Différentes architectures macromoléculaires sensibles à la température, des copolymères linéaires greffés et des hydrogels, ont été développées et leur structure, leurs propriétés rhéologiques ainsi que leurs propriétés mécaniques ont été étudiées. Dans le cas des hydrogels, le phénomène de séparation de phase des segments thermosensibles conduit, en conditions isochores, à une augmentation de la rigidité et de l'élongation à la rupture ainsi qu'à de remarquables propriétés de fatigue. Ce renforcement est de plus totalement réversible en pilotant le processus d'association/dissociation des interactions avec la température. Nous montrons que la topologie des réseaux joue un rôle important sur les performances mécaniques des hydrogels et plus spécialement sur le mode de propagation de fissure au sein de la structure. A partir d'études structurales par diffusion de neutrons complétées par des expériences sous traction, différentes nanostructures sont proposées en fonction de la topologie. Enfin, ce concept de renforcement stimulable des propriétés mécaniques des hydrogels, induit par un mécanisme de micro-séparation de phase, a été élargi à d'autres réseaux polymères combinant des propriétés thermodynamiques de LCST et UCST. / Thermo-responsive linear graft copolymers and hydrogels with different topologies have been designed and their nanostructure, their rheological properties as well as their tunable mechanical properties have been investigated. In the case of hydrogels, the self-assembly of the thermo-responsive sequences, which serve as secondary interactions, induces in isochoric conditions a strong enhancement of both stiffness and elongation at break, including also remarkable fatigue properties. Specifically, this reinforcement is totally reversible by switching on/off the associations. It is clearly shown that the topology of the network displays a crucial influence on the mechanical performance of hydrogels, especially the resistance to fracture. After a careful investigation of the structure by 2-D neutron scattering and tensile experiments, different nanostructures are proposed according to the topology. Finally, this concept of thermo-toughening of hydrogels through a controlled microphase separation has been extended to other polymeric networks combining LCST and UCST type polymers.

Ce travail avait pour objectif la synthèse d’hydrogels d’alginates stables dans le temps et leur évaluation comme support de régénération des voies nerveuses lésées du Système Nerveux Central. Différents dérivés amphiphiles de l’alginate de sodium ont été préparés en fixant chimiquement des chaînes alkyles en C12 à différents taux sur le squelette polymère par l’intermédiaire, soit de liaisons ester (alginates esters), soit de liaisons amide (alginamides) moins sensibles à l’hydrolyse. Le comportement en solution des alginamides a été étudié en termes de stabilité dans le temps, de solubilité, de comportement rhéologique, et de taux de gonflement, puis comparé à celui des alginates esters. Les alginamides ont montré des propriétés en solution différentes de celles des alginates esters, en particulier des contraintes critiques faibles, qui sont les conséquences de la formation d’agrégats liée à l’existence d’une réaction secondaire de réticulation chimique lors de la synthèse. Néanmoins, à des concentrations et taux de greffage appropriés, il est possible d’obtenir un réseau polymère tridimensionnel stabilisé par des associations hydrophobes et pouvant servir de pont de régénération pour l’application visée. L’étude in vivo conclut à l’absence de signe de régénération des voies nerveuses chez les animaux lésées sur une durée d’un an. Toutefois, cette étude a permis de valider la stratégie d’implantation d’un gel physique rhéofluidifiant et thixotrope, de définir des méthodes d’analyse des tissus post mortem en présence d’hydrogel, d’examiner la possibilité d’encapsuler un traitement pharmacologique et de définir un cahier des charges élargi de ce biomatériau (pH, stabilité, gonflement …) / The aim of this work was to synthesise alginate hydrogels, stable in time, and to evaluate their potential use as scaffolds for the damaged nerve regeneration in central nervous system. Various amphiphilic derivatives of sodium alginate were prepared by covalent attachment of alkyl chains (12 carbons) onto the polysaccharide at different substitution ratio, either via ester (alginate ester) or amide (alginamide) linkages, these last ones being more stable toward hydrolysis. The properties in solution of the alginamide derivatives were studied in terms of solubility, stability as function of time, rheological behaviour and swelling ratio. Results were compared to those obtained with the alginate ester family