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An electrically conductive silver–polyacrylamide–alginate hydrogel composite for soft electronics

Nature Electronics volume 4, pages 185–192 (2021)Cite this article

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A Publisher Correction to this article was published on 31 March 2021

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Abstract

Hydrogels offer tissue-like compliance, stretchability, fracture toughness, ionic conductivity and compatibility with biological tissues. However, their electrical conductivity (<100 S cm−1) is inadequate for digital circuits and applications in bioelectronics. Furthermore, efforts to increase conductivity by using hydrogel composites with conductive fillers have led to compromises in compliance and deformability. Here, we report a hydrogel composite that has a high electrical conductivity (>350 S cm−1) and is capable of delivering direct current while maintaining soft compliance (Young’s modulus < 10 kPa) and deformability. Micrometre-sized silver flakes are suspended in a polyacrylamide–alginate hydrogel matrix and, after going through a partial dehydration process, the flakes form percolating networks that are electrically conductive and robust to mechanical deformations. To illustrate the capabilities of our silver–hydrogel composite, we use the material in a stingray-inspired swimmer and a neuromuscular electrical stimulation electrode.

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Fig. 1: Soft, stretchable and electrically conductive hydrogel composite.
Fig. 2: Material characterization.
Fig. 3: Stingray-inspired soft swimmer.
Fig. 4: Neuromuscular electrical stimulation electrode.

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Data availability

The data that support the plots within this paper and the other findings of this study are available from the corresponding author upon reasonable request.

Code availability

The customized tracking algorithm used in this work is available at https://doi.org/10.1184/R1/14039801.

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References

  1. Lin, S. et al. Stretchable hydrogel electronics and devices. Adv. Mater. 28, 4497–4505 (2015).

    Article  Google Scholar 

  2. Schiavone, G. et al. Soft, implantable bioelectronic interfaces for translational research. Adv. Mater. 32, 1906512 (2020).

    Article  Google Scholar 

  3. Pan, L. et al. Hierarchical nanostructured conducting polymer hydrogel with high electrochemical activity. Proc. Natl Acad. Sci. USA 109, 9287–9292 (2012).

    Article  Google Scholar 

  4. Dejace, L., Laubeuf, N., Furfaro, I. & Lacour, S. P. Gallium‐based thin films for wearable human motion sensors. Adv. Intell. Syst. 1, 1900079 (2019).

    Article  Google Scholar 

  5. Qiu, T., Palagi, S., Sachs, J. & Fischer, P. Soft miniaturized linear actuators wirelessly powered by rotating permanent magnets. In Proc. IEEE International Conference on Robotics and Automation 3595–3600 (IEEE, 2018).

  6. Zhang, W., Feng, P., Chen, J., Sun, Z. & Zhao, B. Electrically conductive hydrogels for flexible energy storage systems. Prog. Polym. Sci. 88, 220–240 (2019).

    Article  Google Scholar 

  7. Shi, Y. & Yu, G. Designing hierarchically nanostructured conductive polymer gels for electrochemical energy storage and conversion. Chem. Mater. 28, 2466–2477 (2016).

    Article  Google Scholar 

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

    Article  Google Scholar 

  9. 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 

  10. Kim, J. et al. Battery-free, stretchable optoelectronic systems for wireless optical characterization of the skin. Sci. Adv. 2, e1600418 (2016).

    Article  Google Scholar 

  11. 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 

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

    Article  Google Scholar 

  13. Koh, A. et al. A soft, wearable microfluidic device for the capture, storage, and colorimetric sensing of sweat. Sci. Transl. Med. 8, 366ra165 (2016).

    Article  Google Scholar 

  14. Pan, C. et al. Silver-coated poly(dimethylsiloxane) beads for soft, stretchable, and thermally stable conductive elastomer composites. ACS Appl. Mater. Interfaces 11, 42561–42570 (2019).

    Article  Google Scholar 

  15. Tavakoli, M. et al. EGaIn-assisted room-temperature sintering of silver nanoparticles for stretchable, inkjet-printed, thin-film electronics. Adv. Mater. 30, 1801852 (2018).

    Article  Google Scholar 

  16. 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 

  17. Markvicka, E. J., Barlett, M. D., Huang, X. & Majidi, C. An autonomously electrically self-healing liquid metal–elastomer composite for robust soft-matter robotics and electronics. Nat. Mater. 17, 618–624 (2018).

    Article  Google Scholar 

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

    Article  Google Scholar 

  19. Comley, K. & Fleck, N. A. A micromechanical model for the Young’s modulus of adipose tissue. Int. J. Solids Struct. 47, 2982–2990 (2010).

