Ion Conducting Polymer Microelectrodes for Interfacing with Neural Networks


Tobias Nyberg, Akiyoshi Shimada, Nahoko Kasai, and Keiich Torimitsu
Materials Science Laboratory

   We have examined the stimulation and recording properties of conjugated polymer microelectrode arrays as interfaces with neural networks of dissociated cortical neurons.
 The polymer electrodes were electrochemically polymerized from a blend of poly (3,4-ethylenedioxythiophene)-poly (styrenesulfonate) (PEDOT-PSS) and ethylenedioxythiophene (EDOT) onto indium tin oxide (ITO) microelectrodes. Conducting polymers have been utilized to increase the surface roughness and improve the performance of planar electrodes [1].
 The stimulation properties were investigated as a means of supplying a neural network with information. The impedance of the polymer electrodes (circles) was markedly lower than that of the ITO electrodes (squares) for low and medium frequencies and the phase of the polymer electrodes (solid line) was lower than that of the ITO electrodes (dashed line) for medium frequency as shown in Fig. 1. The peak current was proportional to the applied voltage pulses for polymer electrodes.
 Dissociated cortical neurons from Wister rat embryos (embryonic day 18) were then plated on the electrodes and cultivated to form neural networks. Spontaneous activity was detected by both bare ITO and polymer electrode after 5 days in vitro and the bursting frequency increased as the networks matured. The stimulation efficiency at low voltages was evaluated and referenced to ITO electrodes. Polymer electrode stimulation evoked a much greater response from the network than stimulation from ITO electrodes as seen in Fig. 2. Polymer electrodes could be used at low stimulating potentials for the efficient stimulation of neuronal tissue for more than one month and interfacing could be maintained for several months. These results show that conducting polymer electrodes have the biocompatibility needed microelectrodes for interfacing with neural networks.

[1] T. Nyberg, et al., J. Neurosci. Methods. 160 (2007) 16.

Fig. 1. Bode plot of polymer and ITO electrodes.
Fig. 2. Evoked response for polymer and ITO stimulation.

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