Polysiloxane-based block copolymers with marine bacterial anti-adhesion properties

A type of multifunctional cellulose nanocrystal composite silicone-based polymer coating for marine antibiofouling

Nanocomposite polymer coatings are being used as a new generation of marine antibiofouling coatings because of their toxin-free chemical composition and ease of large-scale adoption. Cellulose nanocrystal (CN) exhibits significant potential for composite reinforcement. Herein, CN was surface-modified via α,ω-bis(3-(2-hydroxyl-terminated polydimethylsiloxane (HTPDMS), resulting in dihydroxyl-terminated poly(dimethylsiloxane)-grafted CN (HP-g-CN). The amine-terminated PDMS as the foundational component was sequentially reacted with isophorone diisocyanate, isophthalaldehyde, and carbon disulfide to produce PDMS-based poly (urea-thiourea-imine) (PDMS-PUTI). Subsequently, a composite (PDMS-PUTI/HP-g-CN) was produced through physical blending. The intrinsic imine bonds and dynamic hydrogen-bonding network were responsible for the self-healing properties, which achieved a healing efficiency of up to 89.2 %. HP-g-CN was grafted with the non-leaching lubricant, HTPDMS, resulting in improved mechanical properties (1.38 MPa of ultimate strength) and adhesion strength (2.43 MPa), along with the self-cleaning and self-lubricating performance (0.700 coefficient) of the coating. Additionally, the fouling resistance to bovine serum albumin (BSA, 10.44 μg cm-2), bacteria (∼97.08 % and ∼ 98.05 % reduction for Pseudomonas sp. (P. sp.) and Shewanella sp. (S. sp.), respectively), and diatoms (∼27 cells mm-2) was further enhanced. Marine field tests conducted over 90 days revealed that the coatings were static fouling-resistant for an extended period. This study demonstrated a multifunctional, high-performance, and environmentally friendly nanocomposite polymer coating for preventing marine biofouling.

Bioinspired Asymmetric-Adhesion Janus Hydrogel Patch Regulating by Zwitterionic Polymers for Wet Tissues Adhesion and Postoperative Adhesion Prevention

Asymmetrically adhesive hydrogel patch with robust wet tissue adhesion simultaneously anti-postoperative adhesion is essential for clinical applications in internal soft-tissue repair and postoperative anti-adhesion. Herein, inspired by the lubricative role of serosa and the underwater adhesion mechanism of mussels, an asymmetrically adhesive hydrogel Janus patch is developed with adhesion layer (AL) and anti-adhesion layer (anti-AL) through an in situ step-by-step polymerization process in the mold. The AL exhibits excellent adhesion to internal soft-tissues. In contrast, the anti-AL demonstrated ultralow fouling property against protein and fibroblasts, which hinders the early and advanced stages of development of the adhesion. Moreover, the Janus patch simultaneously promotes tissue regeneration via ROS clearance capability of catechol moieties in the AL. Results from in vivo experiments with rabbits and rats demonstrate that the AL strongly adheres to traumatized tissue, while the anti-AL surface demonstrate efficacy in preventing of post-abdominal surgery adhesions in contrast to clinical patches. Considering the advantages in terms of therapeutic efficacy and off the shelf, the Janus patch developed in this work presents a promise for preventing postoperative adhesions and promoting regeneration of internal tissue defects.

Fabrication of Poly(ionic liquid) Hydrogels Incorporating Liquid Metal Microgels for Enhanced Synergistic Antifouling Applications

Hydrogels are ideal for antifouling materials due to their high hydrophilicity and low adhesion properties. Herein, poly(ionic liquid) hydrogels integrated with zwitterionic copolymer-functionalized gallium-based liquid metal (PMPC-GLM) microgels were successfully prepared by a one-pot reaction. Poly(ionic liquid) hydrogels (IL-Gel) were obtained by chemical cross-linking the copolymer of ionic liquid, acrylic acid, and acrylamide, and the introduction of ionic liquid (IL) significantly increased the cross-linking density; this approach consequently enhanced the mechanical and antiswelling properties of the hydrogels. The swelling ratio of IL-Gel decreased eight times compared to the original hydrogels. PMPC-GLM microgels were prepared through grafting the zwitterionic polymer PMPC onto the GLM nanodroplet surface, which exhibited efficient antifouling performance attributed to the bactericidal effect of Ga3+ and the antibacterial effect of the zwitterionic polymer layer PMPC. Based on the synergistic effect of PMPC-GLM microgels and IL, the composite hydrogels PMPC-GLM@IL-Gel not only exhibited excellent mechanical and antiswelling properties but also showed outstanding antibacterial and antifouling properties. Consequently, PMPC-GLM@IL-Gel hydrogels achieved inhibition rates of over 90% against bacteria and more than 85% against microalgae.

