Silk-Backed Structural Optimization of High-Density Flexible Intracortical Neural Probes

Abstract

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.[2014-0249]

A Removable Insertion Shuttle for Ultraflexible Neural Probe Implantation with Stable Chronic Brain Electrophysiological Recording

“…However, the low stiffness of flexible neural probe makes it susceptible to bending and buckling during insertion into the brain. To deal with this dilemma, several delicate strategies have been developed to guide the insertion such as transient shuttles with dissolvable support materials such as silk, sugars, hydrogel or polyethylene glycol (PEG) as coatings, metal as rigid backbone layers for insertion, and removable shuttles with SU‐8 shanks or microneedles as temporary carriers. To remove the need of additional materials that may displace tissue in shuttle strategies, mechanically adaptive materials that change modulus on exposure to physiological conditions have been utilized as the probe substrates despite the potential biocompatibility issue.…”

Electron-beam lithography for polymer bioMEMS with submicron features

“…The prototype neural probe shown here is an example of how improved fabrication capabilities can aid polymer MEMS development for biomedical devices. At 32 recording sites on a single polymer shank (133 per mm 2 ), this device has more than double the electrode density of any prior polymer probe 9 , and four times the density of any prior Parylene C-based probe 36 . This is primarily achieved through the narrow width and small spacing of the connective traces, although patterning of the recording sites is designed to increase surface area and reduce electrochemical impedance, allowing for reduction in electrode area without sacrificing fidelity.…”

State-of-the-art MEMS and microsystem tools for brain research

“…In addition, an insertion aid that has a sharp, rigid tip is necessary to pierce the dura or pia matter of the brain (Figure 1). One approach involves the creation of a biodegradable stiffener using silk over a thin parylene-C structure and shaping the silk with a microfabricated mold 123 . As indicated by Equation (2) (rectangular cantilever stiffness),…”