[show abstract][hide abstract] ABSTRACT: Marine biofouling is a longstanding problem because of the constant challenges placed by various fouling species and increasingly restricted environmental regulations for antifouling coatings. Novel nonbiocidal strategies to control biofouling will necessitate a multifunctional approach to coating design. Here we show that slippery liquid-infused porous surfaces (SLIPSs) provide another possible strategy to obtaining promising antifouling coatings. Microporous butyl methacrylate−ethylene dimethacrylate (BMA− EDMA) surfaces are prepared via UV-initiated free-radical polymer- ization. Subsequent infusion of fluorocarbon lubricants (Krytox103, Krytox100, and Fluorinert FC-70) into the porous microtexture results in liquid-repellent slippery surfaces. To study the interaction with marine fouling organisms, settlement of zoospores of the alga Ulva linza and cypris larvae of the barnacle Balanus amphitrite is tested in laboratory assays. BMA−EDMA surfaces infused with Krytox103 and Krytox100 exhibit remarkable inhibition of settlement (attachment) of both spores and cyprids to a level comparable to that of a poly(ethylene glycol) (PEG)- terminated self-assembled monolayer. In addition, the adhesion strength of sporelings (young plants) of U. linza is reduced for BMA−EDMA surfaces infused with Krytox103 and Krytox100 compared to pristine (noninfused) BMA−EDMA and BMA− EDMA infused with Fluorinert FC-70. Immersion tests suggest a correlation between the stability of slippery coatings in artificial seawater and fouling resistance efficacy. The results indicate great potential for the application of this concept in fouling-resistant marine coatings.
[show abstract][hide abstract] ABSTRACT: A versatile, photochemical surface-modification approach using nitrene-insertion reactions has been employed to develop an ultra-thin, two-component, polymer-gradient coating. Perfluorophenyl azide (PFPA) acted as the photosensitive moiety, forming a nitrene radical upon 254 nm UV exposure. Cationic poly(allyl amine) was grafted with PFPA and surface-anchored onto silicon wafers by means of electrostatic self-assembly. After spincoating of polystyrene (PS), the substrate was illuminated from behind a moving shutter, thereby controlling the azide-to-nitrene conversion degree across the substrate, and leading to a gradually varying PS density after rinsing. Backfilling with poly(vinyl pyrrolidone) (PVP) and re-exposing to UV light formed a two-component polymer-density gradient. The composition varied linearly following exposure to a linear UV exposure profile, as determined with spectroscopic ellipsometry (ELM) and X-ray photoelectron spectroscopy (XPS). High-spatial-resolution, time-of-flight secondary ion mass spectrometry (ToF-SIMS) revealed a high degree of mixing between the two incompatible polymers on the micron scale. The dynamic water-contact angle (dCA) was found to depend strongly on the sample history, suggesting adaptive properties of the coating, which was further confirmed by angle-resolved XPS (ARXPS). To confirm the applicability of the system for biological investigations, gradients were exposed to zoospores of the macrofouling alga Ulva linza, and a critical PS composition of 70 % was identified, above which settlement started to increase. It has been shown that a two-component polymer-density gradient can provide a high-throughput platform for determining critical surface properties of polymer blend materials.
[show abstract][hide abstract] ABSTRACT: Natural and artificial substrata immersed in the marine environment are typically colonized by microorganisms, which may moderate the settlement/recruitment of algal spores and invertebrate larvae of macrofouling organisms. This mini-review summarizes the major interactions occurring between microbial biofilms and marine fouling algae, including their effects on the settlement, growth and morphology of the adult plants. The roles of chemical compounds that are produced by both bacteria and algae and which drive the interactions are reviewed. The possibility of using such bioactive compounds to control macrofouling will be discussed.
[show abstract][hide abstract] ABSTRACT: We have developed a model for the prediction of cell attachment to engineered microtopographies based on two previous models, the Attachment Point Theory and the Engineered Roughness Index (ERI) model. The new Surface Energetic Attachment (SEA) model is based on both the properties of the cell-material interface as well as the size and configuration of the topography relative to the organism. We have used Monte Carlo simulation to examine the SEA model's ability to predict relative attachment of the green alga Ulva linza to different locations within a unit cell. We have also compared the predicted relative attachment for Ulva linza, the brown alga Navicula incerta, the marine bacterium Cobetia marina and the barnacle cyprid B. amphitrite to a wide variety of microtopographies. We demonstrate good correlation between the experimental results and the model results for all tested experimental data, and thus show the SEA model may be used as a powerful indicator of the efficacy for antifouling topographies.
