Wraparound implant relieves pain on demand

Researchers have developed a small, soft, flexible implant that relieves pain on demand, a first-of-its-kind device that could provide an alternative to opioids and other addictive medications.

The soft flexible device bends and stretches with the body, without the need for bulky, rigid hardware
The soft flexible device bends and stretches with the body, without the need for bulky, rigid hardware - Northwestern University

Developed by a Northwestern University-led team, the biocompatible, water-soluble device works by wrapping around nerves to deliver precise, targeted cooling, which numbs nerves and blocks pain signals to the brain. An external pump enables the user to remotely activate the device and then increase or decrease its intensity. After the device is no longer needed, it naturally absorbs into the body.

The researchers believe the device could prove its value with patients who undergo routine surgeries or even amputations that commonly require post-operative medications. Surgeons could implant the device during the procedure to help manage the patient’s post-operative pain.

The study is published today (July 1,2022) in Science.

“Although opioids are extremely effective, they also are extremely addictive,” said Northwestern’s John A. Rogers, who led the device’s development. “As engineers, we are motivated by the idea of treating pain without drugs - in ways that can be turned on and off instantly, with user control over the intensity of relief. The technology reported here exploits mechanisms that have some similarities to those that cause your fingers to feel numb when cold. Our implant allows that effect to be produced in a programmable way, directly and locally to targeted nerves, even those deep within surrounding soft tissues.”

Similar to how evaporating sweat cools the body, the device contains a liquid coolant that is induced to evaporate at the specific location of a sensory nerve.


“As you cool down a nerve, the signals that travel through the nerve become slower and slower - eventually stopping completely,” said study co-author Dr. Matthew MacEwan of Washington University School of Medicine in St. Louis. “We are specifically targeting peripheral nerves, which connect your brain and your spinal cord to the rest of your body. These are the nerves that communicate sensory stimuli, including pain. By delivering a cooling effect to just one or two targeted nerves, we can effectively modulate pain signals in one specific region of the body.”

To induce the cooling effect, the device contains tiny microfluidic channels. One channel contains the liquid coolant (perfluoropentane) and the second contains dry nitrogen. When the liquid and gas flow into a shared chamber, a reaction occurs that causes the liquid to evaporate. Simultaneously, an integrated sensor monitors the temperature of the nerve to ensure that it’s not getting too cold, which could cause tissue damage.

“Excessive cooling can damage the nerve and the fragile tissues around it,” Rogers said in a statement. “The duration and temperature of the cooling must therefore be controlled precisely. By monitoring the temperature at the nerve, the flow rates can be adjusted automatically to set a point that blocks pain in a reversible, safe manner. On-going work seeks to define the full set of time and temperature thresholds below which the process remains fully reversible.”

At its widest point, Northwestern said the device is 5mm wide. One end is curled into a cuff that wraps around a single nerve, bypassing the need for sutures. By precisely targeting only the affected nerve, the device spares surrounding regions from unnecessary cooling, which could lead to side effects.