Dimensionally Stable and Mechanically Adaptive Polyelectrolyte Hydrogel

Abstract

Abstract Mechanically adaptive hydrogels with reversible cross‐links can change their mechanical characteristics to adapt to the external environment. However, inevitable swelling/shrinkage occurs with the mechanical property change, which impedes the applications of these hydrogels. In this study, mechanical adaptivity with high dimensional stability is achieved in alginate‐based polyelectrolyte hydrogels by introducing an opposite swelling mechanism. The dually crosslinked alginate‐polystyrene sulfonate (Alg‐PSS) hydrogels are constructed through the copolymerization of alginate‐methacrylate (Alg‐MA) and sodium p ‐styrene sulfonate (NaSS), as well as Ca 2+ crosslinking. In the Alg‐PSS hydrogel network, the reversible Ca 2+ ‐carboxylate and Ca 2+ ‐sulfonate cross‐links can be disrupted by Na + and soften the hydrogels. Moreover, the PSS chains crosslinked in the hydrogel network undergo the coil‐globule transition in concentrated NaCl solutions to suppress hydrogel swelling during softening. The optimized Alg‐PSS hydrogel (Alg 5 ‐PSS 0.75 ‐MBAA 2.5 ) shows a dramatic tensile modulus change from 191.3 kPa in deionized water (DIW) to 15.1 kPa in 2.0 mol L −1 NaCl solution with a negligible volume increase ratio of only 0.6%. The Alg‐PSS hydrogels may find applications in artificial valves or soft robotics, where high dimensional stability and invariable volume are required for smart hydrogels.