Fluidic microactuation of flexible electrodes for neural recording

Abstract

Ultra-flexible microelectrodes that can bend and flex with the natural movement of the brain reduce the inflammatory response and improve the stability of long-term neural recordings.1-5 However, current methods to implant these highly flexible electrodes rely on temporary stiffening agents that increase the electrode size6-10 thus aggravating neural damage during implantation, which leads to cell loss and glial activation that persists even after the stiffening agents are removed or dissolve.11-13 A method to deliver thin, ultra-flexible electrodes deep into neural tissue without increasing the stiffness or size of the electrodes will enable minimally invasive electrical recordings from within the brain. Here we show that specially designed microfluidic devices can apply a tension force to ultra-flexible electrodes that prevents buckling without increasing the thickness or stiffness of the electrode during implantation. Additionally, these “fluidic microdrives” allow us to precisely actuate the electrode position with micron-scale accuracy. To demonstrate the efficacy of our fluidic microdrives, we used them to actuate highly flexible carbon nanotube fiber (CNTf) microelectrodes11,14 for electrophysiology. We used this approach in three proof-of-concept experiments. First, we recorded compound action potentials in a soft model organism, the small cnidarian Hydra. Second, we targeted electrodes precisely to the thalamic reticular nucleus in brain slices and recorded spontaneous and optogenetically-evoked extracellular action potentials. Finally, we inserted electrodes more than 4 mm deep into the brain of rats and detected spontaneous individual unit activity in both cortical and subcortical regions. Compared to syringe injection, fluidic microdrives do not penetrate the brain and prevent changes in intracranial pressure by diverting fluid away from the injection site during insertion and actuation. Overall, the fluidic microdrive technology provides a robust new method to implant and actuate ultra-flexible neural electrodes.

High‐Performance Graphene‐Fiber‐Based Neural Recording Microelectrodes

“…[1] Neural prostheses and therapies based on electrical stimulation or action potential recording, involve electrodes interfaced to central and peripheral nervous systems. [2][3][4] A functional microelectrode is required to communicate with an individual neuron to record bio-signals, while delivering sufficient amount of electrical charge to depolarize the neural tissue and initiate a response. [5] Despite many significant breakthrough discoveries and technological innovations in this field, the existing microelectrode technologies have met significant challenges and limitations.…”

Sputtered porous Pt for wafer-scale manufacture of low-impedance flexible microelectrodes

“…In order to overcome the buckling force that the brain applies to flexible electrodes, they require a shuttle 5,32,33 , stiffener 34 , or tension 35 in order to be implanted. Here we used a silicon shuttle to implant the electrodes using similar methods and materials found in previously published literature 32 .…”

The “sewing machine” for minimally invasive neural recording

“…A second cutting-edge approach uses microfluidic injection of fine carbon-nanotube fibers [52]. This method can be less invasive in that there is no insertion shuttle; however, our approach should reach parity in terms of recording sites / disrupted volume when finer lithography permits 4 or more recording sites per probe.…”