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Special Issue "Selected Papers from the 12th Symposium on Micro-Nano Science and Technology on Micromachines"

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A special issue of Micromachines (ISSN 2072-666X).

Deadline for manuscript submissions: closed (30 April 2022) | Viewed by 20711

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Special Issue Editors

Prof. Dr. Takashi Tokumasu

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Guest Editor

Institute of Fluid Science (IFS), Tohoku University, Sendai 980-8577, Japan
Interests: nanoscale flow; molecular simulation; fuel cell; battery; semiconductor fabrication
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Prof. Dr. Takashi Abe

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Guest Editor

Faculty of Engineering, Niigata University, Niigata 950-2181, Japan
Interests: microfabrication; MEMS; sensors

Prof. Dr. Tetsuo Kan

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Department of Mechanical and Intelligent Systems Engineering, The University of Electro-Communications, Tokyo 182-8585, Japan
Interests: MEMS; plasmonics; metamaterials
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Prof. Dr. Masahiro Motosuke
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Guest Editor

Faculty of Engineering, Tokyo University of Science, Tokyo 125-8585, Japan
Interests: thermal and fluid science; microfluidics
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

This Special Issue will publish selected papers from the 12th Symposium on Micro-Nano Science and Technology on Micromachines, 9–11 November 2021.

We encourage contributions on significant and original works in order to understand physical, chemical, and biological phenomena at the micro/nano scales and to develop applied technologies. The conference will cover the following main topics:

1: Precision machinery, lubrication, and design;
2: Material mechanics;
3: Fluid mechanics;
4: Thermal science and engineering;
5: Production processing and mechanical materials;
6: Robotics and mechatronics;
7: Medical biotechnology;
8: Micro/nano system.

Papers attracting the most interest at the conference, or that provide novel contributions, will be selected for publication in Micromachines. These papers will be peer-reviewed for validation of research results, developments, and applications.

Prof. Dr. Takashi Tokumasu
Prof. Dr. Takashi Abe
Prof. Dr. Tetsuo Kan
Prof. Dr. Masahiro Motosuke
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Micromachines is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

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Published Papers (10 papers)

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Research

11 pages, 4056 KiB

Open AccessArticle

Development of a Flexible MEMS Sensor for Subsonic Flow

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Micromachines 2022, 13(8), 1299; https://doi.org/10.3390/mi13081299 - 12 Aug 2022

Viewed by 3258

Abstract

Detection and control of flow separation is a key to improving the efficiency of fluid machinery. In this study, we developed a flexible MEMS (microelectromechanical systems) sensor for measuring the wall shear stress and flow angle in subsonic airflow. The developed sensor is made of a flexible polyimide film and a microheater surrounded by three temperature sensor pairs. The sensor measures the wall shear stress from the heater output and the flow angle from the temperature gradient around the heater. The geometry and design of the heater and temperature sensors were determined based on numerical simulations. To evaluate the validity of the sensor, we conducted an experiment to measure the wall shear stress and the flow angle in a wind tunnel in different velocities ranging from 30 m/s to 170 m/s, equivalent to Mach numbers from 0.1 to 0.5. The heater output was proportional to one-third power of the wall shear stress. Additionally, the bridge output correlating the temperature difference between two opposing temperature sensors showed sinusoidal variation depending on the flow angle. Consequently, we have clarified that the developed sensor can measure both the wall shear stress and flow direction in subsonic flow. Full article

(This article belongs to the Special Issue Selected Papers from the 12th Symposium on Micro-Nano Science and Technology on Micromachines)

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9 pages, 3393 KiB

Open AccessArticle

Large Curvature Self-Folding Method of a Thick Metal Layer for Hinged Origami/Kirigami Stretchable Electronic Devices

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Micromachines 2022, 13(6), 907; https://doi.org/10.3390/mi13060907 - 08 Jun 2022

