Coatings & surface treatment
high-touch surfaces like counter tops and doorknobs play in pathogen transmission. A consequence of this was a reignition of the discussion around antimicrobial coatings as a strategy to keep microbes at bay in hospitals. Unlike human-led sterility and disinfection procedures, intrinsic antimicrobial surfaces offer a passive system that requires no human intervention, and their action is continuous.
Antimicrobial coatings
The ability to create antimicrobial coatings is nothing new. Early examples used developments in nanotechnology to embed silver ions produced at a nanoscale into a matrix that could be applied to surfaces to give them antimicrobial properties. Silver was an obvious choice and still features in many current antimicrobial coatings due to its ability to interact with four main components in bacterial cells: the cell wall, plasma membrane, bacterial DNA and proteins. Here it causes degradation of the cell wall and cell lysis, preventing the bacteria from reproducing. The ions also penetrate the cell interior and bind to DNA bases, which prevents them from replicating. Although this level of knowledge was acquired long afterwards, the use of silver dates back to 1850 BCE
Egypt, where it was directly applied to wounds to improve healing. Of course, the potential for toxicity was unknown, and although silver is still employed in wound care today, it’s at much lower concentrations and accompanied by other ingredients, like antibiotics. With an established method of killing bacteria,
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it’s worth asking why antimicrobial coatings that use silver, copper (another bactericidal element) or another of the various elements and compounds in these products aren’t employed in hospitals as standard practice. Part of the reason is that, in order to make claims related to the product, manufacturers must provide safety and efficacy data, and as of right now there’s no standardised test to produce it. A 2023 paper titled ‘Antimicrobial coatings: Reviewing options for healthcare applications’ noted that the best available protocol, produced by the US Environmental Protection Agency (EPA). EPA suggests that an effective product should reduce the number of microorganisms on a surface by a factor of 1,000 (so 1,000,000 microorganisms become 1,000) within an hour of application. But the authors went on to say that of the ten coatings they evaluated, only one (cupric oxide) would pass using that criterion. An additional point here is that in order to be viable for reducing HAIs, coatings must demonstrate efficacy against a broad spectrum of pathogens, especially now that the Covid-19 pandemic has added an impetus for defence against viruses. As of now, most manufacturers tend to only provide efficacy data in the form of laboratory testing against gram-positive and gram-negative bacteria. Both of these points lead the authors of the paper to conclude: “Although many possible antimicrobial surface options can be proposed, there are much fewer studies that investigate the ‘fitness for purpose’ where there is an evaluation of durability and sustained activity for activity against the key nosocomial pathogens, including drug-resistant bacteria, endospores, fungi and viruses.” To put it another way, antimicrobial coatings simply haven’t proven themselves to be effective enough to mandate their use in infection control yet – at least when it comes to high-touch surfaces. On the other hand, products like silver alloy coatings for catheters have proven themselves adept at keeping the bacteria responsible for UTIs under control. That’s a lot different to applying an antimicrobial coating to a large surface area, but it proves that biocidal activity is possible. With renewed interest in antimicrobial coatings spurred on by the increasing numbers of antibiotic-resistant bacteria and the experience of the pandemic, hopefully we’re not far from a breakthrough that will give hospitals another weapon against HAIs. ●
Medical Device Developments /
www.nsmedicaldevices.com
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