Energy-Harvesting Knee Brace Could Power Medical Devices

Researchers have been looking for diverse ways to power small medical devices wirelessly or through energy harvesting to eliminate the need for batteries, which can be cumbersome or need invasive surgery to replace. Now an interdisciplinary group of engineers at Rice University have combined both in a knee brace that could one day be used to power an artificial heart.

A group of engineering students at Rice who call themselves the "Farmers" have designed a knee brace that harvests energy from walking, according to a news release on the Rice website. This energy potentially can be reused to power small medical devices.

As a person wearing the brace walks, that leg movement spins a motor inside the brace that generates power. The energy feeds to a lithium-ion battery pack that can be attached to someone's belt and is connected via wire to the brace. However, since energy from walking is variable and not consistent enough to be sent directly to the battery, it first goes through a capacitor which stores the energy for a short time and then delivers it to the battery.

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"The device has two major parts: an electrical subsystem and a mechanical subsystem," mechanical engineering student Chase Gensheimer, a member of the design team, told Design News in an e-mail. "The mechanical subsystem is attached to the leg and includes the motor, gearhead, and all casings. The motor is situated on the outside of the user's knee and it rotates by the gearhead. The power generated is stored through a capacitor in a lithium-ion battery."

The students had corporate sponsorship to design the brace by Houston company Cameron International, which brought the project to Rice as a way to invent wireless power for an artificial heart it's developing. The knee brace is the result of work by the third Rice engineering team to take on the challenge, although the four watts of energy produced by the brace is not quite enough to power the heart, according to researchers.

The energy-harvesting brace is aimed at programs like Doctors Without Borders and other scenarios in which patients in remote locations might need power on the go, students said in a video

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While the brace doesn't look very comfortable or practical to wear, Gensheimer, who's done most of the road testing, said it can be worn for up to a few hours without significant discomfort. However, he added that the invention is just a prototype and there isn't enough evidence yet to determine how comfortable it would be with continued use.

The team said it's happy with the progress it has made on the project since the design of a shoe-based generator from the first team to tackle Cameron's challenge. The engineers expect that a future version of their brace that's been optimized for more comfort, device size and efficiency will eventually be used to power medical devices, Gensheimer said.

Elizabeth Montalbano is a freelance writer who has written about technology and culture for more than 15 years. She has lived and worked as a professional journalist in Phoenix, San Francisco, and New York City. In her free time she enjoys surfing, traveling, music, yoga, and cooking. She currently resides in a village on the southwest coast of Portugal.

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