Biomimetic deposition of calcium phosphates on oxides soaked in a simulated body fluid

³¹P magic-angle-spinning (MAS) NMR spectra were measured for several oxides, such as Al₂O₃, SiO₂, TiO₂ and Ta₂O₅ which were treated with TaCl₅-free H₂O₂ solutions and TaCl₅-containing H₂O₂ solutions and soaked in a simulated body fluid (Kokubo solution; pH = 7.4) for 7 days. The chemical states of phosphate anions deposited on these oxides were determined. A ³¹P MAS-NMR peak at a chemical shift ca. 3 ppm was observed in the spectra of Ta₂O₅ and for the other oxides when they were treated with the TaCl₅-containing H₂O₂ solution. Without the treatment with the TaCl₅-containing H₂O₂ solution no ³¹P MAS-NMR peaks were observed in the spectra of the oxides. The ³¹P chemical shift, ca. 3 ppm, indicated that orthophosphate anions, PO₄^3- as found in hydroxyapatite and a cortical bone (rabbit) were adsorbed on the oxides. The surface of Ta₂O₅ particles and the oxides treated with the TaCl₅-containing H₂O₂ solution induced the deposition of apatite. We concluded that the surface Ta(V) species supported on the oxides induced a bone-like apatite nucleus, even though the base oxides did not deposit apatite.