Silver-Polymethylhydrosiloxane Nanocomposite Coating on Anodized Aluminum with Superhydrophobic and Antibacterial Properties

Wettability and Bactericidal Properties of Bioinspired ZnO Nanopillar Surfaces

Nanomaterials of zinc oxide (ZnO) exhibit antibacterial activities under ambient illumination that result in cell membrane permeability and disorganization, representing an important opportunity for health-related applications. However, the development of antibiofouling surfaces incorporating ZnO nanomaterials has remained limited. In this work, we fabricate superhydrophobic surfaces based on ZnO nanopillars. Water droplets on these superhydrophobic surfaces exhibit small contact angle hysteresis (within 2-3°) and a minimal tilting angle of 1°. Further, falling droplets bounce off when impacting the superhydrophobic ZnO surfaces with a range of Weber numbers (8-46), demonstrating that the surface facilitates a robust Cassie-Baxter wetting state. In addition, the antibiofouling efficacy of the surfaces has been established against model pathogenic Gram-positive bacteria Staphylococcus aureus (S. aureus) and Gram-negative bacteria Escherichia coli (E. coli). No viable colonies of E. coli were recoverable on the superhydrophobic surfaces of ZnO nanopillars incubated with cultured bacterial solutions for 18 h. Further, our tests demonstrate a substantial reduction in the quantity of S. aureus that attached to the superhydrophobic ZnO nanopillars. Thus, the superhydrophobic ZnO surfaces offer a viable design of antibiofouling materials that do not require additional UV illumination or antimicrobial agents.

Water-Repellent Galvanized Steel Surfaces Obtained by Sintering of Zinc Nanopowder

Galvanized steel surfaces are widely used in industry as a solution to prevent corrosion of steel tools that operate in outdoor or corrosive and oxidative environments. These objects are coated with a zinc protective layer deposited by hot dip galvanization. Turning the surface of galvanized steel tools into superhydrophobic may lead to very useful functionalities, although it may be a difficult task, because the preservation of the thin zinc layer is a claim. We propose herein the use of a bottom-up approach based on sandblasting, followed by sintering of zinc nanoparticles on the galvanized steel substrate, which allowed us to produce a zinc-made hierarchical structure required for superhydrophobicity. These samples acquired a double-scale structure that led to superhydrophobicity when they were later hydrophobized with a thin fluoropolymer layer. We found that sandblasting might be useful but not mandatory, unlike the sintering process, which was essential to reach superhydrophobicity. We found that, under certain experimental conditions, the surfaces showed outstanding water-repellent properties. We observed that the sandblasting on galvanized steel caused more damage than the sintering process. Sintering of low-melting-point metal nanoparticles was revealed as a promising strategy to fabricate functional metallic surfaces.

Nature-Inspired Surface Structures Design for Antimicrobial Applications

Surface contamination by microorganisms such as viruses and bacteria may simultaneously aggravate the biofouling of surfaces and infection of wounds and promote cross-species transmission and the rapid evolution of microbes in emerging diseases. In addition, natural surface structures with unique anti-biofouling properties may be used as guide templates for the development of functional antimicrobial surfaces. Further, these structure-related antimicrobial surfaces can be categorized into microbicidal and anti-biofouling surfaces. This review introduces the recent advances in the development of microbicidal and anti-biofouling surfaces inspired by natural structures and discusses the related antimicrobial mechanisms, surface topography design, material application, manufacturing techniques, and antimicrobial efficiencies.

Silver-Polymethylhydrosiloxane-Quaternary Ammonium Coating on Anodized Aluminum with Excellent Antibacterial Property

Multidrug-resistant bacteria are known to survive on high-touch surfaces for days, weeks, and months, contributing to the rise in nosocomial infections. Inducing antibacterial property in such surfaces can presumably reduce the overall microbial burden and subsequent nosocomial infections in hygiene critical environments. In the present study, a one-pot sol-gel process has been deployed to incorporate silver (Ag) and quaternary ammonium salt (QUAT) bactericides in a polymethylhydrosiloxane (PMHS) matrix. The Ag-PMHS-QUAT nanocomposite was coated on anodized aluminum (AAO/Al) by a simple ultrasound-assisted deposition process. The morphological features and chemical composition of the Ag-PMHS-QUAT nanocomposite have been characterized using SEM, XRD spectroscopy, and attenuated total reflection-Fourier transform infrared spectroscopy (ATR-FTIR) to confirm the formation of Ag-QUAT nanocomposites within the polymeric network of PMHS. The Ag-PMHS-QUAT nanocomposite coating on anodized aluminum oxide (AAO/Al) coupon exhibited superior antibacterial property with a 6-log bacterial reduction compared to the 5-log reduction for the commercially available antimicrobial copper coupon.

