Dans un contexte de démarche écoresponsable et pour répondre aux exigences de biocompatibilité notamment dans les applications cosmétiques et biomédicales, nous avons développé de nouveaux hydrogels à base de polysaccharides neutres et anioniques en utilisant deux voies originales. La 1ère approche est biomimétique et a consisté à mimer un phénomène d’élaboration naturelle d’hydrogels que l’on retrouve chez certains végétaux pour lesquels une enzyme, la laccase, permet de créer des liens de réticulation par dimérisation des composés phénoliques (en l’occurrence de l’acide férulique FA) présents sur les arabinoxylanes des mucilages des graines de céréales par exemple. Notre travail a ainsi consisté à greffer de l’acide férulique via deux chimies différentes de type imidazole et carbodiimide respectivement pour des polysaccharides neutres ou anioniques. Nous avons ainsi fonctionnalisé trois polysaccharides : le pullulane ou PUL (neutre modèle), le carboxyméthylpullulane ou CMP (anionique modèle) et l’acide hyaluronique ou HA (anionique d’intérêt). Des taux de greffage compris entre 2 et 25% ont été obtenus. L’étude physicochimique en régimes dilué et semi-dilué a permis de mettre en évidence un comportement associatif lié au caractère amphiphile des polysaccharides fonctionnalisés. La réticulation en présence de laccase, suivie in situ en rhéologie, a été réalisée avec succès sur les différents systèmes envisagés avec des contrôles possibles de la cinétique, des propriétés mécaniques finales ou encore du gonflement des hydrogels en fonction du caractère neutre ou chargé des polysaccharides, du degré de substitution en acide férulique, de la concentration en polymère ou de l’activité enzymatique fixée. Les dérivés synthétisés ont globalement démontré des activités biologiques (antioxydante et cytocompatible) intéressantes. La deuxième approche repose sur la photoréticulation possible de polysaccharides (PUL, CMP et HA) fonctionnalisés par le greffage d’amine/acide gras mono ou polyinsaturé (oleylamine, acide oléique et linoléique) via la chimie des imidazoles. Si le pullulane modifié par l’acide linoléique à 2% s’est avéré non hydrosoluble en raison de son caractère neutre, tous les autres dérivés avec des taux de greffages de 3 et 10% ont démontré une bonne solubilité dans l’eau. Les études physicochimiques mettent en évidence un très fort caractère associatif de ces dérivés amphiphiles avec la formation de gels physiques en régime semi-dilué. La photoréticulation a été démontrée en rhéologie sous irradiation UV in situ en présence d’un photoamorceur de type Darocur 1173®. Les résultats préliminaires obtenus selon cette approche en photoréticulation ouvrent ainsi des perspectives intéressantes. / In the framework of an eco-responsible context and to take advantage of biocompatibility, notably in cosmetic and biomedical applications, we have developed new hydrogels based on neutral and anionic polysaccharides using two original routes. The first approach is biomimetic and consists of mimicking a natural development of hydrogels that is found in certain plants for which an enzyme, laccase, allows to create crosslinks by dimerization of phenolic compounds, in occurrence of ferulic acid (FA) present on arabinoxylans mucilage of cereal seeds for example. Thus, our work consisted in grafting ferulic acid via two different chemical ways that means imidazole and carbodiimide respectively for neutral or anionic polysaccharides. We functionalized three polysaccharides: pullulan or PUL (neutral model), carboxymethylpullulane or CMP (model anionic) and hyaluronic acid or HA (anionic of interest) with grafting rates of between 2 and 25%. The physicochemical study in diluted and semi-diluted regimes evidenced an associative behavior due to the amphiphilic character of the functionalized polysaccharides. The crosslinking in the presence of laccase, followed in situ thanks to rheology, has been successfully performed on the various envisaged systems with possible controls of kinetics, the final mechanical properties or the swelling of the hydrogels as a function of the neutral or charged nature of the polysaccharides, the degree of substitution in FA, the polymer concentration or the enzymatic activity. The synthesized derivatives have generally demonstrated interesting biological activities (antioxidant and cytocompatibility). The second approach is based on the possible photocrosslinking of polysaccharides (PUL, CMP and HA) functionalized by the grafting of mono or polyunsaturated fatty amine/acid (oleylamine, oleic acid and linoleic acid) via imidazole chemistry. If pullulan grafted with 2% of linoleic acid was found to be water-insoluble due to its neutral character, all other derivatives (i.e. anionic ones) with grafting rates of 3 and 10% showed good solubility in water. The physicochemical studies show a very strong associative character of these amphiphilic derivatives with the formation of physical gels in semi-diluted regime. Photocrosslinking has been demonstrated in situ thanks to rheology/UV irradiation in the presence of a Darocur 1173® photoinitiator. The preliminary results according to this photocrosslinking approach thus open interesting perspectives.

