Rus, D. & Tolley, M. T. Design, fabrication and control of soft robots. Nature 521, 467–475 (2015).
Gelebart, A. H. et al. Making waves in a photoactive polymer film. Nature 546, 632–636 (2017).
Wehner, M. et al. Pneumatic energy sources for autonomous and wearable soft robotics. Soft Robot. 1, 263–274 (2014).
He, Q., Wang, Z., Song, Z. & Cai, S. Bioinspired design of vascular artificial muscle. Adv. Mater. Technol. 4, 1800244 (2019).
Palagi, S. et al. Structured light enables biomimetic swimming and versatile locomotion of photoresponsive soft microrobots. Nat. Mater. 15, 647–653 (2016).
Yang, G. Z. et al. The grand challenges of science robotics. Sci. Robot. 3, eaar7650 (2018).
Tawfick, S. & Tang, Y. Stronger artificial muscles, with a twist. Science 365, 125–126 (2019).
Lima, M. D. et al. Electrically, chemically, and photonically powered torsional and tensile actuation of hybrid carbon nanotube yarn muscles. Science 338, 928–932 (2012).
Chu, H. et al. Unipolar stroke, electroosmotic pump carbon nanotube yarn muscles. Science 371, 494–498 (2021).
Kanik, M. et al. Strain-programmable fiber-based artificial muscle. Science 365, 145–150 (2019).
Mu, J. et al. Sheath-run artificial muscles. Science 365, 150–155 (2019).
Yuan, J. et al. Shape memory nanocomposite fibers for untethered high-energy microengines. Science 365, 155–158 (2019).
Yang, Y. et al. Graphene-enabled superior and tunable photomechanical actuation in liquid crystalline elastomer nanocomposites. Adv. Mater. 27, 6376–6381 (2015).
Koerner, H., Price, G., Pearce, N. A., Alexander, M. & Vaia, R. A. Remotely actuated polymer nanocomposites—stress-recovery of carbon-nanotube-filled thermoplastic elastomers. Nat. Mater. 3, 115–120 (2004).
Li, C., Liu, Y., Huang, X. & Jiang, H. Direct sun-driven artificial heliotropism for solar energy harvesting based on a photo-thermomechanical liquid-crystal elastomer nanocomposite. Adv. Funct. Mater. 22, 5166–5174 (2012).
Yang, L., Setyowati, K., Li, A., Gong, S. & Chen, J. Reversible infrared actuation of carbon nanotube-liquid crystalline elastomer nanocomposites. Adv. Mater. 20, 2271–2275 (2008).
Kim, H. et al. Intelligently actuating liquid crystal elastomer‐carbon nanotube composites. Adv. Funct. Mater. 29, 1905063 (2019).
Ahir, S. V. & Terentjev, E. M. Photomechanical actuation in polymer–nanotube composites. Nat. Mater. 4, 491–495 (2005).
Liu, M. et al. Conductive carbon nanofiber interpenetrated graphene architecture for ultra-stable sodiumion battery. Nat. Commun. 10, 3917 (2019).
Al-Dhahebi, A. M., Gopinath, S. C. B. & Saheed, M. S. M. Graphene impregnated electrospun nanofiber sensing materials: a comprehensive overview on bridging laboratory set-up to industry. Nano Converg. 7, 27 (2020).
Zhang, J. et al. Multiscale deformations lead to high toughness and circularly polarized emission in helical nacre-like fibres. Nat. Commun. 7, 10701 (2016).
Roberts, T. J. et al. Three-dimensional nature of skeletal muscle contraction. Physiology 34, 402–408 (2019).
Raez, M. B., Hussain, M. S. & Mohd-Yasin, F. Techniques of EMG signal analysis: detection, processing, classification and applications. Biol. Proced. Online 8, 11–35 (2006).
Ware, T. H., McConney, M. E., Wie, J. J., Tondiglia, V. P. & White, T. J. Actuating materials. Voxelated liquid crystal elastomers. Science 347, 982–984 (2015).
Ohm, C., Brehmer, M. & Zentel, R. Liquid crystalline elastomers as actuators and sensors. Adv. Mater. 22, 3366–3387 (2010).
White, T. J. & Broer, D. J. Programmable and adaptive mechanics with liquid crystal polymer networks and elastomers. Nat. Mater. 14, 1087–1098 (2015).
