How amputees could feel temperature with their prosthetics

By Chris Dyer via SWNS

Amputees could be able to tell if an object is hot or cold when using their prosthetics by harnessing the phenomenon of "phantom limbs," a new study revealed.

Scientists have developed special sensors that use new technology placed on their skin to allow amputees to feel different temperatures.

Researchers used patients' ability to feel the warmth in their missing limb and even in specific missing fingers, to enable this sensation to be integrated into a prosthetic.

The discovery was made when researchers tested the level of heat subjects held in their missing hand when warm sensors were applied to their stump.

One woman who lost her hand said she felt a change in temperature in her phantom limb thanks to a new device.

She even described feeling 'reconnected' to her missing hand.

The projection of the sensation of temperature into the phantom limb has led to the development of new bionic technology, that equips prosthetics with non-invasive temperature feedback allowing amputees to work out what they’re touching.

Researchers have been working on incorporating new sensory feedback into prosthetic limbs to give a more realistic touch to amputees, and this latest study focuses on temperature.

The developers stumbled upon a discovery about temperature feedback that far exceeds their expectations, the team said.

If something hot or cold is placed on the forearm of an intact arm or leg, that person will feel the object’s temperature around the area of contact, directly on their forearm, the experiments indicated.

But in amputees, that temperature sensation on the residual arm may be felt in the phantom, missing hand, the researchers found.

By giving temperature feedback 'non-invasively,' through thermal electrodes - also known as thermodes - placed against the skin on the residual arm, amputees said they felt the temperature in their phantom limb.

They can feel if an object is hot or cold, and can tell if they are touching copper, plastic or glass, experts discovered.

Francesca Rossi is an amputee from Bologna, Italy, who recently took part in a study to test the effects of temperature feedback directly to the skin on her residual arm.

She is one of 17 patients to have felt her phantom, missing hand, change in temperature thanks to this new technology.

Ms. Rossi also reported feeling reconnected to her missing hand.

She said: “When I touch the stump with my hand, I feel tingling in my missing hand, my phantom hand. But feeling the temperature variation is a different thing, something important, something beautiful.

“Temperature feedback is a nice sensation because you feel the limb, the phantom limb, entirely. It does not feel phantom anymore because your limb is back.”

A few years ago, researchers Professor Silvestro Micera and Dr. Solaiman Shokur found out about a system that could give temperature feedback through the skin of healthy subjects, also developed at EPFL and spun off by Metaphysiks.

Prof Micera, Bertarelli Foundation chair in translational neuro-engineering and professor at EPFL and Sant’Anna School of Advanced Studies (SSSA) who also co-led the study, said: “Temperature feedback is essential for relaying information that goes beyond touch, it leads to feelings of affection. We are social beings and warmth is an important part of that."

“For the first time, after many years of research in my laboratory showing that touch and position information can be successfully delivered, we envisage the possibility of restoring all of the rich sensations that one’s natural hand can provide.”

Metaphysiks has been developing neuro-haptic technology, MetaTouch, which connects the body with digital worlds. MetaTouch combines touch and temperature feedback to augment physical products for well-being.

Simon Gallo, co-founder and head of technology at Metaphysiks, said: “This breakthrough highlights the power of haptics to improve medical conditions and enhance the quality of life for people with disabilities.”

For the study, Dr. Shokur and Prof Micera developed the MiniTouch, a device that provides thermal feedback and is specifically built for integration into wearable devices like prosthetics.

The MiniTouch consists of a thin, wearable sensor that can be placed over an amputee’s prosthetic finger.

The finger sensor detects thermal information about the object being touched, more specifically, the object’s heat conductivity.

If the object is metallic, it will naturally conduct more heat or cold than, for instance, a plastic one.

A thermode, one that is in contact with the skin on the amputee’s residual arm, heats up or cools down, relaying the temperature profile of the object being touched by the finger sensor.

The scientists found that small areas of skin on the residual arm project to specific parts of the phantom hand, like the thumb, or the tip of an index finger.

As expected, they discovered that the mapping of temperature sensations between the residual arm and the entire projected phantom one is unique to each patient.

Federico Morosato, who was responsible for organizing the clinical aspect of the trials at Centro Protesi Inail, said: “When we presented the possibility to get back temperature sensation on the phantom limb or the possibility to feel the contact with different materials, we obtained a lot of positive feedback.

“And eventually, we were able to recruit more than 25 volunteers in less than two years.”

Almost a decade ago, Prof Micera and colleagues provided real-time sensory feedback about objects being grasped.

They went on to improve touch resolution by providing feedback about an object’s texture and position information in a reliable way.

Moreover, they discovered that amputees begin to embody their prosthetic hand if provided with sensory feedback directly into their intact nervous system.

The added sensation of temperature feedback is yet another step towards building bionic prosthetics for repairing the human body.

Fine-tuning temperature sensations and integrating these into a wearable device that can be mapped out to each patient are part of the next steps.

The EPFL neuroengineers borrowed MetaTouch which provides thermal feedback directly to a user’s skin.

With this device, they discovered the thermal phantom sensations and subsequently tested it with 27 amputees.

In a collaboration between EPFL, SSSA and Centro Protesi Inail, the technology was successfully tested in 17 out of 27 patients.

Dr. Shokur, EPFL senior scientist neuro engineer who co-led the study, said: “Of particular importance is that phantom thermal sensations are perceived by the patient as similar to the thermal sensations experienced by their intact hand.”

The results of the study were published in the journal Science.