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

Abstract

Abstract 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.