Controlled hydrogel dissolution allows for: 1) atraumatic material removal after it served its function, 2) site-specific delivery of encapsulated therapeutics (e.g., proteins, small molecules), and 3) a tailored administration of an agent with high efficiency. Dissolution of covalently crosslinked hydrogels has been accomplished by incorporating cleavable moieties that undergo ester hydrolysis or enzymatic degradation. Recently, thiol-disulfide exchange, retro Michal-type reactions, retro Diels-Alder reactions, and thiol-thioester exchange chemistries have gained attention, as they provide a responsive synthetic handle for engineering hydrogel dissolution rates. We synthesized, characterized and tested in vivo two on-demand dissolvable dendritic thioester hydrogel dressings for second-degree burn care and hemorrhage control. The hydrogels are composed of lysine-based dendrons and PEG-based crosslinkers, which were prepared in high yields. In context of hemorrhage, there is an unmet clinical need for an on-demand dissolvable sealant for non-compressible hemorrhage or areas of body not amenable to treatment with a torniquet. In a model of in vivo hemorrhage control of intra-abdominal wounds, our hydrogel reduced blood loss by 33% in severe hepatic hemorrhage and by 22% in aortic injury, as compared to untreated controls. There is an unmet clinical need for a second-degree burn dressing that can be removed atraumatically and serve as a barrier to bacterial infection. When our hydrogel was used as a dressing, local and systemic bacterial proliferation after wound contamination was significantly lower than in the untreated group. The total bacterial burden of the burn wound in the positive controls was significantly higher than in the hydrogel group and the negative controls (1.39x10E8 ± 8.30x10E7 CFU/g v. 4.04x10E3 ± 3.99x10E3 CFU/g v. 6.88x10E2 ± 6.38x10E2 respectively; P = 0.009). Also, the total systemic bacterial burden in the positive controls was significantly higher than the hydrogel group and the negative controls (9x10E2 ± 7.76x10E7 CFU/g v. 5x10E1 ± 0 CFU/g v. 5x10E1 ± 0 CFU/g, respectively; P = 0.031). A unique feature of both hydrogel systems is their capability to be dissolved on-demand via thiol-thioester exchange reaction with a biocompatible solution following its initial application – thus the wound area can be re-exposed to allow for definitive surgical care.

A liquid foaming technology was developed to produce bio-foams for packaging applications. Liquid foaming consists in the transformation of a liquid foamed solution into a porous solid polymer through liquid removal. Five bio-based liquid foaming formulations systems were explored in this research: starch-PVA-calcium sulfate, starch-gelatine, gelatine hydrogel, gelatinecomposites and hydrogel alternatives to gelatine. Gelatine hydrogel-composite foams secondary materials included bio-mass powders from agriculture waste, expanded vermiculite particles, silica aero-gel powders and honeycomb sandwich panels. The hydrogel foams alternative to gelatine were based on agar and gellan gum as main biopolymers. The feasibility of each formulation system was explored, and the key parameters of formulation and process conditions were identified. The role of different formulation (e.g. biopolymer content, gelatine strength, surfactant type and content, among others) and processing (e.g. expansion ratio, processing temperature and drying process, among others) factors on foaming and drying behaviour of the liquid foam, and the impact on foam structure and properties (density, drying shrinkage and mechanical, thermal and acoustic properties) of the solid foams were investigated. Hydrogel-foams with comparable densities and thermal conductivity to conventional polymeric foams were produced. Gelatine foams made with both surfactants "A" and C2 exhibited desirable properties for being a strong alternative to conventional plastic foams. Low densities (< 20 kg/m3), thermal conductivity (≈0.039 W/k·m), and relatively low shrinkage level were achieved. Production upscale research would need to consider drying process optimization for drying time reduction and drying shrinkage minimization.