Tagebaumaßnahmen führen durch Entfernung des Oberbodens, Vermischung von Bodenschichten bei der Wiederverfüllung von Restlöchern und Maschineneinsatz dazu, dass auf Tagebaufolgeflächen meist extrem schwierige Standortbedingungen für Pflanzenwachstum herrschen. Dazu zählen v.a. Bodenverdichtung und Bodenversauerung durch die Verwitterung von Eisensulfiden, was Ernährungsstörungen und Belastungen mit Schwermetallen und anderen Schadstoffen zur Folge hat. Die Bodenbedingungen sind auf kleinem Raum sehr heterogen. Das ungünstige Mikroklima der vegetationsfreien Flächen verstärkt die durch Bodenverdichtung schwierige Wasserversorgung. Mykorrhiza-Pilze fehlen oft zunächst. Ziel dieser Arbeit war die Entwicklung eines möglichst wenig aufwendigen Konzeptes, um mit Hilfe geeigneter Baumarten und Bodenhilfsstoffe zumindest auf kleiner Fläche eine Begrünung von Kippen-Rohböden zu erreichen, um so Startpunkte einer Sukzession zu etablieren. Zu diesem Zweck wurden verschiedene Baumarten (Quercus robur, Acer platanoides, Sorbus aucuparia, Alnus glutinosa, Pseudostuga menziesii und Pinus sylvestris) und Bodenhilfsstoffe zur Verbesserung der physikalischen (Perlit, Wasserspeichersubstanzen: sowohl herkömmliches, petrochemisches Hydrogel als auch neuartiger Superabsorber aus pflanzlicher Stärke), chemischen (Kalk), physikalischen und chemischen (Kompost) sowie biologischen (Mykorrhiza-Impfung) Bodeneigenschaften getestet. Die Bodenhilfsstoffe wurden einzeln und miteinander kombiniert eingesetzt. Auf auch Jahre nach der Ablagerung des Haldensubstrats noch vegetationsfreien Flächen im ehemaligen Ronneburger Uranerz-Abbaugebiet wurden Freilandversuche mit knapp 1.000 Bäumen angelegt; Topfversuche im Gewächshaus dienten der Begleitung und Vertiefung. Die physikalischen und chemischen Bodeneigenschaften der Versuchsflächen wurden analysiert, die Effekte der Bodenhilfsstoffe darauf im Topfversuch überprüft. Die Entwicklung der Versuchspflanzen wurde über zwei Jahre hinweg durch regelmäßige Vitalitätsschätzungen auf einer 5-stufigen Skala, Messungen verschiedener Wuchsparameter und Analysen der Elementgehalte in den Assimilationsorganen untersucht. Die Böden wiesen eine sehr geringe Wasserspeicherkapazität und eine stark gestörte Infiltrations- und Wasserleitfähigkeit auf. Das Nährstoffpotential war mit Ausnahme sehr geringer Stickstoff-Gehalte gut. Eine sehr starke Versauerung sowie stark belastende Kupfer- und Schwefel-Gehalte waren die Haupt-Probleme. Auffällig waren hohe Magnesium-Gehalte und -Sättigungen. Die Versuchspflanzen waren entsprechend sehr stark mit Schwefel und Kupfer sowie mit Eisen, Aluminium und teilweise Mangan belastet und zeigten auffallend hohe Magnesium-Gehalte. Sie wiesen Ernährungsdefizite auf, die auf die geringe Stickstoffversorgung, Nährstoffantagonismen/Ionenkonkurrenz und Toxizität zurückgeführt werden können. Im Verlauf des Versuchs entwickelte sich auf einigen Versuchsflächen in Teilbereichen Spontanvegetation (Moose, Calamagrostis epigejos). Bodenuntersuchungen ergaben leicht höhere pH-Werte und eine entsprechend günstigere Ernährungssituation in diesen Bereichen, vermutlich aufgrund einer unregelmäßigen Flächenkalkung einige Jahre vor Versuchsbeginn. Die Entwicklung der Versuchspflanzen wurde stark von den Standortunterschieden beeinflusst. Kalk und Kompost hatten deutlich positive Effekte auf die chemischen Bodenbedingungen und die Pflanzenentwicklung. Mit Kompost war der Einfluss vor allem bei den anspruchsloseren Baumarten Eberesche, Schwarz-Erle und Wald-Kiefer oft größer. Daneben zeigten Mykorrhiza-Impfungen eine starke Wirkung, vor allem in Kombination mit Kalk und/oder