Bundle of Thin Multifunctional Fibers Enables Multi-Colors and Multi-Drugs Delivery and Multi-Site Recordings

A fiber-based multifunctional probe is an excellent interfacing platform for simultaneous electrical recordings, optical stimulations, and drug deliveries within the deep brain. However, the quantities of these modalities in each probe are restricted due to the complexity and challenges at the back-end connections. Here, we present a novel method of increasing the modality quantities through fabricating smaller and denser fibers and bundling them in a custom thermally drawn scaffold. Using the convergence thermal drawing method, we draw a fiber (OD: 50µm) with 15µm tungsten electrodes, an optical waveguide, and a microfluidic channel. Then, the bundling system allows for customizing the final neural probe, where the fibers are the building blocks. We demonstrated various designs of the customized fiber-based probes in the wild-type mice (C57BL6/J x FVB/NJ). Single unit cells, sharp-wave ripples, and the prominent theta waves are recorded at the pyramidal cell layer in CA1. The neural responses to the simultaneous multicolor optical stimulation and drug delivery are demonstrated. Six fiber probes (24 electrodes) are attached to a customized microdrive enabling chronic bilateral recordings and stimulations in the hippocampus. These new bundled fiber-based probes push the limitations and the challenges of the previous fiber-based probes by reducing the tissue damages/imprints and increasing the quantities of electrodes, optical waveguides, and drug channels.