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Northwestern University researchers have created a device that sounds straight out of science fiction: a small, soft, flexible, unique implant 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 valuable for patients undergoing routine surgeries or amputations, which most commonly require post-operative medication. Surgeons could implant the device during the procedure to “manage” the patient’s postoperative pain.
The study was published in the July 1 issue of the journal Science, describes the design of the device and demonstrates its effectiveness in animal models.
The devices use a simple mechanism
“Although opioids are extremely effective, they are also extremely addictive,” Northwestern said John A Rogers, who led the development of the device, in a press release. “As engineers, we are motivated by the idea of treating pain without drugs – in a way that can be toggled on and off instantly, with user control over the intensity of the relief.” The technology described here exploits the mechanism that makes your fingers feel numbers when it’s cold. Our implant demonstrates in animal model studies that this effect can be generated in a programmable manner directly and locally on targeted nerves, even those deep in the surrounding soft tissues.”
So how does it work?
The implant uses a simple concept – evaporation. It contains a liquid coolant that is stimulated to vaporize at a specific point of a sensory nerve.
More specifically, the device works by gently wrapping around nerves to deliver precise and targeted cooling. This in turn numbs nerves and blocks pain signals to the brain. An external pump helps the user remotely activate the device and control its intensity. Once the device is no longer needed, it is naturally assimilated into the body – “eliminating the need for surgical extraction”.
With the thickness of a sheet of paper, the soft, elastic nerve cooling device is ideal for treating highly sensitive nerves.
The co-author of the study, Dr. Matthew MacEwan, of Washington University School of Medicine in St. Louis, said that as the nerves get cooler, the signals traveling through them slow down — until they eventually stop altogether.
“We’re specifically targeting 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. By imparting a cooling effect to just one or two target nerves, we can effectively modulate pain signaling in a specific body region,” he said.
Includes an integrated sensor to monitor nerve temperature
The device contains tiny microfluidic channels to induce the cooling effect. While one channel contains the liquid coolant perfluoropentane (already clinically approved), a second channel contains dry nitrogen. When the liquid and gas flow into a common chamber, a reaction takes place, instantly evaporating the liquid. 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 the tissue.
“By monitoring the temperature at the nerve, flow rates can be automatically adjusted to establish a point that blocks pain in a reversible and safe manner. Ongoing work aims to define the full set of time and temperature thresholds below which the process remains fully reversible,” Rogers said.
Previous cooling therapies and nerve blocks have limitations that the new device overcomes. Cryotherapies, for example, attack large areas of tissue, which can lead to undesirable effects. Here, Northwestern’s tiny device is only five millimeters wide and precisely targets only the affected nerves. This protects the environment from unnecessary cooling.
“You don’t want to inadvertently cool other nerves or tissues unrelated to the nerve carrying the painful stimuli,” MacEwan said. “We want to block the pain signals, not the nerves that control motor functions and allow you to use your hand, for example.”
The last act of disappearance
The device is not Rogers’ first attempt at a bioresorbable electronic device.
The Rogers lab introduced the concept of transient electronics in 2012, and in 2018 Rogers, MacEwan and colleagues demonstrated the world’s first bioresorbable electronic device – a biodegradable implant this accelerates nerve regeneration. Then, in 2021, Rogers and colleagues a transient pacemaker.
All components of the devices are naturally absorbed into the body’s bio-fluids over days or weeks without the need for surgical extraction.
“When you think of soft tissue, fragile nerves, and a body that’s in constant motion, every interface device must have the ability to flex, bend, twist, and stretch easily and naturally,” Rogers said. “Also, you want the device to just disappear when it’s no longer needed to avoid delicate and risky surgical removal procedures.”
