Characterization of flexible ECoG electrode arrays for chronic recording in awake rats

Abstract

We developed a 64 channel flexible polyimide ECoG electrode array and characterized its performance for long term implantation, chronic cortical recording and high resolution mapping of surface evoked potentials in awake rats. To achieve the longest possible recording periods, the flexibility of the electrode array, adhesion between the metals and carrier substrate, and biocompatibility was critical for maintaining the signal integrity. Experimental testing of thin film adhesion was applied to a gold – polyimide system in order to characterize relative interfacial fracture energies for several different adhesion layers, yielding an increase in overall device reliability. We tested several different adhesion techniques including: gold alone without an adhesion layer, titanium-tungsten, tantalum and chromium. We found the titanium-tungsten to be a suitable adhesion layer considering the biocompatibility requirements as well as stability and delamination resistance. While chromium and tantalum produced stronger gold adhesion, concerns over biocompatibility of these materials require further testing. We implanted the polyimide ECoG electrode arrays through a slit made in the skull of rats and recorded cortical surface evoked responses. The arrays performed reliably over a period of at least 100 days and signals compared well with traditional screw electrodes, with better high frequency response characteristics. Since the ultimate goal of chronically implanted electrode arrays is for neural prosthetic devices that need to last many decades, other adhesion layers that would prove safe for implantation may be tested in the same way in order to improve the device reliability.

Electro-Mechanical Testing of Conductive Materials Used in Flexible Electronics

“…The Ta adhesion layer increased the interfacial energy by almost a factor of 10 compared to the Ti adhesion layer. These results follow that of Yeager et al (2008) who used four point bending to measure the adhesion of TiW-PI and Ta-PI interface. In order to apply these adhesion models, especially tensileinduced delamination, it is best to use the first buckles that form (Cordill et al, 2010).…”

“…The first has a 10-nm Ta adhesion layer between the Au and PI while the second system has a 10-nm Ti adhesion layer between the Au and PI with an additional 200-nm Cr overlayer. The adhesion layers were sputter deposited before the 300-nm Au film without breaking vacuum (Yeager et al, 2008). The Cr overlayer was deposited after breaking vacuum in a different sputtering chamber using the parameters for Cr stated above.…”

Deployable and Conformal Planar Micro-Devices: Design and Model Validation

“…We chose polyimide as our membrane material, as it has been widely used as a substrate to construct bio-compatible thin film electrode arrays [18]. The polyimide has a Young's modulus of 2.3 GPa, a Poisson's ratio of 0.34, a liquid-solid surface tension coefficient of γ sl = 0.042 N/m and a contact angle of 70° with water [19][20][21][22].…”

“…Smaller values of s are therefore preferred to make the device more compact in its collapsed state and also to make more of the membrane surface available for functional ECG electrodes. In practice, the minimum value of s is limited by the precision of a manufacturing technique and typically: min hole 2 s s r ≥ ≈ (18) where r hole is the radius of the holes. With s set at its minimum value, one can determine the maximum acceptable value of l using Equation (17).…”

A polymer-based spiky microelectrode array for electrocorticography

“…In order to obtain electrical connection with peripheral nerves, polymer-based sieve (Stieglitz et al 1997), cuff (Rodriguez et al 2000) and transverse (Boretius et al 2010) probes are available. Microfabricated polymer structures are commonly applied for electrocorticography (ECoG) as well (Yeager et al 2008;Myllymaa et al 2009;Rubehn et al 2009;Ochoa et al 2013), which is a widely used method for the localization of epileptogenic zones (Keene et al 2000). In this paper, a novel polymer-based microelectrode array is presented, suitable for performing in vivo neuroscientific experiments, e.g.…”