Cells and Materials


The implantation of calcium phosphate ceramics in the bone environment elicits the differentiation of multinucleated giant cells (MNGCs). MNGC interactions with both crushed and standard hydroxyapatite (HA, Bioapatite ®) particles (cHA and sHA) were studied in rat skull defects. Light microscopy (LM) of undemineralized material after 21 and 42 days of implantation showed that the number of particles in the defect significantly decreased (about SO%) with the two HA forms. Concomitantly, average cHA particle size increased significantly due to the elimination of the smallest particles by the MNGCs. The number of MNGCs per mm2 of defect decreased significantly between 21 and 42 days with the two HA forms as did the number of MNGCs per particle. MNGC-HA interactions were observed at the ultrastructural level with transmission electron microscopy (TEM) in 21 day demineralized samples. MNGCs appeared smaller than in the LM, since several MNGCs formed aggregates of interwoven cells. They were closely apposed to the particle surface but no typical ruffled border or clear zone were seen in any case. An organic material had penetrated the HA particles and scattered in centripetal direction. These results show that (a) the HA conditioning form had no effect on its degradation and integration behavior, (b) the HA was extensively degraded by MNGCs before the embedding of the remaining particles in bone, and (c) MNGCs did not exhibit the distinctive functional apparatus of osteoclasts.