In-vitro Degradation Behaviors And Biocompatibility Of Mg-Zn-Y-Nd-Zr Alloys As Novel Orthopaedic Implant Materials

Mg-Zn-Y-Nd-Zr alloy is developed as a new type of biodegradable orthopaedic implant materials by the author' research group.By extrusion process and adding multiple trace elelments,such as Zn,Y,Nd,and Zr,the mechanical properties and corrosion resistance are improved on a large extent.Compared with WE 43 alloys,the yield strength of as-extruded Mg-Zn-Y-Nd-Zr is improved by nearly 18%,and the corrosion resistance have been increased by nearly 70%,showing great potential as a candidate for orthopaedic implant applications.The biological safety and biocompatibility of biomedical materials must be evaluated in vitro and in vivo thoroughly before its clinical application eventually.In this thesis,a series of in vitro experiments were carried out to evaluate the microstructure and biodegradation behaviors of as-extruded Mg-Zn-Y-Nd-Zr alloy.The electrochemical workstation,pH measurement,weight loss,scanning electron microscope equipped with energy dispersive X-ray spectroscopy were used to analyse the different corrosion behaviors of Mg-Zn-Y-Nd-Zr in simulated body fluid(SBF),simulated body fluid with 10% fetal bovine serum(SBF+10%FBS),DMEM/F12 cell culture medium,MEM cell culture medium and MEM with no phenol red cell culture medium.The influences of different components in the immersion medium on the degradation behavior were investigated.Through the in vitro cell culture,MTT assay and cell morphology observation using the inverted microscope were used to evaluate the cytotoxicity of Mg-Zn-Y-Nd-Zr alloy,and the accumulated ion concentrations in extracts.Both murine fibroblast cells(L929)and murine calvarial preosteoblasts(MC3T3-E1)were utilized in the cytotoxicity evaluation.Alkaline phosphatase test were used to analyse differentiation of BMSCs and alizarin red S(ARS)were used to stain the calcified nodules of BMSCs after co-culture with degradation products of MgZn-Y-Nd-Zr alloy.As-extruded Mg-Zn-Y-Nd-Zr alloy degraded gradually,as shown in the inmersion experiments.The average degradation rate of the alloy during a 10-day immersion in SBF was 0.0932 mg/(cm2·h),while the corresponding value in ?-MEM,MEM with no phenol red and DMEM/F12 were 0.013?0.013?0.016 mg/(cm2·h)respectively.Since the corrosion mediums contained different inorganic salts,proteins,amino acids and buffers,the degradation rates of Mg-REEs changed dramatically accordingly.The nutritional components in different cell culture mediums varied slightly,which affected the degradation behaviors to a large extent.For example,the alloy degraded more slowly in ?-MEM(for the culture of L929 and MC3T3-E1)and MEM with no phenol red(for cytotoxicity test)than in DMEM/F12(for the culture of BMSCs).The cytotoxicity results indicated that the extracts of Mg-Zn-Y-Nd-Zr alloy showed no toxic effect on L929 and MC3T3-E1.During the initial immersion period,the increase of pH value was the primary cause of cell death.In short-term immersion(10 d),the released Mg,Zn,Y,Nd and Zr ions did not show apparent cytotoxicity.In the long-term immersion(60 d),the alloying elements in the solution would accumulated to a certain concentration.The accumulated ion concentrations which resulted in cytotoxicity(survival rate<75%)were measured to be 948-1580 ?g/ml of Mg2+,0.2304-0.384 ?g/ml of Zn2+,0.0395-0.0658 ?g/ml of Y3+,0.0448-0.0747 ?g/ml of Nd3+,0.0098-0.0164 ?g/ml of Zr4+ for L929,and 1580-2212 ?g/ml of Mg2+,0.384-0.538 ?g/ml of Zn2+,0.0658-0.0921 ?g/ml of Y3+,0.0747-0.105 ?g/ml of Nd3+,0.0164-0.0230 ?g/ml of Zr4+ for MC3T3-E1.In addition,cell adhesion test showed that MC3T3-E1 and L929 can be adhered on the surface of alloy;cell proliferation experiments showed that the extracts of MgZn-Y-Nd-Zr promoted the proliferation of L929 in early period and the survival of the cells increased significantly in comparison with control group;ALP activity detection and calcified nodules staining results found that Mg-Zn-Y-Nd-Zr alloy obviously promoted the differentiation process of the stem cells to osteoblasts.The osteoinductivity of Mg-Zn-Y-Nd-Zr alloys had been proved.In summary,the degradation of Mg-Zn-Y-Nd-Zr is slow and its cell compatibility is good.Animal experiments and clinical trials should be performed in the next step.