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Permeable, three-dimensional integrated electronic skins with stretchable hybrid liquid metal solders

Nature Electronics volume 7, pages 598–609 (2024)Cite this article

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Abstract

The development of wearable and on-skin electronics requires high-density stretchable electronic systems that can conform to soft tissue, operate continuously and provide long-term biocompatibility. Most stretchable electronic systems have low-density integration and are wired with external printed circuit boards, which limits functionality, deteriorates user experience and impedes long-term usability. Here we report an intrinsically permeable, three-dimensional integrated electronic skin. The system combines high-density inorganic electronic components with organic stretchable fibrous substrates using three-dimensional patterned, multilayered liquid metal circuits and stretchable hybrid liquid metal solder. The electronic skin exhibits high softness, durability, fabric-like permeability to air and moisture and sufficient biocompatibility for on-skin attachment for a week. We use the platform to create wireless, battery-powered and battery-free skin-attached bioelectronic systems that offer complex system-level functions, including the stable sensing of biosignals, signal processing and analysis, electrostimulation and wireless communication.

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Fig. 1: P3D-eskins.
Fig. 2: Reliable 3D hybrid interfaces using ultrastretchable hLM solder.
Fig. 3: Wireless transcutaneous electrostimulation and electrophysiological sensing using P3D-eskin.
Fig. 4: Battery-free stretchable NFC system based on the P3D-eskin platform.

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Data availability

Source data are provided with this paper. Other data that support the findings of this study are available from the corresponding authors upon request.

Code availability

The code supporting the findings of this study is available from the corresponding authors upon request.

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Acknowledgements

We acknowledge financial support from the RGC Senior Research Fellow Scheme (SRFS2122-5S04), The Hong Kong Polytechnic University (1-ZVQM, 1-BBXR and 1-CD44), Research Grants Council of the Hong Kong Special Administrative Region (grant nos. RFS2324-1S03, 15304823, 11213721, 11215722, 11211523), City University of Hong Kong (grant nos. 9667221 and 9678274) and National Natural Science Foundation of China (NSFC) (grant nos. 61421002 and 62122002), as well as in part by InnoHK Project on Project 2.2—AI-based 3D ultrasound imaging algorithm at the Hong Kong Centre for Cerebro-Cardiovascular Health Engineering (COCHE).

Author information

Author notes

  1. These authors contributed equally: Qiuna Zhuang, Kuanming Yao.

Authors and Affiliations

  1. Laboratory for Advanced Interfacial Materials and Devices, School of Fashion and Textiles, The Hong Kong Polytechnic University, Hong Kong SAR, China

    Qiuna Zhuang, Xian Song, Yufei Zhang, Qiyao Huang & Zijian Zheng

  2. Department of Biomedical Engineering, City University of Hong Kong, Hong Kong SAR, China

    Kuanming Yao, Jingkun Zhou & Xinge Yu

  3. Department of Applied Biology and Chemical Technology, The Hong Kong Polytechnic University, Hong Kong SAR, China

    Chi Zhang & Zijian Zheng

  4. Research Institute for Intelligent Wearable Systems (RI-IWEAR), The Hong Kong Polytechnic University, Hong Kong SAR, China

    Qiyao Huang & Zijian Zheng

  5. College of Information Science and Electronics Engineering, Zhejiang University, Hangzhou, China

    Yizhao Zhou

  6. Hong Kong Centre for Cerebro-Cardiovascular Health Engineering (COCHE), Hong Kong Science Park, Hong Kong SAR, China

    Xinge Yu

  7. Hong Kong Institute for Clean Energy, City University of Hong Kong, Hong Kong SAR, China

    Xinge Yu

  8. Research Institute for Smart Energy (RISE), The Hong Kong Polytechnic University, Hong Kong SAR, China

    Zijian Zheng

  9. State Key Laboratory of Ultra-precision Machining Technology, The Hong Kong Polytechnic University, Hong Kong SAR, China

    Zijian Zheng

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  1. Qiuna Zhuang
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Contributions

Q.Z. and Z.Z. initiated the idea and proposed the project. K.Y. designed the circuits of the electronic systems. Q.Z. and K.Y. characterized the overall systems. Z.Z., X.Y., Q.Z. and K.Y. wrote the paper. C.Z. conducted the FEA. X.S. and Y. Zhou facilitated the design of logic circuits. J.Z. facilitated the debugging process. Y. Zhang and Q.H. gave comments on the organization of figures.

Corresponding authors

Correspondence to Xinge Yu or Zijian Zheng.

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The authors declare no competing interests.

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Nature Electronics thanks John Ho, Yanchao Mao and the other, anonymous, reviewer(s) for their contribution to the peer review of this work.

