Transfer Printing of Conductive Thin Films on PDMS with Soluble Substrates for Flexible Biosensors †

Abstract

The resolution of commercially available electrocorticography (ECoG) electrodes is limited due to the large electrode spacing and, therefore, allows only a limited identification of the active nerve cell area. This paper describes a novel manufacturing process for neural implants with higher spatial resolution combining micro technological processes and Polydimethylsiloxane (PDMS) as the flexible, biocompatible material. The conductive electrode structure is deposited on a water-soluble transfer substrate by Physical Vapor Deposition (PVD) processes. Subsequently, the structure is contacted. Finally, the transfer to PDMS and dissolution of the transfer substrate takes place. In this way, high-resolution conductive structures can be produced on the PDMS. Transferred gold structures exhibit higher adhesion and conductivity than transferred platinum structures. The adhesion was improved by applying a silica surface modification to the conductive layer prior to transferring. Furthermore, the conductive layer is flexible, conductive up to an elongation of 10%, and resistant to sodium chloride solution, mimicking brain fluids. Using the introduced production process, an ECoG electrode was manufactured and characterized for its functionality in an electrochemical impedance measurement. Furthermore, the electrodes are flexible enough to adapt to different shapes. The transfer process can also be carried out in a three-dimensional mold to produce electrodes tailored to the individual patient.