'Marine biofouling', the undesired growth of marine organisms such as microorganisms, barnacles and seaweeds on submerged surfaces, is a global problem for maritime industries, with both economic and ...environmental penalties. The primary strategy for combating marine fouling is to use biocide-containing paints, but environmental concerns and legislation are driving science and technology towards non-biocidal solutions based solely on physico-chemical and materials properties of coatings. Advances in nanotechnology and polymer science, and the development of novel surface designs 'bioinspired' by nature, are expected to have a significant impact on the development of a new generation of environmentally friendly marine coatings.
Marine biofouling is a longstanding problem because of the constant challenges placed by various fouling species and increasingly restricted environmental regulations for antifouling coatings. Novel ...nonbiocidal strategies to control biofouling will necessitate a multifunctional approach to coating design. Here we show that slippery liquid-infused porous surfaces (SLIPSs) provide another possible strategy to obtaining promising antifouling coatings. Microporous butyl methacrylate-ethylene dimethacrylate (BMA-EDMA) surfaces are prepared via UV-initiated free-radical polymerization. Subsequent infusion of fluorocarbon lubricants (Krytox103, Krytox100, and Fluorinert FC-70) into the porous microtexture results in liquid-repellent slippery surfaces. To study the interaction with marine fouling organisms, settlement of zoospores of the alga Ulva linza and cypris larvae of the barnacle Balanus amphitrite is tested in laboratory assays. BMA-EDMA surfaces infused with Krytox103 and Krytox100 exhibit remarkable inhibition of settlement (attachment) of both spores and cyprids to a level comparable to that of a poly(ethylene glycol) (PEG)-terminated self-assembled monolayer. In addition, the adhesion strength of sporelings (young plants) of U. linza is reduced for BMA-EDMA surfaces infused with Krytox103 and Krytox100 compared to pristine (noninfused) BMA-EDMA and BMA-EDMA infused with Fluorinert FC-70. Immersion tests suggest a correlation between the stability of slippery coatings in artificial seawater and fouling resistance efficacy. The results indicate great potential for the application of this concept in fouling-resistant marine coatings.
Natural and artificial substrata immersed in the marine environment are typically colonized by microorganisms, which may moderate the settlement/recruitment of algal spores and invertebrate larvae of ...macrofouling organisms. This mini-review summarizes the major interactions occurring between microbial biofilms and marine fouling algae, including their effects on the settlement, growth and morphology of the adult plants. The roles of chemical compounds that are produced by both bacteria and algae and which drive the interactions are reviewed. The possibility of using such bioactive compounds to control macrofouling will be discussed.
We report on the formation and testing of novel marine coatings comprising hierarchically wrinkled surface topographies (HWTS) having wrinkles of different length scales (generations) ranging from ...tens of nanometers to a fraction of a millimeter. The individual wrinkle generations are arranged in nested patterns, where each larger wrinkle resides underneath and represents a scaled-up version of the smaller wrinkle. We present and discuss results from field tests in seawater and laboratory experiments. The results of our field tests reveal that while coatings with flat topographies foul after relatively short time periods (4-15 weeks), the HWST coatings with the same chemistries as flat coatings remain relatively free of biofouling even after prolonged exposure to seawater (18 months). In contrast to flat coatings, the HWST substrates are not colonized by barnacles. These observations suggest that surface topography plays a dominant role in governing the coating defense against barnacle fouling even without fine-tuning the chemical composition of the overcoat. Laboratory experiments indicate that settlement of zoospores of the green alga Ulva and the strength of attachment of sporelings (young plants) depend on the chemical composition of the coating as well as surface topography.
Novel, non-toxic antifouling technologies are focused on the manipulation of surface topography to deter settlement of the dispersal stages of fouling organisms. This study investigated the effect of ...the aspect ratio (feature height/feature width) of topographical features engineered in polydimethylsiloxane, on the settlement of cyprids of Balanus amphitrite and zoospores of Ulva linza. The correlation of relative aspect ratios to antifouling efficacy was proven to be significant. An increase in aspect ratio resulted in an increase of fouling deterrence for both zoospores and cyprids. The spore density of Ulva was reduced 42% with each unit increase in aspect ratio of the Ulva-specific Sharklet AF™ topography. Similarly, the number of settled cyprids was reduced 45% with each unit increase in aspect ratio. The newly described barnacle-specific Sharklet AF™ topography (40 μm feature height, aspect ratio of 2) reduced cyprid settled by 97%. Techniques have been developed to superimpose the smaller Ulva-specific topographies onto the barnacle-specific surfaces into a hierarchical structure to repel both organisms simultaneously. The results for spore settlement on first-generation hierarchical surfaces provide insight for the efficacious design of such structures when targeting multiple settling species.