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Extended data

Extended Data Fig. 1 Layer-by-layer fabrication of wireless P3D-eskins.

a, Schematic illustration showing the detailed processing flow of layer-by-layer fabrication of P3D-eskins. b, Digital images showing the structure and functions of each layer in P3D-eskins.

Extended Data Fig. 2 Characterizations of the oLM on the SBS fibre mats (oLM/SBS) at different oxidation conditions.

a, SEM images of LM/SBS with various heating durations before and after stretch. The oLM was prepared by oxidizing LM in the air. After heating LM with increasing duration ranging from 0 to 24 h, the size of the gallium (Ga) oxide enhanced from several μm to several hundred μm. After being pre-stretched under 1500% strain for 12 cycles, the continuous thin film (heating duration less than 16 h) can self-organize into a laterally mesh-like and vertically buckled structure, with the formation of nodes from the strong oxide layer. b, XPS results of oLM after various heating durations. Ga 2p (3/2) spectrum shows a predominant peak with a binding energy of 1118.8 eV from Ga2O3, with the presence of Ga metal (1116.5 eV) and Ga2O (1118.2 eV). c, Schematic illustration of the formation of the gallium oxides (Ga2O3, and Ga2O) during the heating of LM. With increasing heating duration, the signals of Ga2O3 and Ga2O became stronger. d and e, Young’s modulus and electrical conductivity of oLM/SBS after various heating durations. Data are presented as (dots) mean values with (error bars) SD; n = 6 independent tests. Due to the strong oxidation of LM, the average modulus of oLM/SBS enhanced from ~0.1 MPa (0.09841 MPa) with the heating duration of 0 h (that is, LM/SBS) to ~0.31314 MPa with the heating duration of 24 h. Accordingly, the stiffness was also enhanced by around 2 folds when the thickness was unchanged. The oLM/SBS with a heating duration of 16 h maintained a high electrical conductivity of over 28,300 S/cm. The error bar in the figure stands for SD, and the scatter value represents mean value. f, Resistance changes of hybrid LMs (weight ratio of oLM and LM and = 1: 2, oLM with various heating durations) on the SBS fibre mats as the function of tensile strain.

Source data

Extended Data Fig. 3 Characterizations of the electrical stability of 3D integrated interfaces of various stretchable logic circuits.

a, Design of the permeable stretchable logic circuits including inverse gate, NOR gate, and clock-controlled switch. b, Outputs of the logics validated with the rigid printed circuit boards. c and d, Digital images of the inverse gate and NOR gate, respectively. e and f, Logic outputs of the inverse gate, and NOR gate respectively. g, Schematic illustration of the permeable 3D integrated stretchable switch array. h, Threshold driving voltage of the switch array at a strain of 100%. i, Statistic analysis of the transconductance of the 64-channel switch array. j, Digital images of the permeable 3D integrated stretchable switch array at 100% strain. The switches were used for controlling loads and in complementary metal-oxide semiconductor (CMOS) digital circuits as they operated between their cut-off and saturation regions. The multi-channel switch array showed a uniform threshold driving voltage (Vg) of ~1.75 V at a strain of 50%, and an average transconductance of ~100 mS.

Source data

Supplementary information

Supplementary Information

Supplementary Notes 1 and 2, Figs. 1–27, Tables 1–4, captions for Videos 1–7 and references.

Reporting Summary

Supplementary Video 1

Demonstration of the wireless communication of P3D-eskins with a mobile device functioning with wireless transcutaneous electrostimulations and electrophysiological sensing.

Supplementary Video 2

Rain test of P3D-eskin system showing its waterproofness.

Supplementary Video 3

Electrical stability test of P3D-eskin system in water and artificial sweat (pH, 4.7 ± 0.1).

Supplementary Video 4

Stretchable and stable electrical interfaces of microresistor (0603) and MOSFET (BSS84) using ultrastretchable hLM solder during the stretch–release process.

Supplementary Video 5

On-skin pressing test of LM 3D circuit without the leakage of LM.

Supplementary Video 6

Stable operation of steamed P3D-eskin on top of boiling water.

Supplementary Video 7

Stretching test of a ten-layered ‘ELECTRONIC’ circuit with nine-layered stretchable VIAs visualized by the backlight of a panel.

Source data

Source Data Fig. 2

Statistical source data.

Source Data Fig. 3

Statistical source data.

Source Data Fig. 4

Statistical source data.

Source Data Extended Data Fig. 2

Statistical source data.

Source Data Extended Data Fig. 3

Statistical source data.

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Zhuang, Q., Yao, K., Zhang, C. et al. Permeable, three-dimensional integrated electronic skins with stretchable hybrid liquid metal solders. Nat Electron 7, 598–609 (2024). https://doi.org/10.1038/s41928-024-01189-x

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