Octopus-Inspired Hydrostatic Artificial Muscle with Variable Stiffness

This study introduces a hydrostatic artificial muscle (HAM) inspired by the octopus arm, the HAM is capable of bi-directional actuation and stiffness adjustment. Different from previously proposed artificial muscles, this HAM employs a hydrostatic structure filled with an incompressible, smooth material to reduce friction and ensure even pressure distribution. Shape Memory Alloy (SMA) springs embedded along longitudinal and transverse directions mimic the octopus arm’s unique muscle structure, enabling both elongation and shortening with enhanced stiffness of the HAM through controlled SMA actuation. This bio-inspired design allows the HAM to dynamically adjust stiffness, delivering stability and adaptability across diverse applications. Experimental results highlight the HAM’s performance under varying load conditions, achieving a contraction rate of approximately 30%, and a stiffness increase of 789% between soft and stiff states. This HAM demonstrates promising potential for soft robotics applications, particularly in tasks requiring high flexibility, load-bearing capacity, and variable stiffness.