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.

Linear Block Copolymer Synthesis

Block copolymers form the basis of the most ubiquitous materials such as thermoplastic elastomers, bridge interphases in polymer blends, and are fundamental for the development of high-performance materials. The driving force to further advance these materials is the accessibility of block copolymers, which have a wide variety in composition, functional group content, and precision of their structure. To advance and broaden the application of block copolymers will depend on the nature of combined segmented blocks, guided through the combination of polymerization techniques to reach a high versatility in block copolymer architecture and function. This review provides the most comprehensive overview of techniques to prepare linear block copolymers and is intended to serve as a guideline on how polymerization techniques can work together to result in desired block combinations. As the review will give an account of the relevant procedures and access areas, the sections will include orthogonal approaches or sequentially combined polymerization techniques, which increases the synthetic options for these materials.

Biomimetic surface coatings for marine antifouling: Natural antifoulants, synthetic polymers and surface microtopography

Marine biofouling is a ubiquitous problem that accompanies human marine activities and marine industries. It exerts detrimental impacts on the economy, environment, ecology, and safety. Traditionally, mainstream approaches utilize metal ions to prevent biological contamination, but this also leads to environmental pollution and damage to the ecosystem. Efficient and environmentally friendly coatings are urgently needed to prevent marine devices from biofouling. Since nature is always the best teacher for humans, it offers us delightful thoughts on the research and development of high-efficiency, broad-spectrum and eco-friendly antifouling coatings. In this work, we focus on the research frontier of marine antifouling coatings from a bionic perspective. Enlightened by three distinctive dimensions of bionics: chemical molecule bionic, physiological mechanism bionic, and physical structure bionic, the research status of three main bioinspired strategies, which are natural antifoulants, bioinspired polymeric antifouling coatings, and biomimetic surface microtopographies, respectively, are demonstrated. The antifouling mechanisms are further interpreted based on biomimetic comprehension. The main fabrication methods and antifouling performances of these coatings are presented along with their advantages and drawbacks. Finally, the challenges are summarized, and future research prospects are proposed. It is believed that biomimetic antifouling strategies will contribute to the development of nontoxic antifouling techniques with exceptional repellency and stability.

Layer-by-layer zwitterionic modification of diverse substrates with durable anti-corrosion and anti-fouling properties

A versatile coating strategy, which is suitable for the anti-corrosion and anti-fouling modification of chemically distinct substrates, is crucial in many industries. The immobilization of zwitterionic polymers onto the surface has been proven to be an excellent approach for the improvement of antibiofouling potency. However, the anti-corrosion property has not always been considered simultaneously. Herein, a layer-by-layer (LBL) zwitterionic surface modification strategy was proposed: the surface was first coated with a polydopamine (PDA) layer for anti-corrosion; then, by self-assembling a monolayer of 3-aminopropyl triethoxysilane (APTES), the anti-corrosion ability was further enhanced and the efficiency of grafting was improved; thereafter, by immobilizing the zwitterionic polysulfobetaine (PSB) polymer brush layer, the surface could effectively repel biofouling. The surface chemical composition and morphology characterization was performed by using attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy, scanning electron microscopy (SEM), atomic force microscopy (AFM), and water contact angle measurements, demonstrating that the modification was stepwise introduced onto the surface. The thickness of coating was observed and measured by SEM cross-sectional analysis. In vitro studies revealed that the PSB coated surfaces dramatically reduced the adhesion of bovine serum albumin (BSA), bovine plasma fibrinogen (Fg), bovine γ-globulin (γ-GL), the mixture of these proteins, fibroblasts, E. coli and S. aureus with superior cytocompatibility and hemocompatibility. Moreover, the electrochemical impedance spectroscopy and acidic corrosion studies indicated that an excellent and durable anti-corrosion property was established successfully on the surfaces of stainless steel, cotton textile and wood plates, confirming the feasibility of the LBL surface modification strategy. Significantly, this LBL surface chemistry may be widely applied for the modification of other materials, such as biosensors, biomedical implants and/or devices, and marine equipment.

