Neural Electrode Array Based on Aluminum: Fabrication and Characterization

Abstract

A unique neural electrode design is proposed with 3 mm long shafts made from an aluminum-based substrate. The electrode is composed by 100 individualized shafts in a 10 × 10 matrix, in which each aluminum shafts are precisely machined via dicing-saw cutting programs. The result is a bulk structure of aluminum with 65 ° angle sharp tips. Each electrode tip is covered by an iridium oxide thin film layer (ionic transducer) via pulsed sputtering, that provides a stable and a reversible behavior for recording/stimulation purposes, a 40 mC/cm2 charge capacity and a 145 Ω impedance in a wide frequency range of interest (10 Hz-100 kHz). Because of the non-biocompatibility issue that characterizes aluminum, an anodization process is performed that forms an aluminum oxide layer around the aluminum substrate. The result is a passivation layer fully biocompatible that furthermore, enhances the mechanical properties by increasing the robustness of the electrode. For a successful electrode insertion, a 1.1 N load is required. The resultant electrode is a feasible alternative to silicon-based electrode solutions, avoiding the complexity of its fabrication methods and limitations, and increasing the electrode performance.The work of A.C. Peixoto was supported in part by the Portuguese Foundation for Science and Technology under Grant SFRH/BD/89509/2012, and the FCT with the reference Project FCOMP 01 0124-EDER-010909 under Grant FCT/PTDC/SAU-BEB/100392/2008. The associate editor coordinating the review of this paper and approving it for publication was Prof. Carlo Morabito

Fabrication and mechanical characterization of long and different penetrating length neural microelectrode arrays

“…Some efforts have been made to obtain 3D MEA with long electrodes based on silicon wafers micromachining which also include microwire electrical discharge machining [24] and self-assembled probes using a heat treatment processes [25] to achieve the final 3D array design. We have previously presented [26] an approach to fabricate 3D MEA with shaft lengths up to 3 mm, which use aluminum as the bulk material instead of silicon. Table 1 compares the 3D MEA with regard to their design parameters.…”

Flexible three-dimensional microelectrode array for neural applications

“…Between the three tested speeds there is a maximum variation of force of 1.24 mN per electrode. The average implantation force is considerably lower than our previous thicker probe [10] and in the same order of magnitude of Das et al [29]. Implantation tests with similar parameters as the agar gel were performed on porcine cadaver brain with the purpose of testing the array robustness, these tests showed significant tissue dimpling without implantation success.…”

“…Due to the various applications of invasive electrodes in neurophysiology, the array's design should be made according to a specific application. Arrays with high-density are preferred when used for applications such as neuroprosthetics or for mapping the interaction between diverse brain's regions [2,10]. The described array has 25 electrodes, one at each tip of a micropillar, with a spacing of 600 µm between each, resulting in an electrode density of 2.8 electrodes per mm 2 .…”

“…This paper also offers a significant improvement in several aspects over a previously described aluminum array [10]. The present encapsulation process relies on the deposition and selective removal of the resin around each pillar, while in the previous version an anodizing process was used.…”

Out-of-plane neural microelectrode arrays fabrication using conventional blade dicing

“…This technology relies on silicon wafer micromachining using blade dicing technique, which resulted in a widely used tool in neuroscience, the Utah Electrode Array (UEA). Using the same technique, we also have previously presented an approach to fabricate 3D MEA using both aluminum [11] and silicon [12] as the bulk materials.…”