Extreme cold can ease pain
An important part of medical care is pain management. This is currently achieved almost exclusively through pharmaceutical approaches where chemicals are used to block nerve activity and pain signals. Some drugs are very effective, but they can also have side effects, and sometimes cause problems even greater than the one they were trying to solve. Like in the case of opioids, where some patients can have addiction to contend with after they have been cured of their previous ailment. So what if there was another way of dealing with pain? Well that’s what the team at Northwestern University are working on: mechanical pain relief. This approach uses physical devices to target nerves and could be used to reduce pain following operations. Julia Ravey spoke with John Rogers…
John - It's a pretty basic effect. Anybody who's been out in cold weather and you have your hands exposed to cold, you'll notice your fingertips become numb, you lose a tactile sensation. And so the idea is to just exploit that basic effect, but allow that cooling to be delivered in a targeted way to nerves that are deep in the body, not just those that are near the surface of the skin and the fingers. And to target those nerves that are carrying pain signals relevant to a specific patient condition. And so what we've been able to do is to create a soft cuff type structure that encircles a targeted region of a particular peripheral nerve, and the consequence of the reduced temperatures that follow from the action of that device is that you literally just block the ability of those pain signals to pass through that region of the peripheral nerve. You can create this numbing effect.
Julia - How did you test if these devices are effective at providing pain relief?
John - Ultimately, in order to show the ability of the devices to work in the targeted manner, we need to do animal model experiments. And so we've used rodent models, rat models, for those in vivo studies. We can test the magnitude by which we are numbing the paws by poking the base of the paw with a fine filament, not one that penetrates the skin or creates any intense sense of pain. But one that does create a sensory response in the absence of cooling and that sensory response causes the animal to retract the paw away from the filament. As we dial up the cooling power, we have to push harder and harder in order to cause the rat to sense that pressure and to retract the paw. And so with the cooling, we can increase that pressure threshold for retraction by about a factor of 10.
Julia - The materials they're made of, does that mean that they would have to be removed in the future? Or can we just leave them in the body? What happens once they're in?
John - All of the constituent materials are naturally bioresorbable, so they dissolve and melt away in the body. In some ways, they're conceptually similar to a resorbable suture in the sense that the device is present when it's needed, but it's engineered to naturally disappear after that pain medication is no longer necessary. And that's an essential aspect of the engineering, because if the device were not resorbable, then one would require a secondary surgical extraction procedure to remove the device after it's no longer needed. That kind of surgery is highly risky because disentangling the device from the targeted region of the nerve, especially after scar tissue is developed, could be very tricky without it. It would be hard to justify a device of this type.