Microtopography and antifouling properties of the shell surface of the bivalve molluscs Mytilus galloprovincialis and Pinctada imbricata

The antifouling mechanism and application of bio-inspired superwetting surfaces with effective antifouling performance

With the rapid development of industries, the issue of pollution on Earth has become increasingly severe. This has led to the deterioration of various surfaces, rendering them ineffective for their intended purposes. Examples of such surfaces include oil rigs, seawater intakes, and more. A variety of functional surface techniques have been created to address these issues, including superwetting surfaces, antifouling coatings, nano-polymer composite materials, etc. They primarily exploit the membrane's surface properties and hydration layer to improve the antifouling property. In recent years, biomimetic superwetting surfaces with non-toxic and environmental characteristics have garnered massive attention, greatly aiding in solving the problem of pollution. In this work, a detailed presentation of antifouling superwetting materials was made, including superhydrophobic surface, superhydrophilic surface, and superhydrophilic/underwater superoleophobic surface, along with the antifouling mechanisms. Then, the applications of the superwetting antifouling materials in antifouling domain were addressed in depth.

Exploring Periostracum as an Alternative Root Canal Irrigant: Insights From Zebrafish Embryo Experiments

Objectives Root canal treatments aim to eliminate biofilms effectively. Considering the limitations of chemical irrigants, there is growing interest in natural alternatives like periostracum due to their antibacterial and fouling-resistant properties. This study aimed to assess periostracum's toxicity as a root canal irrigant by investigating its effects on zebrafish embryos' heart rate, survival rate, and hatching rate, as well as inflammation studies using neutral red assays comparing it to standard irrigants like ethylenediaminetetraacetic acid (EDTA), chlorhexidine (CHX), and sodium hypochlorite (NaOCl). Materials and methods Zebrafish embryos were exposed to varying concentrations of periostracum irrigant and standard irrigants. Heart rate, survival rate, and hatching rate were evaluated as indicators of developmental toxicity using microscopy. Statistical analysis, utilizing GraphPad Prism software (version 5.03, GraphPad Software, LLC, San Diego, California, United States), involved one-way ANOVA and Tukey's post-hoc test to determine significance levels (p < 0.05) across control and other groups based on triplicate means and standard deviation. Results The periostracum irrigant demonstrated superior survival rates, heart rates, and hatching rates at specific concentrations compared to standard irrigants (p < 0.01), maintaining favorable heart rates and hatching rates at those concentrations. However, higher concentrations resulted in diminished hatching rates (p < 0.05). Additionally, this study revealed increased inflammation when larvae were treated with NaOCl, EDTA, and CHX. Conversely, no inflammation was observed when subjected to periostracum irrigants. These findings suggest potential advantages of periostracum as a root canal irrigant due to its increased biocompatibility. Conclusion Periostracum displayed promising attributes in zebrafish embryo experiments, such as stable heart rate, hatching rate, and survival rate, along with reduced developmental toxicity and inflammation, indicating potential advantages as a root canal irrigant, including reduced toxicity compared to conventional agents. Further research involving diverse demographics and long-term effects is crucial to validate periostracum's clinical applicability and safety in endodontic therapies.

Biomimetic Approach to Counter Streptococcus mutans Biofilm: An In Vitro Study on Seashells

Aim This study aimed to investigate the anti-adherent property of the seashell surface and periostracum to prevent the formation of Streptococcus mutans biofilm. Materials and methods The seashells were initially collected from the natural urban beach, and an antibiofilm assay of the shells with and without periostracum was performed against Streptococcus mutans. Furthermore, the seashells were analyzed with a stylus profilometer (Mitutoyo Surftest SJ-301, Mitutoyo America Corporation, Illinois, USA), atomic force microscope (AFM; Nanosurf Easyscan 2, Nanosurf Inc., USA), contact angle assessment, Fourier-transform infrared (FTIR) spectroscopy analysis, and scanning electron microscopy (SEM; JEOL USA, Inc., FE-SEM IT800, Massachusetts, USA) analysis. The ability of seashells to prevent the attachment of Streptococcus mutans and form a biofilm with and without periostracum was studied by crystal violet assay. Results The results revealed that shells without periostracum promoted higher biofilm formation when compared to those having intact periostracum (by 15%, p<0.001). Shell 1 showed the highest biofilm formation, whereas shell 3 showed the least biofilm formation due to the differences in their surface morphologies. The remaining shells (4, 2, 6, and 5) showed interspersed biofilm formation. Conclusion In summary, our study was able to correlate the topologies of the shell surface with the biofilm formed by Streptococcus mutans with the wetting behavior of those shell surfaces and their roughness. More hydrophobic surfaces (with intact periostracum) were observed to lead to less attachment (correlation coefficient=-0.67). This study can pave the way for designing such biomimetic surfaces to prevent bacterial attachment.

