This study aimed at investigating in vitro and in vivo the efficiency of commercially available fibrin as a carrier for controlled and sustained bone morphogenetic protein-2 (BMP-2) release to induce bone formation and reduce the side effects of its use. In vitro release and activity of low-dose recombinant human BMP-2 (rhBMP-2) (37.5 µg/mL) embedded in commercially available fibrin were evaluated and, subsequently, critical-size femur defects in rats were grafted to study bone regeneration and vascularisation by micro-computed tomography (µCT) and histology. In vitro experiments showed a sustained BMP-2 release with a high BMP activity remaining after 28 d. In vivo, fibrin loaded with BMP-2 showed an extremely fast bone healing, with a large amount of new bone formation throughout the entire defect in the first 4 weeks and complete cortical repair and fusion after 8 weeks, with no ectopic bone formation. In contrast, the control fibrin group did not fuse after 12 weeks. Vascularisation was similar in both groups at 4 and 12 weeks after implantation. In conclusion, commercially available fibrin is a very efficient carrier for rhBMP-2 to graft critical-size cortical bone defects and might be a more optimal delivery vehicle for BMP-2-induced bone regeneration than currently available collagen sponges.
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