Adhesion and motility of fouling diatoms on a silicone elastomer

Biofilms on plastic litter in an urban river: Community composition and activity vary by substrate type

In aquatic ecosystems, plastic litter is a substrate for biofilms. Biofilms on plastic and natural surfaces share similar composition and activity, with some differences due to factors such as porosity. In freshwaters, most studies have examined biofilms on benthic substrates, while little research has compared the activity and composition of biofilms on buoyant plastic and natural surfaces. Additionally, the influence of substrate size and successional stage on biofilm composition has not been commonly assessed. We incubated three plastics of distinct textures that are buoyant in rivers, low-density polyethylene (rigid; 1.7 mm thick), low-density polyethylene film (flexible; 0.0254 mm thick), and foamed polystyrene (brittle; 6.5 mm thick), as well as wood substrates (untreated oak veneer; 0.6 mm thick) in the Chicago River. Each material was incubated at three sizes (1, 7.5, and 15 cm2 ). Substrates were incubated at 2-10 cm depths and removed weekly for 6 weeks. On each substrate we measured chlorophyll concentration, biofilm biomass, respiration, and flux of nitrogen gas. We sequenced 16S and 23S rRNA genes at Weeks 1, 3, and 6 to capture biofilm community composition across successional stages. Chlorophyll, biomass, and N2 flux were similar across substrates, but respiration was greater on wood than plastics. Bacterial and algal richness and diversity were highest on foam and wood compared to polyethylene substrates. Bacterial biofilm community composition was distinct between wood and plastic substrates, while the algal community was distinct on wood and foam, which were different from each other and polyethylene substrates. These results indicate that polymer properties influence biofilm alpha and beta diversity, which may affect transport and distribution of plastic pollution and associated microbes, as well as biogeochemical processes in urban rivers. This study provides valuable insights into the effects of substrate on biofilm characteristics, and the ecological impacts of plastic pollution on urban rivers. PRACTITIONER POINTS: Plastic physical and chemical properties act as forces of selection for biofilm. Biofilm activity was similar among three different types of plastic. Community composition between plastic and wood was different.

Investigating the anti-bioadhesion properties of short, medium chain length, and amphiphilic polyhydroxyalkanoate films

Silicone materials are widely used in fouling release coatings, but developing eco-friendly protection via biosourced coatings, such as polyhydroxyalcanoates (PHA) presents a major challenge. Anti-bioadhesion properties of medium chain length PHA and short chain length PHA films are studied and compared with a reference Polydimethylsiloxane coating. The results highlight the best capability of the soft and low-roughness PHA-mcl films to resist bacteria or diatoms adsorption as compared to neat PDMS and PHBHV coatings. These parameters are insufficient to explain all the results and other properties related to PHA crystallinity are discussed. Moreover, the addition of a low amount of PEG copolymers within the coatings, to create amphiphilic coatings, boosts their anti-adhesive properties. This work reveals the importance of the physical or chemical ambiguity of surfaces in their anti-adhesive effectiveness and highlights the potential of PHA-mcl film to resist the primary adhesion of microorganisms.

Diatom adhesive trail proteins acquired by horizontal gene transfer from bacteria serve as primers for marine biofilm formation

Biofilm-forming benthic diatoms are key primary producers in coastal habitats, where they frequently dominate sunlit intertidal substrata. The development of gliding motility in raphid diatoms was a key molecular adaptation that contributed to their evolutionary success. However, the structure-function correlation between diatom adhesives utilized for gliding and their relationship to the extracellular matrix that constitutes the diatom biofilm is unknown. Here, we have used proteomics, immunolocalization, comparative genomics, phylogenetics and structural homology analysis to investigate the evolutionary history and function of diatom adhesive proteins. Our study identified eight proteins from the adhesive trails of Craspedostauros australis, of which four form a new protein family called Trailins that contain an enigmatic Choice-of-Anchor A (CAA) domain, which was acquired through horizontal gene transfer from bacteria. Notably, the CAA-domain shares a striking structural similarity with one of the most widespread domains found in ice-binding proteins (IPR021884). Our work offers new insights into the molecular basis for diatom biofilm formation, shedding light on the function and evolution of diatom adhesive proteins. This discovery suggests that there is a transition in the composition of biomolecules required for initial surface colonization and those utilized for 3D biofilm matrix formation.

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.

Bio-Inspired Active Self-Cleaning Surfaces via Filament-Like Sweepers Array

Hydrodynamic forces from moving fluids can be utilized to remove contaminants which is an ideal fouling-release strategy for underwater surfaces. However, the hydrodynamic forces in the viscous sublayer are greatly reduced owing to the no-slip condition, which restricts their practical applications. Here, inspired by sweeper tentacles of corals, an active self-cleaning surface with flexible filament-like sweepers are reported. The sweepers can penetrate the viscous sublayer by utilizing energy from outer turbulent flows and remove contaminants with adhesion strength of >30 kPa. Under an oscillating flow, the removal rate of the single sweeper can reach up to 99.5% due to dynamic buckling movements. In addition, the sweepers array can completely clean its coverage area within 10 s through coordinated movements as symplectic waves. The active self-cleaning surface depends on the fluid-structure coupling between sweepers and flows, which breaks the concept of conventional self-cleaning.

Integration of Antifouling and Underwater Sound Absorption Properties into PDMS/MWCNT/SiO2 Coatings

Any surface immersed in sea water will suffer from marine fouling, including underwater sound absorption coatings. Traditional underwater sound absorption coatings rely heavily on the use of toxic, biocide-containing paints to combat biofouling. In this paper, an environmentally-friendly nanocomposite with integrated antifouling and underwater sound absorption properties was fabricated by adopting MWCNTs-COOH and SiO₂ into PDMS at different ratios. SEM, FTIR and XPS results demonstrated MWCNTs were mixed into PDMS, and the changes in elements were also analyzed. SiO₂ nanoparticles in PDMS decreased the tensile properties of the coating, while erosion resistance was enhanced. Antibacterial properties of the coatings containing MWCNTs-COOH and SiO₂ at a ratio of 1:1, 1:3, and 1:5 reached 62.02%, 72.36%, and 74.69%, respectively. In the frequency range of 1500-5000 Hz, the average sound absorption coefficient of PDMS increased from 0.5 to greater than 0.8 after adding MWCNTs-COOH and SiO₂, which illustrated that the addition of nanoparticles enhanced the underwater sound absorption performance of the coating. Incorporating MWCNTs-COOH and SiO₂ nanoparticles into the PDMS matrix to improve its sound absorption and surface antifouling properties provides a promising idea for marine applications.

