Biofilms are the aggregation of micro-organisms, which are composed of extracellular polymeric substance (EPS) and many other biochemical components. Though they might be beneficial to some wastewater and soil treatment processes, they may expose chronic infection and risk to personal hygiene in the industrial as well as the clinical context. Despite having a well-established disinfection and hygiene monitoring program for the prevention of formation and growth, biofilm persistently remains in the medical settings because of its antibiotic resistance to antimicrobial agents and even the immune system. In this paper, the contributing factors of antibiotic resistance and the corresponding mechanisms, including heterogeneity inside biofilms, the roles of the EPS matrix, cell density, and quorum sensing, and cell mutability, are reviewed. Moreover, current clinical practice and strategic applications are also suggested to address the biofilm resistance issues.

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Mechanisms and Control Measures of Mature Biofilm Resistance to Antimicrobial Agents in the Clinical Context.

Nature-inspired interfacial materials with special wettability have received considerable attention owing to their superior properties and promising multifunctional applications. Owing to the unique interfacial phase contacts and liquid–repellent property, the interfacial materials with special wettability provide a great potential for corrosion inhibition and biofouling suppression. Thus, this brief review and perspective study provides an overview about the characteristics, fabrication and recent advances of three types of interfacial materials with special wettability, namely superhydrophobic, superamphiphobic and slippery liquid-infused porous surface (SLIPS) toward anti-corrosion and anti-biofouling applications. The bottlenecks and future research priorities of the functional interfacial materials with special wettability were pointed out to accelerate the comprehensive understanding and the development of this research field.

Superhydrophobic, superamphiphobic and SLIPS materials as anti-corrosion and anti-biofouling barriers

We employ micro-particle image velocimetry ($\mu$-PIV) to investigate laminar micro-flows in hydrophobic microstructured channels, in particular the slip length. These microchannels consist of longitudinal micro-grooves, which can trap air and prompt a shear-free boundary condition and thus slippage enhancement. Our measurements reveal an increase of the slip length when the width of the micro-grooves is enlarged. The result of the slip length is smaller than the analytical prediction by Philip et al. [1] for an infinitely large and textured channel comprised of alternating shear-free and no-slip boundary conditions. The smaller slip length (as compared to the prediction) can be attributed to the confinement of the microchannel and the bending of the meniscus (liquid-gas interface). Our experimental studies suggest that the curvature of the meniscus plays an important role in microflows over hydrophobic micro-ridges.

Quantifying effective slip length over micropatterned hydrophobic surfaces

Research progress of environmentally friendly marine antifouling coatings

Titanium dioxide and other nanomaterials based antimicrobial additives in functional paints and coatings: Review

This paper proposes the preparation and formula analysis of anti-biofouling Titania–polyurea (TiO2–SPUA) spray coating, which uses nano-scale antibacterial and photocatalytic agents, titanium dioxide, to construct regularly hydrophobic surface texture on the polyurea coating system. Through formulating analysis of anti-biofouling performance, it is found the causal factors include antibacterial TiO2, surface wettability and morphology in order of their importance. The most optimized formula group is able to obtain uniform surface textures, high contact angle (91.5°), low surface energy (32.5 mJ/m2), and strong hardness (74 A). Moreover, this newly fabricated coating can effectively prevent Pseudomonas aeruginosa and biofilm from enriching on the surface, and there is no toxins release from the coating itself, which makes it eco-friendly, even after long-time exposure. These studies provide insights to the relative importance of physiochemical properties of Titania–polyurea spray coatings for further use in marine, as well as bio medical engineering.

