Mechanical property and microstructure of bioactive organic-inorganic hybrids containing colloidal silica particles

Synthesized through sol-gel processing were Ormosil type hybrid gels containing varied mass fractions of colloidal silica, poly (dimethylsiloxane) (PDMS), tetraethoxysilane (TEOS) and calcium nitrate. Viscoelasticity, mechanical strength and ²⁹Si MAS NMR spectra were measured, and in vitro apatite deposition in a simulated body fluid (SBF) of the Kokubo recipe was examined. The relative height of a T_g peak at about - 100°C in tan δ versus temperature curves grew with the colloidal silica content. This peak growth was accounted for the relative increase in PDMS-colloidal silica interactions. As the increase in the compressive strength followed the increase in colloidal silica content, the number of PDMS-silica bonds and hydrogen bond of colloidal silica increased due to the NMR spectra and tan δ curve. Thus, mechanical strength was dependent on PDMS-silica bonds and the hydrogen bond of colloidal silica. On the other hand, as the relative PDMS content increased, the number of PDMS-silica bonds was little influenced while PDMS chain structure increased. The gel (with a molar ratio TEOS:PDMS:H₂O:HCl:Ca (NO₃)₂·4H₂O = 1:0.48:5.0:0.9:0.10) containing 14 mass% colloidal silica (CS₁₄P_0.48Ca_0.10) exhibited the highest maximum failure strain (about 70%) among all samples. Thus, the relative content of PDMS chain structure depending on PDMS content influenced the maximum failure strain. CS₁₄P_0.48Ca_0.25 could not deposit apatite within 7 d after soaking in SBF, while PDMS/TEOS = 0.24 (molar ratio) could deposit apatite within 3 d. The increase in PDMS content restrained the dissolution of Ca ions.