ABSTRACT
The induction of bone formation requires three components: soluble osteogenetic molecular signals, responding cells and a complementary substratum upon which cells attach and differentiate. The combination of a soluble osteogenetic molecular signal with a complementary substratum does result in the induction of bone formation in heterotopic extraskeletal sites. The analyses and re-analyses of serial sections further cut from decalcified and undecalcified specimen blocks revealed the critical role of a specific geometric configuration that intrinsically initiates the induction of bone formation in a variety of calcium phosphate-based macroporous constructs. The concept that the geometry had a profound impact on the induction of bone formation prompted people to prepare macroporous bioreactors made of crystalline sintered hydroxyapatites as well as solid sintered monolithic hydroxyapatite discs with a series of concavities prepared on both planar surfaces. The induction of bone is always characterized by the presence of continuous vascularization and capillary sprouting within the concavity macroenvironment.