[show abstract][hide abstract] ABSTRACT: 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.
Journal of Coatings Technology and Research 08/2013; 9(3). · 1.09 Impact Factor
[show abstract][hide abstract] ABSTRACT: Laboratory assessment of the adhesion of diatoms to non-toxic fouling-release coatings has tended to focus on single cells rather than the more complex state of a biofilm. A novel culture system based on open channel flow with adjustable bed shear stress values (0-2.4 Pa) has been used to produce biofilms of Navicula incerta. Biofilm development on glass and polydimethylsiloxane elastomer (PDMSe) showed a biphasic relationship with bed shear stress, which was characterised by regions of biofilm stability and instability reflecting cohesion between cells relative to the adhesion to the substratum. On glass, a critical shear stress of 1.3-1.4 Pa prevented biofilm development, whereas on PDMS, biofilms continued to grow at 2.4 Pa. Studies of diatom biofilms cultured on zwitterionic coatings using a bed shear stress of 0.54 Pa showed lower biomass production and adhesion strength on poly(sulfobetaine methacrylate) compared to poly(carboxybetaine methacrylate). The dynamic biofilm approach provides additional information to supplement short duration laboratory evaluations.
[show abstract][hide abstract] ABSTRACT: Bacterial adhesion can be controlled by applying electrical potentials to surfaces incorporating well-spaced negatively charged 11-mercaptoundecanoic acids. When combined with electrochemical surface plasmon resonance, these dynamic surfaces become powerful for monitoring and analysing the passage between reversible and non-reversible cell adhesion, opening new opportunities to advance our understanding of cell adhesion processes.
[show abstract][hide abstract] ABSTRACT: Polysaccharides are a promising material for non-fouling surfaces as their chemical composition makes them highly hydrophilic and able to form water-storing hydrogels. Here we investigated the non-fouling properties of hyaluronic acid (HA) and chondroitin sulfate (CS) in the marine environment. Additionally the free carboxyl-groups of HA and CS were post-modified with the hydrophobic trifluoroethylamine (TFEA) to block free carboxyl groups and render the surfaces amphiphilic. All coatings were tested with respect to their protein resistance and against settlement and adhesion of different marine fouling species. Both, settlement and adhesion strength of a marine bacterium (Cobetia marina), zoospores of the seaweed Ulva linza and cells of a diatom (Navicula incerta) were reduced compared to glass control surfaces. In most cases, TFEA capping increased or maintained the performance of the HA coatings, while for the very well-performing CS coatings the antifouling performance was reduced after capping.
[show abstract][hide abstract] ABSTRACT: The effect of a series of xerogel coatings modified with aminoalkyl/fluorocarbon/hydrocarbon groups on the adhesion of a new test species, the filamentous brown alga Ectocarpus crouaniorum, has been explored, and compared with the green alga Ulva linza. The results showed that E. crouaniorum adhered weakly to the less polar, low wettability coatings in the series, but stronger adhesion was shown on polar, higher surface energy coatings containing aminoalkyl groups. The results from a separate series of coatings tuned to have similar surface energies and polarities after immersion in artificial seawater (ASW), but widely different surface charges, demonstrated that surface charge was more important than surface energy and polarity in determining the adhesion strength of both E. crouaniorum and U. linza on xerogel coatings. No correlation was found between adhesion and contact angle hysteresis. X-ray photoelectron spectroscopy analysis of samples after immersion in ASW confirmed the presence of charged ammonium groups on the surface of the aminoalkylated coatings.
[show abstract][hide abstract] ABSTRACT: Among different surface cues, the settlement of cells and larvae of marine macrofouling organisms has been found to be strongly influenced by surface microtopographies. In this article, the settlement of zoospores of the green alga Ulva linza on a surface topographic gradient has been investigated. 'Honeycomb' gradient structures with feature sizes ranging from 1 µm to 10 µm were prepared by hot embossing, and the effect on the density of spores that attached in settlement assays was quantified. The highest density of spores was found when the size of the microstructures was similar to or larger than the size of the spores. With decreasing size of the structures, spore settlement density decreased. Interestingly, spore settlement density correlated with the Wenzel roughness of the surfaces. "Kink sites" on the surface played an important role and resembled preferred attachment positions. Furthermore, the gradients allowed the minimum pit size that the spores were able to squeeze into to be determined.
