Reduction of bacterial adhesion on titanium-doped diamond-like carbon coatings.

A range of titanium doped diamond-like carbon (Ti-DLC) coatings with different Ti contents were prepared on stainless steel substrates using a plasma-enhanced chemical vapour deposition technique. It was found that both the electron donor surface energy and the surface roughness of the Ti-DLC coatings increased with increasing Ti contents in the coatings. Bacterial adhesion to the coatings was evaluated against Escherichia coli WT F1693 and Pseudomonas aeruginosa ATCC 33347. The experimental data showed that bacterial adhesion decreased with the increases of the Ti content, the electron donor surface energy and surface roughness of the coatings, while the bacterial removal percentage increased with the increases of these parameters. The Ti-DLC coatings reduced bacterial attachment by up to 75% and increased bacterial detachment from 15 to 45%, compared with stainless steel control.

Bacterial attachment and removal properties of silicon- and nitrogen-doped diamond-like carbon coatings.

Si- and N-doped diamond-like carbon (DLC) coatings with various Si and N contents were deposited on glass slides using magnetron sputter ion-plating and plasma-enhanced chemical vapour deposition. Surface energy analysis of the DLC coatings revealed that with increasing Si content, the electron acceptor gamma(s)(+) value decreased while the electron donor gamma(s)(-) value increased. The antifouling property of DLC coatings was evaluated with the bacterium, Pseudomonas fluorescens, which is one of the most common microorganisms forming biofilms on the surface of heat exchangers in cooling water systems. P. fluorescens had a high value of the gamma(s)(-) component (69.78 mN m(-1)) and a low value of the gamma(s)(+) component (5.97 mN m(-1)), and would be negatively charged with the zeta potential of -16.1 mV. The experimental results showed that bacterial removal by a standardised washing procedure increased significantly with increasing electron donor gamma(s)(-) values and with decreasing electron acceptor gamma(s)(+) values of DLC coatings. The incorporation of 2%N into the Si-doped DLC coatings further significantly reduced bacterial attachment and significantly increased ease of removal. The best Si-N-doped DLC coatings reduced bacterial attachment by 58% and increased removal by 41%, compared with a silicone coating, Silastic T2. Bacterial adhesion strength on the DLC coatings is explained in terms of thermodynamic work of adhesion.