4D Printing of Shape-Memory Hydrogels for Soft-Robotic Functions

Hydrogel actuators with soft-robotic functions and biomimetic advanced materials with facile and programmable fabrication processes remain scarce. A novel approach to fabricating a shape-memory-hydrogel-(SMG)-based bilayer system using 3D printing to yield a soft actuator responsive to the methodical application of swelling and heat is introduced. Each layer of the bilayer is composed of poly(N,N-dimethyl acrylamide-co-stearyl acrylate) (P(DMAAm-co-SA))-based hydrogels with different concentrations of the crystalline monomer SA within the SMG network and which exhibit distinctive physicochemical properties that enable anisotropic swelling-induced actuation of the bilayer with reversible shape-memory properties. The deformation, reversibility, and response time of the bilayer actuator are extensively dependent on temperature. Utilizing the proposed SMG bilayer actuator model with its synergistic functions, a nature-inspired flower architecture that changes its shape upon immersion in water and an underwater 3D macroscopic soft gripper that can grab, transport, and release a guest substance are developed to demonstrate the applicability of these hydrogels in biomimetic actuators, encapsulating systems, and soft robotics.