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Soft and elastic hydrogel-based microelectronics for localized low-voltage neuromodulation

Abstract

Narrowing the mechanical mismatch between tissue and implantable microelectronics is essential for reducing immune responses and for accommodating body movement. However, the design of implantable soft electronics (on the order of 10 kPa in modulus) remains a challenge because of the limited availability of suitable electronic materials. Here, we report electrically conductive hydrogel-based elastic microelectronics with Young’s modulus values in the kilopascal range. The system consists of a highly conductive soft hydrogel as a conductor and an elastic fluorinated photoresist as the passivation insulation layer. Owing to the high volumetric capacitance and the passivation layer of the hydrogel, electrode arrays of the thin-film hydrogel ‘elastronics’, 20 μm in feature size, show a significantly reduced interfacial impedance with tissue, a current-injection density that is ~30 times higher than that of platinum electrodes, and stable electrical performance under strain. We demonstrate the use of the soft elastronic arrays for localized low-voltage electrical stimulation of the sciatic nerve in live mice.

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Fig. 1: An ECH and stretchable encapsulation material with tissue-level Young’s modulus.
Fig. 2: Lithographically patterned hydrogel elastronics.
Fig. 3: Aqueous stability and biocompatibility.
Fig. 4: MECHs display high current density and low impedance.
Fig. 5: Low-voltage in vivo neural stimulation.

Data availability

The authors declare that all data supporting the findings of this study are available within the paper and its Supplementary Information.

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Acknowledgements

This work was partly supported by a Bio-X Interdisciplinary Initiatives Seed Grant and by BOE Technology Group Co., Ltd. Part of this work was performed at the Stanford Nano Shared Facilities (SNSF), supported by the National Science Foundation under award ECCS-1542152. Y.L. is supported by a National Science Scholarship (A*STAR, Singapore). H.W. is supported by a NIH NRSA F32 postdoctoral fellowship. A.M.F. thanks the Natural Sciences and Engineering Research Council (NSERC) of Canada for a postdoctoral fellowship. X.W. is supported by a Life Science Research Foundation fellowship and the Gordon and Betty Moore Foundation. We thank X. Liu, Y. Li and K. Zhang from the BOE Technology Group Co., LTD for discussions, A. Tom for assistance with some experiments, and Daikin Co. and Solvay for supplying PFPE-diols.

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Authors

Contributions

Y.L., J.L. and Z.B. designed the project and experiments. Y.L. synthesized the MECH. J.L. and T.L. synthesized the elastic fluorinated photoresist. Y.L. and J.L. fabricated the devices. Y.L., J.L., S.C. and Y.K. performed material and device characterization. Y.L., J.L. and A.M.F. prepared the schematics for elastronics and carried out device photography. Y.L., J.L., X.W. and H.W. performed immunofluorescence staining and data analyses. S.N. and Y.L. carried out the simulation of electrochemical impedance. Y.L. and J.L. carried out periphery nerve stimulation experiments on mice and analysed the data. Y.L., J.L., J.B.-H.T. and Z.B. wrote the manuscript. All authors reviewed and commented on the manuscript.

Corresponding author

Correspondence to Zhenan Bao.

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Stanford University has filed patent applications related to this technology. The patent application number is PCT/US2018/057855.

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Supplementary information

Supplementary Information

Supplementary figures and video captions

Reporting Summary

Supplementary Video 1

Anisotropic swelling of the MECH material

Supplementary Video 2

Electrical stimulation with the MECH electrode on the mouse sciatic nerve elicits toe movement

Supplementary Video 3

Comparison of electrical-stimulation efficiency of the MECH electrode and of a platinum electrode with the same electrode area on the mouse sciatic nerve

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Liu, Y., Liu, J., Chen, S. et al. Soft and elastic hydrogel-based microelectronics for localized low-voltage neuromodulation. Nat Biomed Eng 3, 58–68 (2019). https://doi.org/10.1038/s41551-018-0335-6

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