An ultra-stretchable, tough yet resilient hydrogel with high fatigue fracture threshold

The gel integrates high stretchability, high toughness and high resilience. • The ratio of residual strain to applied strain is as low as 4.48% at 2000% strain. • The gel achieves high fatigue threshold (1.25 kJ/m2) via heterogeneous structure. • The gel maintains good mechanical and electrical performance at −20 °C. Hydrogels have emerged as a research focus in flexible electronics owing to their inherent softness and biocompatibility. However, practical applications are often hindered by insufficient stretchability, flaw sensitivity, significant hysteresis, and a tendency to freeze at subzero temperatures. Here, we designed an anti-freezing hydrogel that combines high toughness, resilience, and notch insensitivity, based on a network of polyacrylic acid (PAA), polyethylene oxide (PEO), CaCl₂, and KCl. The highly entangled PAA/PEO network provides fundamental elasticity, facilitates stress transfer between chains, and ensures resilience. Meanwhile, Ca 2+ ions bind with carboxyl groups from PAA and ether oxygens from PEO, forming robust domains to strengthen the network and impede crack propagation. The unbound parts of CaCl₂ and KCl act not only as mobile ions to enhance ionic conductivity, but also as hydrating agents for freeze resistance. The resulting hydrogel demonstrated remarkable stretchability (2077%), low hysteresis (with the ratio of residual strain to applied strain was as low as 4.48% at 2000% strain), high fracture toughness (7.3 kJ/m 2 ), and high fatigue threshold (1.25 kJ/m 2 ). Its mechanical and electrical properties were well maintained even at −20 °C. This work should provide a promising strategy for designing high-performance hydrogels toward next-generation flexible electronics. Download: Download high-res image (291KB) Download: Download full-size image