Materials and Devices for Micro-invasive Neural Interfacing
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MRS Advances © 2019 Materials Research Society DOI: 10.1557/adv.2019.424
Materials and Devices for Micro-invasive Neural Interfacing Khalil B. Ramadi1,2, Michael J. Cima1,2,3 1
Koch Institute for Integrative Cancer Research, Massachusetts Institute of Technology, Cambridge, MA 02139. 2
Harvard–MIT Health Sciences and Technology Division, Massachusetts Institute of Technology, Cambridge, MA 02139. 3
Department of Materials Science, Massachusetts Institute of Technology, Cambridge, MA 02139.
ABSTRACT There is widespread research and popular interest in developing micro-invasive neural interfacing modalities. An increasing variety of probes have been developed and reported in the literature. Newer, smaller probes show significant benefit over larger ones in reducing tissue damage and scarring. A different set of obstacles arise, however, as probes become smaller. These include reliable insertion and robustness. This review articulates the impact of various design parameters (material, geometry, size) on probe insertion mechanisms, chronic viability, and glial scarring. We highlight various emerging technologies utilizing novel form factors including micron-scale interfaces and bio-inspired designs for probe insertion and steering.
INTRODUCTION TO NEURAL INTERFACING The brain is a heterogeneous organ composed of various cell and tissue types. Brain structures have traditionally been delineated anatomically. Recent research, however, has begun to re-think how we describe the brain, recognizing it as a network of interconnected nodes. These nodes are constantly communicating in harmony. Various neurological and neuropsychiatric disorders are network disorders where a pathological node introduces dysynchrony into network connectivity [1]. This is, for example, the case for Parkinson’s and
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epilepsy [2]. Rectifying pathologic brain waves relies on our ability to reliably record and manipulate them with a high degree of spatial and temporal specificity.
Methods for Neural Interfacing Neural signaling consists of neurons communicating with each other via electrical impulses along their axons. Each impulse generates a potential, V, with respect to a constant reference potential, Vref. The difference in potentials between two locations results in an electric field across them that can be measured using electroencephalography (EEG). Scalp EEG is most straightforward method to record brain activity, using electrically conducting patches on the scalp as electrodes. It is used clinically to diagnose seizures [3] and sleep apnea [4], and commercially for brain-machine interfacing [5]. The resolution, however, is limited to 2-3 cm [6]. Scalp EEG can diagnose seizures, which result in widespread aberrant signals, but is not able to pinpoint where the seizure onset zone is. The spatial resol
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