Development of surface modification technology of titanium alloys for artificial bones using phosphate glasses

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A bioactive calcium phosphate invert glass-ceramic containing β-Ca_3(PO_4)_2 crystals could be joined strongly with a Ti-29Nb-13Ta-4.6Zr alloy consisting of a β-titanium phase by heating the metal, on which the mother glass powders with a composition 60CaO-30P_2O_5-7Na_2O-3TiO_2 in mol% were placed, at 800℃ for 1 h in air ; the tensile joining strength was estimated to be 〜26MPa on average. A compositionally gradient layer was developed on the metallic substrate during the heating. The joining between the glass-ceramic and the metal is suggested to be controlled by viscous, flow of the glassy phase in the glass-ceramic and by reaction of the glassy phase with the oxide phase formed around the surface layer of the metal.Bonelike apatite formation was observed on the glass-ceramic after 20 days of soaking in simulated body fluid (SBF). We found the apatite-forming ability of the glass-ceramic can be easily improved by autoclaving treatment in water. When the autoclaved sample was soaked in SBF, bonelike apatite began to form after 3 days. On the other hand, no apatite formed on the glass-ceramic, which was not autoclaved, even by soaking in SBF for 10 days. During the autoclaving, titanium ions in the amorphous phases around the surface form anatase phase and the hydrated titania groups, which may play an important role in the apatite formation.. A rod sample of the treated titanium alloy was implanted into a femur of rabbit. After 4-week implantation, newly formed bones were seen around the sample and they contacted directly without fibrous tissue.