Pain relief: Implantable device blocks signals by chilling nerves inside the body

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

By Clare Wilson

Putting ice on an injury can ease the pain – and we may be able to get the same effect with an implant that cools down nerve fibres inside the body.

The device can chill nerves to 10°C, reducing pain signals sent to the brain, according to a study that tested a prototype in rats. Made from biodegradable materials, it is designed to be implanted after surgery and then be absorbed by the body as pain from the operation eases.

There is a great need for better ways to treat pain because opioids, the main class of medicines used currently, can be addictive. Ice packs or cooling patches can help temporarily, but these can feel unpleasant and may 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 small channels for chemicals to flow through. One end can be wrapped around a nerve fibre like a cuff. The other end emerges from the skin and is connected to a small pump.

Nitrogen gas and a harmless liquid called perfluoropentane (PFP) are pumped in through separate channels in the strip. The chemicals mix at the far end of the strip, which causes the PFP to evaporate, providing a cooling effect.

The PFP gas and nitrogen return through a third channel to the pump, where they are separated and the PFP changes back to a liquid. The device also contains a temperature sensor, so 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 paws were injured so they became more sensitive. Three weeks later, when each paw was pressed using a sensitive measuring device, it required seven times more force to make the animals retract their leg when the cooling was turned on. “That was a pretty good indication that we had numbed the paw,” says Rogers.

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

Many previous pain-relieving approaches that worked in rats haven’t succeeded in people, but it is well established that cooling nerves blocks their function, says Francis McGlone at Liverpool John Moores University in the UK. “This is basic biophysics. The underlying principle is secure.”

This kind of implant may be most useful for people with severe, long-term pain, as this is harder to treat with opioids without leading to tolerance, says McGlone.

Rogers says a permanent form of the device could also be made if necessary, by using materials that don’t biodegrade. “But the most natural use is in terms of a surgery that needs to happen anyway,” he says.

Journal reference: Science, DOI: 10.1126/science.abl8532

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