Fig. 4. (A) Schematic light-induced shape-memory transitions between the triangle-shaped, high-stiffness hydrogel crosslinked by glucosamine–boronate ester bridges and trans-azobenzene stabilized duplex crosslinkers, and the low-stiffness hydrogel crosslinked by the glucosamine–boronate esters only (the duplex bridges are separated through the photoisomerization of the trans-azobenzene units to the cis-azobenzene states). The glucosamine–boronate ester bridges provide the memory code to regenerate the high-stiffness hydrogel, by the photoisomerization of the cis-azobenzene units to the trans-azobenzene states. Bottom: images corresponding to the reversible and cyclic transitions between the triangle-shaped, stiff hydrogel in state “A” and the quasi-liquid, lower-stiffness, shapeless hydrogel in state “B” upon the photoinduced cyclic transitions between the trans-azobenzene and cis-azobenzene tethers conjugated to the polymer chains. (B) Schematic self-healing of two hydrogel pieces composed of the soft, low-stiffness hydrogel as a result of the photochemically triggered self-healing of the hydrogel pieces by the light-induced transformation of the cis-azobenzene units to the trans-azobenzene units, and the crosslinking of the hydrogel by the glucosamine–boronate esters and the trans-azobenzene units associated with the duplex units. Bottom: images corresponding to the steps involved in the self-healing process.