Dissolving an implantable device relieves pain without drugs

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A Northwestern UniversityA team of researchers led by a team of researchers has developed a small, soft and flexible implant that provides pain relief on demand and without the use of drugs. The first-of-its-kind device could provide a much-needed alternative to opioids and other highly addictive drugs.

The biocompatible, water-soluble device works by gently wrapping around nerves to deliver precise, targeted cooling, which numbs nerves and blocks pain signals to the brain. An external pump allows the user to activate the device remotely and then increase or decrease its intensity. Once the device is no longer needed, it naturally absorbs into the body, obviating the need for surgical extraction. The researchers believe the device will be most useful for patients undergoing routine surgeries or even amputations that typically require postoperative medication. Surgeons could implant the device during the procedure to help manage the patient’s postoperative pain.

“While opioids are extremely effective, they are also extremely addictive,” said John A. Rogers of Northwestern, who led the development of the device. “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 mechanisms that bear some similarities to those that cause your fingers to feel numb from the cold.Our implant allows this effect to be produced programmatically, directly and locally on targeted nerves, even those deep in the surrounding soft tissue. For more information, see the IDTechEx report on Flexible Electronics in Healthcare 2020-2030.

A pioneer in bioelectronics, Rogers holds the Louis Simpson and Kimberly Querrey Chair in Materials Science and Engineering, Biomedical Engineering, and Neurological Surgery at the McCormick School of Engineering and Northwestern University Feinberg School of Medicine. He is also the founding director of the Querrey Simpson Institute for Bioelectronics. Jonathan Reeder, a former postdoctoral fellow in Rogers’ lab, is the paper’s first author.

Although the new device may sound like science fiction, it is based on 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 tricked into evaporating at the specific location of a sensory nerve.

“As you cool a nerve, the signals going through the nerve get slower and slower – eventually stopping altogether,” said study co-author Dr. Matthew MacEwan of Washington University School of Medicine in St. Louis. “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.”

“As engineers, we are driven by the idea of ​​treating pain without drugs – so that it can be turned on and off instantly, with the user controlling the intensity of relief.” — John A. Rogers

To induce the cooling effect, the device contains tiny microfluidic channels. One channel contains the coolant (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 through a common chamber, a reaction occurs that causes the liquid to rapidly evaporate. At the same time, a tiny built-in sensor monitors the nerve’s temperature to ensure it’s not too cold, which could damage tissue.

“Excessive cooling can damage the nerve and the fragile tissues around it,” said Rogers. “The duration and temperature of cooling must therefore be precisely controlled. By monitoring the temperature at the nerve, flow rates can be automatically adjusted to set a point that reversibly and safely blocks pain.”

While other cooling therapies and nerve blockers have been tested experimentally, 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, potentially leading to adverse effects such as tissue damage and inflammation. At its widest point, Northwestern’s tiny device is just 5 millimeters wide. One end is wrapped in a cuff that gently wraps around a single nerve, avoiding the need for sutures. By precisely targeting only the affected nerve, the device saves the surrounding regions from unnecessary cooling, which could lead to side effects.

“You don’t want to inadvertently cool other nerves or tissues that aren’t related to the nerve transmitting the painful stimuli,” said MacEwan. “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 electrical stimulation to silence painful stimuli. These also have limitations. “You can’t shut down a nerve with electrical stimulation without activating it first,” said MacEwan. “This can cause additional muscle pain or twitching and is not ideal, from the patient’s perspective.”

This new technology is the third example of bioresorbable electronic devices from Rogers Lab, which introduced the concept of transient electronics in 2012, published in Science. In 2018, Rogers, MacEwan and their colleagues presented the world’s first bioresorbable electronic device – a biodegradable implant that accelerates nerve regeneration, published in Nature Medicine. Then, in 2021, Rogers and his colleagues introduced a transient pacemaker, published in Nature Biotechnology.

All device components are biocompatible and naturally absorb into the body’s biofluids over days to weeks, without the need for surgical removal. Bioabsorbable devices are completely harmless – similar to absorbable stitches. The thickness of a sheet of paper, the soft and elastic nerve cooling device is ideal for treating very sensitive nerves.

“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.”

Source and top image: Northwestern University

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