Anomalous settlement behavior of Ulva linza zoospores on cationic oligopeptide surfaces

Antifouling Coatings from Glassy Polyelectrolyte Complex Films

Coatings that prevent or decrease fouling are sought for many applications, including those that inhibit the attachment of organisms in aquatic environments. To date, antifouling coatings have mostly followed design criteria assembled over decades: surfaces should be well/strongly hydrated, possess low net charge, and maintain a hydrophilic character when exposed to the location of use. Thus, polymers based on ethylene glycol or zwitterionic repeat units have been shown to be highly effective. Unfortunately, hydrated materials can be quite soft, limiting their use in some environments. In a major paradigm shift, this work describes glassy antifouling films made from certain complexes of positive and negative polyelectrolytes. The dense network of electrostatic interactions yields tough materials below the glass transition temperature, Tg, in normal use, while the highly ionic character of these polyelectrolyte complexes ensures strong hydration. The proximity of equal numbers of opposite charges within these complexes mimics zwitterionic structures. Films, assembled layer-by-layer from aqueous solutions, contained sulfonated poly(ether ether ketone), SPEEK, a rigid polyelectrolyte that binds strongly to a selection of quaternary ammonium polycations. Layer-by-layer buildup of SPEEK and polycations was linear, indicating strong complexes between polyelectrolytes. Calorimetry also showed that complex formation was exothermic. Surfaces coated with these films in the 100 nm thickness range completely resisted adhesion of the common flagellate green algae, Chlamydomonas reinhardtii, which were removed from surfaces at a minimum applied flow rate of 0.8 cm s-1. The total surface charge density of adsorbed cations, determined with a sensitive radioisotopic label, was very low, around 10% of a monolayer, which minimized adsorption driven by counterion release from the surface. The viscoelastic properties of the complexes, which were stable even in concentrated salt solutions, were explored using rheology of bulk samples. When fully hydrated, their Tg values were observed to be above 75 °C.

Marine biofouling and the role of biocidal coatings in balancing environmental impacts

Marine biofouling is a global problem affecting various industries, particularly the shipping industry due to long-distance voyages across various ecosystems. Therein fouled hulls cause increased fuel consumption, greenhouse gas emissions, and the spread of invasive aquatic species. To counteract these issues, biofouling management plans are employed using manual cleaning protocols and protective coatings. This review provides a comprehensive overview of adhesion strategies of marine organisms, and currently available mitigation methods. Further, recent developments and open challenges of antifouling (AF) and fouling release (FR) coatings are discussed with regards to the future regulatory environment. Finally, an overview of the environmental and economic impact of fouling is provided to point out why and when the use of biocidal solutions is beneficial in the overall perspective.

Investigation of N-Substituted Morpholine Structures in an Amphiphilic PDMS-Based Antifouling and Fouling-Release Coating

Biofouling is a major disruptive process affecting the fuel efficiency and durability of maritime vessel coatings. Previous research has shown that amphiphilic coatings consisting of a siloxane backbone functionalized with hydrophilic moieties are effective marine antifouling and fouling-release materials. Poly(ethylene glycol) (PEG) has been the primary hydrophilic component used in such systems. Recently, the morpholine group has emerged as a promising compact alternative in antifouling membranes but is yet to be studied against marine foulants. In this work, the use of morpholine moieties to generate amphiphilicity in a poly(dimethylsiloxane) (PDMS)-based antifouling and fouling-release coating was explored. Two separate coating sets were investigated. The first set examined the incorporation of an N-substituted morpholine amine, and while these coatings showed promising fouling-release properties for Ulva linza, they had unusually high settlement of spores compared to controls. Based on those results, a second set of materials was synthesized using an N-substituted morpholine amide to probe the source of the high settlement and was found to significantly improve antifouling performance. Both coating sets included PEG controls with varying lengths to compare the viability of the morpholine structures as alternative hydrophilic groups. Surfaces were evaluated through a combination of bubble contact angle goniometry, profilometry, X-ray photoelectron spectroscopy (XPS), and marine bioassays against two soft fouling species, U. linza and Navicula incerta, known to have different adhesion characteristics.

