Cooling‐Accelerated Nanowire‐Nitinol Hybrid Muscle for Versatile Prosthetic Hand and Biomimetic Retractable Claw

Abstract

As strong and shape‐conformable as biological muscles, nitinol shape memory alloys (SMAs) artificial muscles have great merit when applied for bio‐inspired robots. However, the low bandwidth and slow actuation speed of SMAs due to their sluggish cooling have long been troublesome, limiting possible applications. Here, to expedite the cooling rate, a Cu nanowire forest is directly grown on the surfaces of 3D shaped SMA coil (SMAc) to increase the surface area by 15 times and boost thermal convection. As a result, the Cu nanowire forest grown SMA coil (CuNF‐SMAc) shows accelerated cooling compared to bare SMAc (B‐SMAc): the actuation speed of CuNF‐SMAc is 100% faster than that of bare SMAc (B‐SMAc) under natural cooling and 170% faster under forced‐air cooling. With this faster actuation, CuNF‐SMAc artificial muscles are employed in a versatile prosthetic hand to bend and flex fingers. The proposed prosthetic hand successfully demonstrates a series of sign language within 4 s for each letter, and rhythmically plays a grand piano. Moreover, unique retractable feline claws are mimicked which demonstrate a fully tunable frictional force just like how cats do it, expanding the potential of a cooling‐accelerated SMAc artificial muscle.

Tethering of twisted-fiber artificial muscles

“…A significantly increased actuation speed was realized for a nitinol shape memory alloy (SMA) coiled muscle by coating it with a copper nanowire forest; this device was used in a bio-inspired prosthetic hand and a biomimetic paw with retractable claws. 151 The accelerated response of the actuation allowed the prosthetic hand to demonstrate a sequence of sign language hand gestures in less than 4 s for each word, grab commonplace daily objects, and play a piano. The artificial feline paw was shown to have the potential to control the traction force of the paw with the ground (Fig.…”

Recent Development of Jumping Motions Based on Soft Actuators

“…SMAs are a type of actuating materials that can generate mechanical deformations upon heating and then restore their original shapes under low-temperature martensitic conditions. [96] SMAs exhibit super-elasticity, shape-memory effect, and elasto-caloric mechanism, while possessing high work density, high stress, and large strain. A typical example is the Ni-Ti alloys with the work density, stress, and strain up to 50 W g −1 , 200 MPa, and 8%, respectively, which is essential for practical applications in soft robotics, energy, and solid-state refrigeration.…”

Pretension-Free and Self-Recoverable Coiled Artificial Muscle Fibers with Powerful Cyclic Work Capability

“…Moreover, before contraction, pretension loading is required to separate the coils and provide space for contraction, ,, limiting the practical applications of coiled artificial muscle fibers, particularly in situations where zero pretension is required. Two-way shape memory polymers and alloys provide self-recoverable actuation; − however, these artificial muscles have limited recovery rates, poor cyclic stability, and a narrow bandwidth. , Liquid crystal elastomers (LCEs) with aligned mesogens in straight fibers exhibit self-recoverable actuation owing to the cross-linked structure, which acts as a returning spring, allowing the fiber to recover from the isotropic phase at the actuated state to the nematic phase when the stimulus is removed. − Recently, Kim et al constructed an artificial muscle fiber with reversible contraction by incorporating an elastic graphene percolation network into LCE . However, LCE-based artificial muscles still have limited work capacity owing to their weak mechanical strength and modulus.…”