Programmed deformations are widespread in nature, providing elegant paradigms to design self-morphing materials with promising applications in biomedical devices, flexible electronics, soft robotics, etc. In this emerging field, hydrogels are an ideal material to investigate the deformation principle and the structure-deformation relationship. One crucial step is to construct heterogeneous structures in a facile yet effective way. Herein, we provide a focus review on different deformation modes and corresponding structural features of hydrogels. Photolithography is a versatile approach to control the outer shape of the hydrogel and spatial distribution of the component in the hydrogel, endowing the patterned hydrogels with programmed internal stress and thus controllable deformations. Specifically, cooperative deformations take place in periodically patterned hydrogels with in-plane gradients, and multiple morphing structures are formed in one patterned hydrogel using selective preswelling to direct the buckling of each unit. The structural control strategy and deformation principles should be applicable to other materials with broad applications in diverse areas.
Keywords: gradient structures; hydrogels; photolithography; programmed deformations.
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