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Cited by 165Conducting polymers and applicationsNeuroscience and Neural EngineeringAdvanced Sensor and Energy Harvesting Materials

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Conductive Polymer Combined Silk Fiber Bundle for Bioelectrical Signal Recording

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Tsukada, Shingo, Nakashima, Hiroshi, Torimitsu, Keiichi·2012·PLoS ONE
DOI 10.1371/journal.pone.0033689PMC PMC3320891
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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.

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Figures

Figure 1 PEDOT-PSS silk thread observation with a conventional microscope and a scanning electron microscope (SEM). A. Macroscopic image of pristine silk thread (left) and PEDOT-PSS combined silk thread (right). B. C. Cross-section of pristine silk (B) and PEDOT-PSS silk thread (C) observed with a transmitted light optical microscope (scale bar 50 µm). D–F. Scanning electron micrograph of pristine silk (D) and PEDOT-PSS silk thread (E, Higher magnification view F). Arrows indicate fine filaments of silk fiber (D) coated with PEDOT-PSS (E). Arrowheads indicate PEDOT-PSS webbing between silk fibers. (F, Scale bar 20 µm). Pristine silk shows charge up and has a blurred image because of its insulation properties (D).
Figure 1 PEDOT-PSS silk thread observation with a conventional microscope and a scanning electron microscope (SEM). A. Macroscopic image of pristine silk thread (left) and PEDOT-PSS combined silk thread (right). B. C. Cross-section of pristine silk (B) and PEDOT-PSS silk thread (C) observed with a transmitted light optical microscope (scale bar 50 µm). D–F. Scanning electron micrograph of pristine silk (D) and PEDOT-PSS silk thread (E, Higher magnification view F). Arrows indicate fine filaments of silk fiber (D) coated with PEDOT-PSS (E). Arrowheads indicate PEDOT-PSS webbing between silk fibers. (F, Scale bar 20 µm). Pristine silk shows charge up and has a blurred image because of its insulation properties (D).CC BY · PubMed Central
Figure 2 Mechanical properties of PEDOT-PSS silk thread. A. Tensile strength of pristine PEDOT-PSS film in dry (left) and wet (right) states (n = 10, error bar: 1 S.D.). B. Stress-elongation curves of pristine silk thread (blue lines 1, 1′), PEDOT-PSS silk thread (red lines 2, 2′), and glycerol treated PEDOT-PSS silk thread (green lines 3, 3′), in dry (1, 2, 3) and wet states (1′, 2′, 3′). The average data of 10 samples are plotted on the graph. Inset: Enlarged view of stress-elongation curves of the 3 groups in a dry condition in a lower strength range, pristine silk thread 1) PEDOT-PSS silk thread 2) and glycerol treated PEDOT-PSS silk thread 3). Glycerol treatment improved the elasticity of PEDOT-PSS silk thread.
Figure 2 Mechanical properties of PEDOT-PSS silk thread. A. Tensile strength of pristine PEDOT-PSS film in dry (left) and wet (right) states (n = 10, error bar: 1 S.D.). B. Stress-elongation curves of pristine silk thread (blue lines 1, 1′), PEDOT-PSS silk thread (red lines 2, 2′), and glycerol treated PEDOT-PSS silk thread (green lines 3, 3′), in dry (1, 2, 3) and wet states (1′, 2′, 3′). The average data of 10 samples are plotted on the graph. Inset: Enlarged view of stress-elongation curves of the 3 groups in a dry condition in a lower strength range, pristine silk thread 1) PEDOT-PSS silk thread 2) and glycerol treated PEDOT-PSS silk thread 3). Glycerol treatment improved the elasticity of PEDOT-PSS silk thread.CC BY · PubMed Central
Figure 3 Glycerol enhanced water sturdiness of PEDOT-PSS silk thread. A. Photograph of the threads soaked in water for three days. 1) Pristine silk thread. 2) PEDOT-PSS silk thread without glycerol. 3) PEDOT-PSS silk thread with glycerol. 4) PEDOT-PSS silk thread without water soaking. B. Repeated cycles of washing with water and drying impaired the electrical conductivity of the PEDOT-PSS silk thread. The conductance of PEDOT-PSS silk thread (red line) and glycerol treated PEDOT-PSS silk thread (green line) after every washing cycle are shown (measured at dry state, averaged data from 10 samples are plotted). The conductance of thread that were not treated with glycerol fell to less than 1% that of the control. Glycerol treated thread retained its conductance after the third washing.
Figure 3 Glycerol enhanced water sturdiness of PEDOT-PSS silk thread. A. Photograph of the threads soaked in water for three days. 1) Pristine silk thread. 2) PEDOT-PSS silk thread without glycerol. 3) PEDOT-PSS silk thread with glycerol. 4) PEDOT-PSS silk thread without water soaking. B. Repeated cycles of washing with water and drying impaired the electrical conductivity of the PEDOT-PSS silk thread. The conductance of PEDOT-PSS silk thread (red line) and glycerol treated PEDOT-PSS silk thread (green line) after every washing cycle are shown (measured at dry state, averaged data from 10 samples are plotted). The conductance of thread that were not treated with glycerol fell to less than 1% that of the control. Glycerol treated thread retained its conductance after the third washing.CC BY · PubMed Central
Figure 4 Electrophysiological recordings obtained using electrodes made with PEDOT-PSS silk glycerol thread. A. Structure of skin surface electrodes using PEDOT-PSS glycerol silk thread. a. String shaped electrode for electrocardiograph (ECG). b. Flat electrode for electroencephalogram (EEG). B. ECG recordings obtained from an experimental rat with bipolar deviation. Inset shows the position of the three electrodes. C. EEG recorded from a rat in an anesthetized condition. Inset shows the position of six different electrodes (flat PEDOT-PSS silk glycerol electrode, Fig. 4A, image b) on scalp and reference electrodes (Ag AgCl) on bilateral auricle. D. Sensory evoked potential (SEP) recorded from a rat parietal area with a flat PEDOT-PSS silk glycerol electrode induced by left posterior leg stimulations via (string shape PEDOT-PSS silk glycerol electrode, Fig. 4A, image a). Averaged data for 200 recorded signals are shown.
Figure 4 Electrophysiological recordings obtained using electrodes made with PEDOT-PSS silk glycerol thread. A. Structure of skin surface electrodes using PEDOT-PSS glycerol silk thread. a. String shaped electrode for electrocardiograph (ECG). b. Flat electrode for electroencephalogram (EEG). B. ECG recordings obtained from an experimental rat with bipolar deviation. Inset shows the position of the three electrodes. C. EEG recorded from a rat in an anesthetized condition. Inset shows the position of six different electrodes (flat PEDOT-PSS silk glycerol electrode, Fig. 4A, image b) on scalp and reference electrodes (Ag AgCl) on bilateral auricle. D. Sensory evoked potential (SEP) recorded from a rat parietal area with a flat PEDOT-PSS silk glycerol electrode induced by left posterior leg stimulations via (string shape PEDOT-PSS silk glycerol electrode, Fig. 4A, image a). Averaged data for 200 recorded signals are shown.CC BY · PubMed Central
Figure 5 Comparison of ECG signals recorded from conventional, PEDOT-PSS silk thread and textile electrodes. Simultaneously recorded rat ECG signals from conventional medical electrodes (a), PEDOT-PSS silk glycerol thread electrodes (b), textile electrodes (c) pressure contact with skin by elastic band wrapping (pressure contact, left) or medical adhesive tape fixation without body movement (middle) and with body movement (right) are shown. ECGs recorded with PEDOT-PSS silk glycerol thread electrodes are comparable to ECGs obtained with conventional medical electrodes (a,b) under all conditions. The tape fixed textile electrode produced a hum (c, middle) and baseline drift (c, right) without and with body movement, respectively.
Figure 5 Comparison of ECG signals recorded from conventional, PEDOT-PSS silk thread and textile electrodes. Simultaneously recorded rat ECG signals from conventional medical electrodes (a), PEDOT-PSS silk glycerol thread electrodes (b), textile electrodes (c) pressure contact with skin by elastic band wrapping (pressure contact, left) or medical adhesive tape fixation without body movement (middle) and with body movement (right) are shown. ECGs recorded with PEDOT-PSS silk glycerol thread electrodes are comparable to ECGs obtained with conventional medical electrodes (a,b) under all conditions. The tape fixed textile electrode produced a hum (c, middle) and baseline drift (c, right) without and with body movement, respectively.CC BY · PubMed Central