O estudo da distribuição e propagação a luz em tecidos biológicos é importante para diversas aplicações em fototerapias e diagnóstico. Os tecidos biológicos são considerados meios túrbidos, onde existe uma combinação de absorção e espalhamento, e a determinação do comportamento da luz dentro deles tem sido estudado através da aplicação de modelos que tem suas limitações. Então, determinar e manipular a distribuição para entrega da melhor dose de luz é crucial para o sucesso dos tratamentos. Para casos de Terapia Fotodinâmica, em particular, os tratamentos de lesões planas lisas, em grande parte dos casos, são bem sucedidos. Este sucesso deve-se ao fato de que existe uma boa possibilidade de distribuição uniforme da luz dentro do tecido da lesão tratada. Por outro lado, para tumores espessos de superfícies irregulares, a iluminação é dificultada devido à presença de sombras, rachaduras entre outras imperfeições sobre a lesão. Deste modo, a entrega da dose de luz inadequada e a iluminação não homogênea, resultam em regiões de necroses parciais e recidiva. Portanto, é decisivo melhorar o perfil da distribuição dentro do tecido. Neste trabalho avaliamos o acoplamento da luz utilizando um gel posicionado entre a fonte ( &#955= 630 nm) e a superfície de um phantom sólido. O acoplamento do feixe foi melhorado incorporando baixas concentrações de espalhadores ao gel. Imagens do perfil de distribuição da luz foram coletadas e transformadas em matrizes de intensidades, e posteriores curvas de isointensidades. Nossos resultados mostraram uma grande melhora na uniformidade da distribuição. De fato, utilizando um meio acoplador, conseguimos entregar um feixe mais homogêneo promovendo uma melhor iluminação. Esta técnica elimina drásticamente os efeitos da rugosidade da superfície do phantom dentro do volume tratado. Acreditamos que esse trabalho mostra uma possibilidade de melhora na dosimetria para fototerapias. / The light propagation and distribution studies in biological media are importante for several phototherapy and diagmostic aplications. The biological tissues are considered turbida medias, where there is absortion and scattering combination, and determinate the light behavior inside this tissues have been studied by models that has some limitations.Then, to determine and control the light distribution to improve the light dose delivery is important for the treatment successful. For particular cases, such as Photodynamic Therapy (PDT) applied on smooth planar lesions treatments is appropriated, since there is a good possibility of uniform distribution of light within the tissue of the treated lesion. On the other hand, tumors with more thickness may not receive the needed doses of energy to cause its death. For an efficient treatment by photodynamic therapy is required an optimal coupling light inside the lesion tissue. Shadow effects, slits or physical irregularities in the lesion can lead a nonhomogeneous light distribution inside the tissue. The results can be a partial necrosis regions and tumor recurrence. Therefore it is crucial improving the light profile inside the tissue to overcome these problems. In this study, we measured the light profile inside the phantom after the light passing through a gel as coupler. We used a solid phantom as biological tissue model and was used a red laser (&#955 = 630 nm) as light source with an optical fiber to direct illumination. The coupling is controlled by introducing a gel with low concentration of scatters between the fiber and de phantom. Was collected pictures of light profile with a camera and the data were processed with MatLab software. Our results shows a strong improvement in the light distribution when the gel with scatters is positioned between fiber and tissue. In fact, a more homogeneous laser bean is delivered to tissue promoting a better light distribution. This technique eliminates drastically the roughness effect of the phantom surface in the bulk. We believe that this work shows a possibility of dosimetry improvement for phototherapy.

In this thesis we focus on a novel experimental exploration of fluid-driven fractures in a brittle hydrogel matrix. Fluid-driven fracturing is a procedure by which a fracture is initiated and propagates due to pressure applied by a fluid introduced inside the fracture. We describe how to construct the experimental setup utilised in this research, including how to synthesise polyacrylamide hydrogels to study the processes linked with fluid-driven fracturing. These transparent, linearly elastic and brittle gels permit fracturing at low pressures and speeds allowing accurate measurements to be obtained. The broad range of modulus and fracture energy values attainable from this medium allow the exploration of particular regimes of importance. Fracturing within these hydrogels also creates beautiful spiral patterns on the plastically deformed surfaces. We analyse these patterns and discuss their formation, while also commenting on their fractal-like nature. Initially, we study single fractures that are driven by an incompressible Newtonian fluid, injected at a constant rate into an elastic matrix. The injected fluid creates a radial fracture that propagates along a plane. We investigate this type of fracture theoretically and then verify the scaling predictions experimentally. We examine the rate of radial crack growth, fracture aperture, shape of the crack tip and internal fluid flow field. We exhibit the existence of two distinct fracturing regimes, and the transition between these, in which propagation is either dominated by viscous flow within the fracture or the material toughness. Particle image velocimetry measurements also strikingly show that the flow in the fracture can alter from an expected radial symmetry to circulation cells, dependent on the regime of propagation. We then expand our research to the problem of two coplanar fluid-driven radial fractures. This was chosen to focus on the physical mechanisms that are key to fracture network formation, related to many geophysical and industrial practices. Initially, the two fractures propagate independently of each other. At a critical separation they begin to interact, with non-uniform growth occurring along the fracture edges due to the evolving stress state in the gel matrix. When the radial extents of the fractures become sufficiently large, they coalesce and form a bridge between them. Following initial contact, a large increase in flow is seen into the newly created bridge and most of the growth is localised along this, perpendicular to the line connecting the injection sources. From experimental measurements, we observe a universal dynamic behaviour for the growth of this bridge. We model this universal behaviour theoretically and construct scalings related to the growth after coalescence, which again identifies both a viscous and toughness regime. The toughness regime is verified experimentally for the bridge growth and the universal shape of the thickness profile along the bridge. The coalesced fractures then transition into a single fracture at late times. Finally, we discuss a number of other interesting scenarios that may occur such as, non-coalescing fractures, asymmetric coalescence and ridge formation.

