| Biodegradable magnesium alloys as medical bone implant materials have full advantages and huge potential for development.Mg-Li-based alloys as ultra-lightweight alloys exhibit good properties required for alloy implants under certain conditions,and magnesium and lithium elements have inhibitory effects on tumor cells.Therefore,mg-Li alloy can be used in bone implant to support and inhibit tumor cells.In this paper,the commonly used Mg-xLi-Zn series alloys(xxx3wt%,6wt%,9wt%)were chosen to study the effects of different elements and contents on the microstructure and mechanical properties of the alloys,and to the bio-safety of the alloys.Full functionality was evaluated.In this paper,the microstructure and phase composition of the alloy were tested and analyzed by means of OM,SEM,XRD,and the effect of element content on the microstructure and phase composition of the alloy was studied.The degradation behavior of Mg-xLi-Zn alloy in simulated body fluid and ?-MEM complete medium suitable for cell growth was studied by electrochemical test,immersion test,SEM&EDS,XPS,pH detection and ion concentration measurement,respectively.Cell culture(human osteosarcoma MG-63 cells,osteoblast MC3T3 cells)was used to study the cytotoxicity and toxicity of alloy on two kinds of cells by MTT method and fluorescence staining method.The effect of mg-Li-based alloy on cell proliferation was studied by ALP activity assay and Annexin V-FITC/PI method,which provided a theoretical basis for the application of mg-Li-based alloy in bone implantation.The results of microstructure analysis showed that with the increase of lithium content in Mg-xLi-Zn alloy,the microstructure of the alloy was homogeneous distributed acicular phase with a small amount of precipitated phase in the coarse dendrite matrix.The phase composition of the alloy changes with a single ?-Mg phase and ?-Mg ?-Li dual-phase structure,and the mechanical properties of the alloy are changed due to the change of microstructure and phase composition.The results of in vitro degradation experiment show that with the prolongation ofthe time in the immersion medium,the alloy degrades gradually in varying degrees,and the pH value of the immersion medium increases gradually with the prolongation of the time during the degradation process.After dipping for 7 days,the value of pH increased from 7.4 to 9.5;The corrosion of the alloy containing 9wt% Li is the most serious corrosion pit,and the corrosion products are lamellae and keep falling off.The degradation of alloy in SBF and ?-MEM complete medium is different.In contrast,the alloy degrades rapidly in SBF and the pH increases rapidly,while the alloy is fully cultured in ?-MEM.The degradation rate of the alloy decreases slightly and the increase of pH value also slows because of the presence of protein in the base.The results of cell experiment showed that the alloy extract had no cytotoxicity to both MG-63 and MC3T3 cells during short-term immersion,and the alloy elements were released and accumulated continuously with the prolongation of immersion time.When the content of Li in the alloy accumulated to 8.9mmol/L,the toxicity to MG-63 cells began to increase with the prolongation of the culture time,and at the same time,with the decrease of ALP activity in the cells and the beginning of apoptosis in the cells;However,the alloy extract had no toxic effect on MC3T3 cells within 7 days of immersion,and did not affect the normal growth of MC3T3 cells and showed no effect on the growth of MC3T3 cells in Li.The activity of ALP in the cells was promoted within the range of 5mmol/L. |
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