P-31 MAS-NMR studies of phosphate salts formation on calcium-containing oxide glasses in a simulated body fluid

P-31 MAS-NMR spectra were measured for pulverized binary and ternary glasses containing Ca2+ ions after soaking in a simulated body fluid (Kokubo solution; pH=7.25) for 1 d, and the chemical state of adsorbed phosphate ions were examined. The P-31 chemical shift indicated that orthophosphate ions, H2PO4-(3-x) (0<x<3), were adsorbed on all the glasses but 60CaO . 40Al(2)O(3); pyrophosphate ions, H2P2O7-(4-x) (0<z<4), were detected on the aluminate glass, indicating that orthophosphate ions in the Kokubo solution were dimerized on the glass surface. For the glasses such as 60CaO . 40Al(2)O(3), 40CaO . 60B(2)O(3), 40CaO . 30B(2)O(3) . 30Al(2)O(3) and 40CaO . 30B(2)O(3) . 30SiO(2), those phosphate ions gave broad P-31 MAS-NMR spectra, hence have a broad distribution by coordinating to the various surface sites of the glasses. On the other hand, sharp P-31 MAS-NMR spectra as for a cortical bone (rabbit) were obtained for the rest of the glasses, (CaO)-Ca-50 . 50SiO(2) and 40CaO . 30B(2)O(3) . 30TiO(2), on which apatite formed in shorter soaking period in the Kokubo solution. It was thus concluded that presence of orthophosphate ions on the glass surfaces favored the deposition of apatite.