Pei, Z. et al. Mouldable liquid-crystalline elastomer actuators with exchangeable covalent bonds. Nat. Mater. 13, 36–41 (2014).
Guin, T. et al. Layered liquid crystal elastomer actuators. Nat. Commun. 9, 2531 (2018).
Lopez-Valdeolivas, M., Liu, D., Broer, D. J. & Sanchez-Somolinos, C. 4D printed actuators with soft-robotic functions. Macromol. Rapid Commun. 39, 1700710 (2018).
Kotikian, A., Truby, R. L., Boley, J. W., White, T. J. & Lewis, J. A. 3D printing of liquid crystal elastomeric actuators with spatially programed nematic order. Adv. Mater. 30, 1706164 (2018).
Roach, D. J., Kuang, X., Yuan, C., Chen, K. & Qi, H. J. Novel ink for ambient condition printing of liquid crystal elastomers for 4D printing. Smart Mater. Struct. 27, 125011 (2018).
Ambulo, C. P. et al. Four-dimensional printing of liquid crystal elastomers. ACS Appl. Mater. Interfaces 9, 37332–37339 (2017).
Kohlmeyer, R. R. & Chen, J. Wavelength-selective, IR light-driven hinges based on liquid crystalline elastomer composites. Angew. Chem. Int. Ed. 52, 9234–9237 (2013).
Sasikala, S. P. et al. Graphene oxide liquid crystals: a frontier 2D soft material for graphene-based functional materials. Chem. Soc. Rev. 47, 6013–6045 (2018).
Kim, F., Cote, L. J. & Huangm, J. Graphene oxide: surface activity and two-dimensional assembly. Adv. Mater. 22, 1954–1958 (2010).
Parvez, K. et al. Exfoliation of graphite into graphene in aqueous solutions of inorganic salts. J. Am. Chem. Soc. 136, 6083–6091 (2014).
Kim, D. W., Kim, Y. H., Jeong, H. S. & Jung, H. T. Direct visualization of large-area graphene domains and boundaries by optical birefringency. Nat. Nanotechnol. 7, 29–34 (2011).
Potts, J. R., Dreyer, D. R., Bielawski, C. W. & Ruoff, R. S. Graphene-based polymer nanocomposites. Polymer 52, 5–25 (2011).
Tang, T. T. et al. A tunable phonon–exciton Fano system in bilayer graphene. Nat. Nanotechnol. 5, 32–36 (2010).
Kim, Y. et al. Stretchable nanoparticle conductors with self-organized conductive pathways. Nature 500, 59–63 (2013).
Benveniste, Y. A new approach to the application of Mori-Tanaka’s theory in composite materials. Mech. Mater. 6, 147–157 (1987).
Azoug, A. et al. Viscoelasticity of the polydomain-monodomain transition in main-chain liquid crystal elastomers. Polymer 98, 165–171 (2016).
Döhler, D. et al. Tuning the self-healing response of poly(dimethylsiloxane)-based elastomers. ACS Appl. Poly. Mater. 2, 4127–4139 (2020).
Papageorgiou, D. G., Kinloch, I. A. & Young, R. J. Mechanical properties of graphene and graphene-based nanocomposites. Prog. Mater. Sci. 90, 75–127 (2017).
Lee, S., Amjadi, M., Pugno, N., Park, I. & Ryu, S. Computational analysis of metallic nanowire-elastomer nanocomposite based strain sensors. AIP Adv. 5, 117233 (2015).
Balandin, A. A. Thermal properties of graphene and nanostructured carbon materials. Nat. Mater. 10, 569–581 (2011).
Savchuk, Ol. A., Carvajal, J. J., Massons, J., Aguiló, M. & Díaz, F. Determination of photothermal conversion efficiency of graphene and graphene oxide through an integrating sphere method. Carbon 103, 134–141 (2016).
Xie, Z. et al. The rise of 2D photothermal materials beyond graphene for clean water production. Adv. Sci. 7, 1902236 (2020).
Yoon, H.-H., Kim, D.-Y., Jeong, K.-U. & Ahn, S.-K. Surface aligned main-chain liquid crystalline elastomers: tailored properties by the choice of amine chain extenders. Macromolecules 51, 1141–1149 (2018).
