Serena Lay-Ming Teo

Biomimetic Anchors for Antifouling and Antibacterial Polymer Brushes on Stainless Steel

Barnacle cement (BC) was beneficially applied on stainless steel (SS) to serve as the initiator anchor for surface-initiated polymerization. The amine and hydroxyl moieties of barnacle cement reacted with 2-bromoisobutyryl bromide to provide the alkyl halide initiator for the surface-initiated atom transfer radical polymerization (ATRP) of 2-hydroxyethyl methacrylate (HEMA). The hydroxyl groups of HEMA polymer (PHEMA) were then converted to carboxyl groups for coupling of chitosan (CS) to impart the SS surface with both antifouling and antibacterial properties. The surface-functionalized SS reduced bovine serum albumin adsorption, bacterial adhesion, and exhibited antibacterial efficacy against Escherichia coli (E. coli). The effectiveness of barnacle cement as an initiator anchor was compared to that of dopamine, a marine mussel inspired biomimetic anchor previously used in surface-initiated polymerization. The results indicate that the barnacle cement is a stable and effective anchor for functional surface coatings and polymer brushes.

Pharmaceuticals as antifoulants: Concept and principles

The hypothesis that pharmaceuticals, with their known syntheses, chemical properties and primary mechanism of action would be an efficient source of new antifouling agents compatible with existing antifouling coating technology was tested. Twenty-three compounds at concentrations from 5 w g ml m 1 to 40 ng ml m 1 were tested for toxicity and inhibition of settlement of barnacle larvae. The compounds had a wide range of solubility in water and covered nine primary mechanisms of action in vertebrates. The upper level of potency was chosen because compounds that are highly potent have greater practical potential. The goal was to find compounds with high inhibition of settlement and low toxicity. Of the 23 compounds tested, 22 had significant effects on barnacle larvae. The variety of chemical structures and their variation in water solubility support the hypothesis that pharmaceuticals that are compatible with existing coatings technology should be considered as antifouling agents. Moreover, factors such as coating compatibility and environmental fate should be addressed early in the development process.

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 N-(3-sulfopropyl)-N-(methacryloxyethyl)-N,N-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.

Stainless steel surfaces with thiol-terminated hyperbranched polymers for functionalization via thiol-based chemistry

Hyperbranched polyethyleneimine (BPEI) was coupled to a polydopamine-coated stainless steel (SS) substrate. Subsequent mercaptoethylation of BPEI with ethylene sulfide produced thiol functional groups on the SS surface. Functionalization of the surface was achieved by end-capping of the hyperbranches with organic molecules via thiol-based chemistry, including thiol–epoxy coupling, thiol–ene radical photo-addition and thiol–Michael addition. The SS-P(HEMA-b-SBMA) surface was prepared via thiol–ene radical photo-addition of the hyperbranches with an alkene-functionalized poly(2-hydroxyethyl methacrylate) (alkene-PHEMA) from atom transfer radical polymerization (ATRP) and subsequent block copolymerization of the zwitterionic monomer, N-(3-sulfopropyl)-N-(methacryloxyethyl)-N,N-dimethyl ammonium betaine (SBMA). The SS-PPEGMA and SS-PMETA surfaces were prepared, respectively, by thiol-initiated photopolymerization of poly(ethylene glycol)methyl ether methacrylate (PEGMA) and 2-(methacryloyloxy)ethyl trimethylammonium chloride (META). The antifouling SS-P(HEMA-b-SBMA) and SS-PPEGMA surfaces exhibit resistance to bacterial adhesion, while the SS-PMETA surface is bactericidal. Metal surfaces with thiol-terminated hyperbranches thus provide a versatile platform for tailoring surface functionalities.

Surface-functionalized and surface-functionalizable poly(vinylidene fluoride) graft copolymer membranes via click chemistry and atom transfer radical polymerization.

