Fig 1

Carbonene artificial muscle fibers with expansion/shrinkage and bending actuation. (a) Charge injection in a nanotube bundle (left) and a DNA/SWNT hybrid system with unbundled SWNT (right). (b) Plot of strain versus time of uncrosslinked and crosslinked DNA/SWNT hybrid fiber during cycling voltammetry. Adapted with permission from Ref. 33. Copyright 2008, Wiley-VCH. (c) Schematic illustration of positioned laser reduction on one side of a GO fiber. (d) Photomicrograph of the top surface of the as-prepared asymmetric G/GO fiber. (e) Representation of the possible bending of a G/GO fiber exposed to different relative humidities. (f–h) Photographs of a G/GO fiber (2 cm in length) under different relative humidities. Adapted with permission from Ref. 37. Copyright 2013, Wiley-VCH."

Fig 2

Carbonene artificial muscle fibers with torsional actuation. (a) Twisted structure of CNT yarns. (b) Schematic illustration of the effect of volume expansion on the twist and length of the yarn, the arrow indicates the untwisting direction of yarn. (c) A one end-tethered yarn configuration with a paddle located at the yarn end. (d) A two-end-tethered configuration with a force/distance transducer at the upper end that maintains constant tensile force on the yarn and measures the axial length change. (e) Photograph of prototype mixer that can be downscaled for a microfluidic circuit. Adapted with permission from Ref. 17. Copyright 2011, AAAS. (f) Plying anode and cathode yarns which infiltrated and coated with PVDF-co-HFP based TEABF4 solid gel electrolyte to make all-solid-state CNT torsional artificial muscle. Adapted with permission from Ref. 39. Copyright 2014, American Chemical Society. (g) Scheme of the torsional graphene-fiber motor (TGF) fabrication (top), SEM images of directly dried GO fiber (middle) and TGF with an applied 5000 turns per meter (down). (h) Schematic rotation of a TGF at the low (left) and high (right) humidity. Adapted with permission from Ref. 29. Copyright 2014, Wiley-VCH. (i) Plasma modification of CNT fiber with hierarchically helical channels, which responses to water and moisture. Adapted with permission from Ref. 40. Copyright 2015, Wiley-VCH. (j) Schematic illustration of the demonstrated use of torsional yarn muscle to precisely rotate mirrors without producing significant torsional oscillations. Adapted with permission from Ref. 41. Copyright 2014, Nature Publishing Group."

Fig 3

Fabrication of composite carbonene yarns by biscrolling. (a) Biscrolling of CNT sheets and functional guests (black dots). SEM micrograph of (b) Fermat scroll (c) Archimedean and (d) dual Archimedean scrolls. Adapted with permission from Ref. 47. Copyright 2011, AAAS."

Fig 4

Mechanical properties, fabrication and tensile actuation of coiled fibers. (a) Singles and (b) two-ply of CNT yarn. (c) Percent change in diameter and length of CNT yarns with different structures as shown in (a) and (b). Symbols: blue circles, initial stretch; green circles, second stress increase; black squares, second stress decrease; red circles, stress increase until yarn rupture. Adapted with permission from Ref. 25. Copyright 2004, AAAS. (d) Fabrication of a coiled CNT fiber from a MWNT forest. Adapted with permission from Ref. 39. Copyright 2014, American Chemical Society. (e) Schematic illustration of the mechanism by which torsional fiber actuation leads to large-stroke tensile actuation for fibers with heterochiral (up) and homochiral (down) coiled structure. Adapted with permission from Ref. 48. Copyright 2014, AAAS."

Fig 5

Carbonene artificial muscle fibers with tensile actuation. (a) Illustration of a plied, coiled yarn muscle with attached weight for tensile actuation measurements, which had been over coated with electrolyte after plying. Adapted with permission from Ref. 39. Copyright 2014, American Chemical Society. (b) The stress dependence of tensile stroke in various electrolytes. Green, blue, and red lines and data points were used in this figure to describe data for 0.2 M TEA·BF4, 0.2 M TBA·PF6, and 0.2 M THA∙PF6 electrolytes, respectively. (c) Optical microscope images of parallel, two-ply coiled yarns before and after coating with gel electrolyte to make a gel electrolyte muscle. (d) The structure of braided muscle. Adapted with permission from Ref. 49. Copyright 2017, WILEY-VCH. Comparisons of (e) bipolar and (f) unipolar artificial muscles. Adapted with permission from Ref. 51. Copyright 2021, AAAS. (g) Schematic illustration of the change in structure of hybrid yarn artificial muscle due to water absorption. Adapted with permission from Ref. 57. Copyright 2016, Nature Publishing Group."

