Exoskeleton Research Steps Up to Challenges

Human trials of assistive technology have been very promising, as devices move from research to commercialization. Wearable robotics and exoskeletons have helped restore lost limb functions resulting from brain damage, allowing injured war veterans to walk again.

Soft robotic gloves can bring relief to stroke patients by helping them open their hands, and therapists and doctors can tailor spinal treatment to patients.

Not only can the injured or elderly benefit from such healthcare robotics; younger patients are also regaining mobility, thanks to exoskeletons and 3D printing.

A mechanical approach

North Carolina State University and Carnegie Mellon University researchers have been working on lightweight lower-leg device, which uses a spring and clutch system working in tandem with calf muscles and the Achilles’ tendon.

They hope it will help people with weak legs walk faster and easier and people with normal legs walk with less effort and strain. The carbon-fiber device weighs about as much as a typical shoe — approximately 500 grams, a bit more than a pound. The device isn’t motorized, so no energy from batteries or other external fuel sources is necessary.

Biomedical engineer and locomotion physiologist Greg Sawicki displaysexoskeleton devices, including ones that increase human walking efficiency by 7 percent. Credit: North Carolina State/University of North Carolina-Chapel Hill.

“The unpowered exoskeleton works like a catapult, said Gregory Sawicki, a biomedical engineer and locomotion physiologist in the joint North Carolina State/University of North

Carolina-Chapel Hill Department of Biomedical Engineering. “It has a spring that mimics the action of your Achilles’ tendon, and works in parallel with your calf muscles to reduce the load placed upon them.”

The device’s clutch engages the spring only while the wearer’s foot is on the ground, enabling it to store and then release elastic energy. “Later, it automatically disengages to allow free motion while the foot is in the air,” Sawicki said.

In a recent study, nine able-bodied adults — after some practice training — strapped an exoskeleton on each leg and walked at a normal pace on a treadmill. The same people also walked without exoskeletons for a baseline comparison.

The researchers tested exoskeletons with springs set to various stiffness levels. The spring that provided the greatest benefit was only moderately stiff. Walking with exoskeletons with springs that were too stiff or too loose resulted in normal or higher-than-normal energy efforts for the study participants.

“A 7 percent reduction in energy cost is like taking off a 10-pound backpack, which is significant,” Sawicki said. “Though it’s surprising that we were able to achieve this advantage over a system strongly shaped by evolution, this study shows that there’s still a lot to learn about human biomechanics and a seemingly simple behavior like walking.”

An exoskeleton for children

A University of Houston engineer is developing a pediatric exoskeleton designed to help children with spinal cord injuries and related mobility disorders walk.

When completed, the system will be customized to its user and designed to grow as the child grows, said Jose Luis Contreras-Vidal, a professor of electrical and computer engineering. There are currently no pediatric exoskeletons that allow children to walk independently, he notes.

Contreras-Vidal is currently working on algorithms that will be able to detect electrical activity in the brain and convert the signal into various exoskeleton movements. The brain-machine interface is designed to work by collecting information through sensors attached to the outside of the user’s scalp.

An exoskeleton for children must be both sturdy and lightweight. Contreras-Vidal plans to build the device out of a carbon-fiber composite.

“Children are playful,” Contreras-Vidal observed, and an exoskeleton needs to help them interact with other children, rather than serving to set them apart. “We don’t want this to be a barrier; we want it to be a tool for the child,” he said.

Development of the exoskeleton is already under way in the university’s Non-Invasive Brain-Machine Interface Systems Laboratory. Contreras-Vidal’s team has already used a 3D printer to inexpensively produce a series of exoskeleton prototypes.

“We were able to print until we got it right,” he said. Contreras-Vidal hopes to begin testing a prototype with children later this year, leading eventually to clinical trials and commercial production.

Contreras-Vidal feels that the exoskeleton’s potential will be limited only by the researchers’ imaginations. “The tools for developing a technology are no longer the bottleneck,” he said. “It’s creativity.”