Antimicrobial surfaces with self-cleaning properties functionalized by photocatalytic ZnO electrosprayed coatings

Breathable Films with Self-Cleaning and Antibacterial Surfaces Based on TiO2-Functionalized PET Membranes

A promising approach that uses the sol-gel method to manufacture new breathable active films with self-cleaning and antibacterial surfaces is based on the PET membranes obtained via ion track technology with a pore density of 10-7 cm-2 and a pore diameter of about 500 ± 15 nm, coated with a layer of TiO2 anatase, with a thickness of up to 80 nm. The formation of the photocatalytically active TiO2 anatase phase was confirmed using Raman analysis. Coating the PET membrane with a layer of TiO2 increased the hydrophobicity of the system (CA increased from 64.2 to 92.4, and the antibacterial activity was evaluated using Escherichia coli and Staphylococcus aureus bacteria with the logarithmic reduction factors of 3.34 and 4.24, respectively).

Functional Fiber Membranes with Antibacterial Properties for Face Masks

Reusable face masks are an important alternative for minimizing costs of disposable and surgical face masks during pandemics. Often complementary to washing, a prolonged lifetime of face masks relies on the incorporation of self-cleaning materials. The development of self-cleaning face mask materials requires the presence of a durable catalyst to deactivate contaminants and microbes after long-term use without reducing filtration efficiency. Herein, we generate self-cleaning fibers by functionalizing silicone-based (polydimethylsiloxane, PDMS) fibrous membranes with a photocatalyst. Coaxial electrospinning is performed to fabricate fibers with a non-crosslinked silicone core within a supporting shell scaffold, followed by thermal crosslinking and removal of the water-soluble shell. Photocatalytic zinc oxide nanoparticles (ZnO NPs) are immobilized on the PDMS fibers by colloid-electrospinning or post-functionalization procedures. The fibers functionalized with ZnO NPs can degrade a photo-sensitive dye and display antibacterial properties against Gram-positive and Gram-negative bacteria (Escherichia coli and Staphylococcus aureus) due to the generation of reactive oxygen species upon irradiation with UV light. Furthermore, a single layer of functionalized fibrous membrane shows an air permeability in the range of 80-180 L/m2s and 65% filtration efficiency against fine particulate matter with a diameter less than 1.0 µm (PM1.0).

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Supplementary Information

The online version contains supplementary material available at 10.1007/s42765-023-00291-7.

Nanoengineered particles for sustainable crop production: potentials and challenges

Nanoengineered nanoparticles have a significant impact on the morphological, physiology, biochemical, cytogenetic, and reproductive yields of agricultural crops. Metal and metal oxide nanoparticles like Ag, Au, Cu, Zn, Ti, Mg, Mn, Fe, Mo, etc. and ZnO, TiO2, CuO, SiO2, MgO, MnO, Fe2O3 or Fe3O4, etc. that found entry into agricultural land, alter the morphological, biochemical and physiological system of crop plants. And the impacts on these parameters vary based on the type of crop and nanoparticles, doses of nanoparticles and its exposure situation or duration, etc. These nanoparticles have application in agriculture as nanofertilizers, nanopesticides, nanoremediator, nanobiosensor, nanoformulation, phytostress-mediator, etc. The challenges of engineered metal and metal oxide nanoparticles pertaining to soil pollution, phytotoxicity, and safety issue for food chains (human and animal safety) need to be understood in detail. This review provides a general overview of the applications of nanoparticles, their potentials and challenges in agriculture for sustainable crop production.

Photoreactive Coating Material as an Effective and Durable Antimicrobial Composite in Reducing Bacterial Load on Surfaces in Livestock

Titanium dioxide (TiO2) is a well-known photocatalytic compound that can be used to effectively reduce the presence of pathogens in human and animal hospitals via ROS release. The aim of this study was to investigate the efficacy of a polymer-based composite layer containing TiO2 and zinc oxide (ZnO) against Escherichia coli (E. coli) of animal origin. We showed that the photocatalyst coating caused a significant (p < 0.001) reduction in pathogen numbers compared to the control with an average reduction of 94% over 30 min. We used six light sources of different wattages (4 W, 7 W, 9 W, 12 W, 18 W, 36 W) at six distances (35 cm, 100 cm, 150 cm, 200 cm, 250 cm, 300 cm). Samples (n = 2160) were taken in the 36 settings and showed no significant difference in efficacy between light intensity and distance. We also investigated the influence of organic contaminant that resulted in lower activity as well as the effect of a water jet and a high-pressure device on the antibacterial activity. We found that the latter completely removed the coating from the surface, which significantly (p < 0.0001) reduced its antibacterial potential. As a conclusion, light intensity and distance does not reduce the efficacy of the polymer, but the presence of organic contaminants does.

