Improvement of hydroxyapatite formation ability of titanium-based alloys by combination of acid etching and apatite nuclei precipitation

The authors aimed to improve hydroxyapatite formation ability of Ti6Al4V, Ti-15Mo-5Zr-3Al alloy, Ti-12Ta-9Nb-6Zr-3V-O alloy (Gummetal®) and commercially pure Ti (cpTi) mesh by a combination of acid etching and apatite nuclei precipitation. Surfaces of specimens were etched with H2SO4 for pores formation on the specimens. Thus-etched specimens were soaked in an alkalinised simulated body fluid (SBF), which was adjusted at higher pH than that of conventional SBF and this solution was subsequently heated. By this treatment, apatite nuclei were precipitated in the pores of the specimens. By a soak in the conventional SBF to check hydroxyapatite formation ability, hydroxyapatite was covered the entire surfaces of the specimens within 1 day and high hydroxyapatite formation ability was successfully shown. The adhesion strength of the hydroxyapatite film formed in the above SBF test showed larger value as increasing the surface roughness of the specimens by adjusting the above acid etching condition depending on the kinds of Ti-based alloys. This is because the adhesion of the hydroxyapatite film occurred by the mechanical interlocking effect. In addition, this method showed shape selectivity of the materials because similar hydroxyapatite formation ability could be introduced to the cpTi mesh.