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Micromachines
Volume 11
Issue 5
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Micromachines, Volume 11, Issue 5 (May 2020) – 88 articles

Cover Story (view full-size image): Gathering precise information on the mass density, size, and weight of cells or cell aggregates is crucial for applications in many biomedical fields. The research interest is especially increasing for 3D models such as spheroids. Consequently, we developed the first flow-apparatus, associated physical method, and operative protocol for the accurate and simultaneous measurements of mass density, size, and weight of sphere-like samples. The technique is based on detection of the terminal velocity of a free-falling sample into a specifically conceived analysis flow-channel. After validation with standardized polystyrene beads, we measured such parameters on a notable number of live SW620 tumor spheroids. This approach can represent a step towards a deeper understanding of 3D models. View this paper
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16 pages, 4672 KiB  
Article
Hemispherical Microelectrode Array for Ex Vivo Retinal Neural Recording
by Yoonhee Ha, Hyun-Ji Yoo, Soowon Shin and Sang Beom Jun
Micromachines 2020, 11(5), 538; https://doi.org/10.3390/mi11050538 - 25 May 2020
Cited by 11 | Viewed by 4763 | Correction
Abstract
To investigate the neuronal visual encoding process in the retina, researchers have performed in vitro and ex vivo electrophysiological experiments using animal retinal tissues. The microelectrode array (MEA) has become a key component in retinal experiments because it enables simultaneous neural recording from [...] Read more.
To investigate the neuronal visual encoding process in the retina, researchers have performed in vitro and ex vivo electrophysiological experiments using animal retinal tissues. The microelectrode array (MEA) has become a key component in retinal experiments because it enables simultaneous neural recording from a population of retinal neurons. However, in most retinal experiments, it is inevitable that the retinal tissue is flattened on the planar MEA, becoming deformed from the original hemispherical shape. During the tissue deforming process, the retina is subjected to mechanical stress, which can induce abnormal physiological conditions. To overcome this problem, in this study, we propose a hemispherical MEA with a curvature that allows retinal tissues to adhere closely to electrodes without tissue deformation. The electrode array is fabricated by stretching a thin, flexible polydimethylsiloxane (PDMS) electrode layer onto a hemispherical substrate. To form micro patterns of electrodes, laser processing is employed instead of conventional thin-film microfabrication processes. The feasibility for neural recording from retinal tissues using this array is shown by conducting ex vivo retinal experiments. We anticipate that the proposed techniques for hemispherical MEAs can be utilized not only for ex vivo retinal studies but also for various flexible electronics. Full article
(This article belongs to the Special Issue Micro/Nanofabrication for Retinal Implants)
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Figure 1

Figure 1
<p>Overview of retinal preparation for ex vivo neural recording on a planar-type microelectrode array (MEA). (<b>a</b>) Cornea and sclera are divided along the limbus. (<b>b</b>) Sclera is cut to isolate the retina. (<b>c</b>) Retina is cut to facilitate flattening. (<b>d</b>) Retina is pressed down by anchor to adhere to the planar-type MEA.</p> Full article ">Figure 2
<p>Structure of the hemispherical MEA. (<b>a</b>) Hemispherical MEA consisting of four layers (liquid crystal (LCP) layer, electrode layer, hemispherical layer, substrate layer). (<b>b</b>) Electrode layer is stretched into the shape of the hemispherical layer.</p> Full article ">Figure 3
<p>Two-dimensional electrode design before stretching into the hemispherical shape. (<b>a</b>) Overall view of electrode. A trapezoidal reference electrode is placed on the left. Thirteen connecting pads are located outside. (<b>b</b>) Zoomed-in image of the area including recording electrodes. Pink lines indicate the openings of the top polydimethylsiloxane (PDMS) insulation layer.</p> Full article ">Figure 4
<p>Fabrication of the hemispherical and substrate layers. (<b>a</b>) Mold with a concave hemispherical shape having the same size as mice retinas. (<b>b</b>) Surface treatment is performed to prevent adhesion between the stainless mold and PDMS. (<b>c</b>) Mold is rinsed with deionized water and dried with nitrogen. (<b>d</b>) PDMS solution is poured into the mold, degassed in the vacuum chamber, and half-cured in the oven. (<b>e</b>) The substrate layer is attached to the hemispherical layer and completely cured. (<b>f</b>) The hemispherical/substrate layers are released from the mold.</p> Full article ">Figure 5
<p>Fabrication of the bottom insulation layer including electrodes. (<b>a</b>) LCP is fixed on the wafer (wafer is not shown). (<b>b</b>) PDMS solution is spin-coated on the LCP and cured. (<b>c</b>) Pt foil is attached to the cured PDMS. (<b>d</b>) Pt electrodes are patterned by laser. (<b>e</b>) The background Pt foil is peeled off except for the electrodes and lines. (<b>f</b>) The bottom insulation layer with the LCP substrate is separated from the wafer. (<b>g</b>) Overall view of the bottom insulation layer (the center area including the electrode sites are enlarged in (<b>a</b>–<b>f</b>)).</p> Full article ">Figure 6
<p>Fabrication of top insulation and LCP layers. (<b>a</b>) PDMS solution is spin-coated onto the wafer (wafer is not shown). (<b>b</b>) LCP is attached to the PDMS. (<b>c</b>) Second PDMS solution is spin-coated. (<b>d</b>) The outlines of electrode sites and alignment holes are cut by laser. (<b>e</b>) LCP is detached from bottom PDMS. (<b>f</b>) The top insulation of the electrode layer and LCP layer is completed. (<b>g</b>) Overall view of the top insulation layer. (The center area including the electrode sites are enlarged in (<b>a</b>–<b>f</b>)).</p> Full article ">Figure 7
<p>Bonding between top and bottom layers. (<b>a</b>) Top and bottom PDMS surfaces are activated and faced toward each other using a customized alignment jig. (<b>b</b>) PDMS-PDMS bonding is performed by pressure and heat. (<b>c</b>) A circle is cut into the top LCP using a laser. (<b>d</b>) Bottom LCP is removed from under the electrode layer. (<b>e</b>) Electrode layer with the LCP layer is completed. (<b>f</b>) Circles cut on the top LCP naturally fall off of the PDMS when assembled with the hemispherical layer. (<b>g</b>) Photograph of the custom alignment jig. (<b>h</b>) Overall view of electrode layer (the center area including the electrode sites are enlarged in (<b>a</b>–<b>f</b>)).</p> Full article ">Figure 8
<p>Two-dimensional simulation results for the strain of the stretched electrode layers under lubricated and dry conditions. (<b>a</b>) Strain color map of the electrode layer according to the surface conditions of the hemispherical layer. (<b>b</b>) Equivalent strain plots overlapped with the hemispherical electrode shape.</p> Full article ">Figure 9
<p>Fabricated hemispherical MEA. (<b>a</b>) Top view of the entire MEA. Twelve microelectrodes are located in the red circle. The trapezoidal reference electrode is on the left side of the chamber. The thirteen connecting pads are located outside of the chamber. (<b>b</b>) Zoomed-in top view of the hemispherical electrode area. (<b>c</b>) Side view of the hemispherical area. (<b>d</b>) Mounted whole retina on the hemispherical MEA.</p> Full article ">Figure 10
<p>Electrochemical impedance spectroscopy of the fabricated hemispherical MEA. (<b>a</b>) Magnitude of impedance. (<b>b</b>) Phase of impedance.</p> Full article ">Figure 11
<p>Spontaneous activity from rd1 mice retina recorded using the fabricated hemispherical MEA. (<b>a</b>) Neural signals from rd1 mice were measured in hemispherical MEAs. (The line in each channel is the value of -5 SD of the noise level for signal detection.) (<b>b</b>) The neural signals detected after 1 h (stabilization) and 5 h were overlaid in channel 4. (<b>c</b>) The spike frequency of the rd1 mice retina over five hours (the gray line is the spike frequency detected at each electrode. The black line is the average spike frequency of seven electrodes). (<b>d</b>) The normalized spike amplitude of the rd1 mice retina over five hours (the gray line is the normalized pike amplitude detected at each electrode. The black line is the average amplitude of seven electrodes).</p> Full article ">
13 pages, 1982 KiB  
Article
Adaptive Tracking Control for the Piezoelectric Actuated Stage Using the Krasnosel’skii-Pokrovskii Operator
by Rui Xu, Dapeng Tian and Zhongshi Wang
Micromachines 2020, 11(5), 537; https://doi.org/10.3390/mi11050537 - 25 May 2020
Cited by 16 | Viewed by 2438
Abstract
In this paper, a discrete second order linear equation with the Krasnosel’skii-Pokrovskii (KP) operator is used to describe the piezoelectric actuated stage. The weights of the KP operators are identified by the gradient descent algorithm. To suppress the hysteresis nonlinearity of the piezoelectric [...] Read more.
In this paper, a discrete second order linear equation with the Krasnosel’skii-Pokrovskii (KP) operator is used to describe the piezoelectric actuated stage. The weights of the KP operators are identified by the gradient descent algorithm. To suppress the hysteresis nonlinearity of the piezoelectric actuated stage, this paper proposes an adaptive tracking control with the hysteresis decomposition on the designed error surface. The proposed adaptive tracking controller dispenses with any form of the feed-forward hysteresis compensation and the unknown parameters of the discrete second order linear equation are adaptively adjusted. Some simulations are implemented to verify the effectiveness of the KP operators, then a series of modeling and control experiments are carried out on the piezoelectric actuated stages experimental systems. The comparative experimental results verify the feasibility of the KP operators modeling method and the adaptive tracking control method. Full article
(This article belongs to the Section E：Engineering and Technology)
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Figure 1
<p>Structure chart of the Krasnosel’skii-Pokrovskii (KP) kernel and Preisach plane. (<b>a</b>) KP kernel; (<b>b</b>) Preisach plane.</p> Full article ">Figure 2
<p>Identification structure diagram of the KP operators with the gradient descent algorithm.</p> Full article ">Figure 3
<p>Simulation results of the KP model with the gradient descent algorithm under the triangular wave voltage signal.</p> Full article ">Figure 4
<p>Simulation results of the KP model with the gradient descent algorithm under the sine wave voltage signal.</p> Full article ">Figure 5
<p>Picture of the piezoelectric actuated stage experimental setup.</p> Full article ">Figure 6
<p>Experimental result of KP operator based on the gradient descent algorithm under the triangular wave voltage signal.</p> Full article ">Figure 7
<p>Experimental result of KP operator based on the gradient descent algorithm under the complex wave signal.</p> Full article ">Figure 8
<p>Estimated parameters <math display="inline"><semantics> <mover accent="true"> <mi>θ</mi> <mo>^</mo> </mover> </semantics></math> and <math display="inline"><semantics> <msub> <mover accent="true"> <mi>g</mi> <mo>^</mo> </mover> <mi>i</mi> </msub> </semantics></math> of the proposed adaptive controller for the triangular wave signal. (<b>a</b>) convergent curve of <math display="inline"><semantics> <mover accent="true"> <mi>θ</mi> <mo>^</mo> </mover> </semantics></math>; (<b>b</b>) convergent curve of <math display="inline"><semantics> <mover accent="true"> <msub> <mi>g</mi> <mi>i</mi> </msub> <mo stretchy="false">^</mo> </mover> </semantics></math>.</p> Full article ">Figure 9
<p>Experimental results of the piezoelectric actuated stage with the triangular wave signal. (<b>a</b>) tracking curve of the piezoelectric actuated stage; (<b>b</b>) tracking error.</p> Full article ">Figure 10
<p>Estimates results of the parameters <math display="inline"><semantics> <mover accent="true"> <mi>θ</mi> <mo>^</mo> </mover> </semantics></math> and <math display="inline"><semantics> <msub> <mover accent="true"> <mi>g</mi> <mo>^</mo> </mover> <mi>i</mi> </msub> </semantics></math>. (<b>a</b>) convergent curve of <math display="inline"><semantics> <mover accent="true"> <mi>θ</mi> <mo>^</mo> </mover> </semantics></math>; (<b>b</b>) convergent curve of <math display="inline"><semantics> <mover accent="true"> <msub> <mi>g</mi> <mi>i</mi> </msub> <mo stretchy="false">^</mo> </mover> </semantics></math>.</p> Full article ">Figure 11
<p>Comparative results of the piezoelectric actuated stage with the complex wave signal. (<b>a</b>) tracking curve of the piezoelectric actuated stage; (<b>b</b>) tracking error.</p> Full article ">
18 pages, 4126 KiB  
Article
Pharmacokinetic Analysis of Epithelial/Endothelial Cell Barriers in Microfluidic Bilayer Devices with an Air–Liquid Interface
by Timothy S. Frost, Linan Jiang and Yitshak Zohar
Micromachines 2020, 11(5), 536; https://doi.org/10.3390/mi11050536 - 25 May 2020
Cited by 7 | Viewed by 3802
Abstract
As the range of applications of organs-on-chips is broadening, the evaluation of aerosol-based therapies using a lung-on-a-chip model has become an attractive approach. Inhalation therapies are not only minimally invasive but also provide optimal pharmacokinetic conditions for drug absorption. As drug development evolves, [...] Read more.
As the range of applications of organs-on-chips is broadening, the evaluation of aerosol-based therapies using a lung-on-a-chip model has become an attractive approach. Inhalation therapies are not only minimally invasive but also provide optimal pharmacokinetic conditions for drug absorption. As drug development evolves, it is likely that better screening through use of organs-on-chips can significantly save time and cost. In this work, bio-aerosols of various compounds including insulin were generated using a jet nebulizer. The aerosol flows were driven through microfluidic bilayer devices establishing an air–liquid interface to mimic the blood–air barrier in human small airways. The aerosol flow in the microfluidic devices has been characterized and adjusted to closely match physiological values. The permeability of several compounds, including paracellular and transcellular biomarkers, across epithelial/endothelial cell barriers was measured. Concentration–time plots were established in microfluidic devices with and without cells; the curves were then utilized to extract standard pharmacokinetic parameters such as the area under the curve, maximum concentration, and time to maximum concentration. The cell barrier significantly affected the measured pharmacokinetic parameters, as compound absorption through the barrier decreases with its increasing molecular size. Aerosolizing insulin can lead to the formation of fibrils, prior to its entry to the microfluidic device, with a substantially larger apparent molecular size effectively blocking its paracellular transport. The results demonstrate the advantage of using lung-on-a-chip for drug discovery with applications such as development of novel inhaled therapies. Full article
(This article belongs to the Section E：Engineering and Technology)
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<p>(<b>a</b>) A photograph of a fabricated and packaged microfluidic bilayer device with green dye in the top and orange dye in the bottom microchannel. (<b>b</b>) A schematic representation of the jet nebulizer setup; the aerosol system is connected to a microdevice’s top channel while the bottom channel is connected to a syringe pump to drive media across the device.</p> Full article ">Figure 2
<p>A brightfield image of the two microchannels converging with a monolayer grown in each channel (A549 top channel, HUVEC bottom channel) along the membrane surface.</p> Full article ">Figure 3
<p>Permeability of 4-dextran, C-dextran, 70-dextran, and insulin in Transwells with and without A549 cell monolayers. Significance determined with student’s <span class="html-italic">T</span>-test with unequal variance (n = 3); * <span class="html-italic">p</span> &lt; 0.05, ** <span class="html-italic">p</span> &lt; 0.01.</p> Full article ">Figure 4
<p>Permeability of 4-dextran, 70-dextran, and insulin in microfluidic bilayer devices with and without an epithelial/endothelial barriers. Significance determined with student’s <span class="html-italic">T</span>-test with unequal variance (n = 3); * <span class="html-italic">p</span> &lt; 0.05.</p> Full article ">Figure 5
<p>A characteristic concentration–time plot illustrating several key pharmacokinetic parameters commonly extracted from such a curve.</p> Full article ">Figure 6
<p>Concentration–time curves for microfluidic bilayer devices: (<b>a</b>) Without cells and (<b>b</b>) with an epithelial/endothelial barriers. * <span class="html-italic">p</span> &lt; 0.05 compared with LMW Dextran.</p> Full article ">Figure 7
<p>Pharmacokinetic parameters extracted from the concentration–time plots: (<b>a</b>) Relative area under the curve, AUC, (<b>b</b>) maximum concentration, <span class="html-italic">C</span><sub>max</sub>, and (<b>c</b>) time to reach maximum concentration, <span class="html-italic">T</span><sub>max</sub>, for the four molecules tested. * <span class="html-italic">p</span> &lt; 0.05, ** <span class="html-italic">p</span> &lt; 0.01, *** <span class="html-italic">p</span> &lt; 0.001 compared with insulin.</p> Full article ">Figure 8
<p>Images of the jet nebulizer platform shortly after a period of agitation for both LMW dextran and Insulin solutions as a function of time.</p> Full article ">Figure 9
<p>Plot of fluorescent intensity in an air–liquid agitated solution as a function of time. Final intensity refers to the solution intensity at time t = 30 min. Normalize by the intensity of un-agitated solutions, <span class="html-italic">I<sub>a</sub></span>/<span class="html-italic">I<sub>u</sub></span>.</p> Full article ">Figure 10
<p>Bottom compartment relative concentration of insulin after 20 min incubation. Agitated insulin was agitated with an air–liquid interface for 5 min and then added to the upper Transwell compartment. * <span class="html-italic">p</span> &lt; 0.05 compared with non-agitated insulin.</p> Full article ">
26 pages, 1218 KiB  
Review
Retinal Prosthetic Approaches to Enhance Visual Perception for Blind Patients
by Shinyong Shim, Kyungsik Eom, Joonsoo Jeong and Sung June Kim
Micromachines 2020, 11(5), 535; https://doi.org/10.3390/mi11050535 - 24 May 2020
Cited by 22 | Viewed by 6751
Abstract
Retinal prostheses are implantable devices that aim to restore the vision of blind patients suffering from retinal degeneration, mainly by artificially stimulating the remaining retinal neurons. Some retinal prostheses have successfully reached the stage of clinical trials; however, these devices can only restore [...] Read more.
