A modified prosthetic limb enabled an amputee to pick up temperature changes and sense when they were in contact with another human.
New Device in Prosthetic Limb Enables Detection of Temperature Changes
For the first time, scientists enabled an amputee to feel temperature changes through his prosthetic hand. This milestone bypasses what is considered one of the final challenges in imbuing prosthetics with the complete spectrum of senses that a human limb has.
The implantation of a tiny device on the prosthetic hand of the patient achieved such a feat. A temperature sensor was placed at the index finger's tip and connected to a thermode linked to the remaining part of the patient's arm.
This led to a feedback loop, wherein temperature changes picked up by the sensor were relayed to the patient's central nervous system. Then, the brain could interpret the temperature changes as being felt in the prosthetic limb.
This took place in the case of 57-year-old Fabrizio. He got a right arm amputation below his elbow back when he was 20 years old. Fabrizio became the first recipient of the novel devices.
In the course of over a year, Fabrizio joined lab experiments that ultimately showed the abilities of his modified prosthetic limb to detect temperatures.
In one specific experiment, Fabrizio successfully distinguished between water, which appeared visually the same, with a temperature range of 20 degrees Celsius to 40 degrees Celsius. He could correctly determine the temperatures whenever the new device was used, as opposed to 33% of the time when the device was turned off.
In a different test, he could sort metal cubes with varying temperatures more quickly with the device than when he was working without it. In another instance, Fabrizio was blindfolded and able to differentiate between a human arm and a prosthetic arm through poking. This was observed in 80% of tests using the device and in 60% of tests without the device.
Prosthetic Technologies
The case was documented in the "A sensory-motor hand prosthesis with integrated thermal feedback" study. The researchers believe that the invention could become helpful in functioning and in making the lives of amputees more enjoyable.
According to Silvestro Micera, a co-senior author of the study and a translational neuroengineering professor at the Swiss Federal Institute of Technology Lausanne, they tend to underestimate the significance of the hand as a way to interact with others effectively.
Throughout the years, technological advances have enhanced the ability of prosthetic limbs to sense touch. However, it has been challenging to replicate the perception of temperature artificially.
In 2023, the Micera team discovered that people who had some arm parts removed still could pick up various temperatures applied to the skin on their residual limbs. Moreover, it is known that amputees often keep on sensing their lost limb as if it were still there, a phenomenon known as phantom limb.
The researchers devised a way to maximize this remaining sensation and embed the technology into a commercial prosthetic limb. This is why testing was done with Fabrizio, who joined the original 2023 study and already had a prosthetic limb.
Micera notes that the device's beauty is that the prosthetic limb of an amputee does not need to be changed. Moreover, the device is also powered by a battery, so plugging it in is unnecessary.
Jeroen Bergmann, an engineering science associate professor from the University of Oxford who did not participate in the study, notes that devices that offer natural ways for patients to have environmental interactions are necessary. Bergmann adds that the feat is a promising approach to addressing this gap. However, further work is necessary to become suitable for actual applications and everyday settings.
The researchers are now working on refining the device. For one, they aim to examine how certain factors, such as humidity and air temperature, could affect its performance. In the near future, they hope to create a prosthesis that could restore all the sensations that the human hand can feel and be utilized in the home.
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