Hydrophilic ZnO thin films doped with ytterbium and europium oxide

Hydrophilic photocatalytically active ZnO and ZnO thin films doped with Yb₂O₃ and Eu₂O₃ (rare earth metal oxide, REM) with optical transmittance exceeding 76% in the visible light range (λ = 550 nm) were prepared by a combination of sol-gel technique, spin-coating and high temperature thermal treatment at 500 and 600 °C. The thin films were tested using advanced research methods, i.e.: morphology and topography and fractures along with approximate thickness values were investigated on scanning electron microscope (SEM), chemical composition was determined using X-ray Energy Dispersive Spectroscopy (X-ray Energy Spectroscopy), topography and roughness were measured on atomic force microscope (AFM), water contact angle values were determined by sitting water droplet method, optical properties of the fabricated materials were investigated using UV/Vis spectrophotometer. The decolorization efficiency of rhodamine B in aqueous solution was analyzed over a period of 190 min, obtaining degradation rates of: 54.7% and 43.1%, for ZnO and ZnO coatings doped with ytterbium oxide and europium oxide, respectively. The roughness of thin hybrid coatings did not exceed 50 nm, ensuring effective absorption of electromagnetic radiation by the layers. The methodology presented by the authors for the fabrication of thin hybrid films characterized by the key properties of self-cleaning coatings can be successfully applied to coatings of photovoltaic panels and architectural glass structures.

Recent Advances in Metal-Based Antimicrobial Coatings for High-Touch Surfaces

International interest in metal-based antimicrobial coatings to control the spread of bacteria, fungi, and viruses via high contact human touch surfaces are growing at an exponential rate. This interest recently reached an all-time high with the outbreak of the deadly COVID-19 disease, which has already claimed the lives of more than 5 million people worldwide. This global pandemic has highlighted the major role that antimicrobial coatings can play in controlling the spread of deadly viruses such as SARS-CoV-2 and scientists and engineers are now working harder than ever to develop the next generation of antimicrobial materials. This article begins with a review of three discrete microorganism-killing phenomena of contact-killing surfaces, nanoprotrusions, and superhydrophobic surfaces. The antimicrobial properties of metals such as copper (Cu), silver (Ag), and zinc (Zn) are reviewed along with the effects of combining them with titanium dioxide (TiO2) to create a binary or ternary contact-killing surface coatings. The self-cleaning and bacterial resistance of purely structural superhydrophobic surfaces and the potential of physical surface nanoprotrusions to damage microbial cells are then considered. The article then gives a detailed discussion on recent advances in attempting to combine these individual phenomena to create super-antimicrobial metal-based coatings with binary or ternary killing potential against a broad range of microorganisms, including SARS-CoV-2, for high-touch surface applications such as hand rails, door plates, and water fittings on public transport and in healthcare, care home and leisure settings as well as personal protective equipment commonly used in hospitals and in the current COVID-19 pandemic.

Nanocoating Is a New Way for Biofouling Prevention

Biofouling is a major concern to the maritime industry. Biofouling increases fuel consumption, accelerates corrosion, clogs membranes and pipes, and reduces the buoyancy of marine installations, such as ships, platforms, and nets. While traditionally marine installations are protected by toxic biocidal coatings, due to recent environmental concerns and legislation, novel nanomaterial-based anti-fouling coatings are being developed. Hybrid nanocomposites of organic-inorganic materials give a possibility to combine the characteristics of both groups of material generating opportunities to prevent biofouling. The development of bio-inspired surface designs, progress in polymer science and advances in nanotechnology is significantly contributing to the development of eco-friendly marine coatings containing photocatalytic nanomaterials. The review mainly discusses photocatalysis, antifouling activity, and formulation of coatings using metal and metal oxide nanomaterials (nanoparticles, nanowires, nanorods). Additionally, applications of nanocomposite coatings for inhibition of micro- and macro-fouling in marine environments are reviewed.

Antimicrobial coatings for environmental surfaces in hospitals: a potential new pillar for prevention strategies in hygiene

Recent reports provide evidence that contaminated healthcare environments represent major sources for the acquisition and transmission of pathogens. Antimicrobial coatings (AMC) may permanently and autonomously reduce the contamination of such environmental surfaces complementing standard hygiene procedures. This review provides an overview of the current status of AMC and the demands to enable a rational application of AMC in health care settings. Firstly, a suitable laboratory test norm is required that adequately quantifies the efficacy of AMC. In particular, the frequently used wet testing (e.g. ISO 22196) must be replaced by testing under realistic, dry surface conditions. Secondly, field studies should be mandatory to provide evidence for antimicrobial efficacy under real-life conditions. The antimicrobial efficacy should be correlated to the rate of nosocomial transmission at least. Thirdly, the respective AMC technology should not add additional bacterial resistance development induced by the biocidal agents and co- or cross-resistance with antibiotic substances. Lastly, the biocidal substances used in AMC should be safe for humans and the environment. These measures should help to achieve a broader acceptance for AMC in healthcare settings and beyond. Technologies like the photodynamic approach already fulfil most of these AMC requirements.

