Optimized silyl ester diblock methacrylic copolymers: A new class of binders for chemically active antifouling coatings

This work focuses on the assessment of the erosion properties and antifouling (AF) performance of silyl ester copolymer-based coatings through laboratory and field tests. Silyl ester diblock copolymers were synthesized via the reversible addition-fragmentation chain transfer polymerization and were selected as binders for developing copper-free chemically active coatings. AF coatings were subsequently prepared using biocides (Sea-Nine™ 211, Preventol^® A4S, and zinc pyrithione). Laboratory-based bioassays, targeting the growth of selected microorganisms (bacteria and microalgae) and barnacle settlement, highlighted that the silyl ester methacrylic-based binders did not inhibit the growth of microorganisms, are essentially non-toxic to nauplii and reduced the settlement of Amphibalanus amphitrite cyprids. The corresponding biocidal coatings are potent toward bacteria and diatoms but were demonstrated to be toxic against the barnacle larvae. Field test results showed variations with geographical locations: in sub-tropical area, the silyl ester methacrylic-based coatings failed to inhibit the settlement of barnacles; however, field tests performed in Mediterranean Sea for 18 months demonstrated that biocidal silyl ester methacrylic-based coatings were promising candidates.     

Synthesis,characterization, and evaluation of antifouling polymers of 4‐acryloyloxybenzaldehyde with methyl methacrylate

In recent years, antifouling (AF) polymers are widely used in marine paints to protect the ship hulls from biofouling. The AF polymer coatings have better leaching characteristics and long lasting efficiency than other conventional formulations. In this study, an attempt has been made to prepare new p‐acryloyloxybenzaldehyde(AcBA) polymers to assess their AF efficiency against marine microfoulers. The monomer, AcBA was prepared by the esterification reaction between p‐hydroxybenzaldehyde (HBA) and acryloyl chloride (Ac) in presence of triethylamine (TEA) in MEK at 0°C. The reaction was monitored by TLC and the prepared monomer was characterized by UV, IR, ¹H‐NMR and GC‐MS. The homo‐[poly(AcBA)] and co‐polymers [poly(AcBA‐co‐MMA)] were prepared by solution polymerization using BPO as initiator. To find out the AF activity of prepared polymers, representatives of marine microfoulers, shipfouling bacteria (Bacillus macroides and Pseudomonas aeruginosa) and microalgae (Amphora coffeaeformis and Navicula incerta) were screened. The contact toxicity and diatom attachment assays were conducted with prepared polymers and microfouling formation on coatings was also investigated using a tubular biofilm reactor. AF potential of these polymers coating is demonstrated. © 2009 Wiley Periodicals, Inc. J Appl Polym Sci, 2009     

A simple method for the fabrication of silica-based superhydrophobic surfaces

The present article reports on a simple and convenient method for the fabrication of superhydrophobic surfaces based on silica particles by spraying the as-prepared silica suspension containing silica sol and silica microspheres on the substrate. The morphologies of the silica particulate coatings could be controlled by varying the silica microsphere concentration. The silica particulate coatings as prepared were exceptionally rough and superhydrophilic, with water contact angles less than 5°. The surface silanol groups of the hydrophilic coatings could be functionalized using 1H,1H,2H,2H-perfluorodecyltriethoxysilane to form hydrophobic groups. The resulting surface showed excellent superhydrophobic property with water contact angle up to 165.6 ± 0.9° and sliding angle of 3.5 ± 0.4°. In addition, the superhydrophobicity of the coating possessed a good stability after 3 months of exposure in air for a wide range of pH values.     