and highlighted a different behaviour for the alginamide series in semi-dilute regime. In particular, alginamide hydrogels exhibited a low critical strain which has been attributed to the presence of aggregates in the solution. The formation of these aggregates was due to the occurrence of a secondary cross-linking reaction during the synthesis of polymers. Nevertheless, it was possible, by appropriate tuning of the substitution yield and of the solution concentration, to obtain a three-dimensional network stabilized by intermolecular hydrophobic interactions, which has been evaluated as regenerative support for the considered application. In vivo studies demonstrated the absence of nerve regeneration for the tested injured animals after one year. However, these studies allowed us to evaluate both the strategy for the implantation of a physical gel exhibiting a shear-thinning and thixotrope behavior and the possibility to encapsulate a pharmacological treatment. An enlarged project specification has also been defined for this biomaterial (pH, stability, swelling ratio…)

Les hydrogels sont des matériaux intrinsèquement mous, fragiles et élastiques, majoritairement composes d'eau. Leur capacité unique à interagir avec leur environnement se traduit par une grande variation de leur volume initial et en font l'objet d'applications variées dans de nombreux domaines tels que le secteur biomédical, l'industrie agro-alimentaire et cosmétique. Plus récemment, des hydrogels ont été développés pour des secteurs de pointe comme la robotique ou l'ingénierie tissulaire, permettant d'élargir le spectre d'utilisation de la matière molle en tant que matériau structurel. De ce fait, la conception d'hydrogels mécaniquement performants représente un enjeu majeur au développement futur de ces applications.L'élaboration de matériaux nanocomposites incorporant des nanocharges à un réseau organique réticule de façon covalente s'est avérée une stratégie de renfort efficace. Le renforcement dépend alors des interactions existantes entre le polymère et les charges ainsi que de l'état de dispersion des nanoparticules au sein du réseau. Des hydrogels hybrides, à base de poly(N-alkylacrylamides) et de nanoparticules de silice ont ainsi été mis au point, démontrant une amélioration significative des propriétés mécaniques (déformation à la rupture, capacités d'autoréparation). Ce phénomène est attribué à l'adsorption réversible du polymère à la surface des nanoparticules. Si les propriétés viscoélastiques de ces composés ont été largement étudiées, peu de travaux ont été effectués sur la caractérisation et la quantification des interactions à l'interface solide/liquide. De même, le comportement au delà du domaine linéaire ne reste que peu étudié à ce jour. La première partie de ces travaux a été dédiée à la synthèse de chaines linéaires de poly- (acrylamide) (PAAm) et poly(N,N-dimethylacrylamide) (PDMA) ainsi qu'à l'étude de leurs capacités d'adsorption sur la silice tout en contrôlant la chimie de surface des nanoparticules. Cela a permis de mettre en évidence le peu d'affinité du PAAm envers la surface de silice, justifiant ainsi son emploi en tant que monomère « inerte ». En second lieu, il s'est agi de moduler les interactions entre le polymère et la silice au sein des hydrogels hybrides en substituant le polymère interagissant avec l'adsorbat (PDMA) par un polymère peu apte à s'adsorber sur la silice (PAAm). La structure de ces composés ainsi que leur comportement mécanique ont été explorés avec un intérêt marqué pour le domaine non linéaire. Le rôle de l'adsorption dans le renfort mécanique a ainsi été confirmé et plus précisément l'importance des groupements silanols à la surface de la silice. La contribution de l'état d'agrégation des nanoparticules sur la structure et les propriétés mécaniques ont ensuite été étudiés. Le comportement non-linéaire aux grandes déformations des hydrogels synthétisés a notamment été investigué par des expériences de rhéologie aux grandes amplitude de cisaillement (LAOS), permettant une caractérisation plus poussée des mécanismes de renfort, par analogie avec les élastomères chargés / Hydrogels are soft and elastic solid materials mainly composed of water. Owing to their ability to interact with their environment through drastic volume change, hydrogels already find a wide range of applications, as superabsorbants, in pharmaceutics as drug delivery systems and more recently, as sensors and actuators, widening even more the possible use of soft materials as structural or load-bearing materials. Hence, providing gels with high mechanical performances is of major importance to meet these demanding applications. Efficient toughening can be achieved by combining inorganic and