TRANSMISSION ELECTRON-MICROSCOPIC OBSERVATION OF GLASS-CERAMIC A-W AND APATITE LAYER FORMED ON ITS SURFACE IN A SIMULATED BODY-FLUID

Glass-ceramic A-W containing crystalline oxyfluorapatite and beta-wollastonite in an MgO-CaO-SiO2 glassy matrix bonds to living bone through an apatite layer which is formed on its surface in the body. It has been confirmed by SEM observation, thin-film X-ray diffraction and FT-IR reflection spectroscopy that the apatite layer can be reproduced on the surface of the glass-ceramic even in an acellular simulated body fluid with ion concentrations nearly equal to those of human blood plasma. In the present study, structures of glass-ceramic A-W and the apatite layer formed on its surface in the simulated body fluid were observed under a high-resolution transmission electron microscope. In the interior of glass-ceramic A-W, both the apatite and beta-wollastonite were homogeneously dispersed in a glassy matrix, taking a form of rice grain 50 nm in width and 100 nm in length. The apatite layer formed on the glass-ceramic in the simulated body fluid consisted of fine needle-like apatite crystals about 10 nm in thickness and 100 nm in length, which are elongated along c-axis and randomly oriented. The apatite crystals in the surface layer were in direct contact with those within the glass-ceramic without intervention of such silica gel layer as observed for Bioglass(R)-type glasses. No crystallographic relation was observed between them. The apatite crystals in the surface layer were calcium-deficient, and contained small amounts of Mg and Si.