<sup>31</sup>P MAS-NMR Studies of Phosphate Salts Formation on Calcium-Containing Oxide Glasses in a Simulated Body Fluid

Abstract

31P 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 1d, and the chemical state of adsorbed phosphate ions were examined. The 31P chemical shift indicated that orthophosphate ions, HxPO4-(3-x) (0<x<3), were adsorbed on all the glasses but 60CaO⋅40Al2O3; pyrophosphate ions, HzP2O7-(4-z) (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⋅40Al2O3, 40CaO⋅60B2O3, 40CaO⋅30B2O3⋅30Al2O3 and 40CaO⋅30B2O3⋅30SiO2, those phosphate ions gave broad 31P MAS-NMR speetra, hence have a broad distribution by coordinating to the various surface sites of the glasses. On the other hand, sharp 31P MAS-NMR spectra as for a cortical bone (rabbit) were obtained for the rest of the glasses, 50CaO⋅50SiO2 and 40CaO⋅30B2O3⋅30TiO2, 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.