Strong Tough Poly Acrylic‐co‐Acrylamide Hydrogels via a Synergistic Effect of Fiber and Metal‐Ligand Bonds as Flexible Strain Sensors

Developing conductive hydrogel-incorporated strain sensors with high gauge factor (GF) and toughness for wearable applications is challenging. Herein, a facile strategy to fabricate strong, tough polyacrylamide-co-acrylic acid [P(AAm-co-AAc)] hydrogels via the synergy of fiber and metal-ligand bonds is proposed. Through the secondary equilibrium approach, the pristine P(AAm-co-AAc) gel network is reconstructed with fiber and carboxyl-Zr4+ (Zirconium ion) coordination bonds intertwined over the entire gel matrix, generating a synergistic reinforcement in mechanical properties. The resultant hydrogels display a maximum tensile strength of 8.50 MPa and a fracture energy of 2.75 kJ m(-2), which is 1-2 orders of magnitude greater than the original P(AAm-co-AAc) gels. It is also experimentally approved that by selecting different natural fibers, multivalent metal ions, and synthetic macromolecules containing carboxyl groups, the proposed approach is effective and can be generalized to fabricate strong, tough gels. Additionally, the electrical properties of obtained gel are evaluated by fabricating it into a stretchable strain sensor for object identification or human motion detection. The results reveal a high GF of 5.07 under a strain smaller 55%. These hydrogels are expected to enable numerous applications in soft robotics or wearable healthcare.