A lithographically-patterned, elastic multi-electrode array for surface stimulation of the spinal cord

Abstract

A new, scalable process for microfabrication of a silicone-based, elastic multi-electrode array (MEA) is presented. The device is constructed by spinning poly(dimethylsiloxane) (PDMS) silicone elastomer onto a glass slide, depositing and patterning gold to construct wires and electrodes, spinning on a second PDMS layer, and then micropatterning the second PDMS layer to expose electrode contacts. The micropatterning of PDMS involves a custom reactive ion etch (RIE) process that preserves the underlying gold thin film. Once completed, the device can be removed from the glass slide for conformal interfacing with neural tissue. Prototype MEAs feature electrodes smaller than those known to be reported on silicone substrate (60 μm diameter exposed electrode area) and were capable of selectively stimulating the surface of the in vitro isolated spinal cord of the juvenile rat. Stretchable serpentine traces were also incorporated into the functional PDMS-based MEA, and their implementation and testing is described.

Materials for stretchable electronics

“…22 , 47 , 48 Freestanding stretchable conductors are fi rst encased in polyimide and then in PDMS for better mechanical matching with the metal conductor (see the Kim et al and Vanfl eteren et al articles). Contact holes through the encapsulation are opened by plasma etching, 47 liftoff, 49 or lithography of a photopatternable elastomer. 50 , 51 Contacts at the edges of the stretchable membrane are opened with procedures similar to liftoff.…”

“…[11][12][13][14][15][16] Sizes and shapes of elastomeric circuits can be changed reversibly by applying mechanical force, 17 by gas pressure, 18,19 or by application of an electric fi eld. 20,21 Now we can make electronic skin, 22 conformable sensors and displays (see the Kim et al and Sekitani and Someya articles in this issue), electronic biointerfaces, 12,[23][24][25] electronic muscles, 20,21,26 and energy harvesters (see the article by Kornbluh et al in this issue). Bending, [7][8][9] shaping, 10,27 stretching (see the Suo article), 11 and electroactuation 20,21 or energy harvesting are illustrated in Figure 1 .…”

Flexible and stretchable micro-electrodes for in vitro and in vivo neural interfaces

“…Such deformations are encountered in vivo when a nerve extends and relaxes over a joint [13,26] or during a mechanical injury [28,42]. Applied tensile strains can reach up to 20% and stretching cycles can occur within milliseconds [28].…”

“…Silicones are widely used in the fabrication of hybrid cuff electrodes in combination with platinum foils [33]. Patterning MEA directly onto the elastomeric substrate is of a recent concern [22,25,26].…”

Elastically Stretchable Insulation and Bilevel Metallization and Its Application in a Stretchable RLC Circuit

“…(1) meander-shaped gold conductors (15 lm thick) akin to a two-dimensional spring, 8 (2) wavy gold conductors that are deposited on prestretched PDMS, 9,10 and (3) straight microcracked gold conductors (20 nm to 100 nm thick). 11 Microcracked gold conductors have several advantages, a major one being that microcracked films can be stretched isotropically, whereas both meander-shaped and wavy gold conductors can only be stretched anisotropically.…”