A Northwestern University-led team of researchers has developed a small, soft, flexible implant that relieves pain on demand and without the use of drugs. The first-of-its-kind device could provide a much-needed alternative to opioids and other highly addictive medications.
The biocompatible, water-soluble device works by softly 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 — bypassing the need for surgical extraction.
The researchers believe the device will be most valuable for 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.
“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.”
A bioelectronics pioneer, Rogers is the Louis Simpson and Kimberly Querrey Professor of Materials Science and Engineering, Biomedical Engineering and Neurological Surgery in the McCormick School of Engineering and Northwestern University Feinberg School of Medicine. He also is the founding director of the Querrey Simpson Institute for Bioelectronics. Jonathan Reeder, a former postdoctoral fellow in Rogers’ laboratory, is the paper’s first author.
How it works
Although the new device might sound like science fiction, it leverages a simple, common concept that everyone knows: evaporation. 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 coauthor 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.”
“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.” — John A. Rogers
To induce the cooling effect, the device contains tiny microfluidic channels. One channel contains the liquid coolant (perfluoropentane), which is already clinically approved as an ultrasound contrast agent and for pressurized inhalers. A second channel contains dry nitrogen, an inert gas. When the liquid and gas flow into a shared chamber, a reaction occurs that causes the liquid to promptly evaporate. Simultaneously, a tiny 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. “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.”