Soft Actuators Enabled by 3D-Architected Low Melting Point Alloys/Polymer Composites with a Large Switching Range

Abstract

Materials with switchable stiffness, especially dynamically switchable stiffness with a large switching range, have aroused considerable interest in the field of soft actuators. Herein, we designed a three-dimensional (3D)-architected Field’s metal (FM) microstructure and embedded it into a kind of designed phase-changing side-chain stiffness variable polymer to obtain a composite (SUFM) with superior stiffness switchable capacity. SUFM exhibits excellent conductivity under low volume fraction (31.5%). What is more, owing to the rapid solid–liquid switch and ultra-high modulus of FM, the rigid/soft stiffness switch ratio of SUFM can reach up to ultra-high 7532-folds. In addition to the superior stiffness switchable capacity, SUFM also exhibits outstanding shape memory and self-healing properties. Subsequently, a SUFM film was attached to a kind of designed 3D-printing fast-response and stiffness-tunable soft actuator as the stiffness variable unit. The soft actuator has a fast heating–cooling cycle of 41 s under 10 A current with 4 °C water as a coolant. Besides, the stiffness and net force of the soft actuator can reach up to 944 mN/mm and 4590 mN, respectively. The high load capacity and superior switchable stiffness are demonstrated by a robotic gripper equipped with three assembled soft actuators on a 3D-printing base, which can lift objects of arbitrary shapes and various weights up to 2 kg. This work may be further developed into smart components that can be widely used in soft actuators.