PSS-dispersed dopamine triggered formation of PAA adhesive hydrogel as flexible wearable sensors.

Catechol-based hydrogels have good adhesion properties; however, since the concentration of catechol is low and it can be easily oxidized to quinone, the adhesion performance of the hydrogels is reduced, which limits their application as self-adhesive flexible wearable sensors. In this work, a dopamine: poly(sodium 4-styrenesulfonate) (DA:PSS)-initiated strategy was proposed to construct adhesive hydrogels, where the semiquinone radicals present in DA:PSS were used to initiate radical polymerization to obtain the DA:PSS/poly(acrylic acid) (DA:PSS/PAA) hydrogel. This hydrogel exhibited good stretchability and adhesion with various substrates. We observed that, even after exposure to air for 21 days under certain relative humidity (76%), the catechol groups hardly oxidized and the DA:PSS/PAA hydrogel presented good adhesion. The DA:PSS/PAA hydrogel also showed good electrical conductivity and fast response ability. Thus, the general strategy of triggering monomer polymerization to form hydrogels based on the semiquinone radical present in DA:PSS offers great potential for their application in flexible electronic devices and wearable sensors.