Prosthetics have come a long way over the past several decades. But to researchers at the University of Michigan, they hadn't come far enough.
Experts there have developed an artificial foot that recycles energy typically wasted between steps, making it easier than ever for amputees to walk. The work is outlined in a recent edition of the journal PLoS ONE.
Most foot prostheses don't factor in the force an ankle uses to push off the ground, so prosthetics users typically expend 23 percent more energy while walking than non-amputees, according to the researchers. "For amputees, what they experience when they're trying to walk normally is what I would experience if I were carrying an extra 30 pounds," said Art Kuo, a biomedical and mechanical engineering professor who co-authored the report.
So Kuo and Steve Collins, associate research fellow at Delft University of Technology in the Netherlands, developed a device that grabs wasted energy and converts it to power for a future ankle push off. When the foot naturally captures the wasted energy, a microcontroller tells it to return the energy into the system at the right time. Click to watch a video showing the device in action.
The device let users expend less energy -- down to 14 percent from 23 percent -- than those walking with typical prosthetics, according to the researchers. "We know there's an energy penalty in using an artificial foot," Kuo said. "We're almost cutting that penalty in half."
The device is the first of its kind, he said, to release energy to supplement push off without an external power source. Other devices can also store and return energy, but they don't give the user a choice as to when and how, Kuo said. The artificial foot is powered by less than one watt of electricity through a small, portable battery.
The research was funded by the National Institutes of Health and the Department of Veterans Affairs. The device is being tested on amputees at the Seattle Veterans Affairs Medical Center. Commercial devices based on the technology are under development.
Photo: Energy-saving prosthetic foot / By Steve Collins