Assessing the Antimicrobial Activity of Polyisoprene Based Surfaces

There has been an intense research effort in the last decades in the field of biofouling prevention as it concerns many aspects of everyday life and causes problems to devices, the environment, and human health. Many different antifouling and antimicrobial materials have been developed to struggle against bacteria and other micro- and macro-organism attachment to different surfaces. However the “miracle solution” has still to be found. The research presented here concerns the synthesis of bio-based polymeric materials and the biological tests that showed their antifouling and, at the same time, antibacterial activity. The raw material used for the coating synthesis was natural rubber. The polyisoprene chains were fragmented to obtain oligomers, which had reactive chemical groups at their chain ends, therefore they could be modified to insert polymerizable and biocidal groups. Films were obtained by radical photopolymerization of the natural rubber derived oligomers and their structure was altered, in order to understand the mechanism of attachment inhibition and to increase the efficiency of the anti-biofouling action. The adhesion of three species of pathogenic bacteria and six strains of marine bacteria was studied. The coatings were able to inhibit bacterial attachment by contact, as it was verified that no detectable leaching of toxic molecules occurred.     

Rechargeable antimicrobial coatings for poly(lactic acid) nonwoven fabrics

A novel heterocyclic N-halamine acetate homopolymer was synthesized and characterized by ATR-IR, NMR and MALDI-TOF spectroscopy and TGA and DSC analysis. The homopolymer was coated onto poly(lactic acid) (PLA) meltblown nonwoven fabric, and the surfaces were rendered biocidal upon exposure to dilute sodium hypochlorite solution. The coatings were quite stable versus UVA and florescent light exposure. Moreover, they exhibited long-term shelf-life stability, and they were rechargeable when oxidative chlorine on the surfaces was partially exhausted after three months storage. It was found that the chlorinated fabrics exhibited effective antimicrobial activity with about six logs inactivation of Staphylococcus aureus and Escherichia coli O157:H7 within 30 min of contact time. The coated PLA possesses potential for use in antimicrobial food packaging, filters, and hygiene products.     

Zwitterionic siloxane-polyurethane fouling-release coatings

An approach to the design of polyurethane coatings having amphiphilic/zwitterionic surfaces via a self-stratification approach has been explored for marine non-fouling applications. Zwitterionic materials such as poly(sulfobetaine methacrylate) poly(SBMA), are used as non-fouling materials due to their protein resistance properties. ABA-type triblock copolymers, poly(SBMA)-block-PDMS-block-poly(SBMA), having PDMS as the central block and poly(SBMA) as the flanking blocks with secondary amines at the junction points were synthesized using ring opening equilibration polymerization (ROEP), Michael addition and atom transfer radical polymerization (ATRP). A series of triblocks were synthesized and incorporated into a polyurethane coating system and were evaluated for water contact angle (WCA), surface energy (SE) and pseudobarnacle adhesion (PB). The fouling-release (FR) performance of the coatings was evaluated in the laboratory using a suite of representative marine organisms. The coatings showed excellent FR performance toward the bacterium Halomonas pacifica and the diatom (microalga) Navicula incerta while the bacterium Cellulophaga lytica and sporelings of the green macroalga Ulva linza showed a relatively higher affinity for amphiphilic coating surfaces when compared to a series of standard control coatings.     

Photoactive sol–gel hybrid coatings from modified fluorocarbon polymers and amorphous titania

A series of organic–inorganic hybrid coatings was prepared through sol–gel chemistry by combining silanized chlorotrifluoroethylene-vinylether (FEVE) binders with tetraalkoxy silicon and titania sols under acidic conditions. The best compositions to obtain highly transparent and homogeneous coatings after thermal curing were determined. All the hybrid coatings easily pass the MEK test and show high scratch hardness. The atomic force microscopy (AFM) shows the formation of very smooth surfaces (R_rms routinely <1 nm) without clear phase separation phenomena. The typical size of the “objects” which may be individuated is in the range of 40–80 nm. Wettability through contact angle measurements shows the formation of moderately hydrophobic surfaces with a low contact angle hysteresis (~20°) which is a further indication of very smooth, homogeneous and chemically stable surfaces. After irradiation with UV-B light only hybrid coatings containing titania phases show a significant switch to a superhydrophilic behavior with a contact angle against H₂O down to 6°, which is only partially recovered after storage of the material in the dark. Titania based hybrid coatings also showed a fast and efficient UV-induced discoloration of the resazurin ink. The formulation of the coatings with photostabilizers belonging to the class of radical scavengers and UV absorbers does not change the photoinduced surface properties while eliminating the yellowing of the coating after UV exposure. It is concluded that titania-fluoropolymer hybrid coating show photoactivity and UV-induced superhydrophylicity mostly through ionic mechanisms, which could be beneficial to develop high durability and self-cleaning protective coatings.     

