Abstract: Due to its real-time control, high folding ratio, and structure self-locking, flexible large curvature self-folding devices have broad application prospects, such as foldable human implants, flexible electronics, and flexible robots. Driven by this background, flexible large curvature folding butterfly (Polyura eudamippus) proboscises were studied in this work. The folding ratio of the proboscises was about 15. The curvature of coiled proboscises ranged from about 150 m?1 to 880 m?1. The external and internal structures of the proboscises were studied by different methods. Three main strategies for large-curvature folding of proboscises were identified: a gradual decrease in thickness, a lower elastic modulus, and (most importantly) large numbers of regular corrugated cracks arranged on the surface. These corrugated cracks can effectively accommodate the coiled strain and provide space for the large curvature folding of proboscises. Finally, a 4D printed coiled sample with corrugated cracks was fabricated to mimic the proboscises stretching process. Large-curvature folding strategies, based on these proboscises, provide insights for the biomimetic design of artificial highly folded components.

Key words: butterfly proboscis, large curvature folding, corrugated crack, 4D printing, bionic