    Article  MATH  Google Scholar 

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

    Article  Google Scholar 

  21. Yuk, H., Lu, B. & Zhao, X. Hydrogel bioelectronics. Chem. Soc. Rev. 48, 1642–1667 (2019).

    Article  Google Scholar 

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

    Article  Google Scholar 

  23. Kim, D.-H. et al. Dissolvable films of silk fibroin for ultrathin conformal bio-integrated electronics. Nat. Mater. 9, 511–517 (2010).

    Article  Google Scholar 

  24. Minev, I. R. et al. Electronic dura mater for long-term multimodal neural interfaces. Science 347, 159–163 (2015).

    Article  Google Scholar 

  25. Xu, L. et al. 3D multifunctional integumentary membranes for spatiotemporal cardiac measurements and stimulation across the entire epicardium. Nat. Commun. 5, 3329 (2014).

    Article  Google Scholar 

  26. Erol, O., Pantula, A., Liu, W. & Gracias, D. H. Transformer hydrogels: a review. Adv. Mater. Technol. 4, 1900043 (2019).

    Article  Google Scholar 

  27. Han, L. et al. A mussel-inspired conductive, self-adhesive, and self-healable tough hydrogel as cell stimulators and implantable bioelectronics. Small 13, 1601916 (2016).

    Article  Google Scholar 

  28. 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 

  29. Lopes, P. A. et al. Soft bioelectronic stickers: selection and evaluation of skin‐interfacing electrodes. Adv. Healthc. Mater. 8, 1900234 (2019).

    Article  Google Scholar 

  30. Yuk, H. et al. Hydraulic hydrogel actuators and robots optically and sonically camouflaged in water. Nat. Commun. 8, 14230 (2017).

    Article  Google Scholar 

  31. Yang, C. & Suo, Z. Hydrogel ionotronics. Nat. Rev. Mater. 3, 125–142 (2018).

    Article  Google Scholar 

  32. Lee, H.-R., Kim, C.-C. & Sun, J.-Y. Stretchable ionics—a promising candidate for upcoming wearable devices. Adv. Mater. 30, 1704403 (2018).

    Article  Google Scholar 

  33. Rivnay, J., Wang, H., Fenno, L., Deisseroth, K. & Malliaras, G. G. Next-generation probes, particles, and proteins for neural interfacing. Sci. Adv. 3, e1601649 (2017).

    Article  Google Scholar 

  34. Lu, B. et al. Pure PEDOT:PSS hydrogels. Nat. Commun. 10, 1043 (2019).

    Article  Google Scholar 

  35. Dvir, T. et al. Nanowired three-dimensional cardiac patches. Nat. Nanotechnol. 6, 720–725 (2011).

    Article  Google Scholar 

  36. Ahn, Y., Lee, H., Lee, D. & Lee, Y. Highly conductive and flexible silver nanowire-based microelectrodes on biocompatible hydrogel. ACS Appl. Mater. Interfaces 6, 18401–18407 (2014).

    Article  Google Scholar 

  37. Lim, C. et al. Stretchable conductive nanocomposite based on alginate hydrogel and silver nanowires for wearable electronics. APL Mater. 7, 031502 (2019).

    Article  Google Scholar 

  38. Jing, X. et al. Stretchable gelatin/silver nanowires composite hydrogels for detecting human motion. Mater. Lett. 237, 53–56 (2019).

    Article  Google Scholar 

  39. Shin, S. R. et al. Carbon-nanotube-embedded hydrogel sheets for engineering cardiac constructs and bioactuators. ACS Nano 7, 2369–2380 (2013).

    Article  Google Scholar 

  40. Jo, H. et al. Electrically conductive graphene/polyacrylamide hydrogels produced by mild chemical reduction for enhanced myoblast growth and differentiation. Acta Biomater. 48, 100–109 (2017).

    Article  Google Scholar 

  41. Zhao, W., Han, Z., Ma, L., Sun, S. & Zhao, C. Highly hemo-compatible, mechanically strong, and conductive dual cross-linked polymer hydrogels. J. Mater. Chem. B 4, 8016–8024 (2016).

    Article  Google Scholar 

  42. Feig, V. R. et al. Mechanically tunable conductive interpenetrating network hydrogels that mimic the elastic moduli of biological tissue. Nat. Commun. 9, 2740 (2018).

    Article  Google Scholar 

  43. Sun, J.-Y. et al. Highly stretchable and tough hydrogels. Nature 489, 133–136 (2012).

    Article  Google Scholar 

  44. Yang, C. H. et al. Strengthening alginate/polyacrylamide hydrogels using various multivalent cations. ACS Appl. Mater. Interfaces 5, 10418–10422 (2013).

