Nanocoatings are an example of how the use of nanomaterials can improve or disrupt the existing technology sectors or create new ones. The use of nanocoatings offers significant performance advantages over traditional coatings, as well as being more cost-effective in the medium-to long-term. Price in relation to traditional coatings is a significant hindrance to widespread uptake and has restricted application in markets requiring both high volume and low price. However, the economic damage caused by the Covid-19 pandemic should render the cost issue irrelevant if public health authorities wish to fully mitigate future public health emergencies.
Antimicrobial
The development of anti-microbial agents with low toxicity and the ability to inhibit microbial contamination is a key issue in the development of new coatings for healthcare, food and drink packaging, and food and pharmaceutical production.
New legislation and the growing microbial resistance against metal ions, anti-biotics and the development of resistant strains have resulted in coating manufacturers seeking alternatives to traditional anti-microbial coatings.
Anti-microbial agents kill bacteria or inhibit their growth by:
- Cell wall damage.
- Inhibition of cell wall synthesis.
- Alteration of cell wall permeability.
- Inhibition of the synthesis of proteins and nucleic acids
- Inhibition of enzyme action.
The classical biocides function in coatings is to either inhibit the growth of bacteria (biostatic) or by kill them (biocidal). This is achieved by incorporating an antimicrobial agent in a coating system, such as nanosilver or an organic biocide. A wide variety of organic or inorganic biocides are available commercially and these demonstrate a wide variety of biocidal and biostatic mechanisms. Antimicrobial agents commonly used in coatings include:
- Metals and metal oxides: Ag, Cu, ZnO.
- Organic salts, such as quaternary ammonium salts-CTAB, CTAC.
- Biocides: organic macromolecule, Chlorides, Bromides etc.
- Natural substances (e.g. chitosan, Tea Tree Oil).
- Photocatalytic coating-anatase TiO2.
New legislation and the growing microbial resistance against metal ions, antibiotics and the development of resistant strains have resulted in coating manufacturers seeking alternatives to traditional antimicrobial coatings. The development of antimicrobial agents with low toxicity and ability to inhibit microbial contamination is a key issue in the development of new coatings for healthcare, packaging and food and pharmaceutical production. The accumulation of bacteria and or other micro-organisms such as fungi, moulds and algae on surfaces is a significant threat to the durability of materials as well as to human and animal health. This problem is widespread on medical devices, healthcare environments, ship- hulls, and any moist environments in households, e.g., showers, bathrooms, and kitchens. In the last few years, the market for antimicrobial textiles has witnessed substantial growth, fuelled by the increased need of consumers for fresh, clean and hygienic clothing. Clothing and textile materials provide susceptible environments for microbial growth, especially under moisture and temperature conditions found in hospitals. Micro organisms can survive on textiles in hospital environments for more than 90 days, contributing to the occurrence of hospital acquired infections.
Nanoparticles that display anti-microbial action include:
- Zinc Oxide nanoparticles.
- Titanium Dioxide nanoparticles.
- Silicon Dioxide nanoparticles.
- Nanosilver.
- Chitosan.
- Copper oxide nanoparticles.
- Nanocellulose.
Nanoparticles are dispersed at the surface and also throughout the coating. Additionally, a higher concentration of anti-microbial particles can be created at the surface. Anti-microbial properties on the surface coating are permanent and remain effective even if the coating is cleaned. Low friction coating properties are also unaffected by the anti-microbial nanoparticles.
Nanocoatings provide a tenacious bonding to surfaces-they do not require an intermediate layer and can uniformly treat all exposed surfaces, without altering the device’s original mechanical or physical properties. Nanoparticles are stabilized with additives and integrated homogeneously into the polymer matrix. Anti-microbial activity does not decrease with time because the solid nanoparticles are not volatile, like many commonly used biocide additives.
Germs, bacteria or fungal spores brought into contact with surfaces coated with nanoparticles, are very quickly eliminated. As the particles interfere with various stages of cell metabolism, it can destroy a wide range of germs and make it difficult for microbes to develop resistance.
