Sweat-activated biocompatible batteries for epidermal electronic and microfluidic systems

Abstract

Recent advances in materials, mechanics and design have led to the development of ultrathin, lightweight electronic devices that can conformally interface with human skin. With few exceptions, these devices rely on electrical power to support sensing, wireless communication and signal conditioning. Unfortunately, most sources of such power consist of batteries constructed using hazardous materials, often with form factors that frustrate incorporation into skin-like, or epidermal, electronic devices. Here we report a biocompatible, sweat-activated battery technology that can be embedded within a soft, microfluidic platform. The battery can be used in a detachable electronic module that contains wireless communication and power management systems, and is capable of continuous on-skin recording of physiological signals. To illustrate the practical utility of our approach, we show using human trials that the sweat-activated batteries can operate hybrid microfluidic/microelectronic systems that simultaneously monitor heart rate, sweat chloride and sweat pH.

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Fig. 1: Working principles and characteristics of an SAC.
Fig. 2: Discharge properties and EIS studies of SAC.
Fig. 3: Power management circuit and its characteristics.
Fig. 4: SAC-powered, skin-interfaced hybrid microfluidic–microelectronic system.

Data availability

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

Code availability

Custom-developed firmware for the electronic module and LabView data acquisition software for hardware characterization are available from the corresponding authors upon reasonable request.

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Acknowledgements

This research was funded by the Air Force Research Laboratory (AFRL) Human Signatures Branch through Core funds provided to Northwestern University under contract FA8650-14-D-6516. S.W., T.H. and S.M. acknowledge support from the ‘Top Open’ programme (Tsinghua University, P. R. China), the visiting scholar programme (grant no. 201706235005, China Scholarship Council) and the Indo-US Science and Technology Forum (grant no. SERB-IUSSTF-2017/192) respectively. This work utilized the Northwestern University Micro/Nano Fabrication Facility (NUFAB), which is partially supported by the Soft and Hybrid Nanotechnology Experimental (SHyNE) resource (NSF ECCS-1542205), the Materials Research Science and Engineering Center (DMR-1720139), the State of Illinois and Northwestern University.

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Contributions

J.A.R., A.J.B., R.G. and S.P.L. conceived the project, designed the studies and analysed and interpreted the data. A.J.B. designed and developed the batteries, microfluidics, pH sensor and chloride sensor. S.P.L. designed and developed the electronics. W.L. developed the firmware. A.J.B., I.H., S.W., T.H., S.M. and N.N. worked on testing and optimizing the batteries. S.P.L., C.-J.S. and P.G. worked on fabricating and testing of the electronics. A.J.B. and J.C. worked on fabricating the microfluidics. J.K. assisted in optical studies. W.J.J., J.T.R. and R.T. assisted in testing the devices. A.J.B., S.P.L., W.J.J., I.H., R.G. and J.A.R. composed the manuscript.

Corresponding authors

Correspondence to R. Ghaffari or J. A. Rogers.

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Competing interests

J.A.R., S.P.L., W.L. and R.G. are cofounders and/or employees of Epicore Biosystems, Inc., a company that pursues commercialization of microfluidic devices for wearable applications.

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Supplementary Figs. 1–9, discussion, equations and Table 1.

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Bandodkar, A.J., Lee, S.P., Huang, I. et al. Sweat-activated biocompatible batteries for epidermal electronic and microfluidic systems. Nat Electron (2020). https://doi.org/10.1038/s41928-020-0443-7

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