University of Utah engineers develop new exoskeleton to help amputees walk more easily

Stan Schaar thought he would never be able to easily walk again after he lost his left leg when it was crushed by a pickup truck seven years ago. Now, a University of Utah-developed exoskeleton allows the 74-year-old Salt Lake resident to effortlessly walk down the road, a sensation as close to walking on his human leg as he's ever experienced.

"The first time I used it, it was like my muscles were totally fused with this exoskeleton, and it was helping them move faster," said Schaar, a retired computer administrator. "It helped my leg to relax and just move forward and walk. I could probably walk for miles with this thing on because it was helping my muscles move."

Led by mechanical engineering assistant professor Tommaso Lenzi, mechanical engineering researchers at the U.'s Bionic Engineering Lab created the lightweight, powered exoskeleton to help lower-limb amputees like Schaar walk.

Made of a carbon-fiber frame, plastic composites and aluminum, the device weighs just 5.4 pounds.

It consists of a harness around the wearer's waist with custom electronic systems, microcontrollers and sensors that connect to a lightweight, efficient electromechanical actuator on the user's thigh right above the amputation. Lenzi said it functions similarly to an e-bike that helps riders pedal uphill, with battery-powered electric motors, embedded microprocessors and advanced algorithms to best accommodate easy walking.

Schaar described it "like a big wind," pushing him down the road.

"I'm a person who doesn't have a lot of muscle left in my residual limb," he says. "This device makes up for a lot of what they had to take away. There's nothing that will ever replace a flesh-and-bone leg, but this comes pretty close."

The group of researchers recorded their findings in a new paper, written by Lenzi and mechanical engineering graduate students and published in Nature Medicine Monday morning.

During most above-knee amputation surgeries, the leg's muscles are removed, resulting in reduced mobility and quality of life for millions of patients.

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

Although standard prosthetics can help with that mobility loss, they cannot entirely replicate the biomechanical functions of a human leg and usually require amputees to overexert their remaining muscles to compensate. The new exoskeleton was created to understand how someone moves and assist in that movement, said University of Utah mechanical engineering graduate student Dante A. Archangeli.

The device isn't meant to add extra strength but rather give just enough of a boost to ease walking.

During their study trials, six people with lower-limb amputations tested the exoskeleton on a treadmill while the researchers recorded their metabolic rate, oxygen intake and carbon dioxide levels and measured them against the same info collected without wearing the device. All of them showed that the device improved their metabolic rate by an average of 15.6%, meaning that walking consumed less energy with the device.

"It's equivalent to taking off a 26-pound backpack. That is a really big improvement," Lenzi said. "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."

Schaar said that he hopes the team can get the device on the market soon to help out more people like him.

Lenzi believes the exoskeleton could become available in as early as a couple of years from now with help from a $985,000 grant from the U.S. Department of Defense — to eventually benefit veteran amputees — and a $584,000 grant from the National Science Foundation.

"The (grants) will enable us to continue this work and build an even better device to help more people walk," he said.