MECHANISM OF APATITE FORMATION ON CAO-SIO2-P2O5 GLASSES IN A SIMULATED BODY-FLUID

It has been shown for various types of glasses and glass-ceramics that the essential condition for them to bond to living bone is the formation of an apatite layer on their surfaces in the body. CaO,SiO2-based glasses formed the surface apatite layer in a simulated body fluid, whereas CaO,P2O5-based glasses did not form it. This means that the rate of the apatite nucleation on the surfaces of the former glasses is much higher than that of the latter glasses. The increase in the degree of the supersaturation of the surrounding fluid with respect to the apatite due to dissolution of the calcium ion from the CaO,SiO2-based glasses was almost equal to that due to dissolution of the phosphate ion from the CaO,P2O5-based glasses. The high rate of the apatite nucleation on the surface of the former glasses is therefore attributed to the lower interface energy between the apatite and the glass surfaces. The CaO,SiO2-based glasses form a silica hydrogel on their surfaces prior to formation of the apatite layer. This means that the hydrated silica provides specific favorable sites for the apatite nucleation.