Mechanical properties of poly(ionic liquid) hydrogel. (a) Diagrams for the hydrogel at stretching, loading 200 g weight, knife pressing, and puncturing. (b) Pressure-compression curves of the hydrogel with different ionic liquid content. (c) Compressive cycle stability of the hydrogel at 20% compression strain. (d, e) Stress-strain curves of the hydrogel with different ionic liquid and lignin contents, respectively. (f) Stretching cycle stability of the hydrogel at 100% tensile strain.