From lotus effect to petal effect: Tuning the water adhesion of non-wetting rare earth oxide coatings

A facile post-deposition plasma treatment was developed to tune the wetting behavior of Yb₂O₃ coatings deposited via the solution precursor plasma spray process. The as-deposited coatings exhibited the lotus effect after vacuum treatment, with a water contact angle of ∼162° and a roll-off angle of ∼5°, due to the hierarchical columnar microstructure. When the plasma torch was scanned over the coatings as a post-deposition treatment, the rough top surfaces of the columns present in the as-deposited coatings became smooth, and the coatings then exhibited the petal effect, with a water contact angle of ∼150° to ∼130° and high, tunable adhesion to water. Analysis of the surface compositions showed that after vacuum treatment hydrocarbon adsorption on the as-deposited coatings and plasma-treated coatings was very similar. A mathematical model correlating surface structures with wetting behaviors was developed to elucidate the transition from the lotus effect to the petal effect.     

Highly potent silver-organoalkoxysilane antimicrobial porous nanomembrane

We used a simple electrospinning technique to fabricate a highly potent silver-organoalkoxysilane antimicrobial composite from AgNO₃-polyvinylpyrrolidone (PVP)/3-aminopropyltrimethoxysilane (APTMS)/tetraethoxysilane (TEOS) solution. Spectroscopic and microscopic analyses of the composite showed that the fibers contain an organoalkoxysilane ‘skeleton,’ 0.18 molecules/nm² surface amino groups, and highly dispersed and uniformly distributed silver nanoparticles (5 nm in size). Incorporation of organoalkoxysilanes is highly beneficial to the antimicrobial mat as (1) amino groups of APTMS are adhesive and biocidal to microorganisms, (2) polycondensation of APTMS and TEOS increases the membrane’s surface area by forming silicon bonds that stabilize fibers and form a composite mat with membranous structure and high porosity, and (3) the organoalkoxysilanes are also instrumental to the synthesis of the very small-sized and highly dispersed silver metal particles in the fiber mat. Antimicrobial property of the composite was evaluated by disk diffusion, minimum inhibition concentration (MIC), kinetic, and extended use assays on bacteria (Escherichia coli, Bacillus anthracis, Staphylococcus aureus, and Brucella suis), a fungus (Aspergillus niger), and the Newcastle disease virus. The membrane shows quick and sustained broad-spectrum antimicrobial activity. Only 0.3 mg of fibers is required to achieve MIC against all the test organisms. Bacteria are inhibited within 30 min of contact, and the fibers can be used repeatedly. The composite is silver efficient and environment friendly, and its membranous structure is suitable for many practical applications as in air filters, antimicrobial linen, coatings, bioadhesives, and biofilms.     

N-halamine copolymers for biocidal coatings

A vinyl N-halamine acrylamide monomer was copolymerized with silane-, epoxide-, and hydroxyl group-containing monomers. The resultant copolymers were coated onto cotton fabric through hydrolysis of alkoxy groups with formation of silyl ether bonding, opening of the epoxide ring and subsequent reaction with hydroxyl groups on cellulose, and by crosslinking between the hydroxyl groups on the copolymer and on cellulose, respectively. The coatings were rendered biocidal upon exposure to dilute household bleach solution. All of the coatings provided complete inactivation of about six log of Staphylococcus aureus and Escherichia coli O157:H7 within minutes of contact time. The effects of the aforementioned tethering groups on wash fastness and ultraviolet light exposure were also studied.     