Wasserspeichersubstanzen. Die positiven Wirkungssynergismen von Mykorrhiza-Impfungen und Wasserspeichersubstanzen auch ohne Kalk-Gaben waren angesichts der sehr stark sauren Standortverhältnisse bemerkenswert. Darüber hinaus hatten Wasserspeichersubstanzen wie auch Perlit keine, teilweise sogar negative Effekte durch Herabsetzung der Kalk-Wirkung in kombinierten Varianten. Zudem wiesen die mit Perlit oder Wasserspeichersubstanzen gepflanzten Bäume teils hohe Schadstoff-Belastungen auf. Die Bodeneigenschaften wurden nicht beeinflusst; die feinbodenreichen Lehmböden mit ihrer geringen Infiltrationsfähigkeit durch Zerscherung der Grobporen bei Verdichtung schienen für den Einsatz von Wasserspeichersubstanzen weniger geeignet zu sein. Das Vorhandensein von Pilz-Partnern zur Mykorrhiza-Bildung ist auf diesen schwierigen Standorten offenbar von besonderer Bedeutung, da diese Symbiose die Wasserversorgung von Pflanzen verbessern kann, außerdem ihre Ernährung fördert und die Schadstoff-Aufnahme hemmt, wie im Rahmen der vorliegenden Arbeit bestätigt werden konnte. So konnten durch kombinierte Mykorrhiza-Impfungen teilweise selbst die extremen Schwefel-Gehalte auf ein normales Maß gesenkt werden, was mit Kalkung allein nicht der Fall war. Die obligat Mykorrhiza bildenden Rot-Eichen und Wald-Kiefern, zwei eigentlich zur Tagebaurekultivierung sehr geeignete und viel verwendete Baumarten, zeigten insgesamt hohe Ausfallraten. Bei den Eichen spielte dabei die schlechte Qualität des Pflanzenmaterials, bei den Kiefern wahrscheinlich starke Trockenheit zum Zeitpunkt der Versuchsanlage im Frühjahr 2005 eine Rolle. Bei den ebenfalls obligat Mykorrhiza bildenden Douglasien war der Standort in günstigeren Bereichen, in denen sich auch Spontanvegetation entwickeln konnte und in die nachweislich Mykorrhiza-Pilze einwanderten, von großer Bedeutung. Wie die als einzige Baumart nicht mit Kupfer belastete Eberesche und die durch ihre Symbiose mit Stickstoff-fixierenden Bakterien sehr gut geeignete Erle, die von allen Baumarten die besten Ergebnisse zeigte, konnte sich auch die Douglasie auf diesen etwas besseren Standorten selbst ohne Bodenhilfsstoffe zufrieden stellend entwickeln. Angesichts des extremen Sommers 2006 kam vermutlich auch ihre Trockenheitstoleranz zum Tragen. Die Spitz-Ahorne zeigten hohe Schadstoff-Belastungen, kaum Wachstum und eine stark gestörte Wurzel-Ausformung. Die Baumart wurde zudem stark verbissen und erwies sich insgesamt als wenig geeignet. Auf Grundlage der Ergebnisse der auf den Ronneburger Tagebaufolgeflächen durchgeführten Untersuchungen wird für die Rekultivierung dieser und vergleichbarer Standorte eine Mischung aus Erlen, Ebereschen und Douglasien empfohlen, wobei die Erle auch aufgrund ihrer Standort verbessernden Eigenschaften den größten Anteil einnehmen sollte. In stärker versauerten (pH KCl < 4), frei von Bodenvegetation bleibenden Bereichen sollte einige Zeit im Vorfeld der Pflanzungen eine Kalkung mit aufgrund der Bodengehalte magnesiumfreiem Kalk erfolgen, um die Voraussetzungen für Bodenvegetation und Mykorrhiza-Pilze zu verbessern. Bei den Ebereschen und Erlen ist eine Kompost-Gabe ins Pflanzloch als Starthilfe sinnvoll. Zumindest bei den Douglasien sollten Mykorrhiza-Impfungen durchgeführt werden, die generell auf diesen Standorten empfehlenswert sind und somit auch für die Ebereschen und Erlen sehr vorteilhaft sein können. Die Dauer der Wirkung der Bodenhilfsstoffe und die über die beobachtete Zeit hinaus gehende Entwicklung der Bäume sind unter den gegebenen, sehr schwierigen Standortbedingungen mit fortschreitender Pyrit-Verwitterung und damit Bodenversauerung offen.

