Temperature-Sensitive Prosthetic Limb Improves Amputees’ Dexterity and Sense of Human Connection

Sensory feedback is important for amputees to explore and interact with their environment. Now, researchers have developed a device that allows amputees to sense and respond to temperature by transmitting thermal information from the prosthetic fingertip to the amputee’s residual limb.

The “MiniTouch” device, presented in the magazine Medical, uses commercially available electronic components, can be integrated into commercially available prosthetic limbs, and does not require surgery. Using the temperature-sensitive prosthetic hand, a 57-year-old transradial amputee was able to manually distinguish and sort objects of different temperatures and feel bodily contact with other humans.

“It’s a very simple idea that can be easily integrated into commercial prosthetics,” says lead author Silvestro Micera of the École Polytechnique Fédérale de Lausanne and the Scuola Superiore Sant’Anna. “Temperature is one of the last frontiers in restoring sensation to robotic hands. For the first time, we are on the verge of restoring the full range of sensation to amputees.”

The team previously showed that their thermosensitive technology could restore passive thermosensation in 17/27 amputees. In the new study, they show that the MiniTouch can be easily integrated into commercial prosthetic limbs and that it enables active thermosensation during tasks requiring feedback between sensory and motor neurons.

Beyond the functional importance of the ability to sense hot and cold, thermal information could also enhance amputees’ sense of embodiment and their ability to experience affective touch.

“Adding temperature information makes touch more human,” says lead author Solaiman Shokur of the École Polytechnique Fédérale de Lausanne. “We believe that having the ability to sense temperature will enhance amputees’ embodiment of the feeling that ‘this hand is mine’.”

To do this, they integrated the MiniTouch into the personal prosthesis of a 57-year-old man who had undergone a transradial amputation 37 years earlier by connecting the device to a point on the participant’s residual limb that was causing thermal sensations in his index finger. ghost. . Next, they tested its ability to distinguish between objects of different temperatures and objects made of different materials.

Using MiniTouch, the participant was able to distinguish between three visually indistinguishable bottles containing cold (12°C), cool (24°C) or hot (40°C) water with 100% accuracy. while without the device, its accuracy was only 33%. The MiniTouch device has also improved its ability to quickly and accurately sort metal cubes of different temperatures.

“When you reach a certain level of dexterity with robotic hands, you really need sensory feedback to be able to use the robotic hand to its full potential,” says Shokur.

Finally, the MiniTouch device improved the participant’s ability to differentiate human arms from prosthetic arms while blindfolded, from 60% accuracy without the device to 80% with the device. However, his ability to sense human contact through his prosthetic was still limited compared to his uninjured arm, and the researchers speculate that this was due to limitations in other non-thermal sensory inputs such as skin softness and texture. Other technologies are available to enable these other sensory inputs, and the next step is to begin to integrate these technologies into a single prosthetic limb.

“Our goal now is to develop a multimodal system integrating the sensations of touch, proprioception and temperature,” explains Shokur. “With this type of system, people will be able to tell you ‘it’s soft and warm’ or ‘it’s hard and cold’.”

The researchers say their technology is ready for use from a technical standpoint, but additional safety testing is needed before it reaches the clinic, and they plan to further improve the device so that it can be installed more easily.

Future models could also rely on Minitouch to integrate thermal information from multiple points on an amputee’s phantom limb. For example, allowing people to differentiate between thermal and tactile sensations on their finger and thumb could help them grip a hot beverage, while still allowing sensation in the body. the back of the hand could improve the feeling of human connection by allowing amputees to feel when another person touches their hand.