Surface functionalization of cellulose membrane via heterogeneous “click” grafting of zwitterionic sulfobetaine

In this article, cellulose membranes (CMs) containing zwitterionic sulfobetaine groups were prepared from cellulose membranes with azide groups and N,N-Diethyl-N-Propargyl-N-(3-sulfopropyl) ammonium via click chemistry in a one pot two-step grafting reaction. The CMs were fully characterized by attenuated total reflectance Fourier transform infrared spectra, X-ray photoelectron spectroscopy, X-ray spectroscopy analysis. Results showed that zwitterionic monomers were successfully grafted from CM surfaces and the surface morphologies were investigated by scanning electron microscope and atomic forced microscope. It has been proved that the surface roughness of zwitterionic sulfobetaine functionalized cellulose membranes were greater than the starting cellulose membranes. This new member has potential for biomedical applications.     

Silver- and Zinc-Decorated Polyurethane Ionomers with Tunable Hard/Soft Phase Segregation

Segmented polyurethane ionomers find prominent applications in the biomedical field since they can combine the good mechanical and biostability properties of polyurethanes (PUs) with the strong hydrophilicity features of ionomers. In this work, PU ionomers were prepared from a carboxylated diol, poly(tetrahydrofuran) (soft phase) and a small library of diisocyanates (hard phase), either aliphatic or aromatic. The synthesized PUs were characterized to investigate the effect of ionic groups and the nature of diisocyanate upon the structure–property relationship. Results showed how the polymer hard/soft phase segregation was affected by both the concentration of ionic groups and the type of diisocyanate. Specifically, PUs obtained with aliphatic diisocyanates possessed a hard/soft phase segregation stronger than PUs with aromatic diisocyanates, as well as greater bulk and surface hydrophilicity. In contrast, a higher content of ionic groups per polymer repeat unit promoted phase mixing. The neutralization of polymer ionic groups with silver or zinc further increased the hard/soft phase segregation and provided polymers with antimicrobial properties. In particular, the Zinc/PU hybrid systems possessed activity only against the Gram-positive Staphylococcus epidermidis while Silver/PU systems were active also against the Gram-negative Pseudomonas aeruginosa. The herein-obtained polyurethanes could find promising applications as antimicrobial coatings for different kinds of surfaces including medical devices, fabric for wound dressings and other textiles.     

RP-HPLC optimization of econea by using artificial neural networks and its antifouling performance on the Turkish coastline

Coverage of artificial surfaces within seawater by fouling organisms is defined as biofouling. Although biofouling is a natural process, it has some disadvantages for shipping industry such as increased fuel consumption, and CO₂ emission. Therefore, the ships' hull must be covered by antifouling (AF) or fouling release type coatings to overcome biofouling. In general, the so-called self-polishing AF paints contain biocides for preventing fouling organisms. Their concentrations and release rates from AF coatings are of great importance and they definitely affect both quality and cost of the coating. In the present study, we aimed at applying a new robust method. In this method, we used a model biocide, i.e., econea, to obtain its RP-HPLC optimization through artificial neural networks (ANN) and to see its antifouling performance. Column temperature, mobile phase ratio, flow rate, concentration and wavelength as input parameters and retention time as an output parameter were used in the ANN modeling. In conclusion, the R&D groups in AF paint industry may use RP-HPLC method supported with ANN modeling in further studies.     

Bioinspired Polydopamine Coatings Facilitate Attachment of Antimicrobial Peptidomimetics with Broad-Spectrum Antibacterial Activity

