GHz Ultrasonic Chip-Scale Device Induces Ion Channel Stimulation in Human Neural Cells
Priya S. Balasubramanian, Ankur Singh, Chris Xu, Amit Lal
Scientific Reports 2020 · 10.1038/s41598-020-58133-0
Abstract
Emergent trends in the device development for neural prosthetics have focused on establishing stimulus localization, improving longevity through immune compatibility, reducing energy re-quirements, and embedding active control in the devices. Ultrasound stimulation can single-handedly address several of these challenges. Ultrasonic stimulus of neurons has been studied extensively from 100 kHz to 10 MHz, with high penetration but less localization. In this paper, a chip-scale device consisting of piezoelectric Aluminum Nitride ultrasonic transducers was engineered to deliver gigahertz (GHz) ultrasonic stimulus to the human neural cells. These devices provide a path towards complementary metal oxide semiconductor (CMOS) integration towards fully controllable neural devices. At GHz frequencies, ultrasonic wavelengths in water are a few microns and have an absorption depth of 10-20 µm. This confinement of energy can be used to control stimulation volume within a single neuron. This paper is the first proof-of-concept study to demonstrate that GHz ultrasound can stimulate neurons in vitro. By utilizing optical calcium imaging, which records calcium ion flux indicating occurrence of an action potential, this paper demonstrates that an application of a nontoxic dosage of GHz ultrasonic waves [Formula: see text] caused an average normalized fluorescence intensity recordings >1.40 for the calcium transients. Electrical effects due to chip-scale ultrasound delivery was discounted as the sole mechanism in stimulation, with effects tested at α = 0.01 statistical significance amongst all intensities and con-trol groups. Ionic transients recorded optically were confirmed to be mediated by ion channels and experimental data suggests an insignificant thermal contributions to stimulation, with a predicted increase of 0.03 o C for [Formula: see text] This paper paves the experimental framework to further explore chip-scale axon and neuron specific neural stimulation, with future applications in neural prosthetics, chip scale neural engineering, and extensions to different tissue and cell types.
Abstract via europepmc.
Exposures
Exposure 1: 1.47 GHz AlN chip-scale transducer, continuous wave, 20 s, SH-SY5Y cells
Target: cultured neurons — “SH-SY5Y neuroblastoma cells differentiated with retinoic acid to a more neural phenotype”
Device: custom-built · piezoelectric AlN thin-film transducers fabricated on double-polished silicon wafers
| Waveform | continuous | |
|---|---|---|
| Fundamental frequency (kHz) | 1,470,000 | ✓✓✓⚑ |
| Pulse duration (ms) | not applicable | |
| Pulse repetition frequency (Hz) | not applicable | |
| Duty cycle (%) | not applicable | |
| Sonication duration (s) | 20 | ✓✓✓ |
| Free-field pressure (kPa) | not reported | |
|---|---|---|
| Free-field Isppa (W/cm²) | 0.013, 0.05, 0.3swept | ✓✓✓⚑ |
| Free-field Ispta (W/cm²) | not reported | |
| In-situ estimate | not applicable | |
| In-situ pressure (kPa) | not applicable | |
| In-situ Isppa (W/cm²) | not applicable | |
| In-situ Ispta (W/cm²) | not applicable |
Single 20 s continuous-wave exposure per recording: at least 10 s without stimulus, 20 s of ultrasound, then post-stimulus recording (about 50 s). Intensities of 0.013, 0.05 and 0.3 W/cm2 (range recorded as 0.013-0.3). Drive 2 V, 5 V (and 10 V for a thermal control at 1.2 W/cm2). A second exposure after a 120 s recovery was used in a recovery experiment.
Consistency checks: f0 out of range.
Flags from extraction
exposures[0].free_field.isppa_w_cm2— Intensities are the paper's estimate "in water" derived from interferometer displacement measured in air at the silicon-air interface; the metric (peak vs average) is not named and the authors say actual intensity at the cells is lower.exposures[0].fundamental_frequency_khz— 1.47 GHz converted to 1,470,000 kHz.n_subjects— Only trial and ROI counts are given (three repeated trials per intensity); no count of cultures or samples stated.exposures[0].timing.protocol_description— Higher 1.2 W/cm2 exposure was used only for thermal imaging, not for the stimulation experiments.