Are silicone foul-release coatings a viable and environmentally sustainable alternative to biocidal antifouling coatings in the Baltic Sea region?

To combat unwanted fouling on immersed hulls, biocidal antifouling coatings are commonly applied to vessels trafficking the Baltic Sea. Here, the efficacy, environmental sustainability and market barriers of silicone foul-release coatings (FRCs) was assessed for this region to evaluate their viability as replacements for biocidal coatings. Coated panels were exposed statically over a 1 year period at three locations in the Baltic Sea region to assess the long-term performance of a biocide-free FRC and two copper coatings. The FRC was found to perform equally well or significantly better than the copper coatings. Even though most silicone FRCs on the market are biocide-free, a review of the literature regarding toxic effects and the identity and environmental fate of leachables shows that they may not be completely environmentally benign, simply for the lack of biocides. Nonetheless, FRCs are substantially less toxic compared to biocidal antifouling coatings and their use should be promoted.

Polyethylene Glycol-b-poly(trialkylsilyl methacrylate-co-methyl methacrylate) Hydrolyzable Block Copolymers for Eco-Friendly Self-Polishing Marine Coatings

Hydrolyzable block copolymers consisting of a polyethylene glycol (PEG) first block and a random poly(trialkylsilyl methacrylate (TRSiMA, R = butyl, isopropyl)-co-methyl methacrylate (MMA)) second block were synthesized by RAFT polymerization. Two PEGs with different molar masses (M_n = 750 g/mol (PEG1) and 2200 g/mol (PEG2)) were used as macro-chain transfer agents and the polymerization conditions were set in order to obtain copolymers with a comparable mole content of trialkylsilyl methacrylate (~30 mole%) and two different PEG mole percentages of 10 and 30 mole%. The hydrolysis rates of PEG-b-(TRSiMA-co-MMA) in a THF/basic (pH = 10) water solution were shown to drastically depend on the nature of the trialkylsilyl groups and the mole content of the PEG block. Films of selected copolymers were also found to undergo hydrolysis in artificial seawater (ASW), with tunable erosion kinetics that were modulated by varying the copolymer design. Measurements of the advancing and receding contact angles of water as a function of the immersion time in the ASW confirmed the ability of the copolymer film surfaces to respond to the water environment as a result of two different mechanisms: (i) the hydrolysis of the silylester groups that prevailed in TBSiMA-based copolymers; and (ii) a major surface exposure of hydrophilic PEG chains that was predominant for TPSiMA-based copolymers. AFM analysis revealed that the surface nano-roughness increased upon immersion in ASW. The erosion of copolymer film surfaces resulted in a self-polishing, antifouling behavior against the diatom Navicula salinicola. The amount of settled diatoms depended on the hydrolysis rate of the copolymers.

Hydrophobic Biodegradable Hyperbranched Copolymers with Excellent Marine Diatom Resistance

As the utilization of degradable polymer coatings increased, the accompanying trade-off between good degradability and high-efficiency antidiatom adhesion due to their hydrophobic nature remains unresolved. The study presents a new hydrophobic surface-fragmenting coating consisting of degradable hyperbranched polymers (hereafter denoted as h-LLA_x) synthesized by reversible complexation-mediated copolymerization with isobornyl acrylate (IBOA) and divinyl-functional oligomeric poly(l-lactide) (OLLA-V₂), both derived from biomass, that exhibited superior resistance (∼0 cell mm^-2) to marine diatom Navicula incerta (N. incerta) attachment with higher OLLA content. The combined impact of the microscale hollow semisphere micelles that self-assembled degradable hyperbranched copolymers and hydrolysis-driven self-renewable surfaces following immersion in seawater may account for the remarkable resistance of h-LLA_x coatings against N. incerta. Detailed investigations were conducted across multiple perspectives, from hydrolytic degradation to broad-spectrum antibacterial attachment to ecotoxicity assessment. The excellent features of high resistance to marine diatoms and bacterial attachment, degradability, and environmental friendliness make the as-prepared h-LLA_x coatings widely sought after for antifouling coating applications.

Studying the Effect of Pre-Polymer Composition and Incorporation of Surface-Modifying Amphiphilic Additives on the Fouling-Release Performance of Amphiphilic Siloxane-Polyurethane Coatings

Combining amphiphilic fouling-release (FR) coatings with the surface-active nature of amphiphilic additives can improve the antifouling/fouling-release (AF/FR) properties needed to offer broad-spectrum resistance to marine biofoulants. This work is focused on further tuning the amphiphilic character of a previously developed amphiphilic siloxane-polyurethane (SiPU) coating by varying the amount of PDMS and PEG in the base system. Furthermore, surface-modifying amphiphilic additives (SMAAs) were incorporated into these amphiphilic FR SiPU coatings in varying amounts. ATR-FTIR, contact angle and surface energy measurements, and AFM were performed to assess changes in surface composition, wettability, and morphology. AF/FR properties were evaluated using laboratory biological assays involving Cellulophaga lytica, Navicula incerta, Ulva linza, Amphibalanus amphitrite, and Geukensia demissa. The surfaces of these coatings varied significantly upon changes in PDMS and PEG content in the coating matrix, as well as with changes in SMAA incorporation. AF/FR properties were also significantly changed, with formulations containing the highest amounts of SMAA showing very high removal properties compared to other experimental formulations, in some cases better than that of commercial standard FR coatings.

