Biomimetic Fabrication of Organic-Inorganic Composite Materials

Abstract

This work deals with mimicking structural features found in nacre to fabricate composite materials as a tough ceramic material and to explore the mechanical properties. It is part of the work package D9 oBiomimetic Ceramicso of the Collaborative Research Centre 599 oSustainable bioresorbable and permanent implants of metallic and ceramic materialso of the DFG. Structural pattern found in nacre at micro level, so called obrick and mortaro assembly is formed in the presence of a mixture of proteins rich in acidic amino acids with aragonite. To mimic this hierarchical pattern, an appropriate inorganic material and an adhesive polymeric partner are the prerequisite. Specific polymers are required that can be used as crystallization controlling agents in order to synthesize inorganic platelets. For this purpose different phosphonic acid functional polymers and copolymers were synthesized. Properties of the basic polymer chains were altered by copolymerization with different monomers to get desired properties. The reactivity parameters of the copolymerizing units were also established. Furthermore a mussel adhesive protein mimic was also synthesized with dopamine functionality. These polymers were tested at Leibniz University Hannover for the controlled crystallization of hydroxyapatite, with a close resemblance to natural bone material and zirconium hydrogenphosphate hydrate, a biocompatible material which layered morphology. Nanoparticles or platelets, respectively, of these inorganic materials were obtained. Layered composites of zirconium hydrogenphosphate hydrate (ZrP) platelets and chitosan were prepared by layer-by-layer assembly. The growth and structural features of the composite films were studied along with their mechanical properties with reference to the number of dipping cycles, concentration and pH. Another composite was fabricated mimicking mussel proteins as organic component. A composite was prepared by LbL assembly using alumina platelets and hydroxyethyl starch modified with dopamine. Resulting composites have shown morphological similarities as found in nacre micro structure. For composites structure-property-relationships were identified. The thickness of the composites was measured with profilometer while structural details were elucidated with SEM. The mechanical properties of the fabricated composites were investigated with nanoindentation in cooperation with Max-Planck Institute for Metals Research Stuttgart.