Stretchable and conductive PAAm@PPy hydrogels with low hysteresis for strain sensing

Conductive hydrogels are promising materials for soft strain sensing because they combine tissue-like mechanics with electrical functionality. However, many existing systems emphasize conductivity or sensitivity at the cost of mechanical reversibility, leading to pronounced hysteresis and limited cyclic stability. Here, we report a two-step fabrication strategy that decouples mechanical and electrical optimization. A highly entangled polyacrylamide (PAAm) hydrogel is first prepared as a mechanically reversible scaffold, followed by in situ polymerization of polypyrrole (PPy) to introduce conductivity, yielding a composite hydrogel (PAAm@PPy). The material exhibits soft-tissue-level stiffness (Young’s modulus of 75 kPa), high stretchability (strain at break of 246%) and low mechanical hysteresis (5.7% at 50% strain). The as-synthesized PAAm@PPy shows an apparent bulk conductivity of 0.094 S cm⁻¹ and a linear positive piezoresistive response with a gauge factor of 2.04 over 0–50% strain, together with stable cyclic sensing (500 cycles at 30% strain). A proof-of-concept finger-bending demonstration confirms its fast response and signal stability. This work establishes a conductive hydrogel design paradigm that prioritizes low hysteresis and cyclic stability through a decoupled two-step co-synthesis of highly entangled hydrogels and conductive polymer, enabling reliable strain sensing for soft electronic applications.