Rotary 4D Printing of Programmable Metamaterials on Sustainable 4D Mandrel

The paper introduces a rotary 4D printing platform that can directly fabricate cylindrical, modular structures with multiple materials and stiffness levels on a programmable, shape-morphing mandrel. The design is inspired by re-entrant auxetic geometries and uses a parametric zigzag pathing strategy to improve stress dissipation and resilience. The authors report both numerical and experimental studies of re-entrant auxetic structures and spiral joints, focusing on strain energy distribution, stiffness tunability, and 4D recovery. They also address fabrication constraints by using a freely available open-source rotary slicing algorithm to enable non-planar, continuous-path toolpaths. To reduce reliance on iterative simulations, the work adds a data-driven predictive model that links geometric and material parameters to final shape-morphing behavior. The paper further describes an integrated design-to-G-code workflow implemented with Python scripting in Grasshopper, enabling direct fabrication of non-planar 4D structures such as multi-spiral universal joints with programmable stiffness and multi-degree-of-freedom motion.