Plastisphere development in relation to the surrounding biotic communities

To study the early colonization processes, polyethylene terephthalate (PET) microfragments were immersed in Lake Sakadaš and the Drava River and sampled weekly together with the surrounding biotic communities - phytoplankton, zooplankton, epixylon in the lake and epilithon in the river. At the end of the study, a rise in water level occurred in the river, which altered the environmental conditions and plankton communities. In studied environments, all of the sampled biotic communities were diverse and abundant. Plastispheres formed in both waters by the seventh day of incubation and developed rapidly, reaching a peak in abundance on the last day of the study. Initial colonization was supported equally by planktonic and periphytic taxa in both environments, but after initial settlement, plastisphere assemblages were affected differently in the river and lake. This study suggests that PET microfragments are a suitable substrate for microphyte settlement and may provide an important pathway for their transport in dynamic freshwater floodplains and river systems.

Effects of Temperature on Transparent Exopolymer Particle Production and Organic Carbon Allocation of Four Marine Phytoplankton Species

Transparent exopolymer particles (TEP) are sticky polymeric substances that are commonly found in the periphery of microbial cells or colonies. They can naturally flocculate smaller suspended particles into larger aggregates and thus play a crucial role in the biological pump and the global carbon cycle. Phytoplankton are the major contributors to marine TEP production, whereas the way TEP production interacts with abiotic factors at the species level is generally unknown but critical for estimating carbon fluxes. In this study, the effects of temperature on TEP production and carbon allocation were studied in two representative diatom species (Nitzschia closterium and Chaetoceros affinis) and two model dinoflagellate species (Prorocentrum micans and Scrippisella trichoidea). The results showed that temperature had a significant impact on TEP production in all species. First, increased temperature promoted the TEP production of all four species. Second, elevated temperature affected the carbon pool allocation, with enhanced dissolved organic carbon (DOC) exudation in the form of TEP in all species. The TEP-C/DOC percentages of N. closterium and P. micans were 93.42 ± 5.88% and 82.03 ± 21.36% at the highest temperature (24 °C), respectively, which was approximately two to five times higher than those percentages at 16 °C. In contrast, TEP’s contribution to the POC pool is lower than that to the DOC pool, ranging from 6.74 ± 0.79% to 28.31 ± 1.79% for all species. Moreover, phytoplankton TEP production may be related to cellular size and physiology. The TEP content produced by the smallest N. closterium (218.96 ± 15.04 fg Xeq./μm3) was ~5 times higher compared to P. micans, S. trichoidea, or C. affinis. In conclusion, TEP production is temperature sensitive and species specific, which should be taken into consideration the regarding TEP-mediated oceanic carbon cycle, particularly in the context of global warming.

Species diversity and community structure of microalgae living on microplastics in Luoyuan Bay, China

This study was carried out in Luoyuan Bay in March 2021. The species composition of microalgae community colonizing on microplastics called epimicroplastic microalgae (EMP-MA) was analyzed and compared with planktonic microalgae (PM) community. The species number of EMP-MA community (73) was higher than that of PM community (56). However Simpson Index and Pielou Evenness Index of EMP-MA community were significantly lower than that of PM community (P < 0.05). Although diatom was the most diverse and abundant taxa in both EMP-MA and PM community, their species compositions were significantly different (P < 0.05). Dominant species were also different between the two communities. Moreover, 12 harmful algal species were found in EMP-MA community, which may drift with microplastics and increase the risks of harmful algal blooms (HABs). This study is helpful to reveal the dispersal mechanism of HABs and potential impacts of EMP-MA on marine ecosystem.

Nontoxic Liquid-Infused Slippery Coating Prepared on Steel Substrates Inhibits Corrosion and Biofouling Adhesion

Wetting of surfaces plays a vital role in many biological and industrial processes. There are several phenomena closely related to wetting such as biofouling and corrosion that cause the deterioration of materials, while the efforts to prevent the degradation of surface functionality have spread over several millennia. Antifouling coatings have been developed to prevent/delay both corrosion and biofouling, but the problems remain unsolved, influencing the everyday life of the modern society in terms of safety and expenses. In this study, liquid-infused slippery surfaces (LISSs), a recently developed nontoxic repellent technology, that is, a flat variation of omniphobic slippery liquid-infused porous surfaces (SLIPSs), were studied for their anti-corrosion and marine anti-biofouling characteristics on metallic substrates under damaged and plain undamaged conditions. Austenitic stainless steel was chosen as a model due to its wide application in aquatic environments. Our LISS coating effectively prevents biofouling adhesion and decays corrosion of metallic surfaces even if they are severely damaged. The mechanically robust LISS reported in this study significantly extends the SLIPS technology, prompting their application in the marine environment due to the synergy between the facile fabrication process, rapid binding kinetics, nontoxic, ecofriendly, and low-cost applied materials together with excellent repellent characteristics.

Squid inspired elastomer marine coating with efficient antifouling strategies: Hydrophilized defensive surface and lower modulus

In antifouling applications for the marine industry, low surface energy coatings entail turbulent water flow to release marine biofouling, which presents a substantial challenge for antifouling in the static situation. The traditional solution is to add environmentally friendly antifouling agents, but it has the problem of exhaustion. Therefore, the low surface energy elastic antifouling coating without antifoulants has high research value. Herein, inspired by soft body and epidermal mucus of squid, the stable polyvinylpyrrolidone (PVP) hydrophilic segments were introduced to modify the polydimethylsiloxane-based polyurethane (PDMS-PU), realizing low surface energy elastomer coatings with hydrophilized defensive surface and reduced elastic modulus (<1.1 MPa). In an aqueous environment, the tailored surface exposed sufficient stable hydrophilic segments, exerting excellent antifouling performance, which improved the anti-adsorption effect on biological proteins, bacteria (antibacterial rate 95.24%) and algae (cover rate <3%). The coating exhibited excellent marine antifouling performance within 150 days and also gave a new impetus to developing an eco-friendly and sustainable solution for no-antifoulant marine antifouling applications.

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.

Reduction of biofilm accumulation by constant and alternating potentials in static and dynamic field experiments

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.

