Upconversion Nanoparticles-Enhanced Hydrogels for Both Strain/Stress Sensors and VOCs Adsorption

This study designs and fabricates an ionically conductive hydrogel reinforced by synergistic dynamic physical cross-linking between polyethylenimine (PEI) and lanthanide-doped upconversion nanoparticles (NaGdF 4:Yb 3+, Er 3+ ). The material exhibits a suite of exceptional properties, including high stretchability (>1200%), notable toughness (4.13 MJ m –3 ), robust adhesion (up to 1.6 MPa on wood), and cryogenic tolerance (−20 °C). Functioning as a strain sensor, it demonstrates high sensitivity (a gauge factor up to 7.31), rapid response (∼90 ms), and outstanding cycling stability, enabling precise monitoring of signals ranging from gross joint movements to subtle physiological pulses. Simultaneously, the porous network structure of the hydrogel confers selective adsorption capacity for volatile organic compounds (VOCs). This work provides a strategy for developing high-performance, multifunctional flexible wearable sensors and environmental remediation materials.