An Implantable Ice Pack Tries to Relieve Pain without Opioids

The age-old advice is to ice it. The low tech treatment is limited by its size. The solution is showing potential as an alternative to drugs that relieve pain. An implant is an ultraminiaturized ice pack applied to a single nerve. The device was implanted in rats and produced relief from pain.

Theanne Griffith is a neuroscientist at the University of California, Davis, who was not involved in the work. For hundreds of years, it has been used to treat pain.

Existing cooling devices are big and clunky and are not new. They can be removed from the body. The new device is made of a soft, stretchy nervelike material called poly(octanediol citrate), orPOC. After a few weeks, the dissolvable material is no longer usable. Local cooling is a good way to relieve pain. This shows you can apply this knowledge in a new way. The study was published in Science.

One day, the system will allow a patient to adjust the setting by remote control, using an electronic interface that measures and controls temperature. The cooling comes from a chemical found in the tubes that has been approved for use as a contrast agent. Dry nitrogen is in another compartment. The chill is produced when the two chemicals meet. The device enwraps a tiny section of a single nerve and directly cools it. The device may not need to be removed in a second surgery.

The device was placed around the sciatic nerve to see if it could be used for pain relief. After cooling to five degrees, it halted signals from the nerve. The device was tested in rats with no nerve damage, an animal model of chronic pain that does not kill a nerve. Two rats showed greater sensitivity after being poked in the paw. The three rats that received the cooling cuff implant had the damaged nerve treated with cooling down to 10 degrees C, which increased the pain sensitivity by sevenfold.

Allan Basbaum, a pain researcher at the University of California, San Francisco, who was not involved in the study, said that the method was cool. It is intriguing. There are still questions about the utility of it.

The treated nerve bundle contains nerve cells that carry pain and other sensations as well as signals that are transmitted by motor and sympathetic nerves. If all of those nerves are silenced, there could be consequences such as numbness or weakness in the limbs. Basbaum says there is a lot going on when you cool the nerve.

He says that most of the pain is caused by abnormal nerve activity. Local anesthetics work very well. If you cool the nerve to the point of blocking all the electrical impulses, you are essentially doing the same thing as the local anesthetic does.

I want to know what the rat actually feels. Is it possible to reduce pain? What is it like to be numb? The person says something. How it can be used in people will be influenced by that. Behavioral tests in rodents will be required to answer these questions. There is more to pain than the initial signaling. There is a central Nervous System. It would be great to see tests that show the higher level of pain.

Matthew MacEwan of Washington University is a co-author of the new study. Nerves stop firing signals when they're cooled down. Rogers, MacEwan and their colleagues were searching for that. He says that they wanted to find a way to deliver mild nerve cooling.

The device could be implanted in people during a surgery that already involves a specific nerve, such as an amputation, which can cause phantom limb pain. MacEwan thinks it could be used for knee replacement.

There are still safety issues that need to be looked at. Damage to nerves can be caused by a low temperature. MacEwan says that they did not see any effects on the nerve fiber, but that they want to explore the idea of extending the cooling time.

You would want to know how much cooling we could deliver before damaging the nerve. I'm not sure, but it's cold.

Basbaum says that the technology needs further development to look at its potential side effects and how it might be used in other applications. He says we aren't there yet. This is not a substitute.