The objective of this project is to develop functionally graded, thin film hydroxyapatite coatings to enhance osseointegration of Dental implants. The coatings will be graded such that they elicit tailored biological response from different layers within the thin film. Highly crystalline regions near the coating/substrate interface will slowly transition to very fine-grained, nearly amorphous HA at the surface of the film. Phase I will evaluate the hypothesis that hydroxyapatite coatings with graded crystallinity both speed up and ultimately enhance device fixation. In recent work, we have demonstrated that optimizing crystallinity of hydroxyapatite coatings enhances bioactivity and osseointegration, leading to more rapid and stronger bone fixation. Finer grained or near-amorphous hydroxyapatite has higher rates of Ca and P dissolution, and therefore, higher bioactivity. Such structures at the coating surface are ideally suited for promoting rapid bone growth during early stages of device integration. More crystalline regions deeper in the film will resorb much slower, ensuring that the coating remains functional for long time periods, until complete integration and fixation is achieved. Optimized crystalline grading profiles will be developed via variation of coating deposition processes and subsequent microstructural analysis (transmission electron microscopy). Coating efficacy will be evaluated in the tibia of a small animal (rat). Both early and long-term bone response will be assessed. Performance will be compared to that of conventional plasma spray hydroxyapatite coatings and also with fully crystalline HA and fully amorphous CaP coatings.