Thermal stress gradient causes increasingly negative effects towards the range limit of an invasive mussel

Environmental filtering (EF), the abiotic exclusion of species, can have first order, direct effects with cascading consequences for population dynamics, especially at range edges where abiotic conditions are suboptimal. Abiotic stress gradients associated with EF may also drive indirect second order effects, including exacerbating the effects of competitors, disease, and parasites on marginal populations because of suboptimal physiological performance. We predicted a cascade of first and second order EF-associated effects on marginal populations of the invasive mussel Mytilus galloprovincialis, plus a third order effect of EF of increased epibiont load due to second order shell degradation by endoliths. Mussel populations on rocky shores were surveyed across 850 km of the south-southeast coast of South Africa, from the species' warm-edge range limit to sites in the centre of their distribution, to quantify second order (endolithic shell degradation) and third order (number of barnacle epibionts) EF-associated effects as a function of along-shore distance from the range edge. Inshore temperature data were interpolated from the literature. Using in situ temperature logger data, we calculated the effective shore level for several sites by determining the duration of immersion and emersion. Summer and winter inshore water temperatures were linked to distance from the mussel's warm range edge (our proxy for an EF-associated stress gradient), suggesting that seasonality in temperature contributes to first order effects. The gradient in thermal stress clearly affected densities, but its influence on mussel size, shell degradation, and epibiosis was weaker. Relationships among mussel size, shell degradation, and epibiosis were more robust. Larger, older mussels had more degraded shells and more epibionts, with endolithic damage facilitating epibiosis. EF associated with a gradient in thermal stress directly limits the distribution, abundance, and size structure of mussel populations, with important indirect second and third order effects of parasitic disease and epibiont load, respectively.

Hydrophilic tyrosine-based phenolic resin with micro-ripples morphology for marine antifouling application

Since biofouling challenges negatively influence the marine and transportation industries, developing effective antifouling materials have attracted extensive concern. A tyrosine-based antifouling phenolic resin (TPP resin) was synthesized using tyrosine as a natural phenol source. TPP exhibited shell-like surface morphology with micro-ripples and excellent anti-adhesion properties against bacteria and diatom. The micro-ripples surface might be caused by the strong hydrogen bonding or ionic interaction among tyrosine units resulting in microphase separation during the curing process. Tyrosine content in TPP resin has a great influence on the surface properties, morphology and antifouling characteristics. The higher the tyrosine content, the higher is the surface hydrophilicity, the denser and more regular is the micro-ripples morphology, and the stronger is the antifouling performance. TPP-60 % exhibited the best antifouling performance. Combination of the surface hydrophilicity and regular micro-ripples surface morphology afford TPP excellent antifouling performance. TPP resins offer a broad prospect for developing phenolic resin in the antifouling field.

Bioinspired Fatty Acid Amide-Based Slippery Oleogels for Shear-Stable Lubrication

Liquid-repellent technology is an efficient means of energy-saving and biofouling avoidance. However, liquid-repellent surfaces suffer from inefficient lubricant retention under shear flow and fouling problem in marine environment. Here, the authors demonstrate a fatty acid amide (FAA)-based oleogel for stable and sustainable lubrication in marine environment. The lubrication management of marine creatures is emulated in synthetic oleogels by incorporating solid (FAA) and liquid lubricants into the molecular meshes of polymeric networks, with the nature-derived solid lubricant providing multifunctional synergistic effects with liquid oil molecules for slippery property and remarkable anti-biofouling. The lubricant-confining gel achieves shear-stable lubricity with efficient oil management. The oleogel provides continued lubrication without biofouling for approximately 4 months in marine field tests. The gel design provides a new paradigm for sustainable and shear-stable lubrication in marine environment.

Counterplotting the Mechanosensing-Based Fouling Mechanism of Mussels against Fouling

Marine organisms react to various factors when building colonies for survival; however, severe accumulation of diverse organisms on artificial structures located close to water causes large industrial losses. Herein, we identify a concept in the development of antifouling surfaces based on understanding the surface stiffness recognition procedure of mussel adhesion at the genetic level. It was found that on a soft surface the combination of decreased adhesive plaque size, adhesion force, and plaque protein downregulation synergistically weakens mussel wet adhesion and sometimes prevents mussels from anchoring, mainly due to transcriptional changes within the mechanosensing pathway and the adhesive proteins in secretory glands. In addition, the use of soft substrates or antagonists of surface mechanosensing behavior suppresses mussel fouling significantly.

