APATITE FORMATION ON SILICA-GEL IN SIMULATED BODY-FLUID - ITS DEPENDENCE ON STRUCTURES OF SILICA-GELS PREPARED IN DIFFERENT MEDIA

It has been shown that the prerequisite for glasses and glass-ceramics to bond to living bone is the formation of a layer of biologically ac tive bonelike apatite on their surfaces, The hydrated silica formed on the surfaces of glasses and glass-ceramics plays an important role in nucleating the apatite, In the present study, the structure of the hy drated silica responsible for the apatite nucleation was investigated in an accellular simulated body fluid with ion concentrations nearly e qual to those of human blood plasma, Three kinds of porous silica gels were prepared by hydrolysis and polycondensation of tetraethoxysilane in pure water or in aqueous solution containing polyethylene glycol o r polyacrylic acid, The silica gels prepared in aqueous solution conta ining polyethylene glycol or polyacrylic acid had micron-size intercon nected pores, whereas the gel prepared in pure water did not, All the gels contained a large volume of nanometer-size pores, almost the same amounts of silanol groups and D2 defect, and showed a high dissolutio n rate of the silica, Despite this, only the gel prepared in the solut ion containing polyethylene glycol formed the apatite on its surface i n the simulated body fluid, This indicates that only a certain type of structural unit of the silanol group is responsible for the apatite n ucleation. (C) 1996 John Wiley & Sons, Inc.