Scientists have developed artificial nerves that could one day enable amputees to feel heat, cold and touch with their prosthetic limbs.
The technique uses thin plastic filaments made from a material called Pedot that can conduct electrical signals. They are wired into the patient’s real nerves and stretch to the ends of the limb.
The scientists behind the invention believe it could eventually enable amputees to play the piano or feel the brush of a real hand against the surface of their man-made one.
Paul Cederna, professor of plastic surgery at the University of Michigan, said: “Someone who has lost both their hands would be able to hold their child’s hand again and feel the warmth.
“So many things we do each day rely on that light touch and pressure sensation feedback, from holding a paper cup of hot coffee to holding a phone against your ear.”
Cederna’s research was unveiled last week at the annual American plastic surgeons’ conference in Seattle. It is being funded by the American military and is one of a number of efforts to improve the treatment of people with missing limbs, sparked partly by the wars in Afghanistan and Iraq.
Since the beginning of last year, 55 British servicemen have had at least one limb amputated.
The most advanced computerised limbs fitted at the Headley Court defence medical centre in Surrey are moved wirelessly by controllers in the patient’s pocket.
The use of Pedot opens up the possibility of effective two-way communication between artificial limbs and the brain because, according to Cederna, it reacts twice as quickly as normal nerve cells. It is also 10 times more efficient at transmitting the nervous system’s electrical signals than the metal materials that are currently used.
In addition, the use of Pedot has been shown to encourage new nerve growth.
“It would feel the same as the real thing,” said Cederna. “There would be no re-learning required from the brain because the nerves already carry all those signals.”
The plastic filaments that transmit the signals will have to be fitted with hundreds of thousands of nanosensors, currently under development, that can distinguish touch, cold, warmth and other sensations.
“Our limitation is going to be how sophisticated they can make the prosthetic for us,” said Cederna.
“If they can provide a prosthetic that has enough sensors to provide sensation for light touch and pressure sensation, then we can provide the communication between it and the patient’s brain.”
Cederna has developed the technology using laboratory animals, but he hopes to begin human trials in three years and to make the technology available to patients within 10 years.
Each year in Britain about 5,000 people have an artificial limb fitted. More than 80% are legs and feet, but the ability to communicate with the patient’s brain will have the greatest impact for artificial hands and arms which require more complex movement.
John Butterworth, 23, is a former RAF weapons engineer who lost his left hand in a rocket attack on Basra airbase, Iraq, in 2007. He is training for a place in Britain’s Paralympic cycling team.
Sometimes he uses a hand with a metal “split hook” that provides lifting power and control. He sometimes changes it for a more discreet i-Limb, covered in artificial skin. This is operated by sensor pads on the surface of his skin that detect electrical signals from the muscles in his stump.
“The split hook is easier to use but with the i-Limb people don’t stare as much,” he said. “I wouldn’t feel happy to pick up a cup of coffee with it.
“You can’t feel pressure and you’ve got to keep looking at the hand to make sure it’s gripping properly. It would be fantastic if it was possible to feel things properly with it.”
Sarah Storey, the Paralympian swimmer and cyclist who was born without a left hand, said: “If it worked on someone like me, it would be fantastic. But I’ve always wondered, if someone could give me a hand, whether I’d know what to do with it.”
Michael Fox, a consultant at the Royal National Orthopaedic hospital in London and who works with amputees at Headley Court, said there would be technical problems to be overcome before such limbs were possible. “You have to be careful when you’re talking about transmitting sensation back to the brain from a limb,” he said.
“There is a great risk of the brain receiving wrong signals. I am excited by these advances but it’s very early days.”
The Sunday Times