The mussel-inspired micro-nano structure for antifouling:A flowering tree

Mussels are typical marine fouling organisms that attach to surfaces though secretions, which is generally the focus of research on mussel-related fouling. This study reveals "a flowering tree" structure on mussel shells with antifouling performance. Based on the antifouling mechanism of surface microstructure, we prepared mussel-like shells (P) using the biomimetic replication method. Mussel adhesion experiments were conducted to examine the anti-mussel performances of the mussel shells and P. The anti-diatom performances of the mussel-like shells were also evaluated using three types of diatoms. The mussels responded differently to different locations on the shells, and the flowering tree microstructure exhibited excellent antifouling performance. In addition, VP (P immersed in vinyl silicon oil) and HP (P immersed in hydroxyl silicone oil) were prepared. The anti-diatom performance of VP was better than those of P and HP, indicating that hydrophobicity has a greater influence on anti-diatom performance than electronegativity. The newly discovered antifouling micro-nano structure was parameterized, revealing that a branch of the flowering tree has an inclination of 13.3° to the surface with a height of 210.1 nm. The results of this study provide insights for further investigations of bionic micro-nano structures in the field of antifouling.

Development of a nanostructured film based on samarium (III)/polydopamine on the steel surface with superior anti-corrosion and water-repellency properties

HYPOTHESIS

The application of various hydrophobic/superhydrophobic coatings on the surface of metals has become the hot topic of the recent studies. The corrosion protection effectiveness and environmental issues are two important factors that should be taken into consideration when developing advanced surface coatings. Recently, the rare-earth elements (i.e., samarium) and biopolymers (i.e., polydopamine) have attracted much attention in the metals' corrosion control field.

EXPERIMENTS

The Sm(NO₃)₃ containing solution was sprayed to the steel (St-12) sheets. Then, the Sm-modified plates were post-modified by polydopamine biopolymers that were synthesized by the self-polymerization (using tris (hydroxymethyl) aminomethane as a buffer), and oxidant-induced (using CuSO₄ as an oxidant) approaches. The structural analysis was carried out by different techniques such as contact angle (CA) test. Moreover, the electrochemical impedance spectroscopy (EIS) and polarization tests were performed to investigate the anti-corrosion performance of various samples.

FINDINGS

The CA test results revealed that by applying the nanostructured Sm-based film, the surface of the metal becomes near superhydrophobic (CA > 140°). EIS results evidenced the significant impact of the post-treatment of the Sm-treated samples by polydopamine (PDA) nanoparticles (NPs) on its corrosion protection ability enhancement. Also, the polarization test results confirmed that all treatments could retard the corrosion of steel via a mixed-type inhibition mechanism.

Research progress of environmentally friendly marine antifouling coatings

The antifouling mechanisms and research progress in the past three years of environmentally friendly marine antifouling coatings are introduced in this work.

Superhydrophobic ZIF-8-Based Dual-Layer Coating for Enhanced Corrosion Protection of Mg Alloy

Magnesium (Mg) and its alloys are regarded as the most promising engineering materials because of their unique property. However, the Mg alloys were easily corroded in humid environments, which restricted their wider applications. Herein, the superhydrophobic ZIF-8/PVDF/LDH (SZPL) double-layered coating was fabricated on Mg alloys via electrodeposition and dip-coating methods, which consisted of the underlying layered double hydroxide (LDH) transition structure and top superhydrophobic zeolitic imidazolate framework-8 (ZIF-8) layer. Besides, the LDH transition structure not only worked as a protection shield but also strengthened the binding force between the substrate and the top superhydrophobic ZIF-8 layer. The top superhydrophobic ZIF-8 layer could serve as an armor on the LDH layer to further prevent the corrosive ions from infiltrating the microporous defects. In addition, the as-prepared SZPL double-layered coating showed robust superhydrophobic and self-cleaning properties, which could block the electrolyte invasion. Furthermore, the electrochemical tests demonstrated that the SZPL coating highly enhanced the corrosion protection ability of Mg alloys. Moreover, the superhydrophobic ZIF-8-based coating could still retain excellent anticorrosion property after immersion in 3.5 wt % NaCl solution for 7 days. The enhanced anticorrosion ability was ascribed to the fact that a synergistic effect of the underlying LDH transition layer hindered the transmission of aggressive ions and the top superhydrophobic ZIF-8-based coating decreased the contact area of the substrate with corrosive solution. Therefore, such coatings offer a new strategy for fabricating excellent anticorrosive coatings with robust superhydrophobicity and self-cleaning performance on metal substrates.

Bio-inspired Surface Texture Modification as a Viable Feature of Future Aquatic Antifouling Strategies: A Review

The imitation of natural systems to produce effective antifouling materials is often referred to as “biomimetics”. The world of biomimetics is a multidisciplinary one, needing careful understanding of “biological structures”, processes and principles of various organisms found in nature and based on this, designing nanodevices and nanomaterials that are of commercial interest to industry. Looking to the marine environment for bioinspired surfaces offers researchers a wealth of topographies to explore. Particular attention has been given to the evaluation of textures based on marine organisms tested in either the laboratory or the field. The findings of the review relate to the numbers of studies on textured surfaces demonstrating antifouling potential which are significant. However, many of these are only tested in the laboratory, where it is acknowledged a very different response to fouling is observed.