[show abstract][hide abstract] ABSTRACT: Settlement of the planktonic dispersal stages of marine organisms is the crucial step for the development of marine biofouling. Four-dimensional holographic tracking reveals the mechanism by which algal spores select surfaces suitable for colonization. Quantitative analysis of the three dimensional swimming trajectories of motile spores of a macroalga (Ulva linza) in the vicinity of surfaces functionalized with different chemistries reveals that their search strategy and swimming behavior is correlated to the number of settled spores found in spore settlement bioassays conducted over 45 min. The spore motility and exploration behavior can be classified into different motion patterns, with their relative occurrence changing with the surface chemistry. Based on the detailed motility analysis we derived a model for the surface selection and settlement process of Ulva zoospores.
[show abstract][hide abstract] ABSTRACT: Amphiphilic copolymers containing different amounts of poly(ethylene glycol)-fluoroalkyl acrylate and polysiloxane methacrylate units were blended with a poly(dimethyl siloxane) (PDMS) matrix in different proportions to investigate the effect of both copolymer composition and loading on the biological performance of the coatings. Laboratory bioassays revealed optimal compositions for the release of sporelings of Ulva linza, and the settlement of cypris larvae of Balanus amphitrite. The best-performing coatings were subjected to field immersion tests. Experimental coatings containing copolymer showed significantly reduced levels of hard fouling compared to the control coatings (PDMS without copolymer), their performance being equivalent to a coating based on Intersleek 700™. XPS analysis showed that only small amounts of fluorine at the coating surface were sufficient for good antifouling/fouling-release properties. AFM analyses of coatings under immersion showed that the presence of a regular surface structure with nanosized domains correlated with biological performance.
[show abstract][hide abstract] ABSTRACT: A two-dimensional array of amphiphilic crosslinked networks was prepared by systematic alteration of both the composition of hyperbranched fluoropolymers (HBFPs) and the relative stoichiometries upon crosslinking with poly(ethylene glycol) (PEG). Results of physicochemical, mechanical, surface and biofouling assessment are described in full. The materials were designed to present complex surface topographies, morphologies, and chemical features over nano- and microscopic dimensions to explicitly inhibit microorganism settlement and adhesion. A multi-dimensional, tunable matrix was generated to understand and optimize the composition–structure–property relationships. The thermal properties of the crosslinked networks were analyzed by thermogravimetric analysis (TGA) and differential scanning calorimetry (DSC), where the onset of thermal degradation, overall thermal stability and phase transition temperatures could be controlled based on the formulation. Investigation of the mechanical properties of the coatings in the water-swollen state found that the Young's modulus, ranging between 10.0 and 121 MPa, was dependent on both the wt% of PEG crosslinker and chemical composition of the HBFP. This result, on average, gives Young's moduli an order of magnitude larger than that previously reported for HBFP–PEG networks. Use of atomic force microscopy (AFM) provided insight into the nanoscale topography of the networks. Interestingly, it was observed that for all networks, surface roughness increased with water swelling going from an average of 115 ± 49 nm (dry) to 214 ± 106 nm (swelled) RMS roughness. Probing the surface chemistry by optical tensiometry revealed an increase in the static water contact angle by as much as 40° after water swelling. These two findings display a counter-intuitive increase of the surface hydrophobicity. Secondary ion mass spectrometry (SIMS) confirmed migration of hydrophobic fluorocarbon units to the surface by quantifying a 24% increase in fluorine species ejected from a dry versus water-swollen surface. Selected formulations of HBFP–PEG that demonstrated complex surface features and an overall high mechanical strength were tested in biological assays and all surfaces (3 formulations × 12 replicates) completely resisted the settlement of barnacle cyprids (Balanus amphitrite). Diatoms (Navicula incerta) were two- to three-times more easily removed from the HBFP–PEG surfaces compared to a homogeneous polydimethylsiloxane elastomer (PDMSe) standard surface. In contrast, algal spores (Ulva linza) were able to colonize the surfaces and were more difficult to remove in comparison to the PDMSe standard, pointing to the challenges associated with the development of a single material that is capable of broad anti-biofouling performance.
