An Experimental Study of Incremental Buckling-Resistant Inchworm-Type Insertion of Microwire Neural Electrodes

Chronically implanting microelectrodes for high-resolution action potential recording is critical for understanding the brain. The smallest and most flexible electrodes, most suitable for chronic recordings, are also the most difficult to insert due to buckling against the thin but hard-to-penetrate brain meninges. To address such implantation challenges without introducing further damage to the brain, this paper presents our design and prototype of an inchworm-type insertion device that conducts a grip-feed-release incremental motion for planar microelectrode insertion. To optimize the operating parameters of the developed inchworm insertion device, experimental studies were conducted on the polyvinyl chloride-based brain-mimicking phantom to investigate the effects of (1) incremental insertion depth, (2) inserter drive shaft rotary speed, and (3) the resulting inchworm insertion speed, on the phantom (1) penetration rupture force and (2) dimpling depth at rupture. Analysis showed that all three factors had a statistically significant impact on the rupture force and dimpling depth. A moderate level of the resulting insertion speed yielded the lowest rupture force and dimpling depth at rupture. Low insertion speed levels were associated with higher rupture force while high insertion speeds led to a large variance in dimpling depth and potential insertion failure. To achieve such a moderate insertion speed, it would be preferred for both the incremental insertion depth and the drive shaft rotary speed to be at a moderate level. Such findings lay the foundation for enabling previously impossible buckling-free insertion of miniaturized flexible planar microelectrodes deep into the brain.