Non-equilibrium hybrid organic plasma processing for superhydrophobic PTFE surface towards potential bio-interface applications

Superhydrophobic surfaces have gained increased attention due to the high water-repellency and self-cleaning capabilities of these surfaces. In the present study, we explored a novel hybrid method of fabricating superhydrophobic poly(tetrafluoroethylene) (PTFE) surfaces by combining the physical etching capability of oxygen plasma with the plasma-induced polymerization of a organic monomer methyl methacrylate (MMA). This novel hybrid combination of oxygen-MMA plasma has resulted in the generation of superhydrophobic PTFE surfaces with contact angle of 154°. We hypothesized that the generation of superhydrophobicity may be attributed to the generation of fluorinated poly(methyl methacrylate) (PMMA) moieties formed by the combined effects of physical etching causing de-fluorination of PTFE and the subsequent plasma polymerization of MMA. The plasma treated PTFE surfaces were then systematically characterized via XPS, FTIR, XRD, DSC and SEM analyses. The results have clearly shown a synergistic effect of the oxygen/MMA combination in comparison with either the oxygen plasma alone or MMA vapors alone. Furthermore, the reported new hybrid combination of Oxygen-MMA plasma has been demonstrated to achieve superhydrophobicity at lower power and short time scales than previously reported methods in the literature. Hence the reported novel hybrid strategy of fabricating superhydrophobic PTFE surfaces could have futuristic potential towards biointerface applications.

Fabrication of superhydrophobic and ice-repellent surfaces on pure aluminium using single and multiscaled periodic textures

Fabricating aluminium surfaces with superhydrophobic and ice-repellent properties present nowadays a challenging task. In this work, multifunctional structures are manufactured by direct laser writing and direct laser interference patterning methods using pulsed infrared laser radiation (1064 nm). Different periodic patterns with feature sizes ranging from 7.0 to 50.0 µm are produced. In addition, hierarchical textures are produced combining both mentioned laser based methods. Water contact angle tests at room temperature showed that all produced patterns reached the superhydrophobic state after 13 to 16 days. In addition, these experiments were repeated at substrate temperatures from −30 °C to 80 °C allowing to determine three wettability behaviours as a function of the temperature. The patterned surfaces also showed ice-repellent properties characterized by a near three-fold increase in the droplets freezing times compared to the untreated samples. Using finite element simulations, it was found that the main reason behind the ice-prevention is the change in the droplet geometrical shape due to the hydrophobic nature of the treated surfaces. Finally, dynamic tests of droplets imping the treated aluminium surfaces cooled down to −20 °C revealed that only on the hierarchically patterned surface, the droplets were able to bounce off the substrate.

Antifouling performance and mechanism of elastic graphene-silicone rubber composite membranes

Composite coatings have attracted great attention as an eco-friendly and economic solution to prevent ship hulls from biofouling. Inspired by the unstable surfaces of marine organisms with antifouling properties, this study describes the preparation of graphene-silicone rubber composite membranes. The membranes are characterized by a low surface energy and an adjustable elastic modulus, and these properties are conducive to preventing biofouling. Bacterial attachment was tested under both quasi-static and hydrodynamic conditions, and one rigid polystyrene sheet was used as the control group to verify the antifouling effects of unstable surfaces. The polystyrene sheet and the elastic membranes showed similar antifouling performance under quasi-static conditions. However, under hydrodynamic conditions, the elastic membranes showed better antifouling performance than the rigid polystyrene sheet. The results obtained using a laser-displacement sensor showed that micron-scale deformations were present on the elastic surface, and a mechanical model was employed to verify this conclusion. This study first confirmed the antifouling effects of the unstable surface, and proposed a model to reveal the antifouling mechanism of the unstable surface. According to the bacterial attachment test, a new generation membrane was made showing antifouling capacity with just 0.36 wt% graphene included during the fabrication of the membrane. This study provided a deeper insight into the antifouling mechanism of the elastic surface, and the membrane (0.36 wt%) may be promising for practical applications.

Nanoscience-Based Strategies to Engineer Antimicrobial Surfaces

Microbial contamination and biofilm formation of medical devices is a major issue associated with medical complications and increased costs. Consequently, there is a growing need for novel strategies and exploitation of nanoscience-based technologies to reduce the interaction of bacteria and microbes with synthetic surfaces. This article focuses on surfaces that are nanostructured, have functional coatings, and generate or release antimicrobial compounds, including "smart surfaces" producing antibiotics on demand. Key requirements for successful antimicrobial surfaces including biocompatibility, mechanical stability, durability, and efficiency are discussed and illustrated with examples of the recent literature. Various nanoscience-based technologies are described along with new concepts, their advantages, and remaining open questions. Although at an early stage of research, nanoscience-based strategies for creating antimicrobial surfaces have the advantage of acting at the molecular level, potentially making them more efficient under specific conditions. Moreover, the interface can be fine tuned and specific interactions that depend on the location of the device can be addressed. Finally, remaining important challenges are identified: improvement of the efficacy for long-term use, extension of the application range to a large spectrum of bacteria, standardized evaluation assays, and combination of passive and active approaches in a single surface to produce multifunctional surfaces.

