Utilization of activated U937 monocytic cells as a model to evaluate biocompatibility and biodegradation of synthetic calcium phosphate

The use of calcium phosphate biomaterials as a bone substitute necessitates the use of normative biocompatibility and biodegradation techniques which must be fast, simple and reproducible. In the present study, we have developed an in vitro model to study and to compare different calcium phosphate ceramics. After activation with 1,25-dihydroxy-vitamin D3 and phorbol 12,13-dibutyrate, the monoblastic U937 cells became multinucleated, expressed tartrate-resistant acid phosphatase and several markers of monocyte/macrophage differentiation. Activated U937 cells did not express the vitronectin receptor (VNR) (as revealed using monoclonal antibodies 23C6 or 13C2) but around 25% of the cells were strongly reactive with 211D, a novel monoclonal antibody that recognizes an osteoclast-specific membrane antigenic determinant. These cells remain active/viable with hydroxyapatite (HA) or β-tricalcium phosphate (β-TCP) ceramics. In conclusion, activated U937 cells are good candidates to use in a normative in vitro method to evaluate new biomaterials.