Whether it’s a simple handshake or a full-body hug, the warmth of another person adds a human touch to social interactions. Now researchers have created a device that allows amputees to experience such natural temperature sensations with their prosthesis.
The team says the innovation is a first and paves the way for the integration of a multitude of sensations in artificial limbs.
Prof Solaiman Shokur, a senior author of the research at the Swiss Federal Institute of Technology Lausanne, said it is known that boosting sensory feedback from a prosthesis can help people feel that an artificial limb is part of their body. .
“To give a natural sensation, you can’t do it without temperature,” he said.
Shokur added that the approach could also enable people with artificial limbs to tell if an object is dangerously hot and help them distinguish between different materials.
“Besides that, it opens a window to the more social aspect of touch,” he said.
Writing in the journal MedShokur and colleagues report how they before showed it was possible to create a person’s perception of warmth or coolness in an amputated hand by heating or cooling specific points on the remaining part of their arm.
Building on this phenomenon, the team created the MiniTouch, in which a temperature sensor was placed on someone’s prosthetic hand at the location from which the phantom thermal sensations appeared to originate.
When the sensor detected a change in temperature away from a baseline of 32C, it sent a signal to a temperature controller. This transmitted the information to another component that was mounted on the upper part of the prosthesis and touched the skin of the arm.
The temperature detected by the sensor was then projected onto the arm at the trigger site for the phantom sensations. In the current study, the device reproduced temperatures from 20C to 40C.
The result is that the person perceived a thermal sensation in their missing hand, at the location of the temperature sensor.
To test the MiniTouch, the researchers fitted it to the prosthesis of Fabrizio, a 57-year-old whose right arm was amputated below the elbow.
The team found that using the device Fabrizio could distinguish between identical bottles containing cold, hot or room temperature water with 100% accuracy. When the device was turned off, its accuracy was 33%.
Fabrizio was also able to distinguish between sheets of copper, glass and plastic using the MiniTouch when blindfolded, with an accuracy equivalent to when using his other, intact hand. However, when the device was turned off, his choices came down to chance.
In addition, the MiniTouch increased Fabrizio’s ability to distinguish between real and prosthetic arms when blindfolded — although his accuracy was higher with his intact hand, Shokur said, possibly because it also perceived information such as texture.
The device also improved Fabrizio’s accuracy, though not speed, when sorting a box of hot and cold steel cubes within a minute.
Fabrizio said the phantom sensation in his missing hand was more intense than in his intact hand when he perceives hot or cold blocks.
“When I had my accident when I was 20 years old, I tried a prosthetic hand that gave me a simple movement; instead, with this new technology, I can better understand what I’m touching,” he said.
While the authors say the device needs to be tested in a larger group of patients, they note that the MiniTouch does not require surgery and is based on readily available electronics – meaning it can be bolted to existing prosthetics, easily personalized and relatively cheap.
Prof Silvestro Micera, another senior author of the paper from the Swiss Federal Institute of Technology Lausanne and the Sant’Anna School of Advanced Studies in Italy, said the team now plans to create a single wearable system that people with amputations will give the ability to experience many different sensations with their prosthesis – including pressure, texture, position, temperature and wetness.
“It would be for us the [really] big next step,” Micera said.
Dr Sigrid Dupan, an expert in sensory feedback for prostheses at University College Dublin, who was not involved in the study, said the fully integrated system was a major step forward in research into thermal feedback for artificial limbs, and could people help their prosthesis was part of their bodies.
But she cautioned that the team had previously shown that it was not possible to induce phantom thermal sensations in all people with amputations, while in some it was not consistent.
“I am excited about the research and it shows promising developments, but … people cannot expect the implementation of these new devices in our healthcare system in a short time frame,” she said.
