Flexible three-dimensional microelectrode array for neural applications

Abstract A neural electrode array design is proposed with 3 mm long sharpened pillars made from an aluminum-based substrate. The array is composed by 25 electrically insulated pillars in a 5 × 5 matrix, in which each aluminum pillar was precisely machined via dicing saw technique. The result is an aluminum structure with high-aspect-ratio pillars (19:1), each with a tip radius of 10 μm. A thin-film of platinum was deposited via sputtering technique to perform the ionic signal transduction. Each pillar was encapsulated with an epoxy resin insulating the entire pillar excluding the tip. This process resulted in mechanically robust electrodes each capable of withstanding loads up to 200 mN before bending. The array implantation tests were conducted on agar gel at speeds of 50 mm/min, 120 mm/min and 180 mm/min which resulted in average implantation forces of 119 mN, 145 mN and 150 mN, respectively. Insertion and withdrawal tests were also performed in porcine cadaver brain showing a necessary force of 66 mN for successful explantation. A three point flexural test demonstrated a displacement of 0.8 mm before array's breakage. The electrode's impedance was characterized showing a near resistive impedance of 385 Ω in the frequency range from 2 kHz to 125 kHz. The resultant array, as well as the fabrication technique, is an innovative alternative to silicon-based electrode solutions, avoiding some fabrication methods and limitations related to silicon and increasing the mechanical flexibility of the array.