Researchers at the University of Southern California have miniaturised the current crop of electrical stimulators that are often implanted into the worst affected individuals, making them smaller and more effective. Their flexible ultrasound-induced wireless implantable (UIWI) stimulator is secured to the spine, and is able to warp and twist alongside the body. It is powered by ultrasound rather than a bulky battery.
“We believe it offers great potential to replace pharmacological schemes and conventional electrical stimulation approaches, aligning with clinical needs for pain mitigation,” said Qifa Zhou, professor of ophthalmology at the Keck School of Medicine at the University of Southern California.
A miniaturised piezoelectric element within the device converts incoming ultrasound energy from an external transmitter (which the patient also wears) into electrical power that stimulates the spinal cord, blocking signals that transmit from the site of pain to the brain.
“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.”
It is a potentially transformational technology that combines the best of AI and practical engineering, monitoring EEG signals from the brain repeatedly to know when to intervene, using a machine learning model that has nearly 95% accuracy.
The device is not the only one aimed at stopping pain for those in need. The Inceptiv closed loop spinal cord stimulator from medical firm Medtronic, approved for use in the US in April 2024, deploys a wafer-thin pulse generator into the lower back, which checks for signals 50 times a second and automatically applies current to keep pain at bay.
Other devices focus on the dorsal root ganglion, a single relay along which pain messages travel through the body. Proclaim’s DRG Neurostimulation system implants tiny thread-like leads to the point where peripheral nerves pass signals to the spinal cord, delivering very low energy pulses. That device is mostly used for lower limb pain.
Some projects use different techniques to dull pain. A water-soluble device developed at Northwestern University in Illinois instead uses precise, targeted cooling on peripheral nerves, before dissolving when it is no longer needed. The lead engineer behind that device, John A Rogers, said that helping relieve pain is a major driver for him and his colleagues.
“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 relief,” he says.
‘Miniaturisation makes all of this possible’
While much of the attention on the Southern California project is likely to be focused on the advanced AI tech that helps decide when to intervene, the design of the device itself is a massive engineering innovation
“The smaller the devices become, the more convenient they are for medical staff to use; the more comfortable and unobtrusive they are for patients to wear; and if implanted, the quicker and easier they are for patients to recover from surgery,” said Tim Burbey, president of Blueshift Materials. “Miniaturisation makes all of this possible.”
As more components – computer chips, sensors and batteries – are crammed into increasingly smaller medical devices, engineers in the sector face more formidable constraints in incorporating thermal protection to ensure both patient safety and device integrity, said Burbey.
“Medical sensors in devices that treat or diagnose conditions are susceptible to thermal noise,” said Burbey. “This noise can lead to fluctuations in readouts, distort images and result in the mismanagement or incorrect diagnosis of patients.”
Overcoming those challenges, alongside the task of shrinking the pieces that make up such a device, is a major endeavour. And when those devices are implanted in the body, other variables come into play. “Because of the space premium with implantable medical devices, mitigating the temperature fluctuations of the surrounding tissues becomes increasingly difficult,” said Burbey.
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