Research Progress on New Environmentally Friendly Antifouling Coatings in Marine Settings: A Review

Preventing biofouling in microalgal photobioreactors

Photobioreactors (PBRs) are used to grow the light-requiring microalgae in diverse commercial processes. Often, they are operated as continuous culture over months period. However, with time, biofouling layer develops on the inner surfaces of their walls. The fouling layer formation deteriorates the PBR performance as foulants reduce light penetration in it. Light is essential for photosynthetic cultures, and a deterioration in lighting adversely impacts algae growth and biomass productivity. Fouling requires a frequent shutdown to clean the PBR and add to the environmental impact of the operation by generating many wastewaters contaminated with the cleaning chemicals. Antibiofouling coatings could be used to modify the surfaces of existing and future PBRs. Therefore, transparent and non-toxic fouling-release coatings, produced using hydrogel technology, could transform the existing PBRs into efficient and enduring microalgae culture systems, requiring only the application of the coating to the inner walls, without additional investments in new PBRs.

Proof of Concept of Natural and Synthetic Antifouling Agents in Coatings

Marine biofouling, caused by the deposition and accumulation of marine organisms on submerged surfaces, represents a huge concern for the maritime industries and also contributes to environmental pollution and health concerns. The most effective way to prevent this phenomenon is the use of biocide-based coatings which have proven to cause serious damage to marine ecosystems. Several research groups have focused on the search for new environmentally friendly antifoulants, including marine and terrestrial natural products and synthetic analogues. Some of these compounds have been incorporated into marine coatings and display interesting antifouling activities caused by the interference with the biofilm-forming species as well as by the inhibition of the settlement of macroorganisms. This review highlights the proof-of-concept studies of emerging natural or synthetic antifouling compounds in coatings, from lab-made to commercial ones, performed between 2019 and 2023 and their results in the field or in in vivo laboratorial tests.

Innovative Acrylic Resin-Hydrogel Double-Layer Coating: Achieving Dual-Anchoring, Enhanced Adhesion, and Superior Anti-Biofouling Properties for Marine Applications

Traditional anti-corrosion and anti-fouling coatings struggle against the harsh marine environment. Our study tackled this by introducing a novel dual-layer hydrogel (A-H DL) coating system. This system combined a Cu2O-SiO2-acrylic resin primer for anchoring and controlled copper ion release with a dissipative double-network double-anchored hydrogel (DNDAH) boasting superior mechanical strength and anti-biofouling performance. An acrylamide monomer was copolymerized and cross-linked with a coupling agent to form the first irreversible network and first anchoring, providing the DNDAH coating with mechanical strength and structural stability. Alginate gel microspheres (AGMs) grafted with the same coupling agent formed the second reversible network and second anchoring, while coordinating with Cu2+ released from the primer to form a system buffering Cu2+ release, enabling long-term antibacterial protection and self-healing capabilities. FTIR, SEM, TEM, and elemental analyses confirmed the composition, morphology, and copper distribution within the A-H DL coating. A marine simulation experiment demonstrated exceptional stability and anti-fouling efficacy. This unique combination of features makes A-H DL a promising solution for diverse marine applications, from ship hulls to aquaculture equipment.

Silicone-geranium essential oil blend for long-term antifouling coatings

This study explores the potential of geranium essential oil as a natural solution for combating marine biofouling, addressing the environmental concerns associated with commercial antifouling coatings. Compounds with bactericidal activities were identified by 13Carbon nuclear magnetic resonance (13C NMR). Thermogravimetric analysis (TGA) revealed minimal impact on film thermal stability, maintaining suitability for antifouling applications. The addition of essential oil induced changes in the morphology of the film and Fourier transform infrared spectroscopy (FTIR) analysis indicated that oil remained within the film. Optical microscopy showed an increase in coating porosity after immersion in a marine environment. A total of 18 bacterial colonies were isolated, with Psychrobacter adeliensis and Shewanella algidipiscicola being the predominant biofilm-forming species. The geranium essential oil-based coating demonstrated the ability to reduce the formation of Psychrobacter adeliensis biofilms and effectively inhibit macrofouling adhesion for a duration of 11 months.

