It is now more than twenty years ago that the first studies of ceramic materials for use in orthopaedics and dentistry were undertaken. Initially one focused on so called inert ceramics, such as aluminum oxide. It was not for long, though, that the concept of bioactive ceramics was introduced, i.e. ceramics with the intrinsic capacity of both promoting bone tissue formation at their surface, as well as the ability to bond to bone. Whereas, phenomenologically, these events are established beyond doubt, there is still no clear understanding of the mechanisms of interaction leading to these phenomena. This evokes concern, since the current uses of these materials are not yet optimized: bioactivity implies subcritical crack propagation, as a result of which calcium phosphate coatings on metallic implants have a time increasing propensity to shear off; and particulate calcium phosphate used to repair, augment or substitute bone tissue, currently is not an expeditious, complication-free therapeutic modality. There are material dependent effects at the ceramic to physiological fluid interface, specifically an enhanced dissolution leads to increased bone tissue formation reaction rate kinetics; and also, mesemchymal differentiation to osteoblasts in areas without direct bone contact is predicated on the presence of a calcium phosphate ceramic or glass. By virtue of these effects, we propose that a thorough understanding on an Angstrom level of the reaction phenomena at the bioactive ceramic to fluid interface will greatly contribute to our ability to tailor make ceramic particles and coatings to specific orthopaedic and dental functions. Furthermore, our understanding of critical factors affecting bone growth by a synthetic material having physical and chemical characteristics similar to the mineral phase of bone will further our understanding of the relationship among mineral phase, organic matrix deposition and cellular activity in bone tissue. Specifically we determine ion exchange, dissolution and precipitation reactions at the ceramic to solution interface as a function of time, type of bioactive ceramic, and solution composition. This is achieved by i/in situ measurements at the interface, i.e. zeta potential measurements, ii/in solution: Ca and PO4 measurements, and iii/on the ceramic, by surface sensitive compositional analysis (electron spectroscopy for chemical analysis, ESCA). The data on compositional and electrical charge distribution and variation at the liquid to ceramic interface, obtained by this work, are incorporated into a model explaining the beneficial in vivo action of bioactive ceramics on bone tissue formation.