Current antifouling strategies are focused on the development of environmentally friendly coatings that protect submerged surfaces from the accumulation of colonizing organisms (i.e., biofouling). ...One ecofriendly approach is the manipulation of the surface topography on nontoxic materials to deter settlement of the dispersal stages of fouling organisms. The identification of effective antifouling topographies typically occurs through trial-and-error rather than predictive models. We present a model and design methodology for the identification of nontoxic, antifouling surface topographies for use in the marine environment by the creation of engineered nanoforce gradients. The design and fabrication of these gradients incorporate discrete micrometer-sized features that are associated with the species-specific surface design technique of engineered topography and the concepts of mechanotransduction. The effectiveness of designed nanoforce gradients for antifouling applications was tested by evaluating the settlement behavior of zoospores of the alga Ulva linza. The surfaces with nanoforce gradients ranging from 125 to 374 nN all significantly reduced spore settlement relative to a smooth substrate, with the highest reduction, 53%, measured on the 374 nN gradient surface. These results confirm that the designed nanoforce gradients may be an effective tool and predictive model for the design of unique nontoxic, nonfouling surfaces for marine applications as well as biomedical surfaces in the physiological environment.
Bioadhesion and surface wettability are influenced by microscale topography. In the present study, engineered pillars, ridges and biomimetic topography inspired by the skin of fast moving sharks ...(Sharklet AF™) were replicated in polydimethylsiloxane elastomer. Sessile drop contact angle changes on the surfaces correlated well (R
2
= 0.89) with Wenzel and Cassie and Baxter's relationships for wettability. Two separate biological responses, i.e. settlement of Ulva linza zoospores and alignment of porcine cardiovascular endothelial cells, were inversely proportional to the width (between 5 and 20 μm) of the engineered channels. Zoospore settlement was reduced by ∼85% on the finer (ca 2 μm) and more complex Sharklet AF™ topographies. The response of both cell types suggests their responses are governed by the same underlying thermodynamic principles as wettability.
Coatings based on polysulfobetaine polymers are being developed as environmentally benign, fouling-resistant marine coatings. Poly(sulfobetaine methacrylate) (polySBMA) brushes were grafted onto ...glass surfaces using surface-initiated atom transfer radical polymerization (ATRP). The settlement, growth, and attachment strength of marine algae were investigated on polySBMA-coated surfaces. Results showed that few spores of the green marine alga, Ulva, settled (attached) on the polySMBA surfaces, and the adhesion strength of both spores and sporelings (young plants) was low. Diatoms were also mostly unable to adhere to the polySMBA surfaces. Assays demonstrated that SBMA polymers in solution were not toxic. The data are discussed in terms of the interfacial properties presented by the polySMBA surfaces. Zwitterionic polymers and coatings exhibit great advantages for their effectiveness to resist marine fouling while being environmentally benign and are promising as ultralow fouling marine coatings.
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.
New amphiphilic block copolymers S nSz m consisting of blocks with varied degrees of polymerization, n and m, of polystyrene, S, and polystyrene carrying an amphiphilic ...polyoxyethylene-polytetrafluoroethylene chain side-group, Sz, were prepared by controlled atom transfer radical polymerization (ATRP). The block copolymers, either alone or in a blend with commercial SEBS (10 wt% SEBS), were spin-coated in thinner films (200-400 nm) on glass and spray-coated in thicker films ( approximately 500 nm) on a SEBS underlayer (150-200 microm). Angle-resolved X-ray photoelectron spectroscopy (XPS) measurements proved that at any photoemission angle, varphi, the atomic ratio F/C was larger than that expected from the known stoichiometry. Consistent with the enrichment of the outer film surface (3-10 nm) in F content, the measured contact angles, theta, with water (theta w > or = 107 degrees ) and n-hexadecane (theta h > or = 64 degrees ) pointed to the simultaneous hydrophobic and lipophobic character of the films. The film surface tension gamma S calculated from the theta values was in the range 13-15 mN/m. However, the XPS measurements on the "wet" films after immersion in water demonstrated that the film surface underwent reconstruction owing to its amphiphilic nature, thereby giving rise to a more chemically heterogeneous structure. The atomic force microscopy (AFM) images (tapping mode/AC mode) revealed well-defined morphological features of the nanostructured films. Depending on the chemical composition of the block copolymers, spherical (ca. 20 nm diameter) and lying cylindrical (24-29 nm periodicity) nanodomains of the S discrete phase were segregated from the Sz continuous matrix (root-mean-square, rms, roughness approximately 1 nm). After immersion in water, the underwater AFM patterns evidenced a transformation to a mixed surface structure, in which the nanoscale heterogeneity and topography (rms = 1-6 nm) were increased. The coatings were subjected to laboratory bioassays to explore their intrinsic ability to resist the settlement and reduce the adhesion strength of two marine algae, viz., the macroalga (seaweed) Ulva linza and the unicellular diatom Navicula perminuta. The amphiphilic nature of the copolymer coatings resulted in distinctly different performances against these two organisms. Ulva adhered less strongly to the coatings richer in the amphiphilic polystyrene component, percentage removal being maximal at intermediate weight contents. In contrast, Navicula cells adhered less strongly to coatings with a lower weight percentage of the amphiphilic side chains. The results are discussed in terms of the changes in surface structure caused by immersion and the effects such changes may have on the adhesion of the test organisms.
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