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  • Review Article
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Untethered soft robotics

Abstract

Research in soft matter engineering has introduced new approaches in robotics and wearable devices that can interface with the human body and adapt to unpredictable environments. However, many promising applications are limited by the dependence of soft systems on electrical or pneumatic tethers. Recent work in soft actuation and electronics has made removing such cords more feasible, heralding a variety of applications from autonomous field robotics to wireless biomedical devices. Here we review the development of functional untethered soft robotics. We focus on recent advances in soft robotic actuation, sensing and integration as they relate to untethered systems, and consider the key challenges the field faces in engineering systems that could have practical use in real-world conditions.

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Fig. 1: Overview of soft robotic systems.
Fig. 2: Methods of soft actuation.
Fig. 3: Modulus and conductivity of various materials in soft robotics.
Fig. 4: Advances in soft sensing, conductivity and artificial skin.
Fig. 5: Implementation of soft actuators into robotic systems.
Fig. 6: Fully untethered robotic systems.

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References

  1. Majidi, C. Soft robotics: A perspective — current trends and prospects for the future. Soft Robot. 1, 5–11 (2014).

    Article  Google Scholar 

  2. Laschi, C., Mazzolai, B. & Cianchetti, M. Soft robotics: Technologies and systems pushing the boundaries of robot abilities. Sci. Robot. 1, eaah3690 (2016).

    Article  Google Scholar 

  3. Rus, D. & Tolley, M. T. Design, fabrication and control of soft robots. Nature 521, 467–475 (2015).

    Article  Google Scholar 

  4. Hammock, M. L., Chortos, A., Tee, B. C. K., Tok, J. B. H. & Bao, Z. 25th anniversary article: The evolution of electronic skin (E-Skin): A brief history, design considerations, and recent progress. Adv. Mater. 25, 5997–6038 (2013).

    Article  Google Scholar 

  5. Sfakiotakis, M., Kazakidi, A., Pateromichelakis, N. & Tsakiris, D. P. Octopus-inspired eight-arm robotic swimming by sculling movements. Proc. IEEE Int. Conf. Robot. Autom. 5155–5161 (2013).

  6. Calisti, M., Corucci, F., Arienti, A. & Laschi, C. Dynamics of underwater legged locomotion: Modeling and experiments on an octopus-inspired robot. Bioinspir. Biomim. 10, 046012 (2015).

    Article  Google Scholar 

  7. Larson, C. et al. Highly stretchable electroluminescent skin for optical signaling and tactile sensing. Science 351, 1071–1074 (2016).

    Article  Google Scholar 

  8. Weigel, M. et al. iSkin. Proc. 33rd Annu. ACM Conf. Hum. Factors Comput. Syst. 2991–3000 (2015).

  9. Jang, K. I. et al. Self-assembled three dimensional network designs for soft electronics. Nat. Commun. 8, 15894 (2017).

    Article  Google Scholar 

  10. O’Neill, C. T., Phipps, N. S., Cappello, L., Paganoni, S. & Walsh, C. J. A soft wearable robot for the shoulder: Design, characterization, and preliminary testing. IEEE Int. Conf. Rehabil. Robot. 1672–1678 (2017).

  11. Li, Y. & Hashimoto, M. PVC gel soft actuator-based wearable assist wear for hip joint support during walking. Smart Mater. Struct. 26, 125003 (2017).

    Article  Google Scholar 

  12. Wehner, M. et al. An integrated design and fabrication strategy for entirely soft, autonomous robots. Nature 536, 451–455 (2016).

    Article  Google Scholar 

  13. Horchler, A. D. et al. Peristaltic locomotion of a modular mesh-based worm robot: Precision, compliance, and friction. Soft Robot. 2, 135–145 (2015).

    Article  Google Scholar 

  14. Jang, K. I. et al. Soft network composite materials with deterministic and bio-inspired designs. Nat. Commun. 6, 1–11 (2015).

    Google Scholar 

  15. Kramer, R. K., Majidi, C. & Wood, R. J. Wearable tactile keypad with stretchable artificial skin. Proc. IEEE Int. Conf. Robot. Autom. 1103–1107 (2011).

