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.