Study On The Fabrication And Properties Of Selective Laser Melted Biomedical Ti30Nb5Ta7Zr Lattices

Low modulus?titanium alloy Ti30Nb5Ta7Zr(TNTZ)has good mechanical properties and biocompatibility.The use of SLM technology to customize the preparation of TNTZ lattices has been found widespread applications in medical implants.This paper takes the as-printed TNTZ lattices as the research object,and studied its manufacturing process window,alloy structure,lattice structure,mechanical properties,and biocompatibility.Furthermore,this paper applies proteomics and other related research tests.The method systematically analyzed the factors affecting the biocompatibility of the as-printed TNTZ alloy at the protein level.The process parameters of TNTZ alloy prepared by SLM technology are listed as follows:scanning speed 800 mm/s,laser power 280 W,layer thickness 50?m,bonding distance 20?m,substrate preheating temperature 180?,Ar atmosphere and corresponding nominal energy density 100 J/mm³.To ensure the integrity and clarity of the outer contour of the material,the width of the straight slit should be higher than300?m,and the diameter of the round hole should be greater than 400?m.Electron Back Scattered Diffraction(EBSD),X-ray diffraction(XRD),X-ray Photoelectron Spectroscopy(XPS),Micro Computed Tomography(Micro-CT)and other means of tissue structure,element composition and defect analysis have been used to observe and characterize the phase composition,surface oxide layer,internal grain morphology and internal defect distribution of the prepared specimens.The average grain size of the as-printed TNTZ alloy is 17.8?m which is one less quantitative level than the as-cast TNTZ alloy;while the microstructure is mainly?phase,and there are a few needle-shaped??phases with an average length of 0.8?m.Neither the texture nor the preferred orientation of the grains is obvious inside the grain.The surface oxide layer is composed of Ti O₂,Nb₂O₅,Zr O₂,Ta₂O₅ and the microhardness is about 305.4 HV.The Young's modulus,yield strength,elongation and the fatigue limit of the as-printed TNTZ alloy are 62.8 GPa,664 MPa,15.3%and is 140 MPa(10⁷nf),respectively.Compared with the as-cast TNTZ alloy,the microhardness and elongation of the as-printed TNTZ alloy are increased,the Young's modulus and yield strength were decreased.The fatigue strength of the as-printed TNTZ alloy was dropped significantly,but still higher than that of human cortical bone,meeting the requirements of implant material applications.According to the fatigue strength model,the analytical expressions of cyclic stress and fatigue life of as-printed TNTZ alloy was established.The relationship between the porosity,yield strength and Young's modulus of the as-printed TNTZ lattices were quantitatively studied.The mechanical behavior of the as-printed TNTZ lattices were revealed,and the fatigue performance of the as-printed TNTZ lattices were studied from the perspective of stress limit.These could be used as a reference for the customized manufacturing of the TNTZ skeleton matching the modulus of the human bone.Micro-CT was used to characterize the distribution of internal defects in the lattices,and combined with fatigue fracture analysis,it was found that the fatigue cracks diffused around the pore defects in a step-like manner.The pore defects inside the as-printed TNTZ alloy were the extended sources of fatigue crack propagation.According to the results of this study,a as-printed TNTZ hip joint implant with lattices whose young's modulus and fatigue strength close to human bones was fabricated.The cytotoxicity test of L929 mouse fibroblasts was performed to evaluate the biocompatibility of as-printed dense TNTZ,TNTZ,TNTZ+n-HA,TNTZ+Pro,TC4,316L.All the experimental groups showed no cytotoxicity and good biocompatibility.According to the RGR value,there were ranked as TNTZ+n-HA>control groups>TNTZ+Pro>TNTZ>TC4>316L.The 9 groups cytotoxicity of as-printed TNTZ lattices were compared by cell density comparison.The experimental groups all met the requirements of implants in China.Combined with the RGR value and fatigue test results,it was found that the RD group with a volume fraction of 30%and a side length of 2 mm(corresponding to an aperture of about 400 m)was suitable to be used as a replacement material for human cortical bone,and a as-printed TNTZ hip joint implant with the characteristics of the lattices was prepared.The reasons for the good biocompatibility of as-printed TNTZ alloys were studied by proteomics-related analysis.Compared with the cells adhesioned on the as-printed Ti6Al4V(TC4)alloy,521 differentially expressed proteins and the unique biological functions between the as-printed TNTZ alloy and L929 cells were found,mainly including important glycolysis and complex formations.Among 271 up-regulated differentially expressed proteins,proteins that promote cell regeneration,enhance cell activity,and accelerate protein binding were found.Through the KEGG signaling pathway analysis,the main pathways of differentially expressed protein were systematically analyzed.Taking the HIF-1 and TGF-Beta signaling pathways with significant expression as an example,the mechanism of the effect of as-printed TNTZ alloy on L929 cells was analyzed:the as-printed TNTZ alloy can activate HIF-1 and TGF-Beta signaling pathways in cells,induce the secretion of proteins that can promote cell proliferation,angiogenesis and maintain genomic stability,and inhibit the activity of telomerase in cancer cells,so that the proliferation of surf-attached cells can be promoted and the proliferation of surface cancer cells can be inhibited.Finally,a preliminary sketch of the interaction in terms of proteomics between the as-printed TNTZ alloy and L929 cells was obtained.Compared with the traditional medical TC4 alloy,the as-printed TNTZ alloy has lower young's modulus,better biocompatibility,furthermore it has the ability to promote the proliferation of surface adherent cells and inhibit the proliferation of surface cancer cells.There is potential for medical application of the as-printed TNTZ alloy.