Their use allows for improvement in the level of hygiene in medical and nursing facilities of all kinds, and also protection against the formation of mould and mildew in bathrooms, toilets, wash areas and kitchens and food processing facilities.
Nanocoatings provide long lasting anti-microbial effect, constant release of the active substances, effectiveness against bacteria and other micro-organisms, no chemical impurities, are easily processed, result in no changes to the characteristics of the equipped material, and no later discolouration of the equipped material.
Anti-viral nanocoatings
Viruses constitute a group of heterogeneous and much simpler organisms. They range in size from 100-300nm, much smaller than bacteria. Viruses are unique in that they have no independent metabolic activities and have to rely solely on infection living hosts to reproduce themselves. Unlike all other life, viruses may contain either DNA or RNA as genetic materials, but not both.
The nucleic materials are surrounded by a protein coat to protect them from harmful agents in the environment. The protein coat also provides the specific binding site necessary for the attachment of virus to its host. Some viruses also contain an outer envelope made up of lipids , polysaccharides , and protein molecules. The lipids and polysaccharides are of host cell organ , and their presence allows a virus to fuse with a host cell and thus gain entry.
A virus not having the outer envelope infects a cell in quit a different manner. Infection is initiated by the attachment of a specialized site on the surface of the protein coat of the virus onto a specific receptor site on the surface of the host cell.
Once this binding is complete viruses can release genetic materials into the host cell and take advantage of the machinery of the host cell to reproduce and assemble themselves. These newly produced viruses are now ready to infect other cells .
Therefore, one of the key processes to disable viruses is through the control of their surface structure, especially their binding sites, so they can no longer recognize the receptor site on the host cells. As many types of nanocoatings attack most effectively on the virus’s surface, they represent an excellent viable technology to destroy the viruses surface structure. Functionalized nanoparticles can affect the viruses due to chemical interactions between the molecules-functionalizers and molecules-receptors at the virus surface.
Nanoparticles that display anti-viral action include:
- Nanosilver (NanoAg).
- NanoGold (NanoAu).
- Nanoparticle titanium dioxide (Nano-TiO2).
- Nano Copper(II) chloride (NanoCuCl2).
- Nano Cerium Oxide (NanoCeO2).
- NanoSilica (Nano-SiO2).
- Graphene oxide.
- Nano Zinc Oxide (NanoZnO).
- Carbon nanotubes.
- Fullerenes.
- Chitosan nanoparticles.
Nanoparticles are effective against different viruses:
- Influenza virus H3N2 and H1N1.
- Hepatitis B virus.
- Herpes simplex virus.
- HIV-1.
- Dengue virus type-2.
- Foot-and-Mouth disease virus.
- Vesicular stomatitis virus.
Studies demonstrate that nanoparticles are adsorbed on the virus surface, which leads to local transformations of the surface, such as agglutination of glycoproteins, thus preventing virus penetration into the cell.
Ag nanoparticles demonstrate better antiviral action as compared to Ag ions due to the nanoparticle adsorption on the virus surface.
The Prague Public Transit Company (DPP) is testing two different disinfectants based on nanopolymers that can eliminate bacteria, viruses, yeasts, molds and other microorganisms with a declared effect of up to 21 days.
Two trams and one bus will be used to verify their effect for 14 days in normal operation in Prague public transport. Both products use have health certificates from the National Institute of Public Health and meet not only the relevant Czech national but also European standards.
Table 1: Nanomaterials utilized in antimicrobial and antiviral nanocoatings coatings-benefits and applications.
