Since the late 1980's when the challenge of in vitro synthesis of bone tissue was first addressed, the investigation of mechanistic effects of materials on cellular functions, specifically cell attachment, proliferation, differentiation and extracellular matrix formation, was at the core of the Center's program. Other studies have focused on the combined effects of microgravity and substrate material on cellular functions; the use of self assembled monolayer chemistry to create highly controlled surfaces; studying the effect of calcification of such surfaces on cell function; and the controlled release of growth factors, cytokines, antibiotics, etc. from bioactive, silica based sol gels.