Interactions of human osteoprogenitors with porous ceramic following diffusion chamber implantation in a xenogeneic host.

Porous calcium phosphate ceramics are useful bone graft substitutes on account of their osteoconductive properties and lack of toxicity, but they lack osteogenicity and are brittle in nature. Osteogenic properties, and increased biomechanical properties, could be induced by combining them with human bone-forming cell populations. Progress has been hampered both by the lack of a suitable experimental assay of in vivo human bone formation and a suitable in vivo test system with which to study such cells in association with biomaterials. Here, trabecular bone-derived cells and marrow stromal fibroblastic cells from four human donors aged between 14 and 27 y have been cultured in vitro then combined with a porous ceramic within diffusion chambers and implanted into athymic mice. Bone and cartilage formation was found within the chambers primed with cells cultured in the continuous presence of dexamethasone and ascorbate. These tissues were found in close apposition to the ceramic, confirming that the material is biocompatible and bioactive. These findings demonstrate both that appropriately primed human-cell populations can express the fully differentiated osteoblastic phenotype in the diffusion-chamber model, and also that this is a useful system in which to test the interactions of such cell populations with putative biomaterials.