Coatings and surface treatment


Silver is one of the precious metals of the world, but its uses go well beyond the decorative. Thanks to its bactericidal properties, it is commonly used in wound care dressings and could be used to great effect in implanted medical devices. The challenge is that, at high doses, silver is toxic to human cells. Abi Millar speaks to Dirk Lange, a microbiologist at the department of urologic sciences at the University of British Columbia, about the silver coating he is developing that could overcome that barrier.


A silver bullet C


olloquially speaking, a ‘silver bullet’ is a simple solution to a difficult problem. To cite the best- known example – when penicillin first became available in the 1930s, it was touted as a silver bullet that would cure an array of bacterial infections. Aptly enough, another silver bullet might just be silver itself. This precious metal has long been recognised as an antimicrobial, with its uses far pre-dating the discovery of microbes. Hippocrates wrote that silver had healing properties, while the Phoenicians stored liquid in silver bottles to prevent spoiling. Further down the line, silver coins were dropped into wine casks on long ocean voyages, and silver compounds were used to prevent infections during the First World War. Until recently, the mechanism responsible remained mysterious. But researchers now know that silver ions can penetrate the cell walls of bacteria. Here they unleash a juggernaut of lethal effects, interfering with certain enzymes and binding with the bacterial DNA. At sufficient concentration, they are extremely toxic for many of the microbes that cross their path. “Silver is very effective at killing a broad spectrum of bacteria,” says Dr Dirk Lange, a microbiologist at


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the department of urologic sciences at the University of British Columbia (UBC). “That includes both gram-positive and gram-negative bacteria, including multidrug-resistant bacterial species. It’s also very effective at killing fungi.”


He adds that silver is already widely used in medicine for this purpose. It is used within the urology space to coat catheters and within the vascular space to coat grafts. Orthopaedic surgeons now routinely implant silver-coated devices, while activated silver dressings and silver sulfadiazine cream have a long pedigree in treating burns. Despite the growing number of applications, challenges remain. Above all, silver can be toxic not just to bacteria, but also to human cells. “If you release the silver too fast and at too high a dose, you run the risk of causing toxicity,” says Lange. “That’s probably one of the biggest issues with silver. The other issue is that if you do release it too fast, then you run out too quickly, and you only have a very short time frame in which it is effective.” Simply put – if you can’t release the silver at doses low enough to avoid toxicity, it’s not going to be viable within medicine.


Medical Device Developments / www.nsmedicaldevices.com


Taves/ Shutterstock.com


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