| Objective:Because of their high mechanical strength and fracture resistance stainless steel,titanium alloy and cobalt alloy are widely used in orthopedic implant.But their elastic modulus are much higher than that of human bone,which is easy to produce“stress shielding effect" and affect bone tissue remodeling.At the same time,it often needs a second operation to be taken out,which increases the pain and economic burden of patients.Because of their good biocompatibility,biodegradability,osteogenic activity,safety and low price,magnesium and its alloys have attracted more and more attention of the researchers.Two new magnesium alloys,Mg-2Zn-0.5Zr-0.5Nd and Mg-2Zn-0.5Zr-0.5Y,were prepared by the Institute of metals,Chinese Academy of sciences through casting and hot extrusion.In this study,the material properties,biocompatibility,antibacterial activity and in vivo safety of Mg-2Zn-0.5Zr-0.5Nd and Mg-2Zn-0.5Zr-0.5Y alloys were studied,analyzed and evaluated comprehensivelyMethods:This research was carried out in four aspects:material properties evaluation,in vitro cell experiment,in vitro antibacterial experiment and in vivo implantation experiment.Material properties evaluation:In this study,the actual chemical composition of the alloy was detected by ICP-OES,and the metallographic structure of the material was observed after etching with picric acid.The yield strength,tensile strength,elongation and elastic modulus of the alloy were tested by tensile test,knocking test,and the fracture morphology was observed.According to international standard(ASTM G31-72),pure Mg,Mg-2Zn-0.5Zr-0.5Nd and Mg-2Zn-0.5Zr-0.5Y were immersed in ?-MEM medium containing 10%FBS in a cell incubator containing 5%CO2 at 37? at an immersion ratio of 20 mL/cm2 for 3 and 10 days,the ion concentration in the solution was measured,the surface morphology of the sample was observed,the corrosion rate was calculated,and the surface composition was analyzed by XRD and EDS.Pure Mg,Mg-2Zn-0.5Zr-0.5Nd and Mg-2Zn-0.5Zr-0.5Y alloys were immersed in ?-MEM medium containing 10%FBS at 37? for electrochemical experiments.The electrochemical impedance curve and potentiodynamic polarization curve were measured.Mg-2Zn-0.5Zr-0.5Nd alloy was loaded at 15 Hz by electronic universal testing machine.True S-N curve was measured and fracture morphology was observed Mg-2Zn-0.5Zr-0.5Nd alloy was immersed in Hank's solution for 7,30,60 and 90 days,then loaded at 2Hz by electronic universal testing machine,the number of fracture cycles was recorded and the fracture morphology was observedIn vitro experiment:The pure Mg,Mg-2Zn-0.5Zr-0.5Nd and Mg-2Zn-0.5Zr-0.5Y alloy were co cultured with mouse embryonic osteoblast precursor cells(MC3T3-E1 cells)for 4 hours and 24 hours.The adhesion of cells on different material surfaces was observed by SEM.According to the international standard(ISO 10993 Part 12),the extracts was prepared at an immersion ratio of 1.25 cm2/mL,and then it was diluted 6 times for cell experiments.MC3T3-E1 cells were subcultured for 24,48 and 72 hours with Mg-2Zn-0.5Zr-0.5Nd and Mg-2Zn-0.5Zr-0.5Y alloy extracts.The cytotoxicity and proliferation of MC3T3-E1 cells were detected by CCK8 test.The cytoskeleton of MC3T3-E1 cells was observed by fluorescence staining of rhodamine labeled Phallin after 4 hours and 24 hours culture in pure Mg and Mg-2Zn-0.5Zr-0.5Nd alloy extracts MC3T3-E1 cells were cultured with pure Mg,Mg-2Zn-0.5Zr-0.5Nd and Mg-2Zn-0.5Zr-0.5Y alloy extracts for 7 and 14 days,and the ALP expression was observed MC3T3-E1 cells were cultured with pure Mg and Mg-2Zn-0.5Zr-0.5Nd alloy extracts for 3 and 7 days.The expression of CoL-I,OCN and TRPM7 was detected by Q-PCR In vitro antibacterial experiment:S.aureus and E.coli were cultured with pure Mg,Mg-2Zn-0.5Zr-0.5Nd alloy and control group 316 stainless steel for 1 day and 3 days respectively.The alive adherent bacteria and planktonic bacteria were counted by plate method.PH value and ion concentration in the medium was measured.The adhesion of S.aureus on the surface of Mg-2Zn-0.5Zr-0.5Nd alloy were observed by scanning electron microscopy,and the surface composition of the material after 1 day was analyzed by EDSIn vivo experiment:The mandibles of male New Zealand white rabbits were prepared with a defect with a diameter of 10 mm and a depth of 2 mm.Pure Mg and Mg-2Zn-0.5Zr-0.5Nd alloy of the same size were implanted into the defect.After 12 weeks,the osteogenesis was observed by