Longtime APL collaborator Johnny Matheny and APL engineers Luke Osborn and Rama Venkatasubramanian detail their journey to restore cold sensation in phantom limbs and prosthetics using a new APL-developed thermoelectric cooling device. (Image: jhuapl.edu)

Johns Hopkins Applied Physics Laboratory (APL) researchers have developed one of the world’s smallest, most intense, and fastest refrigeration devices — the wearable thin-film thermoelectric cooler (TFTEC) — and teamed with neuroscientists to help amputees perceive a sense of temperature with their phantom limbs.

This advancement, one of the first of its kind, enables a useful new capability for a variety of applications, including improved prostheses, haptics for new modalities in augmented reality (AR), and thermally modulated therapeutics for applications such as pain management. The technology also has a variety of potential industrial and research applications (e.g., cooling electronics, lasers, and energy harvesting in satellites).

APL’s TFTEC development began in 2016, when Rama Venkatasubramanian, Chief Technologist for APL’s thermoelectrics research, began developing advanced nano-engineered thermoelectric materials and devices for the Defense Advanced Research Projects Agency (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.

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.

“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 at the Uniformed Services University of the Health Sciences 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. It’s an exciting development that could have huge implications for prostheses and haptics applications.”

“When someone loses part of a limb, the nerves within the residual limb are still there, which can lead to the ‘phantom’ limb sensation,” said Luke Osborn, a neuroengineering researcher who leads much of APL’s noninvasive nerve simulation work. “You can place electrodes on different parts of an amputee’s upper arm where those nerves have regrown and stimulate sensation — typically pressure, but in the current case, temperature — and the individual can tell us where in their phantom hand they feel those sensations.”

“When we started our work in March 2020, we realized that within just a couple of trials we could stimulate the phantom limbs of an amputee,” said Venkatasubramanian. “We heard participants say, ‘Yes, I felt an immediate cold feeling here and a tingle there.’”

For more information, contact Katie Kerrigan at This email address is being protected from spambots. You need JavaScript enabled to view it.; 240-761-9046.