REU at Rutgers: Characterization of a flexible, ultra-fast degrading polymer coated neural microelec

Neural microprobes are utilized in Brain Computer Interface technologies to record the electrical signals from single or multiple neurons. Previous neural probes have not been successful in chronic implantation because of their large and rigid structure, causing a glial scar to form around the probe implant site during prolonged implantation. This glial scar, composed of astrocytes and microglia,

encapsulates the probe, increasing impedance and preventing usable signal acquisition. At Rutgers, a small, flexible, ultra-fast degrading Tyrosine derived terpolymer coated neural microprobe was designed and fabricated that is believed to have the necessary mechanical requirements that would allow for better long term implantation in brain tissue. Because the probe is designed to be mechanically compliant with the neural tissue, it is too flexible for insertion alone. A biodegradable derived polymer coating is used to give the probe a limited rigidity which aids in insertion. Our goal is to electrically characterize said neural microprobe to assure functionality, use image analysis to quantify glial scar formation of different size probes, and to assure that the tyrosine polymer will completely degrade during implantation. Impedance spectroscopy of the coated probe is performed in PBS to monitor polymer degradation. Our results show that the polymer coating around the probe degraded completely in 90 minutes by reaching an uncoated probe impedance value of 4.25 kΩ. Glial scar formation was quantified by immunohistochemically staining slices of post-implant rat brains for astrocytes and profiling for intensity values via Matlab image analysis. Intensity values are the concentration of astrocytes located around implant sites in the images. At 24 weeks post implant, a 30 µm wide × 5 µm thick probe with a polymer coating of 100 µm ×100 µm had an intensity value of 20 while a 320 µm × 5 µm probe and polymer coating of 350 µm × 100 µm had a value of 202. These results show that the smaller probe and polymer coating size has less of a glial scar formation than that of a larger probe and polymer coating.