Investigation of the antimicrobial properties of modified multilayer diamond-like carbon coatings on 316 stainless steel surface and coatings technology

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 (HCPECVD). 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.