Comparative investigation of hydroxyapatite coatings formed on titanium via phosphate chemical conversion

Abstract

Phosphate chemical conversion coatings have attracted much attention on surface modification of metallic implant, due to their in-situ growth pattern and good mechanical performances. Nevertheless, it is difficult to use this method for preparing a pure hydroxyapatite (HA) coating. In this study, a pure HA coating was prepared on titanium (Ti) in an acidic phosphate aqueous via a simple single-step chemical conversion without alkali post-treatment. The microstructure, chemical composition, electrochemical and mechanical performances of the HA coating were characterized in comparison with those of a precursor dicalcium phosphate (CaP) coating which was alkali post-treated (CaP-OH). Results revealed that the one-step chemically converted HA coating was homogeneously nano-structured with higher phase purity and crystallinity. Moreover, the HA coating was thicker (~6.5 μm) than the CaP-OH one (~40 μm) but with better mechanical properties and corrosion resistance. The results encouraged the direct preparation of crystalline HA coating with superior properties on surface of Ti via a single-step phosphate chemical conversion.