Shape-transformative materials that can autonomously adopt three-dimensional (3D) shapes in response to environmental stimuli are of interest for the development of sensors and soft robotics. We herein report a new synthetic strategy to fabricate shape-transformable Eu3+-containing interpenetrating polymer films consisting of poly­(vinyl alcohol) (PVA) and poly­(3-iminodiacetate-2-hydroxypropylmethacrylate-co-acrylic acid) (P­(IDHPMA-co-AA)). Given the dynamic nature of Eu3+-iminodiacetate (IDA) coordination, ink patterning and water/Fe3+ diffusion are used to generate the in-plane or z-directional heterogeneities of Eu-IDA dynamic coordination in the polymer film, respectively. The heterogeneities can be visualized by the distribution of fluorescence emission of Eu3+. When subjected to high humidity, the differences in the swelling ratio and modulus as a result of chemical inhomogeneity further drive various 3D shape morphings, including rolling, helixing, twisting, surface buckling, and folding. Shape transformation is reversible upon the removal of moisture from the polymer films. The ink concentration and environmental humidity are demonstrated to impact the shape transformation kinetics and the final 3D shape along with other geometric parameters. Our work illustrates a novel way to fabricate new-generation biomimetic actuators and sensors.

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We report a new design concept that utilizes the Ag+/Fe3+-catalyzed fast gelation of acrylic acid (AA) or AA/comonomer aqueous solutions (e.g., 56 s for the gelation of the 20 wt % AA solution) to achieve fast healing of covalently cross-linked polymer hydrogels. The fast-generated poly(acrylic acid) (PAA) or AA copolymer hydrogel with a covalent network is highly active for the interfacially igniting gelation (IIG) of AA or the AA/comonomer in water through a frontal polymerization process. Using the AA or AA/comonomer aqueous solution as the “repairing liquid,” the fast-generated hydrogels (polymer concentration of 20 wt %) are repeatedly healed at room temperature through the IIG reaction without extra energy input. This IIG reaction-mediated healing (IIG-healing) has healing efficiencies higher than 90%. The healing time can be shortened from ∼60 min to only ∼1 min by increasing the solid concentration of the fast-generated hydrogel to 92 wt %. The IIG reaction also enabled the coating of a hydrophobic polymer layer on the hydrogel, resulting in higher tensile strength, toughness, and much better water retention capacity. We expect that this Ag+/Fe3+-catalyzed fast gelation strategy will pave a facile and energy-efficient pathway to fabricate versatile and multifunctional healing polymers.

The design of materials that can mimic the complex shape-morphing phenomena in nature is important for applications in soft robotics, biomedical devices, and sensors. Yet, morphing a two-dimensional thin plate into a programmed complex threedimensional (3D) shape is still challenging. Herein, we demonstrate a new paradigm for designing a photothermal shape-transformable Fe 3+ -containing polymer film (FePF) coated with a patterned inactive black-tape strip layer. The near-infrared (NIR) light-triggered dehydrative shrinkage of the FePF layer drives the bending of the inactive layer toward the FePF layer. Various reversible 3D shapes, including a complex "human face" and gripping-force-tunable soft grippers, are fabricated by the experimental pattern design of the inactive layer with the aid of theoretical simulations. The white-light sensitive dynamic coordination of Fe 3+ −Alanine (Ala) enables tunability of the deformation degree under white-light irradiation. The deformation rate is also tunable by adjusting the Fe-to-Ala mole ratio, humidity, NIR light intensity, and FePF thickness. These shape transformations are reconfigurable through the simple peeling off and repatterning of the black-tape strip layers. Our simple and scalable design strategy without an intricate heterogeneity design in material properties provides guidance for fabricating new soft robotics and biomimetic systems.