Einfluss von Proteinen auf das Schaltverhalten stimuliresponsiver Polymerbürsten
Stimuliresponsive polymer brushes are densely grafted arrays of polymer chains on a surface. They offer an opportunity for dynamic, intelligent surface functionalizations, which can respond to a wide range of stimuli, e.g. temperature, pH, or the presence of molecules and ions. For an application-oriented development, fundamental knowledge about the influence of internal, e.g. grafting density, external parameters, e.g. pH or ionic strength and, especially, the influence of biomolecules is required. In this work, comprehensive fundamentals regarding the characterization of polymer brushes, the underlying initiator layers, as well as the interaction between polymer brushes and proteins, are given. Polymer brushes with different affinity towards proteins were examined. Firstly, native polymer brushes were examined using complementary analytical methods, i.e. XPS (X-Ray photoelectron spectroscopy), TOF-SIMS (Time of flight secondary ion mass spectrometry) and AFM (Atomic force microscopy). The switching behavior was determined using a novel photothermal micromanipulation technique. Secondly, the analytical methods then were employed to characterize the adsorption of proteins in polymer brushes of varying grafting density with high chemical specificity and depth resolution. Thirdly, the influence of proteins on the switching behavior of the polymer brushes was probed. Although an unspecific adsorption in the full volume of PDMAEMA [Poly-(Dimethylaminoethyl methacrylate] brushes could be shown for all grafting densities, an influence on the switching behavior occurs only at low grafting density. Surprisingly, specific adsorption of streptavidin on brushes of PDMAEMA copolymerized with HEMA (Hydroxyethyl methacrylate) and further functionalized with biotin was demonstrated to alter the switching behavior to a minor degree. Also, notably, the switching behavior of protein resistant PEGMA [Poly-(Diethyleneglycol methacrylate], in turn, was altered by the presence of the protein BSA, even though experimental data provide no evidence for adsorption of the protein in the dry and collapsed polymer brushes. In addition to investigation of protein adsorption on the switching behavior of polymer brushes, the polymer chain termination for brushes synthesized by ATRP (atom transfer radical polymerization) was identified. Varying the experimental conditions of the surface initiated ATRP resulting in PDMAEMA and PEGMA polymer brushes from bromide-terminated initiators, a termination of the polymer chains with bromide was shown even when using copper chloride as a catalyst. Particularly with regard to literature results, this is highly interesting.
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