Stretchable, Fully Polymeric Electrode Arrays for Peripheral Nerve Stimulation

Abstract

There is a critical need to transition research level flexible polymer bioelectronics toward the clinic by demonstrating both reliability in fabrication and stable device performance. Conductive elastomers (CEs) are composites of conductive polymers in elastomeric matrices that provide both flexibility and enhanced electrochemical properties compared to conventional metallic electrodes. This work focuses on the development of nerve cuff devices and the assessment of the device functionality at each development stage, from CE material to fully polymeric electrode arrays. Two device types are fabricated by laser machining of a thick and thin CE sheet variant on an insulative polydimethylsiloxane substrate and lamination into tubing to produce pre-curled cuffs. Device performance and stability following sterilization and mechanical loading are compared to a state-of-the-art stretchable metallic nerve cuff. The CE cuffs are found to be electrically and mechanically stable with improved charge transfer properties compared to the commercial cuff. All devices are applied to an ex vivo whole sciatic nerve and shown to be functional, with the CE cuffs demonstrating superior charge transfer and electrochemical safety in the biological environment.

Advanced Metallic and Polymeric Coatings for Neural Interfacing: Structures, Properties and Tissue Responses

“…As the geometric size of metallic electrodes is reduced, their suitability for neural recordings may be significantly hindered due to their low charge injection capability and charge storage capacitance. A few soft organic polymers (PDMS ( Figure 1 e) [ 27 , 28 ], PI [ 29 ], parylene C [ 30 ], PU [ 31 ]) have been used to fabricate neural electrodes in order to mitigate the mechanical mismatch in the tissue–electrode interface. Compared to metals and carbon materials, polymeric materials are less efficient for the transfer of the electrical signals due to their low electrical conductivity [ 32 ].…”

Towards All-Polymeric Cochlear Implant Micro-Electrode Arrays

“…Unfortunately, 1 ms was the minimum pulse width that could be applied to distinguish the voltage related to the ohmic resistance of the system, also known as access voltage (Va). This fact is significant as the maximum polarization potentials are calculated by subtracting Va from the total voltage response [121], [122]. In any case, the pulse width was the same in platinum and PEDOT:PSS VTs, and therefore, the experiments are consistent.…”

“…These PEDOT:PSS films are biocompatible [118], transparent in the visible light spectrum, present high conductivity (> 200 S cm −1 [119]), outstanding flexibility [120], and proper thermal stability [117]. These features also favor an optimal implanttissue interface, decreasing inflammatory responses and device rejection [121], [122]. Furthermore, the work function of these films (around 5.0-5.2 eV) benefits high charge injection limits [117].…”

“…For that, the current injected into the electrodes is increased until the limits of water window match with the maximum polarization voltages (Emc and/or Ema). As the CIC might vary depending on the pulse width [122], pulse widths comparable to the ones employed CI stimulation (i.e., 25 s [77], [136]) should be ideally used for this experiment. Unfortunately, 1 ms was the minimum pulse width that could be applied to distinguish the voltage related to the ohmic resistance of the system, also known as access voltage (Va).…”

Strategies for interface issues and challenges of neural electrodes

“…13h). Simultaneously, an all-polymer cuff electrode made of the CE was successfully developed, 227 which demonstrated good stability during manufacture, disinfection, cyclic tensile test, model wearing in vitro and so on. These studies demonstrate that a CE significantly improves the CIL performance of neural electrodes compared with commercial Pt ones.…”