Cited by 10 | Viewed by 2504

Abstract

A self-folding method that can fold a thick (~10 μm) metal layer with a large curvature (>1 mm⁻¹) and is resistant to repetitive folding deformation is proposed. Given the successful usage of hinged origami/kirigami structures forms in deployable structures, they show strong potential for application in stretchable electronic devices. There are, however, two key difficulties in applying origami/kirigami methods to stretchable electronic devices. The first is that a thick metal layer used as the conductive layer of electronic devices is too hard for self-folding as it is. Secondly, a thick metal layer breaks on repetitive folding deformation at a large curvature. To overcome these difficulties, this paper proposes a self-folding method using hinges on a thick metal layer by applying a meander structure. Such a structure can be folded at a large curvature even by weak driving forces (such as those produced by self-folding) and has mechanical resistance to repetitive folding deformation due to the local torsional deformation of the meander structure. To verify the method, the large curvature self-folding of thick metal layers and their mechanical resistance to repetitive folding deformation is experimentally demonstrated. In addition, an origami/kirigami hybrid stretchable electronic device with light-emitting diodes (LEDs) is fabricated using a double-tiling structure called the perforated extruded Miura-ori. Full article

(This article belongs to the Special Issue Selected Papers from the 12th Symposium on Micro-Nano Science and Technology on Micromachines)

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11 pages, 2660 KiB

Open AccessArticle

Efficient Cell Impedance Measurement by Dielectrophoretic Cell Accumulation and Evaluation of Chondrogenic Phenotypes

Natsumi Nakata

Yuko Ishibashi

and

Shogo Miyata

Micromachines 2022, 13(6), 837; https://doi.org/10.3390/mi13060837 - 27 May 2022

Cited by 1 | Viewed by 1286

Abstract

The quantitative and functional analyses of cells are important for cell-based therapies. In this study, to establish the quantitative cell analysis method, we propose an impedance measurement method supported by dielectrophoretic cell accumulation. An impedance measurement and dielectrophoresis device was constructed using opposing comb-shaped electrodes. Using dielectrophoresis, cells were accumulated to form chain-like aggregates on the electrodes to improve the measurement sensitivity of the electrical impedance device. To validate the proposed method, the electrical impedance and capacitance of primary and de-differentiated chondrocytes were measured. As a result, the impedance of the chondrocytes decreased with an increase in the passage number, whereas the capacitance increased. Therefore, the impedance measurement method proposed in this study has the potential to identify chondrocyte phenotypes. Full article

(This article belongs to the Special Issue Selected Papers from the 12th Symposium on Micro-Nano Science and Technology on Micromachines)

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10 pages, 5329 KiB

Open AccessArticle

Gap Effect on Electric Field Enhancement and Photothermal Conversion in Gold Nanostructures

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Micromachines 2022, 13(5), 801; https://doi.org/10.3390/mi13050801 - 21 May 2022

Viewed by 1495

Abstract

Plasmonic optical tweezers and thermophoresis are promising tools for nanomaterial manipulation. When a gold nanostructure is irradiated with laser light, an electric field around the nanostructure is enhanced because of the localized surface plasmon resonance, which increases the optical radiation pressure applied to the nanomaterials. In addition, a temperature gradient is also generated by the photothermal conversion, and thermophoretic force is then generated. This study numerically evaluated the electric and temperature fields induced by the localized surface plasmon resonance between two gold nanostructures. Here, we focused on the effect of the gap width between nanostructures on the optical radiation pressure and thermophoretic force. The simulation results show that the electric field is locally enhanced according to the gap width, but the effect on the temperature rise due to the photothermal heating is small. This fact suggests that the gap effect between the nanostructures is particularly dominant in nanomanipulation using optical force, whereas it has little effect in nanomanipulation using thermophoresis. Full article

(This article belongs to the Special Issue Selected Papers from the 12th Symposium on Micro-Nano Science and Technology on Micromachines)

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19 pages, 4879 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Oscillation Characteristics of an Artificial Cochlear Sensory Epithelium Optimized for a Micrometer-Scale Curved Structure

