An implantable cooling device for pain relief

ByLance T. Lee

Jul 29, 2022

This story about pain relief is part of a long series on regenerative medicine. For other stories on this topic, see and research regenerative medicine. My definition of regenerative medicine is any medical modality that brings us back to normal health when we are damaged by disease, injured by trauma, disadvantaged by birth, or worn down by time. Modalities include: chemicals, genes, proteins and cells used as drugs, gene editing, prostheses and mind-machine interfaces.

Scientists at Northwestern University recently developed a new pain relief device that uses temperature control to block pain signals to the brain. The device is a small, flexible implant that could replace opioids or other highly addictive drugs.

Opioid abuse is an ongoing crisis in the United States that has only grown since the start of the Covid-19 pandemic. Despite this, there are very few alternative treatments for pain relief that are as effective, leading to widespread use of opioids and rising rates of opioid addiction and overdose.

Previous studies have shown that pain signals can be blocked from the brain using cooling implants that lower the temperature of specific nerves. By lowering their temperature, researchers can decrease nerve activity and inhibit the release of pain signals. However, cooling implants have historically been bulky, inaccurate, and required additional surgeries to remove once the patient no longer needs them.

Now, in an article published in the journal Nature, Reeder et al. describes how they developed a new pain-relieving implant that is not only very precise but can also be absorbed by the body after use, thus avoiding any extraction surgery.

To address the challenges of previous cooling implants, Reeder et al. sought to develop a device flexible enough to wrap around specific pain-signaling nerves. This would allow the device to be very precise and target only one nerve at a time. To do this, the researchers began by studying a class of materials called elastomers. Elastomers are very flexible and can be made from plastic, rubber or resin. They can also be water-soluble, which means that if a water-soluble elastomer were implanted in the body, it would dissolve over time.

But how could an elastomer-based device cool the nerve? Reder et al. took up this challenge by taking inspiration from microfluidic systems. A microfluidic system occurs when tiny channels are etched into a material, allowing small amounts of fluid to flow through the channels. By incorporating a microfluidic system into the elastomeric material, Reeder et al. was able to run coolant through the entirety of the implant, ultimately cooling the nerve around which the device wrapped.

After incorporating additional electronics into the device so researchers could track nerve temperature and control the amount of coolant pumped through the implant, the device was ready to begin testing on rats.

The researchers successfully implanted the cooling device in rats with nerve damage to their legs, by wrapping the device around their sciatic nerve which controls lower body muscles. After cooling the sciatic nerve for eight minutes, the researchers found that the activity of the nerve decreased by 92%. Additionally, the time it took for the activity to cross the sciatic nerve was significantly longer. After the device was turned off and the nerve returned to normal body temperature, Reeder et al. found that activity had also returned to normal levels.

Although more research is needed to determine whether or not the results of this study are consistent in humans, these experiments are promising and suggest that we may be on the verge of developing a new method of pain management. Hopefully, as innovative pain relief devices continue to be developed, we will not only see the progression of interesting science, but also how it can help curb the opioid crisis and limit access to highly addictive drugs.

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