Foldable insect wings: from folding and unfolding mechanisms to inspired applications

The unfolding and folding mechanisms of insect wings have always been a research field of concern for scientists. Recently, many engineers have combined these mechanisms with origami to develop innovative foldable structures. This Review discusses the mechanisms of insect hindwing unfolding and folding, particularly in the Coleoptera and Dermaptera, revealing the inherent relationship between folding models and insect wing folding mechanisms, including the construction of bistable systems, the generation of internal elastic forces and the reasons for dual stiffness. In addition, this Review also discusses the effects of hydraulic pressure, thoracic muscles, abdominal movements, wing flapping and other mechanisms on the wings. Finally, we introduce the current applications in aircraft and grippers inspired by these mechanisms. Learning the mechanism of insect wing folding and utilizing mechanical structures and artificial materials to reproduce the delicate folding of insect wings can provide a wide range of inspirations for foldable structure design.