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

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 microtechnological processes and PDMS as flexible, biocompatible material. The conductive electrode structure is deposited on a water-soluble transfer substrate by 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. The transferred gold structures exhibit higher adhesion and conductivity than transferred platinum structures. The adhesion can be 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, which is intended to mimic brain fluids. Using the introduced production process, it is possible to manufacture an ECoG electrode, which was 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 3-dimensional mould to produce electrodes tailored to the individual patient.