Mechanistic study of apatite formation on bioactive glass surface using 31P solid-state NMR Spectroscopy

The molecular mechanism of apatite formation on bioactive glass surface is studied using the techniques of XRD, EDX, SEM, FT-IR, and solid-state P-31 NMR. Using the sol-gel method a bioactive glass system containing glass beads of 2 to 3 microns in size is prepared with the composition containing 30% CaO - 70% SiO2. Our experimental data support the apatite formation mechanism proposed by Hench concerning the precipitation and crystallization of calcium phosphate. The phosphate ions initially deposited on the glass surface are largely in amorphous phase and have substantial amount of water molecules in the surrounding. As the soaking time in simulated body fluid increases, some of the water molecules diffuse out of the phosphate lattice, leading to the formation of a crystalline phase. Our data show that the structure of the crystalline phase is different from type B carbonate apatite but similar to hydroxyapatite.