Resorbability of bone substitute biomaterials by human osteoclasts

Third generation biomaterials are being designed with the aim that once implanted they will help the body to heal itself. One desirable characteristic of these materials in bone is their ability to be remodeled, i.e. that osteoclasts resorb the material and it is subsequently replaced by newly formed bone through osteoblastic activity. So far the only way to test this biological property of bone substitutes are animal experiments with all their limitations like ethics, costs and limited transferability to man. The present study was designed, to develop a human in vitro assay, allowing to generate human osteoclasts directly on the biomaterial. The assay was validated using calcium phosphate cement and PMMA as biomaterials. Quantification was performed by raster electron microscopy and computer assisted image analysis. Dentin was used as internal standard. Our assay shows iso-bone resorbability of calcium phosphate cement in comparison to unresorbable PMMA cement. Both current clinical orthopedic practice and future skeletal engineering may profit from the availability and use of a test system for the assessment of resorption quality. The assay presented here allows to address this question of resorbability and to select the best materials for the use as bone substitutes in specific patients.