A team of scientists has come up with a groundbreaking device that, when refined, may offer ordinary walkers and those with impaired muscles a way to walk using less energy. The scientists, including two from the Carolinas, see it as a boon to firefighters, postal employees and others who spend long hours on their feet, as well as backpackers who want an easier climb up those hills.
And it may offer hope to people suffering from a host of neuromuscular problems, from incomplete spinal cord injuries to cerebral palsy, Parkinson’s disease, and stroke, says one of its creators, Dr. Greg Sawicki.
Building the carbon-fiber exoskeleton “started out as “a grand challenge … to build robotic devices that had no power that could provide assistance with human walking,” Sawicki said. Motors were avoided because of their weight and expense.
Sawicki is a biomedical engineer and locomotion physiologist in the joint N.C. State/University of North Carolina-Chapel Hill Department of Biomedical Engineering. Other team members are Dr. Steven Collins of Carnegie Mellon University and Dr. Bruce Wiggin, a former NCSU graduate student.
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How it works
Attached to the lower leg, a lightweight carbon fiber frame holds a small clutch assembly behind the calf and a spring behind the ankle. The two are connected by a Kevlar cord. A stabilizing extension goes into the shoe.
When the foot begins a step, the clutch grabs the cord. As the step ends and the foot lies flat on the floor, the spring is pulled to its tightest position and the tension is greatest. The spring’s natural response to the tension is to relax, which helps propel the body forward into the next step. Then the clutch disengages, so that the foot and leg can swing freely into the next step.
The action mimics that of the calf muscle and Achilles tendon, but by adding extra energy, reduces the demand on them.
In seven-minute treadmill tests of nine subjects, the reduction in energy averaged 7 percent.
“A 7 percent reduction in energy cost is like taking off a 10-pound backpack, which is significant,” Sawicki said.
Based on his experimental wearing of the device, it’s comfortable, he said. The whole thing weighs a little more than a pound, about what a loafer weighs.
Challenges to come
Sitting down is no problem while wearing the exoskeleton, Sawicki said, but there are other aspects that will require attention before it’s ready for use.
“Going up and down stairs is not very easy at all,” he said. The spring attachment can get caught on stairs.
Also, test results were obtained at only one speed, a comfortable walking speed on the treadmill. Running would require a spring adjustment.
Going up and down hills is another research challenge.
“We’re keenly aware of all these issues,” Sawicki said.
Those and others will be addressed in coming months and years, as the team proceeds.
Help can’t come too soon for the hundreds of people who emailed the team after they published an account of their work April 1 in the journal Nature and a video appeared on an NCSU website.
The writers all had difficulty walking because of various injuries and disease. They wanted to know, “Where can I buy one?” or they simply demanded, “Send me one.”
“On the one hand, you feel really great” after reading the emails, Sawicki said, because of the opportunities the exoskeleton may offer in the future.
On the other hand, he regrets that solutions for many are so far away. They represent “the goal over the next five to 10 years.”
For now, he emphasizes, the exoskeleton is still conceptual, “a very valuable research tool” The team, however, is actively looking for a partner in the product design and development field.
“The implication is that it is possible to use man-made devices to improve performance of already very well-tuned systems,” he said.
“We found a way to make something that evolved over millions of years a little bit better.”
A few of the many areas where Sawicki thinks the exoskeleton might eventually help:
▪ Battlefield injuries. Because of improved medical care, wounded soldiers now are often able to keep their limbs, but in an impaired state, he said. The exoskeleton could take some of the workload from damaged areas.
▪ Peripheral neuropathy in diabetes patients. Even though the muscles are not getting the strong signal from the nerves that they used to, Sawicki said, if movement can be preserved, perhaps good cardiovascular action can be preserved, too. “Muscles respond to being used. If we could provide ways to give function, maybe we could avoid some of the more drastic measures that are taken (like amputation.)”
▪ Strokes, which leave patients with varying degrees of weakness. “The exoskeleton may work when there’s not much going on in the leg. We’re not sure of that yet,” he said. It’s conceivable it could act like a prosthesis “and completely take over what the calf muscle and Achilles tendon would be doing,” he said. But that’s conjecture “until we get down and dirty and start doing the studies.”