Uma variedade de hidrogéis, que correspondem a uma classe de materiais poliméricos altamente hidratados está sendo empregado como biomateriais. Biopolímeros como quitosana, xantana e colágeno apresentam excelente biocompatibilidade e podem ser utilizados na área de queimados e liberação controlada de fármacos. Neste trabalho foram preparados hidrogéis provenientes da mistura entre quitosana, derivada de &beta;-quitina, xantana comercial e colágeno aniônico (derivado de tendão bovino) em proporções variadas. A caracterização das amostras foi realizada por análise térmica (termogravimetria e calorimetria exploratória diferencial), espectroscopia no infravermelho, microscopia eletrônica de varredura e absorção de água. Pelas curvas termogravimétricas os resultados mostraram que todos os hidrogéis apresentam uma grande quantidade de água na sua estrutura e que pela reidratação são capazes de reter novamente essa quantidade de água. Por DSC observou-se que todos apresentaram o pico referente à fusão de água livre em temperaturas deslocadas acima de 0oC pelo aumento da interação água/polímero. Por FT-IR constatou-se a presença de bandas características dos biopolímeros com a ausência de novas bandas e pelo estudo por MEV os hidrogéis apresentaram uma estrutura na forma de folhas e a presença de colágeno é bastante visível participando desta estrutura. / Hydrogel are polymeric materials, which have the capacity to retain a great amount of water, and are often used as biomaterials. Chitosan, xanthan and collagen present biocompatibility and they can be used in tissue regeneration and drug delivery. In this work hydrogels were prepared by the mixture with chitosan (from &beta;-quitina), commercial xanthan and anionic collagen (from bovine tendon) in different proportions. They were characterized by thermal analysis (thermogravimetry and differential scanning calorimetry), infrared spectroscopy (FTIR), scanning electronic microscopy and water absorption. Thermogravimetric curves showed that all hydrogels present a great amount of water and after the rehydratation were capable to keep the same amount of water. Melting point of water in DSC curves were shifted to higher values due the increase of water/polymer interaction. FT-IR showed characteristic bands of biopolymers with the absence of new bands and the morphology (MEV) showed that the hydrogels structures were in sheet form and the collagen fibers are visible in the hole structure.

Der Kehlkopf ist ein stimmerzeugendes knorpelhaltiges Organ und spielt eine wichtige Rolle in der Atemfunktion und beim aspirationsfreien Schluckakt. Funktionsstörungen des Kehlkopfs wie Stimmbandlähmungen werden durch Schädigungen des Kehlkopfnervs nach operativen Eingriffen und Halsverletzungen hervorgerufen. Des Weiteren führen durch Traumen, Teil- und komplette Resektionen verursachte Substanzdefekte des Kehlkopfs zu Funktionsverlusten. Die hierfür notwendigen und komplexen Rekonstruktionen werden durch das schlechte Regenerationspotential von Knorpelgewebe eingeschränkt und können nur bedingt durch synthetische Ersatzmaterialen oder körpereigenes Ersatzgewebe bewerkstelligt werden. Ist es möglich, mit Hilfe des Tissue Engineerings aus körpereigenen Stammzellen und biokompatiblen Trägermaterialien implantierbares Knorpelersatzgewebe herzustellen, welches zur dauerhaften Wiederherstellung der Kehlkopffunktionen eingesetzt werden kann? Die zusätzliche Markierung von Stammzellen mit superparamagnetischen Eisenoxidnanopartikeln (VSOP) als Zellmarker bietet die Möglichkeit der Detektion und der Verfolgung der Zellen mittels nicht-invasiver Nachweismethoden nach deren Implantation. Ist die Verwendung dieser Nanopartikel ohne negative Folgen für die Stammzellen möglich und sind diese für den Einsatz in der Laryngologie geeignet? Fettgewebsstammzellen (ASC) wurden aus humanem Liposuktionsmaterial und Kaninchen-Nackenfett isoliert und expandiert. Die Zellen wurden in Hydrogelkombinationen aus Kollagen Typ-I, Agarose, Fibrin und Hyaluronsäure eingebettet und mit den chondrogenen Wachstumsfaktoren TGF-β3, BMP-6 und IGF-I über 14 Tage differenziert. Anschließend wurden diese Zell-Hydrogelkonstrukte bezüglich Morphologie, extrazellulärer Matrixanreicherung und knorpelspezifischer Genexpression histologisch, immunhistochemisch und molekularbiologisch analysiert. In einem weiteren Schritt wurden die Integration der Zell-Hydrogelkonstrukte in natives Knorpelgewebe sowie die Defektdeckung in einem in vitro- und einem in vivo-Knorpeldefektmodell mit vor- und nicht-vordifferenzierten Zell-Hydrogelkonstrukten untersucht. Die