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This study investigates the micro-topographic surfaces as a benign anti-fouling/fouling-release method. The bio-inspired engineered surfaces were manufactured by controlling the viscoelastic instabilities of carbon nanotubes (CNTs) and polydimethylsiloxane (PDMS) nanocomposites using a customized, scalable two-roll coating process. The effects of manufacturing conditions, i.e., roller speed and roller radius-to-gap ratio, on surface properties, such as Wenzel roughness factor, peak density, water contact angle, and the tensile testing of the nanocomposite, were studied. The results showed that decreasing roller gap distance would significantly increase the hydrophobicity of the samples. Moreover, a positive correlation was observed between surface peak density and roughness factor. A textured sample was manufactured that significantly outperformed the non-textured CNT-PDMS, indicating a correlation between surface roughness and diatom attachment density. The dynamic diatom attachment assay showed up to 35% reduction in surface coverage of textured samples by the Navicula perminuta diatom compared to the non-textured CNT-PDMS control samples.

Biofouling is a major challenge for sustainable shipping, filter membranes, heat exchangers, and medical devices. The development of fouling-resistant coatings requires the evaluation of their effectiveness. Such an evaluation is usually based on the assessment of fouling progression after different exposure times to the target medium (e.g. salt water). The manual assessment of macrofouling requires expert knowledge about local fouling communities due to high variances in phenotypical appearance, has single-image sampling inaccuracies for certain species, and lacks spatial information. Here an approach for automatic image-based macrofouling analysis was presented. A dataset with dense labels prepared from field panel images was made and a convolutional network (adapted U-Net) for the semantic segmentation of different macrofouling classes was proposed. The establishment of macrofouling localization allows for the generation of a successional model which enables the determination of direct surface attachment and in-depth epibiotic studies.

Biofouling on surfaces in contact with sea- or brackish water can severely impact the function of devices like reverse osmosis modules. Single species laboratory assays are frequently used to test new low fouling materials. The choice of bacterial strain is guided by the natural population present in the application of interest and decides on the predictive power of the results. In this work, the analysis of the bacterial community present in brackish water from Mashabei Sadeh, Israel was performed and Rheinheimera sp. was detected as a prominent microorganism. A Rheinheimera strain was selected to establish a short-term accumulation assay to probe initial bacterial attachment as well as biofilm growth to determine the biofilm-inhibiting properties of coatings. Both assays were applied to model coatings, and technically relevant polymers including laser-induced graphene. This strategy might be applied to other water sources to better predict the fouling propensity of new coatings.

The application of electric fields to conductive coatings is an environmentally friendly way to reduce biofilm formation. In particular alternating potentials (APs) have received increasing attention in recent studies. Here, an electrochemical rotating disk setup for dynamic field exposure experiments was developed to study how APs alter the attachment of fouling organisms in a multispecies ocean environment. A specific focus of the device design was proper integration of the potentiostat in the strongly corroding saltwater environment. The effect of APs on the accumulation of fouling organisms in short term field exposures was studied. Potentials on conductive gold surfaces were periodically switched between -0.3 V and 0.3 V or between -0.8 V and 0.6 V at a frequency of 0.5 Hz. APs were capable of significantly reducing the attachment of marine fouling organisms compared with the conductive samples immersed at open circuit potentials.

Polysaccharide multilayers consisting of hyaluronic acid and chitosan were prepared by layer-by-layer assembly. To be used in seawater, the multilayers were crosslinked to a different degree using thermal or chemical methods. ATR-FTIR revealed different amide densities as a result of the crosslinking conditions. AFM showed that the crosslinking affected the roughness and swelling behavior of the coatings. The stability and degradability of the multilayers in aqueous environments were monitored with spectroscopic ellipsometry. The resistance of the coatings against non-specific protein adsorption was characterized by SPR spectroscopy. Settlement assays using Ulva linza zoospores and removal assays using the diatom Navicula incerta showed that the slowly degradable coatings were less prone to fouling than the strongly crosslinked ones. Thus, the coatings were a suitable model system to show that crosslinking the multilayers under mild conditions and equipping the coatings with controlled degradation rates enhances their antifouling and fouling-release properties against marine fouling organisms.

Hydrogel coatings effectively reduce the attachment of proteins and organisms in laboratory assays, in particular when made from zwitterionic monomers. In field experiments with multiple species and non-living material, such coatings suffer from adsorption of particulate matter. In this study, the zwitterionic monomer 3-[ N -(2-methacryloyloxyethyl)- N , N- dimethylammonio] propanesulfonate (SPE) was copolymerized with increasing amounts of the photo-crosslinker benzophenon-4-yloxyethyl methacrylate (BPEMA) to systematically alter the density of crosslinks between the polymer chains. The effect of increasing crosslink density on the antifouling (AF) performance of the coatings was investigated in laboratory assays and fields tests. In both cases, the AF performance was improved by increasing the crosslinker content. The coatings reduced protein, diatom, and barnacle accumulation, and showed better resistance to biomass accumulation. The findings underline that the marine AF performance of hydrogel coatings does not only depend on the specific chemical structure of the polymers, but also on their physico-chemical properties such as rigidity and swelling.