Microfluidics covers the science of manipulating small quantities of fluids using microscale devices with great potential in analysis, multiplexing, automation and high-throughput screening. Compared to conventional systems, microfluidics benefits from miniaturization resulting in shortened time of experiments, decreased sample and reagent consumptions as well as reduced overall costs. For microfluidic devices where further weight and cost reduction is additionally required, stimuli-responsive hydrogels are particularly interesting materials since they can convert an environmental stimulus directly to mechanical work without any extra power source. Hydrogels are used as chemostats, micropumps, and chemo-mechanical valves in microfluidics. Existing studies about hydrogels for flow control reported on hydrogels responsive to only one stimulus, including temperature, pH value, and solvent. Combining temperature and pH stimuli within one material is an interesting approach, which allows internal as well as external flow control and broadens potential applications. Among the variety of temperature- and pH-responsive monomers, N-isopropylacrylamide (NiPAAm) and acrylic acid (AA) are considered as ideal building blocks to obtain a hydrogel with pronounced stimuli response. There are different architectures for realizing a temperature- and pH-responsive hydrogel with NiPAAm and AA (e.g. copolymer gels, interpenetrating polymer networks (IPNs), semi-IPNs, or graft copolymer gels). Each approach has its inherent benefits and disadvantages. Grafted hydrogels with a temperature-responsive backbone and pH-responsive graft chains are a promising architecture overcoming drawbacks of copolymer gels (loss of thermoresponsive behavior due to the comonomer), interpenetrating polymer networks (IPNs, difficult fabrication of structured particles via soft lithography), and semi-IPNs (leakage of penetrating polymer). However, studies about multi-responsive grafted hydrogels for flow control in microfluidics are comparatively rare and further research is needed to emphasize their real potential. For this reason, the overall aim of this work was the synthesis of temperature- and pH-responsive grafted hydrogels based on NiPAAm and AA for flow control in microfluidics. This required the synthesis of a pH-responsive macromonomer by RAFT polymerization. As a suitable chain transfer agent with a carboxylic acid group for an end-group functionalization, 2-(dodecyl-thiocarbonothioylthio)-2-methylpropionic (DTP) acid was employed. The approach towards the synthesis of the pH-responsive macromonomer based on two key steps: (i) attaching a functional group, which retains during RAFT polymerization, and (ii) conducting the RAFT polymerization to synthesize the pH-responsive macromonomer. In total, four functionalizations for the macromonomer were investigated, including allyl, unconjugated vinyl, acrylamide, and styrene. End-group analysis and solubility tests revealed that macromonomers with a styrene functionalization are suitable for the synthesis of graft copolymer gels. A series of grafted net-PNiPAAm-g-PAA-styrene hydrogels with a PNiPAAm backbone and PAA-styrene graft chains (Mn = 4200 g/mol, Mw/Mn = 1.6) were prepared and characterized. The main goal was to identify suitable stimuli for an application as a chemo-mechanical valve and to show reversibility of the swelling and shrinking process. Importantly, the temperature sensitivity should be retained, while a pH response needs to be introduced. Equilibrium swelling studies quantified with the response ratio revealed that a grafting density of PAA-styrene between 0.25 and 1 mol-% provides a suitable response towards temperature, pH, salt, and solvent. Furthermore, the swelling and shrinking process is highly reproducible over four consecutive cycles for all four stimuli. In order to evaluate the swelling kinetics of grafted net-PNiPAAm-g-PAA-styrene hydrogels, the collective diffusion model extended by a volume specific surface was applied. The determined cooperative diffusion coefficients of net-PNiPAAm-g-PAA-styrene indicated faster response time with increasing PAA-styrene content. Remarkably, net-PNiPAAm-g-PAA-styrene containing 1 mol-% PAA-styrene exhibited an accelerated swelling rate by a factor of 9 compared to pure net-PNiPAAm. Rheological analysis of net-PNiPAAm-g-PAA-styrene showed that an increasing graft density leads to decreasing mechanical stability. The photopolymerization experiments showed that the gelation time linearly increases with the grafting density. Grafted net-PNiPAAm-g-PAA-styrene hydrogels were tested in two fluidic setups for flow control. A straightforward fluidic platform was developed consisting of a fluid reservoir, an inlet channel, an actuator chamber and an outlet channel. The actuator chamber was filled with crushed hydrogel particles. Accordingly, the fluid flow was directed by the active resistance of the hydrogel particles in the actuator chamber (i.e. swelling degree) and allowed flow control by the local environmental conditions. Flow rate studies showed that the fluid flow throttles when the inlet channel was provided with a solution in which the hydrogel swells (pH 9 buffer solution at room temperature). In contrast, the hydrogel-based valve opens immediately when a solution was used in which the hydrogel collapses. The advantageous properties of net-PNiPAAm-g-PAA-styrene were highlighted by using pH, salt and solvent stimulus in one experiment. Remarkably, the opening and closing function was reversible over six consecutive cycles. As part of a collaboration project with the chair of polymeric microsystems within the Cluster of Excellence Center for Advancing Electronics Dresden (A. Richter and P. Frank), membrane assures hydraulic coupling in a chemo-fluidic membrane transistor (CFMT) and grafted net-PNiPAAm-g-PAA-styrene hydrogels were combined to emphasize the potential of both systems. Flow rate studies showed that 4 different stimuli can be used to control the opening and closing state of the CFMT. Multiple opening and closing cycles revealed no considerable changes in the valve function emphasizing a high potential for an application in microfluidics.

