Enhanced antibacterial and corrosion resistance performance of fluorine-doped diamond-like carbon coatings on 316 L stainless steel.

Biomedical materials must meet increasingly stringent standards for antibacterial efficacy and corrosion resistance. This study investigates the enhancement of these properties in 316 L stainless steel through the application of fluorine-doped diamond-like carbon (F-DLC) coatings. A series of F-DLC coatings with varying fluorine (F) concentrations were fabricated using plasma-enhanced chemical vapour deposition (PECVD). Fluorine doping increased the sp2/sp3 ratio (0.65-0.93) and enhanced surface hydrophobicity, as indicated by an increase in the contact angle from 63.1° to 79.7°. The impact of F concentration on bacterial adhesion was investigated using Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). DLC coatings with higher F concentrations and sp2/sp3 ratios exhibited a notable reduction in bacterial adhesion - up to 74 % for E. coli and 77 % for S. aureus - compared to uncoated stainless steel. The extended Derjaguin-Landau-Verwey-Overbeek (XDLVO) theory was employed to model bacteria-surface interactions, revealing the role of F in bacterial adhesion behaviour. Furthermore, the F-DLC coatings achieved a significant corrosion inhibition rate of 98.3 % in Hanks' balanced salt solution at 37 °C. Overall, higher F concentrations in the DLC coatings promote antibacterial and anti-corrosion performance by shifting the carbon structure from a three-dimensional sp3-dominated configuration to a two-dimensional sp2-rich structure.