Iridium oxide microelectrode arrays for in-vitro stimulation of individual rat neurons from dissociated cultures

Abstract

We present the first in vitro extracellular stimulation of individual neurons from dissociated cultures with iridium oxide (IrOx) electrodes. Microelectrode arrays with sputtered IrOx films (SIROF) were developed for electrophysiological investigations with electrogenic cells. The microelectrodes were characterized with scanning electron and atomic force microscopy, revealing rough and porous electrodes with enlarged surface areas. As shown by cyclic voltammetry and electrochemical impedance spectroscopy, the large surface area in combination with the good electrochemical properties of SIROF resulted in high charge storage capacity and low electrode impedance. Thus, we could transfer the good properties of IrOx as material for in vivo stimulation electrodes to multi-electrode arrays with electrode diameters as small as 10 μm for in vitro applications. Single rat cortical neurons from dissociated cultures were successfully stimulated to fire action potentials using single or trains of biphasic rectangular voltage-controlled stimulation pulses. The stimulated cell's membrane potential was simultaneously monitored using whole-cell current-clamp recordings. This experimental configuration allowed direct evaluation of the influence of pulse phase sequence, amplitude, and number on the stimulation success ratio and action potential latency. Negative phase first pulses were more effective for extracellular stimulation and caused reduced latency in comparison to positive phase first pulses. Increasing the pulse amplitude also improved stimulation reliability. However, in order to prevent cell or electrode damage, the pulse amplitude is limited to voltages below the threshold for irreversible electrochemical reactions at the electrode. As an alternative to increasing the amplitude, a higher number of stimulation pulses was also shown to increase stimulation success.

All Titanium Microelectrode Array for Field Potential Measurements from Neurons and Cardiomyocytes—A Feasibility Study

“…The coating is usually aimed to reduce noise and improve the impedance characteristics and charge transfer capacity of the microelectrodes, which affect the probability of detecting cellular activity and the stimulation capability. Wide availability and sufficiently good electrical characteristics have made platinum black (Pt black) probably the most commonly used microelectrode surface coating throughout MEA history [1,4,23,24], even if it suffers from adhesion and reproducibility problems [25,26]. TiN is the microelectrode surface material favored by one of the leading commercial MEA manufacturers (Multi Channel Systems (MCS), Reutlingen, Germany) [27][28][29].…”

“…TiN is the microelectrode surface material favored by one of the leading commercial MEA manufacturers (Multi Channel Systems (MCS), Reutlingen, Germany) [27][28][29]. Iridium oxide (IrOx) is widely studied, even though not yet commercialized, microelectrode coating that has excellent charge transfer capacity and high long term stability, but suffers from need for electrochemical (re)activation [25,26,30]. There is no common opinion whether TiN or IrOx has better characteristics [26,28,31].…”

Encapsulation of implantable integrated MEMS pressure sensors using polyimide epoxy composite and atomic layer deposition

“…However, processing of polyimide is challenging due to the evaporation of the solvent (for example N,N -Dimethylformamid, N,NDimethylacetamid or N-Methylpyrrolidon) (Calderón, 2005) and water during the curing process (or imidization) leading to a significant shrinkage of the material which is especially problematic for the encapsulation of the bond wires. Another critical point is the adhesion of pure polyimide which is typically rather poor (Gaw and Kakimoto, 1999). The bonding of two objects is difficult because of the evaporation of the solvent creating pore-like structures during the curing process.…”

“…In particular, polyimide-epoxy composite was identified as a suitable material; here a small amount of epoxy (typically 10-15 %) is added to the polyimide partially replacing the solvent (Gaw and Kakimoto, 1999). This increases adhesive strength, shape stability and reduces the formation of pores.…”

“…Application examples include continuous pressure monitoring (Mokwa, 2007;Gembaczka et al, 2013), nerve and muscle stimulation (Eick et al, 2009) and drug delivery systems (Hang Tng et al, 2012). Usually medically approved micro-electronic implants such as pacemakers (Park and Lakes, 2007), cochlear implants (Loeb, 1990) or brain stimulators (Rezai et al, 2002) are encapsulated by non-flexible materials such as titanium or ceramics with considerable sidewall thickness in the range of 100 µm to 1 mm.…”