The prevention and treatment of biofilm-mediated infections remains an unmet clinical need for medical devices. With the increasing prevalence of antibiotic-resistant infections, it is important that novel approaches are developed to prevent biofilms forming on implantable medical devices. This study presents a versatile and simple polydopamine surface coating technique for medical devices, using a new class of antibiotics—antimicrobial peptidomimetics. Their unique mechanism of action primes them for activity against antibiotic-resistant bacteria and makes them suitable for covalent attachment to medical devices. This study assesses the anti-biofilm activity of peptidomimetics, characterises the surface chemistry of peptidomimetic coatings, quantifies the antibacterial activity of coated surfaces and assesses the biocompatibility of these coated materials. X-ray photoelectron spectroscopy and water contact angle measurements were used to confirm the chemical modification of coated surfaces. The antibacterial activity of surfaces was quantified for S. aureus, E. coli and P. aeruginosa, with all peptidomimetic coatings showing the complete eradication of S. aureus on surfaces and variable activity for Gram-negative bacteria. Scanning electron microscopy confirmed the membrane disruption mechanism of peptidomimetic coatings against E. coli. Furthermore, peptidomimetic surfaces did not lyse red blood cells, which suggests these surfaces may be biocompatible with biological fluids such as blood. Overall, this study provides a simple and effective antibacterial coating strategy that can be applied to biomaterials to reduce biofilm-mediated infections.     

The effect of formulation variables on fouling-release performance of stratified siloxane–polyurethane coatings

The effects of formulation variables, such as type of polyol, solvent type and solvent content, and coating application method, on the surface properties of siloxane–polyurethane fouling-release coatings were explored. Fouling-release coatings allow the easy removal of marine organisms from a ship’s hull via the application of a shear force to the surface. Self-stratified siloxane–polyurethane coatings are a new approach to a tough fouling-release coating system. Combinatorial High Throughput Experimentation was employed to formulate and characterize 24 different siloxane–polyurethane coatings applied using drawdown and drop-casting methods. The resulting coatings were tested for surface energy using contact angle measurements. The fouling-release performance of the coatings was tested using a number of diverse marine organisms including bacteria (Halomonas pacifica and Cytophaga lytica), sporelings (young plants) of the green macroalga (Ulva linza), diatom ((microalga) Navicula incerta), and barnacle (Amphibalanus amphitrite). The performance of the majority of the coatings was found to be better than the silicone standards, Intersleek^® and Silastic^® T2. An increase in solvent content in the formulations increased the surface roughness of the coatings. Coatings made with polycaprolactone polyol appeared to be somewhat rougher compared to coatings made with the acrylic polyol. The adhesion strength of sporelings of Ulva increased with an increase in solvent content and increase in surface roughness. The adhesion strengths of Ulva sporelings, C. lytica, and N. incerta were independent of application method (cast or drawdown) in contrast to H. pacifica adhesion, which was dependent on the application method.     

Poly(ethylene) glycol-modified,amphiphilic, siloxane–polyurethane coatings and their performance as fouling-release surfaces

Amphiphilic siloxane–polyurethane (AmSiPU) coatings were prepared using a series of polyisocyanate prepolymers modified with polydimethyl siloxane (PDMS) and poly(ethylene glycol) (PEG). Fouling-release performance of the AmSiPU coatings was evaluated through laboratory biological assays using several representative marine organisms. First, polyisocyanate prepolymers with compositional variation in PDMS and PEG were synthesized and characterized using Fourier transform infrared spectroscopy (FTIR) and isocyanate titrations. Then, the prepolymers were incorporated into coatings. Surface wettability of the coatings was evaluated using contact angle and surface energy measurements. Coatings’ surfaces were also characterized using attenuated total reflectance Fourier transform infrared spectroscopy (ATR-FTIR), X-ray photoelectron spectroscopy (XPS), and atomic force microscopy (AFM). ATR-FTIR and XPS experiments revealed that both PDMS and PEG moieties were present on the surface suggesting amphiphilic character. AFM phase images show microphase separation. AmSiPU coatings show excellent fouling-release performance toward bacteria (Cellulophaga lytica), the diatoms (Navicula incerta), and the green algae (Ulva linza), demonstrating comparable or superior performance to many commercial amphiphilic fouling-release coatings. Despite the incorporation of hydrophilic PEG, AmSiPU coatings show good macrofouling release which is often challenging with amphiphilic coating systems. AmSiPU coatings are a nontoxic and tough fouling-release solution with comparable performance to benchmarks in the fouling-release coatings market.     

