DEPENDENCE OF APATITE FORMATION ON SILICA-GEL ON ITS STRUCTURE - EFFECT OF HEAT-TREATMENT

The prerequisite for glasses and glass-ceramics to bond to living bone is the formation of biologically active bonelike apatite on their surfaces in the body. Our previous study showed that a silica gel prepared by hydrolysis and polycondensation of tetraethoxysilane in aqueous solution containing poly(ethylene glycol) induces apatite nucleation on its surface in a simulated body fluid. In the present study, the effects of heat treatment of silica gel on its catalytic effects in apatite nucleation was investigated in a simulated body fluid, It was found that apatite forms on the surfaces of silica gels heat-treated below 800 degrees C, but not on those heat-treated above 900 degrees C. The volume of nanometer-range pores in the gel remarkably decreased by heat treatment above 900 degrees C. The concentration of silanol groups in the silica gels gradually decreased with increasing heat treatment temperature. The rate of silica dissolution from the gel into the simulated body fluid decreased remarkably by heat treatment above 900 degrees C. This suggested that a special type of silanol group which is formed by soaking the gel treated below 800 degrees C into the simulated body fluid is responsible for apatite nucleation.