Design, fabrication and characterization of a low-impedance 3D electrode array system for neuro-electrophysiology

Perspectives on Scaffold Designs with Roles in Liver Cell Asymmetry and Medical and Industrial Applications by Using a New Type of Specialized 3D Bioprinter

Cellular asymmetry is an important element of efficiency in the compartmentalization of intracellular chemical reactions that ensure efficient tissue function. Improving the current 3D printing methods by using cellular asymmetry is essential in producing complex tissues and organs such as the liver. The use of cell spots containing at least two cells and basement membrane-like bio support materials allows cells to be tethered at two points on the basement membrane and with another cell in order to maintain cell asymmetry. Our model is a new type of 3D bioprinter that uses oriented multicellular complexes with cellular asymmetry. This novel approach is necessary to replace the sequential and slow processes of organogenesis with rapid methods of growth and 3D organ printing. The use of the extracellular matrix in the process of bioprinting with cells allows one to preserve the cellular asymmetry in the 3D printing process and thus preserve the compartmentalization of biological processes and metabolic efficiency.

3D Electrodes for Bioelectronics

In recent studies related to bioelectronics, significant efforts have been made to form 3D electrodes to increase the effective surface area or to optimize the transfer of signals at tissue-electrode interfaces. Although bioelectronic devices with 2D and flat electrode structures have been used extensively for monitoring biological signals, these 2D planar electrodes have made it difficult to form biocompatible and uniform interfaces with nonplanar and soft biological systems (at the cellular or tissue levels). Especially, recent biomedical applications have been expanding rapidly toward 3D organoids and the deep tissues of living animals, and 3D bioelectrodes are getting significant attention because they can reach the deep regions of various 3D tissues. An overview of recent studies on 3D bioelectronic devices, such as the use of electrical stimulations and the recording of neural signals from biological subjects, is presented. Subsequently, the recent developments in materials and fabrication processing to 3D micro- and nanostructures are introduced, followed by broad applications of these 3D bioelectronic devices at various in vitro and in vivo conditions.

Carbon Nanotube Modified Microelectrode Array for Neural Interface

Carbon nanotubes (CNTs) coatings have been shown over the past few years as a promising material for neural interface applications. In particular, in the field of nerve implants, CNTs have fundamental advantages due to their unique mechanical and electrical properties. In this study, carbon nanotubes multi-electrode arrays (CNT-modified-Au MEAs) were fabricated based on gold multi-electrode arrays (Au-MEAs). The electrochemical impedance spectra of CNT-modified-Au MEA and Au-MEA were compared employing equivalent circuit models. In comparison with Au-MEA (17 Ω), CNT-modified-Au MEA (8 Ω) lowered the overall impedance of the electrode at 1 kHz by 50%. The results showed that CNT-modified-Au MEAs have good properties such as low impedance, high stability and durability, as well as scratch resistance, which makes them appropriate for long-term application in neural interfaces.

Design and Fabrication of a Three-Dimensional Multi-Electrode Array for Neuron Electrophysiology

Neural recording and stimulation with high spatial and temporal resolution are highly desirable in the study of neurocommunication and diseases. Planar multiple microelectrode arrays (MEA) or quasi-three-dimensional (3D) MEA with fixed height have been proposed by many researchers and become commercially available. In this paper, we present the design, fabrication, and test of a novel true 3D multiple electrode array for brain slice stimulation and recording. This MEA is composed of 105 microelectrodes with 50 μm diameter and 125 μm center-to-center spacing integrated in a 1.2 × 1.2 mm2 area. This "true" 3D MEA allows us to precisely position the individual electrodes by piezoelectric-based actuators to penetrate the inactive tissue layer and to approach the active neurons so as to optimize the recording and stimulation of electrical field potential. The capability to stimulate nerve fibers and record postsynaptic field potentials was demonstrated in an experiment using mouse brain hippocampus slice.

Electrical Characterization of 3D Au Microelectrodes for Use in Retinal Prostheses

In order to provide high-quality visual information to patients who have implanted retinal prosthetic devices, the number of microelectrodes should be large. As the number of microelectrodes is increased, the dimensions of each microelectrode must be decreased, which in turn results in an increased microelectrode interface impedance and decreased injection current dynamic range. In order to improve the trade-off envelope between the number of microelectrodes and the current injection characteristics, a 3D microelectrode structure can be used as an alternative. In this paper, the electrical characteristics of 2D and 3D Au microelectrodes were investigated. In order to examine the effects of the structural difference, 2D and 3D Au microelectrodes with different base areas but similar effective surface areas were fabricated and evaluated. Interface impedances were measured and similar dynamic ranges were obtained for both 2D and 3D Au microelectrodes. These results indicate that more electrodes can be implemented in the same area if 3D designs are used. Furthermore, the 3D Au microelectrodes showed substantially enhanced electrical durability characteristics against over-injected stimulation currents, withstanding electrical currents that are much larger than the limit measured for 2D microelectrodes of similar area. This enhanced electrical durability property of 3D Au microelectrodes is a new finding in microelectrode research, and makes 3D microelectrodes very desirable devices.