Bioadhesive hydrogel-coupled and miniaturized ultrasound transducer system for long-term, wearable neuromodulation
Kai Wing Kevin Tang, Jinmo Jeong, Ju-Chun Hsieh, Mengmeng Yao, Hong Ding, Wenliang Wang, Xiangping Liu, Ilya Pyatnitskiy, Weilong He, William D. Moscoso-Barrera, Anakaren Romero Lozano, Brinkley Artman, Heeyong Huh, Preston S. Wilson, Huiliang Wang
Nature Communications 2025 · 10.1038/s41467-025-60181-x
Abstract
Transcranial focused ultrasound is a promising non-invasive method for neuromodulation, particularly for neurodegenerative and psychiatric conditions. However, its use in wearable systems has been limited due to bulky devices and reliance on ultrasound gel, which dehydrates and lacks stable adhesion for long-term use. Here, we present a miniaturized wearable ultrasound device, comparable in size to standard electrophysiological electrodes, integrated with a bioadhesive hydrogel for stable, long-term somatosensory cortical stimulation. Our air-cavity Fresnel lens based self-focusing acoustic transducer was fabricated via a lithography-free microfabrication process, achieving 30.7 W/cm² (1.92 MPa) acoustic intensity and 10 mm focal depth. The hydrogel couplant exhibited less than 13% acoustic attenuation and maintained a stable adhesion force of 0.961 N/cm for 35 days. Using this system, we successfully suppressed somatosensory evoked potentials elicited by functional electrical stimulation over 28 days, demonstrating the device's potential for long-term, wearable neuromodulation applications.
Abstract via europepmc.
Exposures
Exposure 1: SFAT-ACFAL (MiniUlTra) 650 kHz tFUS at left S1 (CP3)
Target: primary somatosensory cortex — “left S1”
Device: custom-built · SFAT-ACFAL / MiniUlTra self-focusing air-cavity Fresnel lens transducer, driven by an IGT BBBoq system ✓
| Waveform | pulsed | |
|---|---|---|
| Fundamental frequency (kHz) | 650 | ✓✓✓ |
| Pulse duration (ms) | 0.36 | ✓✓✓⚑ |
| Pulse repetition frequency (Hz) | 1,000 | ✓✓✓⚑ |
| Duty cycle (%) | 36pulse duration × PRF gives 36% | ✓✓✓ |
| Sonication duration (s) | 0.5 | ✓✓✓⚑ |
| Free-field pressure (kPa) | 1,660 | ✓✓✓ |
|---|---|---|
| Free-field Isppa (W/cm²) | 23.1 | ✓✓✓ |
| Free-field Ispta (W/cm²) | not reported | |
| In-situ estimate | not reported | |
| In-situ pressure (kPa) | not reported | |
| In-situ Isppa (W/cm²) | not reported | |
| In-situ Ispta (W/cm²) | not reported |
Pulses of 360 us ON and 640 us OFF at a PRF of 1 kHz for 500 ms, 500 ms ON and 500 ms OFF, starting 100 ms before median nerve stimulation; 3-min trials of 120 epochs, four trial types per block, five blocks per session.
Consistency checks: intensity pressure inconsistent free field.
Flags from extraction
n_subjects— Two groups of 8 healthy volunteers (7 male 1 female; 8 male) are described for the acute and the long-term experiments; whether they overlap is not stated.n_sessions_per_subject— 3 sessions (days 1, 7, 28) in the long-term experiment; the acute experiment's session count is not stated.exposures[0].unspecified_domain.isppa_w_cm2— 23.1 W/cm2 (1.66 MPa) is stated for the volunteer paradigms; the paper characterised the free-field output but does not say this value is free field or through skull.exposures[0].unspecified_domain.pressure_kpa— 1.66 MPa converted to 1660 kPa; domain not stated.exposures[0].timing.pulse_duration_ms— Discussion states '0.5 ms pulse duration, 1 Hz PRF' while Methods give 360 us ON at 1 kHz PRF and a 500-ms ON / 500-ms OFF gating; Methods values recorded.exposures[0].timing.pulse_repetition_frequency_hz— Inconsistent PRF (1 kHz in Methods, 1 Hz in Discussion).exposures[0].timing.sonication_duration_s— 500 ms ON / 500 ms OFF gating of the 1 kHz pulse train; 120 pulses per 3-min trial.auditory_control— Post-hoc questionnaire asked subjects which trials were FUS; 5 of 8 reported being unaware. No control during the experiment.randomised— Paper states tFUS and sham conditions were not randomised across subjects.
Notes: The paper is primarily a device and hydrogel study; human exposures are in the SEP experiments.