Dorsoventral gradient hydrogel fiber actuators visualized by AIEgen-conjugated nanoparticles

Fiber-shaped actuators made of hydrogels, inspired by plant tendrils, enable large motion and generate more pervasive automation in soft-robotics. However, replicating dorsoventral gradients of plant tendrils in hydrogel fibers remains challenging and unexplored. Herein, we demonstrate a Marangoni flow-induced self-organization of cellulose nanocrystals (CNCs) to construct a dorsoventral gradient network within a single continuous hydrogel fiber allowing helically programmed actuation that mimics plant coiling. Our approach harnesses migration-sedimentation assembly of CNCs in thermosensitive hydrogel precursor solution in the tubing that gradually photocrosslinked to produce monolithic fiber actuators rather than assembly of individual layers with dissimilar swelling properties. In situ fluorescence technology assisted by aggregation-induced emission luminogens (AIEgens) reveals the localization of CNCs in the hydrogel fiber as well as the interaction of CNCs with the gel matrix. The CNCs get arranged in a dorsoventral gradient fashion along the cross-section of hydrogel fibers due to the synergistic effect of gravity and surface tension. The AIE-assisted visualization of the particle positioning and local microenvironment for gradient hydrogel fibers offers advanced and universal characterization technique for nanocomposite hydrogel materials.