3D-printed penetrating neural probes with maskless metallization and encapsulation

Abstract

Three‑dimensional (3D) printing offers new design freedoms for neural interfaces, but reliable metallization and selective encapsulation on complex geometries remain challenging. We present a fully 3D-printed penetrating neural probe fabricated by two-photon polymerization, enabled by two maskless approaches: trench-guided metal deposition via line-of-sight evaporation to define electrodes and interconnect traces, and capillary-driven SU-8 encapsulation, which self-limits at convex edges to preserve exposed electrode sites. The resulting probe incorporates a 2-mm shank with four mushroom-shaped electrodes and demonstrates robust metallization, reliable electrical isolation, and controlled encapsulation achieved purely through geometric design without lithographic masking. Electrochemical characterization confirmed the functionality and integrity of the electrodes, while mechanical testing in 0.6% agarose gel confirmed sufficient buckling resistance for insertion. This approach provides a rapid, maskless, and highly customizable route for fabricating penetrating neural probes. More broadly, this approach establishes a scalable, geometry-driven paradigm for functionalizing complex 3D-printed microstructures, extending beyond neural interfaces to a wide range of bioelectronic and microscale devices.