Hydroxypropyl cellulose-based conductive hydrogels with water-content-regulated electromagnetic shielding and multifunctional sensing

A thermoresponsive PNIPAM/HPC-CNT hydrogel enables dynamic EMI shielding. • Water-content evolution governs the electromagnetic response of hydrogels. • A tunable EMI shielding range of ~21.4 dB is achieved in the X-band. • Reversible EMI shielding ON/OFF switching occurs within a mild temperature window. • The hydrogel integrates EMI shielding with temperature and strain sensing. Thermoresponsive polysaccharide hydrogels have attracted considerable attention for wearable electronics owing to their high water content, flexibility, and stimuli-responsive characteristics. However, the role of hydration-state evolution in regulating electromagnetic behavior remains insufficiently understood. Herein, a hydroxypropyl cellulose (HPC)-based thermoresponsive conductive hydrogel was developed by integrating a poly(N-isopropylacrylamide) (PNIPAM)/HPC double network with a carbon nanotube (CNT)-based conductive framework. The reversible phase transition of the PNIPAM/HPC network induced temperature-dependent dehydration and structural reconstruction, thereby dynamically modulating the conductive pathways, dielectric loss, and impedance matching. Consequently, the representative hydrogel exhibited a shielding effectiveness of approximately 29.8 dB at 25 °C, which decreased to 8.4 dB at 60 °C, corresponding to a tunable range of 21.4 dB. Furthermore, the incorporation of NaCl effectively lowered the phase-transition temperature, enabling reversible temperature-dependent modulation of electromagnetic shielding within a mild temperature window of 15–40 °C. More importantly, the combined changes in hydration state, dielectric dissipation, and effective attenuation ultimately led to a pronounced decrease in shielding effectiveness. In addition to dynamic electromagnetic regulation, the hydrogel demonstrated reversible temperature- and strain-responsive sensing for monitoring skin temperature and human motion. This work highlights hydration-state engineering as an effective strategy for regulating electromagnetic properties in polysaccharide-based hydrogels and provides new opportunities for multifunctional wearable bioelectronics.