Arbitrarily 3D Configurable Hygroscopic Robots with a Covalent–Noncovalent Interpenetrating Network and Self‐Healing Ability

Abstract

Very recently, dynamic exchangeable covalent-bonding-based liquid crystal elastomer provided a new route for actuators with 3D shape mouldability and actuation capacity. [2,13,14] The dynamic transesterification reaction of these materials occurs at a temperature generally above 160 °C to allow shape molding, such as 3D flower and 3D wheel. [11] Meanwhile, Zhang et al. [10] prepared microchannel-programmed actuators through UV lithography template method. The film actuator is capable of reversibly changing its 3D shapes when exposed to acetone vapor. Despite brilliant advances, the manufacturing of those polymeric actuators typically involves high melt temperature, high pressure, hazardous chemical solvent or sophisticated machining equipment, which dramatically restricts the shaping of the actuators with complicated 3D structure. Furthermore, few soft actuators can maintain their inherent 3D structures when completely cut or damaged, and the entire devices have to be disposed. To conclude, a soft actuator with straightforward and eco-friendly shaping and reshaping processing condition and excellent self-healing ability is highly demanded.To address this issue, we present a biopolyester with hydrogen bonding and covalent bonding interpenetrating network, resulting in a mechanically robust, hygroscopic actuator that can arbitrarily shape and reshape the 3D geometric configuration at low ambient temperature (≤35 °C). Meanwhile, it exhibits excellent self-healing ability to maintain high performance of 3D structured actuators. Furthermore, specific 3D structures of the water-gradient-driven actuators are demonstrated to achieve different potential applications. The arbitrary shape deformations that copolyesters undergo at low temperature can inspire a new generation of synthetic soft actuators, which are in demand for actuating technologies, such as biomedical devices, flexible electronics, and soft robotics.To prepare the hygroscopic actuator with shaping and reshaping processability at low ambient temperature (≤35 °C), humidity-responsive macromolecular prepolymer with the melting point (T m = 23.48 °C) was first synthesized through the effective condensation copolymerization reaction of crystalline poly(ethylene glycol) (PEG) and poly(tetramethylene glycol) (PTMG) precursor ( 1 H NMR, gel permeation chromatography (GPC), and differential scanning calorimetry (DSC) analysis Soft materials that can reversibly transform shape in response to moisture have applications in diverse areas such as soft robotics and biomedicine. However, the design of a structurally transformable or mechanically selfhealing version of such a humidity-responsive material, which can arbitrarily change shape and reconfigure its 3D structures remains challenging. Here, by drawing inspiration from a covalent-noncovalent network, an elaborately designed biopolyester is developed that features a simple hygroscopic actuation mechanism, straightforward manufacturability at low ambient temperature (≤35 °C), fast and stable response, robust mechanica...

4D Printed Hydrogels: Fabrication, Materials, and Applications

“…Cao et al fabricated 4D configurable hygroscopic robots with a copolymer between crystalline poly(ethylene glycol) (PEG) and poly(tetramethylene glycol) (PTMG). [ 72 ] As shown in Figure a, the hygroscopic actuator consisted of a moisture‐sensitive layer (namely, an “active layer,” the yellow layer in Figure 5a) made from the PEG–PTMG copolymer and an inactive layer made from beeswax (the thin black layer in Figure 5a). During the humidification and dehumidification processes, the formation and dissociation of the hydrogen bonds in the copolymer led to a fast‐hygroscopic expansion of the copolymer.…”

“…Reproduced with permission. [ 72 ] Copyright 2019, Wiley‐VCH. c) 4D flower shape reverting to a flat configuration upon hydration and recovering the petal shape while drying (dehydration) (scale bar is 10 mm).…”

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