Apatite formation on various silica gels in a simulated body fluid containing excessive calcium ion

Abstract

It was previously shown that a silica gel prepared in a solution containing polyethylene glycol (S-PEG) induces the apatite nucleation in SBF, but those prepared in pure water (S-W) and a solution containing polyacrylic acid (S-PAA) do not induce it. This indicates that a limited type of silanol groups is effective for apatite nucleation. In the present study, apatite-forming ability of these silica gels was examined in SBF containing excessive calcium ion. It was found that all these silica gels formed the apatite on their surfaces in this fluid, although the rate of apatite formation decreased in the order S-PEG > S-PAA > S-W. This indicates that any type of silanol groups has potential for inducing apatite nucleation under this condition. Such environment rich in calcium ion is produced around the surfaces of CaO, SiO2-based glasses and glass-ceramics when they are implanted into living body. The present results indicate that the CaO-SiO2 system can be a good basic composition for bioactive glasses and glass-ceramics.