Coatings and surface treatment
SAFEty first Together with fellow researchers at UBC, Lange has been working on a new, long-acting silver coating for medical implants. This coating, called SAFE (a loose acronym for ‘silver-based film-forming antibacterial engineered’) is designed to tackle these challenges, among others.
“Our coating releases silver effectively for at least 90 days, and this is at active levels – active meaning it remains anti-microbial,” says Lange. “But we also performed cytotoxicity and biocompatibility testing, which showed the amount of silver released does not cause any toxicity, and is biocompatible.” This technology represents a step up on the coatings that are currently available. “With existing coatings, the silver is embedded into the material itself, which means it’s not being released,” says Lange. “What they’re relying on there is contact killing, which means that the bacteria have to physically attach to the material surface in order to be killed.” The problem here is that dead bacteria will adhere to the surface just as well as live ones. As time goes on, you will get a build-up of dead bacteria (a biofilm) on the surface, which essentially renders the technology useless. In the case of a urinary catheter, the debris will also contain proteins, crystals and other undesirable compounds. “The surface just gets covered up and live bacteria will start to attach to the dead bacteria,” says Lange. “Essentially all you’re doing is delaying the onset of infection. This is exactly the reason why previously attempted technologies have failed and never made it into clinical practice.”
The SAFE coating has two advantages here. First, it has antifouling properties, meaning that it will actively repel organic and inorganic components. In doing so, it keeps the surface clear. Secondly, the antimicrobial agent does not just sit inside the coating – it is slowly released into its surroundings, where it attacks the living microbes. “Because it’s anti-fouling, the bacteria remain free swimming, and because we’re releasing the silver effectively, it will kill the free-swimming bacteria,” says Lange. “You basically have a dual mechanism to prevent the surface of the device becoming covered up with waste material, while at the same time killing the bacteria.”
The testing process
In terms of how SAFE was developed, the team began by screening many sets of ingredients. They wanted to develop an all-in-one composition that could be applied to surfaces in a single step. Eventually, they settled on a formula that included two different polymers and dopamine, along with silver nitrate.
Medical Device Developments /
www.nsmedicaldevices.com
Killing bacteria on urinary catheters is where Lange and his team see the biggest potential for their silver coating to make a difference in hospitals.
“The coating consists of three to four components, mixed together in an aqueous solution,” says Lange. “Unlike with some other coating technologies, there’s no pre-treatment of the materials required. You just mix the components together and away you go – it’s that simple.”
In lab tests, this formula (SAFE) was the best at preventing bacterial attachment over the long- term. Unlike other coatings they tried, the SAFE coating completely suppressed bacterial attachment over 28 days, no matter which bacterial species they tested. This suggests it works via a different mechanism from other coatings that have been attempted.
“Silver is very effective at killing a broad spectrum of bacteria. That includes both gram- positive and gram-negative bacteria, including multidrug-resistant bacterial species. It’s also very effective at killing fungi.”
“Our in vitro studies involved coating catheters and then running them through two biofilm models,” say Lange. “One is a static model, where you take the material, put it into a bacterial solution, incubate it for X amount of time, then remove it and quantify the bacteria on the surface.” The other is a flow model, in which artificial urine mixed with the bacteria flows through the catheter and onto its surface. That’s a more realistic simulation of what happens in the urinary tract.
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