![]() Toughness is defined as the energy needed to break the silk. e Stress–strain curves of natural spider silk (S-silk), spider silk with (S-silk spider silk with (S-silk Area under gray dotted curve represents toughness of S-silk. The outer conducting layer is about 2 μm. The core is spider silk, and the diameter is about 3–4 μm. d Cross-sectional scanning electron microscopic image of a spider silk composite. The wrinkled structure prevented any changes in the conductive path, allowing the S-silk composite to maintain its conductivity during stretching and compression. c SEM image showing the wrinkled surface of a single fiber of SWCNT composite formed from the intrinsic shrinkage of the spider silk after immersion in water during PEDOT:PSS and SWCNT coating. Inset shows a single silk fiber has a very smooth surface. b Optical image of a bundle of raw dragline silk from Nephila pilipes. Pink star represents SWCNT composites described in this work. Green represents metals, red is PDMS-based stretchable conductors, and blue represents other special conducting materials/structures. There is, therefore, a demand for materials that are simultaneously flexible, conductive and durable, so they can be easily integrated on a finger to achieve human-like performance and functionality.Ī Graph shows the conductivity and toughness of different flexible materials. 1a and Supplementary Table 1), making these materials unsuitable for robotic applications. Although traditional metals such as Au, Al, and Cu have excellent conductivity, they have low toughness (around 1–10 MJ/m 3) 24 (Fig. For example, the toughness of PDMS-based conductors is only around 0.6–10 MJ/m 3 18, 19, 20, 21, 22, 23. Polymer-based conductors typically show low toughness (<100 MJ/m 3) and poor conductivity (<100 S/cm) 12, 13, 14, 15, 16, 17. Given many of these tendons are non-conductive and have a single function, integrating wires for the transmission of electrical signals from sensing systems and additional fibers as tendons onto a slender robotic finger with the size of a human hand is challenging 2, 3, 9.Ĭurrently, there are no materials or systems that simultaneously have high toughness, conductivity, and stretchability for mechanical engineering applications such as tendons in robotic hands 10, 11. These fibers also suffer from large friction along the narrow tendon path, further lowering their durability 5, 7, 8. However, current tendon fibers, which are typically made from nylon, silicone rubber, or polyethylene terephthalate (PET), have low toughness and therefore, cannot endure many bending and stretching cycles. It has been widely used in humanoid robotic hands, such as the Okada Hand 4, Utah/MIT Hand 5, and DLR Hand 6. Compared to other systems based on leverages, shafts or gears, tendon-driven transmission is simpler in design and offers better dexterity and flexibility. The core component of these robotic hands is the tendon-driven transmission system, which relies on a fiber that resembles the human tendon to transmit power from actuators to joints. ![]() As a result, humanoid robotic hands with capabilities comparable to human limbs have been actively explored for use as prosthesis 1, 2, 3. The loss of appendages can severely affect a person’s quality of life. This material is expected to pave the way for the development of robots and various applications in advanced manufacturing and engineering. Because the electro-tendon can simultaneously transmit signals and force from the sensing and actuating systems, we use it to replace the single functional tendon in humanoid robotic hand to perform grasping functions without additional wiring and circuit components. The electro-tendon, mechanically toughened by single-wall carbon nanotubes (SWCNTs) and electrically enhanced by PEDOT:PSS, can withstand more than 40,000 bending-stretching cycles without changes in conductivity. Here, we report a super tough electro-tendon based on spider silk which has a toughness of 420 MJ/m 3 and conductivity of 1,077 S/cm. However, current tendon fibers have low toughness and suffer from large friction, limiting the further development of tendon-driven robotic hands. Compared to transmission systems based on shafts and gears, tendon-driven systems offer a simpler and more dexterous way to transmit actuation force in robotic hands.
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