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Actuated ankles make fake feet fitter

A new design for a prosthetic foot comes close to letting wearers walk normally.
A new design for a prosthetic foot comes close to letting wearers walk normally.iWalk Inc.

A bionic foot with a battery pack could put the spring back in the step of people who wear leg prostheses. 

Prosthetics company iWalk and an MIT team have designed a bionic ankle that uses energy from a battery to push the foot forward as the person wearing it takes a step.

When people walk, their calves and ankles do 80 percent of the work. As the pace picks up, muscles in the ankles take on more of the load, to push the leg away from the ground and move the body forward. 

But the prostheses that people with leg amputations wear today are only designed to support the weight of the body. They're more of a prop than a pusher, and the wearers burn more energy while walking than they would with a natural leg. While this makes for a good workout, it makes walking slower.

The spruced-up foot design from the MIT Media Labs' Biomechatronics Group contains a battery that's activated while the person wearing it takes a walk. It builds on previous designs of the powered ankle that the lab and others have built, but "one of the biggest steps forward is that now it's condensed down into a small size," Alena Grabowski, who worked on the project, told me.

In earlier versions of the fake foot, all the electronics and batteries were carried separately in a backpack. But this foot is about the size and shape of a real leg. It weighs 4.4 pounds (2 kilograms), the average weight of the leg of a person who weighs 176 pounds (80 kilos). 

So far, people who wear it like it. "They seem very excited and thrilled about it, and that's a very fun thing," Grabowski said.  

Grabowski tested the prosthesis with several test subjects who usually wear commercial non-automated prostheses, to see how fast people walked, and how comfortably and easily they could do it. The results of the study are published in Wednesday's issue of the journal Proceedings of the Royal Society B. "We could confirm with statistical power that the prosthesis was doing what it was supposed to do," Grabowski says.

Further work will go toward making the bionic foot lighter and more stable, but in the meantime, iWalk is making plans to manufacture and sell this design.

More about bionic body parts: 

Grabowski's co-author on the research paper, "Bionic Ankle-Foot Prosthesis Normalizes Walking Gait for Persons With Leg Amputation," is MIT's Hugh Herr, chief of the Biomechatronics Group and co-founder of iWalk.

Nidhi Subbaraman writes about science and technology at Find her on Twitter or Google+, and join our conversation on the Cosmic Log Facebook page.