Bone fractures and pathologic conditions like chronic wounds significantly reduce the quality of life for the patients, which is especially dramatic in an elderly population with considerable multi-morbidity and lead to substantial socio-economic costs. To improve the wound healing capacity of these patients, new strategies for the design of novel multi-functional biomaterials are required: they should be able to decrease extensive pathologic tissue degradation and specifically control angiogenesis in damaged vascularized tissues like bone and skin. Glycosaminoglycans (GAGs) like hyaluronan (HA) and chondroitin sulfate (CS) as important extracellular matrix (ECM) components are involved in several biological processes such as matrix remodeling and growth factor signaling, either by directly influencing the cellular response or by interacting with mediator proteins. This could be useful in functionalizing biomaterials, but native sulfated GAGs (sGAGs) show a high batch-to-batch variability and are limited in their availability. Chemically modified HA and CS derivatives with much more defined characteristics regarding their carbohydrate backbone, sulfate group distribution and sulfation degree are favorable to study the structure-function relationship of GAGs in their interaction with mediator proteins and/or cells and this might be used to precisely modulate activity profiles to stimulate wound healing. By combining collagen type I as the main structural protein of the bone and skin ECM with these GAG derivatives, 2.5-dimensional (2.5D) and 3D artificial ECM (aECM) coatings and hydrogels were developed. These biomaterials as well as the respective GAG derivatives alone were compared to native GAGs and used to analyze how the sulfation degree, pattern and carbohydrate backbone of GAGs influence: i) the activity of tissue inhibitor of metalloproteinase-3 (TIMP-3) and vascular endothelial growth factor-A (VEGF-A) as main regulators of ECM remodeling and angiogenesis, ii) the composition and characteristics of the developed 2.5D and 3D aECMs, iii) the enzymatic degradation of collagen-based aECMs and HA/collagen-based hydrogels, iv) the proliferation and functional morphology of endothelial cells. Surface plasmon resonance (SPR) and enzyme linked immunosorbent assay (ELISA) binding studies revealed that sulfated HA (sHA) derivatives interact with TIMP-3 and VEGF-A in a sulfation-dependent manner. sHA showed an enhanced interplay with these proteins compared to native GAGs like heparin (HEP) or CS, suggesting a further impact of the carbohydrate backbone and sulfation pattern. sGAGs alone were weak modulators of the matrix metalloproteinase-1 and -2 (MMP-1 and -2) activity and did not interfere with the inhibitory potential of TIMP-3 against these proteinases during enzyme kinetic analyses. However, the formation of TIMP 3/GAG complexes reduced the binding of TIMP-3 to cluster II and IV of its endocytic receptor low-density lipoprotein receptor-related protein-1 (LRP-1, mediates the up-take and degradation of TIMP-3 from the extracellular environment) in a sulfation- and GAG type-dependent manner. It is of note that the determined complex stabilities of TIMP-3 with cluster II and IV were almost identical indicating for the first time that both clusters contribute to the TIMP-3 binding. Competitive SPR experiments demonstrated that GAG polysaccharides interfere stronger with the TIMP 3/LRP-1 interplay than GAG oligosaccharides. The importance of the position of sulfation is highlighted by the finding that a sHA tetrasaccharide exclusively sulfated at the C6 position of the N-acetylglucosamine residues significantly blocked the receptor binding, while CS and HEP hexasaccharides had no detectable effects. Thus, sHA derivatives as part of biomaterials could be used to sequester and accumulate TIMP 3 in aECMs in a defined manner where sHA-bound TIMP-3 could decrease the matrix breakdown by potentially restoring the MMP/TIMP balance. GAG binding might extend the beneficial presence of TIMP-3 into wounds characterized by excessive pathologic tissue degradation (e.g. chronic wounds, osteoarthritis). Mediator protein interaction studies with sHA coated surfaces showed the simultaneous binding of TIMP-3 and VEGF-A, even though the sHA/VEGF-A interplay was preferred. Moreover, kinetic analysis revealed almost comparable affinities of both proteins for VEGF receptor-2 (VEGFR-2), explaining their competition that mainly regulates the activation of endothelial cells. Additional SPR measurements demonstrated that the binding of sGAGs to TIMP-3 or VEGF-A decreases the binding of the respective mediator protein to VEGFR-2. Likewise, a sulfation-dependent reduction of the binding signal was observed after pre-incubation of a mixture of TIMP-3 and VEGF-A with sGAG poly- and oligosaccharides. The