Spider Origami: Folding Principle of Jumping Spider Leg Joints for Bioinspired Fluidic Actuators

Abstract

Jumping spiders (Phidippus regius) are known for their ability to traverse various terrains and have targeted jumps within the fraction of a second to catch flying preys. Different from humans and insects, spiders use muscles to flex their legs, and hydraulic actuation for extension. By pressurizing their inner body fluid, they can achieve fast leg extensions for running and jumping. Here, the working principle of the articular membrane covering the spider leg joint pit is investigated. This membrane is highly involved in walking, grasping, and jumping motions. Hardness and stiffness of the articular membrane is studied using nanoindentation tests and preparation methods for scanning electron microscopy and histology are developed to give detailed information about the inner and outer structure of the leg joint and its membrane. Inspired by the stroller umbrella‐like folding mechanism of the articular membrane, a robust thermoplastic polyurethane‐based rotary semifluidic actuator is demonstrated, which shows increased durability, achieves working angles over 120°, produces high torques which allows lifts over 100 times of its own weight and jumping abilities. The developed actuator can be used for future grasping tasks, safe human–robot interactions and multilocomotion ground robot applications, and it can shed light into spider locomotion‐related questions.

Spider‐Inspired Electrohydraulic Actuators for Fast, Soft‐Actuated Joints

“…[ 53 ] Hemolymph is pressurized by muscles in the prosoma of the spider, and the soft bellowed membranes in the joint expand on pressurization, causing the leg to extend. [ 29 , 50 ] Restoring forces to provide flexion rely on either passive elastic components or muscles within the exoskeleton. [ 54 ]…”

“…Several pneumatic technologies have emphasized the advantages of mechanical anisotropy in articulating structures, including the integration of rigid structural components with soft actuation for articulation from mm to cm scales. [ 30 , 31 , 48 , 49 , 50 ] In particular, the pouch motors introduced by Niiyama et al. provide a promising approach for articulation through their distributed design and control, but still suffer from the common pitfalls of pneumatics with the need for a supply of compressed air that is distributed through complex networks of lossy air lines; thus, these are still limited in their bandwidth and controllability for multiple degrees of freedom.…”

Fluid mechanics and rheology of the jumping spider body fluid

“…Although computerized tomography (CT) scans of spiders and spider legs have been conducted in the past, 3,16,32 the resolution was either too low to capture detailed information about the inner construct or the femur-patella leg was often not scanned in an extended position, as spiders usually flex their legs after death. Using our preparation method 13 and enhancing the contrast with iodine, these issues have been resolved. Detailed scans of a small, focused window of the sample (femur-patella joint) were obtained using high-resolution X-ray scanning at the synchrotron in Karlsruhe, Germany.…”

“…As the articular membrane is only a few tens of micrometres thick (30-60 mm), 13 the penetration depth of the OCT was enough to observe inside of the joint. Although hemolymph consists mostly of water, which cannot be detected by the OCT, small particles flowing inside the arteries could be observed.…”

“…The femurpatella joint of jumping spiders is highly involved in running and jumping activities. 13 During extension, the body fluid (hemolymph) leads to the unfolding of the articular membrane on the ventral side of the joint. Scale bar left: 5 mm; right: 0.4 mm.…”