Dennis Aabo Sørensen from Denmark became the first amputee in the world to feel with a sensory-enhanced prosthetic hand in real-time. The hand was surgically wired to nerves in his upper arm. The study was published in Science Translational Medicine and represents a collaboration called Lifehand 2 between several European universities and hospitals.
"The sensory feedback was incredible," reports the 36 year-old amputee from Denmark. "I could feel things that I hadn't been able to feel in over nine years." In a laboratory setting, Sørensen was able to detect how strongly he was grasping, blindfolded with ear plugs, as well as the shape and consistency of different objects he picked up with his prosthetic. "When I held an object, I could feel if it was soft or hard, round or square."
Silvestro Micera and his team at EPFL (Switzerland) measured the tension in artificial tendons that control finger movement and turning this measurement into an electrical current in order to enhance the artificial hand with sensors that detect touch. Then, by using computer algorithms, the team transformed the electrical signal into an impulse that sensory nerves can interpret. The sense of touch was achieved by sending the digitally refined signal through the wires into four electrodes that were surgically implanted into what remains of Sørensen's upper arm nerves.
"This is the first time in neuroprosthetics that sensory feedback has been restored and used by an amputee in real-time to control an artificial limb," says Micera.
The researchers originally had concerns with Sørensen's reduced sensitivity, but that notion faded away once they successfully reactivated his nerves. "We were worried about reduced sensitivity in Dennis' nerves since they hadn't been used in over nine years," says Stanisa Raspopovic, first author and scientist at EPFL and SSSA.
On January 26, 2013, Sørensen underwent surgery to implant the electrodes into two major nerves - the ulnar and median nerves - of Sørensen's left arm by a team of surgeons and neurologists, led by Paolo Maria Rossini. After 19 days of preliminary tests, Micera and his team connected their prosthetic arm to the electrodes connected to Sørensen every day for an entire week.
The ultra-thin electrodes, developed by Thomas Stieglitz's research group at Freiburg University (Germany), were responsible for creating a system that transmits extremely weak electrical signals directly into the nervous system. A great deal of preliminary research was done to ensure that the electrodes would continue to work even after the formation of post-surgery scar tissue. It is also the first time that such electrodes have been transversely implanted into the peripheral nervous system of an amputee.
The next step of the project involves miniaturizing the sensory feedback electronics for a portable prosthetic. Also, the scientists will adjust the sensing technology for haptic (touch) resolution and increase awareness about the angular movement of fingers. The electrodes were removed from Sørensen's arm after one month due to safety restrictions imposed on clinical trials, although the scientists are confident that they could remain implanted and functional without damage to the nervous system for many years.
This research hopes to help amputees use lifelike limbs to sense the world around them again.
Sørensen says, "I was more than happy to volunteer for the clinical trial, not only for myself, but to help other amputees as well." Now he faces the challenge of having experienced touch again temporarily.