organic materials linked by physical and/or chemical interactions. In such nanocomposite materials, the reinforcement depends on the interactions between the polymer and the filler and of the dispersion state of the fillers, allowing to reach the full extent of reinforcement. Hybrid hydrogels based on poly(N-alkylacrylamide) and nanosilica demonstrating great mechanical reinforcement at large strain as well as self-healing capabilities were designed by Hourdet and Marcellan . The drastic improvement of the mechanical behavior is attributed to the reversible adsorption of the polymer onto silica surface. Viscoelastic properties of such hybrids gels have been extensively studied but few studies were carried out to understand and quantify the interactions at the solid/liquid interface. Likewise, the behavior beyond viscoelastic regime of such materials remains scarcely investigated. A first part of this study focused on the synthesis and the adsorption behavior of linear polymer chains of polyacrylamides, more precisely poly(acrylamide) (PAAm), poly(N,N-dimethylacrylamide) (PDMA) onto silica nanoparticles with controlled surface chemistry. It evidenced the non-interacting behavior of PAAm towards silica surface, justifying its choice as a non-interacting polymer. A second part dealt with the modulation of particle/polymer interactions in hybrid gels either by substituting the interacting monomer (DMA) with a non-interacting one (AAm) or by tuning the surface chemistry of the nanoparticles. Then, the study of their structure and mechanical properties was conducted with a special focus on the non-linear behavior. The role of polymer adsorption for gel reinforcement was evidenced and more specifically the importance of the silanol groups at the silica surface for PDMA/silica interactions. The contribution of the dispersion state of silica on the structure and the mechanical response of hydrogels was then addressed and the non-linear domain of the resulting hydrogels was investigated using Large Amplitude Oscillatory Shear experiments. The impact of the chosen monomer and of the dispersion state of the fillers was investigated at large strain, allowing a more precise analysis of the reinforcement mechanisms, by analogy with filled elastomers

Les gliomes sont des tumeurs qui seforment par prolifération anormale de cellules dansle tissu cérébral. La dangerosité de ces tumeursréside dans le fait que la plupart des gliomes sontinvasifs : les cellules tumorales migrent dans le tissusain autour de la tumeur. Ces cellules tumoralesisolées provoquent des récidives quasi systématiquesaprès traitement (chirurgie, chimiothérapie,radiothérapie), rendant ces tumeurs incurablesactuellement et conduisant au décès du patient. Il estimportant d'associer des études fondamentales pourmieux comprendre leur évolution dès l'origine et desétudes plus appliquées en développant de nouveauxsubstrats pour reproduire in vitro leur évolution. Lescellules progénitrices des oligodendrocytes (OPC)représentent la plus grande population de cellules enprolifération et la plus largement distribuée dans lecerveau adulte, ce qui en fait un suspect idéal del’origine des gliomes. A partir de donnéesexpérimentales de la littérature sur la dynamique invivo de ces cellules, un modèle mathématiquereproduisant cette dynamique dans un tissu sain a étédéveloppé.Ce modèle montre également que les OPC pourraientêtre à l’origine de toutes les formes de gliomerencontrées aussi bien de bas grade que de hautgrade. Par ailleurs, l’approche expérimentale utiliséevisait à développer un substrat de culture cellulaireadapté à l’étude des gliomes in vitro. Ainsi, unhydrogel biocompatible, minimaliste et contrôlable aété élaboré. Celui-ci mime l’élasticité de la matriceextracellulaire (MEC) cérébrale avec une rigidité del’ordre de 200 Pa et l’effet adhésif des molécules dela MEC impliqué dans l’adhésion et la proliférationdes cellules tumorales. Grâce à ses propriétés,l’hydrogel favorise la survie de près de 90% desmodèles cellulaires de gliome utilisés dans notreétude et supporte la croissance en trois dimensionsd’agrégats multicellulaires semblables à lamorphologie de micro-tumeurs in vivo. Le modèled’hydrogel est donc validé pour favoriser la viabilitéet la prolifération cellulaires. Les perspectives detravail futures porteront sur l'optimisation de sacomposition pour mimer de manière encore plusréaliste la croissance tumorale in vivo. / Gliomas are brain tumors arising fromanomalous cell proliferation into the brain tissue.The hazard of these tumors resides in their invasiveability : tumor cells migrate into the healthy tissuesurrounding the tumor. These isolated cells causequasi systematic recurrences after treatment(surgery, chemotherapy, radiotherapy) making