The bionic leg that connects to your brain

Using electrodes the size of a human hair...

A BIONIC man is a step closer after scientists created a prosthetic leg which the wearer can really feel.

Although prosthetic limbs are far more advanced than in the 20th century, their flaw is that they are not really part of the amputee’s body.

Wearers cannot feel them, so are at constant risk of falling and must keep an eye on the leg’s position at all times.

Now researchers have solved the problem, allowing people to feel every time their prosthetic foot hits the ground or the knee bends to walk.

Their new leg does this by sending electrical signals to four electrodes implanted into the tibial nerve in the thigh. The nerve would normally pick up feeling from the foot and lower leg and alert the brain, so can be hijacked to do the same for a metal leg and rubber foot with eight sensors attached.

The leg has been found to work for three road accident victims with abovethe-knee amputations, who were able to climb stairs 30 per cent faster and avoid tripping over unseen obstacles.

Djurica Resanovic, one of the amputees, who lost his leg in a motorcycle crash, said: ‘After all of these years, I could feel my leg and my foot again, as if it were my own leg. It was very interesting. You don’t need to concentrate to walk, you can just look forward and step. You don’t need to look at where your leg is to avoid falling.’

Professor Stanisa Raspopovic led the study at Swiss university ETH Zurich.

‘You don’t need to concentrate to walk’

He said: ‘When prosthetics do not work properly, people fall and suffer severe injuries. These electrodes may require less effort to control a leg, because it feels like part of someone’s own body.’

The holy grail for scientists making prosthetic legs, arms and hands is for those who use them to be able to feel their movements. But they have made little progress using electrodes attached to people’s stumps. Only limited feeling has previously been restored in those with amputations above the knee.

The researchers succeeded by embedding electrodes only a little larger than a human hair in the tibial nerve in the thigh. These pick up Bluetooth electrical signals created from seven sensors in the prosthetic foot and one in the knee, to detect the angle at which it bends.

They allowed amputees to walk over an uneven surface, stepping on plastic rocks up to 7cm (2.8in) high while wearing glasses which stopped them looking down to avoid them.

The researchers, whose work is published in the journal Science Translational Medicine, found amputees slipped and had to grip or lean on a handrail 40 per cent of the time when the electrodes were turned off. But they stumbled only five per cent of the time when the electrodes were on and could feel the plastic rocks under their feet. The three men in the study could climb a flight of five stairs 30 per cent faster using the technology.

Brain recordings showed walking – usually hard with an artificial leg – took no more effort than sitting. In a questionnaire, wearers said the leg felt more like their own. Dr Ben Metcalfe, a neural engineering expert from the University of Bath, said: ‘The technology in this work is approaching a like-for-like leg replacement, rather than simply a mechanical stump.

‘This will transform the way we repair injury.’ Dr Bryce Dyer, a biomedical engineering expert from Bournemouth University, said: ‘This could be important in the future as it would allow us to design more effective artificial limbs which are better for everyday tasks and reduce the chances of an accident.’