Programmable Single-Layer Polymer Films For Millimeter And Sub-Millimeter Self-Folding Origami

This paper presents a fabrication method for polymer films with programmable self-folding behavior. The target shape of the films is provided as a polygonal mesh. The unfolding polyhedra method is used to determine the layout of the folds and faces forming a planar origami sheet which can be folded towards the target shape. Photolithographic masks are printed with the determined layout and used in a photolithography process that produces polymer films with compliant folds of low cross-linking density and stiff faces of high cross-linking density. During the development step in the photolithography process, the films exhibit inhomogeneous developer absorption at the folds, with a higher concentration on the side of the folds that is in direct contact with the developer solution. The non-uniformly absorbed developer is removed upon heating the films, causing inhomogeneous strains across the thickness of the folds which leads to thermally-driven self-folding. The folded configuration of the films is made permanent by subsequently cooling the folded films to room temperature and saturating their cross-linking density through UV exposure. In the fabrication method, the fold angle achieved by each fold in the films is modulated by adjusting their width. A formula relating fold angle and fold width is calibrated using experimental data and incorporated into the computational implementation of the unfolding polyhedra method to precisely size the folds when creating the templates for the photolithographic masks. This method thus produces polymer films that are programmed to accurately self-fold into a target shape when heated. The fabrication method is demonstrated by producing various three-dimensional shapes. Potential applications of the fabricated programmable films include packaging of micro-systems and entrapment of cells.