Amphiphilic hydrolyzable polydimethylsiloxane-b-poly(ethyleneglycol methacrylate-co-trialkylsilyl methacrylate) block copolymers for marine coatings. II. Antifouling laboratory tests and field trials

Poly(dimethylsiloxane) (PDMS) elastomer coatings containing an amphiphilic hydrolyzable diblock copolymer additive were prepared and their potential as marine antifouling and antiadhesion materials was tested. The block copolymer additive consisted of a PDMS first block and a random poly(trialkylsilyl methacrylate (TRSiMA, R = butyl, isopropyl)-co-poly(ethyleneglycol) methacrylate (PEGMA) copolymer second block. PDMS-b-TRSiMA block copolymer additives without PEGMA units were also used as additives. The amphiphilic character of the coating surface was assessed in water using the captive air bubble technique for measurements of static and dynamic contact angles. The attachment of macro- and microorganisms on the coatings was evaluated by field tests and by performing adhesion tests to the barnacle Amphibalanus amphitrite and the green alga Ulva rigida. All the additive-based PDMS coatings showed better antiadhesion properties to A. amphitrite larvae than to U. rigida spores. Field tests provided meaningful information on the antifouling and fouling release activity of coatings over an immersion period of 23 months.

Polymerization-Induced Phase Segregation and Self-Assembly of Siloxane Additives to Provide Thermoset Coatings with a Defined Surface Topology and Biocidal and Self-Cleaning Properties

In this work, we report on the incorporation of a siloxane copolymer additive, poly((2-phenylethyl) methylsiloxane)-co(1-phenylethyl) methylsiloxane)-co-dimethylsiloxane), which is fully soluble at room temperature, in a rapid-cure thermoset polyester coating formulation. The additive undergoes polymerization-induced phase segregation (PIPS) to self-assemble on the coating surface as discrete discoid nanofeatures during the resin cure process. Moreover, the copolymer facilitates surface co-segregation of titanium dioxide pigment microparticulate present in the coating. Depending on the composition, the coatings can display persistent superhydrophobicity and self-cleaning properties and, surprisingly, the titanium dioxide pigmented coatings that include the siloxane copolymer additive display high levels of antibacterial performance against Gram-positive (Staphylococcus aureus) and Gram-negative (Pseudomonas aeruginosa) bacteria. This antibacterial performance is believed to be associated with the unique surface topology of these coatings, which comprise stimuli-responsive discoid nanofeatures. This paper provides details of the surface morphology of the coatings and how these relates to the antimicrobial properties of the coating.

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.

Shear Stress as a Major Driver of Marine Biofilm Communities in the NW Mediterranean Sea

While marine biofilms depend on environmental conditions and substrate, little is known about the influence of hydrodynamic forces. We tested different immersion modes (dynamic, cyclic and static) in Toulon Bay (north-western Mediterranean Sea; NWMS). The static mode was also compared between Toulon and Banyuls Bays. In addition, different artificial surfaces designed to hamper cell attachment (self-polishing coating: SPC; and fouling-release coating: FRC) were compared to inert plastic. Prokaryotic community composition was affected by immersion mode, surface characteristics and site. Rhodobacteriaceae and Flavobacteriaceae dominated the biofilm community structure, with distinct genera according to surface type or immersion mode. Cell density increased with time, greatly limited by hydrodynamic forces, and supposed to delay biofilm maturation. After 1 year, a significant impact of shear stress on the taxonomic structure of the prokaryotic community developed on each surface type was observed. When surfaces contained no biocides, roughness and wettability shaped prokaryotic community structure, which was not enhanced by shear stress. Conversely, the biocidal effect of SPC surfaces, already major in static immersion mode, was amplified by the 15 knots speed. The biofilm community on SPC was 60% dissimilar to the biofilm on the other surfaces and was distinctly colonized by Sphingomonadaceae ((Alter)Erythrobacter). At Banyuls, prokaryotic community structures were more similar between the four surfaces tested than at Toulon, due possibly to a masking effect of environmental constraints, especially hydrodynamic, which was greater than in Toulon. Finally, predicted functions such as cell adhesion confirmed some of the hypotheses drawn regarding biofilm formation over the artificial surfaces tested here.

