Closed-Loop and Sustainable 4D Printing of Multi-Stimuli-Responsive Sulfur-Rich Polymer Composites for Autonomous Task Execution.

Shape-programmable polymer networks derived from waste elemental sulfur hold great potential for diverse applications such as 4D printing and soft robotics. However, their crosslinked nature makes it challenging to 3D print complex geometry for soft robots. Herein, a closed-loop 4D printing strategy is reported of poly(phenylene polysulfide) networks (PSNs) and their magnetic particle composites (MPSNs) to fabricate multi-functional soft robots with programmable shape-morphing capabilities. The dynamic S─S bonds within the loosely crosslinked PSNs impart shear-thinning behavior, enabling hot-melt extrusion of both PSNs and MPSNs into complex architectures. After shape-programming, 3D-printed PSN and MPSN structures exhibit heat- or light-triggered shape recovery and allow modular assembly for spatially selective shape-morphing governed by the distinct glass transition temperatures of the PSN series. These architectures can be readily reprinted into new form factors, demonstrating a closed-loop and sustainable 4D printing. With multi-stimuli responsiveness and solvent resistance provided by the PSN composites, the MPSN capsule serves as an on-demand catalyst-releasing magnetic stirring bar in a reagent-containing solution, autonomously releasing catalysts at a preset temperature to facilitate carbamate synthesis. The 4D printable MPSNs offer a sustainable platform not only for adaptable shape-morphing and dynamic actuation but also for autonomous task execution in next-generation soft robotic applications.