Human fibrin is a physiologic delivery system for bone morphogenetic protein.

To investigate a physiologic delivery system, bone morphogenetic protein (BMP) in a carrier of other bone matrix noncollagenous proteins (BMP/NCP) was implanted as a composite of a fibrin clot in the thigh of a mouse. Comparable amounts of BMP/NCP alone and fibrin alone were implanted as controls. New bone yields were measured by random point analysis using a video camera and computer system and by ash weight measurement. Histologic examinations, beginning as early as three to seven days postimplantation, showed more extensive proliferation of mesenchymal cells in response to the composite than to lyophilized BMP alone. Correlated microradiographic and histologic observations showed that the composite also produced larger volumes of new bone than the BMP control group. The composite produced approximately three times more bone than BMP alone, and the difference was consistent and statistically significant. Lyophilized pellets of a composite of fibrin and BMP, prepared as volume control implants, also showed more new bone formation than the BMP alone, but the differences were less than with the wet clot composites. The relatively high yields of new bone from both wet clot and lyophilized composites suggest that the fibrin clot may perform an immunochemical function and act as a distributor of BMP. A human fibrin delivery system for BMP warrants further investigation for reconstructive orthopedic operations.