“…[1][2][3] Therefore, a series of PC materials with vivid structural colors have been fabricated, which have significant application value in sensors, [4][5][6] drug delivery, [7][8][9] actuators, [10][11][12] printing [13][14][15] and other fields. [16][17][18] A hydrogel is a stimulus-responsive material due to its elastic network that can shrink and swell, so it is usually combined with PC to fabricate stimulus-responsive photonic hydrogels, which realize a visual conversion to optical signals by changing structural colors in response to external stimuli, such as light, 19,20 organic compounds and solvents, [21][22][23][24] metal ions, 25,26 temperature, [27][28][29] and pH. [30][31][32] For example, Zhao et al 33 combined a polymeric hydrogel with an SiO 2 inverse opal structure to prepare an inverse opal hydrogel (IOH) sensor which can respond to pH, temperature and ultraviolet light.…”