Investigation of the Antimicrobial Properties of Modified Multilayer Diamond-Like Carbon Coatings on 316 Stainless Steel

Modified diamond-like carbon (DLC) coatings were deposited onto 25-mm-diameter 316 stainless steel discs by pulsed direct-current (DC) hollow-cathode plasma-enhanced chemical vapor deposition (HC-PECVD). Multilayer films of total thickness 1-2 mu m were deposited, with varying quantities of germanium dopant. Characterization of the coatings was performed by scanning electron microscopy coupled with energy dispersive X-ray spectroscopy (SEM/EDX), surface energy/contact angle analysis, and antimicrobial susceptibility testing. Both modified DLC and germanium-doped DLC (Ge-DLC) coatings showed a significant anti-biofouling effect on P. aeruginosa, a Gram-negative bacterium. A 90 % reduction in P. aeruginosa biomass was observed compared to control for both DLC and Ge-DLC; however, this effect could not be attributed to germanium incorporation alone. Neither modified DLC nor Ge-DLC showed a significant inhibitory effect on S. aureus, a Gram-positive bacterium. Scanning electron microscopy of P. aeruginosa biofilms on Ge-DLC coated 316 stainless steel clearly displayed disruption of the cellular wall, as well as leakage of cellular components; this effect was not observed with undoped DLC coating, suggesting that the incorporation of germanium into DLC coatings has a cidal mode of action versus P. aeruginosa biofilms.