Surface characterization and biological assessment of corrosion-resistant a-C:H:SiO_x PACVD coating for Ti-6Al-4V...

The paper focuses on the SiO_x-doped amorphous hydrocarbon (a-C:H:SiO_x) coating on the titanium (Ti-6Al-4V) alloy substrate obtained by plasma-assisted chemical vapor deposition (PACVD) in a mixture of argon gas and polyphenylmethylsiloxane vapor using a bipolar substrate bias. It is shown that the a-C:H:SiO_x coating deposition results in the formation of a negative surface potential important for application of this coating for medical implants. The a-C:H:SiO_x coatings improve the corrosion resistance of Ti alloy to 0.5 M NaCl solution and phosphate-buffered saline. In particular, the corrosion current density of the a-C:H:SiO_x-coated sample in a 0.5 M NaCl solution at 22 °C decreases from 1∙10^-8 to 1.7∙10^-10 A/cm², that reduces the corrosion rate from 9∙10^-5 to 15∙10^-7 mm/year. The a-C:H:SiO_x coating facilitates the surface endothelization of an implant located in the thoracic aorta of a mini pig, and reduces the risk of thrombosis and implant failure. This effect can be explained by the ability of the a-C:H:SiO_x coating ability to reduce in vitro a 24-hour secretion of pro-inflammatory interleukins (IL-6, IL-12(p70), IL-15, and IL-17) and cytokines (IFN-g and TNF-a) by blood mononuclear cells (MNCs) and elevates the concentration of anti-inflammatory interleukin IL-1Ra. In vitro analysis shows no cytotoxicity of the a-C:H:SiO_x coating for the human blood MNCs, suggesting a promising PACVD on Ti alloys for cardiovascular implants, including pumps for mechanical heart support systems.