Electrode impedance analysis of chronic tungsten microwire neural implants: understanding abiotic vs. biotic contributions

Abstract

Changes in biotic and abiotic factors can be reflected in the complex impedance spectrum of the microelectrodes chronically implanted into the neural tissue. The recording surface of the tungsten electrode in vivo undergoes abiotic changes due to recording site corrosion and insulation delamination as well as biotic changes due to tissue encapsulation as a result of the foreign body immune response. We reported earlier that large changes in electrode impedance measured at 1 kHz were correlated with poor electrode functional performance, quantified through electrophysiological recordings during the chronic lifetime of the electrode. There is a need to identity the factors that contribute to the chronic impedance variation. In this work, we use numerical simulation and regression to equivalent circuit models to evaluate both the abiotic and biotic contributions to the impedance response over chronic implant duration. COMSOL® simulation of abiotic electrode morphology changes provide a possible explanation for the decrease in the electrode impedance at long implant duration while biotic changes play an important role in the large increase in impedance observed initially.

Two-photon imaging of chronically implanted neural electrodes: Sealing methods and new insights

“…For example, material failure is believed to range from recording site to insulation damages including delamination, crack propagation, hydration which leads to loss of dielectric properties and iconic contamination (Escamilla-Mackert et al, 2009; Gilgunn et al, 2013; Kim et al, 2014; Kozai et al, 2014a; Kozai et al, 2015a; Kozai et al, 2015b; Prasad et al, 2014; Prasad et al, 2012; Sankar et al, 2014; Ware et al, 2014). On the other hand, biological failure modes are believed to be due to the inflammatory reactive tissue response to the implanted electrode (Gilgunn et al, 2012; Jaquins-Gerstl et al, 2011; Karumbaiah et al, 2012; Kozai et al, 2014a; Kozai et al, 2014b; Kozai et al, 2012a; Kozai et al, 2014c; Kozai et al, 2010; Potter et al, 2013; Rennaker et al, 2007; Turner et al, 1999).…”

Implications of chronic daily anti-oxidant administration on the inflammatory response to intracortical microelectrodes

“…One emerging hypothesis concerning microelectrode failure suggests a leading role for oxidative stress in altering neuronal cell viability and blood brain barrier stability at the device-tissue interface (McConnell et al, 2009; Potter et al, 2013). In addition, it has also been proposed that the same oxidative environment can result in breakdown/corrosion of both the insulator and the metals of the electrode itself (Schmitt et al, 1999; Barrese et al, 2013; Kozai et al, 2014; Prasad et al, 2014; Sankar et al, 2014). Therefore, given this possible role for oxidative stress events, the biological mechanisms that might create and propagate a local oxidative environment around implanted microelectrodes are being investigated.…”

Materials and technologies for soft implantable neuroprostheses

“…By contrast, most neural implants are rigid and static. For example, clinical implants are often prepared with platinum-iridium electrodes and stainless-steel wires embedded in silicone to form flexible, millimetrethick electrode paddles [5][6][7] . They may be machined with a built-in curvature to provide consistent electrode contact with the neural tissue.…”