| Objectives To make magnesium-doped brushite by adding magnesium ions to betatricalcium phosphate(β-TCP),and detecting of its physical and chemical properties.To compare the osteoblastic effect of cements in each group in rabbit radial bone defects,and to explore the feasibility of using Mg-doped brushite cement as the material to repair bone defect,and to provide the corresponding theoretical basis for clinical application.Methods β-TCP was prepared by sintering of calcium hydrogen phosphate dihydrate(Ca HPO4·2H2O)and calcium carbonate(Ca CO3),magnesium hydrogen phosphate three hydrate(Mg HPO4·3H2O)was used to prepare magnesium-substituted β-TCP(β-TCMP),resulting in a molar ratio of Mg/(Mg + Ca)was 6.67% and 26.67%.Brushite and Mgdoped brushite were prepared by β-TCP and β-TCMP reacting with calcium dihydrogen phosphate(Ca(H2PO4)2·H2O)respectively.To analysis the property,composition,morphological structure,compressive strength and biological safety of the cements by Xray diffraction(XRD),scanning electron microscopy(SEM),energy dispersive X-ray(EDX),universal material test machine and hemolytic test.90 healthy rabbits were randomly divided into normal group(n = 36),osteoporosis group(n = 36),osteoporotic castration control group(n = 9),osteoporotic blank control group(n = 9).After successful modeling of osteoporosis,normal group and osteoporosis group were randomly divided into blank control group,brushie group,magnesium-doped 6.67% brushite group and magnesium-doped 26.67% brushite group,with 9 rabbits in each group.All rabbits were defected 15 mm in bilateral radius,the blank control group was not filled with any material,and the rest of the experimental groups were filled with corresponding bone cements.Each group of three animals were killed at fourth,eighth,and twelfth week after operation,observing the image changes of bone defect by X-ray,and observing the expression and distribution of bone morphogenetic protein-2(BMP-2)by immunohistochemistry.To measure the average optical density(MOD)of BMP-2 with Image-Pro-Plus 6.0 software,comparing each group at the same and statistics processing.Results 1 The changes of XRD and EDX showed that Mg2+ successfully replaced the Ca2+ in β-TCP and brushite,and XRD showed that the main diffraction peak of brushite was shifted to larger angle after the incorporation of magnesium;SEM showed the brushite was irregular lamellar crystal and plate crystal,and the magnesium-doped brushite was mostly lumpy crystal with different sizes of micropore among crystals;The compressive strength of magnesium-brushite decreased,namely that the more of magnesium the lower of compressive strength;Hemolysis test showed that the hemolysis rate of bone cements was less than 5%,will not cause hemolysis.2 The results of animal experiment showed that the dissolution rate of magnesium-doped brushite was faster than brushite,and the repair time of bone defect was shorter than brushite group;There was still a large area of defects in the blank group of normal rabbits and osteoporotic rabbits at 12 th week;The bone defects of magnesium-doped brushite group of normal rabbits have been basically repaired at 8th week,while the brushite group repaired until at 12 th week;The bone defects of magnesium-doped 6.67% and 26.67% brushite group of osteoporosis rabbits have been basically repaired at 12 th week,while partial defect of brushite group repaired,unfinishing the renovation of bone defects,the defect was concave and the bone defect was obviously delayed.3 Immunohistochemistry showed that the expression level of BMP-2 was the highest at 4th week,the proliferation of osteoblasts was actively,and decreased graduallyat 8th week and 12 th week;the difference between the groups were statistically significant at 4th week and 8th week(P < 0.05);The difference between the normal group and the osteoporosis group was statistically significant at 4th week and 8th week(P < 0.05).Conclusions 1 The experimental results confirmed that magnesium-doped brushite could be successfully prepared by the incorporation of magnesium hydrogen phosphate trihydrate into β-TCP in the process of high temperature sintering.2 Mg-doped 6.67%and 26.67% brushite could promote the expression of BMP-2 in the early stage of bone repair;3 Mg-doped 6.67% and 26.67% brushite could significantly shorten the repair time of radial bone defects and promote the healing of osteoporotic bone defects,and the effect of Mg-doped 6.67% brushite was more significant. |
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