Wafer‐Scale Fabrication of Conducting Polymer Hydrogels for Microelectrodes and Flexible Bioelectronics

Abstract

Future‐oriented directions in neural interface technologies point towards the development of multimodal devices that combine different functionalities such as neural stimulation, neurotransmitter sensing, and drug release within one platform. Conducting polymer hydrogels (CPHs) are suggested as materials for the coating of standard metal electrodes to add functionalities such as local delivery of therapeutic drugs. However, to make such coatings truly useful for multimodal devices, it is necessary to develop process technologies that allow the micropatterning of CPHs onto selected electrode sites. In this study, a wafer‐scale fabrication procedure is presented, which is used to coat the CPH, based on the hydrogel P(DMAA‐co‐5%MABP‐co‐2,5%SSNa) and the conducting polymer poly(3,4‐ethylenedioxythiophene) (PEDOT), onto flexible neural probes. The resulting material has favorable properties for the generation of recording electrodes and in addition offers a convenient platform for biofunctionalization. By controlling the PEDOT content within the hydrogel matrix, charge injection limits of up to 3.7 mC cm−2 are obtained. Long‐term stability is tested by immersing coated samples in phosphate‐buffered saline solution at 37 °C for 1 year. Non‐cytotoxicity of the coatings is confirmed with a direct cell culture test using a fluorescent neuroblastoma cell line.

Electroresponsive Hydrogels for Therapeutic Applications in the Brain

“…Recently, strong interest has been garnered in developing multifunctional neural interfaces with simultaneous drug release, electric stimulation, and neural recording capabilities. [254] Such interfaces can be developed by selectively patterning the hydrogel at resolutions of a few micrometers. [254] Traditional coating processes lack site-specificity, and a partially conducting hydrogel may limit the recording resolutions, lead to spike sorting, and risk creating short circuits on densely spaced electrodes.…”

“…[254] Such interfaces can be developed by selectively patterning the hydrogel at resolutions of a few micrometers. [254] Traditional coating processes lack site-specificity, and a partially conducting hydrogel may limit the recording resolutions, lead to spike sorting, and risk creating short circuits on densely spaced electrodes. [254] Individual probes should therefore be tailored independently on an array to optimize each site separately, as Kleber and colleagues demonstrated by integrating a wafer scale coating process into the probe fabrication step on a single chip level.…”

“…[254] Traditional coating processes lack site-specificity, and a partially conducting hydrogel may limit the recording resolutions, lead to spike sorting, and risk creating short circuits on densely spaced electrodes. [254] Individual probes should therefore be tailored independently on an array to optimize each site separately, as Kleber and colleagues demonstrated by integrating a wafer scale coating process into the probe fabrication step on a single chip level. [254] This flexible photolithographic coating procedure tuned the electrochemical properties and controlled the hydrogel layering step to reach a predefined thickness.…”

Nanofibrous PEDOT-Carbon Composite on Flexible Probes for Soft Neural Interfacing

“…This result agreed with the corresponding impedance measurements where the 6 nC/µm 2 deposition condition provided a low impedance value with lowest variability (Figure 4D). The optimized CIL value from this work was compared with other PEDOT based composites (Carli et al, 2019;Kleber et al, 2019;Lee et al, 2019) and porous metals deposits (Wang et al, 2009;Vitale et al, 2015;Lu et al, 2016;Shin et al, 2016;Nimbalkar et al, 2018) on flexible neural implants. Figure 5F and Supplementary Table S1 shows that, among all reported electrode materials deposited on flexible metallic substrates, the PEDOT-CNF coating displayed superior electrical properties and charge injection capabilities, thanks to the chemical composition of the material and its physical morphology.…”

Nanofibrous PEDOT-Carbon Composite on Flexible Probes for Soft Neural Interfacing

“…The optimized CIL value from this work was compared with other PEDOT based composites [40,71,72] and porous metals deposits [69,[73][74][75][76] on flexible neural implants. Fig.…”