Strength characterization of silicon microprobes in neurophysiological tissues.

Strength characteristics of thin-silicon probes in neural tissues have been determined experimentally. It is shown that by proper selection of the substrate length, width, and thickness, silicon substrates can be designed and used to penetrate a variety of biological tissues without breakage or excessive dimpling. Thin-silicon structures have a maximum fracture stress which is a factor of six larger than bulk silicon, and are very flexible and capable of bending to angles larger than 90 degrees. Silicon substrates 15 microns thick x 30 microns wide can easily penetrate guinea pig and rat pia arachnoid layers with minimum dimpling and no breakage, while substrates 30 microns thick x 80 microns wide can penetrate guinea pig and rat dura mater repeatedly without breakage. Quantitative comparison on the relative toughness of neurophysiological tissues in rat and guinea pig have also been experimentally obtained.