Bone marrow cell gene expression and tissue construct assembly using octacalcium phosphate microscaffolds

Calcium phosphates have been widely used in bone and soft tissue applications and are of considerable interest as scaffold materials due to properties of osteoconduction, resorbability and in some cases osteoinduction. These materials are microcrystalline and as such are processed using sintering, surface coating or cement technologies. However calcium phosphates containing HPO42− ions often have layered crystal structures and can form macrocrystals in an aqueous environment at room temperature and pressure. This study aimed to investigate the potential of octacalcium phosphate (OCP) crystals for the attachment, proliferation and differentiation of bone marrow stromal cells and the potential of these cell seeded crystals as ‘building blocks’ for manufacture of self-supporting macroscale tissue constructs. An inverse relationship between cell number and crystal surface area was found and marrow cells grown on OCP crystals expressed osteocalcin and osteopontin mRNA, markers of osteoblastic differentiation, even in the absence of inductive media additives. Self-supporting crystal tissue macroscale constructs could be fabricated by culturing cell loaded crystals in moulds of the desired shape. Due to the low packing efficiency as a consequence of the high aspect ratio of OCP crystals, this microscaffold approach may offer the potential for ex vivo construction of large volumes of tissue which forms as a physiologically vascularised tissue.