3D‐Architected low melting point alloys foam microstructure‐reinforced polymer composite with superior stiffness‐switchable for soft actuator

Abstract Stiffness variable materials have aroused extensive research interest in smart devices, especially in soft actuators. However, achieving materials with high stiffness switch range remains challenging. Here, a novel three‐dimensional (3D) lightweight Field's metal (FM) foam was developed. Meanwhile, the polymer composite (SUFF) with superior stiffness switchable capacity was fabricated by embedding FM foam into a kind of designed stiffness variable polymer. The SUFF shows outstanding conductivity under relatively low FM volume fraction of 20.6%. Impressively, because of the extremely high modulus and fast transition of FM foam, the stiffness switch ratio of the SUFF are able to reach an ultra‐high value of 6987.5‐folds. Apart from its exceptional stiffness switchable capacity, the SUFF also possesses remarkable shape memory and self‐healing characteristics. Next, the SUFF was then fastened to a soft actuator as the stiffness changing units. The obtained actuator was able to exhibit a short heating–cooling cycle time of 44 s while using 10 A of current and 4°C water for cooling. Moreover, the actuator can reach remarkable values of 973 mN/mm and 4729 mN, respectively, for its stiffness and net force. Then, a soft robot gripper made up of three obtained actuators mounted on a base demonstrates its excellent load and stiffness switchable ability. It can lift a variety of objects with various forms with weights up to more than 3 kg. This study might provide a reference for application of stiffness variable materials in soft actuators. Highlights The FM foam were designed and synthetized by lost‐wax casting method. The polymer composite exhibits large stiffness switching range. The polymer composite achieves 6987.5‐folds rigid/soft stiffness ratio. A 3D‐printing soft actuator was fabricated using obtained polymer composite. The assembled robotic gripper can lift weights up to more than 3 kg.