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

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 1 d, and the chemical state of adsorbed phosphate ions were examined. The ³¹P chemical shift indicated that orthophosphate ions, H_xPO₄^-(3-x) (0<x<3), were adsorbed on all the glasses but 60CaO·40Al₂O₃; pyrophosphate ions, H_zP₂O₇^-(4-z), 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 spectra, 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.