gross specimen and micro-CT Results:Material properties evaluation:The chemical composition of Mg-2Zn-0.5Zr-0.5Nd alloy is Zn 1.67 wt%,Zr 0.52 wt%,Nd 0.34 wt%;Mg-2Zn-0.5Zr-0.5Y is Zn 1.62 wt%,Zr 0.55 wt%,Y 0.38 wt%;the grain size of the two alloys is about 4-5 ?m In the tensile test,the yield strength,tensile strength,elongation and modulus of elasticity of the two alloys were higher than those of pure Mg,and there was a statistical difference(p<0.05).The fracture morphology was consistent with the ductile fracture In the immersion experiment,the corrosion rate was Mg-2Zn-0.5Zr-0.5Y>Mg-2Zn-0.5Zr-0.5Nd>pure Mg after immersion for 3 days and 10 days.There were significant differences between Mg-2Zn-0.5Zr-0.5Y and pure Mg after immersion for 3 days.On day 10,there were significant differences between Mg-2Zn-0.5Zr-0.5Y other groups The results of ion concentration measurement are consistent with the trend of corrosion rate.Corrosion pits can be seen in pure Mg and Mg-2Zn-0.5Zr-0.5Nd,and deep pits can be seen in Mg-2Zn-0.5Zr-0.5Y.The results of EDS showed that Zn and Zr were on the alloy surface,and XRD showed that Mg3(PO4)2 and Ca3(PO4)2 were on the alloy surface 10 days after immersion.In the electrochemical experiment,the impedance curve showed that the corrosion resistance of pure Mg was higher than that of the alloys,the Ecorr of the alloy in the potentiodynamic polarization curve was higher than that of pure Mg(p<0.05),and icorr of the alloys were higher than that of the alloy(p<0.05)In the fatigue test,the fatigue strength of Mg-2Zn-0.5Zr-0.5Nd alloy is 107.5 MPa With the increase of immersion time,the number of fatigue cycles decreases gradually In vitro experiment:In the cell adhesion experiment,MC3T3-E1 cells adhered on the surface of all three materials at 4 h,a large amount of cells on pure Mg were round-shaped,and a large number of cells on the surface of Mg-2Zn-0.5Zr-0.5Nd could be seen to spread well.24 h later,they all spread well.In CCK8 test,Mg-2Zn-0.5Zr-0.5Nd alloy and pure Mg extract promoted cell proliferation,and all the groups were non-toxic.The RGR of Mg-2Zn-0.5Zr-0.5Nd at 72 hours was significantly higher than that of other groups(p<0.05).After 24 hours,the F-actin expression in Mg-2Zn-0.5Zr-0.5Nd extract was higher than that in pure Mg.In ALP staining,ALP expression in Mg-2Zn-0.5Zr-0.5Nd group was significantly higher than that in other groups on the 7th and 14th day.In q-PCR,Mg-2Zn-0.5Zr-0.5Nd alloy extract increased the mRNA expression of OCN and Col-I at 3 and 7 days(p<0.05).There was no significant difference in the expression of TRPM7 between pure Mg and Mg-2Zn-0.5Zr-0.5Nd alloy(p>0.05)In vitro antibacterial test:Compared with 316 stainless steel in the control group,pure Mg and Mg-2Zn-0.5Zr-0.5Nd alloy showed antibacterial effect on S.aureus and E.coli in both adherent bacteria and planktonic bacteria,and there was no statistical difference between the two groups(p>0.05).SEM showed that bacteria still adhered to the surface of the material after 1 day of co culture.Most of the bacteria adhered to the surface of pure magnesium were round-shaped while the bacteria on the surface of Mg-2Zn-0.5Zr-0.5Nd were shriveled and shrunk;the bacteria on the surface of both materials were shriveled and shrunk after 3 daysIn vivo experiment:The in vivo experiment showed that after 12 weeks' implantation,micro-CT showed that Mg-2Zn-0.5Zr-0.5Nd alloy was well combined with the bone,and osteolysis occurred in the pure Mg groupConclusions:1.Compared with pure Mg,the mechanical properties of hot extruded Mg-2Zn-0.5Zr-0.5Nd and Mg-2Zn-0.5Zr-0.5Y alloys are significantly improved.The corrosion resistance is not significantly improved,but not significant different from that of pure Mg after immersion for a long time2.The extracts of Mg-2Zn-0.5Zr-0.5Nd alloy can promote the proliferation of MC3T3-E1 cells and is non-toxic to cells,and Mg-2Zn-0.5Zr-0.5Y alloy extract is non-toxic to cells.MC3T3-E1 cells can adhere on the surface of Mg-2Zn-0.5Zr-0.5Nd and grow well.Mg-2Zn-0.5Zr-0.5Nd alloy extract promoted the early adhesion and F-actin expression of MC3T3-E1 cells.Mg-2Zn-0.5Zr-0.5Nd alloy extract has good osteogenesis to MC3T3-E1 cells3.Mg-2Zn-0.5Zr-0.5Nd alloy has antibacterial effect on S.aureus and E.coli in vitro 4.After 12 weeks implantation of Mg-2Zn-0.5Zr-0.5Nd alloy into the mandible of New Zealand white rabbits,it showed good biological safety and osteogenesis. |
PDF Full Text Request