WASHINGTON — To feel what you touch — that’s the Holy Grail for artificial limbs. In a step toward that goal, European researchers created a robotic hand that lets an amputee feel differences between a bottle, a baseball and a Mandarin orange.
The patient experimented with the bulky prototype for a week, and it’s far from the bionics of science-fiction movies. But the research released Wednesday is part of a major effort to create more lifelike, and usable, prosthetics.
“It was just amazing,” said Dennis Aabo Sorensen of Aalborg, Denmark, who lost his left hand in a fireworks accident a decade ago and volunteered to pilot-test the new prosthetic. “It was the closest I have had to feeling like a normal hand.”
This isn’t the first time scientists have tried to give some sense of touch to artificial hands; a few other pilot projects have been reported in the United States and Europe. But this experiment, published in the journal Science Translational Medicine, shows that Sorensen could tell differences in the shape and hardness of objects and could quickly react and adjust his grasp.
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“It was interesting to see how fast he was able to master this,” said neuroengineer Silvestro Micera of Switzerland’s École Polytechnique Fédérale de Lausanne, who led the Swiss and Italian research team. “He was able to use this information immediately in a quite sophisticated way.”
Scientists have made great strides in recent years in improving the dexterity of prosthetics. But the sense of touch has been a much more difficult challenge and is one reason many patients don’t use their prosthetic hands as much as they’d like.
Consider: Grab something and your own hand naturally grasps with just enough force to hang on. Users of prosthetic hands have to carefully watch every motion, judging by eye instead of touch how tightly to squeeze. The results can be clumsy, with dropped dishes or crushed objects.
“You always have to look and see what’s going on, so that’s what is so much different from this new hand that I tried,” Sorensen, 36, said.
First, doctors at Rome’s Gemelli Hospital implanted tiny electrodes inside two nerves — the ulnar and median nerves — in the stump of Sorensen’s arm.
Those nerves normally would allow for certain sensations in a hand. When researchers zapped them with a weak electrical signal, Sorensen said it felt like his missing fingers were moving, showing the nerves still could relay information.
Meanwhile, Micera’s team put sensors on two fingers of a robotic hand, to detect information about what the artificial fingers touched.
For one week, cords snaked from a bandage on Sorensen’s arm to the artificial hand, and the electrodes zapped the nerves in proportion to what the sensors detected. They essentially created a loop that let the robotic hand rapidly communicate with Sorensen’s brain.
“It is really putting the brain back in control of the system,” said biomedical engineer Dustin Tyler of Case Western Reserve University, who wasn’t involved with the European work but leads a team in Ohio that recently created and tested a similar touch-enabled hand. “That’s an important step.”
Added neurobiologist Andrew Schwartz of the University of Pittsburgh: “It shows with a few sensors and some pretty elementary technology, that they can recover a fair amount of functionality.”
To be sure Sorensen used touch and didn’t cheat by looking or hearing telltale sounds, he wore a blindfold and headphones as Micera’s team handed him different objects.
“Suddenly I could tell if it was a hard object,” Sorensen recalled. “The response, the feedback from the arm to my nerves and to my brain, they came very strong.”
Micera cautioned that it will take several years of additional research to create a first-generation artificial hand that can feel and looks more like a traditional prosthetic. First, they have to prove these nerve implants can last; for safety reasons, Sorensen’s were surgically removed after the experiment.