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Prosthetic leg

Above-Knee Amputees Harness the Power of Exoskeletons

Oct. 12, 2021
An autonomous powered hip exoskeleton assists the residual limb by decreasing the effort and restoring range of motion.

A new experimental exoskeleton developed by mechanical engineers at the University of Utah’s Bionic Engineering Lab enables an amputee to walk with much less effort, while restoring strength and range of motion.

The exoskeleton was designed to enable an amputee to walk with much less effort. It wraps around the wearer’s leg and uses battery-powered electric motors and embedded microprocessors.

The team of researchers—led by Tommaso Lenzi, an assistant professor of mechanical engineering—explained that above-knee amputation severely reduces the mobility and quality of life for amputees, largely because much of the leg’s muscles are removed during surgery.

“The consequence of this, even though you have the ability to move your hip, is your abilities in walking are quite impaired,” explained Lenzi. “There is a lack of strength and range of motion.”

A standard prosthetic leg for amputees cannot fully replicate the biomechanical functions of a human leg. As a result, an above-knee amputee will need to exert more energy using their residual- and intact-limb muscles to offset the lack of energy from the prosthesis.

Lenzi’s exoskeleton is designed to provide the extra energy so that walking feels natural. It is comprised of a lightweight, efficient electromechanical actuator which attaches to the user’s thigh above the amputation, along with custom electronic systems, microcontrollers and sensors running advanced control algorithms—all of which are attached to a harness secured around the waist.

The lightweight frame is made of a carbon-fiber material, while other parts are constructed of plastic composites and aluminum. The exoskeleton only weighs 5.4 lb.

“The exoskeleton’s AI understands how the person moves and assists how the person moves,” said co-author Dante A. Archangeli. The exoskeleton provides just enough extra power for walking. Lenzi likened the power configuration to an electric bike with a motor that gives the rider assistance in pedaling the bike uphill.

To test the technology, the researchers had six people with above-knee amputations strap on the exoskeleton before their metabolic rate was recorded. The users’ oxygen intake and carbon dioxide levels were measured while having them walk on the treadmill with and without the device.

All of the users improved their metabolic rate (reduced their energy consumption) an average of 15.6% with the exoskeleton strapped on, Lenzi said.

“It’s equivalent to taking off a 26-lb backpack,” Lenzi said. “That is a really big improvement. We’re very close to what an average person would expend at the same speed. The metabolic consumption is almost indistinguishable from that of an able-bodied person, depending on the fitness level.”

Lenzi said the exoskeleton could become available in as early as a couple of years. A $985,000 grant from the U.S. Department of Defense funded the development of this new exoskeleton technology for the benefit of veterans. Earlier this year, Lenzi received a $584,000 grant from the National Science Foundation.    

The research was documented in a paper published in the journal Nature Medicine.

About the Author

Rehana Begg | Editor-in-Chief, Machine Design

As Machine Design’s content lead, Rehana Begg is tasked with elevating the voice of the design and multi-disciplinary engineer in the face of digital transformation and engineering innovation. Begg has more than 24 years of editorial experience and has spent the past decade in the trenches of industrial manufacturing, focusing on new technologies, manufacturing innovation and business. Her B2B career has taken her from corporate boardrooms to plant floors and underground mining stopes, covering everything from automation & IIoT, robotics, mechanical design and additive manufacturing to plant operations, maintenance, reliability and continuous improvement. Begg holds an MBA, a Master of Journalism degree, and a BA (Hons.) in Political Science. She is committed to lifelong learning and feeds her passion for innovation in publishing, transparent science and clear communication by attending relevant conferences and seminars/workshops. 

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