Analyse möglicher zyto- und genotoxischer Effekte von VSOP sowie des Einflusses der Markierung von ASC mit VSOP auf die Proliferation, Migration und das Multidifferenzierungspotential erfolgte nach der Markierung der Zellen mit unterschiedlichen VSOP-Konzentrationen. Außerdem wurden VSOP-markierte ASC in Kaninchenstimmlippen injiziert und die Nachweisbarkeit dieser Zellen im Injektionsareal histologisch und mittels Magnetresonanztomographie (MRT) untersucht. Nach 14-tägiger chondrogener Differenzierung wurde in den Zell-Hydrogelkonstrukten eine knorpelähnliche Morphologie, die Anreicherung knorpelspezifischer Matrixproteine und die Expression chondrogener Markergene nachgewiesen. Die Kombination der chondrogenen Wachstumsfaktoren zeigte keinen verstärkenden Einfluss auf die Chondrogenese von ASC. Hydrogele aus Kollagen Typ I und Hyaluronsäure wiesen die stärkste extrazelluläre Matrixanreicherung auf. Bei den agarosefreien Hydrogelen war eine ausgeprägte Gelschrumpfung auffällig. In den beiden Knorpeldefektmodellen konnte weder eine Integration der Zell-Hydrogelkonstrukte in den Nativknorpel noch eine vollständige Defektdeckung nachgewiesen werden. Nach der Markierung von ASC mit VSOP zeigte sich bei der höchsten Konzentration von 1,5 mM eine genotoxische Wirkung. Zytotoxische Effekte sowie Einflüsse der Markierung auf die Proliferation, Migration und das Multidifferenzierungspotential von ASC waren nicht nachweisbar. VSOP-markierte ASC konnten nach deren Injektion in Kaninchenstimmlippen im Injektionsareal nur vereinzelt mittels MRT und histologisch nachgewiesen werden. Es ist möglich, mit Hilfe des Tissue Engineerings aus körpereigenen Stammzellen und biokompatiblen Trägermaterialien implantierbares knorpelähnliches Gewebe herzustellen. Dabei begünstigen agarosefreie Trägermaterialien die chondrogene Differenzierung von ASC. Diese könnte durch die jeweilige Erhöhung der Zelldichte und Wachstumsfaktorkonzentrationen sowie die Verlängerung der Induktionszeit verstärkt werden. Eine mögliche klinische Anwendung dieser knorpelähnlichen Gewebe in der Laryngologie ist jedoch durch deren Schrumpfung wie auch mangelnde Integration und Defektdeckung noch weit entfernt. Aufgrund ihrer genotoxischen Wirkung kann eine Verwendung von VSOP als Zellmarker auch unterhalb von 1,5 mM ohne negative Folgen für den Organismus nicht sicher ausgeschlossen werden. Der inhomogene Gewebekontrast im Kehlkopf, die schlechte Auflösung im MRT und die geringe Größe von VSOP erschweren die Nachweisbarkeit und Verfolgung markierter Zellen mittels MRT. Daher sind andere nicht-invasive Nachweismethoden für die Verwendung von VSOP im Kehlkopf zu evaluieren. Der möglichen Anwendung dieser knorpelähnlichen Gewebe und VSOP in der rekonstruktiven Laryngologie muss eine erfolgreiche Optimierung und ausführliche positive Validierung in klinischen Tests vorausgehen. / The larynx is a voice-producing and cartilage-containing organ that plays an important role in the respiratory function and aspiration-free swallowing. Dysfunctions of the larynx, such as vocal cord paralysis, are caused by damage to the laryngeal nerve after surgery and neck injuries. Furthermore, tissue defects caused by trauma and partial or complete resection of the larynx lead to loss of functions. The required and complex reconstructions are limited by the poor regeneration potential of cartilage, and can only be partially accomplished by synthetic graft materials or autologous replacement tissue. Is it possible to generate implantable cartilage replacement tissues that can be used for permanent restoration of laryngeal functions out of autologous stem cells and biocompatible scaffolds by the means of tissue engineering? The supplementary labeling of stem cells with very small superparamagnetic iron oxide nanoparticles (VSOP) as cell markers offers the possibility to identify and trace the cells after their implantation using non-invasive detection methods. Can VSOP be used without negative consequences for the stem cells, and are these nanoparticles suitable for application in laryngology? Adipose tissue-derived stem cells (ASC) were isolated from human liposuction material and rabbit nuchal fat. After expansion, the cells were embedded in hydrogel combinations of collagen type I, agarose, fibrin and hyaluronic acid and then differentiated with the chondrogenic growth factors TGF-β3, BMP-6, and IGF-I for 14 days. Subsequently, these cell-seeded hydrogel constructs were analyzed histologically, immunohistochemically and molecular biologically regarding morphology, extracellular matrix accumulation and