Crawling and adhesion behavior of Halamphora sp. based on different parts of Folium Sennae-like film: Evaluation of analytical methods for anti-diatom experimental results

Anti-diatom testing is a basic method to evaluate the anti-fouling performance of coatings. Many existing results of anti-diatom performances are evaluated based on their attachment number or coverage area, ignoring the influence of the crawling and adhesion behavior of diatoms on the analysis results. Here, a Folium Sennae-like film with multiple structural units was prepared by considering the influence of diatom attachment behaviors on the analysis results. The anti-diatom performances of different parts (divided and called four parts: edge, surface, cross striation, and vertical pattern) on the Folium Sennae-like film were evaluated using the counting and area methods. Obviously, the anti-diatom performance of the Folium Sennae-like film was superior to that of epoxy resin without structure. Under equal areas, the average numbers of diatoms on the cross striation and the vertical pattern were similar to the surface. It was found that the attachment behavior of Halamphora sp. is affected by microstructure units, rather than the combined structure of which the scale is much larger than that of diatoms. Meanwhile, the average attachment area for the unit number of diatoms was calculated. The diatom attachment area without microstructure, surface, cross striation, or vertical pattern was 81.751, 106.950, 73.904, and 84.376 μm², respectively. Moreover, the static and dynamic motion behaviors of Halamphora sp. were studied, and the theory for Halamphora sp. attachment was modeled in three dimensions. The variable morphology of Halamphora sp. lead to inaccurate results for diatom analyses based on the counting and area methods, which is summarized here. This study discusses the evaluation method of coatings by anti-diatom performance, further promoting the research of diatoms in the field of antifouling.

Amphiphilic Polyphosphonate Copolymers as New Additives for PDMS-Based Antifouling Coatings

Poly(ethyl ethylene phosphonate)-based methacrylic copolymers containing polysiloxane methacrylate (SiMA) co-units are proposed as surface-active additives as alternative solutions to the more investigated polyzwitterionic and polyethylene glycol counterparts for the fabrication of novel PDMS-based coatings for marine antifouling applications. In particular, the same hydrophobic SiMA macromonomer was copolymerized with a methacrylate carrying a poly(ethyl ethylene phosphonate) (PEtEPMA), a phosphorylcholine (MPC), and a poly(ethylene glycol) (PEGMA) side chain to obtain non-water soluble copolymers with similar mole content of the different hydrophilic units. The hydrolysis of poly(ethyl ethylene phosphonate)-based polymers was also studied in conditions similar to those of the marine environment to investigate their potential as erodible films. Copolymers of the three classes were blended into a condensation cure PDMS matrix in two different loadings (10 and 20 wt%) to prepare the top-coat of three-layer films to be subjected to wettability analysis and bioassays with marine model organisms. Water contact angle measurements showed that all of the films underwent surface reconstruction upon prolonged immersion in water, becoming much more hydrophilic. Interestingly, the extent of surface modification appeared to be affected by the type of hydrophilic units, showing a tendency to increase according to the order PEGMA < MPC < PEtEPMA. Biological tests showed that Ficopomatus enigmaticus release was maximized on the most hydrophilic film containing 10 wt% of the PEtEP-based copolymer. Moreover, coatings with a 10 wt% loading of the copolymer performed better than those containing 20 wt% for the removal of both Ficopomatus and Navicula, independent from the copolymer nature.

Assessment of the environmental compatibility and antifouling performance of an innovative biocidal and foul-release multifunctional marine coating

The control of marine biofouling has raised serious environmental concerns, thus the continuous release of toxic and persistent biocidal agents applied as anti-biofouling coatings have triggered the search for non-toxic strategies. However, most of them still lack rigorous evaluation of their ecotoxicity and antifouling effects under real scenarios and their correlation with simulated assays. In this work, the biocide releasing risk and ecotoxicity of a biocidal and foul-release polydimethylsiloxane (PDMS)-based marine coating containing grafted Econea biocide (<0.6 wt.%) were evaluated under simulated real mechanical wear conditions at a pilot-scale system, and under extreme wear scenarios (washability settings). The coating system demonstrated low environmental impact against the model Vibrio fischeri bacterium and marine algae, associated with the effective biocide grafting in the coating matrix and subsequent biocide release minimization. This multifunctional coating system also showed auspicious antifouling (AF) effects, with an AF performance index significantly higher (API > 89) than a single foul-release system (AF < 40) after two and half years at a real immersion scenario in the Portuguese shore of the Atlantic Ocean. These field results corroborated the antibiofilm performance evaluated with Pseudoalteromonas tunicata at simulated dynamic marine conditions after seven-week assays. This eco-friendly multifunctional strategy, validated by both simulated testing conditions and real field tests, is believed to be a powerful tool for the development of AF technologies and a potential contribution to the quest for new environmentally friendly antifouling solutions.

Amphiphilic Nitroxide-Bearing Siloxane-Based Block Copolymer Coatings for Enhanced Marine Fouling Release

The buildup of organic matter and organisms on surfaces exposed to marine environments, known as biofouling, is a disruptive and costly process affecting maritime operations. Previous research has identified some of the surface characteristics particularly suited to the creation of antifouling and fouling-release surfaces, but there remains room for improvement against both macrofouling and microfouling organisms. Characterization of their adhesives has shown that many rely on oxidative chemistries. In this work, we explore the incorporation of the stable radical 2,2,6,6-tetramethylpipiderin-1-oxyl (TEMPO) as a component in an amphiphilic block copolymer system to act as an inhibitor for marine cements, disrupting adhesion of macrofouling organisms. Using polystyrene-b-poly(dimethylsiloxane-r-vinylmethysiloxane) block copolymers, pendent vinyl groups were functionalized with TEMPO and poly(ethylene glycol) to construct an amphiphilic material with redox active character. The antifouling and fouling-release performance of these materials was investigated through settlement and removal assays of three model fouling organisms and correlated to surface structure and chemistry. Surfaces showed significant antifouling character and fouling-release performance was increased substantially toward barnacles by the incorporation of stable radicals, indicating their potential for marine antifouling applications.

