A prosthetic limb device allows users to ‘feel’ temperature differences

Whether it’s a simple handshake or a full-body hug, the warmth of someone else adds a human touch to social interactions. Now researchers have created a device that allows people with amputations to experience such natural temperature sensations using their prosthetics.

The team says the innovation is a first and paves the way for the integration of a wide range of sensations into artificial limbs.

Prof. Solaiman Shokur, senior author of the study at the Swiss Federal Institute of Technology Lausanne, said it was known that stimulating sensory feedback from a prosthesis could make people feel like an artificial member was part of their body.

“To give a natural feeling, you can’t do that without temperature,” he said.

Shokur added that the approach could also allow people with artificial limbs to sense whether an object was dangerously hot and help them distinguish between different materials.

“Plus, it opens a window to the more social aspect of touch,” he said.

Writing in Med magazineShokur and colleagues report how they do this earlier showed that 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 the arm.

Building on this phenomenon, the team created the MiniTouch, which involved placing a temperature sensor on a person’s prosthetic hand where the thermal phantom sensations seemed to originate.

When the sensor detected a temperature change outside the baseline of 32 degrees Celsius, it sent a signal to a temperature controller. This passed the information to another part 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 reproduced on the arm at the trigger location for the phantom sensations. In the current study, the device reproduced temperatures from 20ºC to 40ºC.

The result is that the person perceives a thermal sensation in his missing hand, at the location of the temperature sensor.

To test the MiniTouch, the researchers placed it on the prosthesis of Fabrizio, a 57-year-old whose right arm was amputated below the elbow.

The team found that when using the device, Fabrizio could distinguish between identical-looking bottles of cold, hot, or room temperature water with 100% accuracy. When the device was turned off, its accuracy was 33%.

Fabrizio was also able to use the MiniTouch to distinguish between sheets of copper, glass and plastic when blindfolded, with accuracy equal to that when he used his other, intact hand. However, when the device was turned off, his choices came down to chance.

In addition, the MiniTouch increases Fabrizio’s ability to distinguish between real and prosthetic arms when blindfolded — although his accuracy was greater with his intact hand, Shokur said, possibly because it also perceived information such as texture.

The device also improved Fabrizio’s accuracy, but not speed, in sorting a box of hot and cold steel cubes in the space of one minute.

Fabrizio said the phantom sensation in his missing hand was more intense than in his intact hand when sensing hot or cold cubes.

“When I had my accident when I was twenty years old, I tried a prosthetic hand that gave me simple movement; instead, these new technologies allow me to better understand what I’m touching,” he said.

Although 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. This means that the device can be bolted onto existing prosthetics, is easily personalized and is relatively inexpensive.

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 planned to create a single wearable system that would give people with amputations the would allow them to experience many different sensations using their prosthetics – including pressure, texture, position, temperature and wetness.

“This would be the (really) big next step for us,” Micera said.

Dr. Sigrid Dupan, an expert in sensory feedback for prosthetics at University College Dublin, who was not involved in the research, said the fully integrated system was a major step forward in research into thermal feedback for artificial limbs, and could allow people help them feel their feelings. prosthetics were part of their bodies.

But she warned that the team had previously shown that it was not possible to induce phantom thermal sensations in all people with amputations, while these were not consistent in some.

“I’m excited about the research and it shows promising developments, but … people cannot expect these new devices to be implemented into our healthcare system anytime soon,” she said.