Ultrasound assisted electrodeposition of photocatalytic antibacterial MoS2-Zn coatings controlled by sodium dodecyl sulfate

Photocatalytic MoS2 with visible light response is considered as a promising bactericidal material owing to its non-toxicity and high antibacterial efficiency. However, photocatalysts always exist as powder, so it is difficult to settle photocatalysts on the metal surface, which limits their application in aqueous environments. To solve this problem, ultrasound and sodium dodecyl sulfate (SDS) were introduced into the co-deposition process of MoS2 and zinc matrix, so that novel MoS2-Zn coatings were obtained. In this process, ultrasound and SDS strongly promoted the dispersion and adsorption of MoS2 on the co-depositing surfaces. Then MoS2 were proved to be composited into the Zn matrix with effective structures, and the addition of SDS effectively increased the loading content of MoS2 in the MoS2-Zn coatings. Besides, the antibacterial performance of the MoS2-Zn coatings was evaluated with three typical fouling bacteria E.coli, S.aureus and B.wiedmannii. The MoS2-Zn coating showed high and broad-spectrum antibacterial properties with over 98 % inhibition rate against these three bacteria. Furthermore, it is proved that the MoS2-Zn coatings generated superoxide (·O2-) and hydroxyl radicals (·OH) under visible light, which played the dominant and subordinate roles in the antibacterial process, respectively. The MoS2-Zn coatings also showed high antibacterial stability after four "light-dark" cycles. According to the results of the attached bacteria, the MoS2-Zn coatings were considered to effectively repel the living pelagic bacteria instead of killing the attached ones, which was highly environmentally friendly. The obtained MoS2-Zn coatings were considered promising in biofilm inhibiting and marine antifouling fields.

Marine antifouling properties of enzyme modified polyaniline coated stainless steel surface

On solid surfaces immersed in a liquid medium, a biofilm layer which is called biofouling formed over time by organic molecules and microorganisms. It is important to produce new eco-friendly ideas can prevent this undesired phenome. In this study, we focused on the antifouling performance of polyaniline (PANI), whose anticorrosive properties have been already known. The main purpose of this study was to immobilize hydrolytic enzymes that could break down biomolecules and microorganisms and how this would contribute to the antifouling performance of the PANI coating. When α-amylase, DNAse, glucose oxidase, α-chymotrypsin, lipase and pectinase enzymes immobilized into PANI that was synthesized in ammonium oxalate (PANIAO) and sodium salicylate (PANISS) electrolytes, α-amylase containing film (PANISS-A) showed the highest performance (76.5% antifouling activity). The surface properties after keeping in the Mediterranean Sea for 12 days were compared by digital photography, Scanning Electron microscope (SEM) and fluorescence microscope images, also with Energy Dispersive X-Ray (EDX) analysis and crystal violet staining. Carbohydrate and protein amounts and CFU (Colony Forming Units) values of biofilms formed on the surface for bare, PANISS and PANISS-A coupons after keeping 12 days in the Mediterranean Sea were determined. Vibrio species (V.harveyi, V.alginolyticus, V.parahaemolyticus) were detected in the biofilms by Matrix- Assisted Laser Desorption/Ionization Time of Flight Mass Spectrometry (MALDI-TOF MS) analysis.

New Insights on Biological Activities, Chemical Compositions, and Classifications of Marine Actinomycetes Antifouling Agents

Biofouling is the assemblage of undesirable biological materials and macro-organisms (barnacles, mussels, etc.) on submerged surfaces, which has unfavorable impacts on the economy and maritime environments. Recently, research efforts have focused on isolating natural, eco-friendly antifouling agents to counteract the toxicities of synthetic antifouling agents. Marine actinomycetes produce a multitude of active metabolites, some of which acquire antifouling properties. These antifouling compounds have chemical structures that fall under the terpenoids, polyketides, furanones, and alkaloids chemical groups. These compounds demonstrate eminent antimicrobial vigor associated with antiquorum sensing and antibiofilm potentialities against both Gram-positive and -negative bacteria. They have also constrained larval settlements and the acetylcholinesterase enzyme, suggesting a strong anti-macrofouling activity. Despite their promising in vitro and in vivo biological activities, scaled-up production of natural antifouling agents retrieved from marine actinomycetes remains inapplicable and challenging. This might be attributed to their relatively low yield, the unreliability of in vitro tests, and the need for optimization before scaled-up manufacturing. This review will focus on some of the most recent marine actinomycete-derived antifouling agents, featuring their biological activities and chemical varieties after providing a quick overview of the disadvantages of fouling and commercially available synthetic antifouling agents. It will also offer different prospects of optimizations and analysis to scale up their industrial manufacturing for potential usage as antifouling coatings and antimicrobial and therapeutic agents.