New Technology Restores Cold Sensation in Amputees’ Phantom Limbs

New Technology Restores Cold Sensation in Amputees’ Phantom Limbs

Researchers have developed the thin-film thermoelectric cooler (TFTEC), one of many world’s smallest and quickest refrigeration units, for functions like improved prosthetics and augmented actuality. Collaboration with neuroscientists has allowed amputees to understand temperature with phantom limbs, a first-of-its-kind development that has implications for prostheses, haptics, and different functions like cooling electronics and power harvesting in satellites. (Artist’s Idea)

Researchers at Johns Hopkins Utilized Physics Laboratory (APL) have developed one of many smallest, most intense, and quickest refrigeration units, referred to as the wearable thin-film thermoelectric cooler (TFTEC). They’ve joined forces with neuroscientists to assist amputees really feel temperature with their phantom limbs.

This pioneering improvement opens up a variety of helpful new functionalities, together with enhanced prosthetics, tactile suggestions in novel augmented actuality (AR) codecs, and thermally-regulated therapies to be used circumstances like ache reduction. The expertise can also be doubtlessly worthwhile in an array of commercial and analysis contexts, comparable to cooling electronics and lasers, and power harvesting in satellites.

TFTEC improvement at APL began in 2016, when Rama Venkatasubramanian, a semiconductor system engineer and chief technologist for APL’s thermoelectrics analysis, started creating superior nano-engineered thermoelectric supplies and units for the Protection Superior Analysis Tasks Company (DARPA) MATRIX program. To support MATRIX, APL developed advanced thin-film thermoelectric materials called Controlled Hierarchically Engineered Superlattice Structures (CHESS), to enable an entirely new set of transduction capabilities for several Department of Defense applications, including cooling computer chips and engine components.

Venkatasubramanian’s strides in CHESS thermoelectrics were so significant by the end of 2019 that Bobby Armiger, who supervises APL’s Exploratory Science Branch, wondered if his devices could be used to facilitate temperature sensation in phantom limbs of amputees for improved prostheses. Since 2006, APL had been leading DARPA’s Revolutionizing Prosthetics program, an effort focused on creating a mentally controlled artificial limb that will restore near-natural motor and sensory capability to upper-extremity amputee patients.

Johnny Matheny Testing

Johnny Matheny, a prosthetics tester, determines which cola can is the coldest using a modular prosthetic limb and thin-film thermoelectric device, both developed by the Johns Hopkins Applied Physics Laboratory. Credit: Ed Whitman / Johns Hopkins University Applied Physics Laboratory

“We’ve known that we can stimulate specific parts of someone’s amputated limb to feel sensations of touch and vibration, but no one has been able to create a cooling sensation with the speed, intensity, and efficiency to restore natural thermal perception with a prosthetic system,” Armiger said. “Restoring temperature sensation has practical applications — like identifying a cold beverage — as well as having the potential to improve the emotional embodiment of the prosthetic device, perhaps by feeling the warmth of a loved one’s hand.”

Venkatasubramanian and the thermoelectrics team began collaborating with Armiger and a team of neuroscientists and roboticists as part of a study supported by the Center for Rehabilitation Sciences Research within the Department of Physical Medicine & Rehabilitation (PM&R) at the Uniformed Services University of the Health Sciences (USU), through a sub-award from The Henry M. Jackson Foundation for the Advancement of Military Medicine to create a wearable thermoelectric cooler fast and intense enough to match the human body’s ability to rapidly sense temperature changes.

From that, the wearable TFTEC was created.

“Our TFTEC is just a little more than one millimeter thick, weighs only 0.05 grams, similar to a thin adhesive bandage, and can provide intense cooling in less than a second,” said Venkatasubramanian. “It’s also two times more energy efficient than today’s most common thermoelectric devices, and can be readily manufactured using semiconductor tools that are also used for manufacturing light-emitting diodes [LEDs]. It’s an thrilling improvement that might have large implications for prostheses and haptics functions.”

To check the TFTEC’s efficacy, researchers mapped thermal sensations within the phantom arms of 4 amputees.

