Silver wound dressing

A new kind of wound dressing uses silver in a way that kills bacteria but does not damage cells needed for healing.

The dressing, developed by Ankit Agarwal, a postdoctoral researcher at the University of Wisconsin-Madison, is made with an ultra-thin material carrying a precise dose of silver.

One square inch contains just 0.4 per cent of the silver that is found in the silver-treated antibacterial bandages now used in medicine.

The amount of silver used in these current wound dressings, Agarwal said, has been shown to kill cells known as fibroblasts that are needed to repair a wound.

In tests, the low concentration of silver killed 99.9999 per cent of the bacteria but did not damage fibroblasts.

Agarwal built the material from polyelectrolyte multilayers - a sandwich of ultra-thin polymers that adhere through electrical attraction. To make the sandwich, Agarwal alternately dipped a glass plate in two solutions of oppositely charged polymers. Finally, he added a precise dose of silver.

‘This architecture is very easily tuned to different applications because it allows exact control of such factors as thickness, porosity and silver content. The final sandwich may range from a few nanometres to several hundred nanometres in thickness,' said Agarwal. 

To kill bacteria, silver must take the form of charged particles, or ions, and the tiny silver nanoparticles that Agarwal embeds in the sandwich can be designed to release ions for days or weeks as needed.

In contrast, Agarwal added, commercial wound dressings contain a large dose of silver ions, which are released faster and with less control.

The required dose of silver can also be reduced because the new material would be designed to stay in close contact with the wound, said Nicholas Abbott, a professor of chemical and biological engineering who advises Agarwal.

‘In a commercial dressing, the silver is part of the bandage that is placed on the wound surface,’ he added. ‘We envision this material becoming incorporated into the wound. The cells will grow over it and it will eventually decay and be absorbed into the body, much like an absorbable suture.’

Abbott said tests on animals will be needed before the new material can be tested on humans.

‘A commercial dressing needs to have a large quantity of silver so it can diffuse to the wound bed, and that quantity turns out to be toxic to mammalian cells in lab dishes,’ he added. ‘We are putting the silver where we need it, so we can use a small loading of silver, which does not exhibit toxicity to mammalian cells because the silver is precisely targeted.’