Hiroki Yamazaki

Yutaro Kohno

and

Satoyuki Kawano

Micromachines 2022, 13(5), 768; https://doi.org/10.3390/mi13050768 - 13 May 2022

Viewed by 1516

Abstract

Based on the modern microelectromechanical systems technology, we present a revolutionary miniaturized artificial cochlear sensory epithelium for future implantation tests on guinea pigs. The device was curved to fit the spiral structure of the cochlea and miniaturized to a maximum dimension of <1 mm to be implanted in the cochlea. First, the effect of the curved configuration on the oscillation characteristics of a trapezoidal membrane was evaluated using the relatively larger devices, which had a trapezoidal and a comparable curved shape designed for high-precision in vitro measurements. Both experimental and numerical analyses were used to determine the resonance frequencies and positions, and multiple oscillation modes were clearly observed. Because the maximum oscillation amplitude positions, i.e., the resonance positions, differed depending on the resonance frequencies in both trapezoidal and curved membrane devices, the sound frequency was determined based on the resonance position, thus reproducing the frequency selectivity of the basilar membrane in the organ of Corti. Furthermore, the resonance frequencies and positions of these two devices with different configurations were determined to be quantitatively consistent and similar in terms of mechanical dynamics. This result shows that despite a curved angle of 50–60°, the effect of the curved shape on oscillation characteristics was negligible. Second, the nanometer-scale oscillation of the miniaturized device was successfully measured, and the local resonance frequency in air was varied from 157 to 277 kHz using an experimental system that could measure the amplitude distribution in a two-dimensional (2D) plane with a high accuracy and reproducibility at a high speed. The miniaturized device developed in this study was shown to have frequency selectivity, and when the device was implanted in the cochlea, it was expected to discriminate frequencies in the same manner as the basilar membrane in the biological system. This study established methods for fabricating and evaluating the miniaturized device, and the proposed miniaturized device in a curved shape demonstrated the feasibility of next-generation cochlear implants. Full article

(This article belongs to the Special Issue Selected Papers from the 12th Symposium on Micro-Nano Science and Technology on Micromachines)

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9 pages, 3216 KiB

Open AccessArticle

Influences of Microscopic Imaging Conditions on Accuracy of Cell Morphology Discrimination Using Convolutional Neural Network of Deep Learning

Masashi Yamamoto

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Shogo Miyata

Micromachines 2022, 13(5), 760; https://doi.org/10.3390/mi13050760 - 11 May 2022

Cited by 1 | Viewed by 1425

Abstract

Recently, automated cell culture devices have become necessary for cell therapy applications. The maintenance of cell functions is critical for cell expansion. However, there are risks of losing these functions, owing to disturbances in the surrounding environment and culturing procedures. Therefore, there is a need for a non-invasive and highly accurate evaluation method for cell phenotypes. In this study, we focused on an automated discrimination technique using image processing with a deep learning algorithm. This study aimed to clarify the effects of the optical magnification of the microscope and cell size in each image on the discrimination accuracy for cell phenotypes and morphologies. Myoblast cells (C2C12 cell line) were cultured and differentiated into myotubes. Microscopic images of the cultured cells were acquired at magnifications of 40× and 100×. A deep learning architecture was constructed to discriminate between undifferentiated and differentiated cells. The discrimination accuracy exceeded 90% even at a magnification of 40× for well-developed myogenic differentiation. For the cells under immature myogenic differentiation, a high optical magnification of 100× was required to maintain a discrimination accuracy over 90%. The microscopic optical magnification should be adjusted according to the cell differentiation to improve the efficiency of image-based cell discrimination. Full article

(This article belongs to the Special Issue Selected Papers from the 12th Symposium on Micro-Nano Science and Technology on Micromachines)

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8 pages, 3022 KiB

Open AccessArticle

Extraction and Evaluation of Discriminative Indexes of the Wearing Condition for High-Precision Blood Pressure Pulse Wave Measurement

Yosuke Osawa

and

Tetsuji Dohi

Micromachines 2022, 13(5), 679; https://doi.org/10.3390/mi13050679 - 27 Apr 2022

Viewed by 1010

Abstract

In this paper, we report a new discriminant index for evaluating the wearing condition of a blood pressure pulse wave measurement device with small variability. The prototype device consists of MEMS 3-axis force sensors, a 3-axis push-in adjustment mechanism, a fixed jig, and a signal processing board. The arterial tonometry method is used by this device to measure blood pressure pulse waves. However, to accurately measure the blood pressure pulse wave, the device must be appropriately worn. The evaluation of the wearing condition using the amplitude of the blood pressure pulse wave was complicated by the wearing process due to the large variability. Therefore, we propose the ratio of the blood pressure pulse wave component to the noise component as an index that can evaluate the wear condition of the device. The correlation coefficient between the discriminant index and the amplitude of the blood pressure pulse wave had a correlation coefficient of 0.879. Furthermore, the discriminant index reduced the coefficient of variation by 12.8%. Therefore, it was suggested that the discriminant index is an index that can evaluate the pressing amount, one of the wearing conditions of the blood pressure pulse wave measurement device with a small influence of variation. Full article

(This article belongs to the Special Issue Selected Papers from the 12th Symposium on Micro-Nano Science and Technology on Micromachines)

