Stabilization Impact of Nano-particles to Polymeric Hydrogels

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The aim of the project is the control of (bio)adhesive and mechanically stable hydrogels. These two properties are often counteracting. Therefore the project addresses the understanding of the relationship between the hydrogel structure, the adhesion property and mechanical/rheological behavior. Mussels can hold strongly to various substrates like rocks, metal, wood structure and marine organisms by secreting mussel foot proteins, which form mussel byssus. A catecholic amino acid called 3,4-dihydroxyphenyl-L-alanine (DOPA) presents a major component of the mussel foot proteins and is crucial for achieving the remarkable underwater adhesion. Inspired by this natural mechanism we aim to obtain strong adhesion by incorporating DOPA within the hydrogel. Nanoparticles will be used to enhance the mechanical strength of the polymer hydrogels. The nanoparticles are polymeric core/shell particles with a polymer brush as a shell (spherical polymer brushes, SPB). Their diameter can be controlled between several tens up to several hundreds of nm. In order to control this strengthening mechanism the interaction between the nanoparticles and the hydrogels will be tailored: electrostatic attraction, hydrogen bonding and chelation in presence of divalent metal cations (Zn2+, Fe2+). In order to offer a large variety in structure and architecture the hydrogel matrix will consist either of cross-linked linear chains where the SPBs are incorporated within the matrix or they the SPBs are mixed with microgels (diameter: 50 nm to 2.5 mikrometer).With perspectives for applications (e.g. hydrogels on stripes) theses hydrogels will be transferred to planar surfaces. In order to understand the relation between structure and mechanical/rheological properties both structure and mechanics/rheology will be analysed on different length scales (10 nm - mm). For instance, the mechanics will be measured via indentation with different indenter sizes on different length scales and under different loads (nN to mN). Beside different length scales and force ranges also different frequency regimes are of interest for the understanding of rheological properties. For this purpose a rheometer and a QCM-D will be used and dynamic AFM experiment will be carried out. A further long-term goal will be to offer a biocompatible gel. In the current proposal we will address the effect of pH and divalent cations like Zn2+, Fe2+ which leads to chelation with the DOPA units. Triggering the system with different outer stimuli is interesting with respect to drug delivery systems or sensorics. Most of the studied gels will be based on PAA. In a few cases PNIPAM- and PEG-based gels will be studied in order to introduce an additional sensitivity against outer temperature changes. The expertise of the Chinese and the German partners is complementary and will lead to strong synergy. Recently, they started a cooperation which would be strengthen by this project.