Ryu, S., Lee, S., Jung, J., Lee, J. & Kim, Y. Micromechanics-based homogenization of the effective physical properties of composites with an anisotropic matrix and interfacial imperfections. Front. Mater. 6, 21 (2019).
Jung, J., Lee, S., Ryu, B. & Ryu, S. Investigation of effective thermoelectric properties of composite with interfacial resistance using micromechanics-based homogenisation. Int. J. Heat Mass Transf. 144, 118620 (2019).
Lee, S., Jung, J. & Ryu, S. Micromechanics-based prediction of the effective properties of piezoelectric composite having interfacial imperfections. Compos. Struct. 240, 112076 (2020).
Kim, I. H. et al. Mussel-inspired defect engineering of graphene liquid crystalline fibers for synergistic enhancement of mechanical strength and electrical conductivity. Adv. Mater. 30, 1803267 (2018).
López, V. et al. Chemical vapor deposition repair of graphene oxide: a route to highly-conductive graphene monolayers. Adv. Mater. 21, 4683–4686 (2009).
Ferrari, A. C. et al. Raman spectrum of graphene and graphene layers. Phys. Rev. Lett. 97, 187401 (2006).
Gupta, A., Chen, G., Joshi, P., Tadigadapa, S. & Eklund, P. C. Raman scattering from high-frequency phonons in supported n-graphene layer films. Nano Lett. 6, 2667–2673 (2006).
Li, D., Muller, M. B., Gilje, S., Kaner, R. B. & Wallace, G. G. Processable aqueous dispersions of graphene nanosheets. Nat. Nanotechnol. 3, 101–105 (2008).
Madden, J. D. W. et al. Artificial muscle technology: physical principles and naval prospects. IEEE J. Ocean. Eng. 29, 706–728 (2004).
Chai, P. & Millard, D. Flight and size constraints: hovering performance of large hummingbirds under maximal loading. J. Exp. Biol. 200, 2757–2763 (1997).
Rome, L. C. & Swank, D. The influence of temperature on power output of scup red muscle during cyclical length changes. J. Exp. Biol. 171, 261–281 (1992).
Stevenson, R. D. & Josephson, R. K. Effects of operating frequency and temperature on mechanical power output from moth flight muscle. J. Exp. Biol. 149, 61–78 (1990).
Wang, L. et al. A room-temperature two-stage thiol–ene photoaddition approach towards monodomain liquid crystalline elastomers. Polym. Chem. 8, 1364–1370 (2017).
Luo, C. et al. 3D printing of liquid crystal elastomer foams for enhanced energy dissipation under mechanical insult. ACS Appl. Mater. Interfaces 13, 12698–12708 (2021).
Urayama, K., Mashita, R., Kobayashi, I. & Takigawa, T. Stretching-induced director rotation in thin films of liquid crystal elastomers with homeotropic alignment. Macromolecules 40, 7665–7670 (2007).
Michal, B. T., McKenzie, B. M., Felder, S. E. & Rowan, S. J. Metallo-, thermo-, and photoresponsive shape memory and actuating liquid crystalline elastomers. Macromolecules 48, 3239–3246 (2015).
Chen, L. et al. Healable and rearrangeable networks of liquid crystal elastomers enabled by diselenide bonds. Angew. Chem. Int. Ed. 60, 16394–16398 (2021).
Ishige, R., Tagawa, K. O. H., Niwano, H., Tokita, M. & Watanabe, J. Elongation behavior of a main-chain smectic liquid crystalline elastomer. Macromolecules 41, 7566–7570 (2008).
He, Q., Wang, Z., Wang, Y., Song, Z. & Cai, S. Recyclable and self-repairable fluid-driven liquid crystal elastomer actuator. ACS Appl. Mater. Interfaces 12, 35464–35474 (2020).
Clarke, S. M., Terentjev, E. M., Kundler, I. I. & Finkelmann, H. Texture evolution during the polydomain-monodomain transition in nematic elastomers. Macromolecules 31, 4862–4872 (1998).
Komp, A. & Finkelmann, H. A new type of macroscopically oriented smectic-A liquid crystal elastomer. Macromol. Rapid Commun. 28, 55–62 (2007).
Wang, Z. et al. Three-dimensional printing of functionally graded liquid crystal elastomer. Sci. Adv. 6, eabc0034 (2020).
Ortiz, C., Wagner, M., Bhargava, N., Ober, C. K. & Kramer, E. J. Deformation of a polydomain, smectic liquid crystalline elastomer. Macromolecules 31, 8531–8539 (1998).