thesetumors currently incurable and leading to patientdeath. Hence, it is important to associatefundamental studies for better understanding of theirevolution from their origin with more appliedstudies developing new substrates for reproducingtheir evolution in vitro. Oligodendrocyte progenitorcells (OPC) are the most widely spread proliferatingpopulation in the adult brain, which makes them themain suspect of causing gliomas origin. Fromexperimental data in the literature about in vivodynamic of OPC, a mathematical model that depictsthis dynamic into a healthy tissue has beendeveloped.This model also shows that OPC could be at theorigin of all glioma forms from low to high grade.Furthermore, the experimental approach used aimedat designing a cell culture substrate adapted toglioma studies in vitro. Thus, a biocompatible,minimalistic and controllable hydrogel has beenperformed. It mimics brain extracellular matrix(ECM) elasticity around 200 Pa and the adhesiveeffect of ECM molecules involved in tumor celladhesion and proliferation. Due to these properties,the hydrogel contributes to around 90% of gliomacell models survival used in our study and promotesmulticellular aggregates growth in three dimensionsthat look like in vivo microtumors morphology. Thishydrogel model is thus validated for cell viabilityand proliferation. Future works will be devoted tothe optimization of its composition for bettermimicking of tumor growth in vivo in a morerealistic manner.

In dieser Arbeit sollte im Tierversuch die lokale Gewebeverträglichkeit der neuen, mit PVVV 80/20 beschichteten, hoch hydrophilen Expander (osmed GmbH, Ilmenau, Deutschland) getestet werden und allgemeine Indikationen für die Anwendung von Hydrogelexpandern erstellt werden. Material und Methoden: Für den Versuch standen 24 Kaninchen als Versuchstiere zur Verfügung, welche in vier Gruppen unterteilt wurden, wobei die Gruppe 1 als Kontrollgruppe (Expander mit Silikonhülle) diente. Die Gruppen 2 - 4 wurden mit den neu entwickelten Hydrogelexpandern („Cylinder M4 x 12“) beschickt. Die Implantation der Expander erfolgte bei allen Versuchstieren in die linke Kniefalte. Nach einem zeitlich vorbestimmten Explantationsplan (nach 10, 21 und 90 Tagen) wurden die Expander entnommen, gewogen und das, den Expander direkt umgebene Gewebe entnommen, histologisch aufbereitet und untersucht. Zusätzlich wurden Proben aus der rechten, nicht implantierten Kniefalte, als Referenzprobe entnommen. Desweiteren wurde die Anwendbarkeit von Hydrogelexpandern anhand von zwei Fallbeispielen vorgestellt und untersucht. Ergebnisse: Histologisch konnte bei beiden Expandertypen eine lokale Fremdkörperreaktion (Entzündungszellinfiltration, Granulationsgewebe), im Sinne einer Kapselbildung, nachgewiesen werden. Die Alterationen des direkt angrenzenden Gewebes der beschichteten Expander sind insgesamt nur geringgradig stärker ausgeprägt als in den Proben mit Verwendung des Implantats mit Silikonhülle. Somit ist die Gewebeverträglichkeit der neu entwickelten Expander mit den silikonumhüllten Expandern vergleichbar. Diese Arbeit konnten weiterhin zeigen, dass die „Cylinder M4 x 12“-Expander mit der PVVV 80/20-Beschichtung ein deutlich höheres Quellverhalten aufweisen als die herkömmlichen, mit Silikonhülle umgebenen, Expander. Die in den Fallbeispielen verwendeten Hydrogelexpander, zeigten in beiden Fällen das gewünschte kosmetische Endergebnis. Schlussfolgerung: Für beide Expandertypen lässt sich eine gute lokale Verträglichkeit ableiten. Damit bieten die getesteten Expander „Cylinder M4 x 12“ mit der PVVV 80/20-Beschichtung die Möglichkeit, die Silikonhülle in ausgewählten Indikationen zu ersetzen und neue Einsatzmöglichkeiten zu erschließen. Zudem bieten die beschichteten Expander den Vorteil, dass es durch ihre minimale Größe nur einer kleinen Inzision für die Implantation bedarf und sie damit besonders für den Einsatz in der minimal invasiven Chirurgie geeignet erscheinen. Einsatzmöglichkeiten der Hydrogelexpander in der Veterinärmedizin sind unter medizinischen und ästhetischen Gesichtspunkten zu betrachten. Im Vordergrund der medizinischen Indikationen stehen vor allem Wunden mit erheblichem Gewebeverlust (z. Bsp. nach Traumata, Verbrennungen u.a.), bei denen eine plastische Operation keine spannungsarme Adaptation der Wundränder gewährleisten kann. Auch die kosmetische Indikation gewinnt immer mehr an Bedeutung. Möglich ist der Einsatz des Expanders zum Beispiel als Hodenimplantat oder als Dauerimplantat nach Enukleatio bulbi und zur Narbenkorrektur. Ihr klinischer Einsatz bedarf jedoch weiterer experimenteller – vor allem – in-vivo-Untersuchungen, um ihre Einsatzmöglichkeiten beim Tier - und in Zukunft auch beim Menschen – zu evaluieren.

