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.

A volatile microemulsion method of preparing water-soluble photo-absorbers for 3D printing of high-resolution, high-water-content hydrogel structures.

Digital light processing (DLP)-based three-dimensional (3D) printing is an ideal tool to manufacture hydrogel structures in complex 3D forms. Using DLP to print hydrogel structures with high resolution requires the addition of water-soluble photo-absorbers to absorb excess light and confine photopolymerization to the desired area. However, the current photo-absorbers for hydrogel printing are neither efficient to absorb the excess light nor water-soluble. Herein, we report a volatile microemulsion template method that converts a wide range of commercial non-water-soluble photo-absorbers including Sudan orange G, quercetin, and many others to water-soluble nanoparticles with solubility above 1.0 g mL-1. After using these water-soluble photo-absorber nanoparticles, the highest lateral and vertical resolutions of printing high-water-content (70-80 wt%) hydrogels can be improved to 5 µm and 20 µm, respectively. Moreover, the quercetin nanoparticle can be easily washed out so that we achieve colorless and transparent printed hydrogel structures with excellent mechanical deformability and biocompatibility as well as thermally controllable variations on transparency and actuation. The proposed methods pave a new efficient way to develop water-soluble photo-absorbers, which helps to greatly improve the printing resolution of the high-water-content hydrogel structure and would be beneficial to extend the application scope of hydrogels.

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.