Surface modifying amphiphilic additives and their effect on the fouling-release performance of siloxane-polyurethane coatings

In this work, surface-modifying amphiphilic additives (SMAAs) were synthesized via hydrosilylation using various polymethylhydrosiloxanes (PMHS) and allyl-terminated polyethylene glycol monomethyl ethers (APEG) of varying molecular weights. The additives synthesized were incorporated into a hydrophobic, self-stratifying siloxane-polyurethane (SiPU) coating system to produce an amphiphilic surface. Contact angle experiments and atomic force microscopy (AFM), in a dry and hydrated state, were performed to assess changes in surface wettability and morphology. The antifouling and fouling-release (AF/FR) performances were evaluated by performing laboratory biological assays using the marine bacterium Cellulophaga lytica, the microalga Navicula incerta, the macroalga Ulva linza, the barnacle Amphibalanus amphitrite, and the marine mussel, Geukensia demissa. Several of the formulations showed improved AF/FR performance vs the base SiPU and performed better than some of the commercial standard marine coatings. Formulations containing SMAAs with a low grafting density of relatively high molecular weight PEG chains showed the best performance overall.

Antifouling Strategies for Sensors Used in Water Monitoring: Review and Future Perspectives

Water monitoring sensors in industrial, municipal and environmental monitoring are advancing our understanding of science, aid developments in process automatization and control and support real-time decisions in emergency situations. Sensors are becoming smaller, smarter, increasingly specialized and diversified and cheaper. Advanced deployment platforms now exist to support various monitoring needs together with state-of-the-art power and communication capabilities. For a large percentage of submersed instrumentation, biofouling is the single biggest factor affecting the operation, maintenance and data quality. This increases the cost of ownership to the extent that it is prohibitive to maintain operational sensor networks and infrastructures. In this context, the paper provides a brief overview of biofouling, including the development and properties of biofilms. The state-of-the-art established and emerging antifouling strategies are reviewed and discussed. A summary of the currently implemented solutions in commercially available sensors is provided and current trends are discussed. Finally, the limitations of the currently used solutions are reviewed, and future research and development directions are highlighted.

Cyclic Copper Uptake and Release from Natural Seawater-A Fully Sustainable Antifouling Technique to Prevent Marine Growth

Unwanted growth of fouling organisms on underwater surfaces is an omnipresent challenge for the marine industry, costing billions of dollars every year in the transportation sector alone. Copper, the most widely used biocide in antifouling paints, is at the brink of a total ban in being used in antifouling coatings, as it has become an existential threat to nontargeted species due to anthropogenic copper inputs into protected waters. In the current study, using a porous and cross-linked poly(ethylene imine) structure under marine and fouling environments, available copper from natural seawater was absorbed and electrochemically released back as a potent biocide at 1.3 V vs Ag|AgCl, reducing marine growth by 94% compared to the control electrode (coupon) at 0 V. The coating can also function as an electrochemical copper sensor enabling real-time monitoring of the electrochemical uptake and release of copper ions from natural seawater. This allows tailoring of the electrochemical program to the changing marine environments, i.e., when the vessels move from high-copper-contaminated waters to coastal regions with low concentrations of copper.

Anti-biofouling properties of poly(dimethyl siloxane) with RAFT photopolymerized acrylate/methacrylate surface grafts against model marine organisms

Biofouling of man-made surfaces by marine organisms is a global problem with both financial and environmental consequences. However, the development of non-toxic anti-biofouling coatings is challenged by the diversity of fouling organisms. One possible solution leverages coatings composed of diverse chemical constituents. Reversible addition-fragmentation chain-transfer (RAFT) photopolymerization was used to modify poly(dimethylsiloxane) (PDMSe) surfaces with polymeric grafts composed of three successive combinations of acrylamide, acrylic acid, and hydroxyethyl methacrylate. RAFT limited conflicting variables and allowed for the effect of graft chemistry to be isolated. While all compositions enhanced the anti-biofouling performance compared with the PDMSe control, the ternary, amphiphilic copolymer was the most effective with 98% inhibition of the attachment of zoospores of the green alga Ulva linza, 94% removal of cells of the diatom Navicula incerta, and 62% removal of cells of the bacterium Cellulophaga lytica. However, none of the graft compositions tested were able to mitigate reattachment of adult barnacles, Amphibalanus amphitrite.

Amphiphilic Marine Antifouling Coatings Based on a Hydrophilic Polyvinylpyrrolidone and Hydrophobic Fluorine-Silicon-Containing Block Copolymer

The development of environmentally friendly and highly efficient antifouling coatings is vastly desirable in the marine industry. Herein, we prepared a novel amphiphilic block copolymer that combined hydrophilic polyvinylpyrrolidone (PVP) with hydrophobic poly(1-(1H,1H,2H,2H-perfluorodecyloxy)-3-(3,6,9-trioxadecyloxy)-propan-2-yl acrylate) (PFA) and polydimethylsiloxane (PDMS). The amphiphilic copolymer (PVP-PFA-PDMS) was blended into a cross-linked PDMS matrix to form a set of controlled surface composition and surface-renewal coatings with efficient antifouling and fouling-release properties. These coatings incorporated the biofouling settlement resistance ability attributed to the hydrophilic PVP segments and the reduced adhesion strength attributed to the low surface energy of fluorine-silicon-containing segments. As expected, the coatings showed an excellent antifouling performance against bacteria and marine unicellular Navicula parva diatoms (98.1 and 98.5% of reduction, respectively) and fouling-release performance against pseudobarnacle adhesion (84.3% of reduction) compared to the pristine PDMS coating. Moreover, a higher-content PVP-based coatings presented higher ability to resist biofouling adhesion. The nontoxic antifouling coating developed in this paper hold the potential to be applied in a variety of marine industrial facilities.

Effects of 'in-service' conditions - mimicked hull roughness ranges and biofilms - on the surface and the hydrodynamic characteristics of foul-release type coatings

To develop a better understanding of 'in-service' performance of modern marine coatings, this study explored the combined effects of different roughness ranges of foul-release coating (FRC) and light biofouling (slime) on the surface, boundary layer and drag characteristics under a range of 'in-service' conditions. Natural and laboratory biofilms were grown dynamically on FRC panels by exposing panels in facilities dedicated to realistic fouling culture. The boundary layer experiments were conducted in a circulating water tunnel. Boundary layer similarity-law scaling was used to predict the combined effects of coating roughness and biofilms on the added frictional resistance (% ΔCF) and added required effective power  (%ΔPE ) for a benchmark KRISO container ship (KCS) and a bulk carrier. The increase in  %ΔPE  due to the presence of biofilms on commercial FRC is estimated to be between 7% and 16% depending on the biofilm type, biofilm thickness and percentage coverage. Significant increases in effective power are estimated for non-fouling control primers with heavy fouling. Moreover, the paper suggests updated roughness allowances ( ΔCF ) for two vessel types assuming FRCs on their hulls with more representative hull roughness ranges and fluffy biofilms.

