Neural Probes with Deploying Electrodes

Today, electrodes that can be implanted into the brain for months or years are an irreplaceable tool for enhancing deep-brain stimulation, brain machine interfaces and neuroscience studies. However, these chronically implanted neural probes suffer from continuous loss of signal quality, limiting their utility. This was traced back to an ongoing chronic inflammation around the implant. Addressing this issue, this thesis presents a new class of implantable intracortical neural probes with enhanced chronic stability based on deploying small recording electrodes away from the large main probe shank after implantation.

To realize this extremely challenging goal, a novel actuation mechanism based on starch-hydrogel coated springs is developed. Mediated by the hydrogel, the springs compress and release, triggered by contact with biological fluids. The springs are designed to have sufficient travel (more than 120 Â µm) to advance electrodes past the local inflammation around the shank. The slow release of the hydrogel leaves sufficient time (tens of seconds) for insertion of the shank. The hydrogel coated springs are integrated into the shanks of silicon neural probes, capable of deploying multiple electrodes.

For a pilot in-vivo experiment, prototypes of this new class of neural probes are fabricated. The employed design supports six deploying electrodes, each at the end of a 5 Â µm wide and thick, and 100 Â µm long needle. These are attached to a shank that is made sufficiently robust (270 Â µm wide, 12 Â µm thick, 3 mm long) for reliable insertion. The results of the study indicate that the fabricated neural probes with deployed electrodes are practical devices, capable of recording action potentials from neurons.