Abstract
To understand the brain functioning mechanisms,electrophysiological methods represent the most matureapproach for recording brain dynamics at millisecond timescalesin either local or large spatial scales. Microwire-basedmicroelectrode arrays (MEAs) are a well-established tool forchronic recording of electrophysiologic signals and furthermorehave the advantage of minimal brain damage if constructed fromcellular-scale (4-100 μm neuron diameter) microwires.However, such cellular-scale MEAs are not widely used byneuroscientists, especially on deep insertion cases, due to thebarrier of implantation. Efforts to reduce the size of microwiresbring collateral difficulties due to buckling during penetrationthrough membranes (dura/pia) and consequent inability toimplant deeply into the brain or in a manner that leaves intactprotective biolayers such as the dura mater. In this paper, wedeveloped a custom skull cap with precision guide holes tostabilize the brain and dura, provide sufficient support tomicrowire along the insertion path, and minimize theunsupported length of microwire during dura penetration anddeeper insertion. A cap matched to individual skull anatomy withoffset for brain stabilization was designed based on computedtomography (CT) scan of the rat head and fabricated bystereolithography. Micro-milling and wax molding wereconducted to fabricate precision insertion guide inside the cap.Animal surgical studies were conducted to test the performanceof skull cap and insertion guide. Rats with skull cap attached hadsurvived for multiple weeks until sacrificed by experimenters.Through a test cube with precision guide, a 25 μm diametertungsten microwire penetrated through the dura mater and wasmanually inserted over 10 mm into the brain without buckling.In comparison, without the precision guide, insertion of the samemicrowire caused over 2 mm dimpling of the dura withoutpenetration and finally led to wire buckling. Results showed thatthe custom skull cap with precision guide holes enabled the insertion of cellular-scale microwire electrodes deep into thebrain through the dura mater without buckling.