Research On The Preparation And Bio-tribological Properties Of Bioceramic Coating On Large Plastic Deformed Titanium

Titanium and titanium alloy have significant medical values. However, they show insufficient bioactivity and poor wear resistance in physiological environments. These factors influence the effectiveness of long-term safe implantation. Accordingly, this study aims to solve the problem by choosing conventional titanium and large plastic deformed titanium made by equal channel angular pressing (ECAP) as research objects. Biological surface modification of the objects is conducted by micro-arc oxidation and hydrothermal method. A systematical research is further performed on key issues, including friction-induced damage and biocompatibility when medical materials are implanted. The innovative achievements of the study are as follows.This dissertation emphasizes the influence of such micro-arc oxidation technological parameters on coating structure as Ca/P ratio, oxidation time, frequency, duty cycle, and electric current density. Results show that decreased frequency and extension of oxidation time improve the average pore size, porosity, roughness, Ca/P ratio, and relative content of rutile TiO2on the surface pore of micro-arc oxidation coating. The average pore size on the coating’s surface increases and then decreases with increased density and decreased Ca/P ratio of electrolyte. The surface morphology of the coating’s surface is improved by increased duty cycle.This study also evaluates the microstructure and physical and chemical properties of the micro-arc oxidation coating on conventional titanium and large plastic deformed titanium. Results reveal that compared with the micro-arc oxidation coating of conventional titanium, pores on the micro-arc oxidation coating of large plastic deformed titanium are more uniformly and compactly distributed, with smaller micro-sized pores, which have larger quantity, higher porosity, smoother and more level surface, more moderate roughness, higher contact angle, lower surface energy, higher hardness value, stronger adhesion strength, and stronger corrosion resistance.This work further compares conventional titanium with large plastic deformed titanium in terms of their tribological properties under different lubricating conditions, including simulated body fluid and calf serum. Results suggest that the tribological properties micro-arc oxidation coating on large plastic deformed titanium is superior to that of conventional titanium under the abovementioned conditions. Considering that calf serum has better lubrication, cooling, and loading effects, the tribological properties of micro-arc oxidation coating on large plastic deformed titanium is better those under the lubricating condition of calf serum.To improve bioactivity, hydrothermal method is adopted to transform the non-amorphous Ca2+and PO43-of micro-arc oxidation coatings on conventional titanium and large plastic deformed titanium into amorphous hydroxyapatite(HA), to prepare TiO2/HA composite ceramic coating, and explore to the influence of hydrothermal synthesis on the wettability of coating structure. Results reveal that HA particle crystalline nucleation on the surface of coating after hydrothermal synthesis can improve the surface energy of the coating, and that with time expands, the number and volume of HA crystal grains on the coating surface is increased, and that its roughness initially decreases and then increases. After seven days of hydrothermal synthesis, needle-like HA crystallization, which is closer to the Ca/P ratio of natural human bone, appears on the surface of composite ceramic coating on large plastic deformed titanium.An experimental study is conducted to explore the compatibility of in-vitro cell and blood on the modified coating. All samples are found to be noncytotoxic and to conform to the hemolysis requirements of medical materials. Moreover, no hemolysis is observed. The composite ceramic coating of large plastic deformed titanium shows optimal cytocompatibility and blood compatibility and could better promote adhesion and spreading of osteoblasts. The two-tier growing structure of osteoblasts is more obvious, and platelets are not activated.In conclusion, the microstructure refinement of large plastic deformed titanium prominently improves its surface structure, hardness, adhesion strength, corrosion resistance, biotribology, and biocompatibility. The improvement is due to the microstructure refinement of substrate, increased crystal defect, strengthening of free energy and diffusion energy, provision of extra energy and diffusion channel for the nucleation of modified coating, and enhanced performance of the surface of modified coating.As mentioned above, excellent performance is observed for micro-arc oxidation coating on large plastic deformed titanium and surface modification material using the hydrothermal method for medical use, providing theoretical references and technological support for the surface modification of new-generation hard tissues and alternative materials.