A man who lost his hand decades ago has been able to perfectly distinguish between heat and cold in his prosthetic hand with a device that uses off-the-shelf electronics and does not require surgery.
Researchers say it 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.
According to a new study in the journal Med, the device allowed a 57-year-old to distinguish between and manually sort objects of different temperatures, as well as sense bodily contact with other humans.
“This is a very simple idea that can be easily integrated into commercial prostheses,” says senior author Silvestro Micera, a neuroengineer at École Polytechnique Fédérale de Lausanne, Switzerland, and Scuola Superiore Sant’Anna in Italy.
“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.”
Researchers integrated the “MiniTouch” device into the personal prosthesis of the man, who had undergone a transradial (wrist) amputation 37 years prior.
The device transmitted thermal information from the fingertip of the prosthetic hand to a point on his residual arm that produced the perception of thermal sensations in his phantom index finger.
The participant was able to distinguish between bottles containing either cold (12°C), cool (24°C), or hot (40°C) water with 100% accuracy while using the device, compared to 33% accuracy without it. It also improved his ability to sort metal cubes of different temperatures.
The MiniTouch device also improved his ability to tell the difference between human and prosthetic arms while blindfolded, from 60% without the device to 80% with it.
Senior author Solaiman Shokur, a neuroengineer at École Polytechnique Fédérale de Lausanne, says that adding temperature information makes touch more human-like.
“We think having the ability to sense temperature will improve amputees’ embodiment – the feeling that ‘this hand is mine,” he says.
Next steps will involve integrating thermal information from more than one point on the amputee’s phantom limb, as well as additional safety tests to make the device ready for use outside of the laboratory.