Controlled Attachment of Pseudomonas aeruginosa with Binary Colloidal Crystal-Based Topographies

Micro- and nanotopographies can interfere with bacteria attachment, however, the interplay existing between surface chemistry and topography remains unclear. Here, self-assembled spherical micrometer- silica and nanometer poly(methyl methacrylate) (PMMA)-sized particles are used to make binary colloidal crystal (BCC) topographical patterns to study bacterial attachment. A uniform surface chemistry of allylamine plasma polymer (AAMpp) is coated on the top of the BCCs to study only the topography effects. The uncoated and coated BCCs are exposed to Pseudomonas aeruginosa, and the surfaces and bacteria are characterized using scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and fluorescence microscopy. It is found that bacteria attachment to the uncoated BCCs is delayed and individual cells are attracted to the small particle regions of the patterns. Surprisingly, this phenomenon is also observed for the AAMpp-coated BCCs, with bacteria attaching to the small particle regions of the pattern, in stark contrast to uniform flat films of AAMpp that are highly adhesive toward P. aeruginosa. Also, the overall levels of bacterial attachment are significantly reduced by the BCC patterns compared to controls. Thus, there is a trade-off that exists between chemistry and topography that can be exploited to delay the onset of P. aeruginosa biofilm formation on surfaces.

Facile Fabrication and Characterization of a PDMS-Derived Candle Soot Coated Stable Biocompatible Superhydrophobic and Superhemophobic Surface

We report a simple, inexpensive, rapid, and one-step method for the fabrication of a stable and biocompatible superhydrophobic and superhemophobic surface. The proposed surface comprises candle soot particles embedded in a mixture of PDMS+n-hexane serving as the base material. The mechanism responsible for the superhydrophobic behavior of the surface is explained, and the surface is characterized based on its morphology and elemental composition, wetting properties, mechanical and chemical stability, and biocompatibility. The effect of %n-hexane in PDMS, the thickness of the PDMS+n-hexane layer (in terms of spin coating speed) and sooting time on the wetting property of the surface is studied. The proposed surface exhibits nanoscale surface asperities (average roughness of 187 nm), chemical compositions of soot particles, very high water and blood repellency along with excellent mechanical and chemical stability and excellent biocompatibility against blood sample and biological cells. The water contact angle and roll-off angle is measured as 160° ± 1° and 2°, respectively, and the blood contact angle is found to be 154° ± 1°, which indicates that the surface is superhydrophobic and superhemophobic. The proposed superhydrophobic and superhemophobic surface offers significantly improved (>40%) cell viability as compared to glass and PDMS surfaces.

Biomolding Technique to Fabricate the Hierarchical Topographical Scaffold of POMA To Enhance the Differentiation of Neural Stem Cells

In this paper, a biomolding technique was first used to fabricate a scaffold of hierarchical topography with biomimetic morphology for tissue engineering. First, poly(ortho-methoxyaniline) (POMA) was synthesized by conventional oxidative polymerization, followed by characterizations with Fourier transform infrared spectroscopy (FTIR) and gel permeation chromatography (GPC). Moreover, the POMA scaffold with 3D biomimetic morphology was fabricated using poly(dimethylsiloxane) (PDMS) as negative soft template from natural leaf surfaces of Xanthosoma sagittifolium, followed by transferring the pattern of PDMS template to POMA. The as-fabricated POMA scaffold with biomimetic morphology was investigated by scanning electron microscopy (SEM). Subsequently, cell-scaffold interactions were carried out by culturing rat neural stem cells (rNSCs) on biomimetic and nonbiomimetic, or flat, POMA scaffolds, as well as on poly(d-lysine) (PDL)-coated substrate, and evaluating the corresponding adhesion, cell viability, and differentiation of rNSCs. Results showed that there was no significant difference in the attachment of rNSCs on the three surface types, however, both the biomimetic and flat POMA scaffolds induced growth arrest relative to the PDL-coated substrate. In addition, the percentage of cells with elongated neurites after 19 days of culture was higher on the biomimetic POMA scaffold relative to flat POMA and PDL. In summary, the POMA scaffold with biomimetic morphology shows promise in promoting rNSCs differentiation and neurite outgrowth for long-term studies on nerve regenerative medicine.

Durable, self-healing, superhydrophobic fabrics from fluorine-free, waterborne, polydopamine/alkyl silane coatings

Superhydrophobic fabrics prepared from a polydopamine coating show high water repellency, good durability and self-healing property.