Title: Spectroscopic Study of the Dynamical Behavior and Interactions in Supramolecular and Macromolecular Systems Author: Marek Radecki Department: Department of Macromolecular Physics Supervisor: Doc. RNDr. Lenka Hanyková, Dr., Department of Macromolecular Physics Abstract: In this thesis, the temperature-induced phase transition in liner polymer solutins and hydrogels of semi-interpenetrating (SIPNs) and interpenetrating (IPNs) polymer networks was studied with respect to various composition, network architecture and procedure. Thermoresponsive linear polymers based on poly(vinyl methyl ether) (PVME) in water and with terc-buthyl based additives, IPNs of polyacrylamide (PAAm), poly(N -isopropylacrylamide) (PNIPAm), poly(N - vinylcaprolactam) (PVCL) and IPNs and SIPNs of poly(N,N -diethylacrylamide) (PDEAAm) were investigated by the methods of nuclear magnetic resonance spectroscopy (NMR), differential scanning calorimetry (DSC), optical microscopy (OM) and swelling experiments. The effect of polymer concentration and presence of additives on the dynamics during the phase separation as well as interactions between the water and the polymer in aqueous solutions of PVME and PVME/additives were established. The increasing content of hydrophilic PAAm component in SIPNs and IPNs shifts the transition toward...

Effective vascularization is crucial for almost any therapeutic tissue engineering concept. In this context, therapeutic angiogenesis attempts to enforce the natural process of blood vessel formation by provision of bioactive effectors. Along these lines, the aim of this work was to evaluate the potential of a modular hydrogel composed of the synthetic star-shaped poly(ethylene glycol) (starPEG) and the naturally occurring biopolymer heparin for the defined and orchestrated delivery of two major angiogenic growth factors, fibroblast growth factor-2 (FGF-2) and vascular endothelial growth factor (VEGF). While starPEG determines the structural properties of the gel materials, effective administration of both cytokines is based on their natural affinity to heparin, the highly charged polysaccharidic building block capable of reversibly binding various growth factors upon geometrically matching electrostatic interactions. Varying the molar ratio of starPEG to heparin upon network formation, different hydrogel types with distinct mechanical characteristics but constant heparin content could be produced. As heparin represents the basis for the growth factor interaction with the scaffolds, the matrices were found to bind and release FGF-2 or VEGF independently of the particular network stiffness and structural properties of the different gel types. Moreover, the material could be utilized for a modular delivery of growth factor combinations over a broad range of concentrations. To evaluate the general suitability for pro-angiogenic stimulation, the provision of FGF-2 and VEGF from starPEG-heparin hydrogels differing in their mechanical characteristics and biofunctionalization with adhesive peptides was studied using human endothelial cells, the cell type that forms the inner layer of any blood vessel. Results showed that the presence of the adhesion ligand was an essential requirement to mediate cell attachment and subsequent growth on the scaffolds. Apart from that, hydrogels with an intermediate stiffness showed beneficial effects on endothelial cell proliferation/survival while in parallel also the differentiation into elongated, pro-tubular structures could be promoted. While the delivery of FGF-2 was able to enhance cell growth, VEGF mainly initiated endothelial cell shape elongation. However, with a parallel administration of both growth factors, their beneficial effects could be combined to obtain high numbers of endothelial cells undergoing differentiation. Furthermore, besides the possibility of growing endothelial cells on top of the biofunctionalized hydrogels, the release of growth factors by starPEG-heparin matrices could be applied as a stimulus to attract the cells to migrate into the direction of the scaffolds. While FGF-2 and VEGF supported cell motility to a similar extent, their combined action was found to exert the strongest effect on endothelial cell migration. Based on the results of these in vitro experiments, matrices most effectively stimulating pro-angiogenic cellular responses were selected for in vivo studies applying the functionalized materials to the chorioallantoic