  16. Ilievski, F., Mazzeo, A. D., Shepherd, R. F., Chen, X. & Whitesides, G. M. Soft robotics for chemists. Angew. Chem. Int. Ed. 50, 1890–1895 (2011).

    Article  Google Scholar 

  17. Cvetkovic, C. et al. Three-dimensionally printed biological machines powered by skeletal muscle. Proc. Natl Acad. Sci. USA 111, 10125–10130 (2014).

    Article  Google Scholar 

  18. Nawroth, J. C. et al. A tissue-engineered jellyfish with biomimetic propulsion. Nat. Biotechnol. 30, 792–797 (2012).

    Article  Google Scholar 

  19. Khalil, A. S. & Collins, J. J. Synthetic biology: Applications come of age. Nat. Rev. Genet. 11, 367–379 (2010).

    Article  Google Scholar 

  20. Madden, J. D. W. et al. Artificial muscle technology: Physical principles and naval prospects. IEEE J. Ocean. Eng. 29, 706–728 (2004).

    Article  Google Scholar 

  21. Drotman, D., Jadhav, S., Karimi, M., Dezonia, P. & Tolley, M. T. 3D printed soft actuators for a legged robot capable of navigating unstructured terrain. Proc. IEEE Int. Conf. Robot. Autom. 5532–5538 (2017).

  22. Tolley, M. T. et al. A resilient, untethered soft robot. Soft Robot. 1, 213–223 (2014). This work achieves untethered functionality by employing large pneumatic actuators and placing all standard auxiliary equipment on board.

    Article  Google Scholar 

  23. Wall, V., Zoller, G. & Brock, O. A method for sensorizing soft actuators and its application to the RBO hand 2. Proc. IEEE Int. Conf. Robot. Autom. 4965–4970 (2017).

  24. Raitor, M., Walker, J. M., Okamura, A. M. & Culbertson, H. WRAP: Wearable, restricted-aperture pneumatics for haptic guidance. Proc. IEEE Int. Conf. Robot. Autom. 427–432 (2017).

  25. Wirekoh, J. & Park, Y.-L. Design of flat pneumatic artificial muscles. Smart Mater. Struct. 26, 035009 (2017).

    Article  Google Scholar 

  26. Fras, J., Noh, Y., Wurdemann, H. & Althoefer, K. Soft fluidic rotary actuator with improved actuation properties. 2017 IEEE/RSJ Int. Conf. Intell. Robot. Syst. 5610–5615 (2017).

  27. Yan, J., Xu, B., Zhang, X. & Zhao, J. Design and test of a new spiral driven pure torsional soft actuator. In Intelligent Robotics and Applications: 10th Int. Conf., ICIRA 2017, Part 1 (eds Huang, Y. et al.) 10462, 127–139 (Springer, 2017).

  28. Yang, D. et al. Buckling pneumatic linear actuators inspired by muscle. Adv. Mater. Technol. 1, 1600055 (2016).

    Article  Google Scholar 

  29. Licht, S., Collins, E., Mendes, M. L. & Baxter, C. Stronger at depth: Jamming grippers as deep sea sampling tools. Soft Robot. 4, 305–316 (2017).

    Article  Google Scholar 

  30. Miriyev, A., Stack, K. & Lipson, H. Soft material for soft actuators. Nat. Commun. 8, 1–8 (2017).

    Article  Google Scholar 

  31. Tolley, M. T. et al. An untethered jumping soft robot. IEEE Int. Conf. Intell. Robot. Syst. 561–566 (2014).

  32. Nemitz, M. P., Mihaylov, P., Barraclough, T. W., Ross, D. & Stokes, A. A. Using voice coils to actuate modular soft robots: Wormbot, an example. Soft Robot. 3, 198–204 (2016).

    Article  Google Scholar 

  33. Zeng, H., Wani, O. M., Wasylczyk, P., Kaczmarek, R. & Priimagi, A. Self-regulating iris based on light-actuated liquid crystal elastomer. Adv. Mater. 29, 1–7 (2017).