Retinal prostheses are implantable devices that aim to restore the vision of blind patients suffering from retinal degeneration, mainly by artificially stimulating the remaining retinal neurons. Some retinal prostheses have successfully reached the stage of clinical trials; however, these devices can only restore vision partially and remain insufficient to enable patients to conduct everyday life independently. The visual acuity of the artificial vision is limited by various factors from both engineering and physiological perspectives. To overcome those issues and further enhance the visual resolution of retinal prostheses, a variety of retinal prosthetic approaches have been proposed, based on optimization of the geometries of electrode arrays and stimulation pulse parameters. Other retinal stimulation modalities such as optics, ultrasound, and magnetics have also been utilized to address the limitations in conventional electrical stimulation. Although none of these approaches have been clinically proven to fully restore the function of a degenerated retina, the extensive efforts made in this field have demonstrated a series of encouraging findings for the next generation of retinal prostheses, and these could potentially enhance the visual acuity of retinal prostheses. In this article, a comprehensive and up-to-date overview of retinal prosthetic strategies is provided, with a specific focus on a quantitative assessment of visual acuity results from various retinal stimulation technologies. The aim is to highlight future directions toward high-resolution retinal prostheses. Full article
(This article belongs to the Special Issue Micro/Nanofabrication for Retinal Implants)
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Figure 1
<p>A summary of retinal prosthetic approaches for enhanced visual resolution.</p> Full article ">Figure 2
<p>Schematic illustration of (<b>A</b>) featured retinal electrode structures for higher visual resolution including arrow-shaped, pillar-shaped, tip-shaped, recessed well-type, and concave hemispherical, and (<b>B</b>) optimized stimulation patterns based on hexagonal layout and virtual electrodes for current focusing and steering. (Adapted from [<a href="#B106-micromachines-11-00535" class="html-bibr">106</a>,<a href="#B107-micromachines-11-00535" class="html-bibr">107</a>,<a href="#B108-micromachines-11-00535" class="html-bibr">108</a>,<a href="#B112-micromachines-11-00535" class="html-bibr">112</a>,<a href="#B113-micromachines-11-00535" class="html-bibr">113</a>,<a href="#B121-micromachines-11-00535" class="html-bibr">121</a>,<a href="#B122-micromachines-11-00535" class="html-bibr">122</a>]).</p> Full article ">Figure 3
<p>A two-dimensional representation comparing spatial resolution and invasiveness of various retinal prosthetic approaches discussed in this article, along with color-coded description on technology readiness.</p> Full article ">
16 pages, 5414 KiB  
Article
High-Speed Manipulation of Microobjects Using an Automated Two-Fingered Microhand for 3D Microassembly
by Eunhye Kim, Masaru Kojima, Yasushi Mae and Tatsuo Arai
Micromachines 2020, 11(5), 534; https://doi.org/10.3390/mi11050534 - 24 May 2020
Cited by 14 | Viewed by 3687
Abstract
To assemble microobjects including biological cells quickly and precisely, a fully automated pick-and-place operation is applied. In micromanipulation in liquid, the challenges include strong adhesion forces and high dynamic viscosity. To solve these problems, a reliable manipulation system and special releasing techniques are [...] Read more.
To assemble microobjects including biological cells quickly and precisely, a fully automated pick-and-place operation is applied. In micromanipulation in liquid, the challenges include strong adhesion forces and high dynamic viscosity. To solve these problems, a reliable manipulation system and special releasing techniques are indispensable. A microhand having dexterous motion is utilized to grasp an object stably, and an automated stage transports the object quickly. To detach the object adhered to one of the end effectors, two releasing methods—local stream and a dynamic releasing—are utilized. A system using vision-based techniques for the recognition of two fingertips and an object, as well automated releasing methods, can increase the manipulation speed to faster than 800 ms/sphere with a 100% success rate (N = 100). To extend this manipulation technique, 2D and 3D assembly that manipulates several objects is attained by compensating the positional error. Finally, we succeed in assembling 80–120 µm of microbeads and spheroids integrated by NIH3T3 cells. Full article
(This article belongs to the Special Issue Microrobotics for Biological, Biomedical, and Surgical Applications)
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Figure 1

Figure 1
<p>System of microhand. (<b>a</b>) Overall system of microhand; (<b>b</b>) System architecture.</p> Full article ">Figure 2
<p>Manipulation process of an object.</p> Full article ">Figure 3
<p>Position detection of the left fingertip and the center of an object.</p> Full article ">Figure 4
<p>Transportation system. (<b>a</b>) Moving two end effectors; (<b>b</b>) Moving substrate.</p> Full article ">Figure 5
<p>Detecting the grasped objects. (<b>a</b>) Before removing two fingers; (<b>b</b>) After removing two fingers.</p> Full article ">Figure 6
<p>Automatic releasing (<b>a</b>) When the object is adhered to left; (<b>b</b>) When the object is adhered to right.</p> Full article ">Figure 7
<p>Releasing process for improving success rate. (<b>a</b>) Flowchart; (<b>b</b>) Image sequence of releasing process.</p> Full article ">Figure 8
<p>Manipulation of several objects outside of the visible space. (<b>a</b>) Moving the stage to find the second object; (<b>b</b>) Searching and grasping the second object; (<b>c</b>) Transporting the second object to the desired position; (<b>d</b>) Releasing the second object.</p> Full article ">Figure 9
<p>Result of the automated manipulation of an object; (<b>a</b>) Placing position of 100 µm microbeads; (<b>b</b>) Placing position of 55 µm microbeads.</p> Full article ">Figure 10
<p>Time-lapse images of the automated manipulation of an object.</p> Full article ">Figure 11
<p>Error recovery to compensate the position error based on a prearranged object. (<b>a</b>) Manipulating the second object by adjusting X-axis; (<b>b</b>) Manipulating the fourth object by adjusting X and Y-axis.</p> Full article ">Figure 12
<p>Results of the manipulation. (<b>a</b>) Several objects for making special characters (“O” and “U”); (<b>b</b>) Nine objects for making 2D structure; (<b>c</b>) Five objects for making 3D structure.</p> Full article ">Figure 13
<p>Results of the manipulation of three objects. (<b>a</b>) 85−120 µm microbeads, (<b>b</b>) 100−120 µm spheroids.</p> Full article ">
22 pages, 7914 KiB  
Article
Protein Dielectrophoresis: I. Status of Experiments and an Empirical Theory
by Ralph Hölzel and Ronald Pethig
Micromachines 2020, 11(5), 533; https://doi.org/10.3390/mi11050533 - 22 May 2020
Cited by 43 | Viewed by 4188
Abstract
The dielectrophoresis (DEP) data reported in the literature since 1994 for 22 different globular proteins is examined in detail. Apart from three cases, all of the reported protein DEP experiments employed a gradient field factor ∇ E m 2 that is much smaller [...] Read more.
The dielectrophoresis (DEP) data reported in the literature since 1994 for 22 different globular proteins is examined in detail. Apart from three cases, all of the reported protein DEP experiments employed a gradient field factor ∇ E m 2 that is much smaller (in some instances by many orders of magnitude) than the ~4 × 1021 V2/m3 required, according to current DEP theory, to overcome the dispersive forces associated with Brownian motion. This failing results from the macroscopic Clausius–Mossotti (CM) factor being restricted to the range 1.0 > CM > −0.5. Current DEP theory precludes the protein’s permanent dipole moment (rather than the induced moment) from contributing to the DEP force. Based on the magnitude of the β-dispersion exhibited by globular proteins in the frequency range 1 kHz–50 MHz, an empirically derived molecular version of CM is obtained. This factor varies greatly in magnitude from protein to protein (e.g., ~37,000 for carboxypeptidase; ~190 for phospholipase) and when incorporated into the basic expression for the DEP force brings most of the reported protein DEP above the minimum required to overcome dispersive Brownian thermal effects. We believe this empirically-derived finding validates the theories currently being advanced by Matyushov and co-workers. Full article
(This article belongs to the Special Issue Micromachines for Dielectrophoresis)
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Figure 1
<p>A dielectric of relative permittivity <span class="html-italic">ɛ<sub>m</sub></span> is shown partly inserted between two electrified electrodes. ‘Free’ charge density <span class="html-italic">σ</span> on the electrodes creates the Maxwell field <span class="html-italic">E</span> and electric displacement <span class="html-italic">D</span> (both = <span class="html-italic">σ/ɛ<sub>o</sub></span>). ‘Bound’ charge density Δ<span class="html-italic">σ</span> created by polarization (charge displacement) of the dielectric generates the polarization vector <span class="html-italic">P</span> (<math display="inline"><semantics> <mrow> <mrow> <mi mathvariant="sans-serif">Δ</mi> <mi>σ</mi> </mrow> <mo>=</mo> <msub> <mi>P</mi> <mi>s</mi> </msub> <mo>⋅</mo> <mover> <mi>n</mi> <mo stretchy="false">^</mo> </mover> <mo>=</mo> <mi>P</mi> </mrow> </semantics></math>), and equates to the number density of polarized molecules—i.e., the dielectric’s dipole moment M per unit volume. These relationships give <span class="html-italic">D</span> = <span class="html-italic">E</span> + <span class="html-italic">P/ɛ<sub>o</sub></span>, and <span class="html-italic">P</span> = <span class="html-italic">ɛ<sub>o</sub>(ɛ<sub>m</sub> − 1)E<sub>o</sub></span> = <span class="html-italic">χ<sub>m</sub>ɛ<sub>o</sub>E<sub>o</sub></span>.</p> Full article ">Figure 2
<p>Globular proteins studied for their dielectrophoresis (DEP) response, with their hydrodynamic (Stokes) radii located on the empirical relationship between protein size and molecular weight (dotted curve) provided by Malvern Panalytical<sup>®</sup> (Zetasizer Nano ZS).</p> Full article ">Figure 3
<p>Insulator-based (iDEP) and electrode-based (eDEP) studies reported for bovine serum albumin (BSA). Most groups observed positive DEP, but two cases of negative iDEP have also been reported [<a href="#B17-micromachines-11-00533" class="html-bibr">17</a>,<a href="#B25-micromachines-11-00533" class="html-bibr">25</a>]. Cao et al. [<a href="#B26-micromachines-11-00533" class="html-bibr">26</a>] report a DEP cross-over frequency between 1~10 MHz.</p> Full article ">Figure 4
<p>A range of aqueous solvent conductivity has been used in DEP studies of BSA. The experimental factors associated with the two cases [<a href="#B17-micromachines-11-00533" class="html-bibr">17</a>,<a href="#B25-micromachines-11-00533" class="html-bibr">25</a>] of negative iDEP and the cross-over of polarity between 1~10 MHz [<a href="#B26-micromachines-11-00533" class="html-bibr">26</a>] are discussed in <a href="#sec3dot2-micromachines-11-00533" class="html-sec">Section 3.2</a>.</p> Full article ">Figure 5
<p>A summary of the DEP responses, at specific frequencies of the applied field, for proteins other than BSA. (HRP: horse radish peroxidase; PSA: prostate specific antigen; eGFP: enhanced green fluorescent protein; TnI-Ab: troponin I antibody).</p> Full article ">Figure 6
<p>Mean distance between BSA and streptavidin molecules for the reported sample concentrations, estimated as the cube root of the volume occupied per protein molecule.</p> Full article ">Figure 7
<p>Values of the field gradient factor <math display="inline"><semantics> <mrow> <mo>∇</mo> <msubsup> <mi>E</mi> <mi>m</mi> <mn>2</mn> </msubsup> </mrow> </semantics></math> as reported by the investigators or estimated by Hayes [<a href="#B5-micromachines-11-00533" class="html-bibr">5</a>]. The minimum value of <math display="inline"><semantics> <mrow> <mo>∇</mo> <msubsup> <mi>E</mi> <mi>m</mi> <mn>2</mn> </msubsup> </mrow> </semantics></math> required to compete against Brownian diffusive effects, calculated according to Equation (9), is shown for the case of BSA. The adjusted value shown for this is based on the empirical relationship described in <a href="#sec3dot4-micromachines-11-00533" class="html-sec">Section 3.4</a>.</p> Full article ">Figure 8
<p>The β-dispersion and δ-dispersion, arising from orientation polarization of the protein and protein-bound water, respectively, exhibited by 0.18 mM BSA (based on Moser et al. [<a href="#B50-micromachines-11-00533" class="html-bibr">50</a>] and Grant el al. [<a href="#B51-micromachines-11-00533" class="html-bibr">51</a>]). The radian frequency of orientation relaxation for BSA is given by the reciprocal of its relaxation time τ. For frequencies below <span class="html-italic">f</span>xo (~1 MHz) the relative permittivity <span class="html-italic">ɛ<sub>r</sub></span> of the BSA solution exceeds that of pure water, and is less than this above <span class="html-italic">f</span>xo. According to Equation (11) the dielectric increment <math display="inline"><semantics> <mrow> <mo>Δ</mo> <msup> <mi>ε</mi> <mo>+</mo> </msup> </mrow> </semantics></math> and decrement <math display="inline"><semantics> <mrow> <mo>Δ</mo> <msup> <mi>ε</mi> <mo>−</mo> </msup> </mrow> </semantics></math>, respectively, specify the frequency ranges where positive and negative DEP, respectively, should be observed for monomer BSA in aqueous solution.</p> Full article ">Figure 9
<p>Schematic of a ‘Russian doll’ model for a protein with a permanent dipole moment M<sub>p</sub>, which occupies the innermost cavity together with its strongly bound water molecules. The protein’s dipole field extends beyond an outer macroscopic, ‘mathematical’, surface where the classical boundary conditions of electrostatics can be applied. Within this mathematical surface is a boundary that contains the protein’s outer hydration sheath, and the hydrodynamic plane of shear that defines the zeta-potential within the protein’s diffuse electrical double-layer.</p> Full article ">Figure 10
<p>(<b>a</b>) Schematic of a dipole formed at the site of a structural defect in a molecular lattice. An example could be the disruption of the hydrogen bond network in bulk water at a protein–water interface—with the possible creation of ferroelectric nanodomains [<a href="#B66-micromachines-11-00533" class="html-bibr">66</a>]. (<b>b</b>) Dipole polarization at a boundary of dielectric inhomogeneity. A solvated protein, with its bound water and surrounding bulk water, represents an inhomogeneous dielectric [<a href="#B68-micromachines-11-00533" class="html-bibr">68</a>]. (<b>c</b>) Dielectric dispersion exhibited by an aqueous suspension of polystyrene nanospheres (R = 94 nm) (based on Schwan et al. [<a href="#B69-micromachines-11-00533" class="html-bibr">69</a>]).</p> Full article ">
17 pages, 10062 KiB  
Article
Development of a Multi-Material Stereolithography 3D Printing Device
by Bilal Khatri, Marco Frey, Ahmed Raouf-Fahmy, Marc-Vincent Scharla and Thomas Hanemann
Micromachines 2020, 11(5), 532; https://doi.org/10.3390/mi11050532 - 22 May 2020
Cited by 46 | Viewed by 6511
Abstract
Additive manufacturing, or nowadays more popularly entitled as 3D printing, enables a fast realization of polymer, metal, ceramic or composite devices, which often cannot be fabricated with conventional methods. One critical issue for a continuation of this success story is the generation of [...] Read more.