Sol-Gel-Based Hybrid Materials as Antifouling and Fouling-Release Coatings for Marine Applications

Hybrid materials (HMs) offer unique properties as they combine inorganic and organic components into a single material. Here, we developed HM coatings for marine antifouling applications using sol-gel chemistry and naturally occurring polysaccharides. The coatings were characterized by spectroscopic ellipsometry, contact angle goniometry, AFM, and ATR-FTIR, and their stability was tested in saline media. Marine antifouling and fouling-release properties were tested in laboratory assays against the settlement of larvae of the barnacle Balanus improvisus and against the settlement and removal of the diatom Navicula incerta. Furthermore, laboratory data were confirmed in short-term dynamic field assays in Florida, USA. All hybrid coatings revealed a superior performance in the assays compared to a hydrophobic reference. Within the hybrids, those with the highest degree of hydrophilicity and negative net charge across the surface performed best. Alginate and heparin showed good performance, making these hybrid materials promising building blocks for fouling-resistant coatings.

A mechanism for temporary bioadhesion

The flatworm Macrostomum lignano features a duo-gland adhesive system that allows it to repeatedly attach to and release from substrates in seawater within a minute. However, little is known about the molecules involved in this temporary adhesion. In this study, we show that the attachment of M. lignano relies on the secretion of two large adhesive proteins, M. lignano adhesion protein 1 (Mlig-ap1) and Mlig-ap2. We revealed that both proteins are expressed in the adhesive gland cells and that their distribution within the adhesive footprints was spatially restricted. RNA interference knockdown experiments demonstrated the essential function of these two proteins in flatworm adhesion. Negatively charged modified sugars in the surrounding water inhibited flatworm attachment, while positively charged molecules impeded detachment. In addition, we found that M. lignano could not adhere to strongly hydrated surfaces. We propose an attachment-release model where Mlig-ap2 attaches to the substrate and Mlig-ap1 exhibits a cohesive function. A small negatively charged molecule is secreted that interferes with Mlig-ap1, inducing detachment. These findings are of relevance for fundamental adhesion science and efforts to mitigate biofouling. Further, this model of flatworm temporary adhesion may serve as the starting point for the development of synthetic reversible adhesion systems for medicinal and industrial applications.

Antifouling Ion-Exchange Resins

Large quantities of organic ion-exchange resins are used worldwide for water decontamination and polishing. Fouling by microorganisms and decomposition products of natural organic matter severely limits the lifetime of these resins. Much research has thus been invested in polymer-based antifouling coatings. In the present study, poly(4-styrenesulfonate) (PSS) and a co-polymer of PSS and a zwitterionic group were used to spontaneously coat commercial Dowex 1X8 anion-exchange resin. UV-visible spectroscopy provided a precise measure of the kinetics and amount of PSS sorbed onto or into resin beads. When challenged with Chlamydomonas reinhardtii algae, uncoated resin was rapidly fouled by algae. Coating the resin with either the homopolymer of PSS or the co-polymer with zwitterion eliminated fouling. Using narrow- and wide-molecular-weight distribution PSS, a cutoff molecular weight of about 240 repeat units was found, above which PSS was unable to diffuse into the resin. Thus, only one monolayer of added PSS was sufficient to confer a highly desirable antifouling property on this resin while consuming less than 0.1% of the exchanger capacity. Radioactive sulfate ions were used to probe the kinetics of (self)exchange, which were virtually unaffected by the PSS coating. This resin treatment is a fast, ultra-low-cost step for potentially enhancing the lifetime of ion exchangers.

Contribution of Charges in Polyvinyl Alcohol Networks to Marine Antifouling

Semi-interpenetrated polyvinyl alcohol polymer networks (SIPNs) were prepared by integrating various charged components into polyvinyl alcohol polymer. Contact angle measurement, attenuated total reflection Fourier transform infrared spectroscopy, field emission scanning electron microscopy, and tensile tests were used to characterize the physicochemical properties of the prepared SIPNs. To investigate the contribution of charges to marine antifouling, the adhesion behaviors of green algae Dunaliella tertiolecta and diatoms Navicula sp. in the laboratory and of the actual marine animals in field test were studied for biofouling assays. The results suggest that less algae accumulation densities are observed for neutral-, anionic-, and zwitterionic-component-integrated SIPNs. However, for the cationic SIPNs, despite the hydration shell induced by the ion-dipole interaction, the resistance to biofouling largely depends on the amount of cationic component because of the possible favorable electrostatic attraction between the cationic groups in SIPNs and the negatively charged algae. Considering that the preparation of novel nontoxic antifouling coating is a long-standing and cosmopolitan industrial challenge, the SIPNs may provide a useful reference for marine antifouling and some other relevant fields.

