2023-05-18 20:00:02
A sophisticated feedback system designed in the Federal Polytechnic School of Lausanne (EPFL) has achieved that a group of people with an amputated hand can once again have sensations in their phantom hand, such as heat.
the researchers Sylvester Micera and Solaiman Shokur have incorporated new sensory feedback into a group of people’s prosthetics to provide a more realistic feel to amputees. And the latest study from him focuses on temperature.
Unlike people without an amputated limb, those who are do not have temperature sensations in their phantom hand. But now, by providing temperature feedback non-invasively, using thermal electrodes (also known as thermodes) placed against the skin on the residual arm, amputees can experience this sensation 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.
In a collaboration between EPFL, the Higher School of Advanced Studies of Sant’Anna (SSSA) and the Inail Prosthesis Center, the technology was successfully tested in 17 of the 27 patients. The results have been published in «Science».
“When I touch the stump with my hand, I feel tingling in my absent hand, my phantom hand. But feeling the temperature variation is something different, something important… something beautiful”, says Francesca Rossi.
Rossi is an amputee from Bologna, Italy who has participated in this study to test the effects of temperature feedback directly on the skin of her residual arm. She is one of the 17 patients who have felt that her phantom hand changes temperature thanks to the new EPFL technology. In addition, she feels reconnected with her missing hand.
The projection of temperature sensations onto the phantom limb has led to the development of a new bionic technology, which equips prostheses with non-invasive temperature feedback that allows amputees to discern what they are touching.
“Temperature feedback is essential for conveying information that goes beyond touch, leading to feelings of affection. We are social beings and warmth is an important part of that,” says Micera, president of the Bertarelli Foundation on Translational Neuroengineering, EPFL and SSSA professor, who also co-led the study. “For the first time, after many years of research in my laboratory demonstrating that touch and position information can be successfully delivered, we contemplated restoring all the sensations that the natural hand can provide.”
The added sensation of temperature feedback is yet another step toward building bionic prosthetics to repair the human body. Fine-tuning the temperature sensations and integrating them into a wearable device that can be assigned to each patient are part of the next steps.
A few years ago, Micera and Shokur discovered a system that could provide temperature feedback through the skin of healthy subjects, also developed at EPFL and derived from Metaphysiks. This is MetaTouch, which connects the body with digital worlds. MetaTouch combines tactile and temperature feedback to increase the well-being of physical products.
MiniTouch
For the study, Shokur and Micera developed the MiniTouch, a device that provides thermal feedback and is specifically designed to be integrated into wearable devices such as prosthetics. The MiniTouch consists of a slim, 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 thermal conductivity of the object. If it is metallic, it will naturally conduct more heat or cold than, for example, a plastic one.. A thermode, which is in contact with the skin of the amputee’s residual arm, heats up or cools down, transmitting the temperature profile of the touching object to the finger sensor.
The scientists found that small areas of skin on the residual arm project to specific parts of the phantom hand, such as the thumb or the tip of an index finger. Unsurprisingly, they found that the mapping of temperature sensations between the residual arm and the entire projected phantom is unique to each patient.
“Temperature feedback is a nice sensation because you feel the limb, the phantom limb, in its entirety. It no longer feels like a ghost because your member is back, “concludes Rossi.
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