Antifouling Coatings via Tethering of Hyperbranched Polyglycerols on Biomimetic Anchors

Hyperbranched polyglycerols (HPG) bearing terminal thiol moieties (HPG-SH) were synthesized via anionic-ring-opening multibranching polymerization of glycidol from pentaerythritol and subsequent 1,1′-carbonyldiimidazole (CDI) coupling with cysteamine. Bioinspired (1) <i>N</i>-dopamine maleimide (DM), (2) tannic acid (TA), and (3) polydopamine (PDA) were employed to produce monolayer, multilayer, and polymeric anchors, respectively, on stainless-steel (SS) substrates. Postfunctionalization of the biomimetic anchor-modified SS surfaces was enacted by tethering of HPG-SH via Michael addition or thiol–ene “click” reaction to confer surface hydrophilicity. The thickness and grafting density of HPG coatings could be controlled by tuning the degree of thiolation. In comparison to the pristine SS surface, the HPG-modified surfaces exhibited substantially reduced initial adhesion and inhibition of the biofilm formation of Gram-negative Pseudomonas sp. and Gram-positive Staphylococcus epidermidis. Qualitative and quantitative assays of settlement of the microalgae Amphora coffeaeformis further demonstrate the low fouling characteristics of the HPG-modified surfaces. Therefore, tethering of HPG coatings on biomimetic anchors provides an environmentally benign alternative to antifouling surfaces

Cross-Linked Polyelectrolyte Multilayers for Marine Antifouling Applications

A polyionic multilayer film was fabricated by layer-by-layer (LbL) sequential deposition followed by cross-linking under mild conditions on a substrate surface to inhibit marine fouling. A novel polyanion, featuring methyl ester groups for an easy cross-linking was used as a generic solution for stabilization of LbL films in a harsh environment. Covalent cross-linking was confirmed by FTIR and XPS spectroscopy. AFM was used to observe film morphology and its variation because of cross-linking, as well as to measure the thickness of the LbL films. Cross-linking improved the stability of the LbL film when it was immersed in artificial seawater, natural seawater, and in a polar organic solvent (DMSO). No changes in the thickness and topography of the film were observed in these media. The LbL films prevented settlement of <i>Amphibalanus amphitrite</i> barnacle cyprids and reduced adhesion of the benthic diatom <i>Amphora coffeaeformis</i>. Assay results indicated that the cross-linking process did not weaken the antifouling effect of LbL films. The high stability and low degree of fouling make these coatings potentially promising candidates in marine applications

Multilayers of Fluorinated Amphiphilic Polyions for Marine Fouling Prevention

Sequential layer-by-layer (LbL) deposition of polyelectrolytes followed by chemical cross-linking was investigated as a method to fabricate functional amphiphilic surfaces for marine biofouling prevention applications. A novel polyanion, grafted with amphiphilic perfluoroalkyl polyethylene glycol (fPEG) side chains, was synthesized and subsequently used to introduce amphiphilic character to the LbL film. The structure of the polyanion was confirmed by FTIR and NMR. Amphiphilicity of the film assembly was demonstrated by both water and hexadecane static contact angles. XPS studies of the cross-linked and annealed amphiphilic LbL films revealed the increased concentration of fPEG content at the film interface. In antifouling assays, the amphiphilic LbL films effectively prevented the adhesion of the marine bacterium Pseudomonas (NCIMB 2021)

Layer-by-Layer Click Deposition of Functional Polymer Coatings for Combating Marine Biofouling

“Click” chemistry-enabled layer-by-layer (LBL) deposition of multilayer functional polymer coatings provides an alternative approach to combating biofouling. Fouling-resistant <i>azido</i>-functionalized poly­(ethylene glycol) methyl ether methacrylate-based polymer chains (<i>azido</i>-poly­(PEGMA)) and antimicrobial <i>alkynyl</i>-functionalized 2-(methacryloyloxy)­ethyl trimethyl ammonium chloride-based polymer chains (<i>alkynyl</i>-poly­(META)) were click-assembled layer-by-layer via alkyne–azide 1,3-dipolar cycloaddition. The polymer multilayer coatings are resistant to bacterial adhesion and are bactericidal to marine Gram-negative Pseudomonas sp. NCIMB 2021 bacteria. Settlement of barnacle (Amphibalanus (=Balanus) amphitrite<i></i>) cyprids is greatly reduced on the multilayer polymer-functionalized substrates. As the number of the polymer layers increases, efficacy against bacterial fouling and settlement of barnacle cyprids increases. The LBL-functionalized surfaces exhibit low toxicity toward the barnacle cyprids and are stable upon prolonged exposure to seawater. LBL click deposition is thus an effective and potentially environmentally benign way to prepare antifouling coatings

