Dissolving implantable device relieves pain without drugs

A team of researchers led by Northwestern University has developed a small, soft, flexible implant that relieves pain on demand and without the use of drugs. Described in a study published in Science, the first device of its kind could provide a much-needed alternative to opioids and other highly addictive drugs.

The biocompatible, water-soluble device works by gently wrapping itself 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 the intensity. After the device is no longer needed, it is naturally absorbed into the body, eliminating the need for surgical extraction.

John Rogers, PhD, the Louis Simpson and Kimberly Querrey Professor of Materials Science and Engineering, Biomedical Engineering and Neurological Surgery, was senior author of the study published in Science.

The scientists believe the device will be of most value to patients undergoing routine surgeries or even amputations that often require postoperative medication. Surgeons may 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 Rogers, PhD, the Louis Simpson and Kimberly Querrey Professor of Materials Science and Engineering, Biomedical Engineering and Neurological Surgery, who led the development of the device. Jonathan Reeder, a former postdoctoral fellow in the Rogers lab, is the lead author of the paper.

“As engineers, we are motivated by the idea of ​​treating pain without drugs — in ways that can be turned on and off instantly, with user control over the intensity of the relief,” said Rogers, who is also the founder of the Querrey Simpson Institute of Bioelectronics† “The technology reported here uses the mechanism that makes your fingers feel like a number when they’re cold. With our implant, that effect can be produced in a programmable way, directly and locally on targeted nerves, even those deep in the brain.” surrounding soft tissues.”

How it works

While the new device may sound like science fiction, it uses a simple, common concept that everyone knows: evaporation. Similar to how evaporative sweat cools the body, the device contains a liquid coolant that is induced to vaporize at the specific location of a sensory nerve.

“As you cool down a nerve, the signals traveling through the nerve slow and slow down — eventually they stop completely,” said study co-author Matthew MacEwan, MD, PhD, of Washington University School of Medicine in St. Louis. “We specifically target peripheral nerves, which connect your brain and spinal cord to the rest of your body. These are the nerves that transmit sensory stimuli, including pain. By delivering a cooling effect to just one or two targeted nerves, we can effectively modulate pain signals in a specific area of ​​the body.”

A team led by Northwestern University has developed a small, pain-relieving implant that could provide a much-needed alternative to opioids and other highly addictive drugs.

To induce the cooling effect, the device contains small microfluidic channels. One channel contains the liquid 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 the liquid and gas flow into a shared chamber, a reaction occurs that causes the liquid to evaporate instantly. At the same time, a small integrated sensor monitors the nerve’s temperature to make sure it doesn’t get too cold, which can cause tissue damage.

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

Precision Power

While other cooling therapies and nerve blockers have been experimentally tested, they all have limitations that the new device overcomes. For example, previously scientists have investigated cryotherapies, which are injected with a needle. Rather than targeting specific nerves, these imprecise approaches cool large areas of tissue, potentially leading to unwanted effects such as tissue damage and inflammation.

At its widest point, the tiny device is just five millimeters wide. One end is curled into a cuff that gently wraps around a single nerve, with no stitches required. By targeting only the affected nerve, the device saves surrounding regions from unnecessary cooling, which could lead to side effects.

“You don’t want to accidentally cool down other nerves or the tissues unrelated to the nerve that transmits the pain stimuli,” MacEwan said. “We want to block the pain signals, not the nerves that control motor skills and allow you to use your hand, for example.”

Previous researchers have also examined nerve blockers that use electrical stimulation to dampen painful stimuli. These too have limitations.

“You can’t shut off a nerve with electrical stimulation without activating it first,” MacEwan said. “That can cause additional pain or muscle contractions and is not ideal from a patient’s perspective.”

Disappearing act

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 colleagues demonstrated the world’s first bioresorbable electronic device – a biodegradable implant that accelerates nerve regeneration, published in naturopathy† Then, in 2021, Rogers and colleagues introduced a transient pacemakerpublished in Nature Biotechnology

All components of the devices are biocompatible and will naturally absorb into the body’s biofluids over days or weeks, without the need for surgical extraction. The bioresorbable devices are completely harmless – similar to absorbable sutures.

At the thickness of a sheet of paper, the soft, elastic nerve cooling device is ideal for the treatment of highly sensitive nerves.

“When you think of soft tissues, fragile nerves and a body that is constantly in motion, any interfacing device should have the ability to bend, bend, twist and stretch easily and naturally,” Rogers said. “In addition, you might want the device to just disappear after it’s no longer needed, to avoid delicate and risky surgical removal procedures.”

The work was supported by the Phil and Penny Knight Campus for Accelerating Scientific Impact, the Querrey Simpson Institute for Bioelectronics, and the National Science Foundation (award number CMM1635443).

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