Additive manufacturing, or nowadays more popularly entitled as 3D printing, enables a fast realization of polymer, metal, ceramic or composite devices, which often cannot be fabricated with conventional methods. One critical issue for a continuation of this success story is the generation of multi-material devices. Whilst in fused filament fabrication or 3D InkJet printing, commercial solutions have been realized, in stereolithography only very few attempts have been seen. In this work, a comprehensive approach, covering the construction, material development, software control and multi-material printing is presented for the fabrication of structural details in the micrometer range. The work concludes with a critical evaluation and possible improvements. Full article
(This article belongs to the Section E：Engineering and Technology)
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<p>Photocurable resin composition: (<b>a</b>) EGDMA; (<b>b</b>) BAEDA; (<b>c</b>) TPO.</p> Full article ">Figure 2
<p>A SolidWorks<sup>®</sup> -designed 3D model of the MMSL device.</p> Full article ">Figure 3
<p>MMSL resin vat: (<b>a</b>) Laser cut PMMA sheets; (<b>b</b>) Assembled vat; (<b>c</b>) Build platform.</p> Full article ">Figure 4
<p>Ready to use MMSL device setup.</p> Full article ">Figure 5
<p>Printer functions screen with motor control.</p> Full article ">Figure 6
<p>Print-cycle flowchart of the MMSL device.</p> Full article ">Figure 7
<p>Viscosities of all investigated resin mixtures as function of (<b>a</b>) shear rate and (<b>b</b>) temperature.</p> Full article ">Figure 8
<p>Impact of the photoinitiator content on the mechanical properties in BE-5050 base resin. (<b>a</b>) Ultimate tensile strength UTS; (<b>b</b>) Maximum strain at break.</p> Full article ">Figure 9
<p>Single-material print with fluorescent dye-doped BE-5050. Printed with B9Creator: (<b>a</b>) Under ambient light; (<b>b</b>) Under a near UV LED. Printed with the MMSL device: (<b>c</b>) Under ambient light; (<b>d</b>) Under a near UV LED.</p> Full article ">Figure 10
<p>Microstructure demonstrators printed with the MMSL device, using a BE-8020 substrate with BE-5050 containing a fluorescent composite of the Lumogen V570 (<b>a,c</b>) and Lumogen F305 dyes (<b>b,d</b>); (<b>a</b>,<b>b</b>) Under ambient light; (<b>c</b>,<b>d</b>) Under near UV light.</p> Full article ">Figure 11
<p>Benchmark artifact for the validation of the MMSL print quality; (<b>a</b>) Rendered 3D overview; (<b>b</b>) 2D projection with measuring points for structural feature heights.</p> Full article ">Figure 12
<p>Microscopic images of the test patterns’ best layer curing time: (<b>a</b>) BE-5050; (<b>b</b>) BE-5050 Lumogen F305; (<b>c</b>) BE-5050 Lumogen V570.</p> Full article ">Figure 13
<p>Fracture images after tensile testing. (<b>a</b>) BE-5050; (<b>b</b>) BE-5050\F305; (<b>b</b>) BE-5050\V570.</p> Full article ">Figure 14
<p>Microscopic images of the MMSL print applying BE-5050 as base plate material (five samples): (<b>a</b>) BE-5050\F305 as feature material; (<b>b</b>) BE-5050\V570 as feature material.</p> Full article ">Figure 15
<p>Representative microscopic images of different material combinations: (<b>a</b>) BE-5050\F305 as base plate with BE-5050 on top; (<b>b</b>) BE-5050\F305 as base plate with BE-5050\V570 on top; (<b>c</b>) BE-5050\V570 as base plate with BE-5050 on top; (<b>d</b>) BE-5050\V570 as base plate with BE-5050\F305 on top.</p> Full article ">Figure 16
<p>Single-material print: Microscopic images of printed micro-features with BE-5050\F305 resin; (<b>a</b>) columns; (<b>b</b>) cuboids.</p> Full article ">Figure 17
<p>Multi-material print: Microscopic images of printed micro-features with BE-5050 as base plate material and BE-5050\F305 as feature material; (<b>a</b>) columns; (<b>b</b>) cuboids.</p> Full article ">
19 pages, 4319 KiB  
Review
A Review on Microdevices for Isolating Circulating Tumor Cells
by Kin Fong Lei
Micromachines 2020, 11(5), 531; https://doi.org/10.3390/mi11050531 - 22 May 2020
Cited by 25 | Viewed by 3557
Abstract
Cancer metastasis is the primary cause of high mortality of cancer patients. Enumeration of circulating tumor cells (CTCs) in the bloodstream is a very important indicator to estimate the therapeutic outcome in various metastatic cancers. The aim of this article is to review [...] Read more.
Cancer metastasis is the primary cause of high mortality of cancer patients. Enumeration of circulating tumor cells (CTCs) in the bloodstream is a very important indicator to estimate the therapeutic outcome in various metastatic cancers. The aim of this article is to review recent developments on the CTC isolation technologies in microdevices. Based on the categories of biochemical and biophysical isolation approaches, a literature review and in-depth discussion will be included to provide an overview of this challenging topic. The current excellent developments suggest promising CTC isolation methods in order to establish a precise indicator of the therapeutic outcome of cancer patients. Full article
(This article belongs to the Special Issue Selected Papers from the 2019 International Conference on Smart Sensors (ICSS))
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<p>Schematic illustration of the microdevice with successively narrower channels for CTC isolation. Varying channel gap widths (20, 15, 10, and 5 μm) separate cells based on size and deformability. (Reprinted from [<a href="#B41-micromachines-11-00531" class="html-bibr">41</a>]).</p> Full article ">Figure 2
<p>Photographs of the (<b>A</b>) 3-dimensional palladium filter cassette and (<b>B</b>) filter sandwiched by the upper and lower cassette piece. SEM images of the (<b>C</b>) three-dimensional palladium filter and (<b>D</b>) tumor cells trapped in the pockets of the filter. (Reprinted from [<a href="#B42-micromachines-11-00531" class="html-bibr">42</a>]).</p> Full article ">Figure 3
<p>Images of cultured prostate cancer cell (<b>A–D</b>) and CTCs from prostate cancer patients (<b>E–L</b>) captured using the CellSearch system. (Reprinted from [<a href="#B35-micromachines-11-00531" class="html-bibr">35</a>]).</p> Full article ">Figure 4
<p>Magnetic sweeper device and cell isolation steps. (<b>A</b>) Magnetic sweeper device showing magnetic rods sheathed in plastic above the capture, wash and release stations. (<b>B</b>) A diagrammatic view of magnetic sweeper cell isolation protocol. (<b>C</b>) A controlled shear force produced by the movement of the magnetic rods in the wash station releases non-specifically bound blood cells. (<b>D</b>) Photomicrograph of a CTC labeled with 4.5 μm immunomagnetic beads. (Reprinted from [<a href="#B44-micromachines-11-00531" class="html-bibr">44</a>]).</p> Full article ">Figure 5
<p>Illustration of the medical wire capturing circulating tumor cells in vivo.</p> Full article ">Figure 6
<p>Illustration of the filtering microstructures in microdevices, including (<b>a</b>) weir, (<b>b</b>) pillar, and (<b>c</b>) pore. Red circles represent the CTCs and blue circles indicate the leukocytes, which are relatively small and easily deformed.</p> Full article ">Figure 7
<p>The outline images show a photograph of the track-etch filter, the microsieve and the TEM grid. The perforated area of each filter is indicated in red. The microsieve contains perforated horizontal bars alternated by support bars, giving rise to the horizontal pattern. The detail shows dark field images for the three filters. Spacing of the pores is random for the track-etch filters, leading to occasional double pores. Microsieves and TEM grids have periodical pore spacing. (Reprinted from [<a href="#B56-micromachines-11-00531" class="html-bibr">56</a>]).</p> Full article ">Figure 8
<p>Particles larger than the critical diameter (D<sub>c</sub>) were deviated towards the left outlet, while smaller particles flowed in the right outlet. The DLD outlet was connected to a T-junction with an oil inlet, for generation of droplets of lengths L<sub>1</sub> and L<sub>2</sub>. (Reprinted from [<a href="#B58-micromachines-11-00531" class="html-bibr">58</a>]).</p> Full article ">Figure 9
<p>Illustration and photograph of the multiplexed spiral microdevice. (Reprinted from [<a href="#B63-micromachines-11-00531" class="html-bibr">63</a>]).</p> Full article ">Figure 10
<p>Schematic image of capturing cells using DEP force. (Reprinted from [<a href="#B66-micromachines-11-00531" class="html-bibr">66</a>]).</p> Full article ">Figure 11
<p>Photography and illustration of the ApoStream<sup>®</sup> instrument. (<b>A</b>) The ApoStream<sup>®</sup> prototype instrument. (<b>B</b>) Illustration of the flow chamber showing V-shaped injection and collection ports. (<b>C</b>) Step 1: Sample processing by Ficoll density gradient separation to isolate blood cells and CTCs. Step 2: Dielectrophoresis (DEP) enrichment starting with sample injection, ion diffusion, DEP separation of CTCs from blood cells, and CTC collection. Step 3: Downstream analysis using immunofluorescence or other techniques for CTC identification and enumeration. (Reprint from [<a href="#B69-micromachines-11-00531" class="html-bibr">69</a>]).</p> Full article ">Figure 12
<p>(<b>a</b>) Schematic diagram of the microdevice for cell separation using multi-orifice flow fractionation (MOFF) and DEP. In the first separation region, the relatively larger cancer cells and a few blood cells passed through the center channel and entered the DEP channel, after which most blood cells exited through outlet I. In the focusing region, all cells experienced a positive DEP force and then aligned along both sides of the channel. Finally, the second separation region selectively isolated cancer cells via DEP. (<b>b</b>) Photography of the fabricated microdevice. (Reprinted from [<a href="#B28-micromachines-11-00531" class="html-bibr">28</a>]).</p> Full article ">Figure 13
<p>(<b>a</b>) Schematic illustration of the microdevice (top-view layout). (<b>b</b>) Photographs of continuous micro-droplet generation process ((I)-(IV)) (Reprinted from [<a href="#B74-micromachines-11-00531" class="html-bibr">74</a>]).</p> Full article ">
23 pages, 4225 KiB  
Review
Recent Advances in Electrochemiluminescence-Based Systems for Mammalian Cell Analysis
by Kaoru Hiramoto, Elena Villani, Tomoki Iwama, Keika Komatsu, Shinsuke Inagi, Kumi Y. Inoue, Yuji Nashimoto, Kosuke Ino and Hitoshi Shiku
Micromachines 2020, 11(5), 530; https://doi.org/10.3390/mi11050530 - 22 May 2020
Cited by 43 | Viewed by 5744
Abstract
Mammalian cell analysis is essential in the context of both fundamental studies and clinical applications. Among the various techniques available for cell analysis, electrochemiluminescence (ECL) has attracted significant attention due to its integration of both electrochemical and spectroscopic methods. In this review, we [...] Read more.
