Man with 'bionic' leg to climb Chicago skyscraper

• Zac Vawter lost his right leg in a motorcycle accident
• He's helping to test a trailblazing prosthetic leg
• He attempts to make history Sunday by climbing Willis Tower

Having to walk up a flight of stairs is a nearly impossible task for anyone who has had a leg amputation. It's tiring and dangerous.

That is unless you're Zac Vawter, who had his leg amputated above the knee after a motorcycle accident three years ago. Sunday, he will use a new bionic leg to climb 2,109 stairs (103 flights) of the Willis Tower during the Rehabilitation Institute of Chicago's fourth annual SkyRise Chicago stairclimb.

"Other artificial limbs are passive and have to be dragged behind you when you climb stairs," says Levi Hargrove, the director of neural engineering at RIC's Center for Bionic Medicine. "People have to move that kind of leg around from the hip and swing it out to the side. This leg allows the patient to walk normally."

Vawter, 31, has been involved in research at RIC since shortly after his accident. With this leg, which has an "actively powered" knee and ankle and is controlled by neural signals from his brain, he can take two stairs at a time, if he wants to, and walk at a faster pace than his regular prosthetic leg allows. It's not built for running fast, but you could "get across a street quickly to get out of the way of a bus," says Hargrove, "and down the road it will allow faster speeds."

When confronted with stairs, many disabled people opt to take elevators, which can make them become sedentary. Regular prostheses are passive in design and can store or dissipate energy, but cannot provide power. They also change a person's gait and can cause hip and back problems, says Hargrove.

Using such prostheses also requires 60% more energy during level walking than for an able-bodied walker, says Michael Goldfarb, director of the Center for Intelligent Mechatronics at Vanderbilt University. Goldfarb developed the bionic leg using the latest technology in microcomputers and batteries. It is built with aluminum alloys, weighs about 9 pounds, and its motion closely resembles a normal gait.

"It's an amazing piece of equipment," says Vawter. "This is a major improvement on going up and down stairs. With my other prosthesis I have to be aware of what it's doing and where it is at any given moment. This one is more natural, closer to a normal leg."

The Department of Defense is behind the push to improve prosthetic devices in an effort to improve the lives of wounded soldiers. The DOD donated $8 million in research money for the development of the leg Vawter is testing. It could be available commercially in several years, Hargrove says, possibly sooner.

The developmental role undertaken by Hargrove is to improve the neural interface between "what Zac is thinking and how the leg responds. Our group is developing a better steering system so he doesn't have to do anything unintuitive to control the leg. There's no remote involved."

What's at work in the neuroscience: When Vawter's surgeon removed his leg, he transplanted nerve cells from the lower leg to his hamstring. Sensors attached on the skin near those nerves communicate information to the bionic leg's microprocessor.

Vawter will make Sunday's climb with his father and longtime friend. "We'll have a good time,'' he says. "This is going to be a lot of fun."