No Effects and No Control of Epibionts in Two Species of Temperate Pycnogonids

Essentially all surfaces of marine plants and animals host epibionts. These organisms may harm their hosts in a number of ways, including impeding gas exchange or increasing the costs of locomotion. Epibionts can also be beneficial. For example, they may camouflage their hosts, and photosynthetic epibionts can produce oxygen. In general, however, the costs of epibionts appear to outweigh their benefits. Many organisms, therefore, shed epibionts by grooming, molting, or preventing them from initially attaching, using surface waxes and cuticular structures. In this study, we examined how epibionts affect local oxygen supply to temperate species of pycnogonids (sea spiders). We also tested the effectiveness of different methods that pycnogonids may use to control epibionts (grooming, cuticle wettability, and cuticular waxes). In two temperate species: Achelia chelata and Achelia gracilipes, epibionts consisted primarily of algae and diatoms, formed layers approximately 0.25-mm thick, and they colonized at least 75% of available surface area. We used microelectrodes to measure oxygen levels in and under the layers of epibionts. In bright light, these organisms produced high levels of oxygen; in the dark, they had no negative effect on local oxygen supply. We tested mechanisms of control of epibionts by pycnogonids in three ways: disabling their ovigers to prevent grooming, extracting wax layers from the cuticle, and measuring the wettability of the cuticle; however, none of these experiments affected epibiont coverage. These findings indicate that in temperate environments, epibionts are not costly to pycnogonids and, in some circumstances, they may be beneficial.

Fabrication of Slippery Lubricant-Infused Porous Surface for Inhibition of Microbially Influenced Corrosion

Microbially influenced corrosion (MIC) accelerates the failure of metal in a marine environment. In this research, slippery lubricant-infused porous surface (SLIPS) was designed on aluminum, and its great potential for inhibiting MIC induced by sulfate-reducing bacteria (SRB) was demonstrated in a simulated marine environment. The inhibition mechanism of SLIPS to MIC was proposed based on its effective roles in the suppression of SRB settlement and isolation effect to corrosive metabolites. The liquid-like property is demonstrated to be the major contributor to the suppression effect of SLIPS to SRB settlement. The effects of environmental factors (static and dynamic conditions) and lubricant type to SRB settlement over SLIPS were also investigated. It was indicated that the as-fabricated SLIPS can inhibit the SRB settlement in both static and dynamic marine conditions, and lubricant type presents a negligible effect on the SRB settlement. These results will provide a series of foundational data for the future practical application of SLIPS in the marine environment, and also a lubricant selecting instruction to construct SLIPS for MIC control.

Superhydrophobic surfaces for applications in seawater

OBJECTIVE

Technological fields in which seawater is implied are numerorus, working in seawater (shipping, oil industry, marine aquaculture,..), and exploiting seawater in plants (cooling heat-exchange, desalination, power plants,..). All suffer from detrimental effects induced by biofouling mainly enhancing material failures and limiting energetic efficiencies. Among the remediation solutions, technologies coniugating economical, green and efficiency criteria should represent the direction. With the aim to meet these criteria, superhydrophobic (SH) technology attracted many researches for the protection of materials operating in contact with seawater.

METHOD

In this work, the literature focusing on such technology for the protection of surfaces in contact with seawater has been reviewed, mainly focusing on boat and ship hull protection.

RESULTS

Despite the growing interest around SH technology in seawater for fouling control and friction drag reduction of hulls, to date literature shows that superhydrophobicity in seawater is still limited if compared with a time window compatible with technological needs (set on years). An evaluation of the causes of early superhydrophobicity loss under operative conditions clearly indicates that, to the best of present knowledge, a SH surface cannot preserve this feature by itself alone (especially in real seawater). Hence, we have considered to highlight the behaviour of SH surfaces in seawater in relation to early stages of biocolonization (conditioning film and pioneering bioslime formation). Considering the annual costs sustained for the biofouling impact control, advantages coming from SH surfaces, in terms of foul control and friction drag reduction, would allow economical savings allowing to cover both the appliance of longevity keeping strategies of the SH surfaces and investments in green technologies of SH coating life cycle (production, storing). In addition a brief outlook is provided on technological fields exploiting seawater in pipelines (power and desalination plants), where the SH surface finishing finds potentially interesting application for fouling and corrosion prevention applications.

