Compositional dependence of apatite formation in sol-gel derived organic-inorganic hybrids

In the present study, we report the bioactivity of PDMS-CaO-SiO2-P2O5 hybrid materials prepared by a sol-gel method. The apatite formation on the surface of the specimen, after soaking in the simulated body fluid (SBF), was analyzed by thin-film X-ray diffraction (TF-XRD) and Fourier transform infrared (FT-IR) reflection spectroscopy. The structure and morphology of the surface layer were observed by FT-Raman spectroscopy, BET, and scanning electron microscopy (SEM). It was found that the bioactivity increased with decreasing PDMS content and increasing CaO content. Also, an increase in P2O5 concentration from 0 to 3 mol % decreased the induction period for apatite formation. A further increase in P2O5 content, however, increased the induction period. It was also noted that an increase in the P2O5 concentration from 0 to 3 mol % increased the surface area and micropore area and volume and decreased the pore diameter. On the other hand, the opposite trends were observed with a further increase in the P2O5 concentration. Among the various ormosil samples prepared with different compositions, the highest bioactivity was obtained from the ormosil with the composition of 20 wt % PDMS [PDMS/(TEOS + PDMS)], 15 mol % CaO [(Ca(NO3)(2)/TEOS) mole ratio], 3 mol % P2O5 [TEP/TEOS mole ratio].