EFFECT OF THE SUBSTITUTION OF Y2O3 FOR CAO ON THE BIOACTIVITY OF 2.5CAO-CENTER-DOT-2SIO(2) GLASS

Glasses were prepared whose composition is defined by the following ge neral formula: (2.5 - x)CaO . x/3Y(2)O(3) . 2SiO(2) (0 less than or eq ual to x less than or equal to 1). Their behaviour when they were soak ed in a simulated body fluid (SBF) and their thermal properties (glass transformation and softening temperatures, T-g and T-s respectively) were studied. T-g and T-s increase with the Y2O3 content. The trend ca n be explained on the basis of the increased structural rigidity when Ca2+ ions are substituted by Y3+ ions, because of the formation of str onger bonds to the oxygen. The bioactivity was studied by means of ele ctron microscopy equipped with an energy dispersive system for element al analysis and IR spectroscopy. All the glasses studied except the on e with the greatest amount of Y2O3, X = 1.0, reacted with SBF by formi ng a calcium phosphate layer. The experimental results suggest that th e bioactivity is negatively influenced by the Y2O3 content: the tenden cy to form a calcium phosphate layer is reduced the greater the amount of CaO substituted. A comparison with literature data indicates that the amount of Y2O3 that can be substituted depends on the CaO content of the base CaO-SiO2 glass. The experimental results are in good agree ment with the mechanism reported in the literature. After 7 days soaki ng, crystalline hydroxyapatite is formed in the Y2O3-free glass and in the glasses of low Y2O3 content (x = 0.2). (C) 1997 Elsevier Science Limited.