cartilage-specific gene expression. In a further step, the integration of pre- and non predifferentiated cell-seeded hydrogel constructs into native cartilage tissue and defect coverage were examined in cartilage defect models in vitro and in vivo. The analysis of potential cytotoxic and genotoxic effects of VSOP, as well as the influence of the nanoparticles on proliferation, migration, and multilineage potential of ASC, was performed after labeling the cells with different VSOP concentrations. In addition, VSOP-labeled ASC were injected into rabbit vocal folds and the detectability of these cells in the injection area was examined histologically and by magnetic resonance imaging (MRI). A cartilage-like morphology, the accumulation of cartilage-specific matrix proteins and the expression of chondrogenic marker genes, was observed in the cell-seeded hydrogel constructs after 14 days of chondrogenic differentiation. The combination of the chondrogenic growth factors had no reinforcing effect on the chondrogenesis of ASC. Hydrogels of collagen type I and hyaluronic acid showed the strongest extracellular matrix accumulation. A pronounced shrinkage was observed with agarose-free hydrogels. In the cartilage defect models neither an integration of the cell-seeded hydrogel constructs into the native cartilage nor a complete defect coverage were detected. The labeling of ASC with the highest VSOP concentration of 1.5 mM induced genotoxic effects. Cytotoxic effects and influences of labeling with VSOP on proliferation, migration and multilineage potential of ASC could not be observed. After their injection into rabbit vocal folds VSOP-labeled ASC were only sporadically detected histologically and by MRI in the injection area. It is possible to generate implantable cartilage-like tissues out of autologous stem cells and biocompatible scaffolds by the means of tissue engineering. Here, agarose-free scaffolds promote the chondrogenic differentiation of ASC. This may be enhanced by increasing the cell density and growth factor concentrations as well as extending the induction time. Because of their shrinkage and the lack of integration and defect coverage, a possible clinical application of these cartilage-like tissues in laryngology is still far away. Due to the genotoxic effects of 1.5 mM VSOP, the use of these nanoparticles as cell markers without negative consequences for the organism cannot be ruled out with certainty at lower concentrations. The inhomogeneous tissue contrast in the larynx, a poor resolution in MRI and the small size of VSOP make labeled cells difficult to detect and trace in the larynx by MRI. Therefore, other non-invasive detection methods for the use of VSOP in the larynx have to be evaluated. The potential application of these cartilage-like tissues and VSOP in reconstructive laryngology must be preceded by successful optimization and extensive positive validation in clinical trials.

The aim of the work was the development of thiol-ene cross-linked hydrogels based on functionalized poly(glycidol)s (PG) and hyaluronic acid (HA) for extrusion based 3D bioprinting. Additionally, the functionalization of the synthesized PG with peptides and the suitability of these polymers for physically cross-linked gels were investigated, in a proof of principle study in order to demonstrate the versatile use of PG polymers in hydrogel development. First, the precursor polymers of the different hydrogel systems were synthesized. For thiol-ene cross-linked hydogels, linear allyl-functionalized PG (P(AGE-co-G)) and three different thiol-(SH-)functionalized polymers, ester-containing PG-SH (PG SHec), ester-free PG-SH (PG-SHef) and HA-SH were synthesized and analysed, The degree of functionalization of these polymers was adjustable. For physically cross-linked hydrogels, peptide-functionalized PG (P(peptide-co-G)), was synthesized through polymer analogue thiol-ene modification of P(AGE-co-G). Subsequently, thiol-ene cross-linked hydrogels were prepared with the synthesized thiol- and allyl-functionalized polymers. Depending on the origin of the used polymers, two different systems were obtained: on the one hand synthetic hydrogels consisting of PG-SHec/ef and P(AGE-co-G) and on the other hand hybrid gels, consisting of HA-SH and P(AGE-co-G). In synthetic gels, the degradability of the gels was determined by the applied PG-SH. The use of PG-SHec resulted in hydrolytically degradable hydrogels, whereas the cross-linking with PG-SHef resulted in non-degradable gels. The physical properties of these different hydrogel systems were determined by