Light-responsive 3D printed fish-shaped actuator based on granular hydrogel inks

Stimuli-responsive soft actuators are key components in soft robotics, enabling programmable shape changes in response to environmental cues. Here, we present a light-responsive, fish-shaped soft actuator fabricated via the 3D-printing of granular hydrogel inks composed of alginate-based microparticles. Four microparticle types with varying size and morphology were fabricated and characterized for their swelling behavior and rheological properties to optimize ink performance. Active granular hydrogel inks were prepared by infiltrating N-isopropylacrylamide (NIPAM) into microparticles to form thermoresponsive networks and embedding gold nanostars (AuNS) to introduce photothermal activity. The resulting granular inks enabled 3D printing of anisotropic structures that underwent reversible bending in response to near-infrared (NIR) light. A fish-shaped actuator, composed of an active AuNS-PNIPAM tail and passive body, exhibited reproducible bending over nine actuation cycles with change in bending angles stabilizing at ∼37° after initial thermal conditioning. Our findings highlight the potential of modular, granular ink formulations to produce programmable soft robotic systems with remote, light-triggered control. • Granular hydrogel inks with alginate microparticles enable stable 3D soft actuators. • PNIPAM and gold nanostars impart thermo/photo-responsiveness for remote actuation. • Microparticle shape and rheology dictate print fidelity and actuation performance. • Anisotropic fish actuators show reproducible NIR-induced bending up to ∼37°.