Fig 6

Carbonene artificial muscle fibers with sheath-core structures. (a) Artificial muscle with sheath-core structure was fabricated by coating a twisted CNT yarn with a polymer sheath, which could be further coiled to have diverse structure as illustrated in (b–d). (e) The surface of a twisted muscle, which was broken by untwisting in liquid N2, showing the distinct boundary between sheath polymer and CNT core. Scale bars, (b) to (e), 35, 200, 200 and 15 mm, respectively. Adapted with permission from Ref. 61. Copyright 2019, AAAS. (f) Preparation of the solid-state electrochemical yarn muscle which integrates two yarn electrodes twisted together and separated by ionic-liquid-infiltrated PVDF-HFP nanofiber separators. Adapted with permission from Ref. 62. Copyright 2021, Wiley-VCH."

Fig 7

Artificial muscle films based on carbonene materials. (a) Photograph of a rigidly end-supported 50-mm-long by 2-mm-wide CNT sheet strip (left) and CNT sheet strip expanded in width by applying 5 kV with respect to ground (right). Adapted with permission from Ref. 64. Copyright 2009, AAAS. (b) Schematic illustration of charge injection in a nanotube-based electromechanical actuator. (c) Schematic edge-view of an actuator operated in aqueous NaCl, which consists of two strips of SWNTs (shaded) that are laminated together with an intermediate layer of double-sided Scotch tape (white). Adapted with permission from Ref. 65. Copyright 1999, AAAS. (d) Schematic illustration of asymmetric plasma treatments of the graphene film with hexane and oxygen, and the wettability of corresponding surface. (e) Curvature change of the actuator as a function of applied CV potential. Adapted with permission from Ref. 66. Copyright 2010, American Chemical Society. (f) Fabrication scheme of the GO film responsive actuator with asymmetric structure. (g) SEM and (h) AFM images of smooth side (left) and rough side (right) of the GO film, respectively. Scale bar of SEM image: 5 μm. Adapted with permission from Ref. 74. Copyright 2016, American Chemical Society. (i) Optical photo series showing the moving process of the weightlifting walking robot. Adapted with permission from Ref. 79. Copyright 2015, American Chemical Society. (j) A demonstration of a gripper consisting of two actuators manipulating a small object. Adapted with permission from Ref. 81. Copyright 2011, American Chemical Society."

Fig 8

Schematic representations of the structures of IPMC and IPGC. (a) Liquid-permeable IPMC actuator with cracks in metal electrodes. (b) Durable and water-floatable IPGC actuator with graphene films as electrodes. Adapted with permission from Ref. 84. Copyright 2014, American Chemical Society."

Fig 9

Mechanical enhancements and multi-functionalization of artificial muscles by carbonene materials. (a) Enhancement on tensile stress and modulus of PVA artificial muscle fibers by compositing GO and CNT. (b) Recovery torque generated by the coiled fibers that have been quenched without being hooked when they are reheated. Adapted with permission from Ref. 92. Copyright 2019, AAAS. (c) Measured and computed thickness strain of dielectric elastomer nanocomposites under applied electric fields. Adapted with permission from Ref. 93. Copyright 2017, AIP. (d) Schematic of the multidirectional actuator. (e–g) The coordinate of the tip of the actuator by applying the following inputs (left to right), X-Ch: Vx = Vxo sin(ω·t), Y-Ch: Vy = Vyo cos(ω·t); X-Ch: Vx = Vxo tringl(ω·t), Y-Ch: Vy = Vyo tringle(ω·t+π/2); X-Ch: Vx = Vxo sin(2ω·t), Y-Ch: Vy = Vyo cos(ω·t). Adapted with permission from Ref. 97. Copyright 2016, WILEY. (h) Schematic of graphic design and laser cutting on BP to make a T-shaped conductive band. (i) Three different ways of processing T-shaped BP electrodes and corresponding actuations. Adapted with permission from Ref. 98. Copyright 2015, American Chemical Society. (j) Wireless antenna sensing of light illumination intensity, wind speed and touch via near-field communication. Adapted with permission from Ref. 106. Copyright 2020, WILEY-VCH."