Robust and Reprocessable Artificial Muscles Based on Liquid Crystalline Elastomers with Dynamic Thiourea Bonds

Herein, we present a new class of liquid crystalline elastomers (LCEs) crosslinked with poly(ether-thiourea) comprising a triethylene glycol spacer (LCE-TUEG) wherein thiourea bonds impart a hydrogen bonding capability as well as permit dynamic covalent bond (DCB) exchange at elevated temperatures. While hydrogen bonding enhances the mechanical properties of LCE-TUEG, the DCB allows the network rearrangement of the LCEs, generating various useful properties that are not present in conventional LCEs, including the ability of welding, melt and solution reprocessing, reprogrammable actuation, and self-healing. By harnessing such dynamic features, we fabricate electrically-driven artificial muscles that can be actuated by Joule heating using a resistive wire. In particular, an excellent specific work is demonstrated (~61 J kg⁻¹) for the artificial muscle, and full recyclability of both the LCE matrix and the metallic heating wire is achieved. Furthermore, a biomimetic artificial hand is created by welding and assembling multiple LCE-TUEG films embedded with heating wires, followed by mechanical alignment. The integration of a microcontroller to the artificial hand enables the selective actuation of each finger, and various hand gestures are successfully demonstrated.