Shota Yamagiwa

Flexible parylene-film optical waveguide arrays

Modulation of neuronal activities by light [e.g., laser or light-emitting diode] using optogenetics is a powerful tool for studies on neuronal functions in a brain. Herein, flexible thin-film optical waveguide arrays based on a highly biocompatible material of parylene are reported. Parylene-C and -N thin layers with the different refractive indices form the clad and the core of the waveguide, respectively, and neural recording microelectrodes are integrated to record optical stimuli and electrical recordings simultaneously using the same alignment. Both theoretical and experimental investigations confirm that light intensities of more than 90% can propagate in a bent waveguide with a curvature radius of >5 mm. The proposed flexible thin-film waveguide arrays with microelectrodes can be used for numerous spherical bio-tissues, including brain and spinal cord samples.

Self-curling and -sticking flexible substrate for ECoG electrode array

We report a flexible electrocorticogram (ECoG) electrode array device with one directionally self-curling and -sticking properties, to solve the difficulty of the handling of thin (<; 10 μm) substrate devices (Fig. 1). As the substrate, we use sandwiched parylene-N/-C which films have different linear expansion coefficients. The thermal dependences of the deflection and curvature radius of the paylene-N/-C system were calculated. Based on the calculations, 2.5-μm parylene-N/2.5-μm paryelen-C “bi-parylene” flexible substrate was prepared. The self-curled substrate with the curvature radius of about 2 mm has been observed. The self-sticking of the curled device has been demonstrated on wet samples, due to the surface tension between the parylene-N and the sample. These results suggest that the bi-parylene substrate becomes a candidate material for easy-to-use flexible thin ECoG devices, enchaining the wrapping property over the brain.

Dissolvable Base Scaffolds Allow Tissue Penetration of High-Aspect-Ratio Flexible Microneedles

Microscale needle technology is important in electrophysiological studies, drug/chemical delivery systems, optogenetic applications, and so on. In this study, dissolvable needle-base scaffold realizes penetration of high-aspect-ratio flexible microneedles (e.g., <5 μm diameter and >500 μm length) into biological tissues. This methodology, which is applicable to numerous high-aspect-ratio flexible microneedles, should reduce the invasiveness and provide safer tissue penetrations than conventional approaches.

A thin film flexible antenna with CMOS rectifier chip for RF-powered implantable neural interfaces

This paper reports a parylene film antenna integrating a CMOS rectifier chip for wireless neural recording devices. An implanted antenna requires the flexibility to fit the shape of brain surface. In addition, an integrating technology with solid-state and flexible substrate is needed because a silicon chip can provide high-performance and multi-functionality. The fabricated device that packages antenna, transformer, and rectifier generates more than 1.5V and achieves a power transmission efficiency of 0.086 %.

Co-Design Method and Wafer-Level Packaging Technique of Thin-Film Flexible Antenna and Silicon CMOS Rectifier Chips for Wireless-Powered Neural Interface Systems

In this paper, a co-design method and a wafer-level packaging technique of a flexible antenna and a CMOS rectifier chip for use in a small-sized implantable system on the brain surface are proposed. The proposed co-design method optimizes the system architecture, and can help avoid the use of external matching components, resulting in the realization of a small-size system. In addition, the technique employed to assemble a silicon large-scale integration (LSI) chip on the very thin parylene film (5 μm) enables the integration of the rectifier circuits and the flexible antenna (rectenna). In the demonstration of wireless power transmission (WPT), the fabricated flexible rectenna achieved a maximum efficiency of 0.497% with a distance of 3 cm between antennas. In addition, WPT with radio waves allows a misalignment of 185% against antenna size, implying that the misalignment has a less effect on the WPT characteristics compared with electromagnetic induction.

Micro-electrode arrays for multi-channel motor unit EMG recording

We report an array of micro-electrodes, which can record multi-channel motor unit (MU) electromyogram (EMG) signals with a high spatial resolution. As a basic structure of the electrode, we fabricated an array of 200-μm-square Si-pyramids with the height of 200 μm by Tetramethylammonium hydroxide (TMAH), in order for robust MU-EMG recordings without conductive gel. Platinum (Pt) was used as the electrode material and parylene-C was used as the insulator for the Pt-electrode. The fabricated μEMG electrode array, which was connected to a recording system, clearly detected MU-EMG action potentials from a human forearm. In addition, different MU-EMG signals between the μEMG electrodes were detected by crooking the fingers. These results indicate that the μEMG array device becomes a powerful tool for medical applications including myoelectric prosthetic technologies.

