Structural Dependence of Apatite Formation on Zirconia Gels in a Simulated Body Fluid.

The apatite-forming ability of zirconia gels with different structures was investigated in a simulated body fluid (SBF) with ion concentrations nearly equal to those of human blood plasma. Zirconia gels with amorphous, tetragonal, or monoclinic structure were prepared by a sol-gel process and subsequent heat treatment at various temperatures. Zirconia gel with an amorphous structure formed only a small amount of apatite on its surface, even after 14 d of immersion in SBF, whereas gels with tetragonal or monoclinic structures formed quite a large amount of apatite on their surfaces after 3 d of immersion, and their surfaces were fully covered with apatite within 14 d of immersion. This result indicates that specific arrangements of Zr-OH groups in tetragonal or monoclinic zirconia are effective in inducing apatite nucleation.