Effect of calcium carbonate on hardening, physicochemical properties, and in vitro degradation of injectable calcium phosphate cements

The main disadvantage of apatitic calcium phosphate cements (CPCs) is their slow degradation rate, which limits complete bone regeneration. Carbonate (CO?2?) is the common constituent of bone and it can be used to improve the degradability of the apatitic calcium phosphate ceramics. This study aimed to examine the effect of calcite (CaCO?) incorporation into CPCs. To this end, the CaCO? amount (0-4-8-12 wt %) and its particle size (12.0-μm-coarse or 2.5-μm-fine) were systematically investigated. In comparison to calcite-free CPC, the setting time of the bone substitute was delayed with increasing CaCO? incorporation. Reduction of the CaCO? particle size in the initial powder increased the injectability time of the paste. During hardening of the cements, the increase in calcium release was inversely proportional to the extent of CO?2? incorporation into apatites. The morphology of the carbonate-free product consisted of large needle-like crystals, whereas small plate-like crystals were observed for carbonated apatites. Compressive strength decreased with increasing CaCO? content. In vitro accelerated degradation tests demonstrated that calcium release and dissolution rate from the set cements increased with increasing the incorporation of CO?2?, whereas differences in CaCO? particle size did not affect the in vitro degradation rate under accelerated conditions.