Loss of superhydrophobicity of hydrophobic micro/nano structures during condensation

Condensed liquid behavior on hydrophobic micro/nano-structured surfaces is a subject with multiple practical applications, but remains poorly understood. In particular, the loss of superhydrophobicity of hydrophobic micro/nanostructures during condensation, even when the same surface shows water-repellant characteristics when exposed to air, requires intensive investigation to improve and apply our understanding of the fundamental physics of condensation. Here, we postulate the criterion required for condensation to form from inside the surface structures by examining the grand potentials of a condensation system, including the properties of the condensed liquid and the conditions required for condensation. The results imply that the same hydrophobic micro/nano-structured surface could exhibit different liquid droplet behavior depending on the conditions. Our findings are supported by the observed phenomena: the initiation of a condensed droplet from inside a hydrophobic cavity, the apparent wetted state changes, and the presence of sticky condensed droplets on the hydrophobic micro/nano-structured surface.

Hierarchically ordered self-lubricating superhydrophobic anodized aluminum surfaces with enhanced corrosion resistance

Herein, we report a facile method for the fabrication of self-lubricating superhydrophobic hierarchical anodic aluminum oxide (AAO) surfaces with improved corrosion protection, which is greatly anticipated to have a high impact in catalysis, aerospace, and the shipping industries. This method involves chemical grafting of as-formed AAO using low surface free energy molecules like long chain saturated fatty acids, perfluorinated fatty acid (perfluorooctadecanoic acid, PFODA), and perfluorosulfonicacid-polytetrafluoroethylene copolymer. The pre and post treatment processes in the anodization of aluminum (Al) play a vital role in the grafting of fatty acids. Wettability and surface free energy were analyzed using a contact angle meter and achieved 161.5° for PFODA grafted anodized aluminum (PFODA-Al). This study was also aimed at evaluating the surface for corrosion resistance by Tafel polarization and self-lubricating properties by tribological studies using a pin-on-disc tribometer. The collective results showed that chemically grafted AAO nanostructures exhibit high corrosion resistance toward seawater and low frictional coefficient due to low surface energy and self-lubricating property of fatty acids covalently linked to anodized Al surfaces.

Self-cleaning, superhydrophobic cotton fabrics with excellent washing durability, solvent resistance and chemical stability prepared from an SU-8 derived surface coating

A self-cleaning, superhydrophobic cotton with excellent washing durability, solvent resistance, and acid/base stability has been prepared using a single-pot solution.

Bioinspired materials: from low to high dimensional structure

The surprising properties of biomaterials are the results of billions of years of evolution. Generally, biomaterials are assembled under mild conditions with very limited supply of constituents available for living organism, and their amazing properties largely result from the sophisticated hierarchical structures. Following the biomimetic principles to prepare manmade materials has drawn great research interests in materials science and engineering. In this review, we summarize the recent progress in fabricating bioinspired materials with the emphasis on mimicking the structure from one to three dimensions. Selected examples are described with a focus on the relationship between the structural characters and the corresponding functions. For one-dimensional materials, spider fibers, polar bear hair, multichannel plant roots and so on have been involved. Natural structure color and color shifting surfaces, and the antifouling, antireflective coatings of biomaterials are chosen as the typical examples of the two-dimensional biomimicking. The outstanding protection performance, and the stimuli responsive and self-healing functions of biomaterials based on the sophisticated hierarchical bulk structures are the emphases of the three-dimensional mimicking. Finally, a summary and outlook are given.

Potential biocontrol agents for biofouling on artificial structures

The accumulation of biofouling on coastal structures can lead to operational impacts and may harbour problematic organisms, including non-indigenous species. Benthic predators and grazers that can supress biofouling, and which are able to be artificially enhanced, have potential value as augmentative biocontrol agents. The ability of New Zealand native invertebrates to control biofouling on marina pontoons and wharf piles was tested. Caging experiments evaluated the ability of biocontrol to mitigate established biofouling, and to prevent fouling accumulation on defouled surfaces. On pontoons, the gastropods Haliotis iris and Cookia sulcata reduced established biofouling cover by >55% and largely prevented the accumulation of new biofouling over three months. On wharf piles C. sulcata removed 65% of biofouling biomass and reduced its cover by 73%. C. sulcata also had better retention and survival rates than other agents. Augmentative biocontrol has the potential to be an effective method to mitigate biofouling on marine structures.

Does seawater acidification affect survival, growth and shell integrity in bivalve juveniles?

