Antimicrobial nanocoatings
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Aarthi Janakiraman, Research Manager, Chemicals and Advanced Materials at TechVision, Frost & Sullivan, argues that antimicrobial nanocoatings will gain prominence due to their functional and preventative benefits

Nanotechnology is steadily gaining influence in various research fields. It has become essential for the development of many products across industries and even geographies. Antimicrobial coatings are one such area where nanotechnology has made significant in-roads in both R&D and commercialisation. Nano-based antimicrobial coatings in various forms are increasingly used to impart a range of functionalities, be it broad-spectrum protection against various microbes or narrow-spectrum protection against a specific sector sub-sect of microbes.

We are living in the COVID era, and it has to be accepted that the pandemic has resulted in hastening the time to market and even revival of many R&D efforts across all industries. Technologies that can detect, protect and mitigate the incidence of COVID-19 are gaining significance, especially those that can be deployed on a broad scale for preventive purposes. One of the technologies that has gained more significance in the current situation is antimicrobial technology, known for its both preventive and functional attributes.

Antimicrobial technologies consist of various sub-technologies, the foremost being antimicrobial coatings. It is known that a wide range of antimicrobial agents are used to manufacture these coatings at various scales; some of the commonly used antimicrobial agents include metal ions, polymers, antimicrobial peptides (AMP), quaternary ammonium compounds, naturally derived antimicrobials and so on.

With countries working towards easing restrictions posed because of the COVID-19 pandemic, it is evident that antimicrobial coatings are experiencing rising demand. The expectations of better functionality, processing capabilities and durability are also set to increase. This has, in turn, hastened the research efforts by various stakeholders to commercialise broad-spectrum antimicrobial coatings with better performance characteristics and applicability. Nano-base coatings are not new in the antimicrobial coatings segement, especially for R&D efforts. Various research studies have already established that nanotechnology (be it nanoadditives or nanoencapsulation or nanomanufacturing) can offer better processing, performance and functional attributes than its conventional counterparts and also help in improving the end-use properties.

Next-generation of antimicrobial coatings set to become mainstream

Antimicrobial nanocoatings are capable of killing both gram-positive and negative bacteria. They can bind themselves to bacterial cell membranes and interfere with the bacterial metabolism to create pathogen-free surfaces. Studies have also proven its effectiveness against certain viruses, fungi and specific microbes such as methicillin-resistant Staphylococcus aureus (MRSA), vancomycin-resistant enterococci (VRE), among others dependent on the type of antimicrobial used.

These coatings can also be applied to various substrates, including plastics (ethylene tetrafluoroethylene, polycarbonate, or polycarbonate, etc.), glass (soda-lime glass, borosilicate and quartz), and various metals & alloys (aluminium, brass, copper, and steel). This, along with its excellent barrier properties makes them attractive for providing long-term sustained protection, especially in public areas where footfall is highest.

Various materials are being investigated for the R&D and manufacture of antimicrobial nanocoatings. Nano- metal ions such as nano-silver and -gold in various forms have already been adopted at a commercial scale. Apart from these, other materials are in focus, the key ones are as follows: metal halides, organic nanoparticles and others; each having its own benefits and challenges.

One of the widely researched materials is the metal halides. For instance, Copper(I) iodide (CuI)- based antimicrobial nanocoatings can provide broad-spectrum protection against microbes and is easy to incorporate into various substrates. While the use of nanomaterials is not uncommon, certain materials can be classified as emerging or even futuristic to potentially replace conventional and even the currently used nanomaterials. These include:

Nanocomposites including titania-) or zinc oxide- hydroxyapatite (HAp) nanocoating can inhibit pathogenic bacterial growth and biofilm formation, especially on implants. Additionally, they can be triggered to form HAp under certain conditions, making them attractive for both dental and orthopaedic use. However, a key disadvantage that current research is trying to overcome is its tendency to crack when a high vapour pressure solvent, such as ethanol is used.

Metal Nanohybrids (usually titanium dioxide-silver or Zinc doped copper oxide nanomaterials) have an added advantage compared to single metal ions as they can be triggered to impart added functionalities. For instance, together they can exhibit both antiviral and antibacterial properties under external stimuli (usually light). They can also offer anti-dirt or self-cleaning properties. Its use can result in a wide range of application prospects in both industrial and commercial setups. Moreover, nanohybrids can help in developing stable and homogeneous coatings with minimal leaching (such as when zinc doped copper oxide nanomaterial is used for manufacturing nanocoatings) and for effective protection against drug-resistant microbes (graphene- metal nanohybrids).

Metal Nanopillars (Zinc oxide, Silver dioxide, Titanium dioxide, and silicon dioxide) is as an interesting area of research within the field of nanoparticles for various coating formulations. These structures usually have a diameter of 10 nm and can strengthen their interaction or adhesion to the bacterial cell wall to provide long- term protection from germs (as in the case of zinc oxide nanopillars). Whilst the manufacture of nanopillars is still at a very nascent stage and can be considered time-consuming, improvements in process time and standardisation can result in nanopillars as a potential material for commercial use.

The final word on antimicrobial nanocoatings

One of the key advantages of antimicrobial nanocoatings is that they can be used in various forms depending on end-use applications; some of the top-priority ones being coatings (industrial, personal and commercial use), paints, and even healthcare.

The next two to three years could witness a spike in commercial interest and R&D activities; however, it is also evident that despite its various advantages, its adoption on a large scale is still at emerging stages. Various factors such as cost, time to market, need to prove long-term efficacy are foremost amongst them. Adherence to regulatory guidelines, proven studies related to environmental non-toxicology can improve commercialisation prospects. Wide application prospects and its ability to impart broad-spectrum protection, improved functionality and sustained R&D efforts to prove its efficacy can help in the commercialisation of a wide range of antimicrobial nanocoatings developed using various functional materials and/or additives.

 

Acknowledgement
I thank the TechVision Group at Frost & Sullivan who helped in providing insights for this article.

References
1. M. Dolores Fernández et al, Graphene Oxide–Silver Nanoparticle Nanohybrids: Synthesis, Characterization, and Antimicrobial Properties, Nanomaterials, 2020, 10(2), 376.
2. Jenkins, J., Mantell, J., Neal, C. et al. Antibacterial effects of nanopillar surfaces are mediated by cell impedance, penetration and induction of oxidative stress. Nat Commun 11, 1626 (2020).
3. Briscoe et al, Natural and bioinspired nanostructured bactericidal surfaces, Advances in Colloid and Interface Science, Volume 248, October 2017, Pages 85-104.

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Research Manager, Chemicals and Advanced Materials
TechVision, Frost & Sullivan
Phone: +91 44 6681 4102
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