Phytic acid and magnesium sulfate synergistically enhanced P(AM-co-AANa)/gelatin/carboxymethyl chitosan hydrogels with high-strength and low-modulus for flexible strain sensors

Conductive hydrogels are ideal candidates for flexible electronics owing to their excellent biocompatibility and flexibility. However, achieving excellent mechanical strength and conductivity simultaneously remains a significant challenge. Herein, we report a mechanically robust and ionically conductive hydrogel that can be readily fabricated via a two-step strategy involving polymerization of a hybrid network composed of poly(acrylamide- co ‑sodium acrylate), gelatin and carboxymethyl chitosan followed by immersion in a mixed solution of phytic acid and magnesium sulfate. Phytic acid reinforced hydrogen bonding interactions and acted as dynamic crosslinkers. Sulfate ions promoted the hydrophobic aggregation and triple helices formation via the Hofmeister effect, and magnesium ions coordinated with carboxy groups among the polymer network. These newly formed interactions synergistically strengthened the hydrogel network. The resulting hydrogel exhibited exceptional tensile strength, high stretchability, and remarkable toughness, yet low modulus. Additionally, the incorporation of free ions endowed the hydrogels with high conductivity, making them suitable for flexible strain sensors. These hydrogel-based sensors demonstrated excellent linear responsiveness over a wide strain range with satisfactory sensitivity, thus enabling accurate monitoring of diverse human motions from large joint bending to subtle vocal vibrations. This work presents an effective strategy to design conductive and tough hydrogels for flexible electronics.