Effects of Hydrothermal Temperature and Time on Surface Physical and Chemical Properties of 3D Printed Ti-6Al-4V Implants

This study aims to explore the optimal process and parameters for preparing polydopamine coating on the surface of 3D printed Ti-6Al-4V implants with micro-nano structure. 3D printing is a promising method for preparing Ti-6Al-4V implants. However, the biological inertness of 3D-printed titanium alloys limits their ability to bind to bone tissue. The micro-nano structure on the surface of titanium alloy implants can promote cell adhesion, proliferation and bone integration. In addition, polydopamine has been shown to promote cell proliferation and reduce cytotoxicity. Therefore, hydrothermal treatment was performed on the 3D printed Ti-6Al-4V implants treated by acid etching and anodic oxidation, and polydopamine was coated on the surface of samples by hydrothermal treatment. The effects of different hydrothermal treatment temperatures and time were analyzed. Moreover, the surface morphology, roughness, elemental composition, surface wettability and corrosion resistance of each sample were characterized by scanning electron microscope, three-dimensional confocal laser microscope, X-ray photoelectron spectroscopy, contact angle measurement instrument and electrochemical workstation. The results showed that a micron-scale pit structure was constructed on the surface by acid etching. Through anodic oxidation, an ordered array of TiO2 nanotubes with a diameter of about 80 nm was constructed on the basis of the original micron-scale structure. Micro-nano structures were successfully prepared on the surface of the implant. With the increase of hydrothermal treatment temperature and time, the diameter of nanotubes gradually decreased from 80 nm to about 40 nm, and even blocked. The three-dimensional topography indicated that the traces of laser scanning during the printing process could be observed on the surface of samples. Through anodic oxidation, the edges and corners became smoother than the surface after acid etching. Going forward, the results of surface element analysis suggested that the N/C value of each sample was close to the theoretical value of 0.125, indicating that the hydrothermal treatment successfully coated polydopamine on the surface based on remaining the micro-nano structure. The carbon and nitrogen elements on the surface of samples after hydrothermal treatment were subjected to peak fitting processing. In addition, the carbon elements were composed of C==O/O—C==O and C—C/C==C, and the nitrogen elements were composed of pyrrolic N, further demonstrating that the hydrothermal treatment successfully added polydopamine to the sample surface. With the increase of reaction time, the surface roughness and contact angle gradually decreased, and the roughness of each group remained between 4-5 μm. The surface contact angle after acid etching was 52.1°. After anodic oxidation, the contact angle decreased to 42.9°. Through hydrothermal treatment, the contact angle was less than 35°, showing excellent hydrophilicity. Compared with the samples after acid etching and anodic oxidation, the corrosion resistance was enhanced through hydrothermal treatment. In addition, the principles of anodic oxidation and dopamine polymerization were discussed in depth. In conclusion, the reaction temperature of 37 ℃ and the reaction time of 24 hours were suitable for the deposition of polydopamine on the surface of titanium alloy implants under the premise that the original micro-nano structure was basically retained. Furthermore, the results of this study provide a reference for the optimization of process parameters of polydopamine self-polymerization on the surface of titanium alloy implants. © 2022, Chongqing Wujiu Periodicals Press. All rights reserved.