The stimulation of healing within a rat calvarial defect by mPCL-TCP/collagen scaffolds loaded with rhBMP-2

Abstract

Bone morphogenetic proteins (BMPs) have been widely investigated for their clinical use in bone repair and it is known that a suitable carrier matrix to deliver them is essential for optimal bone regeneration within a specific defect site. Fused deposited modeling (FDM) allows for the fabrication of medical grade poly epsilon-caprolactone/tricalcium phosphate (mPCL-TCP) scaffolds with high reproducibility and tailor designed dimensions. Here we loaded FDM fabricated mPCL-TCP/collagen scaffolds with 5 microg recombinant human (rh)BMP-2 and evaluated bone healing within a rat calvarial critical-sized defect. Using a comprehensive approach, this study assessed the newly regenerated bone employing micro-computed tomography (microCT), histology/histomorphometry, and mechanical assessments. By 15 weeks, mPCL-TCP/collagen/rhBMP-2 defects exhibited complete healing of the calvarium whereas the non-BMP-2-loaded scaffolds showed significant less bone ingrowth, as confirmed by microCT. Histomorphometry revealed significantly increased bone healing amongst the rhBMP-2 groups compared to non-treated scaffolds at 4 and 15 weeks, although the % BV/TV did not indicate complete mineralisation of the entire defect site. Hence, our study confirms that it is important to combine microCt and histomorphometry to be able to study bone regeneration comprehensively in 3D. A significant up-regulation of the osteogenic proteins, type I collagen and osteocalcin, was evident at both time points in rhBMP-2 groups. Although mineral apposition rates at 15 weeks were statistically equivalent amongst treatment groups, micro-compression and push-out strengths indicated superior bone quality at 15 weeks for defects treated with mPCL-TCP/collagen/rhBMP-2. Consistently over all modalities, the progression of healing was from empty defect<mPCL-TCP/collagen<mPCL-TCP/collagen/rhBMP-2, providing substantiating data to support the hypothesis that the release of rhBMP-2 from FDM-created mPCL-TCP/collagen scaffolds is a clinically relevant approach to repair and regenerate critically-sized craniofacial bone defects.