Assessment of calcium sulfate hemihydrate–Tricalcium silicate composite for bone healing in a rabbit femoral condyle model

Calcium sulfate or plaster of Paris (POP) is considered as a bone cement with a fast degradation rate, which frequently makes it resorb before the bone defect area is completely filled by new bone. The incorporation of tricalcium silicate (C3S) into POP cement has been proven as a feasible approach to reduce the in vitro degradation rate and improve the in vitro bioactivity of the material. However, the in vivo performance of the POP/C3S composite cement is still unclear. Therefore, the aim of the present study is to assess the biodegradability and osteogenesis of POP/C3S composite cement in comparison with those of POP bone cement. To carry out the in vivo evaluation, POP and POP/C3S cements were implanted into a femoral condyle defect model in rabbits (5 mm diameter × 10 mm length) for 4, 8, and 12 weeks duration. The area of the remaining cement and new bone regeneration in bone defect were investigated and quantitatively measured using radiography, micro-computed tomography, and histological staining. For both cements, no sign of inflammation was observed. POP cement was completely degraded at the 8th week of post-implantation. By contrast, only approximately 50% by volume of POP/C3S composite cement degraded at the 12th week, which allowed a long-term framework for new bone formation. The osteogenic ability of POP/C3S composite cement was significantly superior to that of POP as indicated by the higher mineralization rate and maturity of the newly formed bone around the composite cement. In summary, our findings demonstrated that the in vivo degradation behaviors and osteogenic ability of POP cement could be improved by incorporating C3S in vivo, suggesting that POP/C3S composite cement has potential as a biodegradable cement for bone repair.