    Google Scholar 

  34. Baytekin, B., Cezan, S. D., Baytekin, H. T. & Grzybowski, B. A. Artificial heliotropism and nyctinasty based on optomechanical feedback and no electronics. Soft Robot. https://doi.org/10.1089/soro.2017.0020 (2017). This work demonstrates untethered environmental responsiveness (that is, sun tracking) without employing the need for batteries by directly heating shape-memory alloys with sunlight.

  35. Wani, O. M., Zeng, H. & Priimagi, A. A light-driven artificial flytrap. Nat. Commun. 8, 15546 (2017).

    Article  Google Scholar 

  36. Zeng, H., Wani, O. M., Wasylczyk, P. & Priimagi, A. Light-driven, caterpillar-inspired miniature inching robot. Macromol. Rapid Commun. 39, 1700224 (2017).

    Article  Google Scholar 

  37. Palagi, S. et al. Structured light enables biomimetic swimming and versatile locomotion of photoresponsive soft microrobots. Nat. Mater. 15, 647–653 (2016).

    Article  Google Scholar 

  38. Rogóż, 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).

    Article  Google Scholar 

  39. Francis, W., Dunne, A., Delaney, C., Florea, L. & Diamond, D. Spiropyran based hydrogels actuators — Walking in the light. Sens. Actuat. B 250, 608–616 (2017).

    Article  Google Scholar 

  40. Amjadi, M. & Sitti, M. High-performance multiresponsive paper actuators. ACS Nano 10, 10202–10210 (2016).

    Article  Google Scholar 

  41. Loepfe, M., Schumacher, C. M., Lustenberger, U. B. & Stark, W. J. An untethered, jumping roly-poly soft robot driven by combustion. Soft Robot. 2, 33–41 (2015).

    Article  Google Scholar 

  42. Bartlett, N. W. et al. A 3D-printed, functionally graded soft robot powered by combustion. Science 349, 161–165 (2015).

    Article  Google Scholar 

  43. Patino, T., Mestre, R. & Sánchez, S. Miniaturized soft bio-hybrid robotics: a step forward into healthcare applications. Lab Chip 16, 3626–3630 (2016).

    Article  Google Scholar 

  44. Feinberg, A. W. et al. Muscular thin films for building actuators and powering devices. Science 317, 1366–1370 (2007).

    Article  Google Scholar 

  45. Raman, R. et al. Optogenetic skeletal muscle-powered adaptive biological machines. Proc. Natl Acad. Sci. USA 113, 3497–3502 (2016).

    Article  Google Scholar 

  46. Park, S. J. et al. Phototactic guidance of a tissue-engineered soft-robotic ray. Science 353, 158–162 (2016). This work demonstrates untethered control of bio-hybrid robots using light.

    Article  Google Scholar 

  47. Yoon, J., Eyster, T. W., Misra, A. C. & Lahann, J. Cardiomyocyte-driven actuation in biohybrid microcylinders. Adv. Mater. 27, 4509–4515 (2015).

    Article  Google Scholar 

  48. Holley, M. T., Nagarajan, N., Danielson, C., Zorlutuna, P. & Park, K. Development and characterization of muscle-based actuators for self-stabilizing swimming biorobots. Lab Chip 16, 3473–3484 (2016).

    Article  Google Scholar 

  49. Kang, H. W. et al. A 3D bioprinting system to produce human-scale tissue constructs with structural integrity. Nat. Biotechnol. 34, 312–319 (2016).

    Article  Google Scholar 

  50. Wehner, M. et al. Pneumatic energy sources for autonomous and wearable soft robotics. Soft Robot. 1, 263–274 (2014).

    Article  Google Scholar 

  51. Kim, S. et al. Micro artificial muscle fiber using NiTi spring for soft robotics. 2009 IEEE/RSJ Int. Conf. Intell. Robot. Syst. 2228–2234 (2009).

  52. Jin, H. et al. Soft and smart modular structures actuated by shape memory alloy (SMA) wires as tentacles of soft robots. Smart Mater. Struct. 25, 085026 (2016).

