Preparation And Application Of Micro/Nano Composite Structure Coating On Biomedical Metal Surface

3D printed titanium(Ti)implants have excellent mechanical properties and good biocompatibility.Tantalum(Ta)has excellent anti-fatigue properties and chemical stability,which has attracted widespread attention in the field of personalized medicine.However,they are all biologically inert materials and lack osseointegration between the implant and natural bone.Therefore,surface modification is required to improve the surface morphology or chemical composition of the implant to promote osseointegration.This paper mainly focuses on the selective laser melting(SLM)and surface functionalization process of medical titanium alloy Ti-6Al-4V(TC4).Especially the growth characteristics,surface morphology and hydrophobicity of the coating,as well as the biomimetic mineralization mechanism model and the osteogenesis effect.Specifically:(1)Preparation of strontium(Sr)-doped TiO₂ ceramic coating on 3D printed TC4 by micro-arc oxidation(MAO)and hydrothermal method.The inside of the coating is loose and porous,and contains biologically active elements such as Ca,P,Sr,etc.The bonding force between the coating and the substrate is 39.4N,and it has good corrosion resistance.After immersing in simulated body fluid(SBF)for 5 days,it can obviously induce apatite deposition.Apatite is mainly composed of Ca(33.24 wt%),P(16.95 wt%)and O(49.25 wt%),the ratio of Ca/P is 1.69,which is close to the theoretical ratio of hydroxyapatite(HA)1.67.The super-hydrophilicity of the coating(the contact angle is reduced from 56°to 9.6°)is the main reason that affects the formation of apatite.This is because the micro/nano composite structure coating can absorb more volume of SBF solution than a plane with the same contact angle and radius of curvature(Chapter 3).(2)After chemical etching and electrochemical anodization,a biomimetic SrTiO₃/TiO₂ heterostructure similar to the surface morphology of the biomineralized substrate is formed on the surface of the 3D printed TC4.Specifically,the TC4 plate was first placed in a mixed solution of hydrochloric acid and calcium chloride at 60? for 12h to form micron pits,and then in an ethylene dichloride containing 0.3 wt%NH4F and 2 vol%distilled water.Nanotubes are generated by anodizing in the alcohol solution for 20 min,and finally the functional ion Sr(4.22 at%) is introduced by in-situ hydrothermal method.The micro/nano composite structure have a large specific surface area and roughness,good hydrophilicity(7.6°),adhesion strength(10.51N),and corrosion resistance(-0.32V).The hydroxyl-functionalized surface of the coating helps to promote the nucleation and growth of apatite,and release of Ca and P ions from the coating into the SBF will cause the solution near the sample to be supersaturated,thereby accelerating the precipitation of apatite,demonstrates good biomineralization capabilities(Chapter 4).(3)A "cortex-like" Zn-doped(1.35±0.3 wt%)ceramic coating is obtained on pure Ta surface by MAO and hydrothermal treatment.The electrolyte consists of 0.03M calcium gluconate,0.01M?-glycerophosphate disodium and 0.02M zinc gluconate.The roughness(Ra)increases from 0.137?m for Ta to 1.884?m for the high-porosity coating,and releases Zn,Ca,and P ions in a controlled and continuous manner.At the same time,the film exhibits high bonding force(18.9N),excellent corrosion resistance and apatite induction ability,and has excellent biological activity.The selective dissolution of oxides in the electrolyte is the key to the formation of the "cortex-like"micro-nano composite structure,which is also the essential difference from the classic"crater-like" MAO coating(Chapter 5).In summary,by adjusting 3D printing power,electrolyte composition,electrical parameters,etc.,three micro-nano composite structural coatings have been achieved.Its excellent biological activity may open up potential applications in orthopedic implants.The formation mechanism of the micro-nano composite structure,introduction of trace functional elements and improvement of biological properties disclosed in this article provide a reference and basis for the functional modification of metal surfaces,and have important theoretical value and promotion significance.