Fabrication of apatite-forming sol–gel hybrids comprising 2-hydroxyethyl methacrylate, 3-methacryloxypropyltrimethoxysilane, and calcium chloride by visible light-induced polymerization

Abstract

Silicate-based ceramics have been used to repair bone because they are able to form bone-like apatite upon reaction with body fluids, and to bond directly to bone via the apatite layer. Organic–inorganic hybrids that comprise Ca²⁺ and organic polymers with Si–OH groups, i.e., the basic composition that induces apatite formation, are expected to have mechanical properties similar to those of natural bone. The authors have found that hybrids of 2-hydroxyethyl methacrylate (HEMA) and 3-methacryloxypropyltrimethoxysilane (MPS) with added calcium salts form apatite in simulated body fluid (SBF). However, the hybrid takes more than 1 week to prepare. In the present study, the authors synthesized hybrids with various MPS/(MPS + HEMA) ratios by visible light-induced photopolymerization, and investigated their ability to form apatite in SBF and their mechanical properties. Bulk hybrids were obtained within 3 days at any MPS/(MPS + HEMA) ratio, and they formed apatite in SBF within 3 days. The tensile strength of a hybrid with an MPS/(MPS + HEMA) molar ratio of 0.2 or less was approximately 0.2 MPa, and tended to decrease as the MPS content increased. It was noted that the strength increased up to 2.9 MPa when N,N-dimethyl-p-toluidine was not added.