Shape morphing is a critical aptitude for the survival of organisms and is determined by anisotropic tissue composition and directional orientation of micro-and nanostructures within cell walls,resulting in different swelling behaviors.Recent efforts have been dedicated to mimicking the behaviors that nature has perfected over billions of years.We present a robust strategy for preparing 3D periodically patterned single-component sodium alginate hydrogel sheets cross-linked with Ca2+ ions,which can reversibly deform and be retained into various desirable inside-out shapes as triggered by biocompatible ions (Na+/Ca2+).By changing the orientations of the patterned microchannels or triggering with Na+/Ca2+ ions,various 3D twisting,tubular,and plantinspired architectures can be facilely programmed.Not only can the transformation recover their initial shapes reversibly,but also it can keep the designated shapes without continuous stimuli.These inside-out 3D reversible ion-triggered hydrogel transformations shall inspire more attractive applications in tissue engineering,biomedical devices,and soft robotics fields.
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