A man who lost his arm and was making do with a prosthetic hand has now had his sense of touch restored - the first time this has ever been done.
Dennis Aabo Sorensen of Denmark had his left arm amputated after a fireworks accident nine years ago.
Today he can feel, thanks to researchers who embedded electrodes in his arm, and touch sensors in a prosthetic hand that work to stimulate his surviving nerves.
Sorensen is now able to recognise different objects by their feel, and hold them, according to an article in the journal Science Translational Medicine.
"I could feel things that I hadn't been able to feel in over nine years," Sorensen was quoted as saying.
Sorensen is the first to test the prosthesis, and if it proves workable in the long term, it could greatly improve the performance of prosthetic limbs and the quality of life for their users.
The ability to feel is critical for the dexterity humans need to perform basic tasks with their hands. Tactile information tells a person how much force to use when grasping objects as rigid as a coffee mug or as delicate as a grape, the article said.
"Without sensory feedback from our hands, we would have difficulties performing even the most basic activities of daily living," said Sliman Bensmaia, a neuroscientist at the University of Chicago, who was not involved in the research.
Many researchers are developing prosthetic systems aimed at restoring people's ability to control their arms or legs after amputation, spinal cord injury or disease. And increasingly, scientists are also working on incorporating touch-sensitive feedback. The new study is the first to demonstrate such feedback successfully in a human patient.
The team working with Sorensen was headed by Silvestro Micera, a neural engineer at the Scuola Superiore Sant'Anna in Italy.
The team connected touch sensors in the artificial hand to electrodes surgically embedded in the remains of nerves in Sorensen's upper arm. Computer algorithms converted the signals from the sensors into a form the nerves could detect.
During the clinical trial, Sorensen tested the hand, sometimes wearing a blindfold and earplugs so he could rely only on his sense of touch when using the hand. He was able to control how forcefully he grasped objects, and feel their shape and stiffness - and could also detect hard, medium and soft objects.
He found that the artificial sense of touch was similar to the natural feeling he experienced in his other hand.
Unlike previous efforts such as vibrating the skin, the new approach provides "anatomically appropriate feedback", researchers said.
The work is still in its preliminary state as it involved only one person. Also, to be a safe and useful device, the system would need to be fully implantable under the skin, and would need to keep working over a long time.
