| Purpose:Core decompression is considered one of the optimal treatment options for the early stages of osteonecrosis of the femoral head(ONFH).Necrotic bone tissues could be removed by drilling into the femoral head,resulting in a dramatic decline in intramedullary pressure thus improving venous return and promoting bone regeneration.Nevertheless,bone defects caused by core decompression are difficult to regenerate,consequently leading to further collapse of the articular surface.Herein,based on the reported osteogenic and angiogenic properties of strontium(Sr)ions,a strontium carbonate-enhanced calcium phosphate nanocomposite(Sr-CPN)was developed to repair the defects caused by core compression,and the collapse of the articular surface of the femoral head could be avoided by the mechanical support of the material as well as the necrosis of the femoral head could be treated by vascularized bone regeneration.Methods:Based on our previous studies,Sr-CPN was prepared by mixing calcium phosphate cement(CPC),corn starch,barium sulfate,and strontium carbonate at a mass ratio of 5.5:2:1:1.5 with 0.25 M Na2HPO4 solution at a liquid-solid ratio of 0.4 mL/g.The physicochemical properties,namely injectability,setting time,and mechanical properties of Sr-CPN were characterized using injection test,Vicat needle test,and mechanical compression test.The microstructure was observed by scanning electron microscopy and transmission electron microscope,and the phase composition transformation process during solidification was analyzed by X-ray diffraction.The ion release process after degradation was studied by liquid immersion experiment.In addition,finite element analysis was used to simulate human ONFH with material implantation,and the mechanical support effect,stress distribution,and anti-collapse degree of Sr-CPN were observed.Mouse osteoblast precursor cells(MC3T3-E1)and human umbilical vein endothelial cells(HUVECs)were used to respectively evaluate the biocompatibility of Sr-CPN by CCK-8 and live/dead staining.The effect of Sr-CPN on osteogenic differentiation of MC3T3-E1 was further studied by alkaline phosphatase(ALP)staining,ALP activity,alizarin red staining and PCR detection of osteogenic related gene expression,and the bone repair ability of Sr-CPN in vivo was studied in rat calvarial defect model.At the same time,the adhesion and proliferation of HUVECs on Sr-CPN surface were studied by scanning electron microscopy(SEM)and phalloidin immunofluorescence staining.In addition,cell scratch assay,Transwell migration assay,tube formation assay and PCR analysis were performed to evaluate the proliferation,migration and angiogenic ability of Sr-CPN.Simultaneously,rat subcutaneous implantation model was established to examine the angiogenic effects after material implantation in vivo.Finally,a rabbit ONFH model with core decompression and bone cement implantation was established to evaluate the ability of Sr-CPN to promote ONFH repair.The compressive strength,blood perfusion,and the repair of cartilage surface and subchondral bone of the femoral head were observed three months after implantation.Results:According to the test outcomes,Sr-CPN showed satisfactory performance for injection and anti-collapse.The initial setting time of Sr-CPN was 20.70 min,which fully met the requirements of clinical minimally invasive operation.Similar as our previous calcium phosphate nanocomposite(CPN),the compressive strength of Sr-CPN was 45.52±2.64 MPa which was strong enough to offer mechanical support.During solidification,the α-TCP in Sr-CPN gradually transformed into hydroxyapatite.Ca2+ and Sr2+sustained-release during degradation.Furthermore,finite element analysis showed that the filling of Sr-CPN after core decompression reduced the collapse value from 2.14 mm to 2.06 mm compared with the non-filling group.The high stress distribution on the stress surface of the femoral head also decreased,which proved that Sr-CPN had a mechanical support effect on the femoral head that was about to collapse.Sr-CPN was biocompatible with both MC3T3-E1 and HUVECs,as determined from the results of CCK-8 and live/dead staining.PCR analysis results showed that the incorporation of SrCO3 into CPN upregulated the expression of osteogenic genes of MC3T3-E1 and angiogenic genes of HUVECs,respectively.In addition,alkaline phosphatase and alizarin red staining showed Sr-CPN could promote alkaline phosphatase secretion and calcium nodule formation during osteogenic differentiation of MC3T3-E1 cells.Moreover,it enhanced the cell adhesion,migration,and tube formation of HUVECs.Animal experiments further confirmed that the implantation of Sr-CPN was helpful in repairing calvarial defects in rats.Micro-CT analysis revealed that the bone volume ratio was 19.35%in defects,which was much higher than that of the group without implantation(7.68%).New bone formation was observed using histological staining,with a high expression of osteogenic factors around the Sr-CPN.Evident neovascularization was observed around Sr-CPN in the subcutaneous connective tissue of rats.The results showed more blood vessels and bone tissue regeneration around the materials following Sr-CPN tamponage rather than CPN tamponage in the core decompression channels of the rabbit ONFH model,thus protecting the subchondral bones of the femoral head from destruction.Conclusions:The improved injection and anti-collapse abilities of Sr-CPN,with a suitable setting time,makes it a beneficial option in clinical minimally invasive surgery.Finite element analysis confirmed that Sr-CPN implantation after core decompression in ONFH could provide mechanical support for the necrotic area of the femoral head and prevent further collapse of the cartilage surface.Simultaneously,compared with CPN,the dual osteogenic and angiogenic effects of Sr-CPN contribute to vascularized bone regeneration in the necrotic areas of the femoral head.Therefore,Sr-CPN is expected to provide a new treatment option for early stages of ONFH. |
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