Electrical percolation in extrinsically conducting, poly(ε-decalactone) composite neural interface materials

Abstract

By providing a bidirectional communication channel between neural tissues and a biomedical device, it is envisaged that neural interfaces will be fundamental in the future diagnosis and treatment of neurological disorders. Due to the mechanical mismatch between neural tissue and metallic neural electrodes, soft electrically conducting materials are of great benefit in promoting chronic device functionality. In this study, carbon nanotubes (CNT), silver nanowires (AgNW) and poly(hydroxymethyl 3,4-ethylenedioxythiophene) microspheres (MSP) were employed as conducting fillers within a poly(ε-decalactone) (EDL) matrix, to form a soft and electrically conducting composite. The effect of a filler type on the electrical percolation threshold, and composite biocompatibility was investigated in vitro. EDL-based composites exhibited favourable electrochemical characteristics: EDL/CNT—the lowest film resistance (1.2 ± 0.3 kΩ), EDL/AgNW—the highest charge storage capacity (10.7 ± 0.3 mC cm− 2), and EDL/MSP—the highest interphase capacitance (1478.4 ± 92.4 µF cm−2). All investigated composite surfaces were found to be biocompatible, and to reduce the presence of reactive astrocytes relative to control electrodes. The results of this work clearly demonstrated the ability of high aspect ratio structures to form an extended percolation network within a polyester matrix, resulting in the formulation of composites with advantageous mechanical, electrochemical and biocompatibility properties.

Nanomaterial-based microelectrode arrays for in vitro bidirectional brain–computer interfaces: a review

“…For traditional metal nanoparticles such as platinum (Pt) and gold (Au), novel microstructures rejuvenate them: laser-roughened Pt and microporous Pt have been used to fabricate stable electrodes with low threshold potential and low impedance 57 , and a Au hierarchical nanostructure was deposited to improve the electrochemical surface area in a more effective manner 58 . In particular, quasi-1D metal nanowires with substantial length and ductility facilitate a decrease in resistance and an increase in the complexity of the spatial structure 62 .…”

Simulation of electrical conductivity for polymer silver nanowires systems

“…At a certain concentration of the conductive nanofiller, commonly known as the electrical percolation threshold, PNC conductivity increases dramatically 30 . At percolation concentration, nanofillers produce conductive network in the polymer matrix 31 .…”

Strategies for interface issues and challenges of neural electrodes

“…13,14 To achieve a high performance nerve-electrode interface, attention should be paid to the following aspects: (i) the charge transfer mechanism of diverse electrode materials needs to be clarified, since the electrical deviations of neural interfaces bring about obstacles to signal transmission and detection. 15–17 (ii) An excellent electrochemical performance of the neural electrode is highly desired, 18,19 including electrochemical impedance, 20,21 charge storage capacity (CSC), 22,23 charge injection limit (CIL, it is defined as the maximum charge density that can be injected into the tissue under the safe potential window measured by cyclic voltammetry) 24–26 and so on. Among them, a low impedance favors monitoring the electrophysiological signal with more details.…”

“…(iii) Until now, the weak biocompatibility of the neural electrodes is still a rigorous problem. 22,31,32 Although helpful tissue adhesion and survival of nerve cells were observed in vitro , diverse degrees of tissue reaction occurred in vivo , which weakens the transmission of signals of the electrodes. Deservedly, it is imperative to comprehend and resolve the trouble of poor compatibility, which hinders the way for long term and stable implantation of the neural electrodes.…”