iWalk Inc.

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

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: 

• Bionic arms are spreading wider
• Stretchy solar cells to power e-skin
• Robot walks 4.5 miles non-stop

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 msnbc.com. Find her on Twitter or Google+, and join our conversation on the Cosmic Log Facebook page.

Jim Watson / AFP - Getty Images

Todd Kuiken, director of the Center for Bionic Medicine and director of amputee services at the Rehabilitation Institute of Chicago, explains the technology behind the bionic arm being used by Glen Lehman, a retired Army sergeant who received targeted muscle reinnervation surgery after he lost his arm in Iraq,

It's been nine years since the Center for Bionic Medicine installed its first nerve-controlled prosthetic limb — and during that time, bionic arms have become stronger ... faster ... better. They may not yet match the fictional body parts sported by Steve Austin in "The Six-Million Dollar Man," but they're giving scores of amputees the opportunity to lead a more normal life.

Take Glen Lehman, for example: Lehman, a retired Army sergeant who lost his right arm three years ago in a grenade attack in Iraq, showed off his bionic arm this week in Washington during sessions at the annual meeting of the American Association for the Advancement of Science. Lehman twisted and closed a lifelike hand, at the end of a prosthetic arm that took commands from the nerves once leading to his real hand.

Glen Lehman takes a look at his bionic hand.

A video released at the AAAS meeting shows Lehman holding a food tray, grabbing a bag of snacks and handing a drink bottle with the bionic arm, with movements that are close to natural.

"My arm is pretty much in tune with my thoughts," he told reporters Thursday.

That represents a big advance over old-style prosthetic limbs — even over the first bionic arm, which was given to double-amputee patient Jesse Sullivan in 2002. The key innovation was pioneered back then by Todd Kuiken, director of the Center for Bionic Medicine and director of amputee services at the Rehabilitation Institute of Chicago.

Kuiken calls his technique "targeted muscle reinnervation," or TMR. The procedure involves taking the nerves that once led to the missing limb and rerouting them to intact muscles on what's left of the arm. The flexing of those muscles, in turn, sets off actuators that reproduce the movements of the elbow and hand.

"Muscle becomes the biological amplifier," Kuiken explained.

CBM / RIC

Glen Lehman's bionic arm is hooked up to electrical leads that are implanted in his intact upper-arm muscles. Nerves that once went to his amputated arm have been re-routed to go to those particular muscles.

So far, more than 50 amputees have been outfitted with TMR-enabled bionic arms, including more than dozen combat veterans like Lehman. Several surgeons have been trained in the procedure. Lehman's arm surgery was performed by Martin Baechler, a surgeon at Walter Reed Medical Center. The technique could spread wider in the years ahead: This week marked the launch of the first-ever training video for TMR, developed by Kuiken and Gregory Dumanian of Northwestern University's Department of Plastic Surgery.

Kuiken and his colleagues have a couple of tricks they're planning to add to bionic arms — including restoring skin sensation of the missing arm (which involves sensory nerves implanted into tissue) and providing touch feedback for artificial hands (which involves wiring up the hands with sensors that send impulses back into the nerves).

For now, the technique has been used only in arms, and not in legs. "That's an area we've just started to look at," Kuiken told reporters. He explained that the challenge for artificial legs is different from what it is for hands: There are fewer parts that have to be controlled, but those parts have to be controlled very, very well. If there's just one wrong step out of 1,000 that leads to a fall, "that's a problem," Kuiken said.

Other researchers gave a status report on their progress in developing thought-controlled tools for people with disabilities. Here's a sampling:

• Researchers at Switzerland's Ecole Polytechnique Federale de Lausanne are developing brain-computer interfaces that rely on a "thinking cap" — a skullcap outfitted with electrodes that take in electroencephalogram readings and feed them to a computer program. The software uses statistical analysis to translate the typically low-resolution EEG signals into more precise commands. Such a system lets subjects drive a wheelchair or a camera-equipped robot using their thoughts alone, as shown in the video below. Studies have shown that, with training, the effort isn't overly taxing. "People can truly use brain interfaces 24 hours a day, seven days a week," research team leader Jose del R. Millan said.

• A Pentagon-funded project is developing a direct brain-to-bionic control system that involves tiny arrays of electrodes implanted on the surface of the brain. The electrodes read activity from individual neurons, producing signals that can control a robotic limb. So far, the procedure has been tested only in monkeys, but tests with humans are expected to begin late this year. "Our animal studies have shown that we can interpret the messages the brain sends to make a simple robotic arm reach for an object and turn a mechanical wrist," Andrew Schwartz, a neuroscientist at the Pitt School of Medicine, said in a news release. "The next step is to see not only if we can make these techniques work for people, but also if we can make the movements more complex."

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