Nerve-cooling implant may offer pain relief alternative to opioids, researchers say | Medical examination

An implant that can cool nerves to block pain signals has been unveiled by researchers who say the device could provide an alternative to drugs like opioids.

The team behind the device say it may provide benefits for managing acute pain, such as those experienced after amputations, nerve grafts or spinal decompression surgeries.

“We are optimistic that this is a promising starting point for a technical approach to the treatment of pain,” said Prof John Rogers of Northwestern University in Illinois, USA, a co-author of the study.

But, Rogers warned, it could take some time for the implant to be available to patients. “As with any implantable device, the regulatory process can be slow, usually requiring much more extensive animal model studies over a period of years,” he said.

In the journal Science, the team writes how the device, which has so far only been tested on rats, includes a pump, an external control system and an implant made of a soft, rubbery polymer. The latter contains a occluded collection of small channels, which form a tortuous path in the part of the implant that wraps around the target nerve like a cuff.

When liquid coolant and dry nitrogen are allowed to flow through the tortuous path of the implant, the liquid evaporates, causing the temperature to drop. This temperature change is monitored by an electronic sensor in the device, which allows the current to be monitored and the temperature at the nerve to be kept constant.

“All body processes are based on metabolic chemical reactions, movements of ions and flows of fluids [such as blood] — all of which slow down due to cooling,” Rogers said.

“The net effect when cooling is applied to a nerve is to block electrical signals,” he added, noting similarities to the numbing sensation in the fingertips that can occur in cold weather.

Among their experiments, the team followed two rats with an injury that caused sciatica pain, and over a three-week period recorded the minimum force that had to be applied to the hind paw to cause the animal to retract the paw. These data were then compared with those of three rats that were similarly injured but had the implant. The results suggest that periods of cooling the injured nerve from 37°C to 10°C resulted in a reduction in pain, with a seven-fold increase in the force that could be applied to the paw.

The team says the implant has a number of benefits, including that, unlike opioid drugs, it is not addictive. In addition, the implant can break down in the body after use because it is made of water-soluble and biocompatible materials.

“Typical longevity is in the range of weeks and the corresponding time for complete dissolution is in the range of months,” said Rogers, who said the implant can be inserted as an extension of a patient’s initial surgery.

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Prof. dr. David Bennett, a pain expert at the University of Oxford, said in a personal capacity that alternatives should be found to painkillers such as opioids and praised the technique of the implant.

But, he said, the approach has potential drawbacks, including that while it can reduce pain, the device would block all types of nerve fibers, including those for other sensations like touch and those for muscles, potentially resulting in significant weakness.

“The problem is, there’s been very little specificity for pain so far,” Bennett said. “Finally, there may be some of the people in whom cooling can make the pain worse and we should also consider the side effects of prolonged cooling.”

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