Effect of titanium surface topography on plasma deposition of antibacterial polymer coatings

Plasma processing, e.g., functionalisation and deposition of antibacterial coatings, is often used to enhance surface properties of biomaterials. Plasma is, however, a non-uniform active medium, and the result of processing depends on the nature of both the plasma and the substratum. Here we show that when an antibacterial coating (i.e., polyterpenol) is plasma polymerised onto four types of titanium substrata that differ in their micro- and nano-scale topography (but not the bulk chemistry), the distribution of functional groups, e.g., –OH and –C[dbnd]O, in the polymer across the surface differs sufficiently, and so does the antibacterial activity of the resulting material system. While the addition of a coating hinders biofilm formation by Staphylococcus aureus and Pseudomonas aeruginosa, the bactericidal effect is significantly stronger in polymers deposited onto surfaces possessing lower degrees of nanoscale roughness, e.g., substrata after mechanical and chemical polishing. The reduced antibacterial efficacy of polymers on substrata with greater surface roughness (e.g., on mechanically polished or lotus leaf-like surfaces) is attributed to a greater extent of thickness non-uniformity and heterogeneity in the functional group distribution across the surface. These findings suggest that the magnitude and distribution of topographical features of the substratum should be considered when designing plasma-enabled surface modification strategies.