Hydroxyapatite coating on titanium substrate with titania buffer layer processed by sol–gel method

Abstract

Hydroxyapatite (HA) was coated onto a titanium (Ti) substrate with the insertion of a titania (TiO 2) buffer layer by the sol–gel method. The HA layer was employed to enhance the bioactivity and osteoconductivity of the Ti substrate, and the TiO 2 buffer layer was inserted to improve the bonding strength between the HA layer and Ti substrate, as well as to prevent the corrosion of the Ti substrate. The HA layer coated over the TiO 2 showed a typical apatite phase at 400°C and the phase intensity increased above 450°C. The sol–gel derived HA and TiO 2 films, with thicknesses of approximately 800 and 200 nm, respectively, adhered tightly to each other and to the Ti substrate. The bonding strength of the HA/TiO 2 double layer coating on Ti was markedly improved when compared to that of the HA single coating on Ti. The highest strength of the double layer coating was 55 MPa after heat treatment at 500°C. The improvement in bonding strength with the insertion of TiO 2 was attributed to the resulting enhanced chemical affinity of TiO 2 toward the HA layer, as well as toward the Ti substrate. Human osteoblast-like cells, cultured on the HA/TiO 2 coating surface, proliferated in a similar manner to those on the TiO 2 single coating and on the pure Ti surfaces. However, the alkaline phosphatase activity of the cells on the HA/TiO 2 double layer was expressed to a higher degree than that on the TiO 2 single coating and pure Ti surfaces. The corrosion resistance of Ti was improved by the presence of the TiO 2 coating, as confirmed by a potentiodynamic polarization test.