Study On Novel Zr-16Nb-xTi Alloys Microstructures,Properties And Mineralizing Coating For Biomedical Applications

Metallic biomaterials have received extensive attention in the field of clinical medicine due to their outstanding mechanical properties and excellent processing properties.However,the drawbacks of traditional biomedical alloys are becoming increasingly obvious with the continuous improvement of the biomaterials.Especially the Young’s modulus mismatch between alloys with the human bone,the relatively high magnetic susceptibility,the insufficient corrosion resistance in the body fluid environment,most importantly,the poor biocompatibility,and the lack of bioactivity have limited the application of the biomedical materials.Therefore,in order to explore an effective method which is able to deal with these urgent problems,the biomedical Zr-based alloys,with increasingly attractive in recent years,was chosen as the target material.The Zr-16Nb-x Ti（x=0,4,8,12,16 wt.%）alloys were designed and fabricated.The relationships between microstructures and mechanical、magnetic properties were studied.Proper Sn element were optimized for increasing relative performance.Corrosion resistance of these alloys under Hank’s solution were studied.The biocompatibility of the Zr-16Nb-x Ti（x=0,4,8,12,16 wt.%）alloys under simulated body fluid environment were evaluated.Moreover,biocompatibility and bioactivity Zr-16Nb-4Ti and Zr-16Nb-16Ti alloys were improved by conducting bioengineering techniques.Offering new theory and experimental data for metallic biomaterials design,as well as properties optimization,in order to meet the newly higher biomaterials requirement of comprehensive properties with respect to clinical applications.The main research results are as follows:（1）Designing Zr-16Nb-xTi（x=0,4,8,12,16 wt.%）alloys based on CALPHAD method,Zr-16Nb-x Ti alloys containβand a small amount of martensiteα’phase.Alloys possess average Young’s modulus of 52GPa which is lower than most of the Ti based biomedical alloys.The magnetic susceptibility of Zr-16Nb-x Ti alloys is lower than that of the Ti-6Al-4V and Co-Cr-Mo alloys.Among them,Zr-16Nb-4Ti and Zr-16Nb-16Ti have excellent comprehensive performance such as lower Young’s modulus and magnetic susceptibility,higher yield strength and tensile strength,as well as great ductility.（2）Zr-16Nb-xTi-（4～6）Sn alloys containβandα’’martensite phase,The addition of Sn element improves the strength and decreases the Young’s modulus of the alloys,Zr-16Nb-4Ti-6Sn possesses lowest Young’s modulus（47.3 GPa）,the effect of Sn addition on the magnetic properties of Zr-16Nb-x Ti alloy is mainly reflected in the change of the phase composition and the magnetic susceptibility of the Sn element itself,as the Zr-16Nb-4Ti-6Sn owns the lowest value of 1.2241×10^-6 cm³/g.（3）Electrochemical experiments in simulated body fluids illustrated that all Zr-16Nb-x Ti alloys have excellent anticorrosion properties,among them,Zr-16Nb-12Ti has the lowest corrosion current density,and Zr-16Nb-16Ti has the longest passivation zone.The ion release test show that the Zr,Nb and Ti ion concentrations in the solution after immersing Zr-16Nb-x Ti alloys are just slightly higher than the limit concentration that can be detected by equipment.However,with Sn addition,the corrosion resistance of Zr-16Nb-4Ti and Zr-16Nb-16Ti decrease dramatically as their corrosion current became dozens of times larger than the alloys without Sn,meanwhile,the impedance decrease around 5 times than the alloys without Sn,there is no obvious passive region among Zr-16Nb-x Ti-（4～6）Sn alloys.（4）Cytotoxicity experiments showed that after 12 days cultivation,the relative cell viability of Zr-16Nb-x Ti alloys were still higher than 90%,showing excellent cytocompatibility.The alkaline phosphatase ALP activity test showed that the ALP activity of most tested alloys was close to that of the negative control group.The relative activity of ALP of tested alloys ranged from 92%to 108%,displaying excellent osteoblast differentiation function.All Zr-16Nb-x Ti alloys are non-hemolytic materials,and the hemolysis rate is less than 5%.The platelet adhesion state and the number of platelets on the surface of test materials are quite different.A large amount of platelet adhesion and aggregation was observed on the pure Ti surface,while only a little platelet adhesion was observed on the pure Zr surface.In the Zr-16Nb-x Ti alloy,we did not find the formation of platelet pseudopodia,indicating that platelet aggregation and hemolysis are difficult to occur on the surface of these alloys.（5）Mineralized coatings on Zr-16Nb-4Ti and Zr-16Nb-16Ti surfaces were manufactured via ELRs self-assembly technology.MTT assay illustrates the cell viability of mineralized alloys was significantly higher than untreated groups.The alkaline phosphatase ALP activity experiment also showed that the osteoblast differentiation ability of the mineralized alloy was dramatically improved.Subsequent cell adhesion experiments showed that the mineralized structure attracted a large number of MG 63cells to adhere and spread.SEM results showed that MG 63 cells were more likely to grow lamellipodia on the mineralized structure.