Bioactivity of M(2)O-TiO2-SiO2 (M=Na, K) glasses: An in vitro evaluation

The formation of biologically active bonelike apatite on the surfaces of glasses and glass-ceramics is an essential condition for their bonding living bone. In the present study, apatite formation on the surfaces of M(2)O-TiO2-SiO2 (M = Na, K) glasses was examined in a simulated body fluid with ion concentrations nearly equal to those of human blood plasma in order to evaluate their bioactivity. While none of the Na2O-TiO2-SiO2 ternary glasses formed the surface apatite, K2O-TiO2-SiO2 glasses, not only as SiO2-rich glasses but also as TiO2-rich glasses, formed the apatite. The alkali ions in the glasses exchanged with H3O+ ions in the fluid. The TiO2-rich or SiO2-rich hydrogel which was formed on the surfaces of the glasses induced apatite nucleation. The increased degree of the supersaturation of the fluid with respect to the apatite due to the increase in pH provided favorable conditions for apatite nucleation. This indicates that alkali titanates as well as alkali silicates can be basic components of bioactive glasses.