Ectopic bone induction by partially purified bone extract alone or attached to biomaterials

Formation of new bone is suggested to be caused by interaction of a set of chemical factors with mesenchymal target cells. A specific assembly of factors, i.e. chemotaxis-, adhesion-, proliferation- and differentiation-factors, as well as macromolecular structure components, essential for formation of large amounts of ectopic bone was termed "osteopoetin" (OP). In the present study a partially purified osteopoetin containing bovine bone extract (OCBE) was used to induce ectopic bone formation. In order to reduce the amount of OCBE necessary for bone induction, OCBE was seeded onto different commercially available collagens or poly-L-lactic acids (PL). Solid collagens in a sponge-like form were used for the first time to function as an attachment system for an osteoinductive substance. The test substances were implanted into abdominal muscle pouches of male Wistar rats. After 21 days the implants were harvested and evaluated histologically. OCBE resulted in the formation of large ossicles containing hematopoietic bone marrow. The minimal amount of OCBE to elicit ectopic bone formation can be reduced by a factor of 10 when attached to quickly resorbable collagens, but not when attached to slowly resorbable PL. These results suggest that collagens are suitable OCBE attachment systems and useful for clinical application.