Chronic pain affects millions of people globally, often leading to long-term disability and dependence on opioid medications, which carry significant risks of side effects and addiction. While implantable spinal cord stimulators offer a non-opioid alternative, they typically involve invasive surgery, high costs, and require regular battery replacements. Addressing these limitations, biomedical engineers have developed a new wireless, flexible, ultrasound-powered implantable device designed to deliver personalized pain relief without the need for batteries or invasive procedures.

This breakthrough device was developed by researchers at the USC Viterbi School of Engineering (Los Angeles, CA, USA) and detailed in Nature Electronics. The team designed the system as a fully wireless, self-adaptive solution to chronic pain. Called the ultrasound-induced wireless implantable (UIWI) stimulator, the system is secured to the spinal cord and powered externally through a wearable ultrasound transmitter, eliminating the need for internal batteries or hard-wired connections. By leveraging machine learning algorithms, the device also enables real-time adjustments to pain therapy based on each individual’s condition. At the core of the innovation is its wireless energy transfer and adaptive stimulation mechanism. The UIWI stimulator is powered using ultrasound transmitted through the skin, a method that enables safe, non-invasive deep-tissue energy delivery.

The device contains a miniaturized piezoelectric element made of lead zirconate titanate (PZT), which converts the ultrasound’s mechanical energy into electrical pulses via the piezoelectric effect. These pulses stimulate the spinal cord to disrupt pain signals before they reach the brain. Importantly, the stimulator is bendable and twistable, allowing for seamless integration with the spine’s movements. The system also incorporates an artificial intelligence model that interprets brain activity in real time. By analyzing EEG signals, the ResNet-18-based neural network model classifies pain into three categories—slight, moderate, and extreme—with a 94.8% accuracy rate. The wearable transmitter adjusts its ultrasound output based on these inputs, creating a closed-loop feedback system that dynamically delivers the appropriate level of electrical stimulation. This tailored approach ensures the treatment remains aligned with the patient’s current pain level, maximizing relief while minimizing unnecessary stimulation.

To validate the system’s effectiveness, researchers tested the UIWI stimulator in rodent models of chronic neuropathic pain. Results showed that the device significantly reduced responses to both mechanical and thermal stimuli. In behavioral tests, rodents consistently favored environments where the device was active, indicating clear pain relief. These findings confirmed both the physiological and behavioral effectiveness of the system. The flexibility and responsiveness of the device represent a major advancement in neuromodulation-based therapies. Looking to the future, the team aims to miniaturize the system even further, potentially enabling implantation via syringe and integration with untethered ultrasound arrays for enhanced portability. The external wearable could evolve into a patch-based format, combining imaging and stimulation for more precise control. Smartphone integration is also under consideration, allowing users to manage and monitor their pain relief through a digital interface. Altogether, this innovation marks a significant leap toward personalized, non-invasive chronic pain management, moving beyond the limitations of current technologies and offering a more effective, intelligent alternative to opioid medications.

“What truly sets this device apart is its wireless, smart and self-adaptive capability for pain management,” said USC researcher Qifa Zhou, who led the research. “We believe it offers great potential to replace pharmacological schemes and conventional electrical stimulation approaches, aligning with clinical needs for pain mitigation.”

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