text: Various PPGs, often featuring the 2-nitrobenzyl motif, have been used to generate numerous gels. In one example, researchers incorporated PPGs into a silica-based sol-gel. In a second example, a hydrogel was synthesized to include protected Ca ions. Finally, PPGs have been utilized to cross-link numerous photodegradable polymers, which have featured linear, multi-dimensional network, dendrimer, and branched structures.