The synthesis of a novel PEG-based hydrogel formed by amine-Michael type addition is reported. Star-shaped PEG molecules (having 8 arms with acrylate end groups; 8PEG) are utilized as macromonomer, and NH 3 in ammonia solution (30%) is used as cross-linker, a small and volatile molecule, which unreacted remains can be easily removed from the gel matrix. A distinct relationship between hydrogel structure and properties has been obtained, that is, higher amounts of NH 3 in the reaction lead to higher cross-linking density, higher bulk, and surface elasticity and smoother surface morphologies. Moreover, it is demonstrated that the incomplete amine-Michael type addition chemistry leads to gel formation with plenty of residual acrylate groups that are verified by LC-MS analysis and Raman spectra. Those residual acrylate groups enable us on the one hand to (bio)functionalize the gels, for example, via a second Michael-type addition reaction, employing thiol-reactive (bio)functional molecules and/or to perform additional UV-curing (photoinitiated cross-linking) to further stabilize the preformed gels with higher mechanical integrity. The proof of principle of the postgelation reactivity is demonstrated by fabricating nanoscale precise 3D patterns and by using a thiolated fluorescent dye, which reacts at the surface of the cross-linked gel and shows a small but clear penetration profile of around 50 μm from the surface into the bulk of the reactive gel.
Combining gelatins functionalized with the tyrosine-derived groups desaminotyrosine or desaminotyrosyl tyrosine with hydroxyapatite (HAp) led to the formation of composite materials with much lower swelling ratios than those of the pure matrices. Shifts of the infra-red (IR) bands related to the free carboxyl groups could be observed in the presence of HAp, which suggested a direct interaction of matrix and filler that formed additional physical cross-links in the material. In tensile tests and rheological measurements the composites equilibrated in water had increased Young's moduli (from 200 kPa up to 2 MPa) and tensile strengths (from 57 kPa up to 1.1 MPa) compared with the matrix polymers without affecting the elongation at break. Furthermore, an increased thermal stability of the networks from 40 to 85°C could be demonstrated. The differences in the behaviour of the functionalized gelatins compared with pure gelatin as a matrix suggested an additional stabilizing bond between the incorporated aromatic groups and the HAp as supported by the IR results. The composites can potentially be applied as bone fillers.
Microfabrication has its foundations in microelectronics, where photolithography, alongside other techniques, is used to make microfabricated circuits. For use in biology, Xia and Whitesides have developed soft lithography methods to fabricate micropatterned stamps from elastomeric materials [1] which were then employed to print biofunctional molecules on cell culture dishes and glass, [2] mold a second material (replica molding) [3] and make miniaturized flow cells, i.e., microfluidic devices. [4,5] Owing to these developments, the fabrication of micro-and nanostructures for use in biology has become a large area of research spanning a wide range of applications, including biochemical assays and studies of cell adhesion and spreading. [6] Regarding the latter, surface chemistry, topography, and elasticity are known to affect and direct cell adhesion, migration, proliferation, and even differentiation. [7][8][9][10][11][12][13][14] An understanding of these factors and how they induce intracellular processes is a fundamental requirement when designing biomaterials for biomedical applications.In our studies of cellular behavior on micro-and nanopatterned hydrogels we have discovered that a surface topographic pattern induces adhesion and spreading of fibroblasts on intrinsically anti-adhesive poly(ethylene glycol) (PEG) gels. [15,16] In addition, smooth but elastically micropatterned PEG-based hydrogels enabled fibroblast adhe-We have employed our recently developed method Fill-Molding In Capillaries (FIMIC) to fabricate elastically micropatterned substrates, using two poly(ethylene glycol) (PEG)-based polymers with different elastic properties and swelling behavior. We have evaluated the FIMIC process and the quality of the eventual substrates (the ''FIMICs'') by atomic force microscopy (AFM); imaging the surface topography and quantifying the local surface elasticity. Topographical imaging reveals that the surface of the FIMICs is never perfectly smooth; a slight topographic difference of 30 nm up to several hundreds of nm is observed, with the filler material always being depressed with respect to the mold. Moreover, when the FIMICs are immersed in water (or cell culture medium), the topographical landscape changes due to differential swelling of the two constituents of the FIMICs. We have used this differential swelling to our advantage in order to diminish the topography differences present on the sample surface by employing a filler that swells more than the mold. Finally, cell culture experiments with fibroblasts underlines the topographical influence on cell adhesion on the more or less anti-adhesive PEG-based materials.B56
The network structure of hydrogels is a vital factor to determine their physical properties. Two network structures within hydrogels based on eight-arm star-shaped poly(ethylene glycol)(8PEG) have been obtained; the distinction between the two depends on the way in which the macromonomers were crosslinked: either by (i) commonly-used photo-initiated chain-growth polymerization (8PEG–UV), or (ii) Michael addition step-growth polymerization (8PEG–NH3). The crystallization of hydrogels is facilitated by a solvent drying process to obtain a thin hydrogel film. Polarized optical microscopy (POM) results reveal that, while in the 8PEG–UV hydrogels only nano-scaled crystallites are apparent, the 8PEG–NH3 hydrogels exhibit an assembly of giant crystalline domains with spherulite sizes ranging from 100 to 400 µm. Scanning electron microscopy (SEM) and atomic force microscopy (AFM) analyses further confirm these results. A model has been proposed to elucidate the correlations between the polymer network structures and the crystallization behavior of PEG-based hydrogels.
Hybrid surface micro-patterns composed of topographic structures of polyethylene glycol (PEG)-hydrogels and hierarchical lines of gold nanoparticles (Au NPs) were fabricated on silicon wafers. Micro-sized lines of Au NPs were first obtained on the surface of a silicon wafer via "micro-contact deprinting", a method recently developed by our group. Topographic micro-patterns of PEG, of both low and high aspect ratio (AR up to 6), were then aligned on the pre-patterned surface via a procedure adapted from the soft lithographic method MIMIC (Micro-Molding in Capillaries), which is denoted as "adhesive embossing".The result is a complex surface pattern consisting of alternating flat Au NP lines and thick PEG bars.Such patterns provide novel model surfaces for elucidating the interplay between (bio)chemical and physical cues on cell behavior.
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