There are already a number of experimental prosthetic hands that provide users with the tactile sensation of touching an object. The MiniTouch system takes things further, as it allows users to sense the temperature of items that they're touching.
Developed by scientists from Italy's Sant’Anna School of Advanced Studies and Switzerland's École Polytechnique Fédérale in Lausanne (EPFL), MiniTouch can be incorporated into existing third-party prostheses.
The setup incorporates a temperature sensor that covers the prosthetic hand's index finger pad, along with a thermode located in the socket that connects the prosthesis to the residual arm stump. A thermode is a small device that heats up or cools down on command.
As the finger sensor presses against the surface of an object, it produces distinctive electrical signals based on the temperature of that surface. Those signals are relayed to the hard-wired thermode, which responds by heating or cooling the skin in a specific area of the arm stump.
Because the user's brain sees the finger touching the object at the same time that the changes in temperature are picked up by the nerves in the stump, it produces a sense of heat or coldness that is perceived as originating in the tip of that finger. It's not unlike the phenomenon in which recent amputees may feel sensations in a "phantom limb."
MiniTouch has already been successfully tested on a 57-year-old man whose hand had been amputated at the wrist. Utilizing the new system, he was able to differentiate between visually identical bottles that contained cold, cool and hot water, with 100% accuracy – without MiniTouch, his accuracy fell to just 33%.
He was also able to sort metal cubes based on their differing temperatures, plus he was 80% accurate at differentiating between human and prosthetic hands when touching them while blindfolded.
"Temperature is one of the last frontiers to restoring sensation to robotic hands. For the first time, we’re really close to restoring the full palette of sensations to amputees," said Sant’Anna's Prof. Silvestro Micera, who led the research along with EPFL's Dr. Solaiman Shokur. "This study paves the way for more natural hand prostheses that restore a full range of sensations, offering amputees a richer and more natural perception of the tactile world."
A paper on the MiniTouch system was recently published in the journal Med.