A triple-stimuli responsive supramolecular hydrogel based on methoxy-azobenzene-grafted poly(acrylic acid) and β-cyclodextrin dimer

Abstract It has been attracted broad interest to construct stimulus responsive supramolecular hydrogels as smart materials over the past few decades; however, the design of multi-stimuli responsive hydrogels remains a formidable challenge. Herein, a multi-stimuli responsive supramolecular hydrogel has been designed on the basis of methoxy-azobenzene-grafted poly(acrylic acid) (PAA-mAzo) and β-CD dimer, which involves the host-guest and electrostatic interactions. Besides the common thermo-responsive behavior, the hydrogel also exhibits reversible sol-gel transition under green and blue light irradiations because of the disassociation and association of host–guest interaction between mAzo and β-CD. In addition, the hydrogel turns into precipitate at low pH due to the decrease of solubility of PAA in aqueous solution. The electrostatic interaction between the negatively charged carboxylic acid groups and hydrated protons at high pH makes the recovery of hydrogel. At last, the release of rhodamine B loaded in the triple-stimuli responsive hydrogel can be accelerated by green light irradiation and low pH, which demonstrates the potential applications in biomedical materials.