biological consequences of GAGs interfering with VEGF-A/VEGFR-2 and TIMP-3/VEGFR 2 were assessed in vitro using porcine aortic endothelial cells stably transfected with VEGFR 2 (PAE/KDR cells). The presence of sHA both decreased VEGF-A activity and the activity of TIMP-3 to inhibit the VEGF-A-induced VEGFR-2 phosphorylation. The same decreased activities could be observed for the migration of endothelial cells. However, if sHA, TIMP-3 and VEGF-A were present simultaneously, sHA partially restored the TIMP-3-mediated blocking of VEGF-A activity. These findings provide novel insights into the regulatory potential of sHA during endothelial cell activation as an important aspect of angiogenesis, which could be translated into the design of biomaterials to treat abnormal angiogenesis. These sHA-containing materials might control the angiogenic response by modulating the activity of TIMP 3 and VEGF-A. The in vitro fibrillogenesis of collagen type I in the presence of sHA derivatives led to 2.5D collagen-based aECM coatings with stable collagen contents and GAG contents that resemble the organic part of the bone ECM. A burst release of GAGs was observed during the first hour of incubation in buffer with the GAG content remaining almost constant afterwards, implying that the number of GAG-binding sites of collagen restricts the amounts of associated GAGs. Moreover, two differently sulfated HA derivatives could for the first time be incorporated into one multi-GAG aECM as verified via agarose gel electrophoresis and fluorescence measurements. This illustrates the multiple options to modify the aECM composition and thereby potentially their functionality. Atomic force microscopy showed that the presence of sHA derivatives during fibrillogenesis significantly reduced the resulting fibril diameter in a concentration- and sulfation-dependent manner, indicating an interference of the GAGs with the self-assembly of collagen monomers. In line with enzyme kinetic results, none of the GAGs as part of aECMs altered the enzymatic collagen degradation via a bacterial collagenase. Thus aECMs were proven to be biodegradable independent from their composition, which is favorable concerning a potential biomedical usage of the aECMs e.g. as implant coatings. HA/collagen-based hydrogels containing fibrillar collagen embedded into a network of crosslinked HA and sGAGs were developed as 3D aECMs. Scanning electron microscopy demonstrated a porous structure of the gels after lyophilization, which could favor the cultivation of cells. The presence of collagen markedly enhanced the stability of the gels against the enzymatic degradation via hyaluronidase, something beneficial to clinical use as this is often limited by the generally fast breakdown of HA. Binding and release experiments with lysozyme, as positively charged model protein for e.g. pro-inflammatory cytokines, and VEGF A revealed that the sulfation of GAGs increased the protein binding capacity for pure GAG coatings and retarded the protein release from hydrogels compared to hydrogels without sGAGs. Moreover, the additional acrylation of sHA was shown to strongly reduce the interaction with both proteins when the primary hydroxyl groups were targets of acrylation. This stresses the influence of the substitution pattern on the protein binding properties of the GAG derivatives. However, hydrogel characteristics like the elastic modulus remained unaffected. The different interaction profiles of lysozyme and VEGF-A with GAGs demonstrated a protein-specific preference of different monosaccharide compositions, suggesting that the mediator protein binding could be simultaneously adjusted for several proteins by combining different GAG derivatives. This might allow the scavenging of pro-inflammatory cytokines and at the same time a binding and release of wound healing stimulating growth factors. Since there is a growing demand for biomaterials to regenerate injured vascularized tissues like bone and skin, endothelial cells were used to examine the direct effects of solute GAGs and hydrogels containing these GAGs in vitro. In both cases, sHA strongly enhanced the proliferation of PAE/KDR cells. A VEGFR-2-mediated effect of GAGs on endothelial cells as underlying mechanism is unlikely since GAGs alone did not bind to VEGFR-2 and had no influence on VEGFR-2 phosphorylation. Other factors like GAG-induced alterations of cell-matrix interactions and cell signaling could be responsible. In accordance with SPR results, a decreased endothelial cell proliferation stimulating activity of VEGF-A was observed in the presence of solute GAGs or after binding to hydrogels compared to the respective treatment without VEGF-A. However, tube formation could be observed in the presence of solute VEGF A and GAGs and within hydrogels with sGAGs that released sufficient VEGF-A