Tyrosine-derived polycarbonate scaffolds for bone regeneration in a rabbit radius critical-size defect model

The aim of the study was to determine bone regeneration in a rabbit radius critical-size defect (CSD) model using a specific polymer composition (E1001(1k)) from a library of tyrosine-derived polycarbonate scaffolds coated with a calcium phosphate (CP) formulation (E1001(1k) + CP) supplemented with recombinant human bone morphogenetic protein-2 (rhBMP-2). Specific doses of rhBMP-2 (0, 17, and 35 μg/scaffold) were used. E1001(1k) + CP scaffolds were implanted in unilateral segmental defects (15 mm length) in the radial diaphyses of New Zealand White rabbits. At 4 and 8 weeks post-implantation, bone regeneration was determined using micro-computed tomography (µCT), histology, and histomorphometry. The quantitative outcome data suggest that E1001(1k) + CP scaffolds with rhBMP-2 were biocompatible and promoted bone regeneration in segmental bone defects. Histological examination of the implant sites showed that scaffolds made of E1001(1k) + CP did not elicit adverse cellular or tissue responses throughout test periods up to 8 weeks. Noteworthy is that the incorporation of a very small amount of rhBMP-2 into the scaffolds (as low as 17 μg/defect site) promoted significant bone regeneration compared to scaffolds consisting of E1001(1k) + CP alone. This finding indicates that E1001(1k) + CP may be an effective platform for bone regeneration in a critical size rabbit radius segmental defect model, requiring only a minimal dose of rhBMP-2.