Bioactivity and mechanical behavior of PTMO-modified CaO-SiO₂ hybrids prepared by sol-gel process

Triethoxysilyl-terminated polytetramethylene oxide (Si-PTMO)-modified CaO-SiO₂ hybrids were prepared by hydrolysis and polycondensation of Si-PTMO, tetraethoxysilane (TEOS) and calcium nitrate. The effects of CaO and Si-PTMO contents on the bioactivity and mechanical behavior of the hybrids were investigated. The apatite-forming ability which is indicative of bioactivity was evaluated in a simulated body fluid (SBF) and the mechanical properties including strength, Young's modulus and strain at failure were measured in air by tensile testing. As for the series of the samples with a fixed weight ratio, (Si-PTMO)/(TEOS) = 2/3, the apatite-forming ability in SBF remarkably increased with increasing CaO content, although the tensile strength and Young's modulus decreased. The hybrid sample with (Ca(NO₃)₂)/(TEOS) = 0.15 in molar ratio formed the apatite on its surface within only one day. For this series of samples, the strain at failure was found to be about 30% and almost independent of CaO content. As for the series of the samples with a fixed molar ratio, (Ca(NO₃)₂)/(TEOS) = 0.15, the strain at failure increased with increasing Si-PTMO content, but the apatite-forming ability, tensile strength and Young's modulus decreased. Thus, the synthesis of the hybrids exhibiting both high apatite-forming ability and high capability for deformation can be achieved by selecting suitable CaO and Si-PTMO contents. These hybrids may be useful as new kind of bioactive bone-repairing materials.