3D Printed Polycaprolactone/beta-tricalcium Phosphate/magnesium Peroxide Oxygen Releasing Scaffold Enhances Survival Of Seed Cells And The Repair Of Bone Defect

Background:Repair of large bone defects still remains a major clinical challenge even after much studies.Cells in bone defect area are exposed to hypoxic microenvironment due to the far distance of cells from capillaries at early stage,which is considered to be a key factor that increases the difficulty of repairing bone defects.So far,the combined use of oxygen release materials and bone marrow mesenchymal stem cells(BMSCs)in bone defects are extensively studied.Hydrogen peroxide(H2O2)and calcium peroxide(CaO2)are the two most common O2 sources that have been used.But the oxygen release curves are not satisfactory.Rapid and massive O2 release will cause local cytotoxic hyperoxia while short-time O2 release cannot compensate the diffusion limit of oxygen before new capillaries are formed in defect areas.magnesium peroxide(MgO2),as another common solid peroxide,has rarely featured in oxygen generating biomaterials.MgO2 has the slowest O2 release kinetics and lowest cytotoxicity because of its low decomposition rate,which may be an advantage for oxygen generating biomaterials.Another notable advantage of MgO2 is the release of magnesium ion(Mg2+).Mg2+is an important divalent ion which involved in bone development by promoting osteogenic differentiation of BMSCs and enhance the adhesion and spreading of osteoblasts and promote the mineralization process.So,we tried to construct a novel MgO2-based oxygen release scaffold.Objective:1.To construct a novel MgO2-based oxygen released bioscaffold by three-dimensional(3D)printing and detect its physical and chemical properties.2.To study the effects of MgO2 scaffold on survival,proliferation,migration and osteogenic differentiation of bone marrow mesenchymal stem cells under hypoxia in vitro.3.To study the effects of MgO2 scaffold on large bone defect repair in vivo.Methods:1.Use 3D printing technology to construct a polycaprolactone(PCL)/beta-tricalcium phosphate(β-TCP)/magnesium peroxide(MgO2)scaffold.Use Scanning Electron Microscope(SEM)to observe its morphology.Its mechanical performance and oxygen/magnesium ion release curves are also tested.2.Use relative staining tests and quantitative tests to prove the promoting role of MgO2 scaffold in cell survival,proliferation,migration and osteogenic differentiation under hypoxia when co-culture with BMSCs in vitro.3.Use micro-CT,masson staining and immunofluorescence to verify the promoting effect of MgO2 scaffold in Sprague Dawley(SD)rats femoral condyle defect repair after in vivo implantation.Result:1.Corresponding assay proved the suitable mechanical property and sustained O2/Mg2+release behaviour of MgO2 scaffold.2.In vitro,live/dead cell staining and EdU assay proved the promoting effect of MgO2 scaffold on the survival and proliferation of BMSCs under hypoxia.Transwell assay showed that MgO2 scaffold enhances the migration of BMSCs.Several osteogenesis-related assay also proved the pro-osteogenic effect of MgO2 scaffold.3.Micro-CT and masson staining showed that the implantation of MgO2 scaffold can promote the repair of SD rat femoral condyle defect model.Immunofluorescence result proved that MgO2 scaffold enhances the survival of implanted BMSCs.Conclusion:1.The MgO2 scaffold construct by 3D printing has satisfactory physical and chemical properties.2.The MgO2 scaffold can promote survival,proliferation,migration and osteogenic differentiation of bone marrow mesenchymal stem cells under hypoxia;the result of femoral condyle defect model confirmed that the scaffold can promote bone defect repair in vivo.