Silicone-Based Fouling-Release Coatings for Marine Antifouling

Marine biofouling profoundly influences marine industries and activities. It slows the speed and increases the fuel consumption of ships, corrodes offshore platforms, and blocks seawater pipelines. The most effective and economical antifouling approach uses coatings. Fouling-release coatings (FRCs) with low surface free energy and high elasticity weakly adhere to marine organisms, so they can be readily removed by the water shear force. FRCs have attracted increasing interest because they are biocide-free and hence ecofriendly. However, traditional silicone-based FRCs have weak adhesion to substrates, low mechanical strength, and low fouling resistance, limiting their applications. In recent years, many attempts have been made to improve their mechanical properties and fouling resistance. This review deals with the progress in the construction of high-performance silicone-based fouling-release surfaces.

Controlling the Release of Amphiphilic Liposomes from Alginate Hydrogel Particles for Antifouling Paint

As an alternative to the toxic antifouling paint that minimizes the adhesion force between organic molecules on large surfaces, a paint containing hydrogel particles encapsulating amphiphilic liposomes has been suggested. However, the release rate of liposomes, which is important for maximizing the antifouling performance, has not been adequately explored. We investigated the control of the release rate of liposomes encapsulated in alginate. Monodispersed alginate particles were generated using 3D-printed microfluidic devices, and their sizes were varied through the channel size, flow rate, and alginate concentration in the microfluidic devices ([Formula: see text]). The release rate of liposomes from the alginate particles was experimentally monitored under various conditions: alginate concentration, surrounding solution, and ambient fluid flow. The effects of chemical and mechanical stimuli on the effective diffusion coefficient (D_eff) of amphiphilic liposomes were analyzed, and accordingly, the best production conditions for antifouling alginate particles are suggested. This study provides essential physical insights and is useful for optimizing the performance of eco-friendly antifouling paint that includes alginate particles.

Self-assembly of cellular micro-bio machine parts

This paper focusses on intra- and inter-species connections between diatoms; hard bioglass microalgae that adhere through the secretion of sticky extracellular polymeric substances (EPS). We identify entirely new diatom attachment mechanisms, and the associated structures that develop from them. Further, we consider these findings in light of potential strategies for the self-assembled manufacture of micro-bio machine parts, and discuss their possible first-order end uses.

Probing the Adhesion of the Common Freshwater Diatom Nitzschia palea at Nanoscale

Freshwater biofilms play an essential ecological role, but they also adversely affect human activities through undesirable biofouling of artificial submerged structures. They form complex aggregates of microorganisms that colonize any type of substratum. In phototrophic biofilms, diatoms dominate in biomass and produce copious amount of extracellular polymeric substances (EPSs), making them efficient early colonizers. Therefore, a better understanding of diatoms adhesive properties is essential to develop new anti-biofouling strategies. In this context, we used atomic force microscopy (AFM) to decipher the topography and adhesive mechanisms of the common freshwater diatom Nitzschia palea. Images taken in physiological conditions revealed typical ultrastructural features with a few nanometers resolution. Using single-cell force spectroscopy, we showed that N. palea strongly adheres to hydrophobic surfaces as compared to hydrophilic ones. Chemical force spectroscopy with hydrophobic tips further confirmed that the adhesion is governed by surface-associated hydrophobic EPS distributed in clusters at the frustule surface, and mostly composed of (glyco)-lipids as revealed by Raman spectroscopy. Collectively, our results demonstrate that AFM-based nanoscopy, combined with Raman spectroscopy, is a powerful tool to provide new insights into the adhesion mechanisms of diatoms.

Antifouling and Fouling-Release Performance of Photo-Embossed Fluorogel Elastomers

Oil-infused ‘slippery’ polymer surfaces and engineered surface textures have been separately shown to reduce settlement or adhesion strength of marine biofouling organisms. Here, we combine these two approaches in fluorogel surfaces infused with perfluorinated oils, via a facile photo-embossing method that allows the generation of a micro-scale surface relief structure while retaining the properties of lubricant-infused materials. Testing of these surfaces against a range of marine fouling challenges in laboratory assays demonstrated that when the volume percentage of perfluorinated oil was high, adhesion strengths of attached barnacles and biofilms were low. However, diatoms adhered strongly to test surfaces, highlighting the need to explore different combinations of polymer and oil for such surfaces. Furthermore, the tested surface structures increased settlement and adhesion in the assays, demonstrating the need to optimize any surface structure for specific applications. Nevertheless, the results show the feasibility of combining multiple approaches to create future antifouling technologies.

Self-Generating and Self-Renewing Zwitterionic Polymer Surfaces for Marine Anti-Biofouling

Regeneration of antifouling polymer surfaces after contamination or damage is an important issue, especially in complex marine environments. Here, inspired by the self-renewal of silyl acrylate polymers and the protein resistance of zwitterionic polymers, we prepared a novel hydrolysis-induced zwitterionic monomer, tertiary carboxybetaine triisopropylsilyl ester ethyl acrylate (TCBSA), and copolymerized it with methyl methacrylate (MMA). Such a copolymer rapidly self-generates a zwitterionic surface and provides fouling resistance in marine environments. Furthermore, TCBSA was copolymerized with MMA and 2-methylene-1,3-dioxepane (MDO), where MDO causes degradation of the polymers. Our study demonstrates that the degradation of the polymer is controlled, and the degradation rate increases with the external enzyme concentration in the seawater, leading to a self-renewing dynamic surface. Quartz crystal microbalance with dissipation measurements show that the polymeric coating with self-generating zwitterions has excellent protein resistance in seawater. Bioassays demonstrate that the coating can effectively inhibit the adhesion of marine bacteria (Pseudomonas sp.) and diatoms (Navicula incerta). The coating with a self-generating and self-renewing zwitterionic surface is potential to find applications in marine anti-biofouling.

