Mechanical metamaterials based on origami and kirigami

Once merely ancient arts, origami (i.e., paper folding) and kirigami (i.e., paper cutting) have in recent years also become popular for building mechanical metamaterials and now provide valuable design guidelines. By means of folding and cutting, two-dimensional thin-film materials are transformed into complex three-dimensional structures and shapes with unique and programmable mechanical properties. In this review, mechanical metamaterials based on origami and/or kirigami are categorized into three groups: (i) origami-based ones (with folding only), (ii) kirigami-based ones (with cutting only), and (iii) hybrid origami-kirigami-based ones (with both folding and cutting). For each category, the deformation mechanisms, design principles, functions, and applications are reviewed from a mechanical perspective.