Programmable 3D Morphing Bionic Gradient Hydrogel Actuators with Fast Response and Large-Amplitude Deformations

Hydrogel actuators have shown promising applications in biomedical devices, wearable electronics, and soft robotics. To fulfill practical applications, hydrogel actuators must achieve high-speed adaptive motion, programmable large-strain actuation and 3D morphing ability, however, the fabrication of such actuators remains a challenge. In this work, temperature responsive gradient hydrogel is prepared through the UV-absorbing effects of the precursors at specific wavelength of UV light during photopolymerization. Moreover, chito-oligosaccharides (COS) are introduced to enhance the hydrogel's gradient structure by migrating to the low-density side during photopolymerization and acting as porogen, resulting in a hydrogel with an ultrafast bending rate (190°/s) and large amplitude (760°). Furthermore, a light-responsive gradient hydrogel can be easily fabricated using the "naturally derived" genipin-crosslinked gelatin network as the photothermal transducer. By employing the photomask techniques to customize the local gradient structures, hydrogels with programmable 3D₁-to-3D₂ deformation behavior are realized. Inspired by inchworms and springtails, the hydrogels are pre-programmed to harness its fast-response and large-amplitude deformation, enabling light-driven soft robots to achieve biomimetic actuation, including tumbling, jumping, and crawling. This programmable, fast-response, 3D shape-morphing gradient hydrogel actuator expands the possibilities for applications in complex dynamic systems, including soft robotics and bionic devices.