    Article  Google Scholar 

  53. Cheng, S. S., Kim, Y. & Desai, J. P. New actuation mechanism for actively cooled SMA springs in a neurosurgical robot. IEEE Trans. Robot. 33, 986–993 (2017).

    Article  Google Scholar 

  54. Alcaide, J. O., Pearson, L. & Rentschler, M. E. Design, modeling and control of a SMA-actuated biomimetic robot with novel functional skin. Proc. IEEE Int. Conf. Robot. Autom. 4338–4345 (2017).

  55. Bartlett, M. D. et al. High thermal conductivity in soft elastomers with elongated liquid metal inclusions. Proc. Natl Acad. Sci. USA 114, 2143–2148 (2017).

    Article  Google Scholar 

  56. Rodrigue, H., Wang, W., Kim, D. R. & Ahn, S. H. Curved shape memory alloy-based soft actuators and application to soft gripper. Compos. Struct. 176, 398–406 (2017).

    Article  Google Scholar 

  57. Song, S. H. et al. Turtle mimetic soft robot with two swimming gaits. Bioinspir. Biomim. 11, 036010 (2016).

    Article  Google Scholar 

  58. Rich, S., Jang, S.-H., Park, Y.-L. & Majidi, C. Liquid metal-conductive thermoplastic elastomer integration for low-voltage stiffness tuning. Adv. Mater. Technol. 2, 1700179 (2017).

    Article  Google Scholar 

  59. Yuan, C. et al. 3D printed reversible shape changing soft actuators assisted by liquid crystal elastomers. Soft Matter 13, 5558–5568 (2017).

    Article  Google Scholar 

  60. Horiuchi, T., Mihashi, T., Fujikado, T., Oshika, T. & Asaka, K. Voltage-controlled IPMC actuators for accommodating intra-ocular lens systems. Smart Mater. Struct. 26, 045021 (2017).

    Article  Google Scholar 

  61. Carrico, J. D., Kim, K. J. & Leang, K. K. 3D-printed ionic polymer-metal composite soft crawling robot. Proc. IEEE Int. Conf. Robot. Autom. 4313–4320 (2017).

  62. Yang, T. & Chen, Z. Development of 2D maneuverable robotic fish propelled by multiple ionic polymer–metal composite artificial fins. 2015 IEEE Int. Conf. Robot. Biomimetics, IEEE-ROBIO 2015 1, 255–260 (2015).

    Google Scholar 

  63. Duduta, M., Clarke, D. R. & Wood, R. J. A high speed soft robot based on dielectric elastomer actuators. 2017 IEEE Int. Conf. Robot. Autom. 4346–4351 (2017).

  64. Godaba, H., Li, J., Wang, Y. & Zhu, J. A soft jellyfish robot driven by a dielectric elastomer actuator. IEEE Robot. Autom. Lett. 1, 624–631 (2016).

    Article  Google Scholar 

  65. Li, T. et al. Fast-moving soft electronic fish. Sci. Adv. 3, e1602045 (2017).This work demonstrates a fast untethered underwater robot with a long battery life, based on low-power dielectric elastomer actuators.

    Article  Google Scholar 

  66. Sun, W., Liu, F., Ma, Z., Li, C. & Zhou, J. Soft mobile robots driven by foldable dielectric elastomer actuators. J. Appl. Phys. 120, 084901 (2016).

    Article  Google Scholar 

  67. Henke, E.-F. M., Wilson, K. E. & Anderson, I. A. Entirely soft dielectric elastomer robots. Proc. SPIE 10163, 101631N (2017).

    Google Scholar 

  68. Nguyen, C. T., Phung, H., Nguyen, T. D., Jung, H. & Choi, H. R. Multiple-degrees-of-freedom dielectric elastomer actuators for soft printable hexapod robot. Sens. Actuat. A 267, 505–516 (2017).

    Article  Google Scholar 

  69. Shintake, J., Schubert, B., Rosset, S., Shea, H. & Floreano, D. Variable stiffness actuator for soft robotics using dielectric elastomer and low-melting-point alloy. IEEE Int. Conf. Intell. Robot. Syst. 1097–1102 (2015).

