Conductive Polymer Combined with Silk Fibers for Biomedical Electrodes


Shingo Tsukada, Hiroshi Nakashima, and Keiichi Torimitsu
Materials Science Laboratory

 A bio-electrode is an essential tool for nano-bio research as an interface between living organs and electrical devices (circuits). Electrode materials for biomedical signal recordings, such as electrocardiograms (ECG) and electroencephalography (EEG) are expected to be soft, hydrophilic and electro-conductive to minimize the stress imposed on living tissue, especially for long-term monitoring. We have developed and characterized string shaped electrodes consisting of a conductive polymer combined with silk fibers, which provide a new biocompatible interface with living tissue under both dry and wet conditions [1].
 An electro-conductive polyelectrolyte, Poly (3,4-ethylenedioxythiophene) poly (styrenesulfonate) (PEDOT-PSS) was electrochemically combined with silk fibers from Bombyx mori (Fig. 1). The polymer composite 280 µm fiber bundle exhibited a conductivity of 0.0018 S/cm (260 Kohm/mm) and a tensile strength of 1,000 CN in dry and wet states. The chemical addition of glycerol to the PEDOT-PSS silk fiber improved the conductivity to 0.23 S/cm (2 Kohm/mm). Glycerol also controls the wettability of PEDOT-PSS thus improving its durability in water and washing cycles. Without using any electrolytes, pastes or solutions, the electroconductive string directly collects electrical signals from living tissue and transmits them to metal cables (Fig. 2). This PEDOT-PSS silk glycerol fiber composite offers a new class of biocompatible electrodes for biomedical, information and communication technology without imposing any stress on the subjects.

[1] S. Tsukada et al., PLoS ONE 7(4) (2012) e33689.

Fig. 1. a. PEDOT-PSS silk thread (right), bare
silk thread (left). b. Macroscopic image
of PEDOT-PSS silk thread (right) and
bare silk (left). c. SEM image of PEDOTPSS
silk thread (Scale bar 20 µm).
Fig. 2. a. Structure of skin surface electrode made of PEDOTPSS
silk thread. b. Electrocardiogram simultaneously
recorded by PEDOT-PSS silk electrode (1), conventional
medical electrodes (2) and textile electrode (Scale bar
1 sec 50 mV). c. EEG recordings from rat brain (Scale
bar 1 sec 50 µV, F3, F4: Frontal head left & right, C3,
C4: Central left & right).

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