Nonfreezable Water and Polymer Swelling Control the Marine Antifouling Performance of Polymers with Limited Hydrophilic Content

Zwitterionic chemical groups have well-documented resistance to marine fouling species when presented as homogeneous polymer brushes. These model formulations are not, however, suitable for practical fouling-control applications. It is presently unknown if a uniform film of zwitterions is required to elicit nonfouling character via the binding of interfacial water or if the incorporation of zwitterionic functionality into a more practical bulk polymer system will suffice. Here, copolymers of n-butyl methacrylate were synthesized with low incorporation levels (up to 20 mol %) of hydrophilic functionality, including zwitterionic moieties. Their antifouling (AF) properties were evaluated using barnacle cyprids (Balanus improvisus), diatom cells (Navicula incerta), and a multispecies biofilm. The laboratory assays revealed higher resistance of ionic copolymers toward cyprid settlement, which was attributed to their swelling and the presence of nonfreezable water molecules bound tightly to the polymer chains. Additionally, cells of N. incerta and the multispecies biofilm were removed more effectively on polymers containing sulfobetaine methacrylate and sulfopropyl methacrylate moieties. The results indicate that the presence of tightly bound interfacial water is not limited to model systems of pure hydrophilic homopolymers, but that this mechanism can also reduce the settlement and adhesion of fouling species via bulk copolymer systems with limited hydrophilic content. The swelling of polymers with hydrophilic content may also contribute to their AF efficacy, and such materials may therefore represent a route to translation of the well-documented nonfouling character of zwitterions into practical, industrially relevant coating formulations.

Stress-localized durable anti-biofouling surfaces

Growing demands for bio-friendly antifouling surfaces have stimulated the development of new and ever-improving material paradigms. Despite notable progress in bio-friendly coatings, the biofouling problem remains a critical challenge. In addition to biofouling characteristics, mechanically stressed surfaces such as ship hulls, piping systems, and heat exchangers require long-term durability in marine environments. Here, we introduce a new generation of anti-biofouling coatings with superior characteristics and high mechanical, chemical and environmental durability. In these surfaces, we have implemented the new physics of stress localization to minimize the adhesion of bio-species on the coatings. This polymeric material contains dispersed organogels in a high shear modulus matrix. Interfacial cavitation induced at the interface of bio-species and organogel particles leads to stress localization and detachment of bio-species from these surfaces with minimal shear stress. In a comprehensive study, the performance of these surfaces is assessed for both soft and hard biofouling including Ulva, bacteria, diatoms, barnacles and mussels, and is compared with that of state-of-the-art surfaces. These surfaces show Ulva accumulation of less than 1%, minimal bacterial biofilm growth, diatom attachment of 2%, barnacle adhesion of 0.02 MPa and mussel adhesion of 7.5 N. These surfaces promise a new physics-based route to address the biofouling problem and avoid adverse effects of biofouling on the environment and relevant technologies.

Effects of surface texture and interrelated properties on marine biofouling: a systematic review

This systematic review examines effects of surface texture on marine biofouling and characterizes key research methodologies. Seventy-five published articles met selection criteria for qualitative analysis; experimental data from 36 underwent quantitative meta-analysis. Most studies investigated fouling mechanisms and antifouling performance only in laboratory assays with one to several test species. Textures were almost exclusively a single layer of regularly arranged geometric features rather than complex hierarchical or irregular designs. Textures in general had no effect or an inconclusive effect on fouling in 46% of cases. However, effective textures more often decreased (35%) rather than increased (19%) fouling. Complex designs were more effective against fouling (51%) than were regular geometric features (32%). Ratios of feature height, width, or pitch to organism body length were significant influences. The authors recommend further research on promising complex and hierarchical texture designs with more test species, as well as field studies to ground-truth laboratory results.

Contribution of frustules and mucilage trails to the mobility of diatom Navicula sp

The secreted mucilage trails of the diatom Navicula sp. in the process of motility were studied by scanning electron microscopy (SEM), transmission electron microscope (TEM), atomic force microscopy (AFM) and Raman spectra etc. Contrary to previous studies, force measurement was taken directly on the mucilage trails of live cells using the method of in situ force mapping by AFM. The retraction force curve presented an increased tip-substrate peak and a small saw-tooth pattern tip-mucilage peak. Especially, same measurements on various substrates with different surface energy revealed that the mucilage trails actually functioned as a medium increasing the adhesive force between the diatom and substrates, which is crucial to diatom’s adhesion and locomotion. In addition, the mechanical properties of mucilage trails were quite different from mucilage strands in the maximum adhesive force and the maximum polymer extension length. Raman spectra indicated the difference in compositions that both of the two kinds of mucilages had proteins and polysaccharide, but the mucilage strands contained some other components with C=O, —CH₂— and —CH₃ asymmetric and symmetric stretches. This research hammers out more precise information about mucilage trails which would be useful in terms of diatom motility and biofouling prevention.

"Big Dipper" Dynamic Contact Angle Curves for Pt-Cured Poly(dimethylsiloxane) on a Thermal Gradient: Inter-relationships of Hydrosilylation, Si-H Autoxidation, and Si-OH Condensation to a Secondary Network

Platinum cure for poly(dimethylsiloxane) (PDMS) coatings on a thermal gradient (45-140 °C) was carried out to study the effect of temperature on surface chemistry and wetting behavior. The motivation is the interest in surfaces with continuous gradients in wettability for applications such as protein adsorption, controlling bacterial adhesion, directional movement of cells, and biosensors. The Wilhelmy plate method and the advancing/receding drop method were employed for determining the positional dependence of θ_A and θ_R. A strong dependence of receding contact angles (θ_R) on cure temperature was found for Sylgard 184 (S-PDMS) and a Pt-cured laboratory-prepared analogue (Pt-PDMS) of known composition. Cure on the thermal gradient gave rise to striking "Big Dipper" Wilhelmy plate dynamic contact angle curves. High contact angle hysteresis (60-80°) was found for 45 °C cure (CAH = θ_Δ = θ_A - θ_R) but low CAH for 140 °C cure (10-20°). Drop addition/withdrawal using goniometry identified a similar trend. Attenuated total reflectance infrared spectroscopy showed absorptions for Si-OH (3500 cm^-1) and Si-H (1250 cm^-1) that were correlated with wetting behavior and near-surface chemistry. These studies revealed a complex relationship among hydrosilylation, Si-H autoxidation, and condensation of Si-OH. A model for advancing from a single network due to hydrosilylation to a double network for hydrosilylation plus Si-O-Si from condensation of Si-OH best explains evidence from spectroscopic and contact angle studies. These results are relevant to interactions of Pt-cured silicones at bio-interfaces, as receding contact angles determine work of adhesion, as well as applications that benefit from maximum hydrophobicity and minimizing water roll-off angles.

