In vitro and in vivo evaluation of silicated hydroxyapatite and impact of insulin adsorption.

This study evaluates the biological behaviour, in vitro and in vivo, of silicated hydroxyapatite with and without insulin adsorbed on the material surface. Insulin was successfully adsorbed on hydroxyapatite and silicated hydroxyapatite bioceramics. The modification of the protein secondary structure after the adsorption was investigated by means of infrared and circular dichroism spectroscopic methods. Both results were in agreement and indicated that the adsorption process was likely to change the secondary structure of the insulin from a majority of α-helix to a β-sheet form. The biocompatibility of both materials, with and without adsorbed insulin on their surface, was demonstrated in vitro by indirect and direct assays. A good viability of the cells was found and no proliferation effect was observed regardless of the material composition and of the presence or absence of insulin. Dense granules of each material were implanted subcutaneously in mice for 1, 3 and 9 weeks. At 9 weeks of implantation, a higher inflammatory response was observed for silicated hydroxyapatite than for pure hydroxyapatite but no significant effect of adsorbed insulin was detected. Though the presence of silicon in hydroxyapatite did not improve the biological behaviour, the silicon substituted hydroxyapatite remained highly viable.