A flexible protruding microelectrode array for neural interfacing in bioelectronic medicine

Abstract

Recording neural signals from delicate autonomic nerves is a challenging task that requires the development of a low-invasive neural interface with highly selective, micrometer-sized electrodes. This paper reports on the development of a three-dimensional (3D) protruding thin-film microelectrode array (MEA), which is intended to be used for recording low-amplitude neural signals from pelvic nervous structures by penetrating the nerves transversely to reduce the distance to the axons. Cylindrical gold pillars (Ø 20 or 50 µm, ~60 µm height) were fabricated on a micromachined polyimide substrate in an electroplating process. Their sidewalls were insulated with parylene C, and their tips were optionally modified by wet etching and/or the application of a titanium nitride (TiN) coating. The microelectrodes modified by these combined techniques exhibited low impedances (~7 kΩ at 1 kHz for Ø 50 µm microelectrode with the exposed surface area of ~5000 µm²) and low intrinsic noise levels. Their functionalities were evaluated in an ex vivo pilot study with mouse retinae, in which spontaneous neuronal spikes were recorded with amplitudes of up to 66 µV. This novel process strategy for fabricating flexible, 3D neural interfaces with low-impedance microelectrodes has the potential to selectively record neural signals from not only delicate structures such as retinal cells but also autonomic nerves with improved signal quality to study neural circuits and develop stimulation strategies in bioelectronic medicine, e.g., for the control of vital digestive functions.

Development of multi-depth probing 3D microelectrode array to record electrophysiological activity within neural cultures

“…The 60 electrodes in the array are categorized into four groups (G1, G2, G3, and G4) based on the electrode height relative to the substrate surface. The G1 electrodes have a planar topology, whereas G2, G3, and G4 electrodes consist of gold micro-pillars having heights of 35 ± 2 µm, 65 ± 2 µm, and 120 ± 2 µm respectively (figure 4(b)), significantly taller than the previously reported 3D MEAs [28,33,36]. This unique distribution of electrode heights allowed the recording of electrophysiological activities from the surface to multiple depths within the neural culture (figure 4(i)).…”

“…The primary limitations deal with the realization of sufficiently reliable and economically sustainable solutions, offering compatibility with the existing experimental platforms in neurophysiology. To this end, numerous 3D MEAs have been developed using various fabrication technologies, leading to substantial improvements in electrode density and aspect ratio; however, the diversity of cell types and device applications necessitates an ideal 3D MEA device with configurable electrode geometry, density, aspect ratio, and array topology [23][24][25][26][27][28][29][30][31][32][33][34]. A promising step in this direction could be a 3D MEA consisting of partially insulated microstructures with varying and precisely controlled heights of the electrodes [35,36].…”

A flexible implant towards acute intrapancreatic electrophysiology

“…Flexible polyimide-based components were produced following established methods (McDonald et al , 2020; Steins et al , 2022). A first layer of polyimide (6 μm) was spin-coated on 100 mm silicon carrier wafers.…”

Electrochemical Biosensor Arrays for Multiple Analyte Detection

“…They have found wideranging applications in various fields such as multiplex biosensing, neural network analysis, [53] drug screening [54] and the study of neural prostheses. [55] This article will only discuss their use for detecting multiple analytes using electrochemical biosensing arrays.…”