Al3+ coordinated and Hofmeister-reinforced conductive chitosan/PEDOT:PSS hydrogels for highly fatigue-resistant wearable strain sensor

Dual-network design with ion-electron conduction balances mechanical and electrical performance. • High tensile strength, toughness, and conductivity ensure stable sensing foundation. • Rapid photoinitiated fabrication enables efficient and scalable hydrogel preparation. • Long-term stable sensing performance sustained over 1000 stretching cycles. • Broad detection ranges from large joint movements to subtle facial expressions. Achieving mechanically robust yet highly conductive hydrogels remains a central challenge for skin-interfaced wearable sensors, as network reinforcement often compromises charge transport and long-term sensing stability. Here, we report a coordination-Hofmeister dual-network engineering strategy for constructing a chitosan/PAA/PEDOT:PSS conductive hydrogel that integrates high mechanical strength, efficient charge transport, and environmental adaptability. A primary hybrid network (PECA) is formed in an ethylene glycol/water medium through one-pot photoinitiated polymerization, simultaneously establishing covalently crosslinked PAA chains, Al 3+ -mediated coordination between PAA and the PSS component of PEDOT:PSS, together with electrostatic interactions involving chitosan, and a homogeneously distributed conductive polymer phase. Subsequent ammonium-sulfate-induced Hofmeister salting-out promotes polymer-chain dehydration and entanglement, generating a compact secondary physical network and yielding a double-network hydrogel (DECA). The optimized DECA hydrogel achieves a tensile strength of 1.74 MPa, toughness of 6.69 MJ m −3 , and conductivity of 6.52 S/m, corresponding to 6.9-, 5.0-, and 81-fold enhancements over the pristine hydrogel, respectively. Benefiting from reversible coordination/hydrogen-bonding interactions and stable electronic-ionic conductive pathways, the hydrogel sensor maintains reproducible resistance responses after 1000 stretching cycles. When mounted on human skin, the DECA sensor enables real-time monitoring of multi-scale physiological motions, from large joint movements to subtle facial expressions. This work provides a facile strategy for resolving the mechanical-electrical trade-off in conductive hydrogels and advances their application in durable wearable electronics. An Al 3+ coordination and Hofmeister salting-out strategy is used to engineer chitosan/PAA/PEDOT:PSS double-network conductive hydrogels. The coordinated and sulfate-reinforced network simultaneously improves tensile strength, toughness, conductivity, and cyclic sensing stability, enabling skin-mounted strain sensors for real-time monitoring of joint motion and subtle facial expressions. Download: Download high-res image (114KB) Download: Download full-size image