  Current microelectrodes designed to record chronic neural activity suffer
from recording instabilities due to the modulus mismatch between the electrode
materials and the brain. We sought to address this by microfabricating a novel
flexible neural probe. Our probe was fabricated from parylene-C with a WTi
metal, using contact photolithography and reactive ion etching, with three
design features to address this modulus mismatch: a sinusoidal shaft, a rounded
tip and a polyimide anchoring ball. The anchor restricts movement of the
electrode recording sites and the shaft accommodates the brain motion. We
successfully patterned thick metal and parylene-C layers, with a reliable
device release process leading to high functional yield. This novel reliably
microfabricated probe can record stable neural activity for up to two years
without delamination, surpassing the current state-of-the-art intracortical
probes. This challenges recent concerns that have been raised over the
long-term reliability of chronic implants when Parylene-C is used as an
insulator, for both research and human applications. The microfabrication and
design considerations provided in this manuscript may aid in the future
development of flexible devices for biomedical applications.
