An Indian-origin postdoctoral researcher at the University of Wisconsin-Madison has come up with an experimental approach to wound healing that could take advantage of silver's anti-bacterial properties, while sidestepping the damage silver can cause to cells needed for healing.
While making a presentation on the novel approach at the American Chemical Society meeting on Wednesday, Ankit Agarwal said that silver is widely used to prevent bacterial contamination in wound dressings, "but these dressings deliver a very large load of silver, and that can kill a lot of cells in the wound."
Wound healing is a particular problem in diabetes, where poor blood supply that inhibits healing can require amputations, and also in burn wards.
Agarwal said that some burn surgeons would avoid silver dressings despite their constant concern with infection.
He said that his new approach enabled him to craft an ultra-thin material carrying a precise dose of silver.
In tests in lab dishes, the researcher found the low concentration of silver to kill 99.9999 percent of the bacteria, without damaging cells called fibroblasts that are needed to repair a wound.
Agarwal builds the experimental material from polyelectrolyte multilayers - a sandwich of ultra-thin polymers that adhere through electrical attraction.
To make the sandwich, he alternately dips a glass plate in two solutions of oppositely charged polymers, and finally adds a precise dose of silver.
"This architecture is very easily tuned to different applications," Agarwal says, because it allows exact control of such factors as thickness, porosity and silver content.
He says that the final sandwich may range from a few nanometres to several hundred nanometres in thickness.
Nicholas Abbott, a professor of chemical and biological engineering who advises Agarwal, says during the past decade, "about a bazillion papers have been published on polyelectrolyte multilayers. It's been a tremendous investment by material scientists, and that investment is now ripe to be exploited."
The system is said to be so sensitive that increasing the silver dose from 0.4 percent to 1 percent of the level used in a commercial dressing severely damaged the fibroblasts.
The tiny silver nanoparticles that Agarwal embeds in the sandwich can be designed to release ions for days or weeks as needed, while commercial wound dressings contain a large dose of silver ions that are released faster and with less control.
Abbott says that the required dose of silver can also be reduced because the new material would be designed to stay in close contact with the wound.
"In a commercial dressing, the silver is part of the bandage that is placed on the wound surface. 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," said the researcher.
Abbott insists that 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. We are putting the ilver 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," Abbott said.