Preparation and Performance of Biomimetic Composite Coating on Selective Laser Melting Forming TC4 Titanium Alloy Surface for Orthopedic Grade

A polydopamine (PDA) film was prepared on laser selective melting froming TC4 titanium alloy by oxidation self-polymerization, and then hydroxyapatite (HA) was electrodeposited to form a PHA biomimetic composite coating. Through the three-factor three-level orthogonal experiment, the effects of current density (5, 10, 15 mA · cm⁻²), deposition time (5, 10, 15 min) and deposition temperature (20, 30, 40 ℃) on the corrosion resistance and wear resistance of the coating were studied. The microstructure and biocompatibility of the coating were characterized. The results show that the uniform and dense PDA film had a promoting effect on the deposition of HA. Compared with that of the directly deposited HA coating, the bonding strength of PHA composite coating increased by 41.18%. The influence degree on the self-corrosion current density and friction time (the time elapsed during the interval of potential change, for characterizing wear resistance) of PHA composite coating was ranked from large to small as current density, deposition temperature and deposition time. With the increase of current density, the coating structure was destroyed, resulting in an increase in the self-corrosion current density and shortening of the friction time. With the extension of deposition time, the coating tended to be uniform and dense first and then became loose, the self-corrosion current density decreased first and then increased, and the friction time extended first and then shortened. As the deposition temperature increased, the coating became more uniform and dense, the bonding force with the substrate was enhanced, the self-corrosion current density first increased and then decreased, and the friction time extended. The optimal process parameter combination was current density of 5 mA · cm⁻², deposition time of 10 min and deposition temperature of 40 ℃. Under this condition, the self-corrosion current density of the coating was the smallest, the friction time was the longest, and the corrosion protection rate was as high as 98.2%; the corrosion resistance and wear resistance were the best. Meanwhile, a large number of adhered cells and pseudopodia on the surface of the PHA composite coating, shaving better biocompatibility.