Spider Leg Inspired Soft Actuators in Small Robotic Applications: A Brief Review

Bio-inspired soft actuators are often challenging to design due to their complex structure and the difficulties associated with integrating them into robots or devices. These challenges are compounded using soft materials in manufacturing, which typically results in low torque and reduced resistance to deformation. However, actuators inspired by the spider's hydraulic femur-patella or tibia-metatarsus joint offer a simpler design approach and exhibit stable bidirectional driving capabilities, with torque profiles during folding motions comparable to those during unfolding motions. This feature facilitates their integration into a range of robotic applications, from large-scale to small-scale, making them particularly well-suited for use in healthcare and prosthetic applications. These actuators can utilize various stimulants, such as fluidic or electrohydraulic methods, to achieve actuation. Recent research has focused on developing new smart materials and exploring various novel stimuli to replicate the actuation seen in spider legs. This review provides a comprehensive overview of soft actuators inspired by the hydraulic joints of spider legs, particularly focusing on the mechanics of the natural spider leg joint and examining the actuators reported in the literature.