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A Flexible, Robust and Gel-Free Electroencephalogram Electrode for Noninvasive Brain-Computer Interfaces Sen Lin, Junchen Liu, Wenzheng Li, Dong Wang, Ya Huang, Chao Jia, Ziwei Li, Muhammad Murtaza, Haiyang Wang, Jianan Song, Zhenglian Liu, Kai Huang, Di Zu, Ming Lei, Bo Hong, and Hui Wu Nano Lett., Just Accepted Manuscript • DOI: 10.1021/acs.nanolett.9b02019 • Publication Date (Web): 27 Aug 2019 Downloaded from pubs.acs.org on August 28, 2019
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A Flexible, Robust and Gel-Free Electroencephalogram Electrode for Noninvasive Brain-Computer Interfaces Sen Lin1,2†, Junchen Liu2,1†, Wenzheng Li3, Dong Wang1, Ya Huang1, Chao Jia1, Ziwei Li1, Muhammad Murtaza1, Haiyang Wang1, Jianan Song1, Zhenglian Liu1, Kai Huang2, Di Zu1, Ming Lei2,*, Bo Hong3,* and Hui Wu1,* 1
State Key Laboratory of New Ceramics and Fine Processing, School of Materials Science and
Engineering, Tsinghua University, Beijing 100084, China. 2
State Key Laboratory of Information Photonics and Optical Communications and School of
Science, Beijing University of Posts and Telecommunications, Beijing 100876, China. 3
Department of Biomedical Engineering, School of Medicine, Tsinghua University, Beijing
100084, China. *Correspondence to:
[email protected] (Hui Wu),
[email protected] (Bo Hong),
[email protected] (Ming Lei). †These authors contributed equally to this work.
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Abstract: Brain-computer interfaces (BCIs) enable direct and near-instant communication between the brain and electronic devices. One of the biggest remaining challenges is to develop an effective noninvasive BCI that allows the recording electrodes to avoid hair on human skin without the inconveniences and complications of using a conductive gel. In this study, we developed a cost-effective, easily manufacturable, flexible, robust and gel-free silver nanowire/polyvinyl butyral (PVB)/melamine sponge (AgPMS) electroencephalogram (EEG) electrode that circumvents problems with hair. Because of surface metallization by the silver nanowires (AgNWs), the sponge has a high conductivity of 917 S/m while its weight remains the same. The flexible sponge framework and self-locking AgNWs combine to give the new electrode remarkable mechanical stability (the conductivity remains unchanged after 10,000 cycles at 10% compression) and the ability to bypass hair. A BCI application based on steady-state visual evoked potential (SSVEP) measurements on hairless skin shows that the BCI accuracy of the new electrode (86%) is approximately the same as that of conventional electrodes supported by a conductive gel (88%). Most importantly, the performance of the AgPMS on hairy skin is not significantly reduced, which indicates that the new electrode can replace conventional electrodes for both hairless and hairy skin BCIs and other EEG applications. Keywords: brain-computer interfaces, flexible electronics, silver nanowire, gel-free electrode
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Introduction Science and technology that enable direct communication between the brain and a computer is changing the way we interact with the world. Since the 1980s, brain-computer interface (BCI) technology has been improving to acquire brain signals, analyze them, and translate them into commands that are relayed to output devices that carry out desired actions 1. By collecting and analyzing electroencephalogram (EEG) signals, the BCIs provide access to a wealth of real-time brain information, including mental states. Through instruction mapping, people are now able to communicate with or operate various devices without muscular movement
2-3.
Because of the
benefits from their instantaneous, accurate and movement-independent nature, BCI systems have been intensely studied for multiple purposes (Fig. 1a), including disease diagnosis and treatment 4-6, motion-disabled assistance
7-10,
associative learning
11,
driving alertness
12,
and daily health care
applications 13-14. One of the most challenging problems of BCIs is reducing the contact impedance between the electrodes and human skin15-16. Gel-based rigid silver/silver chloride (Ag/AgCl) electrodes are currently the most popular way to sense EEG signals due to their stable electrode potential, sufficiently low impedance (
