An autonomously electrically self-healing liquid metal–elastomer composite for robust soft-matter robotics and electronics

Abstract

Large-area stretchable electronics are critical for progress in wearable computing, soft robotics and inflatable structures. Recent efforts have focused on engineering electronics from soft materials—elastomers, polyelectrolyte gels and liquid metal. While these materials enable elastic compliance and deformability, they are vulnerable to tearing, puncture and other mechanical damage modes that cause electrical failure. Here, we introduce a material architecture for soft and highly deformable circuit interconnects that are electromechanically stable under typical loading conditions, while exhibiting uncompromising resilience to mechanical damage. The material is composed of liquid metal droplets suspended in a soft elastomer; when damaged, the droplets rupture to form new connections with neighbours and re-route electrical signals without interruption. Since self-healing occurs spontaneously, these materials do not require manual repair or external heat. We demonstrate this unprecedented electronic robustness in a self-repairing digital counter and self-healing soft robotic quadruped that continue to function after significant damage.

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Fig. 1: Self-healing soft matter composite.
Fig. 2: Electrical and mechanical characterization.
Fig. 3: Autonomous self-healing response (ϕ = 50%).
Fig. 4: Autonomously self-healing soft robot (ϕ = 50%).

References

  1. 1.

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

    Article  Google Scholar 

  2. 2.

    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 

  3. 3.

    Kim, D.-H. et al. Epidermal electronics. Science 333, 838–843 (2011).

    Article  Google Scholar 

  4. 4.

    Someya, T. et al. Conformable, flexible, large-area networks of pressure and thermal sensors with organic transistor active matrixes. Proc. Natl Acad. Sci. USA 102, 12321–12325 (2005).

    Article  Google Scholar 

  5. 5.

    Sun, Y., Choi, W. M., Jiang, H., Huang, Y. Y. & Rogers, J. A. Controlled buckling of semiconductor nanoribbons for stretchable electronics. Nat. Nanotechnol. 1, 201–207 (2006).

    Article  Google Scholar 

  6. 6.

    Keplinger, C. et al. Stretchable, transparent, ionic conductors. Science 341, 984–987 (2013).

    Article  Google Scholar 

  7. 7.

    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 

  8. 8.

    Chossat, J.-B., Park, Y.-L., Wood, R. J. & Duchaine, V. A soft strain sensor based on ionic and metal liquids. IEEE Sens. J. 13, 3405–3414 (2013).

    Article  Google Scholar 

  9. 9.

    Frutiger, A. et al. Capacitive soft strain sensors via multicore–shell fiber printing. Adv. Mater. 27, 2440–2446 (2015).

    Article  Google Scholar 

  10. 10.

    Dickey, M. D. Stretchable and soft electronics using liquid metals. Adv. Mater. 29, 1606425 (2017).

    Article  Google Scholar 

  11. 11.

    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 

  12. 12.

    Amjadi, M., Kyung, K.-U., Park, I. & Sitti, M. Stretchable, skin-mountable, and wearable strain sensors and their potential applications: A review. Adv. Funct. Mater. 26, 1678–1698 (2016).

    Article  Google Scholar 

  13. 13.

    Chortos, A., Liu, J. & Bao, Z. Pursuing prosthetic electronic skin. Nat. Mater. 15, 937–950 (2016).

    Article  Google Scholar 

  14. 14.

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

    Article  Google Scholar 

  15. 15.

    Rich, S., Wood, R. J. & Majidi, C. Untethered soft robotics. Nat. Electron. 1, 102–112 (2018).

  16. 16.

    Oh, J. Y. et al. Intrinsically stretchable and healable semiconducting polymer for organic transistors. Nature 539, 411–415 (2016).

    Article  Google Scholar 

  17. 17.

    Tee, B. C., Wang, C., Allen, R. & Bao, Z. An electrically and mechanically self-healing composite with pressure-and flexion-sensitive properties for electronic skin applications. Nat. Nanotechnol. 7, 825–832 (2012).

