ABSTRACT
The angiogenic induction in mesenchymal condensations is noteworthy and correlates with the alkaline phosphatase staining. High-power views indicate the migration of mesenchymal stem cells from the angiogenic compartment of the invading mesenchymal condensations to the osteogenic compartment of the differentiating osteogenic cells at the hydroxyapatite interface. Osteoclastic activity re-patterning the surface micro-geometry of the implanted macroporous bioreactors is the key factor resulting in the spontaneous and/or intrinsic induction of bone formation. The critical role of the concavity spontaneously initiating the induction of bone formation was confirmed by intramuscular rectus abdominis implantation of sintered crystalline hydroxyapatites with concavities of specific dimensions on both planar surfaces of the sintered constructs. The central question in developmental biology and thus tissue engineering and regenerative medicine is the molecular basis of pattern formation. Special thanks to Raquel Duarte, Caroline Dickens, Therese Dix-Peek and Rolando Klar, who molecularly assigned the spontaneous induction of bone formation by coral-derived bioreactors.
