Effects of Cross-Linking Agent on Apatite-Forming Ability and Mechanical Property of Organic-Inorganic Hybrids Based on Starch

Abstract

So-called bioactive ceramics can directly bond to living bone through the apatite layer formed on their surfaces in the body. However, hard and brittle character of ceramics limits their clinical applications to low loaded portions. The apatite deposition on the bioactive ceramics is known to be triggered by a catalytic effect of silanol (Si-OH) groups formed on their surfaces and by release of calcium ions (Ca2+) that increases degree of supersaturation of the surrounding fluid with respect to the apatite. It is expected that organic modification of these components would produce bioactive materials with mechanical properties analogous to natural bone. We previously reported that bioactive organic-inorganic hybrids can be prepared from starch by modification with glycidoxypropyltrimethoxysilane (GPS) that provides with Si-OH groups and calcium chloride that releases calcium ions. In this study, we examined effect of synthetic conditions of the hybrids on their bioactivity and mechanical properties. We prepared several hybrids with different content of divinylsulfone as a cross-linking agent. Their bioactivity was examined in simulated body fluid (SBF, Kokubo solution) with inorganic ion concentrations nearly equal to those of human extracellular fluid. Materials that form the apatite on their surfaces in SBF are known to have a potential to show the bone-bonding. It was found that the added cross-linking agent did not decrease apatite-forming ability of the hybrids in SBF. Mechanical properties of the hybrids were further evaluated by a tensile test. Tensile strength and Young’s modulus increased with increasing content of divinylsulfone.