PROCESS OF FORMATION OF BONE-LIKE APATITE LAYER ON SILICA-GEL

It has been proposed that a hydrated silica plays an important role in forming a biologically active apatite layer on the surfaces of bioact ive glasses and glass-ceramics in the body. Recent experiments have sh own that a silica hydrogel actually induces apatite formation on its s urface in a simulated body fluid (SBF). In the present study the proce ss of apatite formation on silica gel was investigated by means of thi n-film X-ray diffraction, Fourier-transformed infrared reflection spec troscopy and scanning electron microscopic observation of the surface of the silica gel, as well as the measurement of changes in the ion co ncentration of the fluid. It was found that the induction period for t he apatite nucleation on the surface of the silica gel was about 6 day s. Once the apatite nuclei were formed they grew, taking a spherulitic form by consuming the calcium and phosphate ions from the surrounding fluid. Each spherulite consisted of a lot of flake that clustered int o a petal-like morphology. The flake was carbonate-containing hydroxya patite of small-crystallites and/or defective structure. The Ca/P rati o of the apatite was estimated as 1.5 1.6. Thus, the apatite formed wa s able to induce secondary nucleation of the apatite.