Preparation and Formula Analysis of Anti-Biofouling Titania–Polyurea Spray Coating with Nano/Micro-Structure

A fluoropolyurethane-encapsulated process was designed to rapidly fabricate low-flow resistance surfaces on the zinc substrate. For the further enhancement of the drag-reduction effect, Cu2+-assisted chemical etching was introduced during the fabrication process, and its surface morphology, wettability, and flow-resistance properties in a microchannel were also studied. It is indicated that the zinc substrate with a micro-nanoscale roughness obtained by Cu2+-assisted nitric acid etching was superhydrophilic. However, after the etched zinc substrate is encapsulated with fluoropolyurethane, the superhydrophobic wettability can be obtained with a contact angle of 154.8° ± 2.5° and a rolling angle of less than 10°. As this newly fabricated surface was placed into a non-standard design microchannel, it was found that with the increase of Reynolds number, the drag-reduction rate of the superhydrophobic surface remained basically unchanged at 4.0% compared with the original zinc substrate. Furthermore, the prepared superhydrophobic surfaces exhibited outstanding reliability in most liquids.

https://www.mdpi.com/2079-6412/10/4/377/pdf

Fabrication of zinc substrate encapsulated by fluoropolyurethane and its drag-reduction enhancement by chemical etching

The recent COVID-19 virus has led to a rising interest in antimicrobial and antiviral coatings for frequently touched surfaces in public and healthcare settings. Such coatings may have the ability to kill a variety of microorganisms and bio-structures and reduce the risk of virus transmission. This paper proposes an extremely rapid method to introduce rare-earth doping nano-ZnO in polyamines for the preparation of the anti-microbial polyurea coatings. The nano-ZnO is prepared by wet chemical method, and the RE-doped nano-ZnO was obtained by mixing nano ZnO and RE-dopants with an appropriate amount of nitric acid. This rapidly fabricated polyurea coating can effectively reduce bacteria from enriching on the surface. Comparing with pure nano-ZnO group, all the polyurea coatings with four different rare-earth elements (La, Ce, Pr and Gd) doped nano-ZnO. The La-doped nano-ZnO formula group indicates the highest bactericidal rate over 85% to Escherichia coli (E. coli) and Pseudomonas aeruginosa (Pseudomonas). Followed by Ce/ZnO, the bactericidal rate may still remain as high as 83% at room temperature after 25-min UV-exposure. It is believed that the RE-doping process may greatly improve the photocatalytic response to UV light as well as environmental temperature due to its thermal catalytic enhancement. Through the surface characterizations and bioassays, the coatings have a durably high bactericidal rate even after repeated usage. As polyurea coating itself has high mechanical strength and adhesive force with most substrate materials without peel-off found, this rapid preparation method will also provide good prospects in practical applications.

Rapid preparation and antimicrobial activity of polyurea coatings with RE-Doped nano-ZnO.

Recent research efforts to combat marine biofouling have focused on foul-release coatings that are not harmful for the marine environment. Inspired by nature, Slippery lubricant infused porous surf...

Laboratory and Field Testing Assessment of Next Generation Biocide-Free, Fouling-Resistant Slippery Coatings

Marine structures often suffer from biofouling, which may lead to macrofouling by marine animals like marine worms and barnacles, weighing down the structures and increasing the drag. This paper analyses the effect of the newly fabricated biological anti-adhesion Titania-Polyurea spray coating, which can effectively reduce biofouling from enriching on the surface. Through the surface characterization, bioassays and micro-channel drag-reduction test, the antibacterial effect caused by the nano-titanium dioxide is systematically studied. Compared to the different weight percentages of nano-TiO₂ in the coating system, the photocatalytic activity, riblet surface structure and hydrophobic wettability are supposed to be the key factors to reduce the flow resistance at a drag reduction rate of 3.0% and further enhance the anti-biofouling performance under dark conditions.

Srikanth Narasimalu

Papers

Preparation and Formula Analysis of Anti-Biofouling Titania–Polyurea Spray Coating with Nano/Micro-Structure

Fabrication of zinc substrate encapsulated by fluoropolyurethane and its drag-reduction enhancement by chemical etching

Rapid preparation and antimicrobial activity of polyurea coatings with RE-Doped nano-ZnO.

Laboratory and Field Testing Assessment of Next Generation Biocide-Free, Fouling-Resistant Slippery Coatings

Effect of Nano-Titanium Dioxide Contained in Titania-Polyurea Coating on Marina Biofouling and Drag Reduction.