Biocompatibility of CO_2apatite preparations with solubility gradients

摘要

CO_3apatite materials with a degradable oute rlayer and a relatively stable core were synthesized at 80+-1deg C and pH 7.4+-0.2 by simultaneously feeding Solution I and Solution II into mechanically stirred 1.3 mol/L acetate buffer solution. Solution I consisted of 0.5 L of 100 mmol/L Ca(CH_3COO)_2; Solution II consisted of 0.5 L of 60 mmol/L NH_4H_2PO_4, into which 0.5 L of 60 mmol/L NH_4H_2PO_4 solution containing a constant concentration of 0,48 and 95 mmol/L (NH_4)_2CO_3 was continuously supplied. X-ray diffraction (XRD) analysis showed a typically apatitic pattern and the (300) diffraction peak shift, indicating a CO_3-for-PO_4 substitution. SEM analysis showed changes in morphology: from needle-like to small aggregated crystals, confirming earlier reports on the effect of CO_3 on reducing apatite crystal size. Electron spectroscopic analyses of pelletized specimen showed a negative gradient of carbonate concentration with depth. The apparent solubility of the CO_3 apatites in 0.5 mol/L acetate buffer solution (37 deg C, pH 4.0) increased with increasing CO_3 content. The CO_3apatites pellets were mixed with an atelocollagen whose antigenicity has been removed by enzymatic treatment and implanted int the periosteum cranii of rats. The composite showed good biocompatibility. In addition, the extent of biodegradation seemed to be related to the CO_3 content. These results suggest that CO_3 apatite materials with controlled biodegradability can be useful biomaterials.