Polymeric hydrogels, as an important class of polymeric materials, have found widespread use in biomedical and pharmaceutical fields due to their excellent physicochemical and biological characteristics. Degradability is an important parameter when considering the application of polymeric hydrogels in the biomedical fields. Stimuli-responsive degradable (SRD) hydrogel is a kind of intelligent materials, whose network structure can be cleaved in response to external environmental triggers, resulting in a gel-sol or swelling-degradation transition behavior. The stimuli-responsive degradability can be realized by incorporation of environment-sensitive labile or cleavable groups into the gel network. Moreover, this characteristic SRD ability has attracted tremendous interests due to the triggered and controlled degradability in space or in time as compared to the conventional hydrolysis and enzymolysis. This review mainly focuses on the design methods, mechanisms of degradation and most recent studies of SRD hydrogels whose bonds responsively broken by pH, photo and redox triggers. Finally, a perspective on the future research directions of the SRD hydrogels is briefly discussed.

Contents
1 Introduction
2 Stimuli-responsive degradable polymeric hydrogels
2.1 pH-responsive degradable polymeric hydrogels
2.2 Photo-responsive degradable polymeric hydrogels
2.3 Redox-responsive degradable polymeric hydrogels
2.4 Others
3 Conclusion and outlook