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Metadata

Authors
Tsukada, S., Nakashima, H., & Torimitsu, K.
Affiliations
NTT (Japan) (JP)
Corresponding author
Tsukada, Shingo
ORCID
Venue
PLoS ONE
Publisher
Public Library of Science (PLoS)
Published
2012-04-06
Volume
7
Issue
4
Pages
e33689
ISSN
1932-6203 (ISSN-L)
DOI
10.1371/journal.pone.0033689
PMC
PMC3320891
OpenAlex
W2084865356
Cited by
163
References
28
Citations by year
2026: 2 · 2025: 5 · 2024: 7 · 2023: 10 · 2022: 15 · 2021: 22 · 2020: 9 · 2019: 17 · 2018: 16 · 2017: 20 · 2016: 9 · 2015: 17 · 2014: 7 · 2013: 5 · 2012: 2
FWCI
7.80
Type
journal article
Language
en
Open access
Licence
Locations
  • PLoS ONE (publishedVersion, cc-by)
  • PubMed Central (publishedVersion, cc-by)
  • PubMed (publishedVersion)
  • DOAJ (DOAJ: Directory of Open Access Journals) (submittedVersion, cc-by-sa)
Topics
  • Physical Sciences › Materials Science › Polymers and Plastics › Conducting polymers and applications
  • Life Sciences › Neuroscience › Cellular and Molecular Neuroscience › Neuroscience and Neural Engineering
  • Physical Sciences › Engineering › Biomedical Engineering › Advanced Sensor and Energy Harvesting Materials
Keywords
conducting polymers, PEDOT:PSS, biocompatible electrodes, electrocardiogram, EEG, sensory evoked potentials, glycerol additive, wettability, tensile strength, skin electrodes, long-term monitoring
MeSH terms
Animals, Biocompatible Materials, Electric Conductivity, Electrocardiography, Electrodes, Electroencephalography, Evoked Potentials, Somatosensory, Glycerol, Humans, Microscopy, Electron, Scanning, Polystyrenes, Bombyx, Tensile Strength, Thiophenes, Water, Wettability, Rats, Sprague-Dawley, Silk, Rats, Electrochemical Techniques

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