Programmed Multiresponsive Hydrogel Assemblies with Light-Tunable Mechanical Properties, Actuation, and Fluorescence

Fabrication strategies for programmed hydrogels that provide precise spatial control with predetermined responses to external stimuli are highly desirable. In this study, a partially reversible light-driven assembly (PRLDA) method is introduced to construct multiresponsive hydrogels utilizing microgel (MG) particle building blocks (swollen diameter of 107 nm). No other material is required to prepare the gels beyond the MGs themselves. Facile preparation of multiresponsive hydrogels that are reversibly responsive to light, pH, and temperature using phototriggered covalent interlinking of coumarin-based MGs is demonstrated. The gels have phototuneable moduli and swelling ratios and show light-assisted healing and reshaping. Remarkably, the intrinsic fluorescence of the gels undergoes a reversible light-triggered wavelength-shift. The emission peak blueshifted from 420 to 390 nm upon irradiation with 365 nm light. The PRLDA gels can be constructed using either positive or negative photopatterning. It is shown that the gels can be exploited for multiresponsive cytocompatible actuators, grippers, and ON/OFF circuit components as well as anticounterfeit gels. The PRLDA method provides new insight into programmed gel property control and has excellent potential for biomaterial and optoelectronic applications.