Article | Published:

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

Nature Materialsvolume 17pages618624 (2018) | Download Citation

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.

Access optionsAccess options

Rent or Buy article

Get time limited or full article access on ReadCube.

from $8.99

All prices are NET prices.

Additional information

Publisher’s note: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

References

  1. 1.

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

  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).

  3. 3.

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

  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).

  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).

  6. 6.

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

  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).

  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).

  9. 9.

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

  10. 10.

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

  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).

  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).

  13. 13.

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

  14. 14.

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

  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).

  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).

  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).

  19. 19.

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

  20. 20.

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

  21. 21.

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

  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).

  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).

  24. 24.

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

  25. 25.

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

  26. 26.

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

  27. 27.

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

  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).

  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).

  31. 31.

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

  32. 32.

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

  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).

  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).

  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).

  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).

  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).

  38. 38.

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

  39. 39.

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

  40. 40.

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

  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).

  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).

  43. 43.

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

  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).

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).

Author information

Author notes

  1. These authors contributed equally: Eric J. Markvicka, Michael D. Bartlett.

Affiliations

  1. Integrated Soft Materials Lab, Carnegie Mellon University, Pittsburgh, PA, USA

    • Eric J. Markvicka
    • , Xiaonan Huang
    •  & Carmel Majidi
  2. Robotics Institute, Carnegie Mellon University, Pittsburgh, PA, USA

    • Eric J. Markvicka
    •  & Carmel Majidi
  3. Material Science & Engineering, Iowa State University, Ames, IA, USA

    • Michael D. Bartlett
  4. Mechanical Engineering, Carnegie Mellon University, Pittsburgh, PA, USA

    • Xiaonan Huang
    •  & Carmel Majidi

Authors

  1. Search for Eric J. Markvicka in:

  2. Search for Michael D. Bartlett in:

  3. Search for Xiaonan Huang in:

  4. Search for Carmel Majidi in:

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.

Competing interests

The authors declare no competing interests.

Corresponding author

Correspondence to Carmel Majidi.

Supplementary information

  1. Supplementary Information

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

  2. 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

  3. 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

  4. 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

  5. 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

  6. 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

About this article

Publication history

Received

Accepted

Published

DOI

https://doi.org/10.1038/s41563-018-0084-7