Silver bullets are said to kill werewolves in folklore, but scientists wanted to use this metal to combat another deadly foe: bacteria. Researchers have attempted but failed, to produce a silver coating for implantable medical devices to protect against infection.
A new type of silver coating (illustrated above) could prevent bacteria from adhering to medical devices. Image Credit: Hossein Yazdani-Ahmadabadi.
However, recently one team of researchers has introduced a novel, long-acting silver-ion releasing coating, in rats, that prevents bacteria from sticking to implants and then kills them. The study was published in the journal ACS Central Science.
Surgeons implant a device, like a tube to drain a wound or the bladder, or to deliver medication directly into the bloodstream, to provide medical care. Bacteria, on the other hand, can attach to and collect on the surfaces of these devices, posing a risk of infection. Researchers have been developing bacteria-repelling coatings, including those that contain silver, which is known to kill microbes.
Their efforts, however, have been hampered by a number of challenges: Silver can be toxic to human cells, and creating a coating that continuously releases small amounts of the metal over extended periods of time, for example, is difficult. Dirk Lange and Jayachandran Kizhakkedathu were looking for a formula that could help them overcome these and other challenges.
To create a simple-to-apply coating, the team tested a variety of ingredients that could be applied to a surface in one step. Silver nitrate, dopamine and two hydrophilic polymers were the most effective ingredients in the formula. In laboratory tests, this silver-based antibacterial engineered (“SAFE”) coating formed stable, silver-containing assemblies that gradually released silver ions.
This novel coating recipe efficaciously kept eight of the most common bacteria that cause severe infections at bay when exposed to them for 28 days. It accomplished this in an unusual way, repelling bacteria from the surface and then destroying them with silver ions. They coated a titanium implant with SAFE and then implanted it beneath the skin of rats to test its effectiveness in a living animal.
After a week, the researchers discovered that implants with the coating had significantly fewer bacteria than those without it. Furthermore, the tissues of the rats showed no signs of toxicity.
After being rubbed and sterilized under harsh conditions, the coating appeared tough, with little wear and tear. The scientists believe that this combination of properties will make the coating useful in a variety of medical devices and implants in the long run to prevent bacterial infection.
The Canadian Institutes of Health Research, the Natural Sciences and Engineering Council of Canada, the Canada Foundation for Innovation, the British Columbia Knowledge Development Fund, and the Michael Smith Foundation for Health Research have all provided financial support to the authors.
Journal Reference:
Yazdani-Ahmadabadi, H., et al. (2022) Durable Surfaces from Film-Forming Silver Assemblies for Long-Term Zero Bacterial Adhesion without Toxicity. ACS Central Science. doi.org/10.1021/acscentsci.1c01556.