Grayscale Stereolithography of Gradient Hydrogel with Site‐Selective Shape Deformation

Abstract Hydrogels can convert external stimuli into shape deformation and mechanical motion, leading to the potential applications in intelligent devices and soft robotics. However, it is difficult to control the site‐selective shape deformation in a single hydrogel system in comparison with the traditional bilayer actuators with difference in structure or composition across the thickness. Here, a strategy to achieve the programmable shape deformation of hydrogel from a single precursor by grayscale stereolithography is proposed. The designed grayscale patterns can govern the spatially gradient crosslinking density of hydrogels, which leads to the heterogeneity in physicochemical performance, especially swelling ability. As a result, the swelling mismatch inducing the nonuniform internal stresses can drive the printed hydrogels to deform as the expected shape in three dimensions although there is no apparent asymmetric features and bilayer configuration. Grayscale light intensity and exposure time, as the digital printing codes can parametrically regulate the predictable shape deformation. More importantly, hydration and dehydration characterizations can endow the reversible feature of shape deformation hydrogel, benefiting to design the hydrogel actuators and sensitive devices. It is believed that integration of the advanced grayscale stereolithography together with the functional hydrogels uncovers a facile strategy to broad opportunities for sensors, soft robots, actuators, and so on.