A prototype prosthetic hand containing sensors, wired to nerves in amputee Dennis Aabo Sørensen’s arm, has given him the ability to feel objects for the first time in nine years. Now its creators plan to miniaturise the electronics required in order to make a viable permanent prosthetic.
A team led by Silvestro Micera, associate professor in neurology at Swiss-based technology institute EPFL (École polytechnique fédérale de Lausanne), designed the hand to interact with the body’s own nervous system.
Sensors on the fingers that detect information about touch, send signals to artificial tendons in the hand. The tendons respond with movements that send an electrical current to electrodes connected to the body’s peripheral nervous system, forming a link from the prosthetic to the brain.
Using computer algorithms, scientists from the EPFL and the Scuola Supriore Sant’Anna in Pisa, where Micera also works, transform those electrical signals into an impulse that the sensory nerves can interpret.
The sense of touch was achieved by sending the digitally refined signal through wires into four electrodes surgically implanted into what remains of the patient’s upper arm nerves.
In an operation in January last year doctors at Rome’s Gemelli Hospital, led by neurologist Paolo Maria Rossini, implanted transneural electrodes into the ulnar and median nerves of Dennis Aabo Sørensen’s arm. The father of three had lost his lower left arm nine years earlier in an accident involving fireworks. After 19 days of preliminary tests, Micera and his team connected Sorensen and his prosthetic arm to the electrodes every day for a week.
The ultra-thin electrodes were developed by biomedic Dr Thomas Stieglitz’s research group at Germany’s Freiburg University. They allow weak electrical signals to be relayed directly into the nervous system via artifical sensors in the prosthetic hand’s fingers.
“The hand has several sensors attached to each tendon of each finger and we can use these sensors to understand the level of force the patient was performing while grasping an object and we use this force information to deliver very precise stimulation to the various sensory nerves in order to restore this real time sensory feeling into the nervous system,” said Micra.
Micera says the tests showed that “it’s possible to restore a real-time sensory feeling in this patient while he was controlling this hand.”
36-year-old Sørensen descirbed the sensory feedback he felt as “amazing”.
“The first time they turned it on and they worked with the new hand it was amazing because suddenly I could feel things that I haven’t been able to in many years and it was kind of, you can feel round things and hard things and soft things, and that was quite amazing,” he said.
During a series of tests Sørensen, wearing a blindfold, could grasp objects and identify their shape and whether they were hard or soft.
The electrodes were removed from Sørensen’s arm after one month owing to safety restrictions imposed on clinical trials, although the scientists are optimistic that they could remain implanted and functional without damage to the nervous system for many years.
Sorensen now wears the commercial prosthetic that he was using before, which detects muscle movement in his stump, allowing him to open and close his hand and hold onto objects, but without sensory feedback.
The researchers are now working on miniaturising the sensory feedback electronics to produce a portable prosthetic, as well as fine-tuning the sensory technology.
“The next step is to be able to bring these results to long-term applicability, so to have the patient using this not for four weeks in the laboratory environment, but long-term, for months or years in his or her own environment, at home and to do that we are also miniaturising, work on miniaturising the electronics to be placed in the patient for this kind of achievement, said Micera.
The study is published in February’s edition of Science Translational Medicine, and represents a collaboration called Lifehand 2 between several European universities and hospitals.