Controlled helical deformation of programmable bilayer structures: design and fabrication

Abstract

Abstract Inspired by natural systems, such as seed pods, pine cones, wheat seeds, flytraps, and vines, representative deformations, including bending, folding, and twisting, have been realized by designing structures and programming deformation for smart materials. In this paper, we present an innovative method of controlled helical structures by designing and fabricating a bilayer structure with a smart material. Our design was numerically studied and experimentally tested. Theoretical analyses were performed to guide the design of the helixing processes. When the bilayer structure was heated above the glass transition temperature, the top layer shrunk and the bottom layer expanded along the printing angle, which resulted in a self-helixing behavior. The parameters affecting the self-helixing behavior of the bilayer structure were studied and discussed. We found that left- and right-handed helical structures were achieved by controlling the printing angle of the top layer. A constitutive model with four main programming parameters was fitted and a helical structure with the desired curvature and gradient angle was achieved and was successfully triggered by heat. An underwater robot gripper programmable structure was achieved to test the feasibility and potential applications of the proposed method. The self-helixing structures could change their shape after fabrication using heat, and this technology has potential applications in the fields of biomedical devices, soft-robotics, and optoelectronic devices.