Chronic pain conditions, characterized by persistent or recurrent pain in specific parts of the body, can be highly debilitating and often significantly reduce the quality of life of the individuals experiencing them. Statistics suggest that approximately 20.9% of adults living in the United States have experienced chronic pain at some point in their lives, while 6.9% have experienced severe chronic pain that significantly impacted their daily functioning and well-being.

Currently, chronic pain is primarily treated using pain-relief medications, many of which are based on opioids. Yet many of these pharmaceutical drugs are highly addictive and have severe side effects, so they often end up causing more harm than good.

In recent years, some scientists and engineers have been trying to devise alternative pain-management strategies that do not rely on opioids and can ease the pain of patients without adversely impacting their health. One proposed solution entails the use of implantable electrical stimulators, devices that can be surgically inserted into a patient’s body, delivering electrical signals to their nerves or spinal cord to reduce the pain they are experiencing.

Despite their potential for the treatment of chronic pain conditions, most existing implantable electrical stimulators have significant limitations. In fact, these devices can damage a patient’s body during the surgeries needed to implant them. Moreover, they are often expensive, and the battery powering them needs to be periodically changed.

Researchers at the University of Southern California and other institutes recently developed a new flexible, wireless and battery-free implantable stimulator that could overcome some of the limitations of previously introduced pain-management solutions. This device, introduced in a paper published in Nature Electronics, is powered via an external wearable ultrasound transmitter and also incorporates machine learning algorithms that can classify a patient’s pain levels, adjusting the intensity of the electrical stimulation that it delivers accordingly.

“Chronic pain management typically involves opioids, which are associated with severe side effects such as addiction,” Yushun Zeng, Chen Gong, and their colleagues wrote in their paper.

“Implantable percutaneous electrical stimulators are a promising alternative approach to pain management. However, they are expensive, can cause damage during surgery and often rely on a battery power supply that must be periodically replaced.”

The key objective of this recent study was to devise a less invasive implantable electrical stimulator that can reduce the pain of patients, and that does not need to be periodically removed to change its batteries. The ultrasonic wireless implant developed by the researchers is comprised of a composite piezoelectric receiver, micro-electronic components, and stimulating electrodes integrated into a flexible printed circuit board.

“We report an integrated, flexible ultrasound-induced wireless implantable stimulator combined with a pain detection and management system for personalized chronic pain management,” wrote Zeng, Gong and their colleagues.

“Power is supplied to the stimulator by a wearable ultrasound transmitter. We classify pain stimuli from brain recordings by developing a machine learning model and program the acoustic energy from the ultrasound transmitter and, therefore, the intensity of electrical stimulation.”

The researchers tested their proposed pain management system in a series of tests involving rodents that were experiencing varying levels of pain. They found that their device accurately predicted the levels of stress experienced by the animal and adapted the electrical stimulations it delivered accordingly, ultimately easing most of the animal’s pain.

“We show that the implant can generate targeted, self-adaptive and quantitative electrical stimulations to the spinal cord according to the classified pain levels for chronic pain management in free-moving animal models,” wrote Zeng, Gong and their colleagues.

In the future, the ultrasonic wireless implant developed by this team of researchers could soon be improved and tested in experiments involving other animals, then eventually in human clinical trials. Moreover, its underlying design could inspire the development of other devices that rely on ultrasound technology for the mitigation of chronic pain.

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