| Nanomaterials | Properties | Applications |
| Nanosilver | • Low toxicity of silver on human cells, long biocide action, high thermal ability and low volatility. • Broad spectrum of biocide activity against 650 bacteria, mushrooms and viruses. • Effective antifungal agent against a broad spectrum of common fungi. • Antiviral agent against HIV-1, hepatitis B virus, respiratory syncytial virus, herpes simplex virus type 1, and monkeypox virus. • Nanosilver particles have higher antiviral activity than silver ions. |
• Medical textiles for maintaining the sterility of equipment and surfaces • Wound dressings. • Construction surfaces • Interiors • Water treatment. • Medical implants. • Medical catheters. • Dental materials. |
| Titanium dioxide nanoparticles | • Very active for microbial destruction, even under limited UV light available in regular fluorescent lights. The bactericidal and fungicidal effects of nano-TiO2 on, for example, Escherichia coli (E. coli), Staphylococcus aureus, and Pseudomonas putida have been widely reported. • Non-toxic. • Anti-fungal. • Deodorizing. |
• Air and water purification. • Hospitals and other bacteria prone environments. • Medical implants • Food processing. • Construction (i.e. concrete blocks, plasters, windows and ceramic tiles). • Textiles. |
| Zinc oxide nanoparticles | • Display high anti-infective activity, improved wound healing, and higher epithelialization rates. • Strong anti-microbial activity against Gram-positive bacteria. • Anti-microbial activity against spores that are resistant to high temperature and high pressure. • Anti-microbial properties are believed to be due to OH radicals, which result from defects in their crystal structure. However, the exact mechanisms of the antibacterial action have not yet been clearly identified. |
• Medical bandages and wound dressings. • Food contact surfaces. • Water treatment. |
| Nanocellulose | • Nanocellulose shows antibacterial activity against both Gram-positive and Gram-negative bacteria. • Cellulose nanofibers in combination with chitosan nanofibers and nanosilver demonstrate dose-dependent antibacterial effects against sensitive bacteria. |
• Wallpaper for hospitals. • Paper wipes. • Impregnated textiles. • Water filters. • Food packaging materials. |
| Copper nanoparticles | • Anti-microbial, anti-biotic and anti-fungal (fungicide). • Surfaces of copper nanoparticles affect/interact directly with the bacterial outer membrane, causing the membrane to rupture and killing bacteria. |
• Medical coatings. • Textiles. |
| Chitosan | • Natural anti-microbial material with high biodegradability and nontoxicity. • Can be used in a variety of forms such as nanofibers, hydrogels, membranes, and multilayer films as well as core-shell particles, depending on the preparation process. |
• Contact lenses • Wound dressings • Packaging materials. |
| Graphene | • Graphene oxide enhances cellular growth of both Gram-positive and Gram-negative bacteria through a mechanism of bacterial attachment, proliferation, and biofilm formation. • Antibacterial activity on Escherichia coli- induced the degradation of the inner and outer cell membranes of Escherichia coli, and reduced their viability. • Graphene oxide is also a potentially effective anti-viral agent and may offer a platform to fight a variety of viral infections (such as the SARS-CoV-2 coronavirus) and possibly in the form of a coating. The potent antiviral activity of both GO and rGO can be attributed to the unique single-layer structure and negative charge. |
• Medical bandages and wound dressings. • Food contact surfaces. • Water treatment. |
Source: Future Markets, Inc.
Companies
Advanced Materials-JTJ s.r.o.
Czech Republic
www.amjtj.com
The photocatalytic air cleaning coatings FN® have been already licensed and distributed in the Czech Republic, Slovakia, Poland, New Zealand, Australia, Canada, Vietnam, Spain, Portugal, Denmark, Sweden, Norway, Island and South Africa. While the largest Czech paint manufacturer Colorlak a.s. supplies exclusively the Czech and Slovak markets, Advanced Materials-JTJ manufactures and distributes the photocatalytic products globally.
Photocatalytic Coatings FN® act as air cleaning systems. The composition is organics, silicate and silicone free, that according to the company are demonstrating 10-100 times higher efficiencies for the pollution removal and bacterial killing than the photocatalytic paints and topcoats that are currently on the market. These suspensions effectively clean industrial and exhaust exhalations, organic contaminants from plastics, allergens and many other substances that are threat to human health and lower the quality of our environment.
GrapheneCA
USA
https://grapheneca.com/
The company is developing a graphene-based coating with anti-bacterial and anti-viral properties. GrapheneCA’s coating is being formulated to be applied in the form of paints and varnishes to walls and surfaces of public settings that are high risk areas for micro-organisms such as bacteria and viruses, including shopping malls, metro stations, airports and event halls. The Company’s formula has been shown in laboratory tests to blocks the metabolism of micro-organisms by restricting cellular respiration and cell division. Furthermore, assessments shown that micro-organisms die when coming into contact with surfaces covered with the coating’s components.
