Polymer-based micro-electrode arrays effectively and safely map brain activity

BrainResearchers at the USC Viterbi School of Engineering in Los Angeles, CA, have developed thin, flexible polymer-based materials for use in micro-electrode arrays to record brain activity. Made of Parylene C, the arrays perform as well as microwire-based devices in terms of recording fidelity and sensitivity, said a researcher. They are also less invasive and gentler on brain tissue and, thus, can be used for longer periods of time.

A paper describing the research, “Acute in vivo testing of a conformal polymer microelectrode array for multi-region hippocampal recordings,” has been published in the Journal of Neural Engineering.

“The information that we can get out is equivalent [to micro-wire or silicone devices], but the damage is much less,” said Professor Ellis Meng of the USC Viterbi Department of Biomedical Engineering. Moreover, the technology allows more specific micro-electrode placement.

Each array is made up of eight “tines,” each with eight micro-electrodes that can simultaneously record from a total of 64 subregions of the brain.

Because the long, thin polymer probes easily buckle upon insertion, a dissolvable brace made of polyethylene glycol (PEG) is used to prevent them from bending.

As with any prosthetic implant, caution must be exercised in terms of the body’s natural immune response to a foreign element, writes Breanne Grady, who reported on the research on the USC Viterbi website. In addition to inflammation, previous micro-electrode brain implants made of silicon or microwires have caused neuronal death and scarred connective tissue in the nervous system. Parylene C is biocompatible and can be microfabricated in extremely thin form to mold well to specific subregions of the brain, allowing for exploration with minimal damage, notes Grady.

So far, the arrays have been used to record synaptic responses of individual neurons within the hippocampus, a part of the brain responsible for memory formation. Injury to the hippocampus may result in a patient’s inability to form new memories. The polymer-based material can conform to a specific location in the hippocampus and “listen in on a conversation” between neurons, said Meng. Because there are many such “eavesdroppers” (i.e., the microelectrodes), much more information about neurons' interconnectivity can be gleaned, reports Grady.

Future research will determine the recording lifetime of polymer-based arrays and their long-term signal-to-noise stability. Also, the team plans to create devices with even higher density, including a double-sided micro-electrode array with 64 electrodes per tine instead of eight, making for a total of around 4,000 electrodes placed in the brain at once.

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