Enhanced bone regeneration with BMP-2 loaded functional nanoparticle–hydrogel complex Yong-Il Chung a , Kang-Min Ahn b,c , Seung-Ho Jeon b , Seung-Young Lee a , Jong-Ho Lee b, ⁎ , Giyoong Tae a, ⁎ a Research Center for Biomolecular Nanotechnology and Department of Materials Science and Engineering, Gwangju Institute of Science and Technology, 1 Oryong-dong, Buk-gu, Gwangju, 500-712, Republic of Korea b Department of Oral and Maxillofacial Surgery, College of Dentistry, Seoul National University, 28-2 Yeongun-dong, Chongro-gu, Seoul, 110-749, Republic of Korea c Department of Oral and Maxillofacial Surgery, School of Medicine, Ulsan University, Asan Medical Center, 388-1 Pungnap-dong, Songpa-gu, Seoul, 138-736, Republic of Korea Received 17 April 2007; accepted 23 May 2007 Available online 2 June 2007 Abstract As an efficient sustained release system of BMP-2, a functional nanoparticle–hydrogel complex, composed of heparin-functionalized nanoparticles and fibrin gel, was developed and used as a bone graft. In vivo bone formation was evaluated by soft X-ray, histology, alkaline phosphatase (ALP) activity, immunostaining, and mineral content analysis, based on the rat calvarial critical size defect model. Significantly improved and effective bone regeneration was achieved with the recombinant BMP-2 (4 μg) loaded nanoparticle–fibrin gel complex, as compared to bare fibrin gel, the nanoparticle–fibrin gel complex without BMP-2, or even the BMP-2 loaded fibrin gel. These improvements included areas such as radiodensity, the bone-specific ALP activity, the osteocalcin immunoreactivity, and the ratios of calcium and phosphate contents with respect to normal bone in the regenerated bone area. The remodeling process of new bone developed with BMP-2 was significantly enhanced, and more mature and highly-mineralized bone was obtained by utilizing the functional nanoparticle–hydrogel complex. These results indicate that the nanoparticle–fibrin gel complex can be a promising candidate for a new bone defect replacement matrix, and an enhanced BMP-2 carrier. © 2007 Elsevier B.V. All rights reserved. Keywords: Bone graft; Growth factor; Controlled release; Heparin; Fibrin 1. Introduction A bone defect replacement matrix is aimed at helping new bone tissue grow and replace damaged parts. It has been used for osteogenic promotion and substitution for injured bone tissues like limb or spine fractures, fracture dislocations, osteo- myelitis, tumor ablation in orthopedics, and alveolar defects in dentistry [1,2]. Typically, autogenous bone, allogeneic bone, xenogeneic bone, and synthetic bone are used as bone grafting materials. However, in addition to a common problem of bone deformation after surgery for all of these materials, each mate- rial has further individual drawbacks that interfere with any of their inherent advantages; thus, none of them have been able to fully satisfy the demands of clinical needs [3,4]. As an alter- native, a new approach for regenerating damaged bone tissues is to provide critical initial input, to activate the regeneration process by supplying functional proteins at the defect site for a certain period. To this end, bone morphogenetic protein (BMP) has been shown as a key molecule in bone regeneration [5–8], and bone regeneration with BMP delivery is predicted to be a more effective method than other bone graft methods [9]. The matrix-based systems for growth factor delivery for regenerating injured tissues [10,11] need to stabilize the loaded signaling molecules, control their release, and also support the structural strength as a template filling the lesion site. For bone regeneration, various materials used in conjunction with BMP Journal of Controlled Release 121 (2007) 91 – 99 www.elsevier.com/locate/jconrel ⁎ Corresponding authors. Tae is to be contacted at Tel.: +82 62 970 2305; fax: +82 62 970 2304. Lee, Tel.: +82 2 2072 2630; fax: +82 2 766 4948. E-mail addresses: leejongh@plaza.snu.ac.kr (J.-H. Lee), gytae@gist.ac.kr (G. Tae). 0168-3659/$ - see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.jconrel.2007.05.029