Soft robotic arm inspired by the octopus: I. From biological functions to artificial requirements

TLDR

Octopuses, molluscs of the Cephalopoda, lack joints and possess arms with limitless freedom of movement, exhibiting stiffness control, compliance, high flexibility, and dexterity, making their study a complex challenge that inspires soft‑robotic designs. The study aimed to develop biologically inspired design concepts for a soft robotic arm by applying novel in‑vivo analysis methods to the octopus arm. The authors employed histology, ultrasound imaging, and in‑vivo functional morphology analysis of internal tissues, including nerve cord sinusoidal patterns and muscle fiber insertions, to inform these design principles. Measurements revealed that the octopus arm can elongate 70 % while reducing diameter by 23 %, exert an average pulling force of 40 N, shorten 20 % at 17.1 mm s⁻¹, and stiffen longitudinally at 2 N mm⁻¹ s⁻¹.

Abstract

Octopuses are molluscs that belong to the group Cephalopoda. They lack joints and rigid links, and as a result, their arms possess virtually limitless freedom of movement. These flexible appendages exhibit peculiar biomechanical features such as stiffness control, compliance, and high flexibility and dexterity. Studying the capabilities of the octopus arm is a complex task that presents a challenge for both biologists and roboticists, the latter of whom draw inspiration from the octopus in designing novel technologies within soft robotics. With this idea in mind, in this study, we used new, purposively developed methods of analysing the octopus arm in vivo to create new biologically inspired design concepts. Our measurements showed that the octopus arm can elongate by 70% in tandem with a 23% diameter reduction and exhibits an average pulling force of 40 N. The arm also exhibited a 20% mean shortening at a rate of 17.1 mm s−1 and a longitudinal stiffening rate as high as 2 N (mm s)−1. Using histology and ultrasounds, we investigated the functional morphology of the internal tissues, including the sinusoidal arrangement of the nerve cord and the local insertion points of the longitudinal and transverse muscle fibres. The resulting information was used to create novel design principles and specifications that can in turn be used in developing a new soft robotic arm.