Direct 4D printing of ceramics driven by hydrogel dehydration.

4D printing technology combines 3D printing and stimulus-responsive materials, enabling construction of complex 3D objects efficiently. However, unlike smart soft materials, 4D printing of ceramics is a great challenge due to the extremely weak deformability of ceramics. Here, we report a feasible and efficient manufacturing and design approach to realize direct 4D printing of ceramics. Photocurable ceramic elastomer slurry and hydrogel precursor are developed for the fabrication of hydrogel-ceramic laminates via multimaterial digital light processing 3D printing. Flat patterned laminates evolve into complex 3D structures driven by hydrogel dehydration, and then turn into pure ceramics after sintering. Considering the dehydration-induced deformation and sintering-induced shape retraction, we develop a theoretical model to calculate the curvatures of bent laminate and sintered ceramic part. Then, we build a design flow for direct 4D printing of various complex ceramic objects. This approach opens a new avenue for the development of ceramic 4D printing technology.

Reconfigurable 4D printing via mechanically robust covalent adaptable network shape memory polymer.

4D printing enables 3D printed structures to change shape over "time" in response to environmental stimulus. Because of relatively high modulus, shape memory polymers (SMPs) have been widely used for 4D printing. However, most SMPs for 4D printing are thermosets, which only have one permanent shape. Despite the efforts that implement covalent adaptable networks (CANs) into SMPs to achieve shape reconfigurability, weak thermomechanical properties of the current CAN-SMPs exclude them from practical applications. Here, we report reconfigurable 4D printing via mechanically robust CAN-SMPs (MRC-SMPs), which have high deformability at both programming and reconfiguration temperatures (>1400%), high Tg (75°C), and high room temperature modulus (1.06 GPa). The high printability for DLP high-resolution 3D printing allows MRC-SMPs to create highly complex SMP 3D structures that can be reconfigured multiple times under large deformation. The demonstrations show that the reconfigurable 4D printing allows one printed SMP structure to fulfill multiple tasks.

Multimaterial 3D printed self-locking thick-panel origami metamaterials.

Thick-panel origami has shown great potential in engineering applications. However, the thick-panel origami created by current design methods cannot be readily adopted to structural applications due to the inefficient manufacturing methods. Here, we report a design and manufacturing strategy for creating thick-panel origami structures with excellent foldability and capability of withstanding cyclic loading. We directly print thick-panel origami through a single fused deposition modeling (FDM) multimaterial 3D printer following a wrapping-based fabrication strategy where the rigid panels are wrapped and connected by highly stretchable soft parts. Through stacking two thick-panel origami panels into a predetermined configuration, we develop a 3D self-locking thick-panel origami structure that deforms by following a push-to-pull mode enabling the origami structure to support a load over 11000 times of its own weight and sustain more than 100 cycles of 40% compressive strain. After optimizing geometric parameters through a self-built theoretical model, we demonstrate that the mechanical response of the self-locking thick-panel origami structure is highly programmable, and such multi-layer origami structure can have a substantially improved impact energy absorption for various structural applications.

Centrifugal multimaterial 3D printing of multifunctional heterogeneous objects.

There are growing demands for multimaterial three-dimensional (3D) printing to manufacture 3D object where voxels with different properties and functions are precisely arranged. Digital light processing (DLP) is a high-resolution fast-speed 3D printing technology suitable for various materials. However, multimaterial 3D printing is challenging for DLP as the current multimaterial switching methods require direct contact onto the printed part to remove residual resin. Here we report a DLP-based centrifugal multimaterial (CM) 3D printing method to generate large-volume heterogeneous 3D objects where composition, property and function are programmable at voxel scale. Centrifugal force enables non-contact, high-efficiency multimaterial switching, so that the CM 3D printer can print heterogenous 3D structures in large area (up to 180 mm × 130 mm) made of materials ranging from hydrogels to functional polymers, and even ceramics. Our CM 3D printing method exhibits excellent capability of fabricating digital materials, soft robots, and ceramic devices.