MXene-doped hydrogels for stretch-insensitive low-pass filters and human motion monitoring

Hydrogel-based flexible electronics have attracted increasing interest due to their mechanical compliance and versatile electrical characteristics. In this work, we develop ultra-stretchable MXene-doped semi-interpenetrating polymer network (semi-IPN) hydrogels with excellent mechanical robustness (elongation at break up to 1210%) and electrical conductivity (1 S/m), enabling reliable sensing over both small (1%–5%) and large (10%–50%) strain ranges with linear responses. The underlying sensing mechanism is attributed to the synergistic evolution of the MXene-based electronic network and ionic migration channels under mechanical deformation. Based on these properties, hydrogel-based resistors and capacitors were fabricated and systematically evaluated under uniaxial stretching. Notably, the resistor and capacitor exhibit opposite strain-dependent behaviors, which allows mutual electrical compensation when integrated into a classic RC architecture. Leveraging this antagonistic coupling, we design a stretch-insensitive hydrogel low-pass filter whose cut-off frequency remains stable under mechanical deformation. Furthermore, benefiting from the hydrogel’s softness, stretchability, and robust signal output, its applicability in epidermal sensing is demonstrated through stable detection of facial expressions and joints motions. This work presents a versatile material–device strategy for constructing stable signal-processing components and multifunctional soft electronic systems.