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.

Dynamic surface antifouling: mechanism and systems

Marine biofouling is a global problem today. High efficiency and eco-friendly antifouling systems are in pressing need. In recent years, we have proposed the concept of dynamic surface antifouling (DSA). That is, a continuously changing surface can effectively prevent marine fouling organisms from landing and adhesion. Based on this strategy, we developed coatings with dynamic surfaces by using degradable polymers including polyester-polyurethane, modified polyester and poly(ester-co-acrylate). They exhibit tunable renewability, and excellent antifouling and mechanical performance. Moreover, the polymers can serve as carrier and controlled release systems of antifoulants so that they have long service life. This paper reviews the progress and trends in marine anti-biofouling, and presents the mechanism and systems of DSA.

Phenotypic Heterogeneity in Attachment of Marine Bacteria toward Antifouling Copolymers Unraveled by AFM

Up to recent years, bacterial adhesion has mostly been evaluated at the population level. Single cell level has improved in the past few years allowing a better comprehension of the implication of individual behaviors as compared to the one of a whole community. A new approach using atomic force microscopy (AFM) to measure adhesion forces between a live bacterium attached via a silica microbead to the AFM tipless cantilever and the surface has been recently developed. The objectives of this study is to examine the bacterial adhesion to a surface dedicated to ship hulls at the population and the cellular level to understand to what extent these two levels could be correlated. Adhesion of marine bacteria on inert surfaces are poorly studied in particular when substrata are dedicated to ship hulls. Studying these interactions in this context are worthwhile as they may involve different adhesion behaviors, taking place in salty conditions, using different surfaces than the ones usually utilized in the literacy. FRC (fouling release coatings)-SPC (self-polishing coatings) hybrids antifouling coatings have been used as substrata and are of particular interest for designing environmentally friendly surfaces, combining progressive surface erosion and low adhesion properties. In this study, a hybrid coating has been synthetized and used to study the adhesion of three marine bacteria, displaying different surface characteristics, using microplate assays associated with confocal scanning laser microscopy (CSLM) and AFM. This study shows that the bacterial strain that appeared to have the weakest adhesion and biofilm formation abilities when evaluated at the population level using microplates assays and CSLM, displayed stronger adhesion forces on the same surfaces at the single cell level using AFM. In addition, one of the strains tested which presented a strong ability to adhere and to form biofilm at the population level, displayed a heterogeneous phenotypic behavior at the single cell level. Therefore, these results suggest that the evaluation of adhesion at the population level cannot always be correlated with adhesion forces measured individually by AFM and that some bacteria are prone to phenotypic heterogeneity among their population.

Recent advances in organic–inorganic well-defined hybrid polymers using controlled living radical polymerization techniques

Controlled living radical polymerizations, such as ATRP and RAFT polymerization, could be utilized for the preparation of well-defined organic–inorganic hybrid polymers based on POSS, PDMS, silica nanoparticles, graphene, CNTs and fullerene.

Effects of surface-active block copolymers with oxyethylene and fluoroalkyl side chains on the antifouling performance of silicone-based films

Block copolymers made from a poly(dimethyl siloxane) (Si) and a poly(meth)acrylate carrying oxyethylene (EG) or fluoroalkyl (AF) side chains were synthesized and incorporated as surface-active components into a silicone matrix to produce cross-linked films with different surface hydrophilicity/phobicity. Near-edge X-ray absorption fine structure (NEXAFS) studies showed that film surfaces containing Si-EG were largely populated by the siloxane, with the oxyethylene chains present only to a minor extent. In contrast, the fluorinated block was selectively segregated to the polymer-air interface in films containing Si-AF as probed by NEXAFS and X-ray photoelectron spectroscopy (XPS) analyses. Such differences in surface composition were reflected in the biological performance of the coatings. While the films with Si-EG showed a higher removal of both Ulva linza sporelings and Balanus amphitrite juveniles than the silicone control, those with Si-AF exhibited excellent antifouling properties, preventing the settlement of cyprids of B. amphitrite.