swelling, mechanical and diffusion studies and subsequently compared among each other. In swelling studies the differences of degradable and non-degradable synthetic hydrogels as well as the differences of synthetic compared to hybrid hydrogels were demonstrated. Next, the stiffness and the swelling ratios (SR) of the established hydrogel systems were examined in dependency of different parameters, such as incubation time, polymer concentration and UV irradiation. In general, these measurements revealed the same trends for synthetic and hybrid hydrogels: an increased polymer concentration as well as prolonged UV irradiation led to an increased network density. Moreover, it was demonstrated that the incorporation of additional non-bound HMW HA hampered the hydrogel cross-linking resulting in gels with decreased stiffness and increased SR. This effect was strongly dependent on the amount of additional HMW HA. The diffusion of different molecular weight fluorescein isothiocyanate-dextran (FITC-dextran) through hybrid hydrogels (with/without HMW HA) gave information about the mesh size of these gels. The smallest FITC-dextran (4 kDa) completely diffused through both hydrogel systems within the first week, whereas only 55 % of 40 kDa and 5-10 % HMW FITC-dextrans (500 kDa and 2 MDa) could diffuse through the networks. The applicability of synthetic and hybrid hydrogels for cartilage regeneration purpose was investigated through by biological examinations. It was proven that both gels support the survival of embedded human mesenchymal stromal cells (hMSCs) (21/28 d in vitro culture), however, the chondrogenic differentiation was significantly improved in hybrid hydrogels compared to synthetic gels. The addition of non-bound HMW HA resulted in a slightly less distinct chondrogenesis. Lastly the printability of the established hydrogel systems was examined. Therefore, the viscoelastic properties of the hydrogel solutions were adjusted by incorporation of non-bound HMW HA. Both systems could be successfully printed with high resolution and high shape fidelity. The introduction of the double printing approach with reinforcing PCL allowed printing of hydrogel solutions with lower viscosities. As a consequence, the amount of additional HMW HA necessary for printing could be reduced allowing successful printing of hybrid hydrogel solutions with embedded cells. It was demonstrated that the integrated cells survived the printing process with high viability measured after 21 d. Moreover, by this reinforcing technique, robust hydrogel-containing constructs were fabricated. In addition to thiol-ene cross-linked hydrogels, hydrogel cross-linking via ionic interactions was investigated with a hybrid hydrogel based on HMW HA and peptide-functionalized PG. Rheological measurements revealed an increase in the viscosity of a 2 wt.% HMW HA solution by the addition of peptide-functionalized PG. The increase in viscosity could be attributed to the ionic interactions between the positively charge PG and the negatively charge HMW HA. In conclusion, throughout this thesis thiol-ene chemistry and PG were introduced as promising cross-linking reaction and polymer precursor for the field of biofabrication. Furthermore, the differences of hybrid and synthetic hydrogels as well as chemically and physically cross-linked hydrogels were demonstrated. Moreover, the double printing approach was demonstrated to be a promising tool for the fabrication of robust hydrogel-containing constructs. It opens the possibility of printing hydrogels that were not printable yet, due to too low viscosities. / Ziel der Arbeit war die Entwicklung von Thiol-En-vernetzten Hydrogelen basierend auf funktionalisierten Poly(glyzidolen) (PG) und Hyaluronsäure (HA) für das extrusionsbasierte 3D-Biodrucken. Um die vielseitigen Anwendungsmöglichkeiten von PG-Polymeren für die Hydrogelentwicklung zu zeigen, wurde darüber hinaus, in einer Proof-of-Principle-Studie, PG mit Peptiden funktionalisiert und die Eignung dieser Polymere für die Herstellung von physikalisch vernetzten Gelen untersucht. Zunächst wurden die Vorläuferpolymere für die verschiedenen Hydrogelsysteme synthetisiert. Für die Thiol-En-vernetzten Hydrogele wurde lineares Allyl-funktionalisiertes PG (P(AGE-co-G)) und drei verschiedene Thiol-(SH )funktionalisierte Polymere, Ester haltiges PG-SH (PG-SHec), Ester freies PG SH (PG-SHef) und HA-SH synthetisiert und analysiert. Dabei war der Funktionalisierungsgrad dieser Polymere einstellbar. Für physikalisch vernetzte Hydrogele wurde Peptid-funktionalisierte PGs (P(Peptid co-G)) mittels polymeranaloger