A man whose lower leg was severed in a motorcycle accident has become the first person to be fitted with a thought-controlled bionic leg.
Zac Vawter, 32, was fitted with the limb by Levi Hargrove of the Rehabilitation Institute of Chicago who told NBC News: "This is a groundbreaking development. It allows people to seamlessly transition between walking along level ground and going up and down stairs and slopes."
The leg reacts to Vawter's desire to move through electrodes that pick up brain signals travelling down his spinal cord and through peripheral nerves.
Though scientists have already developed artificial arms that react to thought, this is the first leg to do so.
Mr Vawter, who lost his leg four years ago, described the new limb as "a big improvement compared to my regular prosthetic leg" because it "responds quickly and more appropriately, allowing me to interact with my environment in a way that is similar to how I moved before my amputation".
Vawter has been closely involved in the development of the limb, visiting scientists regularly to test it and offer feedback.
"In my mind, it's still the same thing in terms of moving my ankle down or up, or extending my leg forward or back," Vawter told Bloomberg.
"It's just like I would normally walk. It's not special training or buttons or tricks. That's a big piece of what I think is groundbreaking and phenomenal about this work."
Troy Turner, a member of the scientific advisory panel of The Amputee Coalition in Manassas, Virginia, said the project "represents the first true effort at letting someone control their prosthetic leg in a way that's very similar to biologic control".
Working with an $8 million grant from the US armed forces, the team of scientists hope the limb could be available for America's one million amputees in about three years.
However Mr Hargrove says the team still have work to do to fine-tune the device by making It less noisy, and reducing the number of malfunctions.
"If you're using a bionic arm and it misbehaves, the elbow may move slightly. If the prosthetic leg misbehaves ... that could be quite a safety issue," Mr Hargrove said.