MiniTouch: Pioneering Thermal Sensation in Prosthetic Limbs

Summary: Researchers have unveiled the “MiniTouch,” a revolutionary device that equips prosthetic limbs with the ability to convey thermal sensations to amputees, bridging a significant gap in sensory feedback technology.

This breakthrough allows a transradial amputee to differentiate between objects of varying temperatures and experience more human-like touch, enhancing both functional use and emotional connection with the prosthesis.

By integrating off-the-shelf electronics without the need for surgical intervention, the MiniTouch marks a significant advancement towards fully restoring the spectrum of sensory experiences to individuals with limb loss, potentially improving their quality of life and interaction with the environment.

Key Facts:

The MiniTouch device enables amputees to accurately sense and discriminate temperatures, facilitating more natural interactions with their environment.
This innovation requires no surgery for integration into existing commercial prosthetic limbs, making it a readily accessible enhancement.
Beyond functional benefits, the device contributes to a greater sense of prosthesis embodiment and affective touch, fostering a deeper emotional connection between amputees and their artificial limbs.

Source: Cell Press

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

The “MiniTouch” device, presented February 9 in the journal Med, uses off-the-shelf electronics, can be integrated into commercially available prosthetic limbs, and does not require surgery.

Using the thermally sensitive prosthetic hand, a 57-year-old transradial amputee was able to discriminate between and manually sort objects of different temperatures and sense bodily contact with other humans.

This shows the hand in action. — A sensory-motor hand prosthesis with integrated thermal feedback. Credit: EPFL/Caillet

“This is a very simple idea that can be easily integrated into commercial prostheses,” says senior author Silvestro Micera of École Polytechnique Fédérale de Lausanne and Scuola Superiore Sant’Anna.

“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.”

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 that require feedback between sensory and motor neurons.

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

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

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

Using the MiniTouch, the participant was able to discriminate between three visually indistinguishable bottles containing either cold (12°C), cool (24°C), or hot (40°C) water with 100% accuracy, whereas without the device, his accuracy was only 33%. The MiniTouch device also improved his 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 to have 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 between human and prosthetic arms while blindfolded—from 60% accuracy without the device to 80% with the device.

However, his ability to sense human touch via his prosthesis 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 integrating those technologies into a single prosthetic limb.

“Our goal now is to develop a multimodal system that integrates touch, proprioception, and temperature sensations,” says Shokur.

“With that type of system, people will be able to tell you ‘this is soft and hot,’ or ‘this is hard and cold.’”

The researchers say that their technology is ready for use from a technical point of view, but more safety tests are needed before it reaches the clinic, and they have plans to further improve the device so that it can be more easily fitted.

Future models could also build upon the Minitouch to integrate thermal information from multiple points on an amputee’s phantom limb—for example, allowing people to differentiate thermal and tactile sensations on their finger and thumb might help them grasp a hot beverage, while enabling sensation in the back of the hand might improve the feeling of human connection by allowing amputees to sense when another person touches their hand.

Funding:

This research was supported by the Bertarelli Foundation, the Swiss National Science Foundation, the European Union’s Horizon 2020 research and innovation program, the Horizon Europe Research & Innovation Programme, and the Ministry of University and Research.