changes in curvature. Computational models provide quantitative guidance in the selection of designs that avoid strains at levels that could result in fracture of the constituent materials, localized deformation, or self-contact. For simple cases, some of these guidelines can be captured in analytical forms (33) (fig. S6). In single helices, the maximum strains increase linearly with both the thicknesses and widths of the 2D precursors, with greater sensitivity to the thickness.
The assembled structures are not restricted to geometries with axial symmetry. Joining closed-form circular 2D serpentines with equally biaxially stretched assembly platforms (fig. S7) yields toroidal coils in isolation, in extended arrays, or in nested configurations. Figure 1G shows an elaborate 3D silicon mesostructure that consists of a concentric pair of toroids, with a separate hemispherical “cage” construct at the center; the corresponding 2D precursor is shown in fig. S8. The remarkably good agreement between experimental results and FEA predictions for this highly complex architecture provides further evidence of the