Naciri, J. et al. Nematic elastomer fiber actuator. Macromolecules 36, 8499–8505 (2003).
Liu, L. et al. Aggregation-induced emission luminogen-functionalized liquid crystal elastomer soft actuators. Macromolecules 51, 4516–4524 (2018).
Liu, L., Liu, M. H., Deng, L. L., Lin, B. P. & Yang, H. Near-infrared chromophore functionalized soft actuator with ultrafast photoresponsive speed and superior mechanical property. J. Am. Chem. Soc. 139, 11333–11336 (2017).
Lu, H. F., Wang, M., Chen, X. M., Lin, B. P. & Yang, H. Interpenetrating liquid-crystal polyurethane/polyacrylate elastomer with ultrastrong mechanical property. J. Am. Chem. Soc. 141, 14364–14369 (2019).
Kent, T. A., Ford, M. J., Markvicka, E. J. & Majidi, C. Soft actuators using liquid crystal elastomers with encapsulated liquid metal joule heaters. Multifunct. Mater. 3, 025003 (2020).
Liu, J. et al. Shaping and locomotion of soft robots using filament actuators made from liquid crystal elastomer–carbon nanotube composites. Adv. Intell. Syst. 2, 1900163 (2020).
Wang, Y., Wang, Z., He, Q., Iyer, P. & Cai, S. Electrically controlled soft actuators with multiple and reprogrammable actuation modes. Adv. Intell. Syst. 2, 1900177 (2020).
Li, C., Liu, Y., Lo, C.-W. & Jiang, H. Reversible white-light actuation of carbon nanotube incorporated liquid crystalline elastomer nanocomposites. Soft Matter 7, 7511–7516 (2011).
Tian, H. et al. Polydopamine-coated main-chain liquid crystal elastomer as optically driven artificial muscle. ACS Appl. Mater. Interfaces 10, 8307–8316 (2018).
He, Q. et al. Electrospun liquid crystal elastomer microfiber actuator. Sci. Robot. 6, eabi9704 (2021).
He, Q. et al. Electrically controlled liquid crystal elastomer-based soft tubular actuator with multimodal actuation. Sci. Adv. 5, eaax5746 (2019).
Li, S. et al. Digital light processing of liquid crystal elastomers for self-sensing artificial muscles. Sci. Adv. 7, eabg3677 (2021).
Saed, M. O. et al. High strain actuation liquid crystal elastomers via modulation of mesophase structure. Soft Matter 13, 7537–7547 (2017).
Kim, H., Boothby, J. M., Ramachandran, S., Lee, C. D. & Ware, T. H. Tough, shape-changing materials: crystallized liquid crystal elastomers. Macromolecules 50, 4267–4275 (2017).
Rafsanjani, A., Zhang, Y., Liu, B., Rubinstein, S. M. & Bertoldi, K. Kirigami skins make a simple soft actuator crawl. Sci. Robot. 3, eaar7555 (2018).
Zou, J., Lin, Y., Ji, C. & Yang, H. A reconfigurable omnidirectional soft robot based on caterpillar locomotion. Soft Robot. 5, 164 (2018).
Li, W.-B., Zhang, W.-M., Zou, H.-X., Peng, Z.-K. & Meng, G. Multisegment annular dielectric elastomer actuators for soft robots. Smart Mater. Struct. 27, 115024 (2018).
Xiao, Y. et al. Anisotropic electroactive elastomer for highly maneuverable soft robotics. Nanoscale 12, 7514–7521 (2020).
Wang, C. et al. Soft ultrathin electronics innervated adaptive fully soft robots. Adv. Mater. 30, 1706695 (2018).
Rogóz, M., Zeng, H., Xuan, C., Wiersma, D. S. & Wasylczyk, P. Light-driven soft robot mimics caterpillar locomotion in natural scale. Adv. Opt. Mater. 4, 1689–1694 (2016).
Tang, X., Li, K., Liu, Y., Zhou, D. & Zhao, J. A soft crawling robot driven by single twisted and coiled actuator. Sens. Actuator A Phys. 291, 80–86 (2019).
Lu, H. et al. A bioinspired multilegged soft millirobot that functions in both dry and wet conditions. Nat. Commun. 9, 3944 (2018).
