Transflex: A Flexible Multi-Shank Implantable Neuroelectrode with Variable Stiffness Based on Patternable Soluble Dextran-Pullulan Support Layer

Flexible neural electrodes are promising for chronic neural interfacing, but their softness complicates implantation. Here, we present a wafer-level fabrication method for an in situ patternable, soluble support layer based on dextran-pullulan composites (DPC). The mechanical properties of the DPC support layer were optimized and characterized. A 30 μm-thick DPC layer compatible with MEMS processes was achieved through photolithography and wet etching. Using this technique, we developed TransFlex electrodes with a polyimide substrate and temporary DPC hard coating. Ex vivo tests in brain-mimicking gels confirmed rapid dissolution of the support. In vivo implantation into the mouse cortex demonstrated precise delivery, with stable local field potential recordings maintained for three months. This approach offers an effective strategy for the implantation of flexible neural electrodes.