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Yameen B.,Max Planck Institute for Polymer Research | Yameen B.,Lahore University of Management Sciences | Khan H.U.,Max Planck Institute for Polymer Research | Knoll W.,AIT Austrian Institute of Technology | And 3 more authors.
Macromolecular Rapid Communications

The deposition of polyallylamine (PAA) adlayers by pulsed plasma polymerization on various types of polymeric substrates has been explored as a general route to amino functionalized polymeric surfaces. These amino groups are highly suitable for anchoring an atom transfer radical polymerization (ATRP) initiator via a robust amide linkage. Subsequent surface initiated ATRP (SI-ATRP) of monomethoxy oligo(ethylene glycol) methacrylate (MeOEGMA) resulted in polyMeOEGMA brush grafted polymer surfaces. This combined strategy of pulsed plasma polymerization with SI-ATRP was demonstrated for five different polymeric substrates namely polyether ether ketone (PEEK), polyethylene terephthalate (PET), polyimide (PI), polypropylene (PP), and polytetrafluoroethylene (PTFE). Analysis of brush layers by attenuated total reflection infrared (ATR-IR) spectroscopy as well as X-ray photoelectron spectroscopy (XPS) fully corroborated the success of the proposed strategy for all substrate types. Pulsed plasma deposited polyallylamine leads to amine functionalized soft surfaces, which is demonstrated as a general route to surface tethering an initiator for highly resourceful atom transfer radical polymerization (ATRP) through a robust amide linkage. The successful fabrication of polymer brushes is ascertained by ATR-IR spectroscopy and XPS. The general scope of presented strategy is demonstrated by employing five different polymer types. © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim. Source

Raccis R.,Max Planck Institute for Polymer Research | Roskamp R.,Max Planck Institute for Polymer Research | Hopp I.,Max Planck Institute for Polymer Research | Menges B.,Max Planck Institute for Polymer Research | And 6 more authors.
Soft Matter

We employed fluorescence correlation spectroscopy to investigate the effect of crosslinking density, annealing in the dry state, temperature, and solvent quality on the one-dimensional swelling, permeability, and mobility of tracer molecules in thermoresponsive hydrogel films. These consist of a carboxylated poly(N-isopropylacrylamide) derivative (PNIPAAm) covalently anchored to glass substrates. Upon increasing the temperature beyond the collapse transition at about 32 °C, the gels shrunk from the swollen to a collapsed state. A molecular dye (Alexa 647) and green fluorescent protein were chosen as tracers as they display only weak interaction with the carboxylated PNIPAAm. At large swelling ratios (low temperatures) the hydrogel layers are spatially homogeneous and both tracers show single Fickian diffusion. Diffusion coefficients scale with the PNIPAAm volume fraction. Upon temperature increase a qualitatively different behavior is observed already in the pretransition region (25-32 °C) concurrently with moderate swelling ratios (<4). This is manifested by an additional, faster Fickian diffusion and structural inhomogeneities, which are also found by optical waveguide mode spectroscopy. Above the collapse transition all diffusants are expelled from the hydrogels at a limiting swelling ratio ∼1.5. Subtle differences in the solvent quality influence the diffusion of tracers in the PNIPAAm hydrogel films. In the transition temperature range structural inhomogeneities at the nanoscale appeared. © 2011 The Royal Society of Chemistry. Source

Brunsen A.,Max Planck Institute for Polymer Research | Brunsen A.,TU Darmstadt | Ritz U.,Johannes Gutenberg University Mainz | Mateescu A.,Bio Organic Materials Chemistry Laboratory | And 9 more authors.
Journal of Materials Chemistry

Functional hydrogel films on solid supports are versatile materials with large potential for cell growth and tissue engineering. Here, we report on a modular approach to generate functional hydrogel composite films for endothelial and osteoblast cell co-culture. The polymer network of the parent hydrogel was formed by a dextran derivative (BP-CMD), which contained carboxymethyl (CM) groups for further chemical functionalization and benzophenone (BP) moieties as a photocrosslinkable unit. BP-CMD could be synthesized by three different routes, first with the benzophenone unit attached via an amide bond, or second by an ether bond, or third as an ion pair between the benzophenone ammonium salt and the carboxylate groups on the dextran backbone. For composite formation, BP-functionalized silica nanoparticles, as well as gelatin particles were mixed with BP-CMD and permanently fixed in the hydrogel matrix by photocrosslinking for mechanical reinforcement and to facilitate cell growth. In the last preparation step the BMP-2 growth factor was covalently coupled to the polymer backbone, which enhanced osteoblast and endothelial cell growth. The swelling behavior and successful BMP-2 immobilization of the hydrogel composite films were investigated with surface plasmon resonance and optical waveguide mode spectroscopy coupled with fluorescence detection. This modular approach allows independent selection and optimization of each component in the hydrogel composite for a wide range of potential applications for targeted cell growth, as successfully shown here with osteoblast-endothelial cell co-culture for bone tissue regeneration. © 2012 The Royal Society of Chemistry. Source

Melzak K.A.,University of Natural Resources and Life Sciences, Vienna | Melzak K.A.,CIC Biomagune | Mateescu A.,Bio Organic Materials Chemistry Laboratory | Toca-Herrera J.L.,University of Natural Resources and Life Sciences, Vienna | And 3 more authors.

Hydrogel films have been used extensively in the preparation of biosensors and biomedical devices. The characteristics of the aqueous interface of the polymer layer are significant for the biosensor or device function; likewise, the changing mechanical properties of thermoresponsive polymers are an important feature that affects the polymer behavior. Atomic force microscopy was used here to characterize both the surface and the mechanical properties of polymeric hydrogel films prepared from a thermoresponsive terpolymer of N-isopropylacrylamide and acrylic acid with benzophenonemethacrylate as a photoreactive cross-linker comonomer. The force distance curves thus obtained were analyzed to assess both the surface forces and the mechanical response that were associated with the hydrogel. These properties were investigated as a function of temperature, in water and in Tris buffer, for different degrees of polymer cross-linking. For samples in water, the distance over which the surface forces were effective was found to remain constant as the temperature was increased from 26 to 42 °C, even though the mechanical response indicated that the samples had been heated past the lower critical solution temperature, or LCST. The bulk of the polymer becomes less soluble above the LCST, although this does not seem to affect the surface properties. This may be due to the segregation of the acrylic acid-rich polymer segments near the gel surface, which is in agreement with reports for related systems. © 2012 American Chemical Society. Source

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