“When somebody loses a part of a limb, the nerves inside the residual limb are nonetheless there, which might result in the ‘phantom’ limb sensation,” mentioned Luke Osborn, a neuroengineering researcher who leads a lot of APL’s noninvasive nerve simulation work. “You’ll be able to place electrodes on completely different elements of an amputee’s higher arm the place these nerves have regrown and stimulate sensation — usually strain, however within the present case, temperature —and the person can inform us the place of their phantom hand they really feel these sensations.”

Nature Biomedical Engineering not too long ago printed outcomes from APL’s in depth TFTEC analysis for such sensory functions, which included lab-scale characterization, trials with amputees, and a real-life demonstration of the strategy. The examine notes that the TFTEC elicited cooling sensations within the phantom limbs of all individuals throughout a chilly detection process, whereas conventional thermoelectric expertise solely did so in half of them — and the TFTEC did so eight instances quicker and with 3 times the depth. Moreover, TFTEC used half the power in comparison with present thermoelectric units.

“We discovered that the TFTEC system was considerably higher at creating quicker and extra intense cooling sensations in comparison with conventional units, although the goal temperature was the identical,” mentioned Osborn. “And that helped individuals make quicker choices and observations.”

The stimulation websites on check individuals remained the identical over 48 weeks of testing, suggesting that the expertise might allow customers to really feel the temperature of their lacking arms for years. This temporal stability together with a wearable noninvasive process are engaging for adoption to real-world use.

“Once we began our work in March 2020, we realized that inside simply a few trials, we might stimulate the phantom limbs of an amputee,” mentioned Venkatasubramanian. “We heard individuals say, ‘Sure, I felt a right away chilly feeling right here and a tingle there.’”

The APL crew continued to good its strategy by way of testing on a number of people with amputation together with these with an intact limb. “These are the developments we dream of as scientists,” Venkatasubramanian continued. “We spend years within the lab, and to see our expertise have an effect on somebody’s high quality of life, like an amputee to understand the pure thermal world, is extremely satisfying.”

Able to producing life like and informative thermal indicators for human notion — at a fraction of the power and measurement in comparison with right this moment’s cooling applied sciences — the units’ low profile, high-speed, and light-weight nature make them appropriate for pores and skin floor functions with out hindrances that might have an effect on motion.

“It has been nice to see the interpretation of this APL-developed thermoelectric expertise into the healthcare area by way of this first-of-kind demonstration in an amputee,” mentioned David Drewry, a biomedical engineer and program supervisor inside APL’s Nationwide Well being Mission Space. “We sit up for increasing the leads to extra strong medical trials and integrating the system into different wearable type components that may be readily deployed to people in want of sensory restoration or haptic suggestions.”

Katy Carneal, a biomedical engineer and assistant program supervisor a biomedical engineer and assistant program supervisor who leads revolutionary health-related analysis at APL sees an unlimited set of future functions for the miniaturized thermoelectric expertise. “There are such a lot of ways in which strain and temperature sensations influence the human physique,” mentioned Carneal. “Along with bettering the standard of life for amputees, we’ve opened a whole lot of analysis doorways that may assist us examine and discover new therapies for neuromuscular ailments or persistent ache.”

Dr. Paul Pasquina, the chair of PM&R at USU, echoed that enthusiasm whereas praising the work of the APL crew. “What a privilege it’s to work with such professional engineers to give you options to assist real-world sufferers, together with our wounded warriors with limb loss,” he mentioned.

APL is uniquely certified to advance the art-of-the-possible for novel well being functions by exploring this intersection of supplies science and digital system engineering with biology and neuroscience. Along with the Revolutionizing Prosthetics program, APL is making vital advances in neural interface analysis, bettering genomics instruments, and monitoring bodily fatigue to forestall warfighter accidents amongst many different developments within the Nationwide Well being Mission Space.

Reference: “Evoking pure thermal perceptions utilizing a thin-film thermoelectric system with excessive cooling energy density and velocity” by Luke E. Osborn, Rama Venkatasubramanian, Meiyong Himmtann, Courtney W. Moran, Jonathan M. Pierce, Priya Gajendiran, Jared M. Wormley, Richard J. Ung, Harrison H. Nguyen, Adam C. G. Crego, Matthew S. Fifer and Robert S. Armiger, 27 July 2023, Nature Biomedical Engineering.
DOI: 10.1038/s41551-023-01070-w

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