In vitro cytocompatibility assessment of beta-tricalcium phosphate/carboxymethyl-chitin composite

A novel bioabsorbable bone substitute composed of a beta-tricalcium phosphate (beta-TCP) and a carboxymethyl-chitin (CM-chitin) sodium has been developed. Rabbit tibia defects (4 mm in diameter) were repaired after 4 weeks more effectively by the composite compared with a sham-operation group. To further investigate the biological safety of the components, genotoxicity and carcinogenicity of an extract prepared from the composite were determined using four different in vitro assays. The main extract component was identified as CM-chitin sodium [average molecular weight (Mw) approximately 230 kDa] as determined by Fourier transform infrared spectroscopy and gel permeation chromatography analysis. The concentrations of P and Ca possibly derived from beta-TCP were 17.7 and 37.1 microg/g, respectively, as determined by inductively coupled plasma mass spectroscopy. Both the metabolic activation and nonactivation (-S9) systems of the rat microsome S9 fraction were used to perform a genotoxicity evaluation using the Ames test and chromosome aberration assay on Chinese hamster lung fibroblast cells treated with the extract. In these assays, no genotoxicity was detected with doses < or =5 mg/mL (maximum concentration). The cell transformation assay using BALB/c 3T3 cells and the metabolic cooperation assay with V79 cells both showed negative results for any tumor-promoting activity caused by the extract (approximately 5 mg/mL). These results indicate that the bioabsorbable beta-TCP/CM-chitin composite is a highly biocompatible bone substitute.