Researchers at Northwestern University have developed a device that seems straight out of science fiction: a small, soft and flexible implant, the first of its kind, that relieves pain on demand, without the use of drugs and dissolves.
The biocompatible, water-soluble device could provide a much-needed alternative to opioids and other highly addictive drugs. According to the researchers, the device could be very useful for patients undergoing routine surgeries or amputations who most often need postoperative medication. Surgeons could implant the device during the procedure to “manage” the patient’s postoperative pain.
The study published in the July 1 issue of the journal Science, describes the design of the device and demonstrates its effectiveness in an animal model.
The devices use a simple mechanism
“While opioids are extremely effective, they are also extremely addictive,” Northwestern said. John A. Rogers, which led the development of the device, in a press release. “As engineers, we are driven by the idea of treating pain without drugs – so that it can be turned on and off instantly, with user control over the intensity of relief. The technology reported here leverages the mechanism that causes your fingers to feel numbers cold.Our implant demonstrates in animal model studies that this effect can be produced programmatically, directly and locally on targeted nerves, even those deep in the tissues surrounding soft.
So how does it work?
The implant relies on a simple concept – evaporation. It contains a coolant that is prompted to evaporate at the specific location of a sensory nerve.
To elaborate, the device works by gently wrapping around the nerves, to provide precise and targeted cooling. This numbs the nerves and blocks pain signals to the brain. An external pump helps the user activate the device remotely and control its intensity. Once the device is no longer needed, it is naturally absorbed by the body — “bypassing the need for surgical extraction”.
The thickness of a sheet of paper, the soft and elastic nerve cooling device is ideal for treating very sensitive nerves.
Study co-author Dr. Matthew MacEwan of Washington University School of Medicine in St. Louis said that as nerves cool, the signals passing through them become slower – eventually completely stop.
“We specifically target the peripheral nerves, which connect your brain and spinal cord to the rest of your body. These are the nerves that communicate sensory stimuli, including pain. By providing a cooling effect to just one or two targeted nerves , we can effectively modulate pain signals in a specific region of the body,” he said.
Includes built-in sensor to monitor nerve temperature
The device contains tiny microfluidic channels to induce the cooling effect. While one channel contains perfluoropentane coolant (which is already clinically approved), a second channel contains dry nitrogen. When liquid and gas flow in a common chamber, a reaction occurs causing the liquid to evaporate immediately. At the same time, a tiny built-in sensor monitors the nerve’s temperature to make sure it doesn’t get too cold, which could damage tissue.
“By monitoring temperature at the nerve, flows can be automatically adjusted to set a point that reversibly and safely blocks pain. Ongoing work aims to define the set of time and temperature thresholds below which the process remains fully reversible,” Rogers said.
Old cooling therapies and nerve blockers have limitations, which the new device overcomes. Cryotherapies, for example, approach large areas of tissue, which could lead to adverse effects. Here, Northwestern’s tiny device is just five millimeters wide and precisely targets only the affected nerves. This saves the surrounding areas from unnecessary cooling.
“You don’t want to inadvertently cool other nerves or tissues that aren’t related to the nerve transmitting the painful stimuli,” MacEwan said. “We want to block pain signals, not the nerves that control motor function and allow you to use your hand, for example.”
The Last Disappearing Act
The device isn’t Rogers’ first attempt at a bioresorbable electronic device.
Rogers Lab introduced the concept of transient electronics in 2012, and in 2018 Rogers, MacEwan and their colleagues introduced the world’s first bioresorbable electronic device — a biodegradable implant which accelerates nerve regeneration. Then, in 2021, Rogers and his colleagues introduced a transient stimulator.
All components of the devices naturally absorb into the body’s biofluids for days or weeks, without the need for surgical removal.
“If you think of soft tissues, fragile nerves, and a constantly moving body, any interface device must have the ability to flex, bend, twist, and stretch easily and naturally,” said Rogers. “Also, you’d like the device to simply disappear once it’s no longer needed, to avoid tricky and risky surgical removal procedures.”
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