Recent breakthroughs of antibacterial and antiviral protective polymeric materials during COVID-19 pandemic and after pandemic: Coating, packaging, and textile applications

The global epidemic owing to COVID-19 has generated awareness to ensuring best practices for avoiding the microorganism spread. Indeed, because of the increase in infections caused by bacteria and viruses such as SARS-CoV-2, the global demand for antimicrobial materials is growing. New technologies by using polymeric systems are of great interest. Virus transmission by contaminated surfaces leads to the spread of infectious diseases, so antimicrobial coatings are significant in this regard. Moreover, antimicrobial food packaging is beneficial to prevent the spread of microorganisms during food processing and transportation. Furthermore, antimicrobial textiles show an effective role. We aim to provide a review of prepared antimicrobial polymeric materials for use in coating, food packaging, and textile during the COVID-19 pandemic and after pandemic.

Biocide mechanism of highly efficient and stable antimicrobial surfaces based on zinc oxide-reduced graphene oxide photocatalytic coatings

Highly efficient photoactive antimicrobial coatings were obtained using zinc oxide-reduced graphene oxide nanocomposites (ZnO-rGO). Their remarkable antibacterial activity and high stability demonstrated their potential use for photoactive biocide surfaces. The ZnO-rGO nanocomposites were prepared by the sol-gel technique to create photocatalytic surfaces by spin-coating. The coatings were deeply characterised and several tests were performed to assess the antibacterial mechanisms. rGO was homogeneously distributed as thin sheets decorated with ZnO nanoparticles. The surface roughness and the hydrophobicity increased with the incorporation of graphene. The ZnO-rGO coatings exhibited high activity against the Gram-positive bacterium Staphylococcus aureus. The 1 wt% rGO coated surfaces showed the highest antibacterial effect in only a few minutes of illumination with up to 5-log reduction in colony forming units, which remained essentially free of bacterial colonization and biofilm formation. We demonstrated that these coatings impaired the bacterial cells due to cell membrane damage and intracellular oxidative stress produced by the photogenerated reactive-oxygen species (ROS). The enhancement of the ZnO photocatalytic performance upon rGO incorporation is due to the increased detected generation of hydroxyl radicals, attributed to the reduction of electron-hole pair recombination. This intimate contact between both components also conveyed stability against zinc leaching and improved the coating adhesion.

Bioaerosol emissions from activated sludge basins: Characterization, release, and attenuation

This article presents a critical review of the peer-reviewed literature related to bioaerosol generation from activated sludge basins. Characterization techniques include a variety of culture- and nonculture-based techniques, each with unique features. Bioaerosols contain a variety of clinical pathogens including Staphylococcus saprophyticus, Clostridium perfringens, and Salmonella enteritidis; exposure to these microorganisms increases human health risks. Release mechanisms involve splashing and bubble burst dynamics. Larger bubbles emit more aerosol particles than smaller ones. Attenuation strategies include covering sources with lids, adjusting the method and intensity of aeration, and using free-floating carrier media. Future studies should combine culture and non-culture based methods, and expand chemical databases and spectral libraries in order to realize the full power of real-time online monitoring.

Thermal-Sprayed Photocatalytic Coatings for Biocidal Applications: A Review

There have been ever-growing demands for disinfection of water and air in recent years. Efficient, eco-friendly, and cost-effective methods of disinfection for pathogens are vital to the health of human beings. The photocatalysis route has attracted worldwide attention due to its highly efficient oxidative capabilities and sustainable recycling, which can be used to realize the disinfection purposes without secondary pollution. Though many studies have comprehensively reviewed the work about photocatalytic disinfection, including design and fabrication of photocatalytic coatings, inactivation mechanisms, or practical applications, systematic reviews about the disinfection photocatalysis coatings from fabrication to effort for practical use are still rare. Among different ways of fabricating photocatalytic materials, thermal spray is a versatile surface coating technique and competitive in constructing large-scale functional coatings, which is a most promising way for the future environmental purification, biomedical and life health applications. In this review, we briefly introduced various photocatalytic materials and corresponding inactivation mechanisms for virus, bacteria and fungus. We summarized the thermal-sprayed photocatalysts and their antimicrobial performances. Finally, we discussed the future perspectives of the photocatalytic disinfection coatings for potential applications. This review would shed light on the development and implementation of sustainable disinfection strategies that is applicable for extensive use for controlling pathogens in the near future.

