He could feel things he hadn't felt for years, says Dennis Aabo Sørensen. He was the first amputee to test a new kind of hand prosthetic, which was developed by researchers at the École Polytechnique Fédérale de Lausanne (EPFL) as part of a European project. The bionic hand provides sensory information in real-time.

At EPFL, Prof. Silvestro Micera (middle), along with his doctoral students Marco Bonizzato and Francesco M. Petrini (left), and postdoc Stanisa Raspopovic (right), are developing a hand prosthetic that conveys sensation.

“A Sensation”, “A Moving Breakthrough”, were the headlines in the international press in February 2014, when EPFL-Professor Silvestro Micera and his team published the results of their tests of a new hand prosthetic. For the first time an amputee was able to feel something again when touching and moving objects. The director of research can still clearly remember the reaction of the prosthetic tester: "You could see from his face how happy he was. That made a big impression on me." Such a thing had been unimaginable before, says Dennis Aabo Sørensen, who lost his left hand in an accident involving fireworks ten years previously: “When I held an object, I could feel if it was soft or hard, round or square.”

With his normal prosthetic the 36-year old Dane can also hold onto objects. Muscle movements in the stump of his arm allow him to open and close the prosthetic. But then he constantly has to watch his prosthetic and check if he is gripping the object correctly, to avoid crushing it. This visual feedback would not be enough if, say, you wanted to pick up an egg in your hand, explains Silvestro Micera. It is only our sense of touch that provides the direct information about the force we are applying, and also about the texture and qualities of the surface of an object as well as its temperature.

The lack of sensation also means that the amputee does not feel the prosthetic to be a part of himself. “This is an important neuropsychological aspect”, the researcher points out. Therefore his aim was to restore this lost information. Besides the EPFL team, scientists in Italy, Germany, Spain and Denmark are also working on the project. The European collaboration is very important, “Not only because of the research funding, but mainly because this is how one can get the best people”, says the native Italian, who has served as director of the EPFL Laboratory for Translational Neural Engineering (Laboratoire d’ingéniere neurale translationelle, TNE) since 2011, and since 2015 has held an endowed professorship (Bertarelli Foundation) for Translational NeuroEngineering.

Robotic hand with a delicate sense of touch

For the prosthetic the researchers used a robotic hand with artificial tendons that control the movements of the fingers. Pressure sensors at the fingertips and in the palm send out an electrical signal, which is then further refined by a computer. For the amputee to receive, process and respond to this information, it has to be fed into the nervous system. “It took us 15 years to find the right kind of connection”, says Silvestro Micera, who had dreamt of developing a bionic hand which was able to provide sensory feedback even when he was a doctoral student at the Scuola Superiore Sant’Anna in Pisa.

The researchers then needed to find a test person to try out the device they had developed. When Dennis Aabo Sørensen learned of this while reading an article in a magazine, he applied to the university hospital in Aalborg in Denmark, which was involved in the project. He was one of 30 applicants who had to undergo various physical and psychological tests, before the research team decided to choose the Dane. “He was highly motivated and capable”, says Silvestro Micera. At the Gemelli hospital in Rome, a team of surgeons and neurologists led by Prof. Paolo M. Rossini implanted four fine electrodes in the remaining part of the left upper arm of the amputee. The doctors chose the ulnar and median nerves for their target, which lead to the fingertips and convey sensation back from the fingers and palm. The electrodes, which basically consist of a thin tungsten needle and a tiny strip of flexible polyimide plastic, were developed by researchers under the leadership of Prof. Thomas Stieglitz at the University of Freiburg in Breisgau.

Pressure sensors in the robotic hand send out an electric signal. Artificial tendons direct the finger movements.

“This is magic”

During the seven-hour operation, the doctors inserted the micro-electrodes transversely through the nerve bundle, so as to achieve a specially good contact, which would allow even extremely weak electrical signals to pass directly into the peripheral nervous system – an operation that was performed on an amputee for the first time. The signal was fed from the robotic hand via wires to the implanted electrodes. The research group waited in excited anticipation to see if the amputee's nerves would show any response, because they had not been used for many years. Then suddenly the Dane turned and exclaimed in surprise, “This is magic! I can feel how my missing hand closes.”

To set up the communication between the brain and the prosthetic, the researchers had developed two computer algorithms. One read the signals from the pressure sensors on the robotic fingers, and fed them through the electrodes, in the form of electrical impulses, into the nervous system. The other one received and processed the signals from the muscles in the stump of the arm, and converted them into commands that could activate the robotic hand. During a preparation period of almost three weeks, the researchers determined the type and amount of sensory information that could be transmitted to the test person by stimulating the various electrodes in the nerves. Only then were the actual tests with the bionic hand carried out.

Every day for a whole week the research group connected their test person to the prosthetic. “It was really difficult for Dennis”, says Silvestro Micera. “He had to do 700 tests, try to apply his grip 700 times.” The researchers kept asking the amputee whether he felt anything, and where it was – in the index finger or the little finger? He learned how to close the artificial hand with just a slight pressure, or a bit more pressure, or very firmly. With his eyes blindfolded, and wearing earplugs, he was able to feel if an object was soft, slightly hard, or very hard. He held and felt a baseball, a mandarin orange and a glass bottle, and he hardly ever let anything fall. “To recognise things that I held, that was incredible”, he recalls. Of course it was not the same as when he used his healthy right hand, but the feeling was similar.

The best technology used in the best way

Following this test series, the research director is confident that the electrodes implanted in the upper arm form an ideal interface between prosthetic and nervous system. In fact there were two other research groups in the USA who had obtained similar results. But, he says, the type of connection developed in Europe was more selective than the method used by the first American colleague, and was less invasive than the second method used by the other colleague. “We have what is probably the best system, and use it in the best way, but we still have to confirm this in the long-term clinical trial that has to be done next”, says Silvestro Micera.

After one month the doctors removed the micro-electrodes again from Dennis Aabo Sørensen's upper arm – for safety reasons. Permission for the clinical study had only been granted under this condition, because of the regulations that apply. The Dane knew from the outset that after this test phase was over he would again have to make do without any sensation in his left hand. He was impressed by the way the dedicated researchers worked with him, and is happy to have been able to contribute to a development that would eventually benefit not only himself but also other amputees as well. “I am happy and grateful”, he says.

The researchers now want to show that the electrodes are sufficiently robust and compatible with the tissues so that they can stay implanted in the body for a long period. “We will need a year for this”, estimates Silvestro Micera. Then the specialists in Rome and at the Lausanne university hospital (CHUV) will have to select two new test persons, who will test the implant over a period of at least one year. Silvestro Micera hopes that the artificial hand will be available for clinical use in eight to ten years. For this, the electronics will have to be miniaturised, though, so that they can be implanted as well. While his tests were being performed, Dennis Aabo Sørensen was still sitting amidst a tangle of electronic wires and switches. So when his children visited him in Rome they called him the ‘cable-guy’.