Charged hydrophilic polymer brushes and their relevance for understanding marine biofouling.

The resistance of charged polymers to biofouling was investigated by subjecting cationic (PDMAEMA), anionic (PSPMA), neutral (PHEMA-co-PEG10MA), and zwitterionic (PSBMA) brushes to assays testing protein adsorption; attachment of the marine bacterium Cobetia marina; settlement and adhesion strength of zoospores of the green alga Ulva linza; settlement of barnacle (Balanus amphitrite and B. improvisus) cypris larvae; and field immersion tests. Several results go beyond the expected dependence on direct electrostatic attraction; PSPMA showed good resistance towards attachment of C. marina, low settlement and adhesion of U. linza zoospores, and significantly lower biofouling than on PHEMA-co-PEG10MA or PSBMA after a field test for one week. PDMAEMA showed potential as a contact-active anti-algal coating due to its capacity to damage attached spores. However, after field testing for eight weeks, there were no significant differences in biofouling coverage among the surfaces. While charged polymers are unsuitable as antifouling coatings in the natural environment, they provide valuable insights into fouling processes, and are relevant for studies due to charging of nominally neutral surfaces.

Hydration and chain entanglement determines the optimum thickness of poly(HEMA-co-PEG10MA) brushes for effective resistance to settlement and adhesion of marine fouling organisms.

Understanding how surface physicochemical properties influence the settlement and adhesion of marine fouling organisms is important for the development of effective and environmentally benign marine antifouling coatings. We demonstrate that the thickness of random poly(HEMA-co-PEG10MA) copolymer brushes affect antifouling behavior. Films of thicknesses ranging from 50 to 1000 Å were prepared via surface-initiated atom-transfer radical polymerization and characterized using infrared spectroscopy, ellipsometry, atomic force microscopy and contact angle measurements. The fouling resistance of these films was investigated by protein adsorption, attachment of the marine bacterium Cobetia marina, settlement and strength of attachment tests of zoospores of the marine alga Ulva linza and static immersion field tests. These assays show that the polymer film thickness influenced the antifouling performance, in that there is an optimum thickness range, 200-400 Å (dry thickness), where fouling of all types, as well as algal spore adhesion, was lower. Field test results also showed lower fouling within the same thickness range after 2 weeks of immersion. Studies by quartz crystal microbalance with dissipation and underwater captive bubble contact angle measurements show a strong correlation between lower fouling and higher hydration, viscosity and surface energy of the poly(HEMA-co-PEG10MA) brushes at thicknesses around 200-400 Å. We hypothesize that the reduced antifouling performance is caused by a lower hydration capacity of the polymer for thinner films, and that entanglement and crowding in the film reduces the conformational freedom, hydration capacity and fouling resistance for thicker films.

Effect of bacterial biofilms formed on fouling-release coatings from natural seawater and Cobetia marina, on the adhesion of two marine algae.

Previous studies have shown that bacterial biofilms formed from natural seawater (NSW) enhance the settlement of spores of the green alga Ulva linza, while single-species biofilms may enhance or reduce settlement, or have no effect at all. However, the effect of biofilms on the adhesion strength of algae, and how that may be influenced by coating/surface properties, is not known. In this study, the effect of biofilms formed from natural seawater and the marine bacterium Cobetia marina, on the settlement and the adhesion strength of spores and sporelings of the macroalga U. linza and the diatom Navicula incerta, was evaluated on Intersleek(®) 700, Intersleek(®) 900, poly(dimethylsiloxane) and glass. The settlement and adhesion strength of these algae were strongly influenced by biofilms and their nature. Biofilms formed from NSW enhanced the settlement (attachment) of both algae on all the surfaces while the effect of biofilms formed from C. marina varied with the coating type. The adhesion strength of spores and sporelings of U. linza and diatoms was reduced on all the surfaces biofilmed with C. marina, while adhesion strength on biofilms formed from NSW was dependent on the alga (and on its stage of development in the case of U. linza), and coating type. The results illustrate the complexity of the relationships between fouling algae and bacterial biofilms and suggest the need for caution to avoid over-generalisation.