Figure 1.

Molecular architecture and responses of a photoresponsive hydrogel (middle). The photoresponsive groups (black) can represent or be: 1) in the crosslinking points, 2) along the polymer or supramolecular backbone or 3) along the side chains, or 4) dissolved in the aqueous medium of hydrogels. Depending on location and type of photoresponsive moiety, photoresponses include shrinking (A) and partial de‐crosslinking (B), which is typically accompanied with an increase in water uptake and thus an increase in hydrogel volume. The opposite case, a photoinduced increase in crosslinking is typically accompanied by hydrogel shrinking. Complete de‐crosslinking leads to hydrogel degradation (i.e., liquification) (B)*. Further hydrogel responses are: C) photothermal excitation (i.e., a local increase in temperature), D) activation or deactivation of reactive sites, and E) release or capture of substrates.