Recent Progress on Microelectrodes in Neural Interfaces

Abstract

Brain‒machine interface (BMI) is a promising technology that looks set to contribute to the development of artificial limbs and new input devices by integrating various recent technological advances, including neural electrodes, wireless communication, signal analysis, and robot control. Neural electrodes are a key technological component of BMI, as they can record the rapid and numerous signals emitted by neurons. To receive stable, consistent, and accurate signals, electrodes are designed in accordance with various templates using diverse materials. With the development of microelectromechanical systems (MEMS) technology, electrodes have become more integrated, and their performance has gradually evolved through surface modification and advances in biotechnology. In this paper, we review the development of the extracellular/intracellular type of in vitro microelectrode array (MEA) to investigate neural interface technology and the penetrating/surface (non-penetrating) type of in vivo electrodes. We briefly examine the history and study the recently developed shapes and various uses of the electrode. Also, electrode materials and surface modification techniques are reviewed to measure high-quality neural signals that can be used in BMI.

Keywords: brain‒machine interface (BMI); chronically implanted neural electrodes; electroencephalogram (EEG) electrode; microelectrode array (MEA); neural electrode; surface modification.

Figure 1

(a) Myocytes of embryonic chicken ventricles are cultured on the planar type MEA as cell culture dish [20]. (b) A whole embryonic heart is kept on a MEA [20]. (c) Each electrode is connected with a contact pad by conductor lines [20]. Copyright 2003, Springer-Verlag.

Figure 2

(a) Whole cell patch electrode configuration [8]. Copyright 2013, Nature Publication; (b) SEM image of the vertical nanowire electrode arrays [29]. Copyright 2012, Nature Publication; (c) TiO_2 nanotube arrays with 100 nm diameter [26]. Copyright 2007, ACS Publication.

Figure 3

The types of microwire neural electrode (a) single wire [38], Copyright 2017, Elsevier; (b) Tetrode [39], Copyright 2017, Elsevier; (c) multi-wire electrode [40], Copyright 2010, Frontiers.

Figure 4

Representative microelectrode (a) Utah electrode [70], Copyright 1999, Elsevier; (b) Michigan electrode [71], Copyright 2004, Elsevier.

Figure 5

(a) Flexible polymer based electrode [76], Copyright 2013, Nature Publication; (b) Polymer electrode with micro channel [81], Copyright 2015, Nature Publication; (c) The 3D polymer electrode [82], Copyright 2013, Nature Publication.

Figure 6

Invasive dry EEG electrodes. (a) MWCNT array [115], Copyright 2008, Elsevier; (b) pin-shaped (up) and cylinder-shaped conductive polymer dry electrodes (down) [116], Copyright 2014, MDPI.

Figure 7

Non-invasive dry EEG electrodes (a) 3D printed electrode [117], Copyright 2012, Elsevier; (b) dry electrode with 17spring contact probes [120], Copyright 2011, MDPI; (c) flexible dry electrode [119], Copyright 2016, Elsevier.

Figure 8

Applications of flexible and stretchable electronics (a) Epidermal electronics on PDMS. Image of a demonstration platform for multifunctional electronics and a commercial temporary transfer tattoo onto skin [137], Copyright 2011, Science Publication; (b) brain‒machine interface on polyamide. Electrode arrays placed on the visual cortex [141], Copyright 2011, Nature Publication; (c) electrocardiogram mapping devices on Ecoflex. Sensor web with no slip page up to ∼22% strain [143], Copyright 2012, National Academy of Sciences; (d) smart or minimally invasive surgical tools on PDMS. Multifunctional inflatable balloon catheters [145], Copyright 2011, Nature Publication.

Figure 9

Various surface modification techniques for improved neural signal recording performance. (a) Electrode modified with CNTs by electrodeposition [180], Copyright 2008, Nature Publishing; (b) electrode modified with gold nanograins [165], Copyright 2013, WILEY-VCH Verlag; (c) electrode modified with platinum nanopillars [169], Copyright 2012, Nature Publishing; (d) electrode modified with CNT‒Au nanocomposite hierarchical structures [184], Copyright 2017, Elsevier.