Implantable Ice Packs Relieve Pain Without Freezing

August 24,2022-cooling a recent injury with ice is arguably one of the most effective ways to relieve pain without medication. But ice is bulky, imprecise, and it melts. But what if you could shrink an ice pack that would never melt and place it directly on the pain-causing nerve? That’s the goal of a team of scientists at Northwestern University who have developed a tiny, flexible implant that can provide 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, which can have serious side effects, including the risk of addiction.

The implant was a paper-thin, 5-millimeter-wide strip of water-soluble material containing a pair of parallel, wavy channels, one filled with liquid coolant and the other with dry nitrogen. Outside there is a pump that releases the liquid and gas into a shared pocket, where a chemical reaction causes the liquid to evaporate, eventually producing a sense of cooling and numbing the nerves. As nerves get colder, the pain signals they send to the brain slow down until they stop altogether, preventing them from reaching the brain.

Because the sliver is designed to wrap around the actual nerve causing the pain, the device provides precise, targeted relief without affecting the surrounding tissue, including the nerve that controls motor function. This means you get the advantage of the numbness you feel when using ice, but more precisely for a single nerve, rather than the entire area that an ice pack might cover.

“We specifically target peripheral nerves that connect your brain and spinal cord to the rest of your body. “These are the nerves that transmit sensory stimuli, including pain,” co-author Matthew McEwen, ph.d. , an assistant professor of Neurosurgery at Washington University School of Medicine in St. Louis, explained in an article from Northwestern University. “By providing a cooling effect to one or both target nerves, we can effectively modulate pain signals in a specific region of the body.”

Because too much cooling can damage the tissue around the nerve, the device includes a tiny sensor that monitors the temperature of the nerve and adjusts the flow of fluids and gases to increase or decrease the amount. Once the device is implanted, it never needs to be removed. All materials are naturally absorbed by the body and dissolve within days or weeks of implantation, the researchers said.

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