Poly(vinylidene fluoride) (PVDF) with azide-functionalized poly(glycidyl methacrylate) (PGMA) side chains (PVDF-g-P[GMA-(N3)(OH)]) were synthesized via free radical-initiated graft copolymerization of glycidyl methacrylate (GMA) from ozone-pretreated PVDF backbone (PVDF-g-PGMA), followed by reaction of the oxirane rings in the GMA side chains with sodium azide. Alkyne-functionalized poly(N-isopropylacrylamide) (alkynyl-PNIPAM), prepared a priori by atom transfer radical polymerization (ATRP), was used for the click reaction with the azido-containing PGMA side chains of the PVDF-g-P[GMA-(N3)(OH)] copolymer to give rise to the thermoresponsive PVDF-g-P[GMA-click-PNIPAM] copolymer. Both the PVDF-g-P[GMA-(N3)(OH)] and PVDF-g-P[GMA-click-PNIPAM] copolymers can be readily cast into microporous membranes by phase inversion in an aqueous medium. The PVDF-g-P[GMA-(N3)(OH)] microporous membranes with azido-containing surfaces could be further functionalized via surface click reaction with alkyne-terminated PNIPAM of controlled chain lengths to obtain the PVDF-g-P[GMA-click-PNIPAM]surface microporous membranes. The surface composition and morphology of the PVDF-g-P[GMA-click-PNIPAM] membranes can be adjusted by the temperature of casting medium, while the flux through both types of membranes exhibits thermoresponsive behavior.

Functional polymer brushes via surface-initiated atom transfer radical graft polymerization for combating marine biofouling

Dense and uniform polymer brush coatings were developed to combat marine biofouling. Nonionic hydrophilic, nonionic hydrophobic, cationic, anionic and zwitterionic polymer brush coatings were synthesized via surface-initiated atom transfer radical polymerization (SI-ATRP) of 2-hydroxyethyl methacrylate, 2,3,4,5,6-pentafluorostyrene, 2-(methacryloyloxy)ethyl trimethylammonium chloride, 4-styrenesulfonic acid sodium and N,N′-dimethyl-(methylmethacryloyl ethyl) ammonium propanesulfonate, respectively. The functionalized surfaces had different efficacies in preventing adsorption of bovine serum albumin (BSA), adhesion of the Gram-negative bacterium Pseudomonas sp. NCIMB 2021 and the Gram-positive Staphylococcus aureus, and settlement of cyprids of the barnacle Amphibalanus amphitrite (=Balanus amphitrite). The nonionic hydrophilic, anionic and zwitterionic polymer brushes resisted BSA adsorption during a 2 h exposure period. The nonionic hydrophilic, cationic and zwitterionic brushes exhibited resistance to bacterial fouling (24 h exposure) and cyprid settlement (24 and 48 h incubation). The hydrophobic brushes moderately reduced protein adsorption, and bacteria and cyprid settlement. The anionic brushes were least effective in preventing attachment of bacteria and barnacle cyprids. Thus, the best approach to combat biofouling involves a combination of nonionic hydrophilic and zwitterionic polymer brush coatings on material surfaces.

Synthesis of catechol and zwitterion-bifunctionalized poly(ethylene glycol) for the construction of antifouling surfaces

The synthesis of catechol-containing small molecules and macromolecules always requires multiple reaction steps, coupling agents, or enzymes. In this study, a simple and scalable strategy for the preparation of catechol-containing poly(ethylene glycol) (CaPEG) by epoxide–amine polymerization of PEG diglycidyl ether with dopamine is described. The as-formed tertiary amine groups in the backbone of CaPEG can be converted into sulfobetaine structures in an alkylsulfonation step, leading to the formation of catechol and zwitterion-bifunctionalized PEG (SBCaPEG). The resulting catechol-containing CaPEG and SBCaPEG can be anchored on various substrate surfaces, including stainless steel (SS), titanium and silicon wafer, under mild conditions. Since SS is susceptible to fouling by a variety of microorganisms, the antifouling properties of the polymer-coated SS surfaces are studied in detail. The CaPEG- and SBCaPEG-coated SS surfaces effectively reduced the adsorption of protein (albumin–fluorescein isothiocyanate conjugate and bovine plasma fibrinogen), as well as the adhesion of bacteria (Pseudomonas sp. and Escherichia coli) and microalgae (Amphora coffeaeformis), as compared to that of the pristine SS surface. In comparison with the CaPEG-coated SS surfaces, the zwitterionic SBCaPEG-coated SS surfaces exhibited even better antifouling efficiencies.

