CHICAGO - Zac Vawter considers himself a test pilot.
After losing his right leg in a motorcycle accident, the 31-year-old software engineer signed up to become a research subject, helping to test a trailblazing prosthetic leg that's controlled by his thoughts.
His whirring, robotic leg responds to electrical impulses from muscles in his hamstring.
And he will put this "bionic" leg to the ultimate test today, when he attempts to climb 103 flights of stairs to the top of Chicago's Willis Tower, one of the world's tallest skyscrapers, in just one hour.
If all goes well, he'll make history with the bionic leg's public debut.
Mr Vawter will think, "climb stairs", and the motors, belts and chains in his leg will synchronise the movements of its ankle and knee, AP reported.
A team of researchers will cheer him on and note the smart leg's performance.
But it will still take years of refining before it will be available on the market.
"Somewhere down the road, it will benefit me and I hope it will benefit a lot of other people as well," Mr Vawter said about the research at the Rehabilitation Institute of Chicago.
"Bionic" - or thought-controlled - prosthetic arms have been available for a few years. But with leg amputees outnumbering people who have lost arms and hands, the Chicago researchers are now focusing more on lower limbs.
The US$8 million (S$9.8 million) project is funded by the US Department of Defence.
The Willis Tower climb will be the bionic leg's first test in public, said lead researcher Levi Hargrove of the institute's Center for Bionic Medicine.
The climb, called "SkyRise Chicago", is a fundraiser for the institute with about 2,700 people climbing.
To prepare, Mr Vawter and the scientists have spent hours adjusting the leg's movements. Recently, 11 electrodes were placed on the skin of his thigh to feed data to the bionic leg's microcomputer.
Mr Vawter likes the bionic leg. Compared to his regular prosthetic, it's more responsive and more fluid, he said.
As an engineer, he enjoys learning how the leg works.
It all started with surgery in 2009.
When his leg was amputated, a surgeon repositioned the residual spaghetti-like nerves that normally would carry signals to the lower leg and sewed them to new spots on his hamstring. This would later allow him to use a bionic leg.
The surgery is called "targeted muscle reinnervation" and is like "rewiring the patient", Mr Hargrove said.
"And now when he just thinks about moving his ankle, his hamstring moves and we're able to tell the prosthesis how to move appropriately."
Mr Hargrove was inspired by fellow Canadian Terry Fox, who attempted a cross-country run on a regular artificial leg to raise money for cancer research in 1980.
Mr Daniel Ferris of the University of Michigan said: "Experts not involved in the project say the Chicago research is on the leading edge.
"Most artificial legs are passive. They're basically fancy wooden legs," he explained.
While other such legs have motorised or mechanical components, they don't respond to the electrical impulses caused by thought.
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