Figure 1: GrapheneCA anti-bacterial and anti-viral coating.
Micro-biological tests on certain components of the formula were conducted in accordance with Japan Industrial Standard (JIS) Z 2801-2000, recognized worldwide as a means of confirming antibacterial effectiveness. Laboratory test data demonstrated that such components in GrapheneCA’s coating provide disinfection of different dangerous gram-positive and gram-negative bacteria, such as staphylococcus golden and E. coli, by 100% or 4 – 6 logarithmic steps. Additionally, laboratory tests suggested that the Company’s formula offers durable activity, enough to provide anti-bacterial protection throughout the entire service life of the coating. GrapheneCA’s formula is chemical-free and has not been shown to adversely affect the environment or human health.
GrapheneCA intends to commence independent testing of the coating’s anti-bacterial and anti-viral properties, and is targeting commercialization of the coating as early as the third quarter of 2020.
Master Dynamic Ltd.
Hong Kong
https://www.master-dynamic.com/
New World Development is investing HK$10 million and working in partnership with Master Dynamic Limited (MD) NanoDiamonds technology to enhance the protective function of mask materials, with the aim to further develop a specialised coating that will kill bacteria and viruses.
Collaborating with Chow Tai Fook (CTF) Jewellery Group, MD has previously successfully developed T MARK, which features a protruded nano-marking technology on diamond tables and antibacterial nano-coating technology on CTF’s gold jewellery and has obtained a number of R&D patents. During the R&D process for this technology, MD discovered that NanoDiamonds coating technology is bacteriostatic with the ability to block off and suppress the growth of bacteria and viruses. The company is exploring ways to apply this specific technology to the non-woven material of surgical masks, which may be used to produce high-performance, breathable and waterproof antibacterial and antiviral masks that can block off, suppress and even kill bacteria and viruses.
A factory with cleanrooms to make surgical masks at ASTM-Level 1 and above will be set up. Each production line can make up to 100,000 masks daily, starting April 2020. The masks produced are for community-based distribution through non-profit organisations to low-income families.
Nanotech Surface
Italy
http://www.nanotechsurface.com/
The company has developed a nanotechnology-based solution using titanium dioxide and silver ions As a key measure taken to stop the spread of the coronavirus in Italy, Milan’s buildings are being disinfected with the coating.
Figure 2: Milan’s buildings are being disinfected with a special nanotechnology-based solution developed using titanium dioxide and silver ions by Nanotech Surface.
According to company’s manager, Alessandro Torretta. “We are here to spray a particular antibacterial substance that makes the surfaces self-sterilizing from six months to two years. It is a nanotechnology and is composed of titanium dioxide and silver ions,” said Torretta.
Nasc Nano Technology Co., Ltd.
Japan
http://medi-coat.com/
The company produce a Medical Nanocoat product that is antibacterial, antifouling and antistatic. MEDICAL NANOCOAT has been confirmed by third-party organization to inactivate influenza viruses as well as viruses and bacteria such as Staphylococcus aureus, Escherichia coli and Legionella. One test conducted at a major international airport in Japan found that MEDICAL NANOCOAT-treated surfaces significantly reduced the presence of bacteria in comparison with non-treated surfaces. The same result was found even after 28 months from initial application.
MEDICAL NANOCOAT not only has antibacterial function, but also has excellent surface hydrophilicity, providing antifouling function making it difficult for dirt to adhere and easy to take off as well as dust repellent antistatic effect.
Figure 3. NascNanoTechnology personnel shown applying MEDICOAT to airport luggage carts.
Further information
The Global Market for Antimicrobial, Antiviral, and Antifungal Nanocoatings 2020
Published March 2020
https://www.futuremarketsinc.com/the-global-market-for-antimicrobial-antiviral-and-antifungal-nanocoatings-2020/
