Body-Temperature-Responsive Balloon Actuator for Adaptive In-Ear Microneedle Electrode Deployment

Abstract

Conventional in-ear electrodes face challenges such as inconsistent skin contact, motion artifacts, and discomfort, limiting their reliability in dynamic conditions. To overcome these limitations, this study presents a body-temperature responsive in-ear balloon actuator (BBA) based on liquid-to-vapor phase change, integrated with silver microneedle electrodes for stable electrophysiological monitoring. The dual-layer balloon structure encapsulates a phase-change fluid core, expanding at 36–37°C to ensure conformal skin contact while minimizing motion artifacts and mechanical pressure. Among 3 tested designs, the dual-material design proved optimal, achieving a peak insertion force of 0.05 N and maintaining impedance fluctuations below 5%. A wearable system was further validated through dynamic tests, demonstrating a 20% reduction in motion artifacts compared to conventional electrodes. These findings highlight the actuator’s potential for stable and comfortable wearable electrophysiological monitoring.