Thiol-En-Modifikation von P(AGE-co-G) synthetisiert. Anschließend wurden Thiol-En-vernetzte Hydrogele auf Basis der synthetisierten Thiol- und Allyl-funktionalisierten Polymeren hergestellt. Je nach Ursprung der verwendeten Polymere wurden zwei verschiedene Systeme erhalten: einerseits synthetische Hydrogele bestehend aus PG-SHec/ef und P(AGE-co-G) und andererseits hybride Gele, bestehend aus HA-SH und P(AGE-co-G). Bei den synthetischen Gelen wurde die Abbaubarkeit der Gele durch das verwendete PG-SH bestimmt. Die Verwendung von PG-SHec resultierte in hydrolytisch abbaubaren Hydrogelen, während die Vernetzung mit PG-SHef zu nicht abbaubaren Gelen führte. Die physikalischen Eigenschaften der verschiedenen Hydrogelsysteme wurden mittels Quell-, mechanischen und Diffusionsexperimenten bestimmt und anschließend miteinander verglichen. Die Quellungsstudien zeigten die Unterschiede von abbaubaren und nicht abbaubaren synthetischen Hydrogelen, sowie die Unterschiede von synthetischen gegenüber hybriden Hydrogelen. Als nächstes wurden die Steifigkeit und das Quellverhältnis (SR) der etablierten Hydrogelsysteme in Abhängigkeit von verschiedenen Parametern wie Inkubationszeit, Polymerkonzentration und UV-Bestrahlung untersucht. Im Allgemeinen zeigten diese Messungen für synthetische und hybride Hydrogele die gleichen Trends: eine erhöhte Polymerkonzentration sowie eine verlängerte UV-Bestrahlung führten zu einer erhöhten Netzwerkdichte. Darüber hinaus wurde gezeigt, dass das Einbringen zusätzlicher, nicht gebundener HMW HA die Hydrogelvernetzung behinderte, was zu Gelen mit verringerter Steifigkeit und erhöhtem SR führte. Dieser Effekt war stark abhängig von der Menge an zusätzlich eingebrachter HMW HA. Die Diffusion von Fluorescein-Isothiocyanat-Dextran (FITC-Dextran) mit unterschiedlichem Molekulargewichten durch hybride Hydrogele (mit/ohne HMW HA) lieferte Informationen über die Maschengröße dieser Gele. Das kleinste FITC-Dextran (4 kDa) diffundierte innerhalb der ersten Woche vollständig durch beide Hydrogelsysteme, während nur 55 % der 40 kDa und 5-10 % HMW FITC-Dextrane (500 kDa und 2 MDa) durch die Netzwerke diffundieren konnten. Die Anwendbarkeit von synthetischen und hybriden Hydrogelen für Knorpelregenerationszwecke wurde durch biologische Experimente untersucht. Es wurde bewiesen, dass beide Gele das Überleben von eingebetteten humanen mesenchymalen Stromazellen (hMSCs) unterstützen (21/28 d in vitro Kultur), jedoch war die chondrogene Differenzierung in hybriden Hydrogelen im Vergleich zu synthetischen Gelen signifikant verbessert. Die Zugabe von nicht gebundenem HMW HA führte zu einer etwas weniger ausgeprägten Chondrogenese. Zuletzt wurde die Druckbarkeit der etablierten Hydrogelsysteme untersucht. Dafür wurden die viskoelastischen Eigenschaften der Hydrogellösungen durch das Einbringen von nicht gebundener HMW HA eingestellt. Beide Systeme konnten erfolgreich mit hoher Auflösung und hoher Formgenauigkeit gedruckt werden. Die Einführung des Doppeldruck-Konzeptes mit verstärkendem PCL ermöglichte das Drucken von Hydrogellösungen mit niedrigeren Viskositäten. Infolgedessen konnte die für den Druck notwendige Menge an HMW HA reduziert und hybride Hydrogellösungen mit eingebetteten Zellen erfolgreich gedruckt werden. Es wurde gezeigt, dass die integrierten Zellen den Druckprozess mit hoher Vitalität überlebten (gemessen nach 21 d). Darüber hinaus wurden mit dieser Verstärkungstechnik robuste Hydrogel-enthaltende Konstrukte hergestellt. Zusätzlich zu den Thiol-En-vernetzten Hydrogelen wurde die Hydrogelvernetzung mittels elektrostatischen Wechselwirkungen mit einem hybriden Gel auf der Basis von HMW HA und Peptid-funktionalisiertem PG untersucht. Rheologische Messungen ergaben eine Erhöhung der Viskosität einer 2 wt.% HMW HA Lösungen durch die Zugabe von Peptid-funktionalisiertem PG. Der Viskositätsanstieg konnte auf die elektrostatischen Wechselwirkungen zwischen dem positiv geladenen PG und der negativ geladenen HMW HA zurückgeführt werden. Zusammenfassend wurde in dieser Arbeit die Thiol-En-Chemie und PG als vielversprechende Vernetzungsreaktion bzw. Polymervorstufe für die Biofabrikation eingeführt. Des Weiteren wurden die Unterschiede von hybriden und synthetischen Hydrogelen sowie von chemisch und physikalisch vernetzten Hydrogelen aufgezeigt. Darüber hinaus wurde gezeigt, dass das Doppeldruck-Konzept eine vielversprechende Methode für die Herstellung von robusten Hydrogel-enthaltenden Konstrukten ist. Es eröffnet die Möglichkeit, Hydrogele zu drucken, die aufgrund zu geringer Viskositäten bis jetzt nicht druckbar waren.