Antialgal activity of poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) brushes against the marine alga Ulva

Marine biofouling has detrimental effects on the environment and economy, and current antifouling coatings research is aimed at environmentally benign, non-toxic materials. The possibility of using contact-active coatings is explored, by considering the antialgal activity of cationic poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) brushes. The antialgal activity was investigated via zoospore settlement and sporeling growth assays of the marine algae Ulva linza and U. lactuca. The assay results for PDMAEMA brushes were compared to those for anionic and neutral surfaces. It was found that only PDMAEMA could disrupt zoospores that come into contact with it, and that it also inhibits the subsequent growth of normally settled spores. Based on the spore membrane properties, and characterization of the PDMAEMA brushes over a wide pH range, it is hypothesized that the algicidal mechanisms are similar to the bactericidal mechanisms of cationic polymers, and that further development could lead to successful contact-active antialgal coatings.

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.

Attachment of Algal Cells to Zwitterionic Self-Assembled Monolayers Comprised of Different Anionic Compounds

The influence of zwitterionic self-assembled monolayers on settlement and removal of algae was studied. The monolayers were constructed either from zwitterionic thiols or from solutions of positively and negatively charged thiols. The cationic component was composed of quaternary ammonium terminated thiols and the anionic component contained sulfate or carboxylate termination. During assembly, all surfaces showed a strong tendency for equilibration of the surface charge. Settlement and adhesion assays with zoospores of Ulva linza and the diatom Navicula incerta, and field tests of the initial surface colonization revealed the relevance of charge equilibration for the biological inertness of the prepared surfaces.

Holographic microscopy provides new insights into the settlement of zoospores of the green alga Ulva linza on cationic oligopeptide surfaces

Interaction of zoospores of Ulva linza with cationic, arginine-rich oligopeptide self-assembled monolayers (SAMs) is characterized by rapid settlement. Some spores settle (ie permanently attach) in a 'normal' manner involving the secretion of a permanent adhesive, retraction of the flagella and cell wall formation, whilst others undergo 'pseudosettlement' whereby motile spores are trapped (attached) on the SAM surface without undergoing the normal metamorphosis into a settled spore. Holographic microscopy was used to record videos of swimming zoospores in the vicinity of surfaces with different cationic oligopeptide concentrations to provide time-resolved insights into processes associated with attachment of spores. The data reveal that spore attachment rate increases with increasing cationic peptide content. Accordingly, the decrease in swimming activity in the volume of seawater above the surface accelerated with increasing surface charge. Three-dimensional trajectories of individual swimming spores showed a 'hit and stick' motion pattern, exclusively observed for the arginine-rich peptide SAMs, whereby spores were immediately trapped upon contact with the surface.

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.

Seaweed-microbial interactions: key functions of seaweed-associated bacteria

Seaweed-associated bacteria play a crucial role in morphogenesis and growth of seaweeds (macroalgae) in direct and/or indirect ways. Bacterial communities belonging to the phyla Proteobacteria and Firmicutes are generally the most abundant on seaweed surfaces. Associated bacterial communities produce plant growth-promoting substances, quorum sensing signalling molecules, bioactive compounds and other effective molecules that are responsible for normal morphology, development and growth of seaweeds. Also, bioactive molecules of associated bacteria determine the presence of other bacterial strains on seaweeds and protect the host from harmful entities present in the pelagic realm. The ecological functions of cross-domain signalling between seaweeds and bacteria have been reported as liberation of carpospores in the red seaweeds and settlement of zoospores in the green seaweeds. In the present review, the role of extracellular polymeric substances in growth and settlement of seaweeds spores is also highlighted. To elucidate the functional roles of associated bacteria and the molecular mechanisms underlying reported ecological phenomena in seaweeds requires a combined ecological, microbiological and biochemical approach.

