Battery-Free Wearable Device Helps Stroke Survivors Walk More Naturally

Scientists in Hong Kong and mainland China have developed a lightweight, battery-free neural prosthesis that uses energy from a wearer's own movements to electrically stimulate muscles, helping stroke survivors flex their ankle and walk more naturally. The device, described in a paper published in Nature Communications on September 2, was created by a team led by researchers at the Hong Kong University of Science and Technology (HKUST) and Hong Kong Polytechnic University.

The device targets "foot drop," a common impairment after stroke in which a person cannot flex the ankle or lift the front of the foot, increasing the risk of falls. Conventional rigid leg braces correct this mainly by restraining the ankle joint rather than restoring its movement, which can cause muscle atrophy with prolonged use, while robotic exoskeletons are often too complex, bulky or hard to calibrate for daily use.

The new device harvests mechanical energy from the wearer's less-affected leg through a component built into the shoe. It then uses that power to run a lightweight neurostimulator strapped around the calf of the weaker leg, delivering an electrical current that helps the muscles contract during walking. In indoor treadmill trials and outdoor walking tests, it produced immediate improvements: a 67.3% increase in walking distance and a 43.5% increase in walking speed.

"Rather than relying on external sensors or battery-powered control, the device operates automatically during walking through mechanically coupled energy harvesting and stimulation delivery," the researchers wrote in their paper. Corresponding author Yang Zhengbao, an associate professor at HKUST, said the design takes advantage of the "natural intelligence" of human walking patterns rather than replacing them.

Lead author Pan Qiqi, a former postdoctoral fellow in Yang's lab now at Huazhong University of Science and Technology, said foot drop was not completely eliminated during the outdoor trials, though the device still significantly improved gait. The team is now developing similar energy-harvesting devices for the knee and hip.