A 36-year-old man from Denmark has become the first amputee in the world to "feel" in real-time with a sensory-enhanced artificial hand. The prosthetic is surgically wired to nerves in his upper arm, allowing him to handle objects and instantly sense what they feel like.
The sensory system connected to the artificial hand was created by Silvestro Micera and colleagues from the École polytechnique fédérale de Lausanne (EPFL) in Switzerland and the Sant'Anna School of Advanced Studies (SSSA) in Italy.
A prototype of the technology was tested in February last year, findings of which have recently been published in the journal Science Translational Medicine.
To create sensors in an artificial hand that detect information from touch, the scientists measured tension in artificial tendons that control finger movement. This measurement was turned into an electrical current.
Because the central nervous system is unable to understand this electric current, the researchers used computer algorithms to change the electric signals into an impulse that can be understood by sensory nerves.
These new impulses were then sent through wires into four electrodes that were surgically implanted into the nerves of the upper arm, therefore producing the sense of touch.
'The sensory feedback was incredible'
Dennis Aabo Sørensen lost his left hand in a firework accident 9 years prior to undergoing surgery for the new sensory system at Gemelli Hospital in Rome in January 2013.
Neurologist Paolo Maria Rossini led the surgery, which required implanting "transneural" electrodes into the ulnar and median nerves of Sørensen's left arm.
Sørensen then underwent 19 days of preliminary tests, before having the prosthetic hand attached to the electrodes every day for 1 week.
The scientists note that the electrodes - created by Thomas Stieglitz and colleagues at Freiburg University in Germany - were ultra-thin, meaning very weak signals could be transmitted directly to the nervous system.
The researchers admit they were concerned that, since the nerves in Sørensen's arm had not been used in 9 years, they could have reduced sensitivity.
However, from a series of laboratory tests that required Sørensen to wear a blindfold and earplugs while grasping various objects using the sensory-enhanced artificial hand, the scientists found the outcome of the surgery to be successful.
Sørensen was able to detect the strength of his grasps on the objects, as well as the shape and consistency of them.
"The sensory feedback was incredible. I could feel things that I hadn't been able to feel in over 9 years. When I held an object, I could feel if it was soft or hard, round or square."
Because of safety restrictions within clinical trials, Sørensen had the electrodes removed from his arm after 1 month.
But the researchers say they are confident that the electrodes could remain implanted with full functionality for many years without causing any damage to the nervous system.
Sørensen and Micera explain how the sensory system works in the video below:
The future of the bionic hand
Although the scientists say this study is the first step toward a bionic hand, they note that it will be many years before a sensory-enhanced prosthetic hand is available.
They say their next step will involve making the electronics for the sensory feedback smaller so they can be used for a portable prosthetic.
The researchers also want to improve the sensory technology in order to create more detailed sensations from touch and improve awareness surrounding the angular movement of fingers.
For now, Sørensen has reverted to using a commercial prosthetic hand that detects muscle movement in his stump. This allows him to hold objects and open and close his hand.
Although the study meant he was only able to experience touch in his left hand for a short period of time, Sørensen says he was pleased to take part.
"I was more than happy to volunteer for the clinical trial, not only for myself, but to help other amputees as well," he says.
Last year, Medical News Today reported on a study detailing neural patterns that occur when animals touch objects - findings that could result in the creation of touch-sensitive prosthetic limbs that communicate directly with the brain.