Construction Of Micro/Nano-structure On The Surface Of Titanium Implant And Its Osteogenic Properties

Titanium(Ti)and its alloys are widely used in the repair and replacement of hard tissue such as bone and teeth because of their low elastic modulus,good mechanical properties,corrosion resistance and biocompatibility.In recent years,additive manufacturing(AM)technology has made continuous progress.Its advantages in customized production of a single piece,realization of complex modeling and processing cycle have become more and more obvious,showing a broad prospect in the biomedical field.However,due to the existence of biological inertia,Ti implants have poor biological bonding ability with bone tissue,which could lead to loose or inflammation of surrounding tissue.Since the surface of Ti implant is firstly in direct contact with the tissue cells after implanted into the human body,the surface properties of materials will greatly affect the biological properties.This study aimed at surface modification of titanium implants fabricated by AM technology.A micro/nano-hierarchical structure composed of micro-roughness and nanotubes was constructed on the surface of Ti in order to improve the biocompatibility and osteogenesis.Firstly,the effect of anodic oxidation parameters on the structure of TiO2 nanotube arrays was studied.By using different electrolytes,voltages and heat treatment processes,the morphology,size and crystal morphology of nanotubes were studied.Modified anodic oxidation process parameters would be selected for subsequent experiments.The results showed that the structure of nanotubes formed in NH4F-glycol electrolysis system is more compact and orderly.The average diameter of nanotubes is positively correlated with the oxidation voltage.After heat treatment,the surface morphology remained unchanged,while the amorphous structure of TiO2 was transformed to anatase,which would be more beneficial to biological activity.Secondly,the construction of micro and nanostructures on Ti surface and its effects on osteoblasts were studied.A ravine-like rough structure was constructed by sandblasting and acid etching.Afterward,nanotube array was fabricated by anodic oxidation on this substrate,forming a micro/nano hierarchical structure on Ti surface.The effects of surface structure on biocompatibility and osteogenic behavior were investigated by surface characterization and in vitro cell experiments.The results showed that the structure improved the wettability and bioactivity of the material,and promoted the cell spreading,proliferation and differentiation.These results verified the regulating effect of micro/nano structure on the behavior of osteoblasts.Then,the construction of micro/nano structure and in vitro cell experiments of AM fabricated TC4 implants were carried out.TC4 sheets were prepared by EBM.followed by acid etching to remove the residual powder,expose the native micron structure and form micron/submicron pits and grooves on the material surface.A hierarchical structure composed of micro-ridges,submicron pits and nanotubes was successfully constructed by further anodizing treatment.The results showed that the micro/nano structure enhanced the wettability and bioactivity of the material,as well as promoted cell adhesion,proliferation and differentiation.Finally,in vivo osteogenic properties of AM implants were investigated.A composite treatment method of ultrasonic acid etching and anodic oxidation for EBM shaped implants was proposed.TC4 titanium rod was modified to construct micro/nano-hierarchical structure on the surface,and was then implanted into the femur of SD rat.Micro-CT and histological staining were performed to investigate the new bone formation around the titanium rod,and the interface bonding strength between Ti implant and bone tissue.The results showed that the residual powder adhered on the surface of EBM Ti rod was more obvious than titanium sheet.After acid etching,the powder residue was removed and a groove-like corrosion pattern was left.Femur implantation experiments showed that the amount of new bone around the titanium rod after micro/nano modification was significantly increased,and the bonding to bone tissue was tighter,indicating that the modified implant had good osteogenic properties.