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Commercially pure titanium was treated with an H₂O₂/TaC1₅ solution. Thus formed titania gel layer remained amorphous when heated below 200°C and transformed to anatase after heated between 300-600°C. The anatase layers were substantially bioactive to deposit carbonate ion-incorporated apatite after soaked for 1 d in a simulated body fluid (Kokubo’s recipe), while the amorphous layers did not deposit up to 7 d. The apatite particles were preferably nucleated inside the cracks which prevailed in the titania gel layers. After soaking only for 2 d, the specimens were almost completely covered by the apatite. The H₂O₂-treated Ti specimens deposited apatite on both the contact and open surfaces, whereas the NaOH treated Ti specimens only deposited on the contact surfaces. The elimination of peroxide radicals out of titania gel and formation of anatase during heating are considered to be responsible for the improvement of apatite deposition ability.

It was already revealed that a sol-gel-derived titania forms an apatite on its surface in a simulated body fluid (SBF). It is, however, not clear what structure of titania gel is effective for inducing apatite nucleation on its surface. In the present study, apatite-forming ability of titania gels with different structures, which were formed in different media and heat-treated at different temperatures, were investigated in SBF. The titania gels heat-treated at 300°C took amorphous phases and did not form the apatite on their surfaces even after 14 days irrespective of the media. The titania gels, which were prepared in media containing no additive or acetylacetone and heat-treated at 500 to 800°C to precipitate anatase, formed the apatite on their surfaces within 7 days in SBF. The titania gels, which were prepared in a medium containing diethanolamine and heat-treated at 700 to 800°C to precipitate rutile, formed the apatite within 14 days in SBF. This indicates that a specific structure of titania such as anatase structure is effective for inducing apatite nucleation.