A man who lost his right leg in a motorcycle accident has reached the top of one of the world's tallest skyscrapers with the help of a bionic leg.
Zak Vawter became the first person ever to get to the top of Chicago's 103-storey Willis Tower wearing a mind-controlled prosthetic limb.
The 31-year-old completed the task in under an hour - and without taking a single break.
Mr Vawter showed off his smart limb for the first time during an annual stair-climbing charity event organised by the Rehabilitation Institute of Chicago, where he is receiving treatment.
Nearly 3,000 climbers participated in this year's SkyRise Chicago, climbing about 2,100 steps to the Willis Tower's SkyDeck level, to raise money for the institute's rehabilitation care and research.
Bionic - or thought-controlled - prosthetic arms have been available for some time, thanks to pioneering work done at the Rehabilitation Institute.
The computerised prosthetic weighs about 10lbs and has two motors which respond to electrical impulses from muscles in the hamstring.
"It's fantastic hardware. We didn't have any issues with it at all. It carried him up 103 storeys," said Levi Hargrove of the institute's Centre for Bionic Medicine.
To prepare for his pioneering climb, Mr Vawter practised on a small escalator at a gym, while researchers spent months adjusting the technical aspects of the leg to ensure that it would respond to his thoughts.
When Mr Vawter goes home to Yelm, Washington, where he lives with his wife and two children, the experimental leg will stay behind in Chicago.
Researchers will continue to refine its technology as it is still years away from being marketed.