BACKGROUND:Our previous studies found that adding barium sulfate could improve the mechanical and radiopaque properties of calcium phosphate cement.However,with the degradation of calcium phosphate,the remaining radiopaque agent is difficult to degrade,and the space-occupying and osteoclast effects at the implantation site affect the bone repair process.Therefore,it is necessary to develop a new biodegradable radiopaque material. OBJECTIVE:To discuss the radiopaque ability of bioactive degradable material strontium polyphosphate(SrPP)and its impact on the physicochemical properties and osteogenic effect of calcium phosphate cement. METHODS:(1)Calcium phosphate cement(CPC),starch modified calcium phosphate cement(CPS)and starch modified calcium phosphate cement(20%SrPP-CPN)containing SrPP(20%mass fraction of bone cement powder)were prepared respectively,and the physicochemical properties of the three groups of bone cements were characterized.(2)The three groups of bone cement extracts were co-cultured with rat bone marrow mesenchymal stem cells,respectively,to detect cell proliferation,energy metabolism,and osteogenic differentiation.(3)Bone defects with a diameter of 5 mm were made on each side of the top of the skull of 24 SD rats,and they were randomly divided into control group(without any intervention),CPC group,CPS group,and 20%SrPP-CPN group for intervention,with 6 rats in each group.Relevant tests were performed after 4 and 12 weeks of intervention. RESULTS AND CONCLUSION:(1)Compared with the other two groups of bone cement,20%SrPP-CPN had enhanced radiopaque ability,increased compressive strength and degradation rate,and prolonged curing time,and 20%SrPP-CPN could release Sr2+ stably during degradation.(2)CCK-8 assay showed that 20%SrPP-CPN did not affect the proliferation of bone marrow mesenchymal stem cells.Cell starvation test(serum-free culture)showed that 20%SrPP-CPN could promote the proliferation of bone marrow mesenchymal stem cells compared with the other two groups of bone cement.Compared with the other two groups of bone cements,20%SrPP-CPN increased adenosine triphosphate concentration in bone marrow mesenchymal stem cells.Alkaline phosphatase and alizarin red staining showed that 20%SrPP-CPN could promote osteogenic differentiation of bone marrow mesenchymal stem cells compared with the other two groups of bone cement.(3)In the rat skull defect experiment,Micro-CT scanning and histological observation(hematoxylin-eosin and Masson stainings)showed that bone cement in 20%SrPP-CPN group was significantly degraded compared with that in CPC and CPS groups,and a large number of new bone tissues were dispersed in degraded bone cement.Immunohistochemical staining showed that Runx2 protein expression was increased in 20%SrPP-CPN group compared with CPC group and CPS group(P＜0.01).(4)These results show that 20%SrPP-CPN has good radiopaque ability and osteogenic properties.