[show abstract][hide abstract] ABSTRACT: Conditioning, ie the adsorption of proteins and other macromolecules, is the first process that occurs in the natural environment once a surface is immersed in seawater, but no information is available either regarding the conditioning of surfaces by artificial seawater or whether conditioning affects data obtained from laboratory assays. A range of self-assembled monolayers (SAMs) with different chemical terminations was used to investigate the time-dependent formation of conditioning layers in commercial and self-prepared artificial seawaters. Subsequently, these results were compared with conditioning by solutions in which zoospores of the green alga Ulva linza had been swimming. Spectral ellipsometry and contact angle measurements as well as infrared reflection absorption spectroscopy (IRRAS) were used to reveal the thickness and chemical composition of the conditioning layers. The extent that surface preconditioning affected the settlement of zoospores of U. linza was also investigated. The results showed that in standard spore settlement bioassays (45-60 min), the influence of a molecular conditioning layer is likely to be small, although more substantial effects are possible at longer settlement times.
[show abstract][hide abstract] ABSTRACT: Coatings derived from surface active block copolymers (SABCs) having a combination of hydrophobic aliphatic (linear hydrocarbon or propylene oxide-derived groups) and hydrophilic poly(ethlyene glycol) (PEG) side chains have been developed. The coatings demonstrate superior performance against protein adsorption as well as resistance to biofouling, providing an alternative to coatings containing fluorinated side chains as the hydrophobe, thus reducing the potential environmental impact. The surfaces were examined using dynamic water contact angle, captive air-bubble contact angle, atomic force microscopy, X-ray photoelectron spectroscopy, and near-edge X-ray absorption fine structure analysis. The PS(8K)-b-P(E/B)(25K)-b-PI(10K) triblock copolymer precursor (K3) initially dominated the dry surface. In contrast to previous studies with mixed fluorinated/PEG surfaces, these new materials displayed significant surface changes after exposure to water that allowed fouling resistant behavior. PEG groups buried several nanometers below the surface in the dry state were able to occupy the coating surface after placement in water. The resulting surface exhibits a very low contact angle and good antifouling properties that are very different from those of K3. The surfaces are strongly resistant to protein adsorption using bovine serum albumin as a standard protein challenge. Biofouling assays with sporelings of the green alga Ulva and cells of the diatom Navicula showed the level of adhesion was significantly reduced relative to that of a PDMS standard and that of the triblock copolymer precursor of the SABCs.
[show abstract][hide abstract] ABSTRACT: Crosslinked siloxane–polyurethane coatings were designed, synthesized, formulated, applied, and characterized using combinatorial
high-throughput experimentation and eight coatings were selected as candidates for further characterization. First, 72 novel
hydroxyalkyl carbamate and dihydroxyalkyl carbamate-terminated poly(dimethylsiloxane) (PDMS) oligomers and their carbamate-linked
block copolymers with poly(ε-caprolactone) (PCL) were synthesized using a high-throughput synthesis system. These PDMS oligomers
and block copolymers were characterized for their molecular weight using high-throughput Gel Permeation Chromatography (Rapid-GPC).
The 72 oligomers were then incorporated into siloxane–polyurethane formulations at four different levels resulting in 288
coatings. After initial screening of these 288 coatings, eight coatings were selected for further characterization. Differential
scanning calorimetry, dynamic mechanical analysis, X-ray photoelectron spectroscopy and surface energy analysis demonstrate
the presence of PDMS on the surface with a polyurethane underlayer. Pseudo-barnacle adhesion and the attachment strength of
reattached live barnacles (Balanus amphitrite) were in good agreement. Out of the eight coatings that were down-selected, two coatings performed well in algal (Ulva), bacterial (Cytophaga lytica, Halomonas pacifica), and barnacle (Balanus amphitrite) laboratory screening assays and are potential candidates for ocean testing.
Journal of Coatings Technology and Research 04/2012; 4(4):435-451. · 1.09 Impact Factor
[show abstract][hide abstract] ABSTRACT: The effect of acrylic polyol composition on the properties of crosslinked siloxane-polyurethane coatings was explored. An
acrylic polyol library was synthesized using batch solution polymerization and characterized using high-throughput gel permeation
chromatography (Rapid-GPC) and differential scanning calorimetry (DSC). Siloxane-polyurethane coatings were prepared from
3-aminopropyl-terminated poly(dimethylsiloxane) (PDMS), the acrylic polyols and a polyisocyanate crosslinker. The siloxane-acrylic-polyurethane
coatings were tested for mechanical and physical properties. The siloxane-polyurethane coatings had a systematic variation
in glass transition temperature and had water contact angles ranging from 95° to 100°. Many of the coatings also showed a
low-force of release in the pseudo-barnacle pull-off adhesion test. Performance testing of the fouling-release properties
of the siloxane-polyurethane coatings on array panels with algae, namely the diatom Navicula and sporelings (young plants) of the green seaweed Ulva was also conducted.
