Fig. 2.

Computed trap models with various strain distributions and layer setups including prestress. Relationship between opening angle and maximum applied strain (A) for measured strain distribution and (B) for interpolated strain distribution for all layer setups including a prestress process as predicted by model 2. The abbreviations correspond to the number of tissue layers (three or two), the behavior of these layers during closure (expansion, +; contraction, −; no actuation, 0), and the extent of expansion or contraction (in %) (see SI Appendix for more details). (C1) Dehydrated trap with larger opening angle. (C2) Trap in ready-to-snap configuration with smaller opening angle. (C3) Closed trap. Deformation states of model 2 for models most closely resembling the snap-trapping: (D1) With layer setup 3+00 (outer epidermis expands, and middle and inner layers remain neutral) in zero-stress state. (D2) After loading with the prestress strain, in ready-to-snap configuration, and (D3) after loading with the closing strain (representing the quantitative strain value measured in the DIC experiments; Fig. 1), in closed configuration. Deformation states for layer setup (E1–E3) 3+0−20 (outer epidermis expands, middle layer remains neutral, and inner epidermis contracts by 20% relative to outer epidermal expansion) and (F1–F3) 3+0−100 (outer epidermis expands, middle layer remains neutral, and inner epidermis contracts as much as outer epidermis). Details for all models can be extracted from SI Appendix, Fig. S3.