Mammalian cell analysis is essential in the context of both fundamental studies and clinical applications. Among the various techniques available for cell analysis, electrochemiluminescence (ECL) has attracted significant attention due to its integration of both electrochemical and spectroscopic methods. In this review, we summarize recent advances in the ECL-based systems developed for mammalian cell analysis. The review begins with a summary of the developments in luminophores that opened the door to ECL applications for biological samples. Secondly, ECL-based imaging systems are introduced as an emerging technique to visualize single-cell morphologies and intracellular molecules. In the subsequent section, the ECL sensors developed in the past decade are summarized, the use of which made the highly sensitive detection of cell-derived molecules possible. Although ECL immunoassays are well developed in terms of commercial use, the sensing of biomolecules at a single-cell level remains a challenge. Emphasis is therefore placed on ECL sensors that directly detect cellular molecules from small portions of cells or even single cells. Finally, the development of bipolar electrode devices for ECL cell assays is introduced. To conclude, the direction of research in this field and its application prospects are described. Full article
(This article belongs to the Special Issue Micro and Nano Devices for Cell Analysis)
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<p>Various electrochemiluminescence (ECL) devices for cell analysis. (<b>a</b>) Chip devices not for microscopic imaging. (<b>b</b>) ECL microscopes. (<b>c</b>) Bipolar electrode (BPE) devices. (<b>d</b>) Probe devices.</p> Full article ">Figure 2
<p>ECL imaging of cell membranes and cell adhesion. (<b>a</b>) ECL imaging of cell membranes. Chinese hamster ovary (CHO) cells were modified with biotin, and streptavidin-modified Ru(bpy)<sub>3</sub><sup>2+</sup> (SA@Ru) was then attached to the membranes. Reproduced with permission from [<a href="#B40-micromachines-11-00530" class="html-bibr">40</a>]. (<b>b</b>) ECL imaging of cell-matrix adhesions. PC12 cells were cultured on the electrode. Scale bar = 20 µm. Reproduced with permission from [<a href="#B21-micromachines-11-00530" class="html-bibr">21</a>]. (<b>c</b>) ECL-based capacitance microscopy for the imaging of antigens on cells. Carcinoembryonic antigen (CEA) was labeled with an anti-CEA antibody. Reproduced with permission from [<a href="#B41-micromachines-11-00530" class="html-bibr">41</a>].</p> Full article ">Figure 3
<p>ECL imaging of H<sub>2</sub>O<sub>2</sub> released from single cells. (<b>a</b>) A double-potential mode was demonstrated to obtain differential ECL images of H<sub>2</sub>O<sub>2</sub> before and after stimulation by phorbol myristate acetate (PMA). Reproduced with permission from [<a href="#B43-micromachines-11-00530" class="html-bibr">43</a>]. (<b>b</b>) The chitosan film was modified on an electrode to improve the diffusion of ECL chemicals. <span class="html-italic">N</span>-Formylmethionyl-leucyl-phenylalanine (fMLP) was used for the stimulation. Reproduced with permission from [<a href="#B44-micromachines-11-00530" class="html-bibr">44</a>]. (<b>c</b>) Silica mesochannels (SMCs) were modified to improve the sensitivity. LH<sup>−</sup>: L012 anion; AP<sup>2−</sup>: 3-aminophthalate anion. Reproduced with permission from [<a href="#B45-micromachines-11-00530" class="html-bibr">45</a>].</p> Full article ">Figure 4
<p>ECL detection of intracellular molecules. (<b>a</b>) ECL detection of intracellular glucose. Individual cells were trapped inside the microwells with an indium tin oxide (ITO) electrode. Cells were lysed to release glucose, and the glucose was reacted with glucose oxidase to produce H<sub>2</sub>O<sub>2</sub>. The H<sub>2</sub>O<sub>2</sub> was visualized using ECL imaging. Reproduced with permission from [<a href="#B52-micromachines-11-00530" class="html-bibr">52</a>]. (<b>b</b>) ECL detection of intracellular microRNA (miRNA). Au nanoclusters (NCs) were introduced as a probe, and reactive oxygen species (ROS) were released after the miRNA recognition. The ROS were visualized using luminol at the fluorine-doped tin oxide (FTO) electrode. Reproduced with permission from [<a href="#B55-micromachines-11-00530" class="html-bibr">55</a>]. (<b>c</b>) ECL detection of intracellular H<sub>2</sub>O<sub>2</sub> using a capillary electrode. Chitosan/luminol was filled with the tip. Intracellular H<sub>2</sub>O<sub>2</sub> was converted into the ECL signals. Reproduced with permission from [<a href="#B56-micromachines-11-00530" class="html-bibr">56</a>].</p> Full article ">Figure 5
<p>Conceptual image of cytosensing by the ECL technique. The choice of ECL probes and substrates for cell capture varies among different kinds of nanomaterials and their combinations.</p> Full article ">Figure 6
<p>Schematic illustration of the luminol-H<sub>2</sub>O<sub>2</sub> system with a glucose oxidase-conjugated sodium alginate (GOx@SA) nanoprobe for the detection of cell surface glycans. Glucose oxidase on the nanoprobe catalyzes the oxidation of glucose to produce hydrogen peroxide, which improves the ECL signal. Reproduced with permission from [<a href="#B67-micromachines-11-00530" class="html-bibr">67</a>].</p> Full article ">Figure 7
<p>Schematic illustration of the dual ECL signal system. ECL signals at cathodic and anodic potentials can be obtained using CdS quantum dots (QDs) and luminol as ECL emitters, respectively. Reproduced with permission from [<a href="#B76-micromachines-11-00530" class="html-bibr">76</a>].</p> Full article ">Figure 8
<p>BPE devices for ECL-based cell analysis. (<b>a</b>) Detection of the respiration activity of the cell aggregates. A closed BPE system was used. Cell aggregates were set on cathodic poles, and ECL signals were acquired at the anodic poles. When the respiration activity was high, the ECL signal was low. Reproduced with permission from [<a href="#B90-micromachines-11-00530" class="html-bibr">90</a>]. (<b>b</b>) Intracellular analysis using the nanopipette. The open BPE system was prepared in the nanopipette and inserted into a single cell. When the intracellular molecules diffused into the nanopipette, the ECL emission was observed. Overlaid images of ECL and bright field allow the visualization of H<sub>2</sub>O<sub>2</sub>, glucose, and sphingomyelinase (SMase) in a single cell. Reproduced with permission from [<a href="#B97-micromachines-11-00530" class="html-bibr">97</a>].</p> Full article ">Scheme 1
<p>The two ECL routes of the Ru(bpy)<sub>3</sub><sup>2+</sup>-tri-<span class="html-italic">n</span>-propylamine (TPrA) system, in which Ru(bpy)<sub>3</sub><sup>2+</sup> and TPrA are both oxidized directly on the electrode.</p> Full article ">Scheme 2
<p>The possible ECL route of the Ru(bpy)<sub>3</sub><sup>2+</sup>-TPrA system in which Ru(bpy)<sub>3</sub><sup>2+</sup> is not directly oxidized on the electrode but reacts with electrogenerated TPrA radicals.</p> Full article ">Scheme 3
<p>The ECL mechanism of the luminol-H<sub>2</sub>O<sub>2</sub> system.</p> Full article ">
13 pages, 2588 KiB  
Article
Investigation on the Stability of Random Vortices in an Ion Concentration Polarization Layer with Imposed Normal Fluid Flow
by Jihye Choi, Ali Mani, Hyomin Lee and Sung Jae Kim
Micromachines 2020, 11(5), 529; https://doi.org/10.3390/mi11050529 - 22 May 2020
Cited by 9 | Viewed by 2929
Abstract
While nanoscale electrokinetic studies based on ion concentration polarization has been actively researched recently, random vortices naturally occur, leading to significantly destabilize in laboratory experiments or practical applications. These random vortices agitate the fluid inside microchannels and let the sample molecules seriously leak [...] Read more.
While nanoscale electrokinetic studies based on ion concentration polarization has been actively researched recently, random vortices naturally occur, leading to significantly destabilize in laboratory experiments or practical applications. These random vortices agitate the fluid inside microchannels and let the sample molecules seriously leak out preventing them from being controlled. Therefore, several trials have been reported to regulate those uninvited fluctuations by fluid flow tangential to a nanoporous membrane. Indeed, the influence of normal flow should be studied since the mass transport happens in the normal direction to the membrane. Thus, in this work, the nonlinear influence of normal flow to the instability near ion-selective surface was investigated by fully-coupled direct numerical simulation using COMSOL Multiphysics. The investigation on the effect of normal flow revealed that a space charge layer plays a significant role in the onset and growth of instability. The normal flow from the reservoir into the ion-selective surface pushed the space charge layer and decreased the size of vortices. However, there existed a maximum point for the growth of instability. The squeeze of the space charge layer increased the gradient of ion concentration in the layer, which resulted in escalating the velocity of vortices. On the other hand, the normal flow from the ion-selective surface into the reservoir suppressed the instability by spreading ions in the expanding space charge layer, leading to the reduction of ion concentration delayed the onset of instability. These two different mechanisms rendered asymmetric transition of stability as a function of the Peclet number and applied voltage. Therefore, this investigation would help understand the growth of instability and control the inevitable random vortices for the inhibition of fluid-agitation and leakage. Full article
(This article belongs to the Special Issue Electrokinetics in Micro-/nanofluidic Devices)
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<p>Schematic of numerical domain. The characteristic length scale was 1 for the <span class="html-italic">y</span>-directional length of the domain, while it was 4 for the <span class="html-italic">x</span>-directional one. The reservoir was assumed to have uniform ion concentration. The ion-selective surface was water-permeable, through which only cations and fluid flow can pass. The periodic boundary condition described an infinite domain case in horizontal direction.</p> Full article ">Figure 2
<p>Cation concentration according to each time lapse and the ion concentration of space charge layer (SCL) when (<b>a</b>) the fluid flow was imposed from the reservoir into the ion-selective surface (<span class="html-italic">Pe</span> = −4), and (<b>b</b>) there was no fluid flow (<span class="html-italic">Pe</span> = 0) and (<b>c</b>) the fluid flow was imposed from the ion-selective surface into the reservoir (<span class="html-italic">Pe</span> = 12.5). The white lines represent stream line and the white arrows indicate the direction of the flow. Note that the ion concentrations were rendered in a log scale and denoted time was dimensionless. In order to avoid confusion between dimensional and dimensionless variables, we notated dimensional time (<math display="inline"><semantics> <mover accent="true"> <mi>t</mi> <mo>˜</mo> </mover> </semantics></math>) at the case of <span class="html-italic">t</span> = 2. This value was corresponded with the case of <span class="html-italic">O</span>(100) μm gap filling with <span class="html-italic">O</span>(100) μM KCl electrolyte.</p> Full article ">Figure 3
<p>The plot of growth rate according to the <span class="html-italic">Pe</span>. The tendency of changes in growth rate was different depending on the direction of normal flow. When the <span class="html-italic">Pe</span> was positive (upward fluid flow), the growth rate decreased monotonically. There was a maximum point of the growth rate when the <span class="html-italic">Pe</span> was negative (downward fluid flow).</p> Full article ">Figure 4
<p>The different behavior of growth rate depending on the sign of <span class="html-italic">Pe</span> (<span class="html-italic">t</span> = 0.2) was attributed to the distribution of ion concentration in the domain. (<b>a</b>) Representative schematic for electrical double layer (EDL), SCL, and mixing layer (ML) (<span class="html-italic">Pe</span> = -20, <span class="html-italic">ϕ</span> = 50). (<b>b</b>) Averaged concentrations at <span class="html-italic">ϕ</span> = 50 with varying <span class="html-italic">Pe</span> from negative to positive.</p> Full article ">Figure 5
<p>(<b>a</b>) A stability map was investigated as a function of both applied voltage and the properties of imposed normal fluid flow. A cross sign indicated that there existed vortices (unstable) and a circle sign indicated that there were no vortices in the domain (stable). Marginal stability curve (dotted line) was also obtained. In the case of positive <span class="html-italic">Pe</span>, the marginal curve followed ~ |<span class="html-italic">Pe</span>|<sup>1.15</sup>. In the case of negative <span class="html-italic">Pe</span>, the marginal curve followed ~ |<span class="html-italic">Pe</span>|<sup>0.45</sup>. (<b>b</b>) The distribution of ion concentration in the domain along increasing <span class="html-italic">Pe</span> from negative to positive value at <span class="html-italic">ϕ</span> = 50.</p> Full article ">
13 pages, 7581 KiB  
Article
Study on Electrical Explosion Properties of Cu/Ni Multilayer Exploding Foil Prepared by Magnetron Sputtering and Electroplating
by Fan Lei, Qin Ye, Shuang Yang and Qiubo Fu
Micromachines 2020, 11(5), 528; https://doi.org/10.3390/mi11050528 - 22 May 2020
Cited by 5 | Viewed by 2963
Abstract
The purpose of this study was to investigate the effects of the microstructure and properties of Cu/Ni multilayer films prepared by magnetron sputtering and electroplating on the electrical explosion performance of the films. In this study, Cu/Ni multilayer films of the same thickness [...] Read more.
The purpose of this study was to investigate the effects of the microstructure and properties of Cu/Ni multilayer films prepared by magnetron sputtering and electroplating on the electrical explosion performance of the films. In this study, Cu/Ni multilayer films of the same thickness were prepared by electroplating (EP) and magnetron sputtering (MS), and their morphology and crystal structure were characterized by scanning electron microscope (SEM) and transmission electron microscope (TEM). XRD was used to observe the crystal structure and size of the samples. In addition, the Cu/Ni multilayer film was etched into the shape of a bridge, and the electric explosion phenomenon in the same discharge circuit of the multilayer foil obtained by the two preparation processes was tested by an electric explosion performance test system. The resistance–time curve and the energy–resistance curve during the electric explosion process were analyzed and calculated. The results showed that compared with the multilayer film prepared by the MS method, the crystal size of the multilayer film prepared by the EP method is smaller and the interface of Cu/Ni is clearer. In the electric explosion experiment, the MS samples had earlier burst times, larger peak resistances, smaller peak energies and higher ionization voltages. Through observation of the morphology of the samples after the electric explosion and combination with gas ionization theory, the internal influencing factors of the peak voltage and the relative resistance of the two samples were analyzed. The influence of the multilayer film mixing layer thickness on the sample energy conversion efficiency was analyzed by modeling the microstructure of the multilayer film exploding foil and electric heating. The results show that the thicker the mixing layer is, the more energy is distributed on the Ni, the faster the resistance increases, and the higher the energy conversion efficiency. Full article
(This article belongs to the Special Issue Miniaturized Pyro Devices)
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<p>The initial morphology (face view, scale bar: 200 nm) and the diagrammatic sketch (side view) of two samples.</p> Full article ">Figure 2
<p>Electric explosion experimental system for multilayer foil. (<span class="html-italic">R</span>—foil resistance; <span class="html-italic">U</span>—foil voltage; <span class="html-italic">R</span><sub>0</sub>—line resistance; <span class="html-italic">U</span><sub>0</sub>—initial charging voltage; <span class="html-italic">L</span><sub>0</sub>—loop resistance.).</p> Full article ">Figure 3
<p>SEM diagram of the foil section of the multilayer bridge (side view, scale bar: 2 μm).</p> Full article ">Figure 4
<p>TEM diagram of the foil section of the multilayer bridge (side view, scale bar: 200 nm).</p> Full article ">Figure 5
<p>Comparison of XRD peaks of EP and MS samples.</p> Full article ">Figure 6
<p>Resistance–time curves of the two samples under different <span class="html-italic">U</span><sub>0</sub>.</p> Full article ">Figure 7
<p>Morphological characteristics of two samples after electric explosion.</p> Full article ">Figure 8
<p>R (resistance)–q (absorption energy) curves of two samples under different <span class="html-italic">U</span><sub>0</sub>.</p> Full article ">Figure 9
<p>Single-layer mixing model of multilayer foil (horizontal direction is its thickness direction).</p> Full article ">Figure 10
<p>Theoretical simulation of the resistance curves of two samples with time under different <span class="html-italic">U</span><sub>0</sub>.</p> Full article ">Figure 11
<p>Simulation results of the temperature–time curve of each part of the two samples with different mixing layer thicknesses (<span class="html-italic">U</span><sub>0</sub> = 2500 V).</p> Full article ">
13 pages, 6290 KiB  
Article
Direct Write of 3D Nanoscale Mesh Objects with Platinum Precursor via Focused Helium Ion Beam Induced Deposition
by Alex Belianinov, Matthew J. Burch, Anton Ievlev, Songkil Kim, Michael G. Stanford, Kyle Mahady, Brett B. Lewis, Jason D. Fowlkes, Philip D. Rack and Olga S. Ovchinnikova
Micromachines 2020, 11(5), 527; https://doi.org/10.3390/mi11050527 - 22 May 2020
Cited by 21 | Viewed by 3977
Abstract
The next generation optical, electronic, biological, and sensing devices as well as platforms will inevitably extend their architecture into the 3rd dimension to enhance functionality. In focused ion beam induced deposition (FIBID), a helium gas field ion source can be used with an [...] Read more.
