In a small clinical study, researchers at Drexel University, Philadelphia, administered a new method to treat chronic wounds using a novel ultrasound applicator that can be worn like a bandage. The applicator delivers low-frequency, low-intensity ultrasound directly to wounds, and was found to significantly accelerate healing in five patients with venous ulcers, the researchers said.

Standard treatment for venous ulcers involves controlling swelling, taking care of the wound by keeping it moist, preventing infection, and compression therapy. However, the wounds often take months and even years to heal. Except for skin graft surgery, very few technologies actively stimulate healing.

The scientists reported that patients receiving low-frequency, low-intensity ultrasound treatment during their weekly check-up, in addition to standard compression therapy, showed a net reduction in wound size after just four weeks. In contrast, patients who didn’t receive ultrasound treatment had an average increase in wound size during the same time period.

Previous research showed therapeutic benefits of ultrasound for wound healing at much higher frequencies, but by reducing the frequency to the range of 20 to 100 kilohertz (kHz), at least an order of magnitude lower, they say that they saw profound changes.

In order to determine the optimal ultrasound frequency as well as treatment duration, the researchers treated patients with either 15 minutes of 20 kHz ultrasound, 45 minutes of 20 kHz ultrasound, 15 minutes of 100 kHz ultrasound, or 15 minutes of a placebo ultrasound. The group receiving 15 minutes of 20 kHz ultrasound showed the greatest improvement, with all patients experiencing complete healing by the fourth treatment.

Surprisingly, the group receiving 45 minutes of treatment didn’t achieve the same benefits as the 15 minute group, leading the researchers to determine that more is not always better.

They said that one of the greatest challenges of the study was designing and creating their battery-powered ultrasound patch. Most ultrasound transducers require a large apparatus and need to be plugged into the wall. In order to make their device fully wearable and portable, they had to make it battery-powered by designing a transducer that could produce medically relevant energy levels using minimum voltage.

The resulting ultrasound patch weighs just 100 grams and is connected to two lithium ion batteries that are fully rechargeable. This gives patients the option of using the transducer in a home environment, while still wearing their compression socks. It also prevents the need for a doctor’s visit, which can be a difficult task for patients with chronic wounds.