human fibroblast. It has been demonstrated that in addition to be non-cytotoxic, this material could be completely colonized by these cells. Finally, the encapsulation of cells in the bulk of this matrix and their proliferation inside were observed.In conclusion, the materials synthesized in this work, IPN containing a fibrin scaffold at physiological concentration and a synthetic polymer network, have sufficient properties to be used as wound dressings or cells culture support for skin regeneration. In addition, the ability to encapsulate fibroblasts in material based on conetwork of PVAm and BSAM makes it suitable for a skin substitute application.Key words: hydrogel, Interpenetrating Polymer Network, fibrin, POE, PVA, BSA, entrapping, fibroblast, tissue engineering, skin.

La rupture du Ligament Croisé Antérieur (LCA) est la blessure ligamentaire la plus fréquente avec une incidence de 1/3000. Elle est efficacement traitée aujourd’hui par une reconstruction par autogreffe tendineuse. Cependant, les problèmes causés par le prélèvement du greffon demeurent une limitation importante. Des substituts artificiels offrent une solution alternative mais la rupture et la génération de débris d’usure ont causé l’échec de la majorité des systèmes développés jusqu’à présent. Récemment, des travaux ont montré que des assemblages de fibres synthétiques d’hydrogel d’Alcool PolyVinylique (APV) reproduisent le comportement en traction du LCA humain. L’objectif principal de cette thèse a été d’explorer le potentiel de ces fibres pour la reconstruction ligamentaire en concevant et caractérisant des systèmes implantables pour une étude in vivo chez l’animal. Pour cela, j’ai réalisé une étude expérimentale depuis l’échelle de la fibre jusqu’à celle de l’implant complet. Deux types de fibres d’APV ont été caractérisés, obtenues par filage voie sèche (VS) et voie humide (VH). A l’échelle de la fibre, une étude microscopique et mécanique a mis en évidence un fort effet de l’orientation moléculaire sur le comportement en traction qui permet d’atteindre des modules élastiques très supérieurs à celui de films isotropes ayant un taux de gonflement équivalent. En particulier, les fibres VS présentent à 20°C un comportement en traction proche de celui du LCA. Cette étude montre également une forte dépendance en température du comportement mécanique et l’existence d’un phénomène de recouvrance par lequel des fibres étirées récupèrent leur comportement initial après un repos. Des observations in situ en diffraction des rayons X aux grands angles ont montré que la structure semi-cristalline des fibres résiste au gonflement et à une déformation représentative des sollicitations physiologiques. Un mécanisme microscopique basé sur ces résultats a été proposé qui explique le comportement mécanique des fibres par la dissociation et la reformation de liaisons hydrogène dans la phase amorphe. A l’échelle des assemblages de fibres, une étude systématique sur des structures torsadées et un modèle mécanique de structure double-hélice ont révélé que le gonflement confiné des fibres au sein des structures induit des états de contrainte interne permettant d’augmenter la rigidité des assemblages. A l’échelle de l’implant, des substituts compatibles avec le geste chirurgical ont été conçus grâce à une collaboration avec des partenaires cliniciens et biomécaniciens. Une étude in vivo sur modèle petit animal (lapin) de ligamentoplastie a permis de vérifier la bonne tolérance aux implants avec une encapsulation fibreuse modérée et a montré que le gonflement in vivo d’implants secs n’entraîne pas une réaction biologique délétère. L’ensemble de ces résultats a conduit à la conception d’implants complets à l’échelle du LCA humain qui ont été évalué dans un modèle grand animal (brebis) de ligamentoplastie. L’étude nécropsique et histologique sur les animaux implantés a montré une biocompatibilité comparable à celle observée sur les animaux reconstruits par autogreffe. En revanche, l’étude biomécanique révèle un taux de rupture intra-articulaire important (92%) des implants en fibres d’APV. Ces résultats permettent d’identifier des causes possibles d’endommagement et de proposer des pistes d’amélioration. Plus généralement, la bonne biocompatibilité des fibres d’hydrogel d’APV et leurs propriétés mécaniques en font des systèmes intéressants pour la reconstruction de tissus souples nécessitant une tenue en traction élevée. / The anterior cruciate ligament (ACL) rupture is the most frequent ligament injury with an occurrence of 1/3000. It is effectively treated nowadays by a reconstruction with tendinous autograft. However, the problems caused by the transplant harvest remain an important limitation. Artificial substitutes offer an alternative but the rupture rate and the generation of wear debris caused the failure of the majority of the systems developed until now. Recently, studies showed that assemblies of Poly(Vinyl Alcohol) hydrogel fibers mimic the human ACL behavior. The main objective of this thesis was to explore the potential of theses fibers for the ligament reconstruction by designing and characterizing implantable systems for an in vivo animal study. For that purpose, I conducted an experimental study from the fiber scale to the complete implant scale. Two types of PVA fibers were characterized, one obtained from dry spinning (DS) and the other from wet spinning (WS). At the fiber scale, a microscopic and mechanical study highlighted a strong effect of the molecular orientation on the tensile behavior, which allows to reach a much higher elastic modulus than that of an isotropic film with the same swelling ratio. In particular, DS fibers at 20°C exhibit a tensile behavior close to that of the ACL. This study also shows a strong temperature dependence of the mechanical behavior and the existence of recovery phenomenon by which the stretched fibers recover their initial behavior after a rest. In situ wide angle X-rays scattering showed that the fibers semi-crystalline structure resists to swelling and physiological range stretching. A microscopic mechanism based on these results was proposed to explain the fibers mechanical behavior by the dissociation and reformation of hydrogen bonds in the amorphous phase. At the fiber assemblies scale, a systematic study on twister structures and a l double-helix structure mechanical model revealed that the fibers confined swelling inside a structure induce internal stress leading to an increase of the assemblies stiffness. At the implant scale, substitutes compatible with the surgery were conceived in collaboration with clinicians and biomechanists. An in vivo study on a small animal ligamentoplasty model (rabbit) allowed to verify the implants tolerance with a moderate fibrous encapsulation and showed that the implants in vivo swelling does not induce noxious biological reaction. These results led to the conception of human scale implants which were evaluated in a large animal ligamentoplasty model (sheep). The necropsy and histological study on implanted animals showed a biocompatibility similar to that observed with animals reconstructed with an autograft. However, the biomechanical study revealed an important intra-articular rupture rate (92%) for PVA fibers implants. These results allow to identify possible damage causes and to offer ways of improvement. In general, the good biocompatibility of PVA hydrogel fibers and their mechanical properties make them interesting systems for the reconstruction of soft tissues with high tensile strength.