Innovative Codeposition of a Ag-Al2O3 Layer: An Attractive Combination of High Durability and Lack of Cytotoxicity for Public Space Applications

Today, the use of silver in surfaces for public environments is very frequent, as it ensures high antimicrobial activities, avoiding the continuous disinfection of the surfaces themselves. Similarly, thanks to its interesting combination of technological properties, anodized aluminum is widely employed in the production of components for applications in public spaces. Therefore, this work describes a simple method of the codeposition of silver and anodized aluminum to combine the remarkable properties of Al₂O₃ layers with the antibacterial performances of silver. The effect of silver in modifying the durability features of the anodized aluminum layer was evaluated by means of various accelerated degradation techniques, such as the exposure in a climatic chamber to UV-B radiation or an aggressive atmosphere simulated by the Kesternich test. These analyses showed the good compatibility between Ag and the alumina matrix, whose durability performances were not particularly influenced by silver. Furthermore, the composite layers did not express relevant cytotoxicity activity, as evidenced by Trypan blue flow cytometry analysis and microscopy observations, ensuring the possible use of this material in applications in close contact with humans. This same conclusion was reached by observing an almost negligible ionic release of Ag by the composite layers, even following severe degradation of the alumina matrix due to exposure to a particular acid solution. In conclusion, this work presents an innovative material that can be used in public spaces, thanks to its interesting combination of high durability and low cytotoxicity.

Anodized Aluminum Surface with Topography-Mediated Antibacterial Properties

Topography-mediated antibacterial surfaces that inactivate bacteria by physical contact have gained attention in recent years. Contrary to conventional antibacterial coatings, topography-mediated antibacterial surfaces do not suffer from coating instability and possible toxicity problems. In this study, a one-step hard anodization process has been deployed to fabricate a topography-mediated antibacterial aluminum surface. By optimizing anodization parameters, such as the concentration of the electrolyte, current density, and anodization time, desirable features of micronanoscale morphology were achieved. The optimum conditions of anodized aluminum that provided pores of a diameter of 151 ± 37 nm effectively killed 100% of E. coli bacteria.

Rapid antibacterial activity of anodized aluminum-based materials impregnated with quaternary ammonium compounds for high-touch surfaces to limit transmission of pathogenic bacteria

Infections caused by multidrug-resistant bacteria are a major public health problem. Their transmission is strongly linked to cross contamination via inert surfaces, which can serve as reservoirs for pathogenic microorganisms. To address this problem, antibacterial materials applied to high-touch surfaces have been developed. However, reaching a rapid and lasting effectiveness under real life conditions of use remains challenging. In the present paper, hard-anodized aluminum (AA) materials impregnated with antibacterial agents (quaternary ammonium compounds (QACs) and/or nitrate silver (AgNO₃)) were prepared and characterized. The thickness of the anodized layer was about 50 μm with pore diameter of 70 nm. AA with QACs and/or AgNO₃ had a water contact angle varying between 45 and 70°. The antibacterial activity of the materials was determined under different experimental settings to better mimic their use, and included liquid, humid, and dry conditions. AA-QAC surfaces demonstrated excellent efficiency, killing >99.9% of bacteria in 5 min on a wide range of Gram-positive (Staphylococcus aureus, Clostridioides difficile, vancomycin-resistant Enterococcus faecium) and Gram-negative (streptomycin-resistant Salmonella typhimurium and encapsulated Klebsiella pneumoniae) pathogens. AA-QACs showed a faster antibacterial activity (from 0.25 to 5 min) compared with antibacterial copper used as a reference (from 15 min to more than 1 h). We show that to maintain their high performance, AA-QACs should be used in low humidity environments and should be cleaned with solutions composed of QACs. Altogether, AA-QAC materials constitute promising candidates to prevent the transmission of pathogenic bacteria on high-touch surfaces.

Fluorinated Carbon Nanotube Superamphiphobic Coating for High-Efficiency and Long-Lasting Underwater Antibiofouling Surfaces

Biofilm formation on the surface of materials has brought great troubles to various industries. Designing surfaces with long-lasting antibiofouling properties can help restrain primary bacterial and protein attachment and subsequent biofilm formation for a long time, which is also of great significance for industrial applications. In this work, we successfully prepared fluorinated carbon nanotubes through a one-step fluorination method using fluorosilane and fabricated a superamphiphobic coating using a simple spray method. This coating with ultralow surface free energy and stable micro/nano structures achieved highly efficient and long-term underwater antibiofouling properties. Tea, milk, BSA, and bacterial solution can bounce highly on this surface without wetting the surface in air. The long-term existence of the underwater air-bubble layer on the surface of the superamphiphobic coating was observed. Thus, this surface can effectively resist BSA and bacterial attachment (E. coli), and the efficiency, respectively, reaches 97.5 and 98.2%. Even if it is fully soaked in BSA and BS solution for 120 h, the whole surface is still able to repel water, BSA, and BS solution very well. In addition, the coating possessed excellent wear resistance, the CAs of BSA and BS solution just decreased slightly (higher than 158°), and the sliding angles increased slightly (lower than 4°) after 50 tape abrasion cycles. Therefore, this superamphiphobic coating may have promising applications for marine devices, biomedical materials, protective clothing, and chemical shielding.