The performance of aminoalkyl/fluorocarbon/hydrocarbon-modified xerogel coatings against the marine alga Ectocarpus crouaniorum: relative roles of surface energy and charge

The effect of a series of xerogel coatings modified with aminoalkyl/fluorocarbon/hydrocarbon groups on the adhesion of a new test species, the filamentous brown alga Ectocarpus crouaniorum, has been explored, and compared with the green alga Ulva linza. The results showed that E. crouaniorum adhered weakly to the less polar, low wettability coatings in the series, but stronger adhesion was shown on polar, higher surface energy coatings containing aminoalkyl groups. The results from a separate series of coatings tuned to have similar surface energies and polarities after immersion in artificial seawater (ASW), but widely different surface charges, demonstrated that surface charge was more important than surface energy and polarity in determining the adhesion strength of both E. crouaniorum and U. linza on xerogel coatings. No correlation was found between adhesion and contact angle hysteresis. X-ray photoelectron spectroscopy analysis of samples after immersion in ASW confirmed the presence of charged ammonium groups on the surface of the aminoalkylated coatings.

Development and characteristics of an adhesion bioassay for ectocarpoid algae

Species of filamentous brown algae in the family Ectocarpaceae are significant members of fouling communities. However, there are few systematic studies on the influence of surface physico-chemical properties on their adhesion. In the present paper the development of a novel, laboratory-based adhesion bioassay for ectocarpoid algae, at an appropriate scale for the screening of sets of experimental samples in well-replicated and controlled experiments is described. The assays are based on the colonization of surfaces from a starting inoculum consisting of multicellular filaments obtained by blending the cultured alga Ectocarpus crouaniorum. The adhesion strength of the biomass after 14 days growth was assessed by applying a hydrodynamic shear stress. Results from adhesion tests on a set of standard surfaces showed that E. crouaniorum adhered more weakly to the amphiphilic Intersleek® 900 than to the more hydrophobic Intersleek® 700 and Silastic® T2 coatings. Adhesion to hydrophilic glass was also weak. Similar results were obtained for other cultivated species of Ectocarpus but differed from those obtained with the related ectocarpoid species Hincksia secunda. The response of the ectocarpoid algae to the surfaces was also compared to that for the green alga, Ulva.

Effects of surface charge and Gibbs surface energy on the settlement behaviour of barnacle cyprids (Balanus amphitrite)

Gibbs surface energy has long been considered to be an important parameter in the design of fouling-resistant surfaces for marine applications. Rigorous testing of the hypothesis that settlement is related to Gibbs surface energy however has never been accomplished, due mainly to practical limitations imposed by the necessary combination of surface engineering and biological evaluation methods. In this article, the effects of surface charge and Gibbs surface energy on the settlement of cyprids of an important fouling barnacle, Balanus amphitrite, were evaluated. Settlement assays were conducted on a range of self-assembled monolayers (SAMs) (CH(3)-, OH-, COOH-, N(CH(3))(3) (+)-, NH(2)-terminated), presented in gold-coated polystyrene well plates, varying in terms of their surface charge and Gibbs surface energy. Contrary to contemporary theory, settlement was not increased by high-energy surfaces, rather the opposite was found to be the case with cyprids settling in greater numbers on a low-energy CH(3)- SAM compared to a high-energy OH- SAM. Settlement was also greater on negatively-charged SAMs, compared to neutral and positively-charged SAMs. These findings are discussed in the context of data drawn from surfaces that varied in multiple characteristics simultaneously, as have been used previously for such experiments. The finding that surface charge, rather than total surface energy, may be responsible for surface selection by cyprids, will have significant implications for the design of future fouling-resistant materials.

Resistance of galactoside-terminated alkanethiol self-assembled monolayers to marine fouling organisms

Self-assembled monolayers (SAMs) of galactoside-terminated alkanethiols have protein-resistance properties which can be tuned via the degree of methylation [Langmuir 2005, 21, 2971-2980]. Specifically, a partially methylated compound was more resistant to nonspecific protein adsorption than the hydroxylated or fully methylated counterparts. We investigate whether this also holds true for resistance to the attachment and adhesion of a range of marine species, in order to clarify to what extent resistance to protein adsorption correlates with the more complex adhesion of fouling organisms. The partially methylated galactoside-terminated SAM was further compared to a mixed monolayer of ω-substituted methyl- and hydroxyl-terminated alkanethiols with wetting properties and surface ratio of hydroxyl to methyl groups matching that of the galactoside. The settlement (initial attachment) and adhesion strength of four model marine fouling organisms were investigated, representing both micro- and macrofoulers; two bacteria (Cobetia marina and Marinobacter hydrocarbonoclasticus), barnacle cypris larvae (Balanus amphitrite), and algal zoospores (Ulva linza). The minimum in protein adsorption onto the partially methylated galactoside surface was partly reproduced in the marine fouling assays, providing some support for a relationship between protein resistance and adhesion of marine fouling organisms. The mixed alkanethiol SAM, which was matched in wettability to the partially methylated galactoside SAM, consistently showed higher settlement (initial attachment) of test organisms than the galactoside, implying that both wettability and surface chemistry are insufficient to explain differences in fouling resistance. We suggest that differences in the structure of interfacial water may explain the variation in adhesion to these SAMs.

