Silk-backed structural optimization of high-density flexible intracortical neural probes

Many chronic neuroscience studies require neural probes that can reliably record with a large number of electrodes in a densely configured array. Previous works have shown that adverse tissue reaction can be significantly reduced as probe shanks are scaled down toward subcellular dimensions. In addition, flexible probes can mitigate shear stress-induced tissue damage due to micromotion. However, both size reduction and flexibility compromise probe's ability to penetrate the pia mater, especially when many electrodes are distributed across multiple probe shanks. In this paper, we present a method to lithographically pattern a biodegradable silk coating that provides temporary mechanical stiffness for the surgical insertion of flexible probes without any conventional design constraints on the probe size, shape, or material. After insertion, the silk is completely dissolved in the tissue, only leaving the flexible minimum-geometry probes inside the brain. We validated the design by successfully inserting silk-backed 64-channel parylene probes into the motor cortex of Long-Evans rats (n=6) and recorded in vivo neural activity for six weeks.