a) Swelling and contraction of photoresponsive hydrogel composed of azobenzoic acid and four-armed PEG. i) Dry hydrogel with trans-azobenzene. ii) Swollen hydrogel loaded with Alexa Fluor 750. iii) After UV illumination, photoisomerization leads to hydrogel contraction and Alexa Fluor 750 release. b) Chemical structure of the biodegradable, biocompatible, amphiphilic block copolymer with paclitaxel (PTX) and Ru complexes (poly (Ru/PTX)). Cleavage of the Ru complex, generation of 1O2 and release of anticancer drug PTX can be induced with red light irradiation. c) Ex vivo histological analyses of tumor sections after different treatments by hematoxylin and eosin (H&E) and (TUNEL) terminal deoxynucleotidyl transferase mediated UTP end labeling staining. Scale bar: 100 μm. Significant tumor cell nuclear ablation and higher level of apoptosis (green) in tumor tissues from mice in the poly (Ru/PTX) can be observed in H&E and TUNEL staining, respectively. Adapted with permission from [224]. Copyright 2018 American Chemical Society. Adapted from [215]