High-performance microelectrode of PEDOT/Pt-black for low voltage neurostimulaiton

Here we report a material for low-voltage and micro-scale electrode stimulation, that combines high charge injecting and low impedance characteristics of poly (3, 4-ethylenedioxythiophene) (PEDOT) with a large effective surface area by using a platform of platinum black (Pt-black). The layer-by-layer assembled PEDOT/Pt-black electrode with the diameter of 30 μm exhibits the charge-injection delivery capacity (QCDC) is 684 mC/cm2, which is 1.6 times value of the same-sized Pt-black electrode. In vivo animal experiments confirm that the 8-μm-diameter PEDOT/Pt-black electrode enables the electrical stimulation of mouses nerves with the voltage of 400 mV, which value is lower than conventional electrodes. The proposed small diameter and high QCDC electrode potentially offers powerful applications, including low voltage stimulation and stimulations of individual neurons in which the cell body has a diameter of ~10 μm.

Single 5 μm diameter needle electrode block modules for unit recordings in vivo

Investigations into mechanisms in various cortical areas can be greatly improved and supported by stable recording of single neuronal activity. In this study, fine silicon wire electrodes (diameter 3 μm, length 160 μm) are fabricated by vapor–liquid–solid (VLS) growth with the aim of stabilizing recording and reducing the invasiveness on the measurement procedure. The electrode is fabricated on a modular 1 ×  1 mm2 conductive silicon block that can be assembled into a number of different device packages, for example on rigid or flexible printed circuit boards (PCB). After plating with a 5 μm diameter platinum black, the needle exhibits an electrical impedance of ~100 kΩ at 1 kHz in saline. The in vivo recording capability of the device is demonstrated using mice, and spike signals with peak-to-peak amplitudes of 200−300 μV in the range 0.5−3 kHz are stably detected, including single-unit activities in cortical layer 2/3. In addition, the device packaged with a flexible PCB shows stable unit recordings for 98.5 min (n = 4). Consequently, our modular, low-invasive needle electrode block devices present an effective route for single-unit recordings in vivo, as well as demonstrating adaptability in device design for a diverse range of experiments.

Vertically aligned extracellular microprobe arrays/(111) integrated with (100)-silicon mosfet amplifiers

We report a heterogeneous integration of vertically aligned extracellular micro-scale silicon (Si)-probe arrays/(111) with MOSFET amplifiers/(100), by IC processes and subsequent vapor-liquid-solid (VLS) growth of Si-probes. To improve the extracellular recording capability of the microprobe with a high impedance of > 1 MΩ at 1 kHz, here we integrated (100)-Si source follower buffer amplifiers by ~700°C VLS growth compatible (100)-Si MOSFET technology. Without on-chip source follower, output/input signal ratio of the microprobe in saline was 0.59, which was improved to 0.72 by the on-chip source follower configuration, while the signal-to-noise ratio (SNR) was improved to 12.5 dB in the frequency of extracellular recording. These results indicate that the integration of the source follower buffer amplifiers becomes a powerful way to enhance the performance of high impedance microprobe electrodes in neural recordings.

Layer-by-layer nanoassembly of iridium oxide/platinum-black for low impedance, high charge injecting microelectrode applications

We report an electrode device with a low impedance and high charge injecting characteristics for a powerful application to micro/nano-scale electrophysiological measurements of neuron/cells. Due to the small effective electrode area, conventional microelectrodes exhibit high interfacial electrode impedance (~10 MΩ at 1 kHz) and low charge injection characteristics, making the targeted cells impossible to record/stimulate. To overcome these limitations, we propose enhanced surface-area of an electrode with a low impedance material, based on layer-by-layer assembled iridium oxide (IrOx)/platinum-black (Pt-black) with nano-scale roughness. The assembled nanorough-IrOx/Pt-black electrode exhibits 2 times lower impedance and 2.4 times larger injection delivery capacity (QCDC) compared to a planer-IrOx electrode with the same size. Additionally, we fabricated nanorough-Ir/Pt-black tipped microprobes and demonstrated in saline, while improved stimulating currents were observed.