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Review
. 2021 Jan 27:15:629056.
doi: 10.3389/fnins.2021.629056. eCollection 2021.

Mechanisms and Applications of Neuromodulation Using Surface Acoustic Waves-A Mini-Review

Danli Peng  1 , Wei Tong  1   2   3 , David J Collins  4 , Michael R Ibbotson  2   3 , Steven Prawer  1 , Melanie Stamp  1
Affiliations
Review

Mechanisms and Applications of Neuromodulation Using Surface Acoustic Waves-A Mini-Review

Danli Peng et al. Front Neurosci. .

Abstract

The study of neurons is fundamental for basic neuroscience research and treatment of neurological disorders. In recent years ultrasound has been increasingly recognized as a viable method to stimulate neurons. However, traditional ultrasound transducers are limited in the scope of their application by self-heating effects, limited frequency range and cavitation effects during neuromodulation. In contrast, surface acoustic wave (SAW) devices, which are producing wavemodes with increasing application in biomedical devices, generate less self-heating, are smaller and create less cavitation. SAW devices thus have the potential to address some of the drawbacks of traditional ultrasound transducers and could be implemented as miniaturized wearable or implantable devices. In this mini review, we discuss the potential mechanisms of SAW-based neuromodulation, including mechanical displacement, electromagnetic fields, thermal effects, and acoustic streaming. We also review the application of SAW actuation for neuronal stimulation, including growth and neuromodulation. Finally, we propose future directions for SAW-based neuromodulation.

Keywords: mechanisms; neuromodulation; neuron; neurostimulation; surface acoustic wave; ultrasound.

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Conflict of interest statement

SP was a shareholder and public officer of Carbon Cybernetics Pty Ltd., a company developing diamond and carbon-based medical device components. SP was a shareholder in iBIONICS, a company developing a diamond based retinal prosthesis. The remaining authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Figures

FIGURE 1
FIGURE 1
Surface acoustic wave (SAW) neurostimulation mechanisms. (A) SAW device. Radio frequency AC voltage is applied to the interdigital transducer (IDT) to generate a SAW which propagates on the surface of the piezoelectric substrate. The SAW refracts the longitudinal wave into the neural medium at the Rayleigh angle. The refracted longitudinal wave results in acoustic streaming. (B) Acoustic effects caused by SAW device. In addition to the acoustic vibration, other effects due to the high frequency electromagnetic field, heating, and shear forces may also be considered. (B–H) Bioeffects caused by acoustic effects. (C) Ion channels can be modulated, and the generated ultrasound can change membrane curvature, surface area, and generate intramembrane cavities. (D) Action Potentials (AP) can therefore be evoked and modulated. (E) The ultrasound can perturb the extracellular matrix and cytoskeleton. (F) Ultrasound can also loosen the extracellular matrix and fluidize the cytoskeleton, analogous to the rejuvenation of soft glassy materials. (G) SAW actuation generates acoustic forces including the acoustic radiation force, intercellular Bjerknes force, and the stokes drag force. (H) Neurite outgrowth can be patterned via SAW. (I) In vitro application using SAW device to stimulate brain slice. (J) Potential In vivo application using wearable or implantable SAW device to treat neurological disorder.
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