membrane (CAM) of fertilized chicken eggs, an assay commonly used to evaluate the vascularization potential of biomaterials. In this assay, the delivery of FGF-2 and/or VEGF by starPEG-heparin hydrogels induced a substantial angiogenic response within the CAM system, while the combination of both growth factors tends to increase vascularization most effectively. In order to adjust the starPEG-heparin hydrogel system to the complex requirements of therapeutic angiogenesis, further options to specifically modulate the FGF-2 or VEGF release were explored. With the incorporation of enzymatically cleavable peptide linkers, not only the possibility for a cellular remodeling of the gel matrix could be permitted, but also the growth factor release was substantially enhanced upon network degradation. Moreover, with the gradual removal of FGF-2 and VEGF interaction sites from heparin upon selective desulfation, the binding of both growth factors to hydrogels composed out of starPEG and desulfated heparin was significantly reduced depending on the remaining sulfate content. Irrespective of the lower immobilized amounts of FGF-2 or VEGF, higher absolute quantities of both growth factors could be released and retained in the medium due to their decreased affinity to heparin, thereby enhancing the delivery efficiency of the scaffolds. Going beyond common concepts for triggered cytokine release, hydrogel-bound FGF-2 or VEGF could be effectively displaced from their heparin binding sites by an application of the competitive, highly-heparin affine molecule chitosan. As chitosan could be introduced at different time points, not only the amounts of delivered growth factor were enhanced, but also the FGF-2 or VEGF release kinetics could be specifically modulated. Taken together, starPEG-heparin hydrogels with independently adaptable physical and biomolecular composition were demonstrated to provide time-resolved multi-factor delivery of pro-angiogenic growth factors resulting in valuable new options for therapeutic angiogenesis.

Articular cartilage is a highly specialized, hierarchically organized tissue covering the articular surfaces of diarthrodial joints that absorbs and distributes forces upon mechanical loading and enables low-friction movement between opposing bone ends. Despite a strong resilience towards mechanical stress, once damaged cartilage is generally not regenerated due to a limited repair potential of the residing cells (chondrocytes) and the local absence of vascularized blood vessels and nerves. Eventually, this may lead to osteoarthritis, a chronic degenerative disorder of the synovial joints which has a strongly growing prevalence worldwide. Modern regenerative therapies that aim to rebuild cartilage tissue in vivo and in vitro using chondrocyte- and stem cell-based methods are still not able to produce tissue constructs with desired biomechanical properties and organization for long-term repair. Therefore, cartilage tissue engineering seeks for new ways to solve these problems. In this regard, the application of hydrogel-based scaffolding materials as artificial matrix environments to support the chondrogenesis of embedded cells and the implementation of appropriate biofabrication techniques that help to reconstitute the zonal structure of articular cartilage are considered as promising strategies for sophisticated cartilage regeneration approaches. In this thesis, a modular starPEG-heparin hydrogel platform as cell-instructive hydrogel scaffold was used in combination with a custom-designed 3D inkjet bioprinting method with the intention to develop a printable 3D in vitro culture system that promotes the chondrogenic differentiation of human mesenchymal stromal cells (hMSC) in printed cell-laden hydrogels with layered architectures in order to fabricate cartilage-like tissue constructs with hierarchical organization. Firstly, the successful bioprinting of horizontally and vertically structured, cell-free and -laden hydrogel scaffolds that exhibit layer thicknesses in the range of the superficial zone, the thinnest articular cartilage layer is demonstrated. The long-term integrity of the printed constructs and the cellular functionality of the plotted cells that generally had a high viability after the printing process are shown by a successful PDGF-BB-mediated hMSC migration assay in a printed multilayered hydrogel construct over a culture period of 4 weeks. Secondly, when the established printing