Anthropogenic emissions of carbon dioxide are leading to decreases in pH and changes in the carbonate chemistry of seawater. Ocean acidification may negatively affect the ability of marine organisms to produce calcareous structures while also influencing their physiological responses and growth. The aim of this study was to evaluate the effects of reduced pH on the survival, growth and shell integrity of juveniles of two marine bivalves from the Northern Adriatic sea: the Mediterranean mussel Mytilus galloprovincialis and the striped venus clam Chamelea gallina. An outdoor flow-through plant was set up and two pH levels (natural seawater pH as a control, pH 7.4 as the treatment) were tested in long-term experiments. Mortality was low throughout the first experiment for both mussels and clams, but a significant increase, which was sensibly higher in clams, was observed at the end of the experiment (6 months). Significant decreases in the live weight (-26%) and, surprisingly, in the shell length (-5%) were observed in treated clams, but not in mussels. In the controls of both species, no shell damage was ever recorded; in the treated mussels and clams, damage proceeded via different modes and to different extents. The severity of shell injuries was maximal in the mussels after just 3 months of exposure to a reduced pH, whereas it progressively increased in clams until the end of the experiment. In shells of both species, the damaged area increased throughout the experiment, peaking at 35% in mussels and 11% in clams. The shell thickness of the treated and control animals significantly decreased after 3 months in clams and after 6 months in mussels. In the second experiment (3 months), only juvenile mussels were exposed to a reduced pH. After 3 months, the mussels at a natural pH level or pH 7.4 did not differ in their survival, shell length or live weight. Conversely, shell damage was clearly visible in the treated mussels from the 1st month onward. Monitoring the chemistry of seawater carbonates always showed aragonite undersaturation at 7.4 pH, whereas calcite undersaturation occurred in only 37% of the measurements. The present study highlighted the contrasting effects of acidification in two bivalve species living in the same region, although not exactly in the same habitat.

Preventing bacterial colonization using colloidal crystals

A monolayer of polystyrene particles inhibits colony formation of Pseudomonas aeruginosa, and causes adsorption in particular locations.

Lotus leaf-like dual-scale silver film applied as a superhydrophobic and self-cleaning substrate

The structure and the mechanism of the lotus leaf-like and petal-like surfaces.

Bivalve mollusks in metal pollution studies: from bioaccumulation to biomonitoring

Contemporary environmental challenges have emphasized the need to critically assess the use of bivalve mollusks in chemical monitoring (identification and quantification of pollutants) and biomonitoring (estimation of environmental quality). Many authors, however, have considered these approaches within a single context, i.e., as a means of chemical (e.g. metal) monitoring. Bivalves are able to accumulate substantial amounts of metals from ambient water, but evidence for the drastic effects of accumulated metals (e.g. as a TBT-induced shell deformation and imposex) on the health of bivalves has not been documented. Metal bioaccumulation is a key tool in biomonitoring; bioavailability, bioaccumulation, and toxicity of various metals in relation to bivalves are described in some detail including the development of biodynamic metal bioaccumulation model. Measuring metal in the whole-body or the tissue of bivalves themselves does not accurately represent true contamination levels in the environment; these data are critical for our understanding of contaminant trends at sampling sites. Only rarely has metal bioaccumulation been considered in combination with data on metal concentrations in parts of the ecosystem, observation of biomarkers and environmental parameters. Sclerochemistry is in its infancy and cannot be reliably used to provide insights into the pollution history recorded in shells. Alteration processes and mineral crystallization on the inner shell surface are presented here as a perspective tool for environmental studies.

Microtopography of the eye surface of the crab Carcinus maenas: an atomic force microscope study suggesting a possible antifouling potential

Marine biofouling causes problems for technologies based on the sea, including ships, power plants and marine sensors. Several antifouling techniques have been applied to marine sensors, but most of these methodologies are environmentally unfriendly or ineffective. Bioinspiration, seeking guidance from natural solutions, is a promising approach to antifouling. Here, the eye of the green crab Carcinus maenas was regarded as a marine sensor model and its surface characterized by means of atomic force microscopy. Engineered surface micro- and nanotopography is a new mechanism found to limit biofouling, promising an effective solution with much reduced environmental impact. Besides giving a new insight into the morphology of C. maenas eye and its characterization, our study indicates that the eye surface probably has antifouling/fouling-release potential. Furthermore, the topographical features of the surface may influence the wettability properties of the structure and its interaction with organic molecules. Results indicate that the eye surface micro- and nanotopography may lead to bioinspired solutions to antifouling protection.

Complementary effects of nanosilver and superhydrophobic coatings on the prevention of marine bacterial adhesion

A superhydrophobic coating composed of silver nanoparticles enclosed in multilayered polyelectrolyte films was deposited onto copper with the aim of preventing bacterial adhesion. Observations from scanning electron microscopy (SEM) and atomic force microscopy (AFM) showed that the amplified exponential growth of the multilayers could induce distinguishable, hierarchical micro- and nanostructures simultaneously. This growth caused the surface roughness to amplify in a lotus-leaf-like manner. UV/visible spectroscopy, X-ray photoelectron spectroscopy (XPS), and transmission electron microscopy (TEM) confirmed the formation of well-dispersed Ag(0) nanoparticles (with sizes from 4-6 nm) in the films. SEM and fluorescence microscope images of the exposed surfaces revealed that the pattern of adhesion and the density of bacterial cells differed depending on the surface energy and the number of Ag(+) ions released during the various immersion time periods. The complementary effects of nanosilver and superhydrophobic coatings can help to effectively reduce bacterial adhesion and the formation of biofilms.