The Efficacy of Bone Morphogenetic Protein-2 Depends on Its Mode of Delivery *Wan-Geun La, †Sun-Woong Kang, †Hee Seok Yang, *Suk Ho Bhang, ‡Sun Hwa Lee, ‡Jung-Ho Park, and *Byung-Soo Kim *School of Chemical and Biological Engineering, Seoul National University, Seoul; †Department of Bioengineering, Hanyang University, Seoul; and; ‡Department of Orthopedic Surgery,Ansan Hospital, College of Medicine, Korea University, Ansan, Republic of Korea Abstract: Bone morphogenetic protein-2 (BMP-2) induces bone regeneration in a dose-dependent manner, with higher doses of BMP-2 inducing greater bone formation. Previously, we showed that long-term delivery of BMP-2 provides better ectopic bone formation than short-term delivery of an equivalent dose. In the present study, we investigated the efficacy of orthotopic bone formation over a range of BMP-2 doses, using different delivery modes. Heparin-conjugated poly(lactic-co-glycolic acid) nano- spheres suspended in fibrin gel were used as a long-term delivery system, and fibrin gel was used as a short-term delivery system. Different doses of BMP-2 were delivered to mouse calvarial defects using either long-term or short- term delivery systems. Eight weeks after treatment, bone regeneration was evaluated by histomorphometry.For both delivery systems, bone regeneration increased as the BMP-2 dose increased up to 1 mg and did not increase beyond this dose. Importantly, at BMP-2 doses higher than 1 mg, long-term delivery resulted in much greater bone for- mation than short-term delivery. This study shows that long-term delivery of BMP-2 is more effective at enhancing orthotopic bone formation than short-term delivery over a range of doses. Key Words: BMP-2 delivery—Bone formation—Fibrin gel—Heparin-conjugated poly(lactic- co-glycolic acid) nanosphere. Bone morphogenetic proteins (BMPs) are the most potent osteoinductive growth factors for bone regeneration (1–3). BMPs induce bone formation by recruiting osteoprogenitor cells and inducing osteo- genic differentiation (1–4). Although bone morpho- genetic protein-2 (BMP-2) and bone morphogenetic protein-7 are used clinically (5–8), problems with their use remain. As BMPs have a very short half- life, BMPs administered in solution may rapidly lose their bioactivity (9). Large, costly doses of BMP-2 are required for clinical treatment, probably because BMP-2 is quickly lost from the collagen sponge carrier (6,8). High doses of BMP-2, coupled with rapid loss from the carrier, may cause side effects such as bone overgrowth and immune response (8). Thus, an appropriate delivery system that can release BMP-2 locally over a sufficiently long period and at appropriate concentrations is needed (4). A number of systems have been designed to deliver BMPs (5,6,8,10). BMP delivery using these systems leads to bone formation (5,6,8,10), but the profiles of BMP release from these systems are suboptimal. The optimal dosing, stability, and osteo- genic efficacy of BMP are likely to be influenced by the delivery systems (4,6,8). Our previous work showed that long-term delivery of BMP-2 led to more ectopic bone formation than short-term deliv- ery of an equivalent dose, with heparin-conjugated poly(lactic-co-glycolic acid) (PLGA) scaffolds or nanospheres used to achieve long-term delivery (10,11). Heparin interacts ionically with BMP-2 to enable sustained release and retain BMP-2 activity (12). In the present study, we compared long-term doi:10.1111/j.1525-1594.2009.00988.x Received May 2009; revised December 2009. Address correspondence and reprint requests to Professor Byung-Soo Kim, School of Chemical and Biological Engineering, Seoul National University, San 56-1, Sillim-dong, Gwanak-gu, Seoul 151-744, Republic of Korea. E-mail: byungskim@snu.ac.kr The first two authors contributed equally to this work. Artificial Organs 34(12):1150–1153, Wiley Periodicals, Inc. © 2010, Copyright the Authors Artificial Organs © 2010, International Center for Artificial Organs and Transplantation and Wiley Periodicals, Inc. 1150