Which type of coating?


It should be noted that there are two types of lasting antimicrobial treatment. The first type is permanent: for this, the antimicrobial agent has to be incorporated into the material at the time of manufacturing. Remember those food cutting boards containing the anti-microbial triclosan? Or maybe the plastic hand soap dispensers containing silver nano particles to prevent microbial contamination?


We have seen textiles being treated with antimicrobial permanent treatments, too. They are permanent because the antimicrobial agent does not leach as it’s incorporated into the material. Apparently, they can remain or keep their anti-microbial properties for years, even after disposal, which has a negative environmental impact.


The second type being promoted currently are the semi- permanent or lasting coatings, and that treatment has to be carried out on site. There are a variety of technologies but, basically, there are coatings with antimicrobial properties that will effectively kill microorganisms that come into contact with a surface or limit the adhesion of the microorganisms to the surface. So, by killing or reducing the attachment of microorganisms to a surface, you make it easier to remove them with normal cleaning routines.


In terms of technologies there is the chemical antimicrobial approach: chemicals and metal ions in the solution, made with a binding agent which you then cover the surface with. Some companies have been developing solutions with a more physical approach that prevents the microorganisms from attaching to a surface. Others have explored textured film, inspired by shark’s skin, comprised of a micron scale pattern of spikes, and because of those extremely small peaks or spikes, bacteria cannot form a biofilm. They cannot attach to the surface, making it easier to remove.


The more complex solutions see both methods combined with some companies using this textured film which is itself impregnated with a chemical anti-microbial agent.


How effective are they?


If we look at the spectrum of activity, the claims around killing bacteria, moulds and yeasts are not surprising. A little more surprising are the claims against viruses. As any doctor or medical scientist will tell you, viruses cannot be killed, but let's say the product interacts with viruses and inactivates them.


Looking at the different procedures recommended by the manufacturers on how to apply these coatings is fascinating. They range from simple - buy the product, clean the surfaces and rinse, leave to dry then spray the surface - through to the more complex where manufacturers are selling the surface treatment service with specialised technicians using electrostatic spraying systems, and wearing respiratory gear. However, the technologies in both instances seem to be the same.


Clearly the principle that you can apply a treatment to a surface and that it should last weeks – if not months – is clearly interesting, especially in the current environment. It means that if you typically disinfect a surface daily or twice


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daily you could move to every week or every month, with all this supported by standard test methods in laboratories that validate and demonstrate the lasting antimicrobial activity.


Results in lab conditions can lead to the antimicrobial activity being maintained for more than three months – but this is only in lab conditions. In reality, the length of the protection is extremely variable and it depends a lot on the quality of the application procedure by an expert or by someone who’s been trained in five minutes, and what happens to the treated surfaces over the course of the coming hours, days and weeks. All this impacts the length of protection offered.


A group of researchers in a hospital in the US who had been evaluating the performance of such treatments applied the treatment on some selected high touch hospital surfaces. Across a large number of surfaces, they could not detect any type of antimicrobial activity, even after the application of the treatment. They repeated the test after 24 and 48 hours because they said maybe they need some time to be activated. They could not detect any lasting nor even any immediate antimicrobial activity.


In their conclusion they did not say these technologies are not working. They said maybe they didn't use the right amount of product or maybe they didn't apply it properly – or maybe it’s because they've been applying the product using microfibre instead of cutting paper or cotton or paper towels, but this exactly raises the problem. The technology may be excellent, but if it's not applied properly, there are no benefits.


In the real world, with people touching the treated surface, regular traffic levels will eventually create some abrasion to the coating which means that the level of protection drops. Consider also that you will not have cleaned the surfaces and every week you will need to retest to validate if the antimicrobial activity is still there.


Even the lightest of cleaning regimes such as dusting will erode the coating, let alone cleaning with a detergent. In fact, some manufacturers provide long lists of cleaning products that should not be using their coatings. The type of cleaning material has been shown to impact the protective layer, for example if you clean with microfibres.


Protecting the environment


In terms of environmental impact, in a few studies it was reported that up to 100% of the antimicrobial substance in the coating was rapidly released with the consequent leaching and diffusion into the water network through cleaning or human contact, which considering also the potential need for people applying the product to wear high levels of protective gear is concerning.


That said if you choose to go with a semi-permanent coating, then you would reduce your consumption of antimicrobial products. Instead of using them twice a day, maybe you would use the same or similar amount of disinfectant once a month or every two months. That would be a benefit again in terms of reduction of pollutant.


If you chose a solution using metal nano particles there is FEATURE | 53


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