    Article  Google Scholar 

  18. 18.

    Williams, K. A., Boydston, A. J. & Bielawski, C. W. Towards electrically conductive, self-healing materials. J. R. Soc. Interface 4, 359–362 (2007).

    Article  Google Scholar 

  19. 19.

    Zhang, S. & Cicoira, F. Water-enabled healing of conducting polymer films. Adv. Mater. 29, 1703098 (2017).

    Article  Google Scholar 

  20. 20.

    Cao, Y. et al. A transparent, self-healing, highly stretchable ionic conductor. Adv. Mater. 29, 1605099 (2017).

    Article  Google Scholar 

  21. 21.

    Blaiszik, B. J. et al. Autonomic restoration of electrical conductivity. Adv. Mater. 24, 398–401 (2012).

    Article  Google Scholar 

  22. 22.

    Palleau, E., Reece, S., Desai, S. C., Smith, M. E. & Dickey, M. D. Self-healing stretchable wires for reconfigurable circuit wiring and 3D microfluidics. Adv. Mater. 25, 1589–1592 (2013).

    Article  Google Scholar 

  23. 23.

    Li, G., Wu, X. & Lee, D.-W. A galinstan-based inkjet printing system for highly stretchable electronics with self-healing capability. Lab Chip 16, 1366–1373 (2016).

    Article  Google Scholar 

  24. 24.

    Boley, J. W., White, E. L. & Kramer, R. K. Mechanically sintered gallium-indium nanoparticles. Adv. Mater. 27, 2355–2360 (2015).

    Article  Google Scholar 

  25. 25.

    Mohammed, M. G. & Kramer, R. All-printed flexible and stretchable electronics. Adv. Mater. 29, 1604965 (2017).

    Article  Google Scholar 

  26. 26.

    Lin, Y. et al. Handwritten, soft circuit boards and antennas using liquid metal nanoparticles. Small 11, 6397–6403 (2015).

    Article  Google Scholar 

  27. 27.

    Fassler, A. & Majidi, C. Liquid-phase metal inclusions for a conductive polymer composite. Adv. Mater. 27, 1928–1932 (2015).

    Article  Google Scholar 

  28. 28.

    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).

  29. 29.

    Park, J. et al. Three-dimensional nanonetworks for giant stretchability in dielectrics and conductors. Nat. Commun. 3, 916 (2012).

    Article  Google Scholar 

  30. 30.

    Van Meerbeek, I. M. et al. Morphing metal and elastomer bicontinuous foams for reversible stiffness, shape memory, and self-healing soft machines. Adv. Mater. 28, 2801–2806 (2016).

    Article  Google Scholar 

  31. 31.

    Bartlett, M. D. et al. Stretchable, high-k dielectric elastomers through liquid-metal inclusions. Adv. Mater. 28, 3726–3731 (2016).

    Article  Google Scholar 

  32. 32.

    Liang, S. et al. Liquid metal sponges for mechanically durable, all-soft, electrical conductors. J. Mater. Chem. C 5, 1586–1590 (2017).

    Article  Google Scholar 

  33. 33.

    Wang, J. et al. Printable superelastic conductors with extreme stretchability and robust cycling endurance enabled by liquid metal particles. Adv. Mater. 30, 1706157 (2018).

    Article  Google Scholar 

  34. 34.

    Jeong, S. H. et al. Mechanically stretchable and electrically insulating thermal elastomer composite by liquid alloy droplet embedment. Sci. Rep. 5, 18257 (2015).

    Article  Google Scholar 

  35. 35.

    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 

  36. 36.

    Chiechi, R. C., Weiss, E. A., Dickey, M. D. & Whitesides, G. M. Eutectic gallium-indium (EGaIn): A moldable liquid metal for electrical characterization of self-assembled monolayers. Angew. Chem. 120, 148–150 (2008).

    Article  Google Scholar 

  37. 37.

