People suffering from pain brought on by body ailments, or having to undergo surgeries or amputations, often need to take expensive medication to relieve their pain and facilitate recovery. Some of these medications are known to be highly addictive and have undesired side-effects.

A team of researchers at Northwestern University in the United States have now developed a small new implantable device that relieves pain without the use of drugs. The biocompatible, water-soluble implant wraps around targeted nerves to deliver precise cooling that numbs the nerves and blocks pain signals to the brain.

An external pump enables the user to remotely activate the device and then increase or decrease its intensity. After the implant is no longer needed, it naturally absorbs into the body, thereby bypassing the need for surgical extraction of the device. The device has the potential to be most valuable for patients who undergo routine surgeries or even amputations that commonly require post-operative medications. The surgeons could easily implant the device during their surgical procedure to help manage the patient’s post-operative pain.

Although opioids are extremely effective in relieving pain, many of them are also extremely addictive. The researchers said they were motivated by the idea of treating pain without drugs, and in a manner that can be turned on and off instantly, with control over intensity of relief resting with the user.

Using the analogy of fingers feeling numb when exposed to cold, the researchers explained their new invention by noting that it enables the same effect, but in a programmable way directly and locally on targeted nerves, even those nerves embedded deep within surrounding tissue. They pointed out that although their new invention could sound outlandish, it leverages the simple, common concept of evaporation. Similar to how evaporating sweat cools the body, the device contains a liquid coolant that is induced to evaporate at the specific location of a sensory nerve.

As the nerve cools down, its ability to transmit signals becomes slower and slower until it eventually stops completely. The device specifically targets peripheral nerves, which connect the brain and the spinal cord to the rest of the body. These are the nerves that communicate sensory stimuli, including pain. By delivering a cooling effect to just one or two targeted nerves, the device can effectively modulate pain signals in specific regions of the body.

To induce the cooling effect, the implant contains tiny microfluidic channels. One channel contains the liquid coolant (perfluoropentane), which is already clinically approved as an ultrasound contrast agent, and for use in 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 promptly evaporate. Simultaneously, a tiny integrated sensor monitors the temperature of the nerve to ensure that it is not getting too cold, which could cause tissue damage.

Since excessive cooling can damage the nerve and the fragile tissues around it, the duration and temperature of the cooling must be controlled precisely. By monitoring the temperature at the nerve, the flow rates can be adjusted automatically to set a point that blocks pain in a reversible, safe manner. On-going work seeks to define the full set of time and temperature thresholds below which the process remains fully reversible.

Previous experiments and studies have employed cooling therapies and nerve blockers to relieve pain, but they all had limitations that the new device overcomes. For example, previously researchers have explored cryo-therapies that are injected with a needle. However, results from these experiments were limited and, moreover, they had several disadvantages. For one, the injected cryo-therapy ended up cooling a wide area of tissues, which potentially led to unwanted side effects such as tissue damage and inflammation.

In contrast, the new device developed at Northwestern University is only 5 millimeters wide with one end curled into a cuff that softly wraps around a single nerve, bypassing the need for sutures. By precisely targeting only the affected nerve, the device spares surrounding regions from unnecessary cooling and avoids the possibility of undesired side effects.

Previous researchers also have explored nerve blockers that use electrical stimulation to silence painful stimuli. These, too, have limitations, as you cannot shut down a nerve with electrical stimulation without activating it first. But the activation process could cause additional pain, or muscle contraction, which makes their use unpleasant from a patient’s perspective.

The idea of using biodegradable material for their device was based on technology developed by researchers at Northwestern University back in 2012, when they demonstrated the world’s first bioresorbable electronic device — a biodegradable implant that speeds nerve regeneration. This invention was followed in 2021, by the researchers involved in the current study developing a transient pacemaker.

The university’s storied legacy of developing successful bioresorbable electronic devices, aided the team behind the new device to ensure all its components are biocompatible and naturally absorb into the body’s biofluids over the course of days or weeks, without needing surgical extraction. The bioresorbable devices are completely harmless, and similar to absorbable stitches that are routinely employed in surgeries around the world. Also, with only the thickness of a sheet of paper, the soft, elastic nerve cooling device is ideal for treating highly sensitive nerves.

The presence of soft tissues, fragile nerves and a body that is in constant motion, makes the need for any implanted device to any interfacing device must have the The ability to flex, bend, twist and stretch easily and naturally enables the new implant to avoid harming the surrounding soft tissues and fragile nerves, as well as skirt other issues posed by a body that is in constant motion.

The added advantage of the device being biodegradable makes it ideal, as this negates the need for patients to undergo the pain and hassle of another operation. For the doctors involved, it avoids having to undertake another delicate and potentially risky surgical intervention required to remove the device once it is no longer needed.


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