A prosthetic hand enhanced with sensors has allowed Dennis Aabo Sørensen a 36 year old man from Denmark to “feel”. He is the first in the world to use the prosthetic which is surgically connected to nerves in his upper arm. It allows him to instantly sense what objects feel like when he touches them.
The sensory system which is part of the artificial hand was created by Silvestro Micera and his colleagues from the École Polytechnique Fédérale de Lausanne (EPFL) in Switzerland and the Sant'Anna School of Advanced Studies (SSSA) in Italy.
A mock up model of the hand was tested in February 2013 and the findings were published in the journal Science Translational Medicine.
The creators of the prosthetic had to measure tension in artificial tendons that control finger movement in order to create sensors that detect information from touch. The results were turned into an electrical current.
The human nervous system is incapable of understanding this electric current. The scientists created computer algorithms which changed the electric signals into an impulse that the nervous system understands.
These impulses were transferred through wires into four electrodes that were surgically attached into the nerves of the upper arm consequently producing the sense of touch.
Dennis Aabo Sørensen who had lost his left hand in a firework accident in 2004 said that “The sensory feedback was incredible”. The surgery which required implanting transneural electrodes into the ulnar and median nerves of the arm was carried out by Neurologist Paolo Maria at Gemelli Hospital in Rome in January 2013.
Sørensen had to undertake many different tests for 19 days to ensure that the surgery was successful and without complications. He then had the prosthetic hand connected to the electrodes everyday for a week.
The electrodes, which were created by Thomas Stieglitz and colleagues at Freiburg University in Germany, are very thin which means that really weak signals can be transmitted directly to the nervous system.
The creators of the artificial hand had disclosed they were worried that the nerves in Sørensen's arm would have reduced sensitivity since they hadn’t been used for 9 years.
Sørensen completed a series of laboratory tests that required him to wear a blindfold and earplugs whilst touching a variety of objects using the sensory-enhanced hand and in spite of their doubts the outcome of the surgery was successful.
The prosthetic hand allowed Sørensen to detect how much pressure he was putting into grasping the objects as well as their shape and consistency.
He explained that: "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."
Unfortunately due to clinical trial safety restrictions Sørensen had the electrodes removed from his arm after 1 month.
However the scientists have said they are confident that the electrodes could remain attached to the nerves with full functionality for many years without causing any damage.
In the video below Sørensen and Micera provide an explanation of how the sensory system works:
The results of this study are the first step towards a bionic hand however scientists say that a sensory-enhanced prosthetic hand won’t be available anytime soon.
They have said that the next step will be to make the electronics much smaller so it can be used for a portable prosthetic as improving the technology to allow more detailed sensations.
Even though the clinical trial only allowed Sørensen to experience touch sensation for a short period of time he declared that he was happy 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.
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