Strong and tough chitosan-based conductive hydrogels cross-linked by dual ionic networks for flexible strain sensors

Conductive hydrogels made of eco-friendly materials have been concerned in the field of flexible electronic devices (FEDs). Great efforts have been made to improve mechanical properties of conductive hydrogels, which are still unsatisfactory for natural polymer hydrogels. Herein, a strategy to improve mechanical properties of chitosan-based hydrogels by constructing dual ionic networks via cations and anions is reported. Through the double crosslinking of high-valent cations (Al³⁺) and anions (SO₄^2-) with the polymers, as well as the salting-out effect of salts, the resulting hydrogels have evolved tensile strength and toughness, which are up to 8 MPa and 28.4 MJ/m³, respectively. The reversible ionic networks play a vital role in tensile recovery, further leading to stability in the relative resistance change of the hydrogels under various deformation. The dual ionic crosslinked hydrogels possess moderate gauge factor (1.2-2.9) at tensile strain from 100 % to 400 %, which are sensitive to monitor human movements as flexible strain sensors. In addition, the hydrogels show perfect antibacterial activity against E. coli and S. aureus. Overall, this work provides an effective way to fabricate strong and tough conductive hydrogels based on chitosan for promising application of FEDs.