Selective Laser Melting Of Biomedical Titanium Alloy And Electrochemical Surface Modification Of Titanium

The main content of this thesis is about selective laser melting?SLM?and electrochemical surface modification of titanium-based metals for their enhanced in vitro biomedical functions.In this study,SLM of titanium alloy,the development of micro/nano topographies on titanium surfaces based on electrochemical method,the response of osteoblast-like cells to micro/nano topographies and the immunomodulatory properites of copper-containing micro-arc oxidized coatings were investigated.Ti-6Al-4V specimens were fabricated through SLM technique by using pre-alloyed Ti-6Al-4V powder as feedstock.It was found that the microstructure of SLM-fabricated Ti-6Al-4V was mainly composed of columnar prior?grains and matensite phase.A mass of defects,such as dislocations and twins,existed within matensite grains.Due to the oxidation during SLM process,inclusions such as hard?case,CaO and Al₂O₃ could be formed within Ti-6Al-4V matrix.Three heat treatment strategies were proposed based on phase transformation mechanism of titanium alloy.They were classified as subtransus,supersolvus and mixed heat treatment.After heat treatment,the ductility and strength of SLM-fabricated Ti-6Al-4V were increased and decreased,repectively.Among these three heat treatment strategies,subtransus heat treatment resulted in the best tensile properies which combined favorable strength and ductility.Biomimetic micro/nano topographical coatings were developed on titanium surface through the combination use of micro-arc oxidation and post hydrothermal treatment.Tunable silicate nanostructures could be prepared by adjusting relavant parameters during hydrothermal process.According to the morphological features,these nanostructures could be classified as nanorod,nanoplate and nanoleaf.Osteoblast-like cell response,such as adhesion,proliferation and differentiation,to various micro/nano topographies was investigated.It was found that nanoplate surface promoted cell adhesion but slowed down cell proliferation.Nanoleaf surface enhanced both cell proliferation and differentiation.The enhanced differentiation could be related to the elongated cell morphology on nanoleaf surface.Copper-containing biomimetic micro/nano toporaphical coatings were prepared by introducing Cu ions during hydrothermal process.It was found that micro/nano topographical coating with appropriate amount of Cu ion release significantly promoted osteblast speading,adhesion,proliferation and differentiation.The immunomodulatory properties of Cu-containing micro-arc oxidized?MAO?coatings were investigated.Anti-inflammatory cytokine IL-10 release of macrophages was promoted on Cu-containing MAO coating.However,pro-inflammatory cytokine TNF-?release was not significantly affected.The immuno-microenviroment created by Cu-containing MAO coating and macrophages enhanced the proliferation,collagen sythesis and calcium nodule formation of osteoblast-like cells.It indicates that Cu-containing MAO coating has positive osteoimmunomodulatory effects.Macrophages treated with Cu ions exhibited a trend to polarize to M1 phenotype.Cu ions with a concentration of 6.5 ppm exhibited positive osteoimmunomodulatory effects.Cu-containing MAO coating with osteogenic and antibacterial functions is potential to be used as surface coating for the applications of bone implant surface modification.