Bioactive ceramics are known to bond directly to bone and to stimulate bone formation. This has led to their constantly increasing clinical use. Numerous studies have contributed to enhancing our understanding regarding the stimulatory effect of bioactive calcium phosphates on osteoblast function and bone tissue formation. Significant progress has been made in revealing solution-mediated surface reactions that take place close to the surface of bioactive ceramics. Advanced surface analysis methods have been combined with molecular techniques in order to facilitate a better understanding of the surface transformations of bioactive, resorbable ceramics and glasses and the serum protein adsorption events associated with immersion in biological fluids. Increasing knowledge has been generated regarding the effect of bioactive ceramics on osteoblast differentiation in vitro. Furthermore, the effect of various bioactive ceramics on osteoblast differentiation and tissue maturation in vivo has been studied thereby allowing correlation of in vitro and in vivo events. More recent research efforts provided insight into integrin-mediated cell adhesion and the subsequently activated intracellular signaling pathways that regulate osteoblast cell function including differentiation and cell survival. Also the effect of ionic dissolution products of bioactive ceramics on intracellular signaling of the various cell types involved in osteogenesis has been increasingly studied in recent years. Current challenges furthermore involve developing appropriate co-culture models, which adequately mimic the stem cell niche and thereby can serve as platform, which will enable both the surface-mediated as well as the solution-mediated effects of bioactive ceramics on the true in situ regenerative niche to be investigated in vitro. Establishing co-culture models which include macrophages in addition to osteoblasts and endothelial cells represents a very recent step into this direction. Once reaction pathways are clearly identified materials can be created which preferentially boost the osteogenic cascade and thus are optimally tailored toward their clinical application.
