Degradation of calcium phosphate ceramics.

Degradation of three types of sintered calcium phosphate ceramic spheres was investigated in vitro at low pH conditions (LPC) and in an in vivo model, that is, injection into a mouse peritoneal cavity. Degradation was observed under both conditions. The rate of degradation depended on the type of ceramic, with beta-TCP degrading faster than HA and HA degrading faster than FA. Degradation was characterized by dissolution of the necks and the formation of cracks and irregularities in the grains. Intraperitoneal injection of the spheres into a mouse peritoneal cavity led to the formation of foreign body granulomas in which degradation could be observed. The in vivo degradation pattern was similar to that observed in vitro, but longer implantation times resulted in a further degradation. Small fragments rich in Ca and P were present in inclusion bodies. Calcium phosphate crystals sometimes also were observed in mitochondria, many of which were subject to lysis. We observed that ceramic type and implantation period also were related to the number of dead cells in the granulomas. Furthermore, extracellular deposits were seen between cells and ceramic spheres. Ca and P and also Fe were detected in these deposits. The presence of Fe is indicative of a lysosomal origin and thus of exocytotic activity.