Electrochemical Neural Interface and Iontronics
Authors: Chung Taek Dong , Han Seok Hee , Jeon Joohee , Kim Sung Il , Oh Min-Ah , Cho Wonkyung , Yoon Sun-heui , Kim Ji Yong , Shin Chang Il 
Published: December 2020

Electrochemistry is closely related to biological system in many aspects such as the information processing based on electrical signal, and signal transduction of biological phenomena. Many biomarkers or related events can be analyzed in electrochemical manner as a form of biosensor. Sometimes, electrochemistry also endows a breakthrough to bridge the biological system to solid-state electronics, or even to demonstrate biomimetic, bioinspired functions and events. In this talk, we introduce two of our researches; (i) formation of neural interface using an electrode modified with synaptic protein, and (ii) iontronics as a platform for biomimetic, ion-based information signal processing. The former is to make robust interaction platform between neural system and electrode. There have been numerous studies modifying an electrode with a variety of materials such as conducting polymer, hydrogel, and proteins to improve its softness, stability, and in vivo compatibility. We suggested new approach to make a neural interface using a synaptic protein. Synapse is a specialized region in neurons, where the communication between neurons occurs via chemical signaling. Formation of a synapse is triggered by membrane protein binding between neurons. We genetically engineered the neuroligin1(Nlg1) which is known to induce the presynaptic terminal without assistance of other proteins, and immobilize it to solid supports to investigated the feasibility of an induced synapse as a neural interface. Using engineered Nlg1-modified microbeads and primary cultured hippocampal neurons, the durability and scalability of the artificial synapses were examined. Electrode arrays in this work were modified with the engineered Nlg1 to make artificial presynapse-electrode interface.

Secondly, we present iontronics, which ultimately aims at ion-based signal processing just like what is found in neurological systems, or mimicking various biological structures, especially neuronal plasma membrane with support of ionic circuits designed to functionally control the ion flow. Iontronic devices have evolved employing ionic circuits based on charge-selective membranes like polyelectrolyte gels (hydrogels) on microfluidic platform as a form of ionic diode, transistor, logic circuits and many others. The ionic diode composed of a bipolar membrane (BPM) rectifies the ionic current, which is reminiscent of the unidirectional signal transmission in nervous system. We can also construct a fully aqueous and ionic circuitry by combining ionic circuits with reverse electrodialysis (RED) as an ionic power source, where neither external electronic power supply nor metallic component is needed likewise with biological components including neurons. Most recently, we succeeded in materializing hydrogel-based iontronics on PDMS microchip by adopting new chip preparation and chemical functionalization methods. We designed the ionic regulator device on PDMS microchip that outputs several different voltage levels with support of mechanical switch integrated on PDMS substrate, which allowed us to biomimic the characteristics of excitatory and inhibitory synapses. The convergence of electrochemical and neurological knowledge will lead us to open up a new vista in both fields creating numberless inspirations.