A biodegradable porous silicon and polymeric hybrid probe for electrical neural signal recording

This paper reports on a novel design and fabrication strategy to develop a hybrid porous silicon (PSi)-polyimide-based neural interface probe. The PSi is soluble in the tissue matrix, leaving the flexible polyimide shank inside the tissue as a permanent probe-implant. The flexibility of the PSi-dissolved polyimide shank is possible to reduce the tissue response, resulting from the probe-implant. In-vitro degradation experiment was conducted in phosphate buffer solution (PBS), pH 7.4, at 37 °C. The PSi with over 50% porosity was dissolved in less than 6 days. The electrode contacts were made of Au or Pt; impedance measurements gave values of 6.83 MΩ and 656 kΩ @1 kHz, respectively. The minimum critical bucking force among the fabricated probes was tested to be 71 mN, corresponding to the highest porosities of 70% and 5 mm shank length. Assessment of the cell viability was done using mouse fibroblast cell line, indicating that there was no sign of obvious cell lysis and reduction of cell growth on the device surface. Lastly, the functionality of the probe was proved by successful implantation in rat cortex. The local field potential action spikes were recorded with ±40 μV peak and signal to noise ratio of 7.8.