Reversible self-bending soft hydrogel microstructures with mechanically optimized designs

- The capabilities of self-folding reconfigurable microstructure are characterized.
- The finite element method (FEM) provides information in engineering design.
- A rational design methodology for programmable soft materials is provided.

A rational design methodology for materials with optimal mechanical properties is a prerequisite for developing programmable soft matter that undergoes structural changes in response to external stimuli. The goals of this study are to experimentally characterize the capabilities of a self-bending reconfigurable microstructure, provide fundamental information in engineering design, and validate simulations of physics-based models. In this study, the self-bending behavior of hydrogel bilayers, composed of an active layer and a passive layer, is investigated experimentally and theoretically. This self-bending is completely reversible and allows the structure to fold and unfold without permanent deformation. Experimentally, the effects of design parameters on the self-bending behavior of the microstructures of hydrogel bilayers are explored by varying the extrinsic geometric variables. The study of finite element method (FEM) simulations shows that the final shape of the bilayer sheet is governed by intrinsic properties, including the elastic modulus and the swelling ratio, and extrinsic geometrical factors, such as the thickness ratio of the bilayer and the aspect ratio of the structure. Therefore, the self-bending behavior of the planar hydrogel bilayer was confirmed by experiments and simulations in which multiple values were assigned for each of the primary design parameters in origami-based engineering.

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