Dual delivery of BMP-2 and IGF-1 through injectable hydrogel promotes cranial bone defect healing

Critical size cranial bone defect remains a great clinical challenge. With advantages in regenerative medicine, injectable hydrogels incorporated with bioactive molecules show great potential in promoting cranial bone repair. Recently, we developed a dual delivery system by sequential release of BMP2 followed by IGF1 in microparticles (MPs), and an injectable alginate/collagen (alg/col)-based hydrogel. In this study we aim to evaluate the effect of dual delivery of BMP2 and IGF1 in MPs through the injectable hydrogel in critical-size cranial bone defect healing. The gelatin MPs (gMPs) loaded with BMP2 and poly(lactic-co-glycolic acid)-poly(ethylene glycol)-carboxyl (PLGA-PEG-COOH) MPs (pMPs) loaded with IGF1 were prepared, respectively. The encapsulation efficiency and release profile of growth factors in MPs were measured. A cranial defect model was applied to evaluate the efficacy of the dual delivery system in bone regeneration. Adult SD rats were subjected to osteotomy to make an ⌀8-mm cranial defect. The injectable hydrogel contained MPs loading with BMP2 (2 µg), IGF1 (2 µg), or a combination of BMP2 (1 µg) and IGF1 (1 µg) were injected to the defect site. New bone formation was evaluated by micro-CT, histological analysis, and immunohistochemistry after 4 or 8 weeks. Data showed that dual delivery of the low-dose BMP2 and IGF1 in MPs through alg/col-based hydrogel successfully restored cranial bone as early as 4 weeks after implantation, whose effect was comparable to the single delivery of high-dose BMP2 in MPs. In conclusion, this study suggests that dual delivery of BMP2 and IGF1 in MPs in alg/col-based hydrogel achieves early bone regeneration in critical size bone defect, with advantage in reducing the dose of BMP2.