A Monolithic Janus Hydrogel Pressure Sensor for Wearable Motion and Physiological Monitoring

Sensitive pressure sensors with easy fabrication and stable performance are essential for next-generation wearable electronics. Here, we report a monolithic Janus hydrogel-based capacitive pressure sensor composed of two conductive layers and an intervening dielectric layer, forming an all-hydrogel sensing architecture. The conductive layers are fabricated from poly(3,4-ethylenedioxythiophene) (PEDOT) incorporated poly(ethylene glycol) diacrylate (PEGDA) hydrogels, while the dielectric layer consists of a pristine PEGDA matrix, enabling intimate interfacial bonding without the need for additional adhesives. The mechanical properties of the hydrogel system reveal tunable swelling behavior and elastic modulus as a function of PEGDA concentration. The resulting sensor displays  a sensitivity of 0.27 kPa^-1 in the pressure range of 0.49 to 3.43 kPa, and the operating range could extend upto 5.39 kPa. Additionally, the sensor exhibits stable electromechanical performance, featuring a short response time of 23 ms for the rising edge and 36 ms for the falling edge, allowing it to detect the pressure applied under repeated stimuli. Owing to its flexible nature, the designed sensor demonstrates reliable detection of a wide range of mechanical stimuli, from small physiological signals to human motions. Our results highlight that the Janus hydrogel with integrated conductive and dielectric layers could be a promising platform for wearable health monitoring.