Engineering Hydrogel-coated Neural Interfaces for Chronic Deep Brain Recording

Implanted brain electrodes provide a unique way of electrically interfacing with individual neurons in vivo. However, chronic recording or stimulating capabilities of neural implants are often impaired by a strong immune response resulting in a fibrous scarring tissue forming around the implant. Growing evidence suggests the role of mechanical mismatches between the implant and biological tissues in sustaining the immune response, encouraging the development of flexible neuroelectronic interfaces. Soft coatings matching the brain's elastic modulus as well as miniaturized, flexible implants promise increased biocompatibility and stability of implanted brain electrodes. Here, we optimized a micrometric zwitterionic hydrogel coating for neural implant to take advantage of both its soft and ultralow fouling properties while limiting the implant's footprint. This coating was integrated onto microfabricated polyimide neural probes that are 150 µm wide, 1 cm long and 10 µm thick. These probes were then implanted chronically in deep structures of the brain that experience elevated degrees of micromotion. Recording sessions in freely moving rats were conducted weekly and sustained chronic recording capability for at least 8 weeks with high signal-to- noise ratio was achieved. We anticipate that such a system will further enable us to conduct non-biased, chronic investigation of deep neural circuits implicated in motor control.