A MEMS ultrasound stimulation system for modulation of neural circuits with high spatial resolution in vitro
Jungpyo Lee, Kyungmin Ko, Hyogeun Shin, Soo-Jin Oh, C. Justin Lee, Namsun Chou, Nakwon Choi, Min Tack Oh, Byung Chul Lee, Seong Chan Jun, Il-Joo Cho
Microsystems & Nanoengineering 2019, 5 · 10.1038/s41378-019-0070-5
Abstract
Neuromodulation by ultrasound has recently received attention due to its noninvasive stimulation capability for treating brain diseases. Although there have been several studies related to ultrasonic neuromodulation, these studies have suffered from poor spatial resolution of the ultrasound and low repeatability with a fixed condition caused by conventional and commercialized ultrasound transducers. In addition, the underlying physics and mechanisms of ultrasonic neuromodulation are still unknown. To determine these mechanisms and accurately modulate neural circuits, researchers must have a precisely controllable ultrasound transducer to conduct experiments at the cellular level. Herein, we introduce a new MEMS ultrasound stimulation system for modulating neurons or brain slices with high spatial resolution. The piezoelectric micromachined ultrasonic transducers (pMUTs) with small membranes (sub-mm membranes) generate enough power to stimulate neurons and enable precise modulation of neural circuits. We designed the ultrasound transducer as an array structure to enable localized modulation in the target region. In addition, we integrated a cell culture chamber with the system to make it compatible with conventional cell-based experiments, such as in vitro cell cultures and brain slices. In this work, we successfully demonstrated the functionality of the system by showing that the number of responding cells is proportional to the acoustic intensity of the applied ultrasound. We also demonstrated localized stimulation capability with high spatial resolution by conducting experiments in which cocultured cells responded only around a working transducer.
Abstract via europepmc.
Exposures
Exposure 1: pMUT array stimulation of cocultured cortical neurons and astrocytes
Target: cultured neurons, cultured glia — “cocultured neurons and astrocytes”
Device: custom-built
| Waveform | pulsed | |
|---|---|---|
| Fundamental frequency (kHz) | 430 | ✓✓✓ |
| Pulse duration (ms) | 0.233 | ✓✓✓⚑ |
| Pulse repetition frequency (Hz) | 2,000 | ✓✓✓ |
| Duty cycle (%) | not reportedpulse duration × PRF gives 46.52% | ⚑ |
| Sonication duration (s) | 180 | ✓✓✓ |
| Free-field pressure (kPa) | not reported | |
|---|---|---|
| Free-field Isppa (W/cm²) | 0.025, 1.12swept | ✓✓✓ |
| 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 |
Pulses of 100 cycles of sinusoidal ultrasound were applied at a pulse repetition frequency of 2 kHz. For calcium-imaging experiments, cells were monitored for 120 s baseline, then the transducer was turned on continuously for 180 s (120-300 s), followed by 300 s of post-stimulation observation. Intensity was varied via input voltage (0-66 V) at a fixed distance (1 mm) and frequency; a separate localization test varied horizontal distance from the active transducer channel.
Flags from extraction
exposures[0].timing.pulse_duration_ms— Pulse composed of 100 cycles; converting cycles/frequency requires choosing between the 500 kHz design target and the 430 kHz measured/used resonant frequency, which are both stated but not reconciled by the paper; left not_reported.exposures[0].timing.duty_cycle_pct— Not stated directly; would require the ambiguous pulse duration above plus the 2 kHz PRF, so left not_reported rather than computed.n_subjects— Different response-rate experiments used different numbers of independent culture plates (4 or 5 per condition); no single total number of independent cultures/subjects is stated.