Hydroxyapatite/Titania Hybrid Coatings on Titanium by Sol-Gel Process

Abstract

Sol-gel thin films of hydroxyapatite and titania have received a great deal of attention in the area of bioactive surface modification of titanium implants. Sol-gel process offers lots of advantages over other coating techniques, e.g. increased homogeneity due to atomic level mixing; finer grain microstructure and lower temperature of the crystallization. In this study, we fabricated hydroxyapatite/titania hybrid coatings on titanium by sol-gel method to combine advantages of both materials: the adhesion strength of the titanium dioxide on the substrate and the bioactivity of the hydroxyapatite. Sol-gel coatings of pure hydroxyapatite and titania, and four hydroxyapatite composites with 10~70 mol% titania were developed on titanium substrates. The characteristics of coatings, such as crystallinity, roughness and composition of surface, were observed. The composite coatings showed the characteristic peaks of pure hydroxyapatite and titania with anatase and rutile structures. When the titania amounts adding into the hydroxyapatite sol increased, the surface of the composite coatings became slightly rougher. The critical load strength between coating and substrate slightly increased to 3.151, 4.168, and 5.389 N when the amount of titania added into hydroxyapatite sol increased to 30, 50, and 70 mol%, respectively. For bioactivity test, calcium phosphate deposits were observed on the film surfaces after the soaking in SBF for 1 week, except of titania coatedsubstrate. The in vitro cellular responses to the coatings were assessed in terms of cell attachment and proliferation. Hydroxyapatite composite coating with 70 mol% titania had the most excellent attachment of MG63 cells as cells tend to attach more readily to surfaces with a rougher microtopography. Statistically analysis revealed that there were no significant differences between the proliferation of osteoblastic cells on the various materials (p>0.05).