Programmable Sequential 4D Actuation in Multistable Kirigami Metamaterials

Programmable shape transformation is essential for adaptive soft mechanisms operating in constrained or dynamic environments. This study presents a modular kirigami metamaterial platform that enables programmable multistability and sequential 4D actuation through thermally triggered recovery. Inspired by geometric motifs from traditional Korean Dancheong patterns, in which symmetry and motif stacking govern pattern formation, two kirigami unit cells with different slit configurations are designed to exhibit distinct bistable responses and directional auxetic behavior. Using dual-material additive manufacturing, each cell integrates thermally responsive and passive thermoplastics to achieve cold-programmed bistability and sequential 4D actuation. This approach is validated through three functional mechanisms: (i) multimodal bridging structures capable of both mechanically and thermally induced reconfigurations; (ii) multistable 4D grippers capable of inward and outward transformations; and (iii) a biomimetic underwater cleaning robot that autonomously collects and encloses floating debris through sequential thermal recovery. All functions are achieved without electronic or pneumatic actuators, relying entirely on mechanically encoded transformations and thermal activation. Furthermore, the use of thermoplastics provides higher stiffness than elastomer-based actuators, opening new opportunities for thermo-mechanically encoded actuation with improved mechanical robustness.