The next generation optical, electronic, biological, and sensing devices as well as platforms will inevitably extend their architecture into the 3rd dimension to enhance functionality. In focused ion beam induced deposition (FIBID), a helium gas field ion source can be used with an organometallic precursor gas to fabricate nanoscale structures in 3D with high-precision and smaller critical dimensions than focused electron beam induced deposition (FEBID), traditional liquid metal source FIBID, or other additive manufacturing technology. In this work, we report the effect of beam current, dwell time, and pixel pitch on the resultant segment and angle growth for nanoscale 3D mesh objects. We note subtle beam heating effects, which impact the segment angle and the feature size. Additionally, we investigate the competition of material deposition and sputtering during the 3D FIBID process, with helium ion microscopy experiments and Monte Carlo simulations. Our results show complex 3D mesh structures measuring ~300 nm in the largest dimension, with individual features as small as 16 nm at full width half maximum (FWHM). These assemblies can be completed in minutes, with the underlying fabrication technology compatible with existing lithographic techniques, suggesting a higher-throughput pathway to integrating FIBID with established nanofabrication techniques. Full article
(This article belongs to the Special Issue Nanofabrication with Focused Electron/Ion Beam Induced Processing)
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Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>Focused-ion-beam-induced deposition (FIBID) diagram, calibration structure growth, and parametrization. (<b>a</b>) FIBID process in the helium ion microscopy (HIM) diagram, different structures are obtained by changing the beam pitch. (<b>b</b>) PtC structure array, made at 25 kV, 0.54 pA beam current with a 5 μm aperture with 8.142 mm working distance, columns are varying dwell times of 4, 6, 9, and 12 ms, and rows are varying pitch of 0.25, 0.5, 1.0 and 1.5 nm, respectively. (<b>c</b>) An example of a parametrized pillar grown for calibration of growth parameters with pillar values extracted.</p> Full article ">Figure 2
<p>(<b>a</b>) Plot of the segment angle versus the He<sup>+</sup> dwell time at different pixel point pitches for a beam energy of 25 keV, a beam current of 0.54 pA and a precursor chamber pressure of 1 × 10<sup>−5</sup> Torr. (<b>b</b>) Plot of the resultant segment height (<span class="html-italic">h</span>) for a fixed lateral scan length (<span class="html-italic">sl</span>) versus dwell time per lateral displacement (DTPLD) (s nm<sup>−1</sup>), (<b>c</b>) plot of the vertical growth per current (nm-pA-1). Beam energy of 25 keV, beam currents of 0.38 pA, 0.54 pA and 2.3 pA, and a precursor chamber pressure of 1 × 10<sup>−5</sup> torr used in (<b>b</b>,<b>c</b>).</p> Full article ">Figure 3
<p>(<b>a</b>) Plot of <span class="html-italic">w</span> as a function of the dwell time per lateral displacement (DTPLD) (s nm<sup>−1</sup>), for beam energy of 25 keV, beam currents of 0.38 pA, 0.54 pA and 2.3 pA, and a precursor chamber pressure of 1 × 10<sup>−5</sup> Torr. (<b>b</b>) Example of two pillars bending in segments grown at 25 keV, 2.3 pA, with 12 ms dwell time, and 0.25 nm and 2 nm pixel pitches, respectively.</p> Full article ">Figure 4
<p>EnvizION Monte Carlo simulation results. (<b>a</b>) Schematic of the initial geometry for sputtering simulations. (<b>b</b>) Pillar corresponding to the 4 ms dwell time scan (~5.6 million ions), and (<b>c</b>) pillar corresponding to the 12 ms dwell time scan (~16.8 million ions).</p> Full article ">Figure 5
<p>Examples of grown structures with ~16 nm features at full width half maximum (FWHM). (<b>a</b>) Side view of the structures with increasing dwell time of 4, 6, and 8 ms, respectively. (<b>b</b>) Top view of the structures in (<b>a</b>). (<b>c</b>) Line profile of the structures along the green line shown in panel (<b>b</b>) with zoom in of FWHM = 16.8 nm pillar.</p> Full article ">Figure 6
<p>Complex 3D structures made with FIBID, (<b>a</b>) deltahedron grown on a pillar on a conductive substrate and (<b>b</b>) a truncated icosahedron a conductive substrate (<b>c</b>) pillars and (<b>d</b>) deltahedron grown on insulating SiO<sub>2</sub>.</p> Full article ">Figure 7
<p>Energy dispersive X-ray spectroscopy (EDS) purity analysis of FIBID structures at three different currents. Blue = 0.52 pA, Green = 1.35 pA, Red = 2.70 pA.</p> Full article ">
13 pages, 3122 KiB  
Article
Development of a Portable SPR Sensor for Nucleic Acid Detection
by Yafeng Huang, Lulu Zhang, Hao Zhang, Yichen Li, Luyao Liu, Yuanyuan Chen, Xianbo Qiu and Duli Yu
Micromachines 2020, 11(5), 526; https://doi.org/10.3390/mi11050526 - 21 May 2020
Cited by 30 | Viewed by 4006
Abstract
Nucleic acid detection is of great significance in clinical diagnosis, environmental monitoring and food safety. Compared with the traditional nucleic acid amplification detection method, surface plasmon resonance (SPR) sensing technology has the advantages of being label-free, having simple operation, and providing real-time detection. [...] Read more.
Nucleic acid detection is of great significance in clinical diagnosis, environmental monitoring and food safety. Compared with the traditional nucleic acid amplification detection method, surface plasmon resonance (SPR) sensing technology has the advantages of being label-free, having simple operation, and providing real-time detection. However, the angle scanning system in many SPR angle modulation detection applications usually requires a high-resolution stepper motor and complex mechanical structure to adjust the angle. In this paper, a portable multi-angle scanning SPR sensor was designed. The sensor only uses one stepping motor to rotate a belt, and the belt pulls the mechanical linkages of incident light and reflected light to move in opposite directions for achieving the SPR angle scanning mode that keeps the incident angle and reflected angle equal. The sensor has an angle scanning accuracy of 0.002°, response sensitivity of 3.72 × 10−6 RIU (refractive index unit), and an angle scanning range of 30°–74°. The overall size of the system is only 480 mm × 150 mm × 180 mm. The portable SPR sensor was used to detect nucleic acid hybridization on a gold film chip modified with bovine serum albumin (BSA). The result revealed that the sensor had high sensitivity and fast response, and could successfully accomplish the hybridization detection of target DNA solution of 0.01 μmol/mL. Full article
(This article belongs to the Special Issue Microfluidics for Nucleic Acid Analysis)
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<p>(<b>a</b>) Schematic of angle modulation (Position 1); (<b>b</b>) schematic of angle modulation (Position 2).</p> Full article ">Figure 2
<p>Real surface plasmon resonance (SPR) instrument set-up in this paper.</p> Full article ">Figure 3
<p>Schematic illustration of the experimental protocol.</p> Full article ">Figure 4
<p>Angle scanning curve of deionized water.</p> Full article ">Figure 5
<p>Linear regression curves of unmodified gold film chip.</p> Full article ">Figure 6
<p>Linear regression curves of gold film chip modified with bovine serum albumin (BSA).</p> Full article ">Figure 7
<p>(<b>a</b>) Reaction curve of streptavidin (SA) binding to BSA; (<b>b</b>) reaction curves of DNA probes binding to SA.</p> Full article ">Figure 8
<p>Reaction curves of DNA hybridization detection.</p> Full article ">Figure 9
<p>Standard curve of target DNA sequences.</p> Full article ">
11 pages, 2628 KiB  
Article
Investigation on Threshold Voltage Adjustment of Threshold Switching Devices with HfO2/Al2O3 Superlattice on Transparent ITO/Glass Substrate
by Yejoo Choi, Jaemin Shin, Seungjun Moon and Changhwan Shin
Micromachines 2020, 11(5), 525; https://doi.org/10.3390/mi11050525 - 21 May 2020
Cited by 4 | Viewed by 4041
Abstract
Threshold voltage adjustment in threshold switching (TS) devices with HfO2/Al2O3 superlattice (by means of changing the cycle ratio of HfO2 to Al2O3 in atomic layer deposition) is investigated to implement a transparent cross-point array. [...] Read more.
Threshold voltage adjustment in threshold switching (TS) devices with HfO2/Al2O3 superlattice (by means of changing the cycle ratio of HfO2 to Al2O3 in atomic layer deposition) is investigated to implement a transparent cross-point array. TS devices with different cycle ratios (i.e., 3:1, 3:2, and 3:3) were fabricated and studied. The threshold voltage of the devices was increased from 0.9 V to 3.2 V, as the relative contents of Al2O3 layer in the superlattice were increased. At the same time, it is demonstrated that the off-resistance values of the devices were enhanced from 2.6 × 109 to 6 × 1010 Ω as the atomic layer deposition (ALD) cycle ratio of HfO2 to Al2O3 layer was adjusted from 3:1 to 3:3. However, the hold voltage and the on-current values were almost identical for the three devices. These results can be understood using the larger barrier height of Al2O3 layer than that of HfO2 layer. Full article
(This article belongs to the Special Issue Deformable Bioelectronics Based on Functional Micro/nanomaterials)
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<p>(<b>a</b>) Structure of HfO<sub>2</sub>/Al<sub>2</sub>O<sub>3</sub> superlattice (HAO)-based TS devices: DUT (Device Under Test)_A (left), DUT_B (middle), and DUT_C (right). (<b>b</b>) Fabrication process of HAO-based TS devices on a transparent ITO/glass substrate.</p> Full article ">Figure 2
<p>(<b>a</b>) Illustration of filaments in memory switching device. The stable filaments are formed in the dielectric layer with the compliance current higher than a critical current value. The filament is composed of top electrode material. (<b>b</b>) Illustration of filaments in threshold voltage switching device. The unstable filaments are formed in the dielectric layer with the compliance current smaller than a critical current value. Therefore, the unstable filament can be dissolved with a sufficiently small positive voltage (i.e., hold voltage). The filament is composed of top electrode material.</p> Full article ">Figure 3
<p>(<b>a</b>) Measured current vs. voltage of the HAO−based TS devices: DUT_A, DUT_B, and DUT_C. The compliance current is set to 10<sup>−6</sup> A for realizing threshold switching characteristics. (<b>b</b>) The threshold voltage and hold voltage characteristics of the fabricated HAO-based TS devices. DUT_A, DUT_B, and DUT_C have a HfO<sub>2</sub>:Al<sub>2</sub>O<sub>3</sub> cycle ratio of 3:1, 3:2, and 3:3, respectively.</p> Full article ">Figure 4
<p>(<b>a</b>) The energy band diagram of Ag/HfO<sub>2</sub>/ITO device (<b>left</b>) and Ag/Al<sub>2</sub>O<sub>3</sub>/ITO device (<b>right</b>). Due to the larger bandgap energy (i.e., 7 eV) of Al<sub>2</sub>O<sub>3</sub>, the Al<sub>2</sub>O<sub>3</sub> layer acts as diffusion barrier, and thus it increases the threshold voltage and the off-resistance value. (<b>b</b>) The cross-sectional view of HfO<sub>2</sub>/Al<sub>2</sub>O<sub>3</sub> superlattice TS device. In this superlattice, the Al<sub>2</sub>O<sub>3</sub> layers act as a diffusion barrier.</p> Full article ">Figure 5
<p>(<b>a</b>) The measured resistance vs. voltage of the HAO-based TS devices before being turned-on: DUT_A, DUT_B, and DUT_C. (<b>b</b>) The measured resistance vs. voltage of the HAO-based TS devices before being turned-off: DUT_A, DUT_B, and DUT_C. When the devices are fully turned-on, the resistance values are not extracted because the on-current values are identical to the compliance current of 10<sup>−6</sup> A.</p> Full article ">
13 pages, 4644 KiB  
Article
PIN-PMN-PT Single Crystal 1-3 Composite-based 20 MHz Ultrasound Phased Array
by Wei Zhou, Tao Zhang, Jun Ou-Yang, Xiaofei Yang, Dawei Wu and Benpeng Zhu
Micromachines 2020, 11(5), 524; https://doi.org/10.3390/mi11050524 - 21 May 2020
Cited by 25 | Viewed by 4779
Abstract
Based on a modified dice-and-fill technique, a PIN-PMN-PT single crystal 1-3 composite with the kerf of 12 μm and pitch of 50 μm was prepared. The as-made piezoelectric composite material behaved with high piezoelectric constant (d33 = 1500 pC/N), high electromechanical coefficient [...] Read more.
Based on a modified dice-and-fill technique, a PIN-PMN-PT single crystal 1-3 composite with the kerf of 12 μm and pitch of 50 μm was prepared. The as-made piezoelectric composite material behaved with high piezoelectric constant (d33 = 1500 pC/N), high electromechanical coefficient (kt = 0.81), and low acoustic impedance (16.2 Mrayls). Using lithography and flexible circuit method, a 48-element phased array was successfully fabricated from such a piezoelectric composite. The array element was measured to have a central frequency of 20 MHz and a fractional bandwidth of approximately 77% at −6 dB. Of particular significance was that this PIN-PMN-PT single crystal 1-3 composite-based phased array exhibits a superior insertion loss compared with PMN-PT single crystal and PZT-5H-based 20 MHz phased arrays. The focusing and steering capabilities of the obtained phased array were demonstrated theoretically and experimentally. These promising results indicate that the PIN-PMN-PT single crystal 1-3 composite-based high frequency phased array is a good candidate for ultrasound imaging applications. Full article
(This article belongs to the Special Issue Piezoelectric Transducers: Materials, Devices and Applications)
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<p>Schematic of the modified dice-and-fill method used for phased array fabrication.</p> Full article ">Figure 2
<p>Photographs of (<b>A</b>) Au patterned PIN-PMN-PT single crystal 1-3 composite (<b>B</b>) with Flexible Circuit and (<b>C</b>) electrical connections; (<b>D</b>) the side-looking phase array in 3D-printed housing.</p> Full article ">Figure 3
<p>The simulated pulse-echo waveform and frequency spectrum of the transducer using the PiezoCAD software.</p> Full article ">Figure 4
<p>(<b>A</b>) Electrical impedance magnitude and (<b>B</b>) phase as a function of frequency for 48 elements. (<b>C</b>) Electrical impedance magnitude and (<b>D</b>) phase as a function of frequency for the 24th element.</p> Full article ">Figure 5
<p>(<b>A</b>) Measured pulse-echo response performance of random element; (<b>B</b>) sensitivity and bandwidth of the pulse-echo signal for each element.</p> Full article ">Figure 6
<p>(<b>A</b>) Measured one-way azimuthal directivity responses of a representative array element (24th element). (<b>B</b>) The acoustic output in the axial direction of a representative array element (24th element) and the entire array.</p> Full article ">Figure 7
<p>Point spread function phantom-imaged (<b>A</b>) without and (<b>B</b>) with apodization. (<b>C</b>) Simulated phased array acoustic pressure of emission mode when the steering angle is 0°. (<b>D</b>) Simulated acoustic beam generated by the 48-element phased array when the steering angle is 45°and the focal distance is 3 mm.</p> Full article ">Figure 8
<p>Schematic diagram of tungsten wire phantom in deionized water.</p> Full article ">Figure 9
<p>(<b>A</b>) Acquired image of custom-made fine-wire phantom. (<b>B</b>) Pseudo-color image of custom-made fine-wire phantom.</p> Full article ">Figure 10
<p>(<b>A</b>) Axial and (<b>B</b>) lateral line spread functions for the second wire of the wire phantom.</p> Full article ">Figure 11
<p>Schematic diagram of copper wire phantom in PDMS.</p> Full article ">Figure 12
<p>(<b>A</b>) Copper wires phantom image. (<b>B</b>) Pseudo-color image of copper wires phantom.</p> Full article ">
13 pages, 3791 KiB  
Article
Magnetostrictive Performance of Electrodeposited TbxDy(1−x)Fey Thin Film with Microcantilever Structures
by Hang Shim, Kei Sakamoto, Naoki Inomata, Masaya Toda, Nguyen Van Toan and Takahito Ono
Micromachines 2020, 11(5), 523; https://doi.org/10.3390/mi11050523 - 21 May 2020
Cited by 13 | Viewed by 3920
Abstract
The microfabrication with a magnetostrictive TbxDy(1−x)Fey thin film for magnetic microactuators is developed, and the magnetic and magnetostrictive actuation performances of the deposited thin film are evaluated. The magnetostrictive thin film of TbxDy(1−x)Fey [...] Read more.
