Repair Of Rabbit Raidus’ Large Bone Defect By Porous CPC With Three Different Pore Sizes

Background: Repair of large bone defect caused by a variety of reasons hasbeen one of the greatest challenges for orthopaedic surgeon. Althoughimplantations of autogenous and allogenous bone graft has been considered asthe gold standard treatment, they have several disadvantages, such as theshortage of donor supply, the risk of virus transmission,immunological reactionand so on. With the development of tissue engineering technology, it has becomeone of the promising methods to repair large bone defects and has a broadapplication prospect. Bone tissue engineering comprises of three elements:scaffold, growth factors and seed cells and scaffold materials is a foundationamong them. Some related studies have showed that the structure of scaffold isan important morphological property which can affect materials’ mechanical andbiological properties. Therefore, the structure of scaffold is one important factorto be considered during the scaffold’ designing and selecting. The structuralparameters of scaffold include pore size, porosity, porous structure andconnectivity. The pore size, one of the most important factors, can significantly affect the proliferation and adhesion of cells and the new bone formation.Therefore, the researchers have been exploring the best pore size of the differentscaffolds to benefit the growth of bone. However, the optimum pore size ofscaffolds is still debated. Our previous results revealed that scaffolds withdifferent pore sizes showed significantly different ability to form the new bonefrom the distribution and abundance in the environment of non-bone andcancellous bone defect. In this study, three kinds of pore size (200-300μm,300-450μm,450-600μm) of CPC with the same porosity will be used to repairrabbit large weight-bearing bone defects in order to evaluate bone defectrepairing capacity of CPC with different pore sizes and screen out theappropriate pore size. In this way, we found the optimum pore size for thescaffold to achieve unification of osteogenesis and good biomechanics andprovide the basis for the clinical application.Objective: To investigate the effect of pore sizes of porous calcium phosphatecement on repair of large bone defect.Methods: Three kinds of CPC scaffolds with different pore sizes (200~300μm,300~450μm,450~600μm) but same porosity（68.3±3.3%） were manufacturedby salt fractionation. We implanted the scaffolds into the rabbit large bone defectmodel. At4,12and24weeks after the operation, we took the generalobservation, X-ray examination, serum bone alkaline phosphatase (ALP) testing,histology and biomechanical testing.Results: The X-ray examination showed that good bone healing occurred in thegroup which pore size is200~300μm in12weeks after the operation, at4and24weeks there were no significant difference among the three groups. The ALPvalues in200~300μm group were significantly higher than the other groups in4week（sP<0.05）, but there were no significant difference among the three groups in12and24weeks. Histomorphology analysis indicated that the area of newbone formation in200~300μm group was larger than the others in12weeks（P<0.05）, three groups of material new bone formation are higher percentagebut the difference was not statistically significan（tP>0.05）. The mechanical testshowed that the maximum compression load and elastic modulus in200~300μmgroup was significantly higher than the other groups in12weeks（P<0.05）, butthe results there were no significant difference among the three groups in24weeks（P>0.05）.Conclusions: Pore sizes can affect osteogenesis of scaffolds in vivo. Thesmaller pore sizes of scaffolds in the present study can stimulate the new boneformation.