  70. Shintake, J., Rosset, S., Schubert, B., Floreano, D. & Shea, H. Versatile soft grippers with intrinsic electroadhesion based on multifunctional polymer actuators. Adv. Mater. 28, 231–238 (2016).

    Article  Google Scholar 

  71. Kazem, N., Hellebrekers, T. & Majidi, C. Soft multifunctional composites and emulsions with liquid metals. Adv. Mater. 29, 1–14 (2017).

    Article  Google Scholar 

  72. Khang, D.-Y., Jiang, H., Huang, Y. & Rogers, J. A. A stretchable form of single-crystal. Science 311, 208–212 (2006).

    Article  Google Scholar 

  73. Liu, Y. et al. Epidermal mechano-acoustic sensing electronics for cardiovascular diagnostics and human-machine interfaces. Sci. Adv. 2, e1601185 (2016).

    Article  Google Scholar 

  74. Kim, J. et al. Battery-free, stretchable optoelectronic systems for wireless optical characterization of the skin. Sci. Adv. 2, e1600418 (2016). This work shows battery-free biological sensing that can wirelessly deliver data to an NFC-enabled device.

    Article  Google Scholar 

  75. Bartlett, M. D., Markvicka, E. J. & Majidi, C. Rapid fabrication of soft, multilayered electronics for wearable biomonitoring. Adv. Funct. Mater. 26, 8496–8504 (2016).

    Article  Google Scholar 

  76. Kaltenbrunner, M. et al. An ultra-lightweight design for imperceptible plastic electronics. Nature 499, 458–463 (2013).

    Article  Google Scholar 

  77. Yokota, T. et al. Ultraflexible organic photonic skin. Sci. Adv. 2, e1501856 (2016).

    Article  Google Scholar 

  78. Lee, W. et al. Integration of organic electrochemical and field-effect transistors for ultraflexible, high temporal resolution electrophysiology arrays. Adv. Mater. 28, 9722–9728 (2016).

    Article  Google Scholar 

  79. Plovie, B. et al. Arbitrarily shaped 2.5D circuits using stretchable interconnects embedded in thermoplastic polymers. Adv. Eng. Mater. 19, 1–8 (2017).

    Article  Google Scholar 

  80. Vásquez Quintero, A., Verplancke, R., De Smet, H. & Vanfleteren, J. Stretchable electronic platform for soft and smart contact lens applications. Adv. Mater. Technol. 2, 1700073 (2017).

    Article  Google Scholar 

  81. Bandodkar, A. J. et al. Soft, stretchable, high power density electronic skin-based biofuel cells for scavenging energy from human sweat. Energy Environ. Sci. 10, 1581–1589 (2017).

    Article  Google Scholar 

  82. Miyamoto, A. et al. Inflammation-free, gas-permeable, lightweight, stretchable on-skin electronics with nanomeshes. Nat. Nanotech. 12, 907–913 (2017).

    Article  Google Scholar 

  83. Varga, M., Ladd, C., Ma, S., Holbery, J. & Tröster, G. On-skin liquid metal inertial sensor. Lab Chip 17, 3272–3278 (2017).

    Article  Google Scholar 

  84. Xu, T. et al. Three-dimensional and ultralight sponges with tunable conductivity assembled from electrospun nanofibers for highly sensitive tactile pressure sensor. J. Mater. Chem. C 5, 10288–10294 (2017).

  85. Luo, W., Wu, T., Chen, B., Liang, M. & Zou, H. Highly stretchable conductors based on expanded graphite macro-confined in tubular rubber. ACS Appl. Mater. Inter. 9, 43239–43249 (2017).

    Google Scholar 

  86. Segev-Bar, M., Konvalina, G. & Haick, H. High-resolution unpixelated smart patches with antiparallel thickness gradients of nanoparticles. Adv. Mater. 27, 1779–1784 (2015).

    Article  Google Scholar 

  87. Yuen, M. C., Tonoyan, H., White, E. L., Telleria, M. & Kramer, R. K. Fabric sensory sleeves for soft robot state estimation. Proc. IEEE Int. Conf. Robot. Autom. 5511–5518 (2017).

