Mesh-size adjustable hydrogel via light and pH induction

The ability of stimuli-responsive hydrogels to swell and shrink is an important property that enables their wide range of applications. We prepared a novel azopyridine-based hydrogel by free radical copolymerization and investigated its multi-responsive behaviors to pH and UV light. The hydrogel swelled rapidly in acidic environments, reaching 303% of its mass in neutral conditions at equilibrium. The hydrogel also swelled significantly in the presence of alpha-cyclodextrins (alpha-CDs) due to host-guest interactions, reaching 276% of its mass in distilled water at equilibrium. The hydrogel shrank reversibly under UV light.