Researchers in mechanical engineering have created a lightweight powered exoskeleton that allows lower-limb amputees to walk with much less effort. The device, like an e-bike, uses motors, microprocessors, and advanced algorithms to assist users in walking.
Stan Schaar, who lost his left leg in an accident while assisting a neighbor, never imagined he’d be able to walk with two healthy legs again. He then donned a new experimental exoskeleton created by mechanical engineers at the University of Utah’s Bionic Engineering Lab. “It just felt like a big wind was behind me, pushing me down the road,” says the 74-year-old Salt Lake County, Utah, man of his experience with the new device.
Schaar was one of a half-dozen lower-limb amputees who tested the new exoskeleton designed by a team led by mechanical engineering assistant professor Tommaso Lenzi at the University of Utah. The exoskeleton, which wraps around the wearer’s waist and leg, is powered by battery-powered electric motors and embedded microprocessors, allowing an amputee to walk with significantly less effort.
The findings of the group’s research have been published in the journal Nature Medicine. The paper’s co-authors include U mechanical engineering graduate students Marshall K. Ishmael and Dante A. Archangeli, in addition to Lenzi.
Mechanical engineering researchers have developed a lightweight powered exoskeleton that helps lower-limb amputees walk with much less effort.
Reduced quality of life
Millions of people’s mobility and quality of life are severely impacted by above-knee amputation, owing in large part to the removal of many of the leg’s muscles during surgery. “As a result of this, even though you have the ability to move your hip, your walking abilities are quite impaired,” Lenzi says. “I don’t have enough strength or range of motion.”
The biomechanical functions of a human leg cannot be fully replicated by a standard prosthetic leg for amputees. As a result, above-knee amputees work harder while walking, overexerting their residual-limb and intact-limb muscles to compensate for the prosthesis’s lack of energy.
The goal of Lenzi’s exoskeleton is to provide that extra energy so that walking feels natural again. The device includes a lightweight, efficient electromechanical actuator that is attached to the user’s thigh above the amputation. A harness around the waist houses custom electronic systems, microcontrollers, and sensors that run advanced control algorithms. “The exoskeleton’s AI understands how the person moves and assists how the person moves,” Archangeli explains. To accommodate either leg, the actuator can be moved between the right and left sides of the main harness.
Like an electric bike
Unlike the powered suit that gives the Marvel superhero Iron Man extra strength, or other exoskeleton suits that aid workers in lifting heavy loads, Lenzi’s exoskeleton only gives the user enough extra power to walk. The professor compares it to an electric bike with a motor that assists the rider in pedaling uphill.
Six people with above-knee amputations tested the exoskeleton while their metabolic rate was recorded, according to the research team. The patients walked on a treadmill while their oxygen intake and carbon dioxide levels were measured, both with and without the device.
According to Lenzi, all of those who tested the exoskeleton improved their metabolic rate, or reduced their energy consumption by an average of 15.6 percent while wearing it. “It’s the same as removing a 26-pound backpack. That is a significant improvement “he claims. “We’re very close to what a typical person would expend at the same rate. Depending on fitness level, metabolic consumption is almost indistinguishable from that of an able-bodied person.”
Another distinguishing feature of this device, according to Lenzi, is its light weight. The frame is made of carbon fiber, while the other parts are made of plastic composites and aluminum. The exoskeleton weighs only 5.4 pounds in total.
“Walk for miles”
The experience of using the exoskeleton, according to Schaar, was as close to his human leg as anything else. “The first time I used it, it felt like my muscles were completely fused with this exoskeleton, and it was assisting them in moving faster,” the retired computer administrator says. “It allowed my leg to relax and simply walk forward. Because it was assisting my muscles in moving, I could probably walk for miles with this thing on.”
Schaar was helping a friend jump-start two pickup trucks seven years ago when one of the vehicles lurched forward, crushing Schaar’s leg. Doctors had to remove much of his leg muscles during the subsequent amputation surgery, as well as during a follow-up surgery.
“I’m the type of person who doesn’t have a lot of muscle left in my residual limb,” he explains. “This device compensates for a large portion of what they had to remove. Nothing will ever be able to replace a flesh-and-bone leg, but this comes close. I’m hoping to see this thing on the market soon.”
That moment, according to Lenzi, could come quickly. He believes the exoskeleton could be available within a couple of years. The development of this new exoskeleton technology for the benefit of veterans was funded by a $985,000 grant from the United States Department of Defense. The National Science Foundation awarded Lenzi a new $584,000 grant earlier this year.