4D Printing: Design and Fabrication of 3D Shell Structures With Curved Surfaces Using Controlled Self-Folding

Abstract

Self-folding structures such as origami-based structures have been studied by artists, mathematicians and engineers. New applications are emerging in fields such as biomedical and electronics. Self-folding structures can potentially extend three-dimensional (3D) printing into four-dimensional (4D) printing by intelligently designed material distribution in order to achieve controlled shape deformation over time. Traditionally, self-folding structures are folded along pre-defined hinges such that neighboring facets can transform their shapes. In this study, we present a new design and fabrication approach of self-folding structures with no foldable hinges. A significant benefit is its capability in fabricating shapes with smooth curved surfaces. Our self-folding method is based on a thermally responsive mechanism, where a thermal responsive film is used as the active material while another polymer material coated on the film is used as the constraining material. When the structure is heated, the two sides of the film will shrink differently due to the constraining material. Consequently the structure will fold. By changing the constraining patterns and coated material properties, the film can be self-folded into different shapes. Three types of folding features are presented in our study. Based on them, an unfolding algorithm is presented for a given shell structure with curved surfaces. Theoretical analysis and experimental tests are presented to demonstrate the capability of the self-folding method. Its limitation and future work are also discussed.