In vitro and in vivo methods to determine the interactions of osteogenic cells with biomaterials

To assess new biomaterials for possible use as bone graft substitutes, a nu mber of techniques allow interactions with osteoblastic cells to be studied , with respect to effects on proliferation and differentiation of osteoprog enitors. In vitro models include the use of bone explant cultures, fetal ra t calvarial-derived osteoblast cells, primary stromal populations, transfor med and non-transformed cell lines and immortalized osteoblast cell lines. However, these assessments are limited by the extent of osteogenic differen tiation and bone formation that can be observed in vitro, species differenc es and phenotypic drift of cells cultured in vitro. The use of in vivo expe rimental systems such as the segmental/calvarial bone defect model, the sub cutaneous implant model and the diffusion chamber implantation model circum vent some of these issues and, in the appropriate model, provide data on ef ficacy, biocompatibility and osteointegration of a biomaterial. The combina tion of in vitro and in vivo approaches together with the development of ne w cell labeling techniques, in particular the ability to genetically mark a nd select specific human bone cell populations provides new avenues for the ir potential evaluation in combination with appropriate biomaterials for cl inical use. These in vitro and in vivo techniques are reviewed and those re cently developed for assessment of human osteogenic cells should be applica ble to many other cell systems where knowledge of specific human tissue or cell interactions with biomaterials is required. (C) 1999 Kluwer Academic P ublishers.