Bonelike apatite formation on calcium-containing silica and titania gels in simulated body fluid

The bioactivity of calcium-containing silica and titania gels were examined. Pure silica and titania gels are bioactive and they demonstrate the capability of inducing apatite formation in simulated body fluid (SBF). The apatite formation on both silica and titania gels was expected to accelerate by incorporating calcium ions into the gels. In the present study, 10, 20, 30, and 40 mol% of calcium was added to the silica and titania gels, respectively. 50 mol% calcium addition was also studied for the silica gel. Multiple layers of gel coatings were applied to the titanium plate surfaces, and heat-treated at 500°C before soaking in SBF for up to two weeks. It was found that the incorporation of calcium ions into silica gels greatly enhanced apatite formation. In contrast, the apatite formation was substantially retarded by the incorporation of calcium ions into titania gels, despite of the high calcium ion release rate of these gels. However, increasing the heat-treatment temperature to 700°C resulted in apatite formation on the surfaces of both 10C90T and 20C80T gels, but not the rest of the calcium-containing titania gels.