Barnacle Cement as Surface Anchor for “Clicking” of Antifouling and Antimicrobial Polymer Brushes on Stainless Steel

Barnacle cement (BC) was utilized ‘beneficially’ as a surface anchor on stainless steel (SS) for coupling of functional polymer brushes via “click” reactions in both “grafting-to” and “grafting-from” processes. Ethylene sulfide (ES), propargyl carbonylimidazole (PPC) and azidoethyl carbonylimidazole (AEC) reacted with amine and/or hydroxyl groups in BC to introduce the corresponding thiol, alkyne, and azide groups on SS surfaces (SS-thiol, SS-alkyne, and SS-azide, respectively). Antifouling zwitterionic SS-PMPC surface was prepared by thiol–ene photopolymerization of 2-methacryloyloxyethyl phosphorylcholine (MPC) from the SS-thiol surface. Protein-resistant SS-PPEGMA and protein-adsorbing SS-PPFS surfaces were prepared by coupling of the respective azide-functionalized poly­(poly­(ethylene glycol)­methyl ether methacrylate) (<i>azido</i>-PPEGMA) and poly­(2,3,4,5,6-pentafluorostyrene) (<i>azido</i>-PPFS) polymer brushes in azide–alkyne “click” reaction. Antifouling alkyne-functionalized poly­(<i>N</i>-hydroxyethyl acrylamide) (<i>alkynyl</i>-PHEAA) and antibacterial alkyne-functionalized poly­(2-(methacryloyloxy)­ethyl trimethylammonium chloride) (<i>alkynyl</i>-PMETA) polymer brushes were clicked on the SS-azide surface. Adsorption of bovine serum albumin and bacteria fouling of Gram-negative Escherichia coli (E. coli) and Gram-positive Staphylococcus epidermidis (S. epidermidis) were investigated on the polymer-functionalized SS surfaces. The versatile bioanchor and functional polymer brush coatings are stable in an abiotic aqueous environment for over a month

Tea Stains-Inspired Initiator Primer for Surface Grafting of Antifouling and Antimicrobial Polymer Brush Coatings

Inspired by tea stains, plant polyphenolic tannic acid (TA) was beneficially employed as the primer anchor for functional polymer brushes. The brominated TA (TABr) initiator primer was synthesized by partial modification of TA with alkyl bromide functionalities. TABr with trihydroxyphenyl moieties can readily anchor on a wide range of substrates, including metal, metal oxide, polymer, glass, and silicon. Concomitantly, the alkyl bromide terminals serve as initiation sites for atom transfer radical polymerization (ATRP). Cationic [2-(methacryloyloxy)­ethyl]­trimethylammonium chloride (META) and zwitterionic 2-methacryloyloxyethyl phosphorylcholine (MPC) and <i>N</i>-(3-sulfopropyl)-<i>N</i>-(methacryloxyethyl)-<i>N</i>,<i>N</i>-dimethylammonium betaine (SBMA) were graft-polymerized from the TABr-anchored stainless steel (SS) surface. The cationic polymer brushes on the modified surfaces are bactericidal, while the zwitterionic coatings exhibit resistance against bacterial adhesion. In addition, microalgal attachment (microfouling) and barnacle cyprid settlement (macrofouling) on the functional polymer-grafted surfaces were significantly reduced, in comparison to the pristine SS surface. Thus, the bifunctional TABr initiator primer provides a unique surface anchor for the preparation of functional polymer brushes for inhibiting both microfouling and macrofouling

Fate of Nanoplastics in Marine Larvae: A Case Study Using Barnacles, Amphibalanus amphitrite

The exposure of nanoplastics was investigated by observing their interaction with Amphibalanus amphitrite (commonly known as acorn barnacles). Poly­(methyl methacrylate) (PMMA) and fluorescent perylene tetraester (PTE) dye were used to prepare highly fluorescent nanoplastic particles. At concentrations of 25 ppm, the PMMA particles showed no detrimental impact on barnacle larvae and their microalgae feed, Tetraselmis suecica and Chaetoceros muelleri. PMMA nanoplastics were ingested and translocated inside the body of the barnacle nauplii within the first 3 h of incubation. The fluorescent PMMA particles inside the transparent nauplius were tracked using confocal fluorescence microscopy. Subsequently, the nanoplastics were fed to the barnacle nauplii under two conditionsacute and chronic exposure. The results from acute exposure show that nanoplastics persist in the body throughout stages of growth and developmentfrom nauplius to cyprid and juvenile barnacle. Some egestion of nanoplastics was observed through moulting and fecal excrement. In comparison, chronic exposure demonstrates bioaccumulation of the nanoplastics even at low concentrations of the plastics. The impacts of our study using PMMA nanoparticles exceeds current knowledge, where most studies stop at uptake and ingestion. Here we demonstrate that uptake of nanoparticles during planktonic larval stages may persist to the adult stages, indicating potential for the long-term impacts of nanoplastics on sessile invertebrate communities

