Inflammatory response and degradation of three types of calcium phosphate ceramic in a non-osseous environment

The cellular response and inflammatory reaction to three types of calcium phosphate ceramic spheres, namely fluorapatite (FA), hydroxyapatite (HA), and beta-tricalcium phosphate (TCP), were investigated. The degradation at ultrastructural level of these ceramics was also studied. The mouse peritoneal cavity was used as a model compartment for this study. To minimize the influence of a wound reaction, the spheres were implanted by injection. Intraperitoneal injection of latex beads of 6.4 and 25.7 microns showed that an inflammatory reaction is influenced by the size of injected particles; therefore, ceramic spheres with the same average diameter (11.3 microns) were used. After 2 and 4 days and 1, 2, 4, 8, 12, and 24 weeks, the spheres were harvested. All materials gave rise to a short, mild inflammatory reaction. The ceramic spheres aggregated rapidly, and foreign body granulomas were formed within 2 weeks. Degradation of all materials was observed in this study, and degradation products were frequently seen both intracellularly and extracellularly. After 2 weeks TCP and HA showed the formation of crystals at their surface and between individual grains of the spheres. This was most prominently seen with TCP. At 4 weeks, HA and TCP granulomas showed the formation of extracellular, globular deposits between macrophages or multinucleated giant cells and fragments of the ceramic. They consisted of an organic matrix containing apatite-like crystals and iron, and had an average diameter of 10 microns. The number of deposits was the highest for TCP. For FA, calcium phosphate precipitation and the formation of deposits was not observed before the 8-week interval and remained at a low level.