procedures were applied for the chondrogenic differentiation of hMSCs, it was found that the printed cell-laden constructs showed a limited potential for in vitro chondrogenesis as indicated by a weaker immunostaining for cartilage-specific markers compared to casted hydrogel controls. In order to increase the post-printing cell density to tackle the limited printable cell concentration which was regarded as the primary reason for the impaired performance of the printed scaffolds, different conditions with varying culture medium and hydrogel compositions were tested to stimulate 3D cell proliferation. However, a significant 3D cell number increase could not be achieved which ultimately resulted in shifting the further focus to casted hMSC-laden starPEG-heparin hydrogels. Thirdly, the chondrogenic differentiation of hMSCs in casted hydrogels proved to be successful which was indicated by a uniform deposition of cartilage-specific ECM molecules comparable with the outcomes of scaffold-free MSC micromass cultures used as reference system. However, the quantitative analysis of biochemical and physical properties of the engineered hydrogel constructs yielded still significant lower values in relation to native articular cartilage tissue. Fourthly, in order to improve these properties and to enhance the chondrogenesis in starPEGheparin hydrogels, a dualistic strategy was followed. In the first part, specific externally supplied stimulatory cues including a triple growth factor supply strategy and macromolecular crowding were applied. As second part, intrinsic properties of the modular hydrogel system such as the crosslinking degree, the enzymatic degradability and the heparin content were systematically and independently altered. It was found that while the external cues showed no supportive benefits for the chondrogenic differentiation, the reduction of the heparin content in the hydrogel proved to be a key trigger that resulted in a significantly increased cartilage-like ECM deposition and gel stiffness of engineered constructs with low and no heparin content. In conclusion, this work yielded important experiences with regards to the application of inkjet bioprinting for hMSC-based cartilage tissue engineering approaches. Furthermore, the obtained data provided valuable insights into the interaction of MSCs and a surrounding hydrogel-based microenvironment that can be used for the further development of chondrosupportive scaffolding materials which may facilitate the fabrication of cartilage-like tissue constructs.

Mechanoresponsive Systeme antworten auf mechanische Reize mit einer Eigenschaftsänderung. Diese Dissertation umfasst die Arbeiten mit zwei mechanoresponsiven Systemen, die optisch auf mechanische Reize antworten. Sie basieren auf polymeren Strukturen, einer Polymerbürste und einem Hydrogelnetzwerk. Ihr optischer Antwortmechanismus ermöglicht die Beobachtung wirkender Kräfte als ein Ansatz zur in situ-Kraftmessung. Im ersten Teil wird ein existierendes, mechanoresponsives System zur Anwendung gebracht, das auf einer mit Fluoreszenzfarbstoff markierten Polyelektrolytbürste basiert. Die Ladungen des Polyelektrolyts können die Fluoreszenz des Farbstoffs unterdrücken, sodass lokale Kompression und Zugspannung über die Fluoreszenzintensität unterschieden werden können. Die mechanoresponsive Polymerbürste wurde als mechanosensitive Oberflächenbeschichtung angewandt, um Unterschiede in der Kontaktspannungsverteilung von Gecko-inspirierten adhäsiven Mikrostempelstrukturen aufzuklären. Die erarbeiteten Ergebnisse und daraus abgeleiteten Ablösemechanismen der Mikrostempeltypen deckten sich qualitativ mit Vorhersagen aus theoretischen Ansätzen. Aufgrund geometrischer Einschränkungen einer planaren Oberflächenbeschichtung zielt der zweite Teil darauf ab, dieses mechanoresponsive Prinzip in ein dreidimensionales Netzwerk zu überführen und ein mechanoresponsives Hydrogelnetzwerk als Plattform zur Kraftmessung zu entwickeln. Konzeptionell besitzt ein homogenes Netzwerk vorhersagbare mechanische Eigenschaften, sodass lokale optische Antworten auf mechanische Kräfte ermöglichen könnten, die wirkenden Kräfte zu lokalisieren und quantifizieren. Basierend auf einer Gestaltung nach der Flory-Rehner-Theorie wurden Präkursoren mit vordefinierter Größe und Architektur für die Hydrogelherstellung eingesetzt, um auf ein homogenes Netzwerk abzuzielen. Zu diesem Zweck wurde das Mischungsvolumen durch Tropfenmikrofluidik