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13 pages, 19309 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Frequency Characteristics of Pulse Wave Sensor Using MEMS Piezoresistive Cantilever Element

Taiga Nabeshima

Thanh-Vinh Nguyen

and

Hidetoshi Takahashi

Micromachines 2022, 13(5), 645; https://doi.org/10.3390/mi13050645 - 19 Apr 2022

Cited by 3 | Viewed by 2342

Abstract

Wearable sensor devices with minimal discomfort to the wearer have been widely developed to realize continuous measurements of vital signs (body temperature, blood pressure, respiration rate, and pulse wave) in many applications across various fields, such as healthcare and sports. Among them, microelectromechanical systems (MEMS)-based differential pressure sensors have garnered attention as a tool for measuring pulse waves with weak skin tightening. Using a MEMS-based piezoresistive cantilever with an air chamber as the pressure change sensor enables highly sensitive pulse-wave measurements to be achieved. Furthermore, the initial static pressure when attaching the sensor to the skin is physically excluded because of air leakage around the cantilever, which serves as a high-pass filter. However, if the frequency characteristics of this mechanical high-pass filter are not appropriately designed, then the essential information of the pulse-wave measurement may not be reflected. In this study, the frequency characteristics of a sensor structure is derived theoretically based on the air leakage rate and chamber size. Subsequently, a pulse wave sensor with a MEMS piezoresistive cantilever element, two air chambers, and a skin-contacted membrane is designed and fabricated. The developed sensor is 30 mm in diameter and 8 mm in thickness and realizes high-pass filter characteristics of 0.7 Hz. Finally, pulse wave measurement at the neck of a participant is demonstrated using the developed sensor. It is confirmed that the measured pulse wave contains signals in the designed frequency band. Full article

(This article belongs to the Special Issue Selected Papers from the 12th Symposium on Micro-Nano Science and Technology on Micromachines)

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8 pages, 1742 KiB

Open AccessArticle

Wearable Microfluidic Sensor for the Simultaneous and Continuous Monitoring of Local Sweat Rates and Electrolyte Concentrations

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Micromachines 2022, 13(4), 575; https://doi.org/10.3390/mi13040575 - 06 Apr 2022

Cited by 10 | Viewed by 3488

Abstract

Temperature elevation due to global warming increases the risks of dehydration, which can induce heat-related illness. Proper rehydration with appropriate amounts of water and electrolytes is essential to aid body fluid homeostasis. Wearable sweat sensors which can monitor both the sweat rate and sweat electrolyte concentration may be an effective tool for determining appropriate rehydration. Here, we developed a novel potentially wearable sensor that can monitor both the local sweat rate and sweat electrolyte concentration continuously. The new device includes a system with a short microfluidic pathway that guides the sweat appearing on the skin to a small space in the device to form a quantifiable droplet. The sweat rate is assessed from the time for the droplet to appear and droplet volume, while an integrated electric sensor detects the sodium chloride concentration in each sweat droplet. We demonstrated that this new device could record both the flow rates of artificial sweat and its sodium chloride concentration in ranges of human sweating with an accuracy within ±10%. This is equivalent to the accuracy of commercially available sweat rate meters and sweat ion sensors. The present study provides a new perspective for the design of wearable sensors that can continuously monitor sweat rates and sweat electrolyte concentrations for potential application to a healthcare device. Full article

(This article belongs to the Special Issue Selected Papers from the 12th Symposium on Micro-Nano Science and Technology on Micromachines)

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17 pages, 7103 KiB

Open AccessArticle

Estimation of Position and Size of a Contaminant in Aluminum Casting Using a Thin-Film Magnetic Sensor

Tomoo Nakai

Micromachines 2022, 13(1), 127; https://doi.org/10.3390/mi13010127 - 14 Jan 2022

Cited by 4 | Viewed by 1094

Abstract

Advanced manufacturing processes require an in-line full inspection system. A nondestructive inspection system able to detect a contaminant such as tool chipping was utilized for the purpose of detecting a defective product as well as damaged machine tools used to fabricate the product. In a previous study, a system able to detect magnetic tool steel chipping in conductive material such as aluminum was developed and tested. In this study, a method of position and size estimation for magnetic chipping was investigated and is described. An experimental confirmation of the proposed method was also carried out using an actual prototype system. Full article

(This article belongs to the Special Issue Selected Papers from the 12th Symposium on Micro-Nano Science and Technology on Micromachines)

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