A Customizable 3D-Printed Neural Probe Array Using Two-Photon Polymerization with Millimeter-Scaled Conductive Polymer as an Electrode Material

Microelectrode arrays are an essential tool for interfacing with nerve tissue to better understand brain functioning, as well as for therapeutic applications. Yet, the structural customizability of microelectrode arrays and the integration of specific materials into electrode designs remain challenging. Two-photon polymerization (2PP) is a high-resolution additive fabrication technique capable of producing micro- and nanoscale architectures, thus offering design flexibility for microelectrode arrays. However, due to the limited electrical conductivity of photo-cross-linkable polymers, 2PP three-dimensional (3D) printing is not widely adopted for the fabrication of microelectrode arrays yet. In this work, we present the millimeter-scaled integration of the conductive polymer poly(3,4-ethylenedioxythiophene):tetrafluoroborate (PEDOT:BF₄) into 2PP 3D-printed neural probe architectures via electrochemical deposition. Unlike state-of-the-art thin-film PEDOT coatings, this approach enables the formation of vertically extended, entirely polymer-based electrodes with a length in the millimeter range. These all-polymer electrode arrays exhibit low impedance, excellent electrochemical and mechanical stability, and enable neural recordings in freely moving rats. This fabrication process may thus provide a platform technology for customizable microelectrode arrays, demonstrating the effective integration of a conductive polymer into 2PP 3D-printed microneedle arrays. This platform could be leveraged for a wide range of applications in the broader field of bioelectronics.