Key Points

This groundbreaking device, detailed in Nature Electronics, represents a significant leap forward in pain therapy. While current spinal cord stimulators can be unwieldy and are hard-wired to batteries, the new device is designed to bend and twist with movement and is powered by a wearable ultrasound transmitter without the need for a battery.

It also harnesses machine learning algorithms to customise treatment for each patient. The work was led by Zohrab A. Kaprielian Fellow in Engineering Qifa Zhou, who is also a professor of ophthalmology at the Keck School of Medicine of USC.

At the heart of this innovation is its wireless power supply, eliminating the need for bulky batteries and complex wired interfaces that often require repeated surgeries.

The UIWI stimulator receives its energy from an external, wearable ultrasound transmitter (WUT).

Ultrasound offers a safe, effective, non-invasive method for deep-tissue penetration. The device converts mechanical waves into electrical signals through a phenomenon called the piezoelectric effect.

The core of the UIWI stimulator is a miniaturised piezoelectric element made from lead zirconate titanate (PZT), a highly efficient material for converting incoming ultrasound energy into the electrical power needed for stimulation.

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

Ph.D. candidate in the Zhou Lab and lead author Yushun (Sean) Zeng said the wireless smart miniaturized stimulator had the ability to produce sufficient electrical stimulation intensity by using ultrasound energy, resulting in a more personalized, targeted and localized treatment.

"This energy-converting type is critical for deep stimulation, as ultrasound is a non-invasive and highly penetrating energy in clinical and medical areas," Zeng said.

"By leveraging wireless ultrasonic energy transfer and closed-loop feedback system, this UIWI stimulator removes the necessity for bulky implanted batteries and allows for real-time, precisely adjustable pain modulation," added Zeng.

"From a clinical standpoint, incorporating deep learning-based pain assessment enables dynamic interpretation and response to fluctuating pain states, which is essential for accommodating patient-specific variability," added Zhou Lab Ph.D. candidate Chen Gong, also a lead author on the paper.

The system continuously monitors brain recordings, specifically electroencephalogram (EEG) signals, which reflect a patient's pain levels.

Harnessing AI to assess pain levels: A sophisticated machine learning model, based on a neural network called ResNet-18, analyzes these brain signals and classifies pain into three distinct levels: slight pain, moderate pain, and extreme pain.

This AI model boasts a 94.8% overall accuracy in distinguishing between these pain states. Adapting treatment as needed: Once a pain level is identified, the wearable ultrasound transmitter automatically adjusts the acoustic energy it transmits.

The UIWI stimulator can then sense the propagated energy and convert it into electrical intensity, stimulating the spinal cord. This creates a closed-loop system that provides real-time, personalised pain management.

The UIWI stimulator itself is flexible, bendable, and twistable, allowing for optimal placement on the spinal cord. The electrical stimulation it provides to the spinal cord works by rebalancing the signals that transmit and inhibit pain, effectively suppressing the sensation of pain.

Demonstrated Success in the Lab The Zhou Lab team tested the UIWI stimulator in rodent models, with results demonstrating its effectiveness for pain management.

Researchers successfully relieved chronic neuropathic pain caused by both mechanical stimuli (like a pin prick) and acute thermal stimuli (infrared heat).

Lab tests showed that treatment from the UIWI stimulator led to significant reductions in pain indicators. In one experiment to evaluate whether an animal associates an environment with pain relief, rodents showed a clear preference for the chamber where the pain management system was activated, further confirming the device's effectiveness.

- ANI