amounts over time. Overall the presence of GAGs and VEGF-A strongly promoted the endothelial cell proliferation compared to the treatment with GAGs or VEGF-A alone. Thus, HA/collagen-based hydrogels functionalized with sHA derivatives offer a promising option for the design of “intelligent” biomaterials that direct and regulate the cellular behavior instead of simply acting as inert filling material. They could be used for the controlled delivery and/or scavenging of multiple mediator proteins, thus enhancing the local availability or reducing the activity of these GAG-interacting mediator proteins, or by directly influencing the cellular response. This might be applied to a range of pathological conditions by tuning the biomaterial compositions to patient-specific needs. However, extensive in vivo validation is required to show whether these in vitro findings could be used to control the biological activity of for instance TIMP-3 and VEGF-A, especially under the pathological conditions of extended matrix degradation and dysregulated angiogenesis.

Polyelectrolyte hydrogels are viscoelastic electroactive polymers which respond to external physical or chemical stimuli by a reversible volume phase transition. Novel fabrication methods allow the creation of hydrogel layer composites in which each layer shows a different sensitivity (e.g. to a different stimulus). This offers new opportunities, for example, in the design of new microsensors, microactuators and microfluidic devices as well as for high-selective membranes and target-specific drug delivery systems. Since only few research groups numerically investigated the transport mechanisms in hydrogel layer composites, a gap remains to describe the movement and transient distribution of ions inside the layer system. In this article, the multifield formulation is adopted to describe the transient distribution of ions in salt-sensitive hydrogel layer composites on the basis of a numerical simulation. For this, the Nernst-Planck and the Poisson equation are solved using one-dimensional finite elements for both anionic-anionic and anionic-cationic gel layer composites under chemical stimulation. Between adjacent gels, an additional interlayer is introduced to account for the physical and chemical bonding region between the gels. Adaptive mesh refinement provides a good resolution close to the interface between the adjacent gel layers. The obtained results are used to predict the osmotic pressure inside the gels and the dependent swelling of the gel layer composite. The excellent agreement of the obtained results with the Donnan equilibrium demonstrates the high potential of the method applied to predict the behavior of hydrogel layer composites.

For everyday cycling, one needs to carry rainproof clothing just for the case of unexpected downpours. In the present research, we present a concept for a helmet which is automatically rainproof when the rain starts. When the sun comes out, the helmet is breathable again even before it completely dries up. This functionality is provided by active hydrogel meshes. Hydrogel meshes offer great advantages due to their ability to change the aperture size with swelling and deswelling. In our current work, we present the design and modeling steps for hydrogel-layered active meshes which use (i) swelling and deswelling in hydrated state and (ii) swelling starting from the dry state. The main goal is to close the air openings of a bicycle helmet when rain starts as an automatic rainproofing. This can be achieved through the swelling of the hydrogel pNiPAAM-co-chlorophyllin in the meshes, which leads to closing when hydrated. At the same time, the light-sensitive behavior leads to opening of the apertures under direct sun exposure, i.e. when the sun appears again after the rain. We present the steps of modeling and design using the Normalized Extended Temperature-Expansion-Model (NETEM) to perform simulations in Abaqus. The model is capable of describing both the swelling of the hydrogel under light stimulus and the volume change due to hydration. It is based on the analogy between free swelling and thermal expansion and defined for nonlinear displacements. We also discuss the fabrication process of hydrogel-layered fibers and challenges in their application and simulation. As a proof of concept for hydrogel-layered meshes, we show preliminary experimental results of a poly(acrylamide)/poly(2-acrylamido-2-methyl-1-propanesulfonic acid) (PAAm/PAMPS) hydrogel with semi-interpenetrated network (SIPN) structure and its swelling capacities on a mesh. Starting from the active hydrogel meshes as presented in the current work, the next step can be smart textiles that harness the power of hydrogels: the adaptation to combinations of stimuli - like humidity, temperature and brightness - that define environments.

