Advanced Actuator Materials Powered by Biomimetic Helical Fiber Topologies

Abstract

where conventional mechanical drive systems, such as electric motors, are too large or too heavy. [13] Natural skeletal muscle is often used as a benchmark for comparing and evaluating synthetic artificial muscles. The three key attributes of any actuator are the force generated, the amount of movement produced, and the time taken to complete a full actuation cycle. Skeletal muscle, e.g., generates a blocked stress of ≈0.3 MPa, free strain of ≈20%, responds in ≈0.1 s, and has a density of 1037 kg m −3 . Combining these parameters gives a reasonable estimate of the peak powerto-weight ratio (PWR) for muscle at ≈300 W kg −1 . [14] The PWR for conventional motors, engines, and other actuators covers a wide range (1-10 4 W kg −1 ), and there is a rough scaling between weight and PWR. This scaling means that small motors are less powerful and at sizes of less than a few tens of grams, muscle outperforms any available engine or motor. This limitation is currently hampering the development of many needed technologies. For example, the current state-of-the-art, motor-driven prosthetic hands are impressive but still do not match the dexterity of a healthy human. In theory, low-profile and high PWR artificial muscles could replicate the full range of motion, grip types, and strengths of the hand. Recent demonstrations of artificial muscle powered robotic hands [15] highlight the need for improved actuator materials, fabrication strategies, and control processes. In fact, biomimetic actuators are yet to be developed that match all of the features of natural muscle including large stroke, high speed, efficiency, long operating life, silent operation, and safety for use in human contact. Great progress has been made in the development of artificial muscles, and the most recent significant example of twisted and coiled polymer fibers [16] exploits a helical fiber topology that has a similarity with many constructs found in nature. Helices are a recurring feature in many of nature's actuators, which poses the question of whether the helix introduces any particular mechanical advantage.The helix is a striking and ubiquitous feature in biology [17] with several examples illustrated in Figure 1. The double stranded DNA molecule is probably the most famous helix (or double helix), but similar structures pervade biology at all length scales from molecular to the macroscopic. Many protein molecules adopt an alpha-helix conformation and assemble into helical filaments, such as the thin filament in skeletal muscle.Helical constructs are ubiquitous in nature at all size domains, from molecular to macroscopic. The helical topology confers unique mechanical functions that activate certain phenomena, such as twining vines and vital cellular functions like the folding and packing of DNA into chromosomes. The understanding of active mechanical processes in plants, certain musculature in animals, and some biochemical processes in cells provides insight into the versatility of the helix. Most of these natural systems consist of helically orien...

Revisited Japanese research literature on the stalk contraction and relaxation of stalked ciliates

“…Harnessing live Vorticellidae in a microsystem is challenging due to maintenance of their viability. As such, helical soft actuators mimicking the stalk of Vorticellidae have been developed (Sareh & Rossiter 2013;Yoshida et al 2018;Spinks 2020;Zou et al 2021). Such helical actuators can be further advanced by incorporating reconstructed Ca 2+responding filaments similar to those in the spasmoneme.…”

Bio‐Inspired Conformable and Helical Soft Fabric Gripper with Variable Stiffness and Touch Sensing

“…The core driving component of the soft, helical gripper is a hydraulically driven soft actuator that can be extended or contracted under the fluid pressure, similar to the anisotropic morphology of certain plant cells. [ 54 ] The core actuator consists of a stretchable silicone tube that is radially constrained by a helical coil made of inextensible fibers. A non‐stretchable guide tube or fluid transmission tube conveys water from a miniature syringe via a blunt needle.…”

DNA-Helix Inspired Wire Routing in Cylindrical Structures and Its Application to Flexible Surgical Devices

“…In fact, the helix structure of the DNA inspires the antenna related field to increase the bandwidth 1,2 and optical related field as broadband circular polarizers using square arrays of three-dimensional (3D) gold helices [3][4][5] and parallel double helix wire-shaped supercapacitor. 6 Moreover, the helix structure is applied to the actuator materials inspired by the biomimetic helical fiber topologies for artificial muscles, 7 in the construction of tubular electromechanical actuators based on polypyrrole, 8 and superhydrophobic helix to transport the bubble in an aqueous environment. 9 With respect to the DNA nanotechnology, the DNA structure has inspired the biological ion channels, 10,11 and stress sensitive hydrogel was controlled using the characteristic of DNA nanoswitch.…”