THE ROLE OF HYDRATED SILICA, TITANIA, AND ALUMINA IN INDUCING APATITEON IMPLANTS

Pure soluble silica prepared by a sol-gel method induced bone-like hyd roxyapatite formation onto its surface when the silica was immersed in a simulated body fluid (SBF), whereas silica glass and quartz did not . This finding directly supports the hypothesis that hydrated silica p lays an important role in biologically active hydroxyapatite formation on the surfaces of bioactive glasses and glass-ceramics, which leads to bone-bonding. Gel-derived titania is also a hydroxyapatite inducer because of its abundant TiOH groups. These results provide further ins ight into the unique osseointegration of titanium and its alloys. It i s suspected that gel-derived titania develops an apatite layer by taki ng calcium and phosphate from the body fluid, thus producing bone-bond ing. Although sufficient A1OH groups may remain in the alumina gel, th ey do not serve to initiate apatite generation when immersed in SBF. T his phenomenon explains the fact that an intermediate fibrous tissue i s usually found to separate the alumina implant from bone. One may inf er that both abundant OH groups and negatively charged surfaces of gel -derived silica and titania are important for hydroxyapatite induction . Material which possesses and/or develops both a negatively charged s urface and abundant OH groups in a physiologically-related fluid is mo st likely to be an efficient apatite inducer. Such materials are suita ble candidates to serve as bone-bonding biomaterials. (C) 1994 John Wi ley and Sons, Inc.