Creating a stable hydroxyapatite coating on the surface of metallic implants is a research topic of considerable interest: Poor bonding at the interface between the metallic surface of the implant and the hydroxyapatite overlayer leads to low mechanical strength of the bone-to-implant juncture and the possibility of subsequent implant failure. The purpose of this proposed research is to develop a new paradigm for enhancing adhesion between hydroxyapatite and the surface of a titanium alloy (Ti-6AI-4V) implant. It will be demonstrated that protocols for the preparation of strong bone-to-metal implant interactions can be devised through the use of modern surface science and solid state synthesis methodologies. The hypothesis to be tested is that: 1) controlled growth of a robust zirconium phosphate surface layer on titanium metal can be accomplished under mild conditions, based on surface organometallic chemistry; and 2) that this layer can be used to nucleate the growth of hydroxyapatite. This new methodology will enable strong adhesion between a metallic implant and incipient bone via a network of strong chemical bonds. The research strategy will be to determine how: 1) to optimize bonding of zirconium alkoxides to the titanium alloy native oxide layer; 2) to grow a thin coating of a zirconium phosphate adhesion layer on this modified surface; and 3) to grow hydroxyapatite on this thin layer. A significant difference between the proposed methodology and currently employed techniques is that each successive complex layer of the bone-to-metal implant can be linked to the underlying layer by strong chemical bonding, yet still maintain chemically highly reactive sites for superlayer growth. Details of interface structure and stability will be elucidated using novel surface science based methodologies. Development of the bone-tometal implant interface will be accomplished in the following sequence: 1) surface activation of titanium alloy; 2) synthesis of discrete surface zirconium alkoxide complexes; 3) synthesis of discrete surface zirconium phosphate species; 4) creation of a zirconium phosphate multilayer interface by solution processing; 5) hydroxyapatite synthesis on the zirconium phosophate adhesion layer by solution processing; and 6) optimization of mechanical adhesion of """"""""metal to bone"""""""" as a function of variation in steps 3-5 (an iterative approach).
