The In Vitro Study Of Strontium-calcium Sulfate Compounds As Bioactive Bone Grafted Substitute

Objective: Bone defect and nonunion are still the dilemmas of reconstructive orthopedic surgery nowadays. Autograft, allograft and synthetic bone substitute materials play important roles in treating the problems, but they have their intrinsic disadvantages and cannot meet the demands in all situations. For the destination of overcoming the disadvantages, scholars in the medical field and biomaterial science field have focus much energy on the preparation of an ideal biomaterial to replace bone graft and to repair bone defect. Calcium sulfate is an osteoconductive material, and it is well tolerated by tissues. Meanwhile, strontium has been gradually recognized during the research of treatment for osteoporosis. It enhances the replication of preosteoblastic cells and decreases bone resorption. In this study we will invent a strontium-Calcium sulfate compounds to make a new bioactive material with osteoconductive and osteoinduceable activity for bone repairing in clinic.Methods: Powders of a-calcium sulfate hemihydrate and SrC12 was mixed completely to make Sr-calcium sulfate compounds materials with 6 different concentration of Sr, which contains 0%,1%,0.3%,0.5%,1% and 2% of Sr. Then the materials were prepared to be cylinders shaped as 5mmxl2mm and discs shape as 15mm×2mm. Scanning electron microscope (SEM) was used to observe the configuration of the new materials. And the compressive strength of the materials were tested. The materials were soaked into simulated body fluid (SBF) to test the features of degradation, which includes pH, weight loss, compressive strength decline and the changes of ion concentration of strontium. Then the leaching liquor of materials with different strontium concentration was used to do cytotoxicity test with ROS17/2.8 cell line, and cell proliferation were tested by MTT method. The ALP activity was tested in cells treated with different leaching liquors of the different materials. Histochemical method was also used to test the function of ALP in cells. The cells were seeded onto discs made with materials with different strontium concentrations and cultured for 4 days. The cells' number was counted in 2 and 4 days, and the cells were observed with SEM.Results: All of the strontium-Calcium sulfate compounds made in this study seem to be the same with naked eyes. The crystal appearances are influenced by incorporating of strontium. The crystal appearance will be uneven and spared as the concentration of strontium reach to 2%. The compressive strength of non-strontium incorporating calcium sulfate is 15.85±1.58 Mpa. And as the concentration of strontium increasing the compressive strengths of the materials trends to decline. The compressive strength reached to 8.66±1.40 Mpa as strontium concentration reached to 2%. The pH value of the SBF declined the time of degradation increased but all of them are very stable. All of materials got weight loss after soaked in SBF for several of weeks. The weight loss is slightly in 4 weeks and it became dramatic after 4 weeks. There is no significant difference between 0.1% and 0.3% strontium contained materials considered of weight loss (P=0.988, P=0.158). As the concentration of strontium increasing, the weight loss is becoming more rapid and significant. The compressive strength also decreased during degradating in SBF. The strength decreased slower during 0-4 weeks as the strontium concentration below 0.5%; and as the strontium concentration become higher, the decrement of strength became faster. The strength of strontium incorporated materials decreased much faster as compared with non-strontium incorporated materials (P=0.988, P=0.158) . The concentration of ion strontium in SBF increase faster after 4 weeks during degradating in SBF. As the concentration of strontium increasing, the strontium ion concentration in SBF became higher, and it reached to 64.63±9.47μmol/L in SBF contained 0.1% Sr-contained materials to 175.64±11.25μmol/L in SBF contained 2% sr-contained materials. All of strontium-Calcium sulfate compounds were proven to be without cytotoxicity. The OD value of MTT test demonstrated the leaching liquor of strontium incorporated materials has some beneficial outcome with cell multiplication of ROS17/2.8 cell line (P<0.05) . Strontium incorporated materials also can increase activity of ALP in cells (P<0.05), especially when it contain 0.5% strontium. The cells can live and grow well in the compound materials. There is no statistical differences in cell number between experiment and control groups (P>0.05) .Conclusion: (1) The new compound materials made by mixing of a-calcium sulfate hemihydrate and SrC12 can provide some compressive strength for supporting in defected area in bone. (2)The feature of degradation of the materials are very stable. The new materials can release a lot of bone inducible substance—strontium ion to repair bone defection after 4 weeks degradation. (3)The new materials do no harms to cells, and can promote the function of osteoblast like cells. (4) The new materials has good cell compatibility, osteoblast like cells can live and grow well on it. (5) It can be concluded that the new materials can release strontium ion which can induce bone formation during repairing process in bone defect areas.