Text

theses

Brain computer interfaces (BCI) establish communication between the brain and external devices by recording and decoding neural signals and using the signals to drive the devices. Implanted neural microprobes are one means of recording these signals. Despite the short term feasibility of currently available neural prosthetic devices, most of these devices suffer from long term gliosis. In order to address this challenge, it is hypothesized that smaller, more flexible probes that match the mechanical properties of brain tissue could allow better long term integration with neural tissue. The goal of this work is to investigate and understand different device design parameters (e.g., size and material) that might affect brain tissue responses of a long term chronic intracortical neural probe. The miniaturized probe is coated with an ultrafast degrading Tyrosine-derived polycarbonate (E5005(2K)). The polymer is mechanically stiff, which allows it to act as a temporary insertion aid for the probes to penetrate tissue, yet has been designed to degrade within several hours, leaving the flexible probes in place for high fidelity recording. First, a fabrication process was developed incorporating both probe fabrication and polymer coating procedures. The probes were characterized to ensure consistent quality. Second, the probes were evaluated using an in-vivo rat model to assess glial tissue response via immunohistochemistry. Finally, the microfabrication process was expanded to electrically functionalize the probes via metallization, to create electrodes for signal recording. In vivo animal study suggested that both polymer coating and probe sizes play roles in glial scar formation. The larger polymer coating devices introduced more severe glial scar response despite polymer degradation within a few hours post device implantation, which might result from the more severe insertion mechanical trauma. The experimental results also confirmed our hypothesis that the smaller probe/polymer coating devices performed better with minimal glial response compared to the larger probe/polymer coating devices in both short/long terms. Finally, we demonstrated the probe’s recording feasibility using in vitro models, and showed that the electrode remained intact during polymer coating and degradation for the proper device operation. In conclusion, the flexible microprobe with an ultrafast degrading polymer coating as an insertion aid demonstrates promising results to address challenges in electrode-cell interface. Future work will evaluate the electrical recording performance of the miniaturized probe to confirm consistent signal quality while attenuating tissue reaction for prolonged device operation.

ETD_6714

Ph.D.

Includes bibliographical references

by Meng-chen Lo

doi:10.7282/T3KH0QBQ

ETD doctoral

The author owns the copyright to this work.