Layer-by-layer deposition of antifouling coatings on stainless steel via catechol-amine reaction

Stainless steel (SS) has been widely used as a construction material in maritime structures due to its good corrosion resistance. However, bacteria, algae, barnacles and other marine organisms can readily adhere to its surface in the process of biofouling, leading to serious structure failures and economic losses. In this work, layer-by-layer (LBL) deposition of functional polymer coatings on SS surface provides an alternative approach to combating marine fouling. The catechol-containing antifouling copolymer of dopamine methacrylamide and poly(ethylene glycol) methyl ether methacrylate (P(DMA-co-PEGMEMA)), and amino-rich branched poly(ethyleneimine) (PEI) were assembled sequentially on the SS surface via catechol-amine reaction in a LBL manner. The PEI/P(DMA-co-PEGMEMA) multiple bilayer-coated SS surfaces can effectively reduce the adhesion of bacteria and microalgae (microfouling), and settlement of barnacle cyprids (macrofouling), as compared to the pristine SS surface. The antifouling efficiencies of PEI/P(DMA-co-PEGMEMA) bilayer-coated SS surfaces were also significantly higher than that of the P(DMA-co-PEGMEMA) monolayer-coated SS surface.

Photoinduced anchoring and micropatterning of macroinitiators on polyurethane surfaces for graft polymerization of antifouling brush coatings

Poly[3-azido-2-(2-bromo-2-methylpropanoyloxy)propyl methacrylate] (PAzBrMA) was synthesized as the macroinitiator and anchor for a functional polymer brush coating on polyurethane (PU) films. Ring-opening reaction of the epoxide group of poly(glycidyl methacrylate) with sodium azide produced the hydroxyl and azide functional groups. The hydroxyl groups were substituted with 2-bromoisobutyryl bromide to introduce the alkyl halide initiator. For anchoring, ultraviolet irradiation was applied to convert the azide groups of PAzBrMA physically coated on the PU surface into nitrene intermediates. The nitrene groups reacted with hydrocarbon moieties on the PU surface through hydrogen abstraction to form amine linkages. A photomask could then be employed to create a patterned surface during irradiation. Thus, the anchoring of a PAzBrMA macroinitiator can be achieved under mild conditions, without the use of strong solvents and high temperatures, which will swell or degrade the PU substrates. Finally, 2-hydroxyethyl methacrylate (HEMA) and poly(ethylene glycol) methacrylate (PEGMA) are graft-polymerized on the PAzBrMA-anchored PU film by surface-initiated atom transfer radical polymerization. In comparison with the pristine PU surface, the PU surfaces with grafted HEMA and PEGMA brush coatings were effective in reducing bovine serum albumin adsorption (protein fouling), adhesion of Staphylococcus epidermidis and Pseudomonas sp. (microfouling), and barnacle cyprid settlement (macrofouling). The present surface modification approach provides a simple and versatile means for micropatterning and functionalization of the polymer surfaces.

Fouling-Release Performance of Silicone Oil-Modified Siloxane-Polyurethane Coatings

The effect of incorporation of silicone oils into a siloxane-polyurethane fouling-release coatings system was explored. Incorporation of phenylmethyl silicone oil has been shown to improve the fouling-release performance of silicone-based fouling-release coatings through increased interfacial slippage. The extent of improvement is highly dependent upon the type and composition of silicone oil used. The siloxane-polyurethane (SiPU) coating system is a tough fouling-release solution, which combines the mechanical durability of polyurethane while maintaining comparable fouling-release performance with regard to commercial standards. To further improve the fouling-release performance of the siloxane-PU coating system, the use of phenylmethyl silicones oils was studied. Coatings formulations were prepared incorporating phenylmethyl silicone oils having a range of compositions and viscosities. Contact angle and surface energy measurements were conducted to evaluate the surface wettability of the coatings. X-ray photoelectron spectroscopy (XPS) depth profiling experiments demonstrated self-stratification of silicone oil along with siloxane to the coating-air interface. Several coating formulations displayed improved or comparable fouling-release performance to commercial standards during laboratory biological assay tests for microalgae (Navicula incerta), macroalgae (Ulva linza), adult barnacles (Balanus amphitrite syn. Amphibalanus amphitrite), and mussels (Geukensia demissa). Selected silicone-oil-modified siloxane-PU coatings also demonstrated comparable fouling-release performance in field immersion trials. In general, modifying the siloxane-PU fouling-release coatings with a small amount (1-5 wt % basis) of phenylmethyl silicone oil resulted in improved performance in several laboratory biological assays and in long-term field immersion assessments.