Reprogrammable Humidity-Driven Liquid Crystalline Polymer Actuator Enabled by Dynamic Ionic Bonds

Abstract

Liquid crystalline polymer (LCP) is a promising candidate in the design and fabrication of intelligent soft materials due to the combination of programmable anisotropy and elasticity. Here, a novel strategy to fabricate reprogrammable humidity-responsive LCP materials enabled by dynamic ionic cross-links were put forward. The prepared LCP film deforms reversibly with the change of relative humidity (RH). However, the humidity responsivity loses after soaking the film into CaCl2 solution because of the lock of hygroscopic groups by the formed ionic bonds. By selectively cross-linking specific regions of the LCP film, distinctive humidity-driven motions of the film could be realized. More interestingly, by the EDTA-2K solution treatment, ionic cross-links can be interrupted, leading the LCP film responsive to humidity again. Thanks to feasibly removable ionic cross-links, the humidity-directed soft actuator was totally reprogrammable. The behavior of the novel actuator could be manipulated by either the mesogens alignment or the spatially ionic treatment, providing a feasible but robust strategy to fabricate complex humidity-driven soft robots.

Bioinspired Self-Resettable Hydrogel Actuators Powered by a Chemical Fuel

“…Inspired by the movements of soft living tissues, hydrogel-based soft actuators that can mimic biological functions have been an active area of research and discussion. − The mechanical actuation of hydrogels is usually achieved by volume change through absorbing and releasing water in and out of their networks in response to external stimuli. Along this line, diverse elegant hydrogel actuators have been created under the control of environmental parameters like pH, − temperature, − light, − electric field, − ions, − and magnetic field. − However, so far, the vast majority of the reported examples are switched between different thermodynamic equilibrium states by sequentially turning on/off the external stimuli, , showing limited autonomous capability. ,, In stark contrast, the actuation of soft living tissues is highly autonomous, which is usually realized by nonequilibrium chemical reaction networks (CRNs) powered by high-energy biomolecules, such as adenosine triphosphate (ATP). For example, muscles contract by consuming the energy released by the conversion of ATP into adenosine diphosphate (ADP) and spontaneously relax to the original state once ATP is used (Figure a). , Thus, access to autonomous hydrogel actuators powered by chemical fuels, analogous to living tissues, would be extremely advantageous for lifelike soft robotics yet remains a formidable task.…”

Bioinspired humidity-responsive liquid crystalline materials: from adaptive soft actuators to visualized sensors and detectors

“…More recently, a novel reprogrammable humidity-driven LCN actuator was prepared by introducing ionic crosslinks in an ordered LCN matrix. 84 The hygroscopic carboxylic salty network could be locked by ions, losing its water absorbing ability. In this case, the water swellable regions could be arbitrarily controlled, resulting in diverse and programmable deformation of the LCN film with a change in RH.…”

Edible Origami Actuators Using Gelatin-Based Bioplastics

“…Biopolymer-based hydrogel actuators are particularly advantageous in applications where ultracompliant and biocompatible materials are required or external power sources are impractical, such as internal medicine. As a result, hydrogels with swelling ratios of up to 1000× applied to a great effect for tissue engineering, drug delivery, and wound repair. − Some examples of biopolymer-based hydrogels include cellulose, chitosan, polysaccharides (agarose, alginate, and starch), and proteins like collagen or gelatin . Despite their accessibility and biocompatibility, these materials may struggle to achieve wide-scale adoption as moisture-responsive actuators due to slow response kinetics, hysteresis, chemical degradation, and insufficient Young’s moduli. − …”