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 let an amputee feel differences between a bottle, a baseball and a mandarin orange.
The patient got to experiment with the bulky prototype for just a week, and it's far from the bionics of science fiction movies. But the research published 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 a sense of touch to artificial hands; other pilot projects have been reported in the United States and Europe. But this newest experiment, published in the journal Science Translational Medicine, shows that Mr. Sorensen not only could tell differences in objects' shape and hardness, but also quickly react and adjust his grasp.
"It was interesting to see how fast he was able to master this," said neuroengineer Silvestro Micera of Switzerland's Ecole Polytechnique Federale de Lausanne, who led the Swiss-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 would like.
Consider: Grab something, and your own hand naturally grasps with just enough force to hang on. Users of prosthetic hands must watch every motion carefully, judging by eye instead of touch how tightly to squeeze. Results can be clumsy, with dropped dishes or crushed objects.
Doctors at Rome's Gemelli Hospital implanted tiny electrodes inside two nerves -- the ulnar and median nerves -- in the stump of Mr. Sorensen's arm. Those nerves normally would allow for certain sensations in a hand. When researchers zapped them with a weak electrical signal, Mr. Sorensen said it felt like his missing fingers were moving, showing that the nerves still could relay information.
Meanwhile, Mr. 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 Mr. 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 Mr. Sorensen's brain.
"It shows, with a few sensors and some pretty elementary technology, that they can recover a fair amount of functionality," University of Pittsburgh neurobiologist Andrew Schwartz said.
Mr. Schwartz's team is about to test another approach: a brain-controlled robotic hand for the paralyzed that would "feel" through electrodes implanted in a brain region called the sensory cortex.