  88. O’Connor, T. F. et al. The language of glove: Wireless gesture decoder with low-power and stretchable hybrid electronics. PLoS One 12, e0179766 (2017).

    Article  Google Scholar 

  89. You, B., Kim, Y., Ju, B. K. & Kim, J. W. Highly stretchable and waterproof electroluminescence device based on superstable stretchable transparent electrode. ACS Appl. Mater. Inter. 9, 5486–5494 (2017).

    Google Scholar 

  90. Shuai, X. et al. Highly sensitive flexible pressure sensor based on silver nanowires-embedded polydimethylsiloxane electrode with microarray structure. ACS Appl. Mater. Inter. 9, 26314–26324 (2017).

    Google Scholar 

  91. Ma, L., Shuai, X., Zhu, P. & Sun, R. A highly sensitive flexible pressure sensor based on multi-scale structure and silver nanowires. 2017 Int. Conf. Electron. Packag. Technol. 1366–1370 (2017).

  92. Liu, N. et al. Ultratransparent and stretchable graphene electrodes. Sci. Adv. 3, e1700159 (2017).

    Article  Google Scholar 

  93. Pyo, S., Choi, J. & Kim, J. Flexible, transparent, sensitive, and crosstalk-free capacitive tactile sensor array based on graphene electrodes and air dielectric. Adv. Electron. Mater. 4, 1700427 (2017).

    Article  Google Scholar 

  94. White, E. L., Yuen, M. C., Case, J. C. & Kramer, R. K. Low-cost, facile, and scalable manufacturing of capacitive sensors for soft systems. Adv. Mater. Technol. 2, 1700072 (2017).

    Article  Google Scholar 

  95. Muth, J. T. et al. Embedded 3D printing of strain sensors within highly stretchable elastomers. Adv. Mater. 26, 6307–6312 (2014).

    Article  Google Scholar 

  96. Sencadas, V., Mutlu, R. & Alici, G. Large area and ultra-thin compliant strain sensors for prosthetic devices. Sens. Actuat. A 266, 56–64 (2017).

    Article  Google Scholar 

  97. Wang, Y. et al. A highly stretchable, transparent, and conductive polymer. Sci. Adv. 3, e1602076 (2017).

    Article  Google Scholar 

  98. Majidi, C., Park, Y. L., Kramer, R., Brard, P. & Wood, R. J. Hyperelastic pressure sensing with a liquid-embedded elastomer. J. Micromech. Microeng. 20, 125029 (2010).

    Article  Google Scholar 

  99. Zhang, B., Dong, Q., Korman, C. E., Li, Z. & Zaghloul, M. E. Flexible packaging of solid-state integrated circuit chips with elastomeric microfluidics. Sci. Rep. 3, 1098 (2013).

    Article  Google Scholar 

  100. Dickey, M. D. Emerging applications of liquid metals featuring surface oxides. ACS Appl. Mater. Inter. 6, 18369–18379 (2014).

    Google Scholar 

  101. Dickey, M. D. et al. Eutectic gallium-indium (EGaIn): A liquid metal alloy for the formation of stable structures in microchannels at room temperature. Adv. Funct. Mater. 18, 1097–1104 (2008).

    Article  Google Scholar 

  102. Fassler, A. & Majidi, C. 3D structures of liquid-phase GaIn alloy embedded in PDMS with freeze casting. Lab Chip 13, 4442–4450 (2013).

    Article  Google Scholar 

  103. Boley, J. W., White, E. L., Chiu, G. T. C. & Kramer, R. K. Direct writing of gallium-indium alloy for stretchable electronics. Adv. Funct. Mater. 24, 3501–3507 (2014).

    Article  Google Scholar 

  104. Lin, Y. et al. Vacuum filling of complex microchannels with liquid metal. Lab Chip 17, 3043–3050 (2017).

    Article  Google Scholar 

  105. Hirsch, A., Michaud, H. O., Gerratt, A. P., de Mulatier, S. & Lacour, S. P. Intrinsically stretchable biphasic (solid–liquid) thin metal films. Adv. Mater. 28, 4507–4512 (2016).

