4D printing is a rapidly emerging field in which 3D printed stimuli-responsive materials produce morphing and multifunctional structures, with time being the fourth dimension. This approach enables the 3D printing of pre-programmed responsive sheets, which transition into complex curved shapes upon exposure to external stimuli, resulting in a substantial reduction in material consumption and printing time (70 - 90 %). Commonly used materials for 4D printing are polymer composites, such as hydrogels, polydimethylsiloxane (PDMS), liquid crystal elastomers (LCEs), and shape memory polymers (SMPs). However, the low elastic modulus (E) that these materials exhibit during shape change (E range of 10-4 – 10 MPa) limits their scalability, actuation stress, and load bearing. Moreover, these materials exhibit low ultimate stresses, leading to correspondingly low toughness (K) values in the range of 0.08 to 5 MJ m-3. Consequently, this results in structures with low damage tolerance. Therefore, an existing challenge for the field of 4D printing is to develop materials that can maintain their large and predictable morphing mechanism for complex shape transformation, while improving the E and K for high performance applications. Furthermore, many existing approaches rely on passive structures that necessitate the control of global conditions of the surrounding environment (e.g., hot plates, ovens, external magnets, water baths) to provide the stimulus for actuation. In this work, we tackle these challenges by introducing novel materials, ink formulations, and innovative printing techniques for multi-material Direct Ink Writing (DIW). We aim to create electrically controllable 4D printed structures that exhibit exceptional stiffness and toughness, all while preserving a large and predictable morphing mechanism for intricate shape transformations. First, we introduce multiscale heterogeneous polymer composites as a novel category of stiff, electrically controllable thermally responsive 4D printed materials. These composites consist of an epoxy matrix with an adjustable cross-link density and a plurality of isotropic and anisotropic nanoscale and microscale fillers. Leveraging this platform, we generate a set of 37 inks covering a broad range of negative and positive linear coefficients of thermal expansion. This set of inks exhibits an elastic modulus range that is four orders of magnitude greater than that of existing 4D printed materials and offers tunable electrical conductivities for simultaneous Joule heating actuation and self-sensing capabilities. Utilizing electrically controllable bilayers as building blocks, we design and print a flat geometry that changes shape into a 3D self-standing lifting robot, displaying record actuation stress and specific force when compared to other 3D printed actuators. We integrate this lifting robot with a closed-loop control system, achieving autoregulated actuation exhibiting a 4.8 % overshoot and 0.8 % undershoot, while effectively rejecting disturbances of up to 170 times the robot's weight. Furthermore, we employ our ink palette to create and 3D print planar lattice structures that transform into various self-supporting complex 3D surfaces. Ultimately, we achieve a 4D printed electrically controlled crawling robotic lattice structure, highlighting its capacity to transport loads up to 144 times its own weight. Finally, we introduced a printable PDMS adhesive that serves as synthetic fascia to hold our epoxy-based synthetic muscle together, enhancing the K of our 4D printed structures, all while maintaining high stiffness, large, predictable, and addressable actuation mechanism. Through the integration of these soft adhesive materials with high-stiffness thermally responsive epoxies via DIW, we achieved an improvement of about two orders of magnitude in the K of the resulting synthetic muscle composite, all while maintaining high stiffness and morphing mechanism. Utilizing this fabrication method, we printed an electrically controllable bilayer exhibiting damage detection and tolerance, enduring up to 7 fractures while continuing to function effectively. Furthermore, we integrated the synthetic muscle composite into our lifting robot design, setting yet again new records in specific force and actuation stress when compared to other 3D printed actuators. Notably, even after failure, the actuator maintained its operational integrity and high performance. Ultimately, we present a 4D printed lattice structure featuring the incorporation the synthetic muscle composite, showcasing a sensitive electrically responsive surface with fracture detection capabilities. To emphasize this, we subjected one of these 4D printed lattices to extreme conditions, driving a car over it. Notably, the lattice structure detected fractures and exhibited high resilience, enduring external compressive damage equivalent to 331,060 times its own weight. / 2026-05-23T00:00:00Z