N‐(hydroxymethyl) acrylamide as a multifunctional finish to cotton and a tether for grafting methacrylamide for biocidal coatings

N‐(hydroxymethyl) acrylamide (NMA) was immobilized on cotton surfaces through etherification, and then methacrylamide (MA) was grafted onto the treated surface. The coatings were characterized by ATR‐IR spectroscopy and were rendered biocidal upon exposure to dilute household bleach. The treated fabrics were challenged with Gram‐negative and Gram‐positive bacteria; both NMA and NMA/MA‐treated fabrics inactivated about 8 logs of Escherichia coli O157:H7 and Staphylococcus aureus within only 5 min of contact time. The coatings were also quite stable toward ultraviolet (UVA) light exposure and repeated laundering. Moreover, a substantial improvement in wrinkle recovery angle was obtained for the NMA/MA‐treated fabrics. The new acyclic acrylamide N‐halamine coating should be less expensive to produce and use than previous cyclic N‐halamine coatings developed in these laboratories. © 2012 Wiley Periodicals, Inc. J. Appl. Polym. Sci., 2013     

Adhesive Antimicrobial Peptides Containing 3,4-Dihydroxy-L-Phenylalanine Residues for Direct One-Step Surface Coating

Bacterial colonization and transmission via surfaces increase the risk of infection. In this study, we design and employ novel adhesive antimicrobial peptides to prevent bacterial contamination of surfaces. Repeats of 3,4-dihydroxy-L-phenylalanine (DOPA) were added to the C-terminus of NKC, a potent synthetic antimicrobial peptide, and the adhesiveness and antibacterial properties of the resulting peptides are evaluated. The peptide is successfully immobilized on polystyrene, titanium, and polydimethylsiloxane surfaces within 10 min in a one-step coating process with no prior surface functionalization. The antibacterial effectiveness of the NKC-DOPA₅-coated polystyrene, titanium, and polydimethylsiloxane surfaces is confirmed by complete inhibition of the growth of Escherichia coli, Pseudomonas aeruginosa, and Staphylococcus aureus within 2 h. The stability of the peptide coated on the substrate surface is maintained for 84 days, as confirmed by its bactericidal activity. Additionally, the NKC-DOPA₅-coated polystyrene, titanium, and polydimethylsiloxane surfaces show no cytotoxicity toward the human keratinocyte cell line HaCaT. The antimicrobial properties of the peptide-coated surfaces are confirmed in a subcutaneous implantation animal model. The adhesive antimicrobial peptide developed in this study exhibits potential as an antimicrobial surface-coating agent for efficiently killing a broad spectrum of bacteria on contact.     

Challenges for the Development of New Non-Toxic Antifouling Solutions

Marine biofouling is of major economic concern to all marine industries. The shipping trade is particularly alert to the development of new antifouling (AF) strategies, especially green AF paint as international regulations regarding the environmental impact of the compounds actually incorporated into the formulations are becoming more and more strict. It is also recognised that vessels play an extensive role in invasive species propagation as ballast waters transport potentially threatening larvae. It is then crucial to develop new AF solutions combining advances in marine chemistry and topography, in addition to a knowledge of marine biofoulers, with respect to the marine environment. This review presents the recent research progress made in the field of new non-toxic AF solutions (new microtexturing of surfaces, foul-release coatings, and with a special emphasis on marine natural antifoulants) as well as the perspectives for future research directions.     

Transparent antifouling coatings via nanoencapsulation of a biocide

Transparent coatings releasing an antifouling agent (AF) can be used to reduce the marine fouling of optical lenses. A variety of water‐borne coatings based on poly(methyl methacrylate‐co‐butyl acrylate) (PMMA‐co‐PBA) were synthesized using a two‐stage miniemulsion process. During this process, the AF, SeaNine 211, was nanoencapsulated in domains small enough not to scatter light. The release rate of SeaNine 211 was studied for the polymers of different T_g, and found to be sufficient to impart AF properties. However, over time, the coatings were found to develop a whitish aspect (blushing) due to water retrodiffusion. © 2007 Wiley Periodicals, Inc. J Appl Polym Sci, 2007