    Article  Google Scholar 

  106. Gao, Y. et al. Wearable microfluidic diaphragm pressure sensor for health and tactile touch monitoring. Adv. Mater. 29, 1701985 (2017).

    Article  Google Scholar 

  107. Tiziani, L. O., Cahoon, T. W. & Hammond, F. L. Sensorized pneumatic muscle for force and stiffness control. 2017 IEEE Int. Conf. Robot. Autom. 5545–5552 (2017).

  108. King, J. P., Valle, L. E., Pol, N. & Park, Y.-L. Design, modeling, and control of pneumatic artificial muscles with integrated soft sensing. 2017 IEEE Int. Conf. Robot. Autom. 4985–4990 (2017).

  109. Moon, Y. G. et al. Freely deformable liquid metal grids as stretchable and transparent electrodes. IEEE T. Electron. Dev. 1–6 (2017).

  110. Choi, J. et al. Soft, skin-mounted microfluidic systems for measuring secretory fluidic pressures generated at the surface of the skin by eccrine sweat glands. Lab Chip 17, 2572–2580 (2017).

    Article  Google Scholar 

  111. Choi, J., Kang, D., Han, S., Kim, S. B. & Rogers, J. A. Thin, soft, skin-mounted microfluidic networks with capillary bursting valves for chrono-sampling of sweat. Adv. Healthc. Mater. 6, 1–10 (2017).

    Google Scholar 

  112. Koh, A. et al. A soft, wearable microfluidic device for the capture, storage, and colorimetric sensing of sweat. Sci. Transl. Med. 8, 366ra165 (2016). This work shows a method for electronics-free chemical sensing (that is, sweat analysis) by employing microfluidic channels and enzymatic reactions.

    Article  Google Scholar 

  113. Kim, C. C., Lee, H. H., Oh, K. H. & Sun, J. Y. Highly stretchable, transparent ionic touch panel. Science 353, 682–687 (2016).

    Article  Google Scholar 

  114. Darabi, M. A. et al. Skin-inspired multifunctional autonomic-intrinsic conductive self-healing hydrogels with pressure sensitivity, stretchability, and 3D printability. Adv. Mater. 29, 1–8 (2017).

    Google Scholar 

  115. Lin, S. et al. Stretchable hydrogel electronics and devices. Adv. Mater. 28, 4497–4505 (2016).

    Article  Google Scholar 

  116. Wirthl, D. et al. Instant tough bonding of hydrogels for soft machines and electronics. Sci. Adv. 3, e1700053 (2017).

    Article  Google Scholar 

  117. Xu, L. et al. Bio-inspired annelid robot: A dielectric elastomer actuated soft robot. Bioinspir. Biomim. 12, 025003 (2017).

    Article  Google Scholar 

  118. Malley, M., Rubenstein, M. & Nagpal, R. Flippy: A soft, autonomous climber with simple sensing and control. 2017 IEEE/RSJ Int. Conf. Intell. Robot. Syst. https://doi.org/10.1109/IROS.2017.8206563 (2017).

  119. Marchese, A. D., Katzschmann, R. K. & Rus, D. A recipe for soft fluidic elastomer robots. Soft Robot. 2, 7–25 (2015).

    Article  Google Scholar 

  120. Marchese, A. D., Onal, C. D. & Rus, D. Autonomous soft robotic fish capable of escape maneuvers using fluidic elastomer actuators. Soft Robot. 1, 75–87 (2014).

    Article  Google Scholar 

  121. Shui, L., Zhu, L., Yang, Z., Liu, Y. & Chen, X. Energy efficiency of mobile soft robots. Soft Matter 13, 8223–8233 (2017).

    Article  Google Scholar 

  122. Lin, H. T., Leisk, G. G. & Trimmer, B. GoQBot: A caterpillar-inspired soft-bodied rolling robot. Bioinspir. Biomim. 6, 026007 (2011).

