Pain relief: implantable device blocks signals by cooling nerves in the body

An implant made of biodegradable materials cools nerves to 10°C, reduces pain signals sent to rats’ brains and can be absorbed into the body over time


June 30, 2022

Dissolvable implant relieves pain.  Hybrid microfluidic and electronic system for cooling and simultaneous measurement of nerve temperature.

This implant consists of a flexible strip with small channels through which chemicals can flow

Northwestern University

Putting ice on an injury can ease the pain — and we may be able to get the same effect with an implant that cools nerve fibers in the body.

The device can cool nerves to 10°C, reducing pain signals to the brain, according to a study that tested a prototype in rats. It is made of biodegradable materials and is designed to be implanted after surgery and then absorbed by the body as the pain from surgery subsides.

There is a great need for better ways to manage pain because opioids, the main class of drugs in use today, can be addictive† Ice packs or cooling patches may help temporarily, but they can feel uncomfortable and can damage the skin if used for too long. John Rogers at Northwestern University in Illinois wanted to target pain nerves directly.

His team has developed a thin, flexible strip of material that contains tiny channels for chemicals to flow through. One end can be wrapped around a nerve fiber like a cuff. The other end comes out of the skin and is connected to a small pump.

Nitrogen gas and a harmless liquid called perfluoropentane (PFP) are pumped into the strip through separate channels. The chemicals mix at the end of the strip, causing the PBB to evaporate, giving a cooling effect.

The PBB gas and nitrogen return through a third channel to the pump, where they are separated and the PBB liquefies again. The device also includes a temperature sensor so that the effect can be monitored and adjusted.

To test the device, it was implanted around the sciatic nerve in the legs of three rats, and their legs were injured, making them more sensitive. Three weeks later, when each paw was pressed with a sensitive measuring device, it took seven times more force to retract the animals’ paw when the refrigerator was turned on. “That was a pretty good indication that we had numbed the paw,” Rogers says.

After six months, the device was absorbed into the body and no nerve damage was observed. The team now needs to continue testing the implant in animals to understand how many nerves can be cooled — and for how long — without causing damage, Rogers says.

Many previous pain-relieving approaches that worked in rats have failed in humans, but cooling nerves are well known to block their function, says Francis McGlone at Liverpool John Moores University in the UK. “This is basic biophysics. The underlying principle is safe.”

This type of implant may be most helpful for people with: severe, long-lasting painbecause this is more difficult to treat with opioids without leading to tolerance, McGlone says.

Rogers says a permanent form of the device can also be made if needed by using materials that are not biodegradable. “But its most natural use is in terms of surgery that has to happen anyway,” he says.

Reference magazine: ScienceDOI: 10.1126/science.abl8532

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