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) hollow cathode plasma enhanced chemical vapour deposition (HC-PECVD). Multilayer films of total thickness 1-2 μm were deposited, both with and without germanium dopant. Characterisation of the coatings was performed by SEM/EDX, surface energy/contact angle analysis, and assessment of possible biofilm-inhibiting properties. 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 modified DLC coating. This suggests that germanium-doped DLC coatings may potentially exhibit a cidal mode of action versus P. aeruginosa biofilms.