Scientists have developed a small ultrasound patch that speeds the healing of chronic wounds.

A new invention about the size of a large Band-Aid delivers low-frequency ultrasound waves to skin wounds to hyper-charge the healing process. A small clinical trial at Drexel University in Pennsylvania examined 20 patients with chronic leg ulcers, assigning them to five-person groups.

In one of the groups, whose treatment was 15 minutes of ultrasound at 20kHz, all five patients saw their wounds heal completely after just four treatments. This suggests the gentle mechanical pressure of the ultrasound waves activates and boosts the body’s own natural healing process.

The discovery was described in a paper published this month in the Journal of the Acoustical Society of America by Joshua Samuels, a Ph.D candidate at Drexel, working with Dr. Peter Lewin and Dr. Michael Weingarten.

The most common type of leg ulcer is a venous ulcer, which forms when the valves in the veins that return blood from the limbs to the heart malfunction, causing blood to pool. Cells in these stressed veins start to leak, causing inflammation and eventually forming an ulcer. Current treatments are passive, including heating and cleaning the wound and having patients wear compression socks to push blood back toward the heart.

These passive treatments do little to encourage skin ulcers to heal. In many patients, the ulcers can become chronic, lingering for months or even years.

“Venous ulcers affect younger and older patients, making it a very big socioeconomic burden,” Samuels said in an interview with Healthline. “Patients with large ulcers have limited ability to work and reduced quality of life due to the pain of the wound.”

More than half a million patients in America are treated for venous ulcers every year, and these treatments rack up almost one percent of all healthcare costs in the western world. As of 2009, the treatment of chronic wounds, including venous ulcers and diabetic ulcers, cost the American healthcare system $25 billion a year.

It can cost more than $2,400 a month for a person to receive proper wound care, and this doesn’t take into account lost wages or other impacts on quality of life.

“There are relatively few active therapies for venous ulcers, and the few that do exist are extremely expensive,” Samuels said. “We wanted a simple, easy to wear, and cost effective active therapy.”

His device is about an inch and a half square and plugs into a rechargeable lithium ion battery pack about the size of two stacked decks of cards. Samuels hopes to continue to shrink the device and improve its power efficiency to create a unit that can fit into a compression wrap, providing a single, integrated ulcer treatment patients can use at home.

Researchers don’t know how exactly the ultrasound patch speeds healing.

“The identification of the mechanism by which this process works is still very much a mystery,” explained Dr. Hector Lopez, Program Director for Diagnostic and Therapeutic Ultrasound at the National Institute of Biomedical Imaging and Bioengineering, in an interview with Healthline. “The problem with that is, until these mechanisms are very well understood, it’s very hard to control them. The forces created by ultrasound can be quite destructive if not in the right hands or not fully understood.”

The scientists also need to fine-tune the dosage of ultrasound patients are given. The test group that received a 20kHz ultrasound for 15 minutes saw their wounds heal completely, while another group that received a 20kHz stimulation for 45 minutes only saw a partial improvement.

“We were surprised that the group receiving 45 minutes of treatment didn’t achieve the same benefits as the 15 minute group, but sometimes we learn that more is not always better,” said Samuels in a press release. “There may be a dosing effect.”

The technology also holds promise for healing other types of external wounds. “Chronic wounds are the most difficult wounds to heal,” Lopez said. “The reason they’re called ‘chronic’ is that for some people, they don’t heal for a very long time, or don’t heal at all. If you can help heal these with ultrasounds, you would think that with ordinary wounds, this would work just as well, if not better.”

Fortunately, the U.S. Food and Drug Administration (FDA) doesn’t need scientists to be able to fully explain a new medical device in order to approve it for use—they only need evidence that the device works and doesn’t cause harm. Samuels hopes to have the device approved, licensed, and cheaply available within five to seven years.

This research was publicly funded by the NIBIB, a division of the National Institutes of Health.