This paper presents the design, simulation, assembly and testing of a force-compensated hydrogel-based pH sensor. In the conventional deflection method, a piezoresistive pressure sensor is used as a chemical-mechanical-electronic transducer to measure the volume change of a pH-sensitive hydrogel. In this compensation method, the pH-sensitive hydrogel keeps its volume constant during the whole measuring process, independent of applied pH value. In order to maintain a balanced state, an additional thermal actuator is integrated into the close-loop sensor system with higher precision and faster dynamic response. Poly (N-isopropylacrylamide) (PNIPAAm) with 5 mol% monomer 3-acrylamido propionic acid (AAmPA) is used as the temperature-sensitive hydrogel, while poly (vinyl alcohol) with poly (acrylic acid) (PAA) serves as the pH-sensitive hydrogel. A thermal simulation is introduced to assess the temperature distribution of the whole microsystem, especially the temperature influence on both hydrogels. Following tests are detailed to verify the working functions of a sensor based on pH-sensitive hydrogel and an actuator based on temperature-sensitive hydrogel. A miniaturized prototype is assembled and investigated in deionized water: the response time amounts to about 25 min, just half of that one of a sensor based on the conventional deflection method. The results confirm the applicability of the compensation method to the hydrogel-based sensors.

Le liquide interstitiel est aujourd’hui considéré comme un candidat prometteur comme alternative, ou complément, à l’analyse sanguine pour la quantification de biomarqueurs. Localisé notamment dans la peau, sa composition demeure peu décrite dans la littérature. Cela peut s’expliquer par le fait que le prélèvement de liquide interstitiel reste problématique. En effet, les méthodes d’extraction actuelles sont chronophages, douloureuses et conduisent au prélèvement de volumes très faibles ne permettant pas toujours une analyse subséquente. L’utilisation de timbres de microaiguilles conçus en hydrogel superabsorbant représente une solution indolore, rapide et efficace pour le prélèvement du liquide interstitiel. Un premier type de timbre a été conçu par photopolymérisation, un processus de fabrication caractérisé par sa rapidité. Ce type de timbre de microaiguilles présente une capacité d’absorption très élevée et peut trouver une application dans l’élaboration des profils protéomique, métabolomique et lipidomique du liquide interstitiel dermique. Le second type de timbres de microaiguilles est obtenu par chauffage d’une formulation contenant des polymères superabsorbants. Ce procédé s’avère plus long mais conduit à un hydrogel superabsorbant riche en groupements chimiques permettant d’envisager une fonctionnalisation pour la capture et la détection in situ de biomarqueurs spécifiques du liquide interstitiel dermique. In fine, les timbres de microaiguilles développés pourraient donc permettre d’approfondir notre connaissance de la composition du liquide interstitiel; mais laissent également entrevoir la possibilité de développer des dispositifs médicaux portables permettant le diagnostic, ou la surveillance, rapide et indolore de certaines pathologies. Ces dispositifs pourraient diminuer les coûts normalement associés à ces pratiques et améliorer la prise en charge des patients. C’est le cas notamment de l’insuffisance cardiaque, dont la gestion pourrait être considérablement facilitée par le suivi à domicile du biomarqueur NT-proBNP. / Nowadays, interstitial fluid is considered a valid alternative for blood analysis and biomarker monitoring. However, its composition is scarcely described in the literature. Notably located in the skin, its collection remains a challenge as current methods are time-consuming, painful and the extracted volume limits subsequent analysis. Here we put forward the use of superabsorbant hydrogel-based microneedle patches to enable a painless, rapid and efficient sampling of dermal interstitial fluid. A first kind of microneedle patch was obtained using UV-curing, a rapid fabrication process. This type of microneedle patch enables the collection of a high volume of liquid and can therefore be utilized for subsequent proteomic, metabolomic and lipidomic analyses of the dermal interstitial fluid that had been extracted in a painless fashion. The second class of microneedle patch developed was fabricated from superabsorbant polymers using heating. Although time consuming, this process produced hydrogel-based microneedle patches that could be functionalized for the in situ detection of specific biomarkers in the dermal interstitial fluid. In fine, the aforementioned microneedle patches have the potential to broaden our understanding of the interstitial fluid composition, as well as be integrated in novel portable biosensing devices for a rapid and painless diagnosis, or for the monitoring of certain medical conditions. For example, quantifying the NT-proBNP biomarker in the dermal interstitial fluid could significantly improve the quality of life of heart failure patients.

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