A Danish man who lost his left hand in a fireworks accident nine years ago is now able to feel different kinds of pressure on three fingers of a prosthetic, robotic hand. The work involved a new kind of implanted device that delivers feedback directly to the remaining nerves in the man’s arm. The implant was left in place for 31 days, allowing the man to feel gradations of touch pressure, depending on the amount of electrical stimulus delivered.
The work, carried out by researchers at the Swiss Federal Institute of Technology in Lausanne, Switzerland, adds to remarkable recent advances in prosthetics that can convey sensation. In another project, researchers at Case Western Reserve University are testing a different type of implant that delivers varying kinds of sensations and has been attached to an Ohio man’s arm for 19 months. This implant is still reliably delivering sensations—such as touching ball bearings, sandpaper, or cotton balls—on 20 spots on his hand and fingers (see “An Artificial Hand with Real Feelings”).
To achieve their result, the Swiss researchers inserted electrodes into two of the patient’s three major arm nerves: the ulnar and median. Forces detected on the fingertips of an artificial hand are translated into electrical stimuli delivered to the electrodes.
“It was quite amazing, because suddenly I was able to feel something I hadn’t been feeling for nine years,” the subject, Dennis Aabo Sørensen, said in a video provided by the Swiss institute. “I could feel round things and hard things and soft things. The feedback was totally new to me. Suddenly, when I was doing the movements, I could feel what I was doing, instead of looking at what I was doing.”
Details of the Swiss implant are published today in the journal Science Translational Medicine.
Stimulation in the ulnar nerve produced sensations in the man’s pinky, while stimulation in the median produced sensations in the index finger and thumb. The researchers were able to adjust stimulation levels to correspond with the amount of pressure being applied to a digit, producing sensations ranging from the lightest touch to major pressure. What’s more, Sørensen was able to tell how forcefully he was holding an object, allowing him to prevent it from slipping without squeezing too hard. Sørensen could even tell if he was gripping something round, made of wood, or a rolled up cloth—even when blindfolded and wearing noise-suppressing ear coverings.
“This is very important,” says Stanisa Raspopovic, a scientist in the Translational Neural Engineering Laboratory at the Swiss institute, and one of the researchers on the project. “This graded sensation is done in real time, and he can immediately feel the difference.”
The Swiss institute said in a press release that the Danish man was “the first amputee in the world to feel—in real time—with a sensory-enhanced prosthetic,” but other such trials are underway. The implants in one of Case Western’s subjects in Ohio, Igor Spetic, a 48-year-old man who lost his right hand in an industrial accident, has been in place the longest.
Jack Judy, director of the Nanoscience Institute for Medical and Engineering Technologies at the University of Florida, Gainesville, and a former U.S. Defense Research Projects Agency program manager working on neural interfaces, says “the results look good in the short run,” but adds that “the real concern is the long-term stability” of the technology. “When the long-term performance of the new neural interface is established, this novel alternative approach could significantly improve the quality of life of amputees,” he says.
Raspopovic says in earlier studies in rats the Swiss implant lasted nine to 12 months, adding: “We are very much confident, that this can last for a long, long period.”
The Swiss study is the result of a collaboration called Lifehand 2, using a robotic hand, under development by several European universities and hospitals. A patient controls the movement of the hand with standard technology in which muscles in the residual limb activate mechanical parts on the prosthesis.
Other efforts underway around the world aim to improve prosthetic control, by rewiring nerve fibers to control more sophisticated prosthetics (see “A Lifelike Prosthetic Arm”), for example, or improving brain interfaces to allow for thought control (see “Brain Helps Quadriplegics Move Robotic Arms with Their Thoughts”).
Susan Young contributed reporting to this story.