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A 1.3-micrometre-thick elastic conductor for seamless on-skin and implantable sensors

Abstract

On-skin and implantable electronics require elastic conductors that are only a few micrometres thick and soft enough to form a seamless contact with three-dimensional structures. However, fabricating thin conductors that are mechanically durable and have consistent electrical properties with stretching is challenging. Here we report polydimethylsiloxane (PDMS)–gold conductors that are around 1.3 µm thick and have a controlled morphology of microcracks in the gold film. The microcracks are formed by evaporating a 50-nm-thick gold film onto a 1.2-µm-thick PDMS film that is supported during fabrication by a 100-µm-thick PDMS film on glass; thermal expansion of the thick PDMS film causes the evaporated gold to form a microcracked structure on the thin PDMS. The resulting conductors can be stretched by up to 300% and remain highly conductive after strain release. We use them to create on-skin electrodes that are breathable and water resistant, and can continuously record electrocardiogram signals. We also use the conductors to create on-skin sensors with less than 3 µm thickness that can detect small mechanical forces and create implantable nerve electrodes that can provide signal recording and stimulation.

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Fig. 1: Design of stretchable ultrathin conductors.
Fig. 2: Mechanism of microcracked morphology formation and mechanical/electrical characterization.
Fig. 3: On-skin sensors based on ultrathin conductors.
Fig. 4: Implantable neural interfaces based on ultrathin conductors.

Data availability

The data that support the findings of this study are available from the corresponding authors on reasonable request.

Code availability

The codes used for analysing the neural signals are available from the corresponding authors upon reasonable request.

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Acknowledgements

Parts of this work were conducted in RIKEN, Japan, supported by JSPS KAKENHI under grant nos. JP18H05469 and 17H06149. Parts of this work were conducted in Nanyang Technological University, Singapore, supported by the National Research Foundation Singapore (NRF) under NRF’s Medium Sized Centre: Singapore Hybrid-Integrated Next-Generation μ-Electronics (SHINE) Centre funding programme and the Agency for Science, Technology and Research (A*STAR) under its AME Programmatic Funding Scheme (Project #A18A1b0045; X.C.). Parts of this work were conducted in the University of Macau, China, supported by the Science and Technology Development Fund, Macau SAR (FDCT) (file nos. 0059/2021/AFJ and 0040/2021/A1). The implantable experiments were conducted in the National University of Singapore and they were supported by the National Research Foundation, Prime Minister’s Office, Singapore, under the NRF Investigatorship Programme (award no. NRF-NRFI05-2019-0003) and NUS NANONASH Programme (NUHSRO/2020/002/NanoNash/LOA; R143000B43114).

Author information

Authors and Affiliations

Authors

Contributions

Z.J., K.F., X.C. and T.S. conceived and designed the research. Z.J. designed the the ultrathin PDMS–Au and performed the characterization of the mechanical, electrical and morphological properties. Z.J., S.J. and F.Z. designed the on-skin ECG sensor and performed the related characterizations. Z.J. and J.Z. designed the ultrathin sensor and performed the related characterizations. Z.J. and N.C. designed and fabricated the neural electrodes, and N.C. and Z.Y. performed the implantable experiments. R.L. and Yang Wang performed the COMSOL simulations. Yan Wang, H.L., Z.L., T.Y. and K.F. assisted in the experiment or analysed the data. All the authors discussed the results and commented on the manuscript. Z.J., K.F., X.L., X.C. and T.S. wrote the manuscript. We would like to thank Y. Jiang, J. Yi, W. Li and C. Cao from Nanyang Technological University and G. Gammad from National University of Singapore for their technical support and discussion.

Corresponding authors

Correspondence to Kenjiro Fukuda, Xiaodong Chen or Takao Someya.

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The authors declare no competing interests.

Peer review

Peer review information

Nature Electronics thanks Xue Feng, Wei Gao, Massimo Mariello 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. 1–46, Tables 1 and 2 and experimental section.

Reporting Summary

Supplementary Video 1

Laminating the ultrathin PDMS film onto the thick PDMS-coated glass substrate.

Supplementary Video 2

Stretch test of the ultrathin conductor.

Supplementary Video 3

Adhesion test of the ultrathin electrode when the volunteer washed hands.

Supplementary Video 4

Adhesion test of the thick electrode when the volunteer washed hands.

Supplementary Video 5

Resistance measurement on the ultrathin electrode when moving the arm.

Supplementary Video 6

Demonstration of powering a liquid-crystal display using the ultrathin mechanical sensor.

Supplementary Video 7

Selective muscle activation by stimulating the nerve using the ultrathin neural electrodes.

Supplementary Video 8

Selective muscle activation by stimulating the nerve using thick electrodes.

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Jiang, Z., Chen, N., Yi, Z. et al. A 1.3-micrometre-thick elastic conductor for seamless on-skin and implantable sensors. Nat Electron 5, 784–793 (2022). https://doi.org/10.1038/s41928-022-00868-x

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