Hydrophilic coatings exhibit ultra-low fouling properties in numerous laboratory experiments. In stark contrast, the antifouling effect of such coatings in vitro failed when performing field tests in the marine environment. The fouling release performance of nonionic and zwitterionic hydrophilic polymers was substantially reduced compared to the controlled laboratory environment. Microscopy and spectroscopy revealed that a large proportion of the accumulated material in field tests contains inorganic compounds and diatomaceous soil. Diatoms adhered to the accumulated material on the coating, but not to the pristine polymer. Simulating field tests in the laboratory using sediment samples collected from the test sites showed that incorporated sand and diatomaceous earth impairs the fouling release characteristics of the coatings. When exposed to marine sediment from multiple locations, particulate matter accumulated on these coatings and served as attachment points for diatom adhesion and enhanced fouling. Future developments of hydrophilic coatings should consider accumulated sediment and its potential impact on the antifouling performance.

Quick and reliable testing is crucial for the development of new fouling release (FR) coatings. Exposure of these coatings to natural multispecies communities is essential in evaluating their efficacy. To this end, we present a rotating disk setup for dynamic field exposure. To achieve a well-defined flow on the surface of the disk, an easy to use sample mounting system was developed that provides a smooth and even surface. We related the angular velocity of the disk to the wall shear stress on the surface with a hydrodynamic model. The wall shear stress was adjusted to values previously found to be suitable to discriminate dynamic diatom attachment on different coating chemistries in the lab. The effect of the dynamic conditions was shown by comparing polystyrene slides under static and dynamic exposure. Using a set of self-assembled monolayers, the discrimination potential of the assay in a multispecies environment was demonstrated.

Surface topography plays a key role in the colonization of substrata by the colonizing stages of marine fouling organisms. For the innovation of marine antifouling coatings, it is essential to understand how topographic cues affect the settlement of these organisms. In this study, tapered, spiked microstructures and discrete honeycombs of varying feature dimensions were designed and fabricated in order to examine the influence of topography on the attachment of zoospores of the green macroalga Ulva linza and cells of the diatom (microalga) Navicula incerta. Contrasting results were obtained with these two species of algae. Indeed, the preferred location of cells of N. incerta was dominated by attachment point theory, which suggested a positive correlation between the density of cells adhering and the amount of available attachment points, while the settlement of spores of U. linza was mainly regulated by both Wenzel roughness and local binding geometry.

The attachment of cancer cells to the endothelium is an essential step during metastatic dissemination. The cell surface receptor CD44 is capable of binding to hyaluronan (HA) produced by tumor cells and by cells of the tumor microenvironment, including blood endothelial cells. Here, we investigated the role of CD44 in the interaction between the liver cancer cell line HepG2Iso and HA surfaces. The rolling interaction was quantitatively analyzed using a microfluidic shear force setup. It was found that rolling of the liver cancer cells on HA depends on CD44, which mediates a catch-bond interaction and thus a flow-induced rolling of the cells. Reduction of CD44 expression by means of siRNA, inhibition of the interaction of CD44 with HA by antibody blocking, and treatment with low molecular weight HA inhibited liver cancer cell rolling on HA-coated surfaces. The results not only clearly show the dependency of the shear-induced catch-bond interaction of HepG2Iso cells on CD44 and HA, but also for the first time demonstrate CD44-mediated rolling for epithelium-derived cells that are typically adherent.

Testing of fouling release (FR) technologies is of great relevance for discovery of the next generation of protective marine coatings. In this paper, an accumulation assay to test diatom interaction under laminar flow with the model organism Navicula perminuta is introduced. Using time lapse microscopy with large area sampling allows determination of the accumulation kinetics of the diatom on three model surfaces with different surface properties at different wall shear stresses. The hydrodynamic conditions within the flow cell are described and a suitable shear stress range to perform accumulation experiments is identified at which statistically significant discrimination of surfaces is possible. The observed trends compare well to published adhesion preferences of N. perminuta. Also, previously determined trends of critical wall shear stresses required for cell removal from the same set of functionalized interfaces shows consistent trends. Initial attachment mediated by extracellular polymeric substances (EPS) present outside the diatoms leads to the conclusion that the FR potential of the tested coating candidates can be deducted from dynamic accumulation experiments under well-defined hydrodynamic conditions. As well as testing new coating candidates for their FR properties, monitoring of the adhesion process under flow provides additional information on the mechanism and geometry of attachment and the population kinetics.

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.

Testing of new coatings to control fouling frequently involves single-species laboratory bioassays. Barnacle cyprids are among the most widely used model organisms in marine biofouling research, and surfaces that inhibit their settlement are considered to be promising candidates for new coating concepts. An analysis of motility parameters (mean velocity and swimming area coefficient) and distribution of cyprids of Balanus amphitrite in different swimming regions in the vicinity of model surfaces (self-assembled monolayers) is presented. The data are correlated with the settlement preferences of cyprids on these surfaces. Cyprids were predominantly found in interfacial regions and the transition frequencies between swimming regions of different depths were determined.

Conditioning, ie the adsorption of proteins and other macromolecules, is the first process that occurs in the natural environment once a surface is immersed in seawater, but no information is available either regarding the conditioning of surfaces by artificial seawater or whether conditioning affects data obtained from laboratory assays. A range of self-assembled monolayers (SAMs) with different chemical terminations was used to investigate the time-dependent formation of conditioning layers in commercial and self-prepared artificial seawaters. Subsequently, these results were compared with conditioning by solutions in which zoospores of the green alga Ulva linza had been swimming. Spectral ellipsometry and contact angle measurements as well as infrared reflection absorption spectroscopy (IRRAS) were used to reveal the thickness and chemical composition of the conditioning layers. The extent that surface preconditioning affected the settlement of zoospores of U. linza was also investigated. The results showed that in standard spore settlement bioassays (45-60 min), the influence of a molecular conditioning layer is likely to be small, although more substantial effects are possible at longer settlement times.