Surface Topography Designed to Provide Osteoconductivity to Titanium after Thermal Oxidation

Abstract

Hydroxyapatite formation on the surface of materials in the body is an essential condition for demonstrating osteoconduction after implantation in bony defects. This paper reports a technique for providing hydroxyapatite formation properties to titanium metals by using specially designed surface topography followed by thermal oxidation. Two pieces of titanium thermally oxidized at 400°C were set together in a V-shape with varied mouth opening. They showed the formation of hydroxyapatite on both facing surfaces after exposure to a simulated body fluid (SBF), when the gap height was approximately less than 600 μm. Moreover, pure titanium specimens with macro-grooves less than 1000 μm in depth and 800 μm in width were able to form hydroxyapatite deposits in SBF within 604.8 ks, after they were thermally oxidized at 400°C for 3.6 ks. Hydroxyapatite also formed on the internal surfaces of macro-grooves made in Ti-15-Zr-4Ta-4Nb within 604.8 ks of soaking in SBF, after the sample was thermally oxidized at 500°C for 3.6 ks, whereas it was not deposited on alloy made of Ti-6Al-4V extra low interstitial processed in the same way. These findings indicate that titanium and its alloys can be conferred with hydroxyapatite-forming ability, i.e. osteoconduction, within a controlled spatial gap and thermal oxidation. We conclude that bioactive titanium substrate showing osteoconduction can be produced by using a specially designed surface topography followed by thermal oxidation at an appropriate temperature.