Smart calcium phosphate-based bioceramics with intrinsic osteoinductivity

Bioceramics based on calcium phosphate compounds have been observed to exhibit intrinsic osteoinductivity under certain conditions. This response is highly dependent on factors such as the animal model and the geometry/surface of the porous ceramic material. In the present study several different ceramic materials were produced and implanted intramuscularly in primates (Papio ursinus, baboon) to determine the effect of a specific geometry on osteoinductivity. The various ceramic types exhibited very different behaviour in vivo, with bone formation ranging from extensive to none. A clear osteoinductive response was elicited by ceramics with high micro-porosity, high surface roughness and suitable concavities, with new bone initiating exclusively in concavities rather than on convex or flat surfaces. The response was suppressed when using ceramics with dense macropore walls and smooth sintered surfaces. The influence of the ceramic surface is profound, particularly the presence of suitable concavities with associated microporosity which specifically bind BMPs, initiators of bone formation and initiating what we have defined as geometric induction of bone formation. The concavities are endowed with shape memory, recapitulating events which occur in the normal course of embryonic development and appearing to act as gates, giving or withholding permission for growth and differentiation.