The microfabrication with a magnetostrictive TbxDy(1−x)Fey thin film for magnetic microactuators is developed, and the magnetic and magnetostrictive actuation performances of the deposited thin film are evaluated. The magnetostrictive thin film of TbxDy(1−x)Fey is deposited on a metal seed layer by electrodeposition using a potentiostat in an aqueous solution. Bi-material cantilever structures with the Tb0.36Dy0.64Fe1.9 thin-film are fabricated using microfabrication, and the magnetic actuation performances are evaluated under the application of a magnetic field. The actuators show large magnetostriction coefficients of approximately 1250 ppm at a magnetic field of 11000 Oe. Full article
(This article belongs to the Section D：Materials and Processing)
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<p>Energy-dispersive X-ray spectroscopy <b><span class="html-italic">(</span></b>EDX) spectrum of the Tb<sub>x</sub>Dy<sub>(1−x)</sub>Fe<sub>y</sub> film formed at an electrochemical potential of −930 mV.</p> Full article ">Figure 2
<p>Composition dependence on the applied working electrode potential on a Cu seed layer.</p> Full article ">Figure 3
<p>In-plane magnetization measurement of the Tb<sub>x</sub>Dy<sub>(1−x)</sub>Fe<sub>y</sub> film using vibrating sample magnetometer (VSM).</p> Full article ">Figure 4
<p>Atomic force microscopy image of the deposited film.</p> Full article ">Figure 5
<p>Magnetic force microscopy the deposited film.</p> Full article ">Figure 6
<p>Fabrication process of the magnetostrictive bi-material cantilevers.</p> Full article ">Figure 7
<p>SEM images of fabricated Tb<sub>0.34</sub>Dy<sub>0.65</sub>Fe<sub>1.9</sub> bi-material cantilevers. (<b>a</b>) Low magnification of bi-material cantilevers; (<b>b</b>) High magnification of bi-material cantilevers.</p> Full article ">Figure 8
<p>Optical images of side view for the typical magnetostrictive actuation of the Si- Tb<sub>0.34</sub>Dy<sub>0.65</sub>Fe<sub>1.9</sub> bi-material cantilever for the cases without magnetic field and with a magnetic field of 11 kOe along the cantilever direction.</p> Full article ">Figure 9
<p>Observed displacements of the cantilevers with different lengths (700, 1000, 1100 µm).</p> Full article ">Figure 10
<p>Magnetostriction coefficients of the Tb<sub>0.36</sub>Dy<sub>0.64</sub>Fe<sub>1.9</sub> film obtained from three cantilevers with lengths 700, 1000, 1100 µm.</p> Full article ">Figure 11
<p>Generated forces of Tb<sub>0.36</sub>Dy<sub>0.64</sub>Fe<sub>1.9</sub> obtained from three cantilevers with lengths 700, 1000, 1100 µm.</p> Full article ">Figure 12
<p>Comparison of energy densities for Tb<sub>0.36</sub>Dy<sub>0.64</sub>Fe<sub>1.9</sub> and another types of actuators [<a href="#B40-micromachines-11-00523" class="html-bibr">40</a>].</p> Full article ">
13 pages, 2473 KiB  
Article
Mechanically Enabled Two-Axis Ultrasonic-Assisted System for Ultra-Precision Machining
by Nan Yu, Jinghang Liu, Hélène Mainaud Durand and Fengzhou Fang
Micromachines 2020, 11(5), 522; https://doi.org/10.3390/mi11050522 - 20 May 2020
Cited by 7 | Viewed by 4100
Abstract
With the use of ultrasonic-assisted diamond cutting, an optical surface finish can be achieved on hardened steel or even brittle materials such as glass and infrared materials. The proposed ultrasonic vibration cutting system includes an ultrasonic generator, horn, transducer, cutting tool and the [...] Read more.
With the use of ultrasonic-assisted diamond cutting, an optical surface finish can be achieved on hardened steel or even brittle materials such as glass and infrared materials. The proposed ultrasonic vibration cutting system includes an ultrasonic generator, horn, transducer, cutting tool and the fixture. This study is focused on the design of the ultrasonic vibration cutting system with a high vibration frequency and an optimized amplitude for hard and brittle materials, particularly for moulded steel. A two-dimensional vibration design is developed by means of the finite element analysis (FEA) model. A prototype of the system is manufactured for the test bench. An elliptical trajectory is created from this vibration system with amplitudes of micrometers in two directions. The optimization strategy is presented for the application development. Full article
(This article belongs to the Special Issue Ultra Precision Technologies for Micromachining)
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<p>Schematic of the ultrasonic vibration cutting (UVC) system.</p> Full article ">Figure 2
<p>Development scheme of the proposed UVC system.</p> Full article ">Figure 3
<p>Design of the UVC system including a cooling arrangement.</p> Full article ">Figure 4
<p>The modal analysis of the horn. (<b>a</b>) The amplitude in x direction; (<b>b</b>) The vibration in z direction; (<b>c</b>) The fixation position on the horn.</p> Full article ">Figure 5
<p>Harmonic response analysis of the UVC system: (<b>a</b>) the amplitude in z direction; (<b>b</b>) the vibration in x direction.</p> Full article ">Figure 6
<p>Offline test of the UVC system. (<b>a</b>) Experimental set-up on the optical table; (<b>b</b>) the displacement measurement in the vertical direction of the tool rest of the horn.</p> Full article ">Figure 7
<p>(<b>a</b>) Schematic of the vibration system including an adjustable seismic mass; (<b>b</b>) experimental measurements of the vertical displacement in a set of seismic mass.</p> Full article ">
15 pages, 3283 KiB  
Article
Route to Intelligent Imaging Reconstruction via Terahertz Nonlinear Ghost Imaging
by Juan S. Totero Gongora, Luana Olivieri, Luke Peters, Jacob Tunesi, Vittorio Cecconi, Antonio Cutrona, Robyn Tucker, Vivek Kumar, Alessia Pasquazi and Marco Peccianti
Micromachines 2020, 11(5), 521; https://doi.org/10.3390/mi11050521 - 20 May 2020
Cited by 47 | Viewed by 4194
Abstract
Terahertz (THz) imaging is a rapidly emerging field, thanks to many potential applications in diagnostics, manufacturing, medicine and material characterisation. However, the relatively coarse resolution stemming from the large wavelength limits the deployment of THz imaging in micro- and nano-technologies, keeping its potential [...] Read more.
Terahertz (THz) imaging is a rapidly emerging field, thanks to many potential applications in diagnostics, manufacturing, medicine and material characterisation. However, the relatively coarse resolution stemming from the large wavelength limits the deployment of THz imaging in micro- and nano-technologies, keeping its potential benefits out-of-reach in many practical scenarios and devices. In this context, single-pixel techniques are a promising alternative to imaging arrays, in particular when targeting subwavelength resolutions. In this work, we discuss the key advantages and practical challenges in the implementation of time-resolved nonlinear ghost imaging (TIMING), an imaging technique combining nonlinear THz generation with time-resolved time-domain spectroscopy detection. We numerically demonstrate the high-resolution reconstruction of semi-transparent samples, and we show how the Walsh–Hadamard reconstruction scheme can be optimised to significantly reduce the reconstruction time. We also discuss how, in sharp contrast with traditional intensity-based ghost imaging, the field detection at the heart of TIMING enables high-fidelity image reconstruction via low numerical-aperture detection. Even more striking—and to the best of our knowledge, an issue never tackled before—the general concept of “resolution” of the imaging system as the “smallest feature discernible” appears to be not well suited to describing the fidelity limits of nonlinear ghost-imaging systems. Our results suggest that the drop in reconstruction accuracy stemming from non-ideal detection conditions is complex and not driven by the attenuation of high-frequency spatial components (i.e., blurring) as in standard imaging. On the technological side, we further show how achieving efficient optical-to-terahertz conversion in extremely short propagation lengths is crucial regarding imaging performance, and we propose low-bandgap semiconductors as a practical framework to obtain THz emission from quasi-2D structures, i.e., structure in which the interaction occurs on a deeply subwavelength scale. Our results establish a comprehensive theoretical and experimental framework for the development of a new generation of terahertz hyperspectral imaging devices. Full article
(This article belongs to the Special Issue Nonlinear Photonics Devices)
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<p>Conceptual description of time-resolved nonlinear ghost imaging (TIMING). (<b>a</b>) Schematic of the experimental setup. (<b>b</b>,<b>c</b>) Simulation of the TIMING reconstruction of a semi-transparent sample, including the average field transmission (panel b) and the full spatiotemporal image of the sample (panel c). The simulated object size was 10.24 cm × 10.24 cm, sampled with a spatial resolution of 512 × 512 pixels (Δ<span class="html-italic">x =</span> 200 µm) and a temporal resolution of Δ<span class="html-italic">t</span> = 19.5 fs. The nonlinear crystal thickness was <math display="inline"><semantics> <mrow> <msub> <mi>z</mi> <mn>0</mn> </msub> <mo> </mo> </mrow> </semantics></math>= 10 μm. n.u.: normalised units, TDS: Time-domain spectroscopy.</p> Full article ">Figure 2
<p>Walsh–Hadamard image reconstruction. (<b>a</b>) Generation of incident patterns from the Walsh–Hadamard matrix. Each pattern is defined as the tensor product between two columns of the generating matrix. The patterns can be generated from different configurations of a Hadamard matrix: we show the Walsh, or “sequency”, order (top, used in TIMING) and the standard Hadamard, or “natural”, order (bottom). (<b>b</b>,<b>c</b>) Reconstructed Walsh spectrum of the peak-field object transmission. Interestingly, only a fraction of the patterns (8.1%) were associated with a spectral amplitude exceeding the −60 dB threshold (with 0 dB being the energy correlation of the fittest pattern—panel c). Nevertheless, these patterns were sufficient to provide a high-fidelity reconstruction of the image (insets). (<b>d</b>,<b>e</b>) Pearson correlation coefficients between reconstructed and original images as a function of the number of patterns employed in the reconstruction. The results refer to the entire scan (panel d) and the initial 10% of patterns (panel e).</p> Full article ">Figure 3
<p>Influence of the pinhole size on the Fourier detection of TIMING reconstruction coefficients. <b>(a</b>–<b>d</b>) The spatial average of the transmitted field (<b>b</b>) associated with each incident pattern (<b>a</b>) could be measured by performing a point-like detection in the centre of the Fourier plane (<b>c</b>,<b>d</b>). In realistic implementations, the centre of the Fourier plane is sampled using a sampling function <span class="html-italic">PH</span> of finite diameter <span class="html-italic">d</span>. (<b>e</b>) Spatial correlation between the reconstructed and original image as a function of the sampling function diameter. A departure from the point-like approximation led to a significant corruption of the reconstructed image (insets). Interestingly, the typical image degradation did not necessarily involve the total disappearance of highly resolved details.</p> Full article ">Figure 4
<p>Influence of the pinhole displacement on the Fourier detection of TIMING reconstruction coefficients. (<b>a</b>) Spatial correlation between the reconstructed and original image as a function of the sampling function position in the focal plane. The displacement <span class="html-italic">(Δx, Δy)</span> was measured with respect to the lens axis and the sampling function diameter was set to <span class="html-italic">d</span> = 0.36 mm, corresponding to a spatial correlation of 100% at the centre of the Fourier plane (cf. <a href="#micromachines-11-00521-f003" class="html-fig">Figure 3</a>e). (<b>b</b>–<b>d</b>) Examples of image reconstruction with off-axis detection, illustrating the appearance of spurious spatial frequencies. Interestingly, the object morphology was still noticeable, even at a relatively large distance from the optical axis.</p> Full article ">Figure 5
<p>Surface emission driving mechanisms. (<b>a</b>) Surface optical rectification—a surface field at the air–semiconductor barrier combines with the optical field in a four-wave mixing process (cubic), generating a terahertz mixing product (see Equation (7)). (<b>b</b>) Measurement of the terahertz emission using surface optical rectification with an optical pulsed excitation fluence of 7 mJ/cm<sup>2</sup> (1 kHz repetition rate) and a pulse with a wavelength of 800 nm and a duration of 90 fs. (<b>c</b>) Simplified sketch of the photo-Dember process in InAs. The absorption of an ultrashort pulse generates a high density of photogenerated hole–electron pairs within the optical penetration depth (140 nm). The fast diffusion of the electrons induces a transient current <span class="html-italic">J</span><sub>THz</sub>, which is the source of the terahertz emission. (<b>d</b>) Measurement of the terahertz emission by photo-Dember mechanism with an optical pulsed excitation fluence of 0.28 µJ/cm<sup>2</sup> (80 MHz repetition rate) and pulse with a wavelength of 800 nm and a duration of 140 fs.</p> Full article ">
18 pages, 5075 KiB  
Article
Performance and Accuracy of the Shifted Laser Surface Texturing Method
by Jiří Martan, Denys Moskal, Ladislav Smeták and Milan Honner
Micromachines 2020, 11(5), 520; https://doi.org/10.3390/mi11050520 - 20 May 2020
Cited by 15 | Viewed by 3291
Abstract
A shifted laser surface texturing method (sLST) was developed for the improvement of the production speed of functional surface textures to enable their industrial applicability. This paper compares the shifted method to classic methods using a practical texturing example, with a focus on [...] Read more.
A shifted laser surface texturing method (sLST) was developed for the improvement of the production speed of functional surface textures to enable their industrial applicability. This paper compares the shifted method to classic methods using a practical texturing example, with a focus on delivering the highest processing speed. The accuracy of the texture is assessed by size and circularity measurements with the use of LabIR paint and by a depth profile measurement using a contact surface profiler. The heat accumulation temperature increase and laser usage efficiency were also calculated. The classic methods (path filling and hatch) performed well (deviation ≤ 5%) up to a certain scanning speed (0.15 and 0.7 m/s). For the shifted method, no scanning speed limit was identified within the maximum of the system (8 m/s). The depth profile shapes showed similar deviations (6% to 10%) for all methods. The shifted method in its burst variant achieved the highest processing speed (11 times faster, 146 mm2/min). The shifted method in its path filling variant achieved the highest processing efficiency per needed laser power (64 mm2/(min·W)), lowest heat accumulation temperature increase (3 K) and highest laser usage efficiency (99%). The advantages of the combination of the shifted method with GHz burst machining and the multispot approach were described. Full article
(This article belongs to the Special Issue Advanced Techniques for Ultrafast Laser Nano/Micro Patterning)
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<p>Schematic representation of the laser surface texturing (LST) methods: (<b>a</b>) classic path filling, (<b>b</b>) shifted path filling, (<b>c</b>) classic hatch and (<b>d</b>) shifted burst. Green dots represent laser pulses. Numbers describe the order of laser processing. Black arrows indicate the movement of the laser beam during pulsing. Curved arrows for shifted methods represent the shifting of the raster during the process.</p> Full article ">Figure 2
<p>Sketch of the methodology for the determination of the surface dimple diameter by using LabIR paint, an optical microscope and software analysis.</p> Full article ">Figure 3
<p>Example of the analysis by a Matlab function: (<b>a</b>) high contrast image of dimples from an optical microscope, (<b>b</b>) analyzed microscope image with shown fitted ellipses and their axes (red—major axis, blue—minor axis).</p> Full article ">Figure 4
<p>Sketch of the methodology for the determination of the dimple depth profile: (<b>a</b>) measured 3D profile, (<b>b</b>) top view of the 3D profile with a diagonal line, (<b>c</b>) measured linear depth profile in the diagonal compared with the goal profile (blue area represents deviation), (<b>d</b>) detail of the bottom part.</p> Full article ">Figure 5
<p>Measured relative deviation of the surface dimple diameter depending on the laser beam speed for different laser texturing methods (scanning strategies).</p> Full article ">Figure 6
<p>Microscope pictures of the surface dimple shapes for different texturing methods (scanning strategies) and laser beam speeds.</p> Full article ">Figure 7
<p>Measured relative deviation of the dimple depth profile for different laser texturing methods (scanning strategies) at their highest allowed scanning speeds.</p> Full article ">Figure 8
<p>Comparison of the depth profiles of the dimple produced by different laser texturing methods (scanning strategies) at their highest allowed scanning speeds.</p> Full article ">Figure 9
<p>Comparison of the 3D profiles of the dimples produced by different methods (scanning strategies) at their highest allowed scanning speeds. Images are taken from different places on the sample: L—left, C—center, R—right.</p> Full article ">Figure 10
<p>Processing speed obtained for different laser texturing methods (scanning strategies) at their highest allowed scanning speeds. The data are based on the measured processing times for two different processed areas.</p> Full article ">Figure 11
<p>Processing speed calculated for different laser scanning speeds and for different laser texturing methods (scanning strategies). The data are based on the processing time calculated by the scanning software for the processed area of 2.4 × 170 mm<sup>2</sup>.</p> Full article ">
21 pages, 8089 KiB  
Review
Vertical GaN-on-GaN Schottky Diodes as α-Particle Radiation Sensors
by Abhinay Sandupatla, Subramaniam Arulkumaran, Ng Geok Ing, Shugo Nitta, John Kennedy and Hiroshi Amano
Micromachines 2020, 11(5), 519; https://doi.org/10.3390/mi11050519 - 20 May 2020
Cited by 20 | Viewed by 5547
Abstract
Among the different semiconductors, GaN provides advantages over Si, SiC and GaAs in radiation hardness, resulting in researchers exploring the development of GaN-based radiation sensors to be used in particle physics, astronomic and nuclear science applications. Several reports have demonstrated the usefulness of [...] Read more.
