Compositional Dependence of Bioactivity of Glasses in the System CaO-B₂O₃-SiO₂: Its in vitro Evaluation

Abstract

The essential condition for glasses and glass-ceramics to bond to living bone is the formation of a biologically active bone-like apatite layer on their surfaces in the body. In the present study, in order to investigate fundamentally the effect of B₂O₃ on the bioactivity of glasses and glass-ceramics, the compositional dependence of apatite formation on the surface of glasses in the system CaO-B₂O₃-SiO₂ was examined in the simulated body fluid. Substitution of small amounts of B₂O₃ for SiO₂ in CaO·SiO₂ formula increased the rate of apatite formation on the surface of the glass, while substitution of more than 30 mol% B₂O₃ for SiO₂ decreased it. The substitution of B₂O₃ for SiO₂ in CaO-SiO₂ binary glasses accelerated the dissolution of Ca(II) ion from the glasses, and hence enhanced the increasing rate of degree of supersaturation of the surrounding fluid with respect to apatite. The decrease in the apatite forming ability by substitution of large amounts of B₂O₃ for SiO₂ is attributed to the suppression of formation of silica hydrogel layer which plays an important role in apatite nucleation.