Conductive polymer combined silk fiber bundle for bioelectrical signal recording.

Shingo Tsukada,Keiichi Torimitsu,Hiroshi Nakashima,Alexander G Obukhov

doi:10.1371/journal.pone.0033689

Shingo Tsukada, Keiichi Torimitsu + Show 2 more

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https://doi.org/10.1371/journal.pone.0033689

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Journal: PloS one	Publication Date: Apr 6, 2012
Citations: 162	License type: CC BY 4.0

Affiliation: NTT Basic Research Laboratories

Abstract

Electrode materials for recording biomedical signals, such as electrocardiography (ECG), electroencephalography (EEG) and evoked potentials data, are expected to be soft, hydrophilic and electroconductive to minimize the stress imposed on living tissue, especially during long-term monitoring. We have developed and characterized string-shaped electrodes made from conductive polymer with silk fiber bundles (thread), which offer a new biocompatible stress free interface with living tissue in both wet and dry conditions.An electroconductive polyelectrolyte, poly(3,4-ethylenedioxythiophene) -poly(styrenesulfonate) (PEDOT-PSS) was electrochemically combined with silk thread made from natural Bombyx mori. The polymer composite 280 µm thread exhibited a conductivity of 0.00117 S/cm (which corresponds to a DC resistance of 2.62 Mohm/cm). The addition of glycerol to the PEDOT-PSS silk thread improved the conductivity to 0.102 S/cm (20.6 kohm/cm). The wettability of PEDOT-PSS was controlled with glycerol, which improved its durability in water and washing cycles. The glycerol treated PEDOT-PSS silk thread showed a tensile strength of 1000 cN in both wet and dry states. Without using any electrolytes, pastes or solutions, the thread directly collects electrical signals from living tissue and transmits them through metal cables. ECG, EEG, and sensory evoked potential (SEP) signals were recorded from experimental animals by using this thread placed on the skin. PEDOT-PSS silk glycerol composite thread offers a new class of biocompatible electrodes in the field of biomedical and health promotion that does not induce stress in the subjects.

Highlights

Electrode materials for recording biomedical signals are expected to be soft, hydrophilic and electroconductive to make them suitable for water rich environments and the functionalities of living tissue
A membranous covering of PEDOT-PSS over the entire surface of the silk fibers was revealed by scanning electron microscope (SEM) observation (Fig. 1E, 1F)
A membrane webbing was observed in the gaps between the silk fibers indicating that PEDOT-PSS was deposited at the interspaces and on the surface of the silk thread

Summary

Introduction

Electrode materials for recording biomedical signals are expected to be soft, hydrophilic and electroconductive to make them suitable for water rich environments and the functionalities of living tissue. Metal electrodes have been widely used for bio electrodes [1]. Conventional metal electrodes are hydrophobic and made of hard material. The interfacial mismatch between living tissue and engineered electrodes causes an increment in the contact resistance and noxious stimulation induced by the mechanical strain between the electrode and tissue [1,2]. Gel or paste electrolytes are usually used to improve the interfacial mismatch between metal electrodes and living tissues, they disperse with time, and this results in an increase in both contact resistance and mechanical strain

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