Study On Biofunctionalization Effect Of TiCu Alloy And Its Surface Modification

Though the bio-metal implants(such as titanium alloy,stainless steel)widely used in orthopedic clinics have good biocompatibility,they are prone to loosening with bone tissues during long-term implantation due to their biological inertness,which would make those patients to have longer fixation recovery period in the poor bone formation environment,and have poor bonding stability at the interface between implants and bones.Considering that copper(Cu),an essential trace element in human body,has excellent antibacterial function and can regulate the expression of relevant genes in the process of angiogenesis and osteogenesis,our research group has developed a new antibacterial Ti-5wt%.Cu(TiCu)alloy and demonstrated that the alloy has excellent comprehensive mechanical properties,antibacterial performance,angiogenic and osteogenic promotion effects,and biocompatibility.On this basis,this thesis investigated the osteogenic behavior of TiCu alloy in the harsh osteoporotic osseointegration environment.Furthermore,through the surface modification,the relationship among the microstructure,mechanical properties and biological functions of the biofunctional hard multilayer coatings were systematically studied.The main work and research conclusions of this thesis are as follows:(1)Study on promoting osteointegration effect of Cu alloyed titanium(TiCu)in osteoporosis modeled animals.Osteoporosis is a common skeletal disease associated with increased age,making patients be prone to the osteoporotic fracture(OPF).Osteoporotic fractures are difficult to heal and prone to the secondary fractures,which seriously affects patients’ safety and quality of life.In this thesis,we firstly constructed a primary osteoporotic bone microenvironment in the osteoporosis modeled animal(ovariectomized rats),implanted TiCu alloy screws into the tibia of rats,and then investigated the osteointegration effect and underlying mechanism of TiCu alloy through general observation,Micro-CT analyses(blood vessels and bone tissues),biomechanical analysis,and histological analysis.The results showed that after implantation for 4 weeks,TiCu alloy could promote the reconstruction of vascular network around the implant by up-regulating expression of vascular endothelial growth factor(VEGF).After 8 weeks implantation,the alloy could further promote the proliferation and differentiation of osteoblasts,mineralization and deposition of collagens,and then significantly increasing bone mineral density(BMD)around the implant.In conclusion,TiCu alloy would enhance the fixation stability,accelerate the osteointegration,and thus could reduce the risk of aseptic loosening during the long-term implantation in the osteoporosis environment.(2)Study on TiCuN/ZrN multilayer hard coatings with biofunctions fabricated on TiCu alloyTiCu alloy,as an orthopedic implant material,will inevitably face the problem of friction and wear during long-term implantation.The resulting wear particles released into the surrounding tissues can induce the inflammatory reaction,destroy the bone growth balance,and then affect the stability of implantation,which possibly leads to the revision surgery.TiCu alloy has been demonstrated to have excellent mechanical properties,antimicrobial performance,osseointegration ability and biocompatibility.In order to further improve the wear resistance of TiCu alloy,a multilayer coating composed of high hardness TiCuN and ZrN was deposited on the surface of TiCu by axial magnetic field enhanced pulsed bias arc ion plating(AMFE-AIP)system.Then,the corresponding relationship between the layer thickness in TiCuN/ZrN multi-layers and the microstructure of the coating was studied as the thickness of the monolayer was changed from μm to nm levels,and the influence mechanism of the microstructure on the strengthening effect,wear resistance and Cu ions release of the multi-layers were deeply analyzed.The results showed that in the multi-layers,the atoms in adjacent layers interface were arranged in a coherent/semi-coherent manner,and there was a "Cu nail/bridge"structure which was biased perpendicular to the direction of the film layers.With decrease of the modulation period(A)in the multi-layers,the film strength first increased and then decreased,the friction coefficient and the wear rate decreased,and the adhesion of the film and the wear resistance of the film increased.What’s more,the release of Cu ions from the coating was gradually increased,which resulted in the improvement of antibacterial performance and cell proliferation promotion effect of the coating.Thus,the TiCuN/ZrN multilayer coating is promised to be a new kind of biofunctionalized coating with properties that can be regulated on demand for adapting various implant environment.In summary,TiCu alloy has good osteogenic and angiogenic promotion properties in the osteoporotic environment.The TiCuN/ZrN multilayer coating fabricated on its surface has excellent comprehensive mechanical properties,wear resistance and biofunctional behaviors without hindering the release of Cu ions from the TiCu alloy matrix,and has good prospects for future applications.Therefore,the research results of this thesis on TiCu alloy and the related TiCuN/ZrN multilayer coating with ondemand tunable surface properties provide a research basis for the design and development of biofunctionalized implantable devices applied in harsh implantation environments.