Engineered antifouling microtopographies: the role of Reynolds number in a model that predicts attachment of zoospores of Ulva and cells of Cobetia marina

A correlation between the attachment density of cells from two phylogenetic groups (prokaryotic Bacteria and eukaryotic Plantae), with surface roughness is reported for the first time. The results represent a paradigm shift in the understanding of cell attachment, which is a critical step in the biofouling process. The model predicts that the attachment densities of zoospores of the green alga, Ulva, and cells of the marine bacterium, Cobetia marina, scale inversely with surface roughness. The size and motility of the bacterial cells and algal spores were incorporated into the attachment model by multiplying the engineered roughness index (ERI(II)), which is a representation of surface energy, by the Reynolds number (Re) of the cells. The results showed a negative linear correlation of normalized, transformed attachment density for both organisms with ERI(II) x Re (R(2) = 0.77). These studies demonstrate for the first time that organisms respond in a uniform manner to a model, which incorporates surface energy and the Reynolds number of the organism.

A model that predicts the attachment behavior of Ulva linza zoospores on surface topography

A predictive model for the attachment of spores of the green alga Ulva on patterned topographical surfaces was developed using a constant refinement approach. This 'attachment model' incorporated two historical data sets and a modified version of the previously-described Engineered Roughness Index. Two sets of newly-designed surfaces were used to evaluate the effect of two components of the model on spore settlement. Spores attached in fewer numbers when the area fraction of feature tops increased or when the number of distinct features in the design increased, as predicted by the model. The model correctly predicted the spore attachment density on three previously-untested surfaces relative to a smooth surface. The two historical data sets and two new data sets showed high correlation (R(2) = 0.88) with the model. This model may be useful for designing new antifouling topographies.

The role of "inert" surface chemistry in marine biofouling prevention

The settlement and colonization of marine organisms on submerged man-made surfaces is a major economic problem for many marine industries. The most apparent detrimental effects of biofouling are increased fuel consumption of ships, clogging of membranes and heat exchangers, disabled underwater sensors, and growth of biofoulers in aquaculture systems. The presently common-but environmentally very problematic-way to deal with marine biofouling is to incorporate biocides, which use biocidal products in the surface coatings to kill the colonizing organisms, into the surface coatings. Since the implementation of the International Maritime Organization Treaty on biocides in 2008, the use of tributyltin (TBT) is restricted and thus environmentally benign but effective surface coatings are required. In this short review, we summarize the different strategies which are pursued in academia and industry to better understand the mechanisms of biofouling and to develop strategies which can be used for industrial products. Our focus will be on chemically "inert" model surface coatings, in particular oligo- and poly(ethylene glycol) (OEG and PEG) functionalized surface films. The reasons for choosing this class of chemistry as an example are three-fold: Firstly, experiments on spore settlement on OEG and PEG coatings help to understand the mechanism of non-fouling of highly hydrated interfaces; secondly, these studies defy the common assumption that surface hydrophilicity-as measured by water contact angles-is an unambiguous and predictive tool to determine the fouling behavior on the surface; and thirdly, choosing this system is a good example for "interfacial systems chemistry": it connects the behavior of unicellular marine organisms with the antifouling properties of a hydrated surface coating with structural and electronic properties as derived from ab initio quantum mechanical calculations using the electronic wave functions of oxygen, hydrogen, and carbon. This short review is written to outline for non-experts the hierarchical structure in length- and timescale of marine biofouling and the role of surface chemistry in fouling prevention. Experts in the field are referred to more specialized recent reviews.

Antimicrobial behavior of semifluorinated-quaternized triblock copolymers against airborne and marine microorganisms

Semifluorinated-quaternized triblock copolymers (SQTCs) were synthesized by chemical modification of polystyrene-block-poly(ethylene-ran-butylene)-block-polyisoprene ABC triblock copolymers. Surface characterization of the polymers was performed by X-ray photoelectron spectroscopy (XPS) and near-edge X-ray absorption fine structure (NEXAFS) analysis. The surface of the SQTC showed very high antibacterial activity against the airborne bacterium Staphylococcus aureus with >99 % inhibition of growth. In contrast in marine fouling assays, zoospores of the green alga Ulva settled on the SQTC, which can be attributed to the positively charged surface. The adhesion strength of sporelings (young plants) of Ulva and Navicula diatoms (a unicellular alga) was high. The SQTC did not show marked algicidal activity.

