Biodegradable polymer adhesives, hybrids and nanomaterials
Authors:   , Mylonakis Andreas , Wei Yen 
Published: July 2021

Biodegradable polymeric products and organic-inorganic hybrid materials for a diversity of applications are the two main fields on which this research has been focused. A novel biodegradable adhesive, which mimics marine adhesive proteins, has been synthesized by the covalent incorporation of 3,4-dihydroxybenzoic acid onto the chitosan backbone. The adhesive strength of these materials varies with the molecular weight of the polysaccharide, the amount of diphenolics present and the curing time. Infrared spectroscopy (IR), nuclear magnetic resonance spectroscopy (NMR) and ultraviolet-visible spectroscopy (UV) have been used to qualitatively and quantitatively establish the amount of the diphenolic moiety present on the backbone of the biodegradable polymers. The as synthesized polymers combine both the adhesive capability of the diphenolic function and the healing effect of chitosan. The biocompatibility and biodegradability of these modified chitosans offer the promise of utility of these novel materials in dental and medical applications. Organic-inorganic hybrid materials with low volume shrinkage and excellent mechanical properties were synthesized by the covalent incorporation of 2-hydroxyethyl methacrylate and glycidyl methacrylate on pre-hydrolyzed sol-gel silica. These hybrid materials exhibited low volume shrinkage during polymerization and were crack-free during storage for about twelve months. The mechanical properties of these materials are composition dependent. Incorporation of silica effectively increased the compressive yield stress and modulus of the obtained poly(HEMA-GMA-silica) hybrid materials. A series of new electroactive hybrid materials have been synthesized by covalent incorporation of polyaniline into polyacrylate-silica hybrids. The formulation involves the radical co-polymerization of glycidyl methacrylate-polyaniline (GMA-PANi) and glycidyl methacrylate-2-hydroxyethyl methacrylate-silica (GMA-HEMA-silica) to yield poly(HEMA-GMA-silica)-polyaniline (PHGS-PANi) hybrids. The chromoelectrochemical study suggests that these materials can have tunable colors upon change of potential and/or pH, and thus may find applications as chemical or biological sensors and electro-optical devices. Moreover, conductivity measurements and mechanical testing of these materials show that these materials can be prepared to have both a reasonably high conductivity and excellent mechanical properties. A novel technology for maintaining the enzymatic activity, during storage in harsh media, such as organic solvents and high pH aqueous solutions, has been explored. The non-surfactant templated sol-gel method has been utilized to incorporate horseradish peroxidase (HRP) enzyme into the pores of mesoporous organosilicas followed by the application of a second acrylic protective layer. Results indicate that such doubly encapsulated HRP showed many orders of magnitude higher residual activity after storage in harsh media, as compared to the native enzyme under the same conditions. This method is expected to be useful for stabilizing other enzymes as well, in hostile environments. The electrochemical study of a novel electroactive aniline trimer-silane compound and other well defined aniline oligomers with end group substitution has been investigated. Results demonstrate that substitution with electron-donating or electron-withdrawing groups has a profound effect on the electrochemistry of such compounds. Additionally, the formation of interesting oxygen adducts by both wet and dry prolonged oxygenation of iron phthalocyanines ([alpha]- and [beta]-form) has been achieved. Finally, the fabrication of a novel fluorescent nanoelectrode with applications in neuroscience has been explored.