Study On Degradation Behavior Of RhBMP-2 Porous Magnesium Alloy And Repair Of Bone Defects

Biomagnesium alloy has the advantages of good degradability,avoidance of stress shielding effect and osteoinductivity.Its porous structure can promote the flow of nutrients and cell adhesion,and enhance the bonding strength of bone and scaffold.However,the degradation rate of porous magnesium scaffold in vivo was too fast,which may result in implantation failure.In this study,we introduced a composite coating carrying rhBMP-2 to improve the degradation of magnesium scaffold,and study whether the porous structure of magnesium scaffold and the osteogenic protein factor rhBMP-2 can synergistically promote the growth of new bone along the scaffold holes and repair the femoral condyle defect in rats.In this paper,an anisotropic porous ZE21C alloy scaffold with a porosity of 50%and a pore size of 500 ?m was designed based on bone biomechanics.Porous scaffolds were prepared by mechanical electrical discharge machine.Racemic polylactic acid,which can be loaded with rhBMP-2,was selected as the coating material to evenly coat the surface of scaffolds after passivation pretreatment to achieve slow release of growth factor rhBMP-2 and reduce the degradation rate of porous scaffolds.SEM and compression test were used to analyze pore size and implant support strength of the scaffolds.Microstructure observation was used to analyze whether the mechanical processing can change the grain size and morphology of the materials.SEM?XRD?XPS tests were used to analyze the coating uniformity.The degradation of porous magnesium scaffold in vitro was studied by electrochemical and immersion weight loss tests.A rat femoral condyle defect model was established and the entire femur was removed after different experimental periods.SEM & EDS and Micro-CT reconstruction were used to analyze the degradation of porous magnesium scaffolds in vivo,and compare the degradation behaviors of porous scaffolds in vivo and vitro.DR and Micro-CT imaging were used to analyze the performance of porous scaffolds in vivo osteogenesis and bone defect repair.In order to study the effect of porous structure on the growth of new bone,the rat femoral condyle was subjected to hard tissue cutting with HE staining?methylene blue basic fuchsin and fluorescence labeling analysis.Finally,the femoral condyles implanted with porous scaffolds at different times were analyzed by decalcification HE staining to determine the changes in bone tissue healing morphology.The results of microstructure analysis and performance test of porous scaffolds revealed that mechanical micro-machining did not change the microstructure of the material,and the mechanical properties of porous scaffolds basically met requirements.The coating test results indicated that the composite coating was evenly coated on the scaffold surface,which reduced the degradation rate of scaffold and improved the stability of scaffold implantation.SEM & EDS analysis showed that rhBMP-2-loaded porous scaffolds could accelerate cell adhesion,form extracellular matrix and promote new bone formation;with the extension of time,the interface between porous scaffolds and bone gradually shrank and was replaced by degradation products and new bone.The degradation products were composed of magnesium hydroxide,osteoid and calcium phosphate salt.The calcium phosphate salt deposited in the osteoid was recognized and absorbed by osteoclasts to form new bone.DR and Micro-CT imaging analysis showed that the porous scaffold did not shift and fall during the healing cycle,and maintained a complete appearance at 2 weeks after surgery.The average degradation rate of porous scaffold in vivo was 0.54 mm/year was much lower than the in vitro degradation rate of 6 mm/year.The new bone grew along the holes and around degradation of the scaffold,and gradually matured.At 20 weeks after the operation,trabecular bone structure was formed and well healed.The results of HE,methylene blue basic fuchsin and fluorescent label analysis indicated that new bone could grow along the scaffold holes and connected with each other to form trabecular structure.In conclusion,an anisotropic porous magnesium scaffold with porosity of 50%and pore size of 500 ?m coated with rhBMP-2 composite coating can promote the growth of new bone along the scaffold holes and connect to each other to form a good bone trabecular structure,achieve the purpose of high-quality repair of bone defects,and provide new ideas for clinical bone injury repair treatment.