The integration of swellable metal-organic frameworks (MOFs) into polymeric composite films is a straightforward strategy to develop soft materials that undergo reversible shape transformations derived from the intrinsic flexibility of MOF crystals. However, a crucial step toward their practical application relies on the ability to attain specific and programmable actuation, which enables the design of self-shaping objects on demand. Herein, a chemical etching method is demonstrated for the fabrication of patterned composite films showing tunable self-folding response, predictable and reversible 2D-to-3D shape transformations triggered by water adsorption/desorption. These films are fabricated by selective removal of swellable MOF crystals allowing control over their spatial distribution within the polymeric film. Upon exposure to moisture, various programmable 3D architectures, which include a mechanical gripper, a lift, and a unidirectional walking device, are generated. Remarkably, these 2D-to-3D shape transformations can be reversed by light-induced desorption. The reported strategy offers a platform for fabricating flexible MOF-based autonomous soft mechanical devices with functionalities for micromanipulation, automation, and robotics.
Keywords: composite film; metal-organic framework; self-folding; smart material; stimulus-response.
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