    Article  Google Scholar 

  45. Mondal, S., Das, S. & Nandi, A. K. A review on recent advances in polymer and peptide hydrogels. Soft Matter 16, 1404–1454 (2020).

    Article  Google Scholar 

  46. Ogden, R. W. Large deformation isotropic elasticity—on the correlation of theory and experiment for incompressible rubberlike solids. Rubber Chem. Technol. 46, 398–416 (1973).

    Article  Google Scholar 

  47. 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 

  48. Huang, X., Kumar, K., Jawed, M. K., Ye, Z. & Majidi, C. Soft electrically actuated quadruped (SEAQ)—integrating a flex circuit board and elastomeric limbs for versatile mobility. IEEE Robot. Autom. Lett. 4, 2415–2422 (2019).

    Article  Google Scholar 

  49. Li, H., Erbaş, A., Zwanikken, J. & Cruz, M. O. D. L. Ionic conductivity in polyelectrolyte hydrogels. Macromolecules 49, 9239–9246 (2016).

    Article  Google Scholar 

  50. Lake, D. A. Neuromuscular electrical stimulation. Sports Med. 13, 320–336 (1992).

    Article  Google Scholar 

  51. Yuk, H., Zhang, T., Lin, S., Parada, G. A. & Zhao, X. Tough bonding of hydrogels to diverse non-porous surfaces. Nat. Mater. 15, 190–196 (2016).

    Article  Google Scholar 

  52. Xu, S., Cai, S. & Liu, Z. Thermal conductivity of polyacrylamide hydrogels at the nanoscale. ACS Appl. Mater. Interfaces 10, 36352–36360 (2018).

    Article  Google Scholar 

  53. Hugh, D. Y. & Freedman, R. A. University Physics (Addison-Wesley, 1992).

  54. Thibodeau, J. & Ignaszak, A. Flexible electrode based on MWCNT embedded in a cross-linked acrylamide/alginate blend: conductivity vs. stretching. Polymers 12, 181 (2020).

    Article  Google Scholar 

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Acknowledgements

We acknowledge support from the NOPP Award (N000141812843; Research Collaborator R. Beach). We thank S. Kim for help with the FEA simulation of Joule heating using ANSYS software.

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Author notes

  1. These authors contributed equally: Yunsik Ohm, Chengfeng Pan.

Authors and Affiliations

  1. Soft Machines Lab, Carnegie Mellon University, Pittsburgh, PA, USA

    Yunsik Ohm, Chengfeng Pan, Michael J. Ford, Xiaonan Huang, Jiahe Liao & Carmel Majidi

  2. Mechanical Engineering, Carnegie Mellon University, Pittsburgh, PA, USA

    Yunsik Ohm, Chengfeng Pan, Michael J. Ford, Xiaonan Huang & Carmel Majidi

  3. Robotics Institute, Carnegie Mellon University, Pittsburgh, PA, USA

    Jiahe Liao & Carmel Majidi

  4. Materials Science & Engineering, Carnegie Mellon University, Pittsburgh, PA, USA

    Carmel Majidi

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  1. Yunsik Ohm
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Contributions

Y.O., C.P., M.J.F., X.H., J.L. and C.M. designed the research; Y.O. and C.P. fabricated the materials; Y.O., C.P. and M.J.F. performed the experiments; Y.O., C.P., M.J.F., J.L. and C.M. analysed the data; Y.O., C.P. and X.H. produced the demonstration of the soft stingray-inspired swimmer; Y.O., C.P. and J.L. demonstrated the neuromuscular electrical stimulation electrodes; Y.O., C.P., M.J.F., X.H., J.L. and C.M. wrote the manuscript. Y.O., C.P., M.J.F. and C.M. revised the manuscript.

Corresponding author

Correspondence to Carmel Majidi.

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The authors declare no competing interests.

Additional information

Peer review information Nature Electronics thanks Guo Zhan Lum, Shaoting Lin and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Supplementary information

Supplementary Information

Supplementary Figs. 1–20, Discussions 1 and 2, and Table 1.

Reporting Summary

Supplementary Video 1

LED circuitry.

Supplementary Video 2

Stingray-inspired soft swimmer.

Supplementary Video 3

Neuromuscular electrical stimulation electrode on the tibialis anterior muscle of the leg.

Supplementary Video 4

Neuromuscular electrical stimulation electrode on the posterior muscle of the arm.

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Ohm, Y., Pan, C., Ford, M.J. et al. An electrically conductive silver–polyacrylamide–alginate hydrogel composite for soft electronics. Nat Electron 4, 185–192 (2021). https://doi.org/10.1038/s41928-021-00545-5

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