Microstructure And Properties Of Degradable Biomedical Zn-Li Alloys

In recent years,biodegradable alloys have been widely concerned and studied,and can be used as a new choice of biomedical implant materials due to their good mechanical properties.Biodegradable alloys are mainly divided into three categories:magnesium-based alloys,iron-based alloys and zinc-based alloys,among which there are lots of studies on the first two.However,the degradation rate of magnesium-based alloy is too fast,and the degradation rate of iron-based alloy is too slow,while the electrode potential of zinc-based alloy is located between the two,so zinc-based alloy has a suitable degradation rate,which is more in line with clinical needs.However,its inherent mechanical properties are poor since pure zinc has a close-packed hexagonal structure.Alloying and deformation processing can optimize structure and improve the mechanical properties.Lithium and Magnesium are the most effective non-toxic strengthening elements in zinc alloys.In this paper,lithium is selected as an additional element,and the effects of four different lithium element additions on the microstructure,mechanical properties,biocompatibility and corrosion properties of as cast zinc alloys are studied.The specific components are Zn-0.05Li,Zn-0.15Li,Zn-0.45Li and Zn-0.75Li.The lithium content was determined by Inductively coupled plasma optical emission spectrometer(ICP-OES),and the phase and micro structure of the alloys were determined by scanning electron microscope(SEM),X-ray diffraction(XRD),and metallurgical microscope;the mechanical properties of the alloys were analyzed by microhardness and tensile test;the corrosion performance of the alloys were analyzed through the immersion weight loss test and electrochemical test;the biocompatibility of the alloys were analyzed through the cytotoxicity test(MTT),high-content imaging(HCS).It shows that with the increase of lithium addition,the comprehensive performance of the zinc alloy increases first and then decreases.The Zn-0.45Li alloy with the best performance is selected for next research.The next step is to analyze and compare the effects of three different deformation processing methods on the microstructure,mechanical properties,biocompatibility and corrosion properties of Zn-0.45Li alloy.The specific processes are hot extrusion processing,hot extrusion+multi-pass drawing processing,and rotary forging processing.In addition to conducting the same research experiments on as cast zinc alloys,transmission electron microscopy(TEM)and electron backscatter diffraction(EBSD)were used to determine the existence of the second phase LiZn4,and the grain size was analyzed,and ultrafine grained can be obtained after sufficient passes of deformation processing.The mechanical properties of the three kinds of deformation zinc alloy have been greatly improved,especially plasticity,in which hot extrusion+multi-pass drawing processing has the best mechanical properties,the yield strength can reach 416 MPa,the tensile strength can reach 567 MPa,and the elongation after fracture can reach 55%.The weightlessness experiment of immersion in simulated body fluid(c-SBF)shows that the degradation rates of all zinc alloys are lower than 0.2mm/year,and the corrosion morphologies after deformation processing are more uniform.At the same time,the cytotoxicity experiment also shows that Zn-Li alloy has an effect on L-929 cells have low toxicity at low concentrations,and can meet the requirements of medical implant materials.Considering all aspects of performance comprehensively,animal experiments of three different deformation processing Zn-0.45Li alloys can be carried out in the follow-up to study their biocompatibility in vivo.