Self-shaping of 3D forms from solid bilayers

Traditionally, most construction and design materials are manufactured as flat sheets, which are then modified into 3D objects by operations involving the application of external forces to the materials (bending, molding, pressing, etc.). A new trend in structural engineering is to provide flat-formed materials with the ability to automatically transform into volumetric structures through the relaxation of internal mechanical stresses. The technology is advancing rapidly in the field of heterostructured semiconductor films, where it is being explored for the production of microelectromechanical systems (MEMS). This article describes the generalization of the approach to bilayer elastic polymer films, to which the spontaneous bending moment is transmitted when a filler material is extracted from the lattice of one of the layers. Elastic energy relaxation of specifically designed 2D polydimethylsiloxane sheets results in various 3D objects, such as spheres, cylinders, cages, etc., whose characteristic size is of the order of a centimeter. Sub-millimeter tubes, formed by self-winding, offer unprecedented possibilities for the functionalization of microfluidic devices.