Bioresorbable nerve cooling device blocks pain signals
A dissolvable implant that relieves pain is a much-needed alternative to highly addictive pain medications. The idea sounds farfetched, but a Northwestern University-led team of researchers have successfully developed such a device: a biocompatible, water-soluble implant that leverages the concept of evaporation i.e., how evaporating sweat cools the body, to numb the nerves and block pain signals to the brain.
The tiny device targets peripheral nerves that provide sensory stimuli, including pain – the device’s promising results in animal studies have led the researchers to believe in its potential as an alternative management for post-operative pain.
While other cooling therapies and nerve blockers that use electrical stimulation have been tested experimentally, all have limitations that the new device overcomes. Cryotherapies, for example, 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 5 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.
“You don’t want to inadvertently cool other nerves or the tissues that are unrelated to the nerve transmitting the painful stimuli,” said research fellow Dr. Matthew MacEwan of Washington University School of Medicine in St. Louis. “We want to block the pain signals, not the nerves that control motor function and enables you to use your hand, for example.”
To induce the cooling effect, the device contains tiny microfluidic channels, one containing the liquid coolant, a clinically approved ultrasound contrast agent; and a second channel containing dry nitrogen 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,” said John Rogers, Professor of Materials Science and Engineering, Biomedical Engineering and Neurological Surgery, Northwestern University Feinberg School of Medicine. “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.”
The set cooling time and temperature thresholds have yet to be determined below which the process remains fully reversible, Rogers added.
This new technology is the third example of bioresorbable electronic devices from the Rogers lab, which introduced the concept of transient electronics in 2012. In 2018, Rogers, MacEwan and colleagues demonstrated the world’s first bioresorbable electronic device – a biodegradable implant that speeds nerve regeneration. Later, in 2021, Rogers and colleagues introduced a transient pacemaker.
Bioresorbable devices naturally absorb into the body over the course of days or weeks, without needing surgical extraction. The devices are completely harmless – similar to absorbable stitches.
