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Light-coded digital crystallinity patterns toward bioinspired 4D transformation of shape-memory polymers

Editorgroup5  Date2020-03-24 11:52:22   Hits:387

    Spatially heterogeneous distribution of active components is key to the diverse shape morphing behaviors of active materials and their associated functions. The type of heterogeneity involved include crosslinking density for hydrogels, compositional distribution for shape memory polymers (SMP), and domain orientation for liquid-crystalline elastomers. Typically, the spatial heterogeneity is introduced during the material synthesis/fabrication step and cannot be altered afterwards. SMP is a unique class of shape morphing materials in that its shape shifting pathway can be programmed. The geometries of the permanent shapes of SMP devices play a decisive role in their functions, yet mechanisms that allow their manipulation are scarce and still have some limitations.

    To address the above challenges, we report herein an approach that allows spatio-selective programming of crystallinity in a well-known thermoplastic SMP (poly(L-lactide)) by a digital photothermal effect. The light-patternable crystallinity affects greatly the shape morphing behavior. Consequently, a pre-stretched 2D film with spatial heterogeneity in crystallinity can morph with time into designable 3D permanent shapes, achieving the 4D transformation. Our approach utilizes a reprocessible thermoplastic SMP and the programming relies on a physical phase transformation (crystallization) instead of chemical heterogeneity. This allows repeated erasing and reprogramming using the same material, suggesting a versatile and sustainable means for manufacturing advanced morphing devices.