The team behind the device says it could reap benefits for managing acute pain, such as those that occur after amputations, nerve grafts or spinal decompression surgeries. “We are optimistic that this represents a promising starting point for a mechanical approach to treating pain,” said Professor John Rogers of Northwestern University in Illinois, one of the study’s authors. But Rogers warned it could be some time before the implant was made available to patients. “As with any implantable device, the regulatory process can be slow, usually involving much more extensive animal model studies over a period of years,” he said. Writing in the journal Science, the team reports that 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, elastic polymer. The latter incorporates a sealed collection of tiny channels, which form a serpentine path in the portion of the implant that sits around the target nerve like a cuff. When liquid coolant and dry nitrogen are allowed to flow through the implant winding path, the liquid evaporates, resulting in a drop in temperature. This temperature change is monitored by an electronic sensor in the device, allowing the flow to be controlled and the temperature in the nerve to be kept constant. “All body processes are based on metabolic chemical reactions, ion movements and fluid flows [such as blood] “It all slows down as a result of cooling,” Rogers said. “The net effect when cooling a nerve is applied is to block electrical signals,” he added, noting similarities to the numbness in the fingertips that can occur in cold weather. Among their experiments, the team monitored two rats with injuries that caused hip pain, recording over a period of three weeks the minimum force that had to be applied to the hind leg to force the animal to withdraw the leg. These data were then compared with those of three rats that were similarly injured but had the implant. The results suggest that cooling seizures of the injured nerve from 37 C to 10 C led to a reduction in pain, with a sevenfold increase in force that could be applied to the leg. The team says the implant has a number of benefits – including that unlike opioids, it is not addictive. In addition, as the implant is made of water-soluble and biocompatible materials, it can break down in the body after use. “The typical operating time is in the area of weeks and the corresponding time for complete dissolution is in the area of months,” said Rogers, who said the implant could be inserted as an extension of a patient’s initial surgery. Subscribe to the First Edition, our free daily newsletter – every morning at 7 p.m. BST Speaking in private, Professor David Bennett, a pain specialist at Oxford University, said there was a need to find alternatives to painkillers such as opioids and praised the mechanics of the implant. However, he said, the approach has potential drawbacks, such that while it can reduce pain, the device will block all types of nerve fibers, including those that serve other senses such as touch and those in the muscles, with the potential for significant weakness. “The thing is, as it turns out so far, there is very little specialization in pain,” Bennett said. “Finally, there may be a percentage of people in whom the cold could make the pain worse, and we should also look at the side effects of long-term cold.”