Polysulfobetaine-grafted surfaces as environmentally benign ultralow fouling marine coatings

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.

Physicochemical properties of (ethylene glycol)-containing self-assembled monolayers relevant for protein and algal cell resistance

The influence of the number of repeating units in self-assembled monolayers (SAMs) of ethylene glycol and of their end-group termination on the settlement and adhesion of two types of algal cells, viz., zoospores of the macroalga Ulva and cells of the diatom Navicula , was studied. The findings are related to the resistance of these surfaces against fibrinogen adsorption. Results showed that settlement and adhesion of algal cells to oligo(ethylene glycol) (OEG; 2-6 EG units) and poly(ethylene glycol) (PEG; MW = 2000, 5000) SAMs was low, while resistance was less effective for mono(ethylene glycol) (EG(1)OH)-terminated surfaces. These findings concur with former protein adsorption studies. In situ microscopy showed that PEG surfaces inhibited the settlement of zoospores, i.e., zoospores did not attach to the surfaces and remained motile. In contrast, on EG(2-6)OH surfaces, although zoospores settled, i.e., they secreted adhesive and lost motility, adhesion between secreted adhesive and the surface was extremely weak, and the settled spores were unable to bond to the surfaces. The influence of surface properties such as hydration, conformational degrees of freedom, and interfacial characteristics of the SAMs is discussed to understand the underlying repulsive mechanisms occurring in (ethylene glycol)-based coatings.

Interactions of zoospores of Ulva linza with arginine-rich oligopeptide monolayers

We recently reported on the strong interactions of zoospores of the green alga, Ulva linza with an arginine-rich oligopeptide self-assembled monolayer (SAM) [Biofouling 2008, 24, 303-312], where the arginine-rich peptide induced not only high spore settlement, but also a form of abnormal settlement, or "pseudo-settlement", whereby a proportion of spores do not go through the normal process of surface exploration, adhesive exocytosis, and loss of flagella. Further, it was demonstrated that both the total number of settled spores and the fraction of pseudosettled spores were related to the surface density of the arginine-rich peptide. Here we present a further investigation of the interactions of zoospores of Ulva with a set of oligomeric, de novo designed, arginine-rich peptides, specifically aimed to test the effect of peptide primary structure on the interaction. Via variations in the peptide length and by permutations in the amino acid sequences, we gain further insight into the spore-surface interactions. The interpretation of the biological assays is supported by physicochemical characterization of the SAMs using infrared spectroscopy, ellipsometry, and contact angle measurements. Results confirm the importance of arginine residues for the anomalous pseudosettlement, and we found that settlement is modulated by variations in both the total length and peptide primary structure. To elucidate the causes of the anomalous settlement and the possible relation to peptide-membrane interactions, we also compared the settlement of the "naked" zoospores of Ulva (which present a lipoprotein membrane to the exterior without a discrete polysaccharide cell wall), with the settlement of diatoms (unicellular algae that are surrounded by a silica cell wall), onto the peptide SAMs. Cationic SAMs do not notably affect settlement (attachment), adhesion strength, or viability of diatom cells, suggesting that the effect of the peptides on zoospores of Ulva is mediated via specific peptide-membrane interactions.

Marine antifouling laboratory bioassays: an overview of their diversity

In aquatic environments, biofouling is a natural process of colonization of submerged surfaces, either living or artificial, involving a wide range of organisms from bacteria to invertebrates. Antifouling can be defined as preventing the attachment of organisms onto surfaces. This article reviews the laboratory bioassays that have been developed for studying the control of algae and invertebrates by epibiosis (chemical ecology) and the screening of new active compounds (natural products and biocides) to inhibit settlement or adhesion, ie fouling-release coatings. The assays utilize a range of organisms (mainly marine bacteria, diatoms, algae, barnacles). The main attributes of assays for micro- and macroorganisms are described in terms of their main characteristics and depending on the biological process assessed (growth, adhesion, toxicity, behavior). The validation of bioassays is also discussed.