    Article  Google Scholar 

  123. Cao, J., Qin, L., Lee, H. P. & Zhu, J. Development of a soft untethered robot using artificial muscle actuators. Proc. SPIE 10163, 101631X (2017).

    Google Scholar 

  124. Bartlett, N. W. et al. Robot powered by combustion. Science 349, 161–165 (2015).

    Article  Google Scholar 

  125. Zamarayeva, A. M. et al. Flexible and stretchable power sources for wearable electronics. Sci. Adv. 3, e1602051 (2017). This work provides a potential power source for soft, untethered systems by demonstrating a stretchable battery.

    Article  Google Scholar 

  126. O’Connor, T. F. et al. Wearable organic solar cells with high cyclic bending stability: Materials selection criteria. Sol. Energy Mater. Sol. Cells 144, 438–444 (2016).

    Article  Google Scholar 

  127. Chen, X. et al. On-skin triboelectric nanogenerator and self-powered sensor with ultrathin thickness and high stretchability. Small 13, 1702929 (2017).This work demonstrates a tactile sensing system that is powered by an on-board nano-generator, requiring neither battery nor power cable.

    Article  Google Scholar 

  128. Yang, H., Chen, Y., Sun, Y. & Hao, L. A novel pneumatic soft sensor for measuring contact force and curvature of a soft gripper. Sens. Actuat. A 266, 318–327 (2017).

    Article  Google Scholar 

  129. Naserifar, N., LeDuc, P. R. & Fedder, G. K. Drop casting of stiffness gradients for chip integration into stretchable substrates. J. Micromech. Microeng. 27, 045018 (2017).

    Article  Google Scholar 

  130. Naserifar, N., LeDuc, P. R. & Fedder, G. K. Material gradients in stretchable substrates toward integrated electronic functionality. Adv. Mater. 28, 3584–3591 (2016).

    Article  Google Scholar 

  131. Park, C. W. et al. Photolithography-based patterning of liquid metal interconnects for monolithically integrated stretchable circuits. ACS Appl. Mater. Inter. 8, 15459–15465 (2016).

    Google Scholar 

  132. Mariangela, M., Cacucciolo, V. & Cianchetti, M. Stiffening in soft robotics: A review of the state of the art. IEEE Robot. Autom. Mag. 23, 93–106 (2016).

    Google Scholar 

  133. Yang, W. et al. On the tear resistance of skin. Nat. Commun. 6, 6649 (2015).

    Article  Google Scholar 

  134. Terryn, S., Brancart, J., Lefeber, D., Van Assche, G. & Vanderborght, B. Self-healing soft pneumatic robots. Sci. Robot. 2, eaan4268 (2017).

    Article  Google Scholar 

  135. Walker, S. et al. Using an environmentally benign and degradable elastomer in soft robotics. Int. J. Intell. Robot. Appl. 1, 124–142 (2017).

    Article  Google Scholar 

  136. McEvoy, M. A. & Correll, N. Materials that couple sensing, actuation, computation, and communication. Science 347, 1261689 (2015).

    Article  Google Scholar 

  137. Pfeifer, R. & Gomez, G. Morphological computation — Connecting brain, body, and environment. In Creating Brain-Like Intelligence (eds Sendhoff, B., Körner, E., Sporns, O., Ritter, H. & Doya, K.) 66–83 (Springer, 2009).

  138. Brown, E. et al From the cover: Universal robotic gripper based on the jamming of granular material. Proc. Natl Acad. Sci. USA 107, 8809–18814 (2010).

    Article  Google Scholar 

  139. Rogers, J. A. Wearable electronics: Nanomesh on-skin electronics. Nat. Nanotech. 12, 839–840 (2017).

    Article  Google Scholar 

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S.I.R. compiled the references and wrote the manuscript. C.M. and R.J.W conceived and structured the paper. All authors contributed to editing and reviewing.

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Correspondence to Carmel Majidi.

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Rich, S.I., Wood, R.J. & Majidi, C. Untethered soft robotics. Nat Electron 1, 102–112 (2018). https://doi.org/10.1038/s41928-018-0024-1

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