Antifouling Coatings of Catecholamine Copolymers on Stainless Steel

Stainless steel (SS) exhibits good corrosion resistance in aquatic environments. Nevertheless, SS is susceptible to fouling by a variety of micro- and macro-organisms. In this work, the deposition of catecholamine-containing oligopoly­(ethylene glycol) (oligoPEG)- or <i>N</i>-hydroethyl acrylamide (HEA)-based copolymers and terpolymers on the SS surfaces provide an alternative to deter biofouling. The mussel-inspired copolymers- and terpolymers-coated SS surfaces effectively reduced the adhesion of bacteria (Pseudomonas sp.) and microalgae (Amphora coffeaeformis) as compared to that of the pristine SS surface. A fluorescence technique was adopted to quantitatively determine the number of <i>Amphora</i> cells adhered on the SS substrates. In comparison to the pristine and copolymers-coated SS surfaces, the terpolymers-coated SS surfaces were more effective in reducing the settlement of barnacle cyprids (<i>Amphibalanus</i> (= <i>Balanus</i>) <i>amphitrite</i>). Overall, the antifouling efficiencies of oligoPEG-based copolymers and terpolymers coatings were higher than that of HEA-based coatings

Polyion Multilayers with Precise Surface Charge Control for Antifouling

We report on a molecular fabrication approach to precisely control surface ζ potentials of polymeric thin layers constructed by electrostatic layer-by-layer (LbL) assembly methods. The protocol established allows us to achieve surface isoelectric points (IEP) in the pH range of 6–10. Poly­(acrylic acid) (PAA, a weak polyanion) and poly­(diallyldimethylammonium chloride) (PDADMAC, a strong polycation) were chosen to build up the bulk films. The weak polycation polyethylenimine (PEI) was applied as a top layer. A unique feature of this approach is that the chemical composition of the top layer is not affected by the manipulation of the ζ potential of the films. Surface charge tuning is achieved by controlling the degree of ionization of the weak polyelectrolytes at various pH values and subsequent manipulation of the amount of polyelectrolyte deposited in the penultimate and last layers, respectively. Following assembly and characterization, the films were used as candidates for antifouling surfaces. The fouling behavior of barnacle cyprids and bacteria on the LbL films with similar hydrophilicity and roughness but different surface charge densities were studied. We found that more cyprids of Amphibalanus amphitrite settled on the negatively charged LbL film compared to the neutral or positively charged LbL film. In bacterial adhesion tests employing Pseudomonas, Escherichia coli, and Staphylococcus aureus, more bacteria were observed on the positively charged LbL film compared with the neutral and negatively charged LbL films, possibly as a result of the negative potential of the bacterial cell wall. The procedures proposed allow one to adjust surface isoelectric points of LbL architectures to achieve optimal antifouling performance of a given material taking into account specific pH values of the environment and the character of the fouler

Comparison of laboratory and field testing performance evaluations of siloxane-polyurethane fouling-release marine coatings

<p>A series of eight novel siloxane-polyurethane fouling-release (FR) coatings were assessed for their FR performance in both the laboratory and in the field. Laboratory analysis included adhesion assessments of bacteria, microalgae, macroalgal spores, adult barnacles and pseudobarnacles using high-throughput screening techniques, while field evaluations were conducted in accordance with standardized testing methods at three different ocean testing sites over the course of six-months exposure. The data collected were subjected to statistical analysis in order to identify potential correlations. In general, there was good agreement between the laboratory screening assays and the field assessments, with both regimes clearly distinguishing the siloxane-polyurethane compositions comprising monofunctional poly(dimethyl siloxane) (PDMS) (m-PDMS) as possessing superior, broad-spectrum FR properties compared to those prepared with difunctional PDMS (d-PDMS). Of the seven laboratory screening techniques, the <i>Cellulophaga lytica</i> biofilm retraction and reattached barnacle (<i>Amphibalanus amphitrite</i>) adhesion assays were shown to be the most predictive of broad-spectrum field performance.</p