Journal of Coatings Technology and Research 04/2012; 4(4):453-461. · 1.09 Impact Factor
[show abstract][hide abstract] ABSTRACT: Four-component xerogel films consisting of 1 mole-% n-octadecyltrimethoxysilane (C18) and 50 mole-% tetraethoxysilane (TEOS) in combination with 1-24 mole-% tridecafluoro-1,1,2,2-tetrahydrooctyltriethoxysilane (TDF) and 25-48 mole-% n-octyltriethoxysilane (C8) and a 1:49:50 mole-% C18/TDF/TEOS were prepared. Settlement of barnacle cyprids and removal of juvenile barnacles, settlement of zoospores of the alga Ulva linza, and strength of attachment of 7-day sporelings (young plants) of Ulva were compared amongst the xerogel formulations. Several of the xerogel formulations were comparable to poly(dimethylsiloxane) elastomer with respect to removal of juvenile barnacles and removal of sporeling biomass. The 1:4:45:50 and 1:14:35:50 C18/TDF/C8/TEOS xerogels displayed some phase segregation by atomic force microscopy (AFM) pre- and post-immersion in water. Imaging reflectance infrared microscopy showed the formation of islands of alkane-rich and perfluoroalkane-rich regions in these same xerogels both pre- and post-immersion in water. Surface energies were unchanged upon immersion in water for 48 h amongst the TDF-containing xerogel coatings. AFM measurements demonstrated that surface roughness on the 1:4:45:50 and 1:14:35:50 C18/TDF/C8/TEOS xerogel coatings decreased upon immersion in water.
[show abstract][hide abstract] ABSTRACT: The use of the phenomenon of self-stratification to design polyurethane coatings having amphiphilic surfaces was explored. A novel hydrophobic siloxane polymer having orthogonal carboxylic acid groups was used to create the amphiphilic surface. The acid functional siloxane polymers were synthesized using ring opening equilibration polymerization (ROEP) of two cyclic siloxane monomers and thiol-ene click chemistry was used to introduce pendant carboxylic acid groups. The acid functional siloxane polymers were then used to prepare acid functional siloxane–polyurethane (PDMS-A) coatings. The coatings were characterized for their surface properties using water contact angle (WCA), confocal raman microscopy (CRM), and attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectroscopy. The characterization revealed the presence of the acid functional siloxane polymer at the coatings’ surface due to self-stratification. WCA data indicated the coatings became more hydrophilic after immersion in water and artificial seawater (ASW), indicating the presence of the carboxylic acid groups at the surface. The PDMS-A coatings showed excellent fouling-release performance towards microalgae and good release performance towards bacteria. However, macroalga and adult barnacles showed better removal from hydrophobic PDMS-containing coatings compared to the amphiphilic PDMS-A coatings.
[show abstract][hide abstract] ABSTRACT: Species of filamentous brown algae in the family Ectocarpaceae are significant members of fouling communities. However, there are few systematic studies on the influence of surface physico-chemical properties on their adhesion. In the present paper the development of a novel, laboratory-based adhesion bioassay for ectocarpoid algae, at an appropriate scale for the screening of sets of experimental samples in well-replicated and controlled experiments is described. The assays are based on the colonization of surfaces from a starting inoculum consisting of multicellular filaments obtained by blending the cultured alga Ectocarpus crouaniorum. The adhesion strength of the biomass after 14 days growth was assessed by applying a hydrodynamic shear stress. Results from adhesion tests on a set of standard surfaces showed that E. crouaniorum adhered more weakly to the amphiphilic Intersleek® 900 than to the more hydrophobic Intersleek® 700 and Silastic® T2 coatings. Adhesion to hydrophilic glass was also weak. Similar results were obtained for other cultivated species of Ectocarpus but differed from those obtained with the related ectocarpoid species Hincksia secunda. The response of the ectocarpoid algae to the surfaces was also compared to that for the green alga, Ulva.