Fast Prototyping of Thin-Film Polyimide Electrodes for Neural Interfacing: Tantalum Metallization as an Alternative to Noble Metals

Thin-film electrodes represent a promising approach for developing safe and stable brain–computer interfaces (BCIs). This study presents a method for fabricating thin-film electrodes that incorporates laser processing of metal films sputtered onto a polyimide base. This method is cheaper and faster and allows for rapid design changes and prototyping compared to traditional approaches, such as lithography. The electrodes can be adapted for both stimulation and recording, and their geometrical design can be modified for various applications including brain electrocorticography arrays, penetrating probes, and wrappings around peripheral nerves, among others. Electrodes can be designed and fabricated from scratch within 3 days, with an estimated cost of a single electrode around $1. Using this method, 12 μm thin electrodes can be produced and the contact size can be minimized to approximately 20 μm. Also, this study introduced the use of tantalum as the conductive layer. Tantalum serves as a cost-effective alternative to noble metals and improves electrode resistance to delamination, thereby enhancing the long-term reliability. Additionally, a platinum coating was used to tailor the electrochemical properties of tantalum, making them comparable to those of pure noble metal electrodes. The safety of the electrodes fabricated using this method was thoroughly evaluated. The electrodes were found to be safe for surrounding tissues, even in long-term, high-mobility applications. Histological examination of rat sciatic nerves after six months of implantation showed no signs of serious tissue damage.