A cranial window imaging method for monitoring vascular growth around chronically implanted micro-ECoG devices

Abstract

Implantable neural micro-electrode arrays have the potential to restore lost sensory or motor function to many different areas of the body. However, the invasiveness of these implants often results in scar tissue formation, which can have detrimental effects on recorded signal quality and longevity. Traditional histological techniques can be employed to study the tissue reaction to implanted micro-electrode arrays, but these techniques require removal of the brain from the skull, often causing damage to the meninges and cortical surface. This is especially unfavorable when studying the tissue response to electrode arrays such as the micro-electrocorticography (micro-ECoG) device, which sits on the surface of the cerebral cortex. In order to better understand the biological changes occurring around these types of devices, a cranial window implantation scheme has been developed, through which the tissue response can be studied in vivo over the entire implantation period. Rats were implanted with epidural micro-ECoG arrays, over which glass coverslips were placed and sealed to the skull, creating cranial windows. Vascular growth around the devices was monitored for one month after implantation. It was found that blood vessels grew through holes in the micro-ECoG substrate, spreading over the top of the device. Micro-hematomas were observed at varying time points after device implantation in every animal, and tissue growth between the micro-ECoG array and the window occurred in several cases. Use of the cranial window imaging technique with these devices enabled the observation of tissue changes that would normally go unnoticed with a standard device implantation scheme.

The effect of micro-ECoG substrate footprint on the meningeal tissue response

“…The layout of the solid micro-ECoG device was identical to that of the standard, fenestrated micro-ECoG array reported previously (10), except that there were no holes through the Parylene substrate. In the mesh device, since each individual trace was insulated separately and enough insulation was required to create a tight seal around the traces and electrode sites, the total size of the array, in terms of the surface area of cortex it would cover, was larger than that of the fenestrated and solid micro-ECoG devices.…”

“…Micro-ECoG devices were fabricated following the protocol described previously (4,10). In this case, since two electrode arrays were to be implanted in a single animal to allow for direct comparison, both the mesh and the solid micro-ECoG devices were affixed to a single printed circuit board (PCB) connector, with the mesh device on one side of the connector and the solid device on the other side (Figure 1(f)).…”

Patterned Optogenetic Modulation of Neurovascular and Metabolic Signals

“…21 The microelectrocorticography arrays 21,22 were implanted on top of the dura mater to localize cortical activity across the surface of the brain. We used photolithography to define 16 platinum electrode sites (150 μm diameter) in a 4 × 4 grid (0.5-mm site-to-site spacing).…”

Materials approaches for modulating neural tissue responses to implanted microelectrodes through mechanical and biochemical means

“…The ability to image detailed cellular and sub-cellular anatomy in thick sections that contain devices, or in fully intact biological systems (Woolley et al, 2011, 2013a, 2013b, 2013c) are major technological improvements. The ability to image device-tissue interactions in vivo provides another step forward, allowing longitudinal observations (Schendel et al, 2013). Better evaluation techniques will also enable a deeper examination of the contributions of surgical technique variability to the overall variations in tissue responses.…”