    Kim, H.-J., Son, C. & Ziaie, B. A multiaxial stretchable interconnect using liquid-alloy-filled elastomeric microchannels. Appl. Phys. Lett. 92, 011904 (2008).

    Article  Google Scholar 

  38. 38.

    Hessert, M. J. et al. Foot pressure distribution during walking in young and old adults. BMC Geriatr. 5, 8 (2005).

    Article  Google Scholar 

  39. 39.

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

    Google Scholar 

  40. 40.

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

    Article  Google Scholar 

  41. 41.

    Shepherd, R. F., Stokes, A. A., Nunes, R. & Whitesides, G. M. Soft machines that are resistant to puncture and that self seal. Adv. Mater. 25, 6709–6713 (2013).

    Article  Google Scholar 

  42. 42.

    Cademartiri, L. et al. Electrical resistance of AgTS–S(CH2) n 1CH3//Ga2O3/EGaIn tunneling junctions. J. Phys. Chem. C 116, 10848–10860 (2012).

    Article  Google Scholar 

  43. 43.

    Regan, M. et al. X-ray study of the oxidation of liquid-gallium surfaces. Phys. Rev. B 55, 10786 (1997).

    Article  Google Scholar 

  44. 44.

    Pendergraph, S. A., Bartlett, M. D., Carter, K. R. & Crosby, A. J. Opportunities with fabric composites as unique flexible substrates. ACS Appl. Mater. Interfaces 4, 6640–6645 (2012).

    Article  Google Scholar 

Download references

Acknowledgements

The authors acknowledge support from the NASA Early Career Faculty Award (NNX14AO49G; Research Collaborator: B. Bluethmann) and AFOSR Multidisciplinary University Research Initiative (FA9550-18-1-0566; Program Manager: K. Goretta). M.D.B. also acknowledges support from Iowa State University start up funds. Sensor and mechanical characterization was performed on equipment supported through an Office of Naval Research (ONR) Defense University Research Instrumentation Program (DURIP) (N00014140778; Bioinspired Autonomous Systems; Program Manager: T. McKenna).

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Contributions

E.J.M., M.D.B., X.H. and C.M. designed the research; E.J.M., M.D.B. and X.H. performed the research; E.J.M., M.D.B., X.H. and C.M. analysed the data; E.J.M., M.D.B. and C.M. wrote the paper.

Corresponding author

Correspondence to Carmel Majidi.

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Supplementary information

Supplementary Information

1 supplementary note with 1 reference, Supplementary Figures 1–11

Supplementary Movie 1:

Electrical activation of LM composite. The video illustrates the electrical activation of the LM composite using a 2D plotter and the ability to pattern geometrically intricate designs

Supplementary Movie 2:

Elapsed time counter with autonomously self-healing electronics. The video illustrates the ability of the composite to autonomously self-heal under extreme damage without manual intervention, use of external energy sources, or redundant electronics. A complementary illustration is shown with traditional electrical wiring, which immediately fails after damage

Supplementary Movie 3:

Elapsed time counter with selectively patterned autonomously self-healing electronics. The video demonstrates the ability of the composite to be selectively patterned and autonomously self-heal under extreme damage without unintended electrical shorting, without manual intervention, use of external energy sources, or redundant electronics

Supplementary Movie 4:

Electrical stability of the autonomously self-healing electronics under normal walking conditions. The video demonstrates the ability of the composite to undergo normal walking conditions for up to 31 steps with 10 footwear variations

Supplementary Movie 5:

An autonomously self-healing soft robot. The video demonstrates the ability to use the self-healing composite for soft robots that require on-board circuitry that are resistant to damage and can support large bursts of electrical power

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Markvicka, E.J., Bartlett, M.D., Huang, X. et al. An autonomously electrically self-healing liquid metal–elastomer composite for robust soft-matter robotics and electronics. Nature Mater 17, 618–624 (2018). https://doi.org/10.1038/s41563-018-0084-7

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