Highly bioactive P2O5-Na2O-CaO-SiO2 glass-ceramics

Glasses having a chemical composition between 1Na(2)O-2CaO-3SiO(2) (1N2C3S) and 1.5Na(2)O-1.5CaO-3SiO(2), containing 0, 2, 4 and 6 wt% P2O5, were crys tallized to several volume percent through thermal treatments in the range 550-700 degreesC. These glasses and glass-ceramics were exposed to a simula ted body fluid solution (SBF-K9 which is close to human plasma) for several time periods. Fourier transform infrared spectroscopy (FTIR) was used to d etermine the rate of hydroxy carbonate apatite (HCA) formation. Crystalliza tion decreased the kinetics but did not inhibit the development of a HCA la yer, even in fully crystallized ceramics. The onset time for crystallizatio n of HCA varied from 8 h for a glass containing 6% P2O5 to 35 h for a fully crystallized 1.07Na(2)O-2CaO-3SiO(2) ceramic, The HCA layer formation of t hese compositions in in vitro' tests is much faster than in commercial bioa ctive materials such as synthetic hydroxyapatite ceramic, A/W glass-ceramic , Ceravital and Bioverit, for which the onset time usually takes at least s even days. FTIR and inductive coupled plasma studies confirmed the formatio n of an apatite layer which indicates bioactivity in the 1N2C3S crystal pha se. X-ray diffraction experiments show that the phosphorus ions are kept in solid solution in the crystal phase. An apatite-like compound only appeare d when the specimens were submitted to very long additional thermal treatme nts. The bioactivity of commercial materials is based on the apatite crysta l phase, while the high level of bioactivity of this new generation of glas s-ceramics is attained due to the combination of two mechanisms acting simu ltaneously, a non-phosphate bioactive crystal phase (1N2C3S) and the phosph orus ions in solid solution which are easily released from the structure, p romoting a faster HCA layer formation similar to 45S5 Bioglass (R). (C) 200 1 Elsevier Science B.V. All rights reserved.