Highly Dispersed Nanocomposite of AgBr in g-C3N4 Matrix Exhibiting Efficient Antibacterial Effect on Drought-Resistant Pseudomonas putida under Dark and Light Conditions

Synthesis of nanocomposites possessing intimately mixed components is highly challenging to bring out the best possible properties of the materials. The challenge is mainly due to the difficulties associated with controlling the phase segregation of individual components as a result of high interfacial tension between them and cohesive forces within each component during the synthesis. Here, we show a single-step synthesis of representative nanocomposites of g-C₃N₄/AgBr through a rationally designed approach, wherein melamine, the precursor of g-C₃N₄, has been intimately mixed with the AgBr precursor, silver-tetraoctylammonium bromide. Subsequent calcination of the obtained solid at 500 °C has resulted in the formation of highly dispersed g-C₃N₄/AgBr. The key to such a high dispersion lies in the surfactant-based AgBr precursor that minimized the interfacial tension during the process. The AgBr content has been varied between 2 and 20 wt % with respect to the g-C₃N₄ content. The obtained nanocomposites have been thoroughly characterized using XRD, XPS, ED-XRF, FE-SEM, HR-TEM, DRS, TCSPC, and BET surface area techniques. The studies revealed a high dispersion of AgBr in the g-C₃N₄ matrix. The nanocomposites have been found to exhibit remarkable antimicrobial properties over a drought-resistant bacterial strain of Pseudomonas putida under both dark and light conditions compared with similar compositions obtained through other methods reported so far. The present study offers a new approach for synthesizing highly dispersed and efficient nanocomposites.

Loading of Zn/ZnO particles in the precursor feedstock affects the characteristics of liquid plasma sprayed nano-ZnO coatings for photocatalytic applications

It is known that ZnO is an n-type semiconductor with photocatalytic performances under ultraviolet light irradiation. Constructing a superior structure for a modified electron band has been one of the major research goals for photocatalytic ZnO. Here we report a new technical route for making nano-ZnO coatings with a porous topographic morphology. The coatings were fabricated by plasma spraying the mixture of suspension and solution liquid precursors. Pre-loading of ZnO and Zn powders in the precursor was carried out for the purpose of tailoring the structure of the coatings. The coatings in micron thicknesses showed a porous skeleton and a fluffy top layer consisting of ultrafine ZnO grains. Photocatalytic testing by measuring the degradation of methylene blue revealed significantly enhanced activities of the coatings deposited using the ZnO/Zn loaded precursor. The hybrid-structured ZnO coatings exhibited a narrowed band gap and modified oxygen defects as compared to those deposited from the single liquid feedstock. The results shed light on a one-step easy thermal spray fabrication of polytropic nanostructured functional coatings by employing solid powder-loaded liquid as the starting feedstock.

Multipronged Approach to Combat Catheter-Associated Infections and Thrombosis by Combining Nitric Oxide and a Polyzwitterion: a 7 Day In Vivo Study in a Rabbit Model

The development of nonfouling and antimicrobial materials has shown great promise for reducing thrombosis and infection associated with medical devices with aims of improving device safety and decreasing the frequency of antibiotic administration. Here, the design of an antimicrobial, anti-inflammatory, and antithrombotic vascular catheter is assessed in vivo over 7 d in a rabbit model. Antimicrobial and antithrombotic activity is achieved through the integration of a nitric oxide donor, while the nonfouling surface is achieved using a covalently bound phosphorylcholine-based polyzwitterionic copolymer topcoat. The effect of sterilization on the nonfouling nature and nitric oxide release is presented. The catheters reduced viability of Staphylococcus aureus in long-term studies (7 d in a CDC bioreactor) and inflammation in the 7 d rabbit model. Overall, this approach provides a robust method for decreasing thrombosis, inflammation, and infections associated with vascular catheters.

Photo-responsive chitosan/Ag/MoS2 for rapid bacteria-killing

Bacterial infection is a serious problem threatening human health. The chitosan (CS)-modified MoS₂ coating loaded with silver nanoparticles (Ag NPs) was designed on the surface of titanium (Ti) to kill bacteria rapidly and efficiently under 660 nm visible light. Ag/MoS₂ exhibited high photocatalytic activity due to the rapid transfer of photo-inspired electrons from MoS₂ to Ag NPs, resulting in higher yields of radical oxygen species (ROS) to kill bacteria. The covering of CS made the composite coating positively charged to further enhance the antibacterial property of the coating. In addition, CS/Ag/MoS₂-Ti also showed a certain photothermal effect. in vitro results showed that the antibacterial efficiency of the coating on Staphylococcus aureus and Escherichia coli was 98.66% and 99.77% respectively, when the coating was irradiated by 660 nm visible light for 20 min. Cell culture tests showed that CS/Ag/MoS₂-Ti had no adverse effects on cell growth. Hence, this surface system will be a very promising strategy for eliminating bacterial infection on biomedical device and implants safely and effectively within a short time.