Multiscale Heterogeneous Polymer Composites for High Stiffness 4D Printed Electrically Controllable Multifunctional Structures

4D printing is an emerging field where 3D printing techniques are used to pattern stimuli‐responsive materials to create morphing structures, with time serving as the fourth dimension. However, current materials utilized for 4D printing are typically soft, exhibiting an elastic modulus (E) range of 10−4 to 10 MPa during shape change. This restricts the scalability, actuation stress, and load‐bearing capabilities of the resulting structures. To overcome these limitations, multiscale heterogeneous polymer composites are introduced as a novel category of stiff, thermally responsive 4D printed materials. These inks exhibit an E that is four orders of magnitude greater than that of existing 4D printed materials and offer tunable electrical conductivities for simultaneous Joule heating actuation and self‐sensing capabilities. Utilizing electrically controllable bilayers as building blocks, a flat geometry that morphs into a 3D self‐standing lifting robot is designed and printed, setting new records for weight‐normalized load lifted and actuation stress when compared to other 3D printed actuators. Furthermore, this ink palette is employed to create and print planar lattice structures that transform into various self‐supporting complex 3D shapes. Finally these inks are integrated into a 4D printed electrically controlled multigait crawling robotic lattice structure that can carry 144 times its own weight. Electrically controlled stiff morphing structures are designed and built by 4D printing new multiscale heterogeneous polymer composites. This enables the fabrication of active 3D autonomous structures programmed to actuate via Joule heating. These robotic structures are capable of self‐sensing actuation, unprecedented levels of actuation stress and specific mass lifted while undergoing shape change, and self‐regulated actuation via closed‐loop control. Integrating these materials with lattice designs enables large scale complex 3D surfaces that are loadbearing, culminating in a multigait crawling robotic lattice.