Flexible High-Resolution Force and Dimpling Measurement System for Pia and Dura Penetration During In Vivo Microelectrode Insertion Into Rat Brain.

Lei Chen,Annie Li,Albert Shih,Brendon Watson,Jeremiah Hartner,Tianshu Dong

doi:10.1109/tbme.2021.3070781

Abstract

Objective:Understanding the in vivo force and tissue dimpling during micro-electrode implantation into the brain are important for neuro-electrophysiology to minimize damage while enabling accurate placement and stable chronic extracellular electrophysiological recordings. Prior studies were unable to measure the sub-mN forces exerted during in vivo insertion of small electrodes. Here, we have investigated the in vivo force and dimpling depth profiles during brain surface membrane rupture (including dura) in anesthetized rats.Methods:A µN-resolution cantilever beam-based measurement system was designed, built, and calibrated and adapted for in vivo use. A total of 244 in vivo insertion tests were conducted on 8 anesthetized rats with 121 through pia mater and 123 through dura and pia combined.Results:Both microwire tip sharpening and diameter reduction reduced membrane rupture force (insertion force) and eased brain surface penetration. But dimpling depth and rupture force are not always strongly correlated. Multi-shank silicon probes showed smaller dimpling and rupture force per shank than single shank devices.Conclusion:A force measurement system with flexible range and µN-level resolution (up to 0.032 µN) was achieved and proved feasible. For both pia-only and dura-pia penetrations in anesthetized rats, the rupture force and membrane dimpling depth at rupture are linearly related to the microwire diameter.Significance:We have developed a new system with both µN-level resolution and capacity to be used in vivo for measurement of force profiles of various neural interfaces into the brain. This allows quantification of brain tissue cutting and provides design guidelines for optimal neural interfaces.

Highlights

T HE mammalian brain operates via billions of neurons firing action potentials to transmit electrical signals
Out of the 238 effective microwire insertion tests conducted, the microwire penetrated the membrane in 215 trials and buckled in 23 trials, including 3 buckled trials for pia-only penetration and 20 for dura-pia penetration
An initial rise in the force resulted from the microwire compressing and deforming the the force might become negative because of frictional forces preventing the wire from extraction

Summary

Introduction

T HE mammalian brain operates via billions of neurons firing action potentials to transmit electrical signals. These neuronal electrical signals are believed to underlie cognitive processes (e.g., perception, motion, memory, sleep) [1], [2]. The viability of microwire electrodes for neuronal recordings in live mammals was first demonstrated in 1958 by Strumwasser [4] using 80 μm diameter stainless steel wire electrodes. Microwire-based microelectrodes have demonstrated the ability to record activity for months and even years due to the smaller diameter and greater flexibility, which lessens brain tissue inflammation [23]

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