Scientists have hailed the first test of a "groundbreaking" mind-controlled artificial leg as an overwhelming success.

American Zac Vawter lost his right leg from the knee down in a motorcycle accident in 2009. But last year he was fitted with an experimental prototype of a new artificial limb which is directly controlled by his thoughts.

Most artificial legs are either basic mechanical devices, or can have more complex direct controls.

But the Rehabilitation Institute of Chicago (RIC)'s device - the result of a four-year, $8 million study detailed in the New England Journal of Medicine - instead directly interacts with his brain via a connection with the sciatic nerve. By monitoring these signals and adjusting how the limb responds, the team was able to accurately map his thoughts to the operation of the limb.

"This provided robust and intuitive control of ambulation - with seamless transitions between walking on level ground, stairs, and ramps - and of the ability to reposition the leg while the patient was seated," the study says.

Since using it Vawter has been able to climb the 103-storey Willis Tower in Chicago, and improve his day-to-day life with a "seamless" range of motion. "I just interact with my environment how a normal person would," Vawter said.\

Take a look at how it works, below.