reduziert. Für den optischen Antwortmechanismus wurden die Hydrogelnetzwerk-Präkursoren mit zwei verschiedenen Fluorophoren markiert, die sich durch abstandsabhängige Emission über Förster-Resonanzenergietransfer auszeichnen. Die Funktionalität des optischen Antwortmechanismus wurde auf globaler Ebene durch Kollabieren und kontrolliertes Quellen des Netzwerks, dann auf lokalisierter Ebene durch definierte mechanische Belastung mit Rasterkraftmikroskopie gezeigt. Durch ihre Anpassbarkeit könnte die Hydrogelplattform zukünftig verschiedenste Anwendungen im Bereich intrisischer Kraftmessung weicher Materie bedienen. / Mechanoresponsive systems respond to mechanical triggers by changes in a certain property. This thesis covers the work conducted with two mechanoresponsive systems that respond optically to mechanical triggers. These two systems are based on polymer structures, a polymer brush and a hydrogel network. Thus, the optical response mechanism allows observing acting forces as an approach to force sensing in situ. In the first part, an existing mechanoresponsive system based on a polyelectrolyte brush labeled with a fluorescent dye is engaged in application. The charges of the polyelectrolyte are able to quench the fluorescence of the dye so that local compression or tension can be distinguished from the local fluorescence intensity. The mechanoresponsive polymer brush was applied as mechanosensitive surface coating to elucidate differences in the contact stress distributions of gecko-inspired adhesive micropillar structures. The determined results and the derived detachment mechanisms of the micropillar types were in qualitative accordance with predictions from theoretical approaches. Overcoming the geometrical limitations of a planar surface coating, the second part aims at translating the mechanoresponse principle to a three-dimensional network and developing a mechanoresponsive hydrogel as a platform for force sensing. Conceptually, a homogeneous network allows to predict mechanical properties so that localized optical mechanoresponses could enable locating and quantifying acting forces. Based on network design principles from the Flory-Rehner theory, precursors with predefined size and architecture were utilized in hydrogel preparation, aiming for a homogeneous network. Further in this regard, the mixing volume was reduced by employing droplet microfluidics. As optical response mechanism, the hydrogel network precursors were labeled with two kinds of fluorophore, featuring distance-dependent emission from Förster Resonance Energy Transfer. The functionality of the optical response mechanism was demonstrated on global level by collapsing and controlled swelling of the network, and on a localized level by defined mechanical stress, applied with Atomic Force Microscopy. Owing to its adjustability, the hydrogel platform might be employed in various applications that require intrinsic force sensing of soft matter in future.

Despite great progress of lab-on-a-chip (LoC) technology platforms in the last 30 years, there is a lack of standardized microfluidic components, real on-chip utomation and progressive functional scalability of the fluidic circuits. Hydrogel-based microfluidic circuits have a high scaling potential and provide on-chip automation, but are complex in system design. An advanced circuit concept for planar microfluidic chip architectures, originating from the early era of the semiconductor-based resistor-transistor-logic (RTL) is presented and the hydrogel-based chemical volume phase transition transistor (CVPT) for logic gate operations is implemented. The circuit concept (CVPT-RTL) is robust and simple in design, feasible with common materials and manufacturing techniques of the LoC technology. Thereby, three major challenges are solved: contamination issues, maintaining the signal compliance for cascadability, and chemical signal inversion. As a central element, a CVPT cascode is introduced. The functionality of the concept is verified by a 24 h test of the NAND gate operation and a self-automated chemofluidic analog-to-digital converter, utilized as interface between bioreactors and extended microfluidic logic circuits. Moreover, the CVPT-RTL cascode demonstrates the expected selfstabilizing performance of the NAND gate. Accompanying simulations of the component behavior based on a network description implemented in Matlab Simscape match with the experimental results.