Basic physics teaches us that the frictional force (lateral force) needed to move objects on surfaces are proportional to load (normal force) – Amonton’s Laws. In tribology, this force is proportional to contact area, whereas Amonton is just a special case for contact area scaling with load. Such established laws do not seem to apply to small drops on flat, smooth surfaces in which frictional forces have an inverse relation to contact area and have time component prior to movement. Such phenomena can be explained by Shanahan-deGennes were intermolecular forces are considered for a deformed surface. Graphene is a special case where no time component is observed and frictional forces are attributed to its chemical homogeneity and stability. In the second part of this thesis, graphene is considered as nanofiller to build up polymer nanocomposites via Layer by Layer (LbL). Graphene Nanoribbons derived from multi-walled carbon nanotubes (MWCNT) offers a special case for thermoplastic polyurethane nanocomposites in that of thermally activated twisting morphology influences nanocomposite properties. Finally an electric field driven transdermal hydrogel drug delivery device has been demonstrated by just using CNTs, polyvinyl-borax gel and a CNT membrane

There are two primary objectives of this dissertation research. The first objective was to prepare a library of inorganic-organic hydrogels from methacrylated star polydimethylsiloxane (PDMSstar-MA) and diacrylated poly(ethylene oxide) (PEO-DA) with tunable chemical and physical properties for use as tissue engineering scaffolds. These inorganic-organic hydrogels provide a useful platform to study the effect of scaffold properties on cell behavior in tissue culture. Twenty compositionally unique hydrogels were prepared by photo-crosslinking varing molecular weights (Mn) of PEO-DA (Mn = 3.4k and 6k g/mol) and PDMSstar-MA (Mn = 1.8k, 5k and 7k g/mol) at varying weight ratios (up to 20 wt% PDMSstar-MA). Introduction of PDMSstar-MA caused formation of discrete PDMS-enriched "microparticles" dispersed within the PEO hydrogel matrix. The swelling ratio, mechanical properties in tension and compression, non-specific protein adhesion and cytotoxicity of hydrogels were studied. The second objective was to prepare thermoresponsive nanocomposite hydrogels, which are mechanically robust and can remove adhered cells via thermal modulation. Such hydrogels may be useful as "self-cleaning" membranes for implanted biosensors to extend their lifetime and efficiency. These hydrogels are comprised of a poly(Nisopropylacrylamide) (PNIPAAm) hydrogel matrix and polysiloxane colloidal nanoparticles (~220 nm and 50 nm ave. diameter). Due to the low preparation temperature, the nanocomposite hydrogels exhibited a homogeneous morphology by SEM analysis. The volume phase transition temperature (VPTT, ~33 degrees C) of the nanocomposite hydrogels was not altered versus the pure PNIPAAm hydrogel, which is near body temperature. Generally, nanoparticles led to improve mechanical properties versus pure PNIPAAm hydrogels. When these nanocomposite hydrogels are heated above the VPTT, they become more hydrophobic. When they are reversibly switched from a water-swollen to a deswollen state, the change in surface properties, as well as swelling-deswelling, was effective upon the removal of adhered cells.

The development of novel, peptide based structures for tissue engineering materials has been widely researched, and its popularity can be attributed to advancements in technological analysis methods. Using principles based on protein structure and organization, this work describes the novel self-assembly of depsipeptides, which incorporate alternating esters within a native peptide backbone. Chapter 1 introduces and reviews peptide mimics for their utility for tissue engineering applications. Chapter 2 describes the methodology in synthesizing and characterization a depsipeptide library using both solution and solid phase methods. Chapter 3 discusses the effects of depsipeptide length, concentration, and sequence within a range of ionic concentrations and pH ranges on the self-assembly of depsipeptides into spherical nanostructures, fibers, or hydrogels. Chapter 4 describes proposed methods to increase the rate of gelation, followed by discussions of biocompatibility studies from other self-assembling peptide and modified-peptide systems in vitro and in vivo. The work described in this dissertation demonstrates that the synthesis and self-assembly of a depsipeptide family which alternates esters into a native peptide backbone does not disrupt the formation of higher order structures. This study illustrates the potential to synthesize a wide range of depsipeptides with variable side chains and hydrophobic character, as understanding these effects on self-assembly is imperative to the development of biomimetic materials for tissue engineering applications. / text