Among the different semiconductors, GaN provides advantages over Si, SiC and GaAs in radiation hardness, resulting in researchers exploring the development of GaN-based radiation sensors to be used in particle physics, astronomic and nuclear science applications. Several reports have demonstrated the usefulness of GaN as an α-particle detector. Work in developing GaN-based radiation sensors are still evolving and GaN sensors have successfully detected α-particles, neutrons, ultraviolet rays, x-rays, electrons and γ-rays. This review elaborates on the design of a good radiation detector along with the state-of-the-art α-particle detectors using GaN. Successful improvement in the growth of GaN drift layers (DL) with 2 order of magnitude lower in charge carrier density (CCD) (7.6 × 1014/cm3) on low threading dislocation density (3.1 × 106/cm2) hydride vapor phase epitaxy (HVPE) grown free-standing GaN substrate, which helped ~3 orders of magnitude lower reverse leakage current (IR) with 3-times increase of reverse breakdown voltages. The highest reverse breakdown voltage of −2400 V was also realized from Schottky barrier diodes (SBDs) on a free-standing GaN substrate with 30 μm DL. The formation of thick depletion width (DW) with low CCD resulted in improving high-energy (5.48 MeV) α-particle detection with the charge collection efficiency (CCE) of 62% even at lower bias voltages (−20 V). The detectors also detected 5.48 MeV α-particle with CCE of 100% from SBDs with 30-μm DL at −750 V. Full article
(This article belongs to the Special Issue Wide Bandgap Based Devices: Design, Fabrication and Applications)
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<p>Schematic set-up of an Ionization detector [<a href="#B2-micromachines-11-00519" class="html-bibr">2</a>,<a href="#B3-micromachines-11-00519" class="html-bibr">3</a>].</p> Full article ">Figure 2
<p>Schematic set-up of a Scintillation detector [<a href="#B3-micromachines-11-00519" class="html-bibr">3</a>].</p> Full article ">Figure 3
<p>Schematic diagram of GaAs Schottky Barrier Diodes for α-particle detection.</p> Full article ">Figure 4
<p>Cross-sectional schematic of GaN p-n diodes for α-particle detectors.</p> Full article ">Figure 5
<p>Cross-sectional schematic of GaN PIN diode structure for α-particle detector.</p> Full article ">Figure 6
<p>Sandwich structure of alpha particle detectors.</p> Full article ">Figure 7
<p>α-particle range in GaN calculated by stopping range of ions in matter (SRIM).</p> Full article ">Figure 8
<p>(<b>a</b>) X-ray diffraction (XRD), (<b>b</b>) TDD (MPPL), (<b>c</b>) Atomic force microscopy (AFM) and (<b>d</b>) SIMS Characteristics of the wafer.</p> Full article ">Figure 9
<p>Fabrication of 1 mm GaN Schottky barrier diodes (SBD).</p> Full article ">Figure 10
<p>(<b>a</b>) Reverse and (<b>b</b>) Forward <span class="html-italic">I-V</span> characteristics of SBDs with 15 μm and 30 μm GaN DL.</p> Full article ">Figure 11
<p>Variation of capacitance and DW with voltage of 0.5 mm diameter GaN SBDs with 15 µm.</p> Full article ">Figure 12
<p>I-V-T characteristics of vertical GaN SBDs with (<b>a</b>) 15 µm DL, (<b>b</b>) 30 µm DL. Adapted from [<a href="#B58-micromachines-11-00519" class="html-bibr">58</a>] A. Sandupatla et al. 2020 Appl. Phys. Express in press <a href="https://doi.org/10.35848/1882-0786/ab93a0" target="_blank">https://doi.org/10.35848/1882-0786/ab93a0</a>. Copyright [2020] by Japanese Society of Applied Physics.</p> Full article ">Figure 13
<p>Change of CM with voltage zones and temperature ranges in SBDs with (<b>a</b>) 15 µm DL and (<b>b</b>) 30 µm DL. Adapted from [<a href="#B58-micromachines-11-00519" class="html-bibr">58</a>] A. Sandupatla et al. 2020 Appl. Phys. Exp. <a href="https://doi.org/10.35848/1882-0786/ab93a0" target="_blank">https://doi.org/10.35848/1882-0786/ab93a0</a>. Copyright [2020] by Japanese Society of Applied Physics.</p> Full article ">Figure 14
<p>Reverse breakdown voltage characteristics of SBDs with 15 μm and 30 μm in (<b>a</b>) log and (<b>b</b>) linear scale.</p> Full article ">Figure 15
<p>Benchmarking of measured reverse breakdown voltages of vertical GaN SBDs with state-of-the-art results.</p> Full article ">Figure 16
<p>(<b>a</b>) Packaged Device and (<b>b</b>) Schematic drawing of Source-Detector measurement setup (not to scale).</p> Full article ">Figure 17
<p>(<b>a</b>) Acquired α-particle spectra of compensated detectors for different voltages (−20 V to −80 V) and (<b>b</b>) Comparison of variation in CCE with voltages (−20 V to −80V) for state-of-the-art α-particle detectors.</p> Full article ">Figure 18
<p>(<b>a</b>) α-particle spectra of compensated GaN detectors for different applied voltages (−100 V to −300 V) and (<b>b</b>) Comparison of variation in CCE with voltages (−100 V to −550 V) for state-of-the-art α-particle detectors.</p> Full article ">Figure 19
<p>Acquired α-particle energy spectra of GaN SBDs at different voltages in vacuum.</p> Full article ">Figure 20
<p>Acquired α-particle energy spectra of GaN SBDs at −100 V under air and in a vacuum.</p> Full article ">Figure 21
<p>Benchmarking of extracted CCE of compensated detectors with epitaxial-grown GaN detectors (squares) and bulk GaN detectors (triangles) at low voltages.</p> Full article ">
13 pages, 1915 KiB  
Article
The Fabrication of Micro Beam from Photopolymer by Digital Light Processing 3D Printing Technology
by Ishak Ertugrul
Micromachines 2020, 11(5), 518; https://doi.org/10.3390/mi11050518 - 20 May 2020
Cited by 20 | Viewed by 5098
Abstract
3D printing has lately received considerable critical attention for the fast fabrication of 3D structures to be utilized in various industrial applications. This study aimed to fabricate a micro beam with digital light processing (DLP) based 3D printing technology. Compound technology and essential [...] Read more.
3D printing has lately received considerable critical attention for the fast fabrication of 3D structures to be utilized in various industrial applications. This study aimed to fabricate a micro beam with digital light processing (DLP) based 3D printing technology. Compound technology and essential coefficients of the 3D printing operation were applied. To observe the success of the DLP method, it was compared with another fabrication method, called projection micro-stereolithography (PμSL). Evaluation experiments showed that the 3D printer could print materials with smaller than 86.7 µm dimension properties. The micro beam that moves in one direction (y-axis) was designed using the determined criteria. Though the same design was used for the DLP and PμSL methods, the supporting structures were not manufactured with PμSL. The micro beam was fabricated by removing the supports from the original design in PμSL. Though 3 μm diameter supports could be produced with the DLP, it was not possible to fabricate them with PμSL. Besides, DLP was found to be better than PμSL for the fabrication of complex, non-symmetric support structures. The presented results in this study demonstrate the efficiency of 3D printing technology and the simplicity of manufacturing a micro beam using the DLP method with speed and high sensitivity. Full article
(This article belongs to the Special Issue 3D Printing of MEMS Technology)
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<p>Dimensions of the micro beam.</p> Full article ">Figure 2
<p>(<b>a</b>) Schematic of a digital light processing (DLP) system [<a href="#B53-micromachines-11-00518" class="html-bibr">53</a>]; (<b>b</b>) 3D printing process in progress; (<b>c</b>) MiiCraft 3D printer.</p> Full article ">Figure 3
<p>Schematic of the projection micro-stereolithography (PμSL) method [<a href="#B62-micromachines-11-00518" class="html-bibr">62</a>].</p> Full article ">Figure 4
<p>CAD design of the micro beam. The structures at the top of the design were designed as support.</p> Full article ">Figure 5
<p>The step-by-step diagram of the 3D printing operation.</p> Full article ">Figure 6
<p>Image of the micro beam fabricated with the DLP method.</p> Full article ">Figure 7
<p>CAD design of the micro beam. The support structures under the micro beam are removed.</p> Full article ">Figure 8
<p>Image of the micro beam fabricated with the PμSL method.</p> Full article ">
16 pages, 5454 KiB  
Article
Bidirectional Linear Motion by Travelling Waves on Legged Piezoelectric Microfabricated Plates
by Víctor Ruiz-Díez, Jorge Hernando-García, Javier Toledo, Abdallah Ababneh, Helmut Seidel and José Luis Sánchez-Rojas
Micromachines 2020, 11(5), 517; https://doi.org/10.3390/mi11050517 - 20 May 2020
Cited by 8 | Viewed by 3447
Abstract
This paper reports the design, fabrication and performance of MEMS-based piezoelectric bidirectional conveyors featuring 3D printed legs, driven by linear travelling waves (TW). The structures consisted of an aluminium–nitride (AlN) piezoelectric film on top of millimetre-sized rectangular thin silicon bridges and two electrode [...] Read more.
This paper reports the design, fabrication and performance of MEMS-based piezoelectric bidirectional conveyors featuring 3D printed legs, driven by linear travelling waves (TW). The structures consisted of an aluminium–nitride (AlN) piezoelectric film on top of millimetre-sized rectangular thin silicon bridges and two electrode patches. The position and size of the patches were analytically optimised for TW generation in three frequency ranges: 19, 112 and 420 kHz, by the proper combination of two contiguous flexural modes. After fabrication, the generated TW were characterized by means of Laser–Doppler vibrometry to obtain the relevant tables of merit, such as the standing wave ratio and the average amplitude. The experimental results agreed with the simulation, showing the generation of a TW with an amplitude as high as 6 nm/V and a standing wave ratio as low as 1.46 for a device working at 19.3 kHz. The applicability of the fabricated linear actuator device as a conveyor was investigated. Its kinetic performance was studied with sliders of different mass, being able to carry a 35 mg silicon slider, 18 times its weight, with 6 V of continuous sinusoidal excitation and a speed of 0.65 mm/s. A lighter slider, weighting only 3 mg, reached a mean speed of 1.7 mm/s at 6 V. In addition, by applying a burst sinusoidal excitation comprising 10 cycles, the TW generated in the bridge surface was able to move a 23 mg slider in discrete steps of 70 nm, in both directions, which is a promising result for a TW piezoelectric actuator of this size. Full article
(This article belongs to the Special Issue Piezoelectric Thin Film MEMS)
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<p>Schematic diagram of the device design. A bridge structure of length L and width W consisting of a silicon substrate with thickness <math display="inline"><semantics> <mrow> <msub> <mi>t</mi> <mi>s</mi> </msub> </mrow> </semantics></math>, covered by an AlN piezoelectric layer of thickness tp. Two symmetrically disposed metallic electrodes were placed closed to the edges, starting at a distance <math display="inline"><semantics> <mrow> <msub> <mi>l</mi> <mn>1</mn> </msub> </mrow> </semantics></math> and ending at a distance <math display="inline"><semantics> <mrow> <msub> <mi>l</mi> <mn>2</mn> </msub> </mrow> </semantics></math>.</p> Full article ">Figure 2
<p>Mode shapes involved in the travelling waves (TW) generation obtained from the finite element method (FEM) analysis. (<b>a</b>) Modes (4,0) and (5,0) in the low frequency (LF) range, (<b>b</b>) modes (10,0) and (11,0) in the intermediate frequency (IF) range and (<b>c</b>) modes (19,0) and (20,0) in the high frequency (HF) range. Resonant frequency is also included. Colour bar represents the normalised modal displacement in the <span class="html-italic">Z</span>-axis.</p> Full article ">Figure 3
<p>Second derivatives <math display="inline"><semantics> <mrow> <msup> <mi>φ</mi> <mo>″</mo> </msup> </mrow> </semantics></math> (solid lines) of the modes involved in the TW generation in the (<b>a</b>) low frequency (LF) range, (<b>b</b>) intermediate frequency (IF) range and (<b>c</b>) high frequency (HF) range. The positions of the zeros (dotted vertical lines) and optimum patch design (green area) are also indicated. A double-headed arrow indicates the patch based on the zeros of the second derivative.</p> Full article ">Figure 4
<p>Resultant envelopes from the simulations with optimal patches and patches deduced from the approach based on the zeros of the second derivative in the (<b>a</b>) LF range, (<b>b</b>) IF range and (<b>c</b>) HF range. The dotted vertical lines indicate a centred 50% of the length.</p> Full article ">Figure 5
<p>Photographs of the fabricated devices. (<b>a</b>) Silicon dice containing two HF designs, wire bonded to a printed circuit board (PCB), (<b>b</b>) detail of the legs attached and (<b>c</b>) the experimental setup, with a gold-patterned slider on top of a legged TW motor, and constrained to a lane by four glass pieces.</p> Full article ">Figure 6
<p>Measured conductance of three different fabricated devices: (<b>a</b>) LF, (<b>b</b>) IF and (<b>c</b>) HF. Modal identification was deduced from laser Doppler vibrometer by accounting for the number of nodal lines. The dashed vertical line indicates the driving frequency.</p> Full article ">Figure 7
<p>TW magnitude (per unit of applied voltage) and phase for different devices along the bridge length. Measurement (solid lines) and calculation (dotted line) in (<b>a</b>) LF, (<b>b</b>) IF and (<b>c</b>) HF devices. The dashed vertical lines indicate a centred 50% of length.</p> Full article ">Figure 8
<p>Measured results for the 3 mg slider on the LF device with 4 legs. (<b>a</b>) Slider position and (<b>b</b>) deduced velocities during the experiment with 2 V excitation signals at 19.3 kHz. The phase difference between the signals of the patches was alternated between 90° and −90° every second.</p> Full article ">Figure 9
<p>Results from the kinetic characterization of the LF device: (<b>a</b>) average speed of the sliders versus their mass for a voltage amplitude of 6 V and (<b>b</b>) average speed of the 23 mg slider at different excitation amplitudes.</p> Full article ">Figure 10
<p>Study of the minimum displacement of the slider for 10 sinusoidal cycles of 10 V at 19 kHz. (<b>a</b>) Discrete steps on the direction of propagation of the TW (<span class="html-italic">X</span>-axis) and the orthogonal one (<span class="html-italic">Y</span>-axis) and (<b>b</b>) estimated step height.</p> Full article ">
10 pages, 2145 KiB  
Article
A Facile Preparation and Energetic Characteristics of the Core/Shell CoFe2O4/Al Nanowires Thermite Film
by Chunpei Yu, Wei Ren, Ganggang Wu, Wenchao Zhang, Bin Hu, Debin Ni, Zilong Zheng, Kefeng Ma, Jiahai Ye and Chenguang Zhu
Micromachines 2020, 11(5), 516; https://doi.org/10.3390/mi11050516 - 20 May 2020
Cited by 5 | Viewed by 3231
Abstract
In this study, CoFe2O4 is selected for the first time to synthesize CoFe2O4/Al nanothermite films via an integration of nano-Al with CoFe2O4 nanowires (NWs), which can be prepared through a facile hydrothermal-annealing route. [...] Read more.
In this study, CoFe2O4 is selected for the first time to synthesize CoFe2O4/Al nanothermite films via an integration of nano-Al with CoFe2O4 nanowires (NWs), which can be prepared through a facile hydrothermal-annealing route. The resulting nanothermite film demonstrates a homogeneous structure and an intense contact between the Al and CoFe2O4 NWs at the nanoscale. In addition, both thermal analysis and laser ignition test reveal the superb energetic performances of the prepared CoFe2O4/Al NWs nanothermite film. Within different thicknesses of nano-Al for the CoFe2O4/Al NWs nanothermite films investigated here, the maximum heat output has reached as great as 2100 J·g−1 at the optimal thickness of 400 nm for deposited Al. Moreover, the fabrication strategy for CoFe2O4/Al NWs is also easy and suitable for diverse thermite systems based upon other composite metal oxides, such as MnCo2O4 and NiCo2O4. Importantly, this method has the featured advantages of simple operation and compatibility with microsystems, both of which may further facilitate potential applications for functional energetic chips. Full article
(This article belongs to the Special Issue Miniaturized Pyro Devices)
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<p>Schematic diagram for the fabrication of the core/shell CoFe<sub>2</sub>O<sub>4</sub>/Al nanothermite film.</p> Full article ">Figure 2
<p>The XRD patterns of the CoFe<sub>2</sub>O<sub>4</sub> nanowires (NWs) film and the CoFe<sub>2</sub>O<sub>4</sub>/Al NWs nanothermite film.</p> Full article ">Figure 3
<p>The scanning electron microscopy (SEM) images of the (<b>a</b>,<b>b</b>) CoFe<sub>2</sub>O<sub>4</sub> NWs film, (<b>c</b>) CoFe<sub>2</sub>O<sub>4</sub> NWs film from the side view, (<b>d</b>) CoFe<sub>2</sub>O<sub>4</sub>/Al NWs nanothermite film (Al = 200 nm), (<b>e</b>) CoFe<sub>2</sub>O<sub>4</sub>/Al NWs nanothermite film (Al = 400 nm), (<b>f</b>) CoFe<sub>2</sub>O<sub>4</sub>/Al NWs nanothermite film (Al = 600 nm) and (<b>g</b>) elemental mappings of CoFe<sub>2</sub>O<sub>4</sub>/Al NWs nanothermite film (Al = 400 nm).</p> Full article ">Figure 4
<p>The transmission electron microscopy (TEM) images of the (<b>a</b>) CoFe<sub>2</sub>O<sub>4</sub> NWs, (<b>b</b>) CoFe<sub>2</sub>O<sub>4</sub>/Al NWs (Al = 200 nm), (<b>c</b>,<b>d</b>,<b>e</b>) high resolution transmission electron microscopy (HRTEM) images of CoFe<sub>2</sub>O<sub>4</sub>/Al NWs (Al = 200 nm), and (<b>f</b>) the corresponding element mappings of CoFe<sub>2</sub>O<sub>4</sub>/Al NWs.</p> Full article ">Figure 5
<p>The differential scanning calorimetry (DSC) curve of the CoFe<sub>2</sub>O<sub>4</sub>/Al NWs nanothermite film (Al = 400 nm).</p> Full article ">Figure 6
<p>The high-speed camera photos of the ignition process of the CoFe<sub>2</sub>O<sub>4</sub>/Al NWs nanothermite film (Al = 400 nm).</p> Full article ">
11 pages, 2960 KiB  
Article
A Simple and Rapid Fungal DNA Isolation Assay Based on ZnO Nanoparticles for the Diagnosis of Invasive Aspergillosis
by Zhen Qiao, Huifang Liu, Geun Su Noh, Bonhan Koo, Qingshuang Zou, Kyusik Yun, Yoon Ok Jang, Sung-Han Kim and Yong Shin
Micromachines 2020, 11(5), 515; https://doi.org/10.3390/mi11050515 - 19 May 2020
Cited by 7 | Viewed by 5849
Abstract
Invasive aspergillosis (IA) is an important cause of morbidity and mortality among immunocompromised people. Imaging and specimen tests used in the clinical diagnosis of aspergillosis with weak and indistinct defects leads to delay in the treatment of early aspergillosis patients. The developing molecular [...] Read more.
Invasive aspergillosis (IA) is an important cause of morbidity and mortality among immunocompromised people. Imaging and specimen tests used in the clinical diagnosis of aspergillosis with weak and indistinct defects leads to delay in the treatment of early aspergillosis patients. The developing molecular techniques provide a new method for the aspergillosis diagnosis. However, the existing methods are complex, time-consuming and may even be potentially hazardous. In this study, we developed a simple and rapid Aspergillus fumigatus spores DNA isolation assay using synthesized zinc oxide (ZnO). ZnO nanoparticles were used to take the place of the traditional commercial lysis buffer. The quality and quantity of the extracted DNA were sufficient for further diagnostics with polymerase chain reaction (PCR) analysis. This method offers easy, green, and economic alternative DNA isolation for the diagnosis of invasive aspergillosis. Full article
(This article belongs to the Special Issue Molecular Diagnostic Devices and Clinical Applications)
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<p>Diagram of the ZnO-based fungal DNA isolation assay. A schematic illustrating nucleic acid (NA) isolation using the lysis buffer replacement method based on ZnO (the ZnO-based fungal DNA isolation assay) instead of using the traditional lysis buffer in the commercial fungal DNA extraction kit. The ZnO-based fungal DNA isolation assay (<b>top</b>) and commercial kit assay (<b>bottom</b>) both have four steps involving different lysis buffers but the same filter column, wash buffer, and elution buffer. For lysis process, in the optimized ZnO-based fungal DNA isolation assay, 100 μL <span class="html-italic">A. fumigatus</span> spores was mixed with 100 μg ZnO for 30 min at room temperature only without any further lysis step. In the commercial kit assay, 10 μL <span class="html-italic">A. fumigatus spores</span> was mixed with 120 μL of YD digestion buffer and 5 μL of R-Zymolyase<sup>TM</sup> (RNase A + Zymolyase<sup>TM</sup>) for 40–60 min at 37 °C, then YD lysis buffer and chloroform were added into the mixture. In the binding, washing, and elution steps, the buffer and columns used were the same in both methods. Subsequently, the NA extracted by both methods could be detected in downstream analysis.</p> Full article ">Figure 2
<p>Study on the application of ZnO for the lysis of fungal spore cells. (<b>A</b>) Scanning electron microscope (SEM) images of synthesized nanoparticles ZnO-S-300; (<b>B</b>) SEM images of untreated <span class="html-italic">A. fumigatus</span> spore cells; (<b>C</b>) SEM image of the lysis process of ZnO-S-300 on <span class="html-italic">A. fumigatus</span> spore cells. (<b>D</b>,<b>E</b>) Fluorescence signals and melt data from real-time PCR analyses of amplified DNAs extracted by the ZnO-based fungal DNA isolation assay (Blue line) and kit assay (Green line). For the ZnO-based fungal DNA isolation assay, the cells were incubated for 60 min at room temperature. The extracted DNA of <span class="html-italic">A. fumigatus</span> spore cells (10<sup>8</sup> cells) was eluted in 100-μL elution buffer. The orange line was the negative control which is pure elution buffer. Fluorescence intensity is measured in relative fluorescence units (RFU) by real-time polymerase chain reaction (PCR).</p> Full article ">Figure 3
<p>Optimization of the work conditions for ZnO nanoparticle synthesis in the ZnO extraction method. (<b>A</b>) SEM images of commercial nanoparticles ZnO-C-100. (<b>B</b>) SEM images of synthesized nanoparticles ZnO-S-300, (<b>C</b>) SEM images of commercial nanoparticles ZnO-C-5000. (<b>D</b>,<b>E</b>) Performance evaluation of the ZnO lysis buffer DNA extraction method using the synthesized ZnO (~300 nm, ZnO-S-300) nanomaterial at three different incubation temperatures (<b>D</b>) and times (<b>E</b>) by comparing the cycle threshold (Ct) of real-time PCR against two other commercially available ZnO types (~100 nm,~5000 nm). The extracted DNA of <span class="html-italic">A. fumigatus</span> spore cells (10<sup>8</sup> cells) was eluted in 100-μL elution buffer. Error bars indicate standard deviation from the mean based on at least three independent experiments. * <span class="html-italic">p</span> &lt; 0.05, ** <span class="html-italic">p</span> &lt; 0.01.</p> Full article ">Figure 4
<p>Performance evaluation of the DNA extraction assay using either the ZnO-based fungal DNA isolation assay or the commercial kit assay with <span class="html-italic">A. fumigatus</span> spore concentrations ranging from 1 to 10<sup>8</sup> cells/100 μL by comparing the cycle threshold (Ct) of real-time PCR. Error bars indicate standard deviation from the mean, based on at least three independent experiments. Error bars indicate standard deviation from the mean, based on at least three independent experiments. * <span class="html-italic">p</span> &lt; 0.05.</p> Full article ">Figure A1
<p>Synthesized ZnO nanoparticles for lysis of bacterial cells. We used 100 μL (10<sup>4</sup> colony-forming units (CFU)/mL) other bacterial species including Gram-positives (<span class="html-italic">Staphylococcus aureus</span> and <span class="html-italic">Bacillus cereus</span>) and Gram-negatives (<span class="html-italic">Escherichia coli</span> and <span class="html-italic">Brucella ovis</span>) to test of the performance of the ZnO-based DNA isolation assay. * <span class="html-italic">p</span> &lt; 0.05.</p> Full article ">
14 pages, 2193 KiB  
Article
Label-Free, High-Throughput Assay of Human Dendritic Cells from Whole-Blood Samples with Microfluidic Inertial Separation Suitable for Resource-Limited Manufacturing
by Mohamed Yousuff Caffiyar, Kue Peng Lim, Ismail Hussain Kamal Basha, Nor Hisham Hamid, Sok Ching Cheong and Eric Tatt Wei Ho
Micromachines 2020, 11(5), 514; https://doi.org/10.3390/mi11050514 - 19 May 2020
Cited by 13 | Viewed by 4008
Abstract
Microfluidics technology has not impacted the delivery and accessibility of point-of-care health services, like diagnosing infectious disease, monitoring health or delivering interventions. Most microfluidics prototypes in academic research are not easy to scale-up with industrial-scale fabrication techniques and cannot be operated without complex [...] Read more.
Microfluidics technology has not impacted the delivery and accessibility of point-of-care health services, like diagnosing infectious disease, monitoring health or delivering interventions. Most microfluidics prototypes in academic research are not easy to scale-up with industrial-scale fabrication techniques and cannot be operated without complex manipulations of supporting equipment and additives, such as labels or reagents. We propose a label- and reagent-free inertial spiral microfluidic device to separate red blood, white blood and dendritic cells from blood fluid, for applications in health monitoring and immunotherapy. We demonstrate that using larger channel widths, in the range of 200 to 600 µm, allows separation of cells into multiple focused streams, according to different size ranges, and we utilize a novel technique to collect the closely separated focused cell streams, without constricting the channel. Our contribution is a method to adapt spiral inertial microfluidic designs to separate more than two cell types in the same device, which is robust against clogging, simple to operate and suitable for fabrication and deployment in resource-limited populations. When tested on actual human blood cells, 77% of dendritic cells were separated and 80% of cells remained viable after our assay. Full article
(This article belongs to the Special Issue Microfluidics Technologies for Cell-based Assays)
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<p>An inertial spiral microfluidic device for separating fluorescent beads of 3 different sizes: (<b>a</b>) (<b>i</b>) a PDMS device is designed with channel widths exceeding 200 μm, so that the mold can be fabricated with low-cost xurography. Scanning Electron Microscope images of (<b>ii</b>) planar and (<b>iii</b>) cross-sectional views of the device show that the mold produces smooth channel walls. (<b>b</b>) The largest beads (green) are focused at earlier turns of the device, migrate closest to the inner channel wall and are collected at the first outlet. Focused particle streams are spaced closely together.</p> Full article ">Figure 1 Cont.
<p>An inertial spiral microfluidic device for separating fluorescent beads of 3 different sizes: (<b>a</b>) (<b>i</b>) a PDMS device is designed with channel widths exceeding 200 μm, so that the mold can be fabricated with low-cost xurography. Scanning Electron Microscope images of (<b>ii</b>) planar and (<b>iii</b>) cross-sectional views of the device show that the mold produces smooth channel walls. (<b>b</b>) The largest beads (green) are focused at earlier turns of the device, migrate closest to the inner channel wall and are collected at the first outlet. Focused particle streams are spaced closely together.</p> Full article ">Figure 2
<p>Computational fluid dynamics simulations were used in the design of our device. (<b>a</b>) Simulation of particle streamlines verify that particles larger than 13 μm enter collection Outlet 1, particles between 8 and 12 μm enter collection Outlet 2 and particles between 6 and 7 μm enter Outlet 3. (<b>b</b>) Simulations verify that Dean forces are more rapidly reduced in the spiral with expanding channel widths.</p> Full article ">Figure 3
<p>Our device was designed to perform a blood-cell separation assay. (<b>a</b>) Images of red blood cells, white blood cells and dendritic cells, together with (<b>b</b>) the distribution of cell sizes, suggest that blood-cell types can be separated reasonably according to size. (<b>c</b>) Inertial focusing and high flow rates do not harm cells, because cell viability in all four collection outlets exceed 80%.</p> Full article ">Figure 4
<p>Evaluation of blood-cell-separation efficiency at a flow rate of 1.9 mL/min: (<b>a</b>) the majority of dendritic cells are collected in Outlet 1, white blood cells in Outlet 2 and red blood cells in Outlet 3 when the spiral microfluidic device is tested with fluid containing a single cell type only at 100× dilution. (<b>b</b>) The majority of dendritic cells are still collected in Outlet 1, although with lower efficiency, when tested with fluid containing all three types of blood cells.</p> Full article ">Figure 5
<p>Simulation studies at three different fluid velocities show the spectrum of particle behaviors in the spiral microfluidic device. At 0.3 m/s, there are