Electrodes serve as the first critical interface to the biological organ system. In neuroprosthetic applications, for example, electrodes interface to the tissue for either signal recording or tissue stimulation. In this review, we consider electrodes for recording neural activity. Recording electrodes serve as wiretaps into the neural tissues, providing readouts of electrical activity. These signals give us valuable insights into the organization and functioning of the nervous system. The recording interfaces have also shown promise in aiding treatment of motor and sensory disabilities caused by neurological disorders. Recent advances in fabrication technology have generated wide interest in creating tiny, high-density electrode interfaces for neural tissues. An ideal electrode should be small enough and be able to achieve reliable and conformal integration with the structures of the nervous system. As a result, the existing electrode designs are being shrunk and packed to form small form factor interfaces to tissue. Here, an overview of the historic and state-of-the-art electrode technologies for recording neural activity is presented first with a focus on their development road map. The fact that the dimensions of recording electrode sites are being scaled down from micron to submicron scale to enable dense interfaces is appreciated. The current trends in recording electrode technologies are then reviewed. Current and future considerations in electrode design, including the use of inorganic nanostructures and biologically inspired or biocomapatible materials are discussed, along with an overview of the applications of flexible materials and transistor transduction schemes. Finally, we detail the major technical challenges facing chronic use of reliable recording electrode technology.
Neural
electrodes are developed for direct communication with neural
tissues for theranostics. Although various strategies have been employed
to improve performance, creating an intimate electrode–tissue
interface with high electrical fidelity remains a great challenge.
Here, we report the rational design of a tunnel-like electrode coating
comprising poly(3,4-ethylenedioxythiophene) (PEDOT) and carbon nanotubes
(CNTs) for highly sensitive neural recording. The coated electrode
shows a 50-fold reduction in electrochemical impedance at the biologically
relevant frequency of 1 kHz, compared to the bare gold electrode.
The incorporation of CNT significantly reinforces the nanotunnel structure
and improves coating adhesion by ∼1.5 fold. In vitro primary neuron culture confirms an intimate contact between neurons
and the PEDOT-CNT nanotunnel. During acute in vivo nerve recording, the coated electrode enables the capture of high-fidelity
neural signals with low susceptibility to electrical noise and reveals
the potential for precisely decoding sensory information through mechanical
and thermal stimulation. These findings indicate that the PEDOT-CNT
nanotunnel composite serves as an active interfacing material for
neural electrodes, contributing to neural prosthesis and brain–machine
interface.
He maintains his position as a Professor of Biomedical Engineering, Electrical and Computer Engineering, and Neurology at Johns Hopkins University in USA. His technical expertise is in the field of neuroengineering, including neural instrumentation, neuromorphic engineering, neural microsystems, optical imaging of the nervous system, neural control of prosthesis, brain-machine interfaces, and cognitive engineering.
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