Editors' ChoiceNEUROMODULATION

Not “dust” any neural stimulator

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Science Translational Medicine  18 Mar 2020:
Vol. 12, Issue 535, eabb2775
DOI: 10.1126/scitranslmed.abb2775

Abstract

An untethered, ultrasound-powered milliscale device can stimulate peripheral nerves in rats.

External stimulation of nerves with stimulation devices has shown therapeutic benefits for a myriad of conditions, such as chronic pain, Parkinson’s disease, depression, incontinence, and heart conditions. Currently available clinical neural stimulators are battery-powered and occupy over a teaspoon of volume, necessitating implantation in pockets under the skin and tunneling of leads to a distant site where they interface with the central and peripheral nervous system. Challenges such as infection, lead fatigue, and power failure remain, motivating the design of miniaturized, untethered devices.

To address these challenges, Piech et al. have reported a tiny device called StimDust: a wireless, lead-free neural stimulator about the same volume as a bubble in a bottle of sparkling water. It includes a piezoceramic transducer that acts as the antenna of the system, a tiny integrated circuit, and a charge storage capacitor. The device has electrodes that contact a nerve through a surrounding cuff. By using ultrasound and a centimeter-scale external component, the device can receive and transmit data. A wireless protocol designed by the researchers allows programmability and reduces power consumption and the need for on-board memory.

Piech et al. demonstrated that this device can harvest ultrasonic power, decode data for stimulation parameters, and generate corresponding stimulation pulses—even when embedded in explanted porcine tissue at a depth > 5 cm from the external transceiver. In an in vivo demonstration of StimDust function, the cuff was implanted on the sciatic nerve in a rat model, and the external transceiver was coupled to the skin with ultrasound gel. The system produced repeatable action potentials in the sciatic nerve and corresponding twitches in the innervated muscles, as measured by electromyography. Moreover, the authors showed that the device functions at less than 10% of the safety limit for diagnostic ultrasound.

Questions that will need to be addressed before chronic clinical implantation include whether the parylene encapsulation will be hermetically sufficient and whether the host response will substantially affect the electrical impedance of the peri-implant tissue. Potential delamination of the components should also be considered. Nevertheless, this “magic dust” has vast promise in closing the loop for neural stimulation for a wide range of therapeutic applications.

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