Hydrolyzable Additive-Based Silicone Elastomers: A New Approach for Antifouling Coatings

Fouling Release Coatings are marine antifouling coatings based on silicone elastomers. Contrary to commonly used biocide-based antifouling coatings, they do not release biocides into the marine environment, however, they suffer from poor antifouling efficacy during idle periods. To improve their antifouling performances in static conditions, various amounts of hydrolyzable polymers were incorporated within a silicone matrix. These hydrolyzable polymers were chosen for the well-known hydrolytic degradation mechanism of their main chain, e.g. poly(ε-caprolactone) (PCL), or of their ester pending groups, e.g. poly(bis(trimethylsilyloxy)methylsilyl methacrylate) (PMATM2). The degradation kinetics of such hydrolyzable silicone coatings were assessed by mass loss measurements during immersion in deionized water. Coatings containing PMATM2 exhibited a maximum mass loss after 12 weeks, whereas PCL-based coatings showed no significant mass loss after 24 weeks. Dynamic contact angle measurements revealed the modifications of the coatings surface chemistry with an amphiphilic behavior after water exposure. The attachment of macrofoulers on these coatings were evaluated by field tests in the Mediterranean Sea, demonstrating the short or long-term antifouling effect of these hydrolyzable polymers embedded in the silicone matrix. The settlement of A. amphitrite barnacles on the different coatings indicated inhospitable behaviors towards larval barnacles for coatings with at least 15 wt % of additives.

Oxidation-Mediated, Zwitterionic Polydopamine Coatings for Marine Antifouling Applications

We synthesized a zwitterionic dopamine derivative ( ZW-DOPA) containing both catechol and amine groups, and we demonstrated an excellent marine antifouling surface by controlling the oxidation of ZW-DOPA. The oxidation was mediated by the deprotonation of catechol or the addition of an oxidant (ammonium persulfate (AP) or sodium periodate (NaIO₄)). The oxidation and subsequent molecular transformation of ZW-DOPA was investigated over time by UV-vis spectroscopy. Among the different oxidation conditions tested, NaIO₄-induced ZW-DOPA coating was the most efficient and successfully formed on various substrates, such as titanium dioxide, stainless steel, and nylon. Compared with uncoated substrates, ZW-DOPA-coated substrates showed high resistance to marine diatom adhesion. Considering the ease of use and substrate independence of the ZW-DOPA coating, this method shows promise as a basis for inhibiting marine fouling on a variety of substrates used in the marine industry and aquatic environments.

Exploring the antifouling effect of elastic deformation by DEM–CFD coupling simulation

The influence of elastic deformation and elastic modulus on the release of adhered bacteria was investigated in this paper. Four silicone elastomers (SE) with different elastic moduli and one rigid polystyrene sheet were prepared to verify the antifouling effect of elastic deformation. The SE film has an elastic deformation effect under the stimulus of fluid medium, which makes the surface unstable. That could reduce the adhesion of fouling organisms and provide a foul-release basis. Distinct anti-adhesion properties were observed in our study in that cells more easily adhered to the rigid surface than the elastic surfaces under hydrodynamic conditions. However, the bacterial attachment test showed a similar antifouling performance of SE and the rigid surface under static conditions. To investigate the anti-adhesion ability of the elastic surface and rigid surface, the bacterial adhesive kinetics were studied by Discrete Element Method (DEM)–Computational Fluid Dynamics (CFD) coupling simulation. Results indicated the number of bacteria adhering on the elastic wall was significantly lower than on the rigid wall. And as the elastic modulus increased, the bacterial adhesion increased accordingly within a certain range. This work should not only enhance understanding of elastomer-based antifouling materials, but also facilitate the design and construction of other types non-toxic foul-release materials.

The bacterial adhesive kinetics with different morphology on elastic surface and rigid surface was studied by DEM–CFD coupling simulation.

Mini-review: effect sizes and meta-analysis for antifouling research

It is widely recognised that findings from experimental studies should be replicated before their conclusions are accepted as definitive. In many research areas, synthesis of results from multiple studies is carried out via systematic review and meta-analysis. Some fields are also moving away from null hypothesis significance testing, which uses p values to identify 'significant' effects, towards an estimation approach concerned with effect sizes and confidence intervals. This review argues that these techniques are underused in biofouling and antifouling (AF) research and discusses potential benefits of their adoption. They enable comparison of test surfaces even when these are not tested simultaneously, and allow results from repeated tests on the same surfaces to be combined. They also enable the use of published data to explore effects of different variables on the functioning of AF surfaces. AF researchers should consider using these approaches and reporting results in ways that facilitate future research syntheses.

Fouling-Release Properties of Dendritic Polyglycerols against Marine Diatoms

Dendritic polyglycerols (PGs) were grafted onto surfaces using a ring-opening polymerization reaction, and the fouling-release properties against marine organisms were determined. The coatings were characterized by spectroscopic ellipsometry, contact angle goniometry, ATR-FTIR, and stability tests in different aqueous media. A high resistance toward the attachment of different proteins was found. The PG coatings with three different thicknesses were tested in a laboratory assay against the diatom Navicula incerta and in a field assay using a rotating disk. Under static conditions, the PG coatings did not inhibit the initial attachment of diatoms, but up to 94% of attached diatoms could be removed from the coatings after exposure to a shear stress of 19 Pa. Fouling release was found to be enhanced if the coatings were sufficiently thick. The excellent fouling-release properties were supported in dynamic field-immersion experiments in which the samples were continually exposed to a shear stress of 0.18 Pa.