Earwig wing-inspired bistable origami: Non-Euclidean units with soft joints

Origami-inspired folding enables structures to achieve multiple stable configurations, but predicting and controlling these states remain challenging. In nature, insects such as the earwig (Forficula auricularia) utilize non-Euclidean folding principles, leveraging asymmetric resilin-rich creases for compact storage and rapid deployment. Inspired by this, we investigate the bistable and multi-stable behavior of origami-inspired eggbox and saddle units, focusing on how mirroring configurations dictate stability. Through analytical energy modeling and experiments, we confirm that bistability in single units arises from a dominant folding (dihedral) angle – similar to the primary hinge regulation in earwig wings – enabling single-input actuation. In two-unit assemblies, mirroring along the dominant fold axis enforces synchronized snap-through, yielding a coupled bistable system, whereas mirroring along a secondary axis allows independent flipping, resulting in four stable states. Building upon this bioinspired principle, we extend the design to incorporate both deficit and redundant angles while maintaining a symmetric folding scheme, offering a systematic approach to programming multi-stability in origami-based structures. These findings provide a bioinspired strategy for programming multi-stable origami structures through geometric constraints and mirroring. The ability to toggle between synchronized and independent snap-through simplifies control and enables shape transformations without continuous actuation. This approach has broad applications in deployable structures, bioinspired soft robotics, and adaptive materials, leveraging multi-stability for efficient morphing.