EUROPA PRESS.- A team of researchers led by Northwestern University in the United States has developed a small soft and flexible implant that relieves pain on demand and without the need for drugs. This first-of-its-kind implantable pain device could provide a much-needed alternative to opioids and other highly addictive drugs, its authors write in the journal Science.
The device, biocompatible and water solublegently wraps around nerves to provide precise, targeted cooling that numbs nerves and blocks pain signals that reach the brain. An external pump allows the user to remotely activate the device and increase or decrease its intensity. When the device is no longer needed, it is naturally absorbed into the body, avoiding the need for surgical removal.
The researchers believe the device could be invaluable for patients undergoing routine surgeries or even amputations that often require postoperative medications. Surgeons could implant the device intraoperatively to help control a patient’s postoperative pain.
“Although opiates are very effective, they are also very addictive,” recalls Northwestern’s John A. Rogers, who led the development of the device. As engineers, we are motivated by the idea of treating pain without drugs, so that it can turn on and off instantlywith user control over intensity of relief.
“The technology presented here takes advantage of mechanisms that have some similarities to those that make fingers feel numb when they are cold,” he continues. Our implant allows this effect to be produced in a programmable way, directly and locally in the selected nerves, even in the depths of the surrounding soft tissues”.
A pioneer of bioelectronics, Rogers is the Louis Simpson and Kimberly Querrey Professor of Materials Science and Engineering, Biomedical Engineering, and Neurological Surgery at Northwestern University’s McCormick School of Engineering and Feinberg School of Medicine. He is also the founding director of the Querrey Simpson Institute for Bioelectronics. Jonathan Reeder, a former Ph.D. candidate in the Rogers lab, is the paper’s first author.
Although the new implantable pain device may seem like science fiction, it takes advantage of a simple and common concept that everyone knows: evaporation. Similar to how the evaporation of sweat cools the body, the device contains a coolant that is induced to evaporate at a specific location on a sensory nerve.
«As a nerve cools, the signals traveling through it become slower and slower. and they eventually stop completely,” explains study co-author Dr. Matthew MacEwan, of Washington University School of Medicine in St. Louis.
“We specifically target the peripheral nerves, which connect the brain and spinal cord with the rest of the body, he continues. They are the nerves that communicate sensory stimuli, including pain. By applying a cooling effect to just one or two selected nerves, we can effectively modulate pain signals in a specific region of the body.”
To induce the cooling effect, the device contains tiny microfluidic channels. One channel contains the liquid refrigerant (perfluoropentane), which is already clinically approved as an ultrasound contrast agent and for pressurized inhalers. A second channel contains dry nitrogen, an inert gas.
When liquid and gas flow into a shared chamber, a reaction occurs that causes the liquid to rapidly evaporate. Simultaneously, a tiny built-in sensor monitors the nerve’s temperature to ensure it doesn’t get too cold, which could cause tissue damage.
“Excessive cooling can damage the nerve and the fragile tissues around it,” explains Rogers. That is why the duration and temperature of the cooling must be precisely controlled. By monitoring the temperature in the nerve, flow rates can be automatically adjusted to set a point that reversibly and safely blocks pain. Ongoing work attempts to define the full set of time and temperature thresholds below which the process remains fully reversible.
Although other cooling therapies and nerve blockers have been experimentally tested, they all have limitations that the new device overcomes. Previously, researchers have explored cryotherapies, for example, which are injected with a needle. Instead of targeting specific nerves, these imprecise approaches cool large areas of tissue, which can lead to unwanted effects such as tissue damage and inflammation.
At its widest point, Northwestern’s tiny device it only measures 5 millimeters. One of its ends is rolled into a sleeve that gently wraps a single nerve, avoiding the need for sutures. By precisely targeting only the affected nerve, the device prevents surrounding regions from being unnecessarily cooled, which could lead to side effects.
“We don’t want to inadvertently cool other nerves or tissues that aren’t related to the nerve that’s transmitting the pain stimulus,” MacEwan explains. We want to block pain signals, not the nerves that control motor function and allow you to use your hand, for example.”
Previous researchers have also explored nerve blockers that use the electrical stimulation to silence painful stimuli, which also have limitations.
“You can’t turn off a nerve with electrical stimulation without activating it first,” MacEwan says. That can cause additional pain or muscle contractions and is not ideal, from the patient’s perspective.”
This new technology is the third example of bioresorbable electronic devices from the Rogers lab, which introduced the concept of transient electronics in 2012, published in Science.
In 2018, Rogers, MacEwan and their colleagues demonstrated the world’s first bioresorbable electronic device: a biodegradable implant that accelerates nerve regeneration, published in Nature Medicine. Then, in 2021, Rogers and colleagues presented a transient pacemaker, published in Nature Biotechnology.
All components of the devices are biocompatible and naturally absorbed into the body’s biofluids over days or weeks, without the need for surgical removal. Bioresorbable devices are completely harmless, similar to absorbable stitches.
With the thickness of a sheet of paperthe soft and elastic nerve cooling device is ideal for treating very sensitive nerves.
“If you think about soft tissues, fragile nerves, and a body that is in constant motion, any interconnecting device must have the ability to flex, bend, twist, and stretch easily and naturally,” Rogers says. Furthermore, it is desired that the device simply disappear when it is no longer needed, to avoid delicate and risky surgical removal procedures.”
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