Fig. 3.

Visual imaging of the stiffness changes of the triggered CDN hydrogels. a The E₁-induced transition of the medium-stiffness CDN hydrogel X to the stiffer CDN hydrogel Y and the E₁’-stimulated reverse process. The transition of hydrogel X to the stiffer hydrogel Y is evident by the shrinkage of the triangle-shaped hydrogel. The E₁’-induced transition of hydrogel Y to X is evident by the regeneration of the original larger size of the triangle. b The E₂-induced transition of the triangle-shaped, medium-stiffness hydrogel X into the low-stiffness CDN hydrogel Z. Scale bars in all images correspond to 0.5 cm