Researchers have developed a small, soft, flexible implant that relieves pain on demand 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.

The new device developed by a team of researchers at the Northwestern University (Evanston, IL, USA) 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. To induce a 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.

While other cooling therapies and nerve blockers have been tested experimentally, all have limitations that the new device overcomes. Previously researchers have explored cryotherapies, for example, which are injected with a needle. Instead of targeting specific nerves, these imprecise approaches cool large areas of tissue, potentially leading to unwanted effects such as tissue damage and inflammation. At its widest point, Northwestern’s tiny device is just five millimeters wide. One end is curled into a cuff that softly 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. All components of the device are biocompatible and naturally absorb into the body’s biofluids over the course of days or weeks, without needing surgical extraction. The bioresorbable device is completely harmless - similar to absorbable stitches.

“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,” said Northwestern’s John A. Rogers, who led the device’s development. “Furthermore, you would like the device to simply disappear after it is no longer needed, to avoid delicate and risky procedures for surgical removal.” 

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