Implantable Ice Pack Relieves Pain Without Freezing

Aug. 24, 2022 — Cooling a recent injury with ice can be one of the most effective ways to ease pain without medication. But ice is bulky and imprecise, and, it melts. But what if you could shrink an ice pack that never melts and place it directly on the nerves causing pain? That’s what a group of scientists at Northwestern University have aimed to do by developing a tiny, flexible implant that delivers pain relief on demand.

The researchers tested the device on rats and published their findings in the journal Science. They hope it will provide a future alternative to opioids and other prescription painkillers that can have serious side effects, including the risk of addiction.

The implant is a paper-thin, 5mm-wide strip of water-soluble material that contains a pair of parallel wave-shaped channels, one filled with a liquid coolant and the other with dry nitrogen. There is a pump on the outside that releases the liquid and gas that move into a shared pocket where a chemical reaction causes the liquid to evaporate, ultimately creating a cooling sensation that numbs the nerve. As the nerve becomes cooler, the pain signals it sends to the brain gradually slow down until they stop entirely, preventing those signals from ever reaching the brain.

Since the thin strip is designed to be wrapped around the actual nerve causing pain, the device delivers precise, targeted relief that doesn’t affect surrounding tissue, including nerves controlling motor function. That means you get the advantage of the numbness you feel when using ice, but more precision targeting a single nerve versus the entire area an ice pack might cover.

“We are specifically targeting peripheral nerves, which connect your brain and your spinal cord to the rest of your body. These are the nerves that communicate sensory stimuli, including pain,” co-author Matthew MacEwan, PhD, an assistant professor of neurological surgery at the Washington University School of Medicine in St. Louis, explained in an article at Northwestern. “By delivering a cooling effect to just one or two targeted nerves, we can effectively modulate pain signals in one specific region of the body.”

Since too much cooling can damage tissue around the nerve, the device includes a tiny sensor that monitors the temperature of the nerve and can adjust the flow rates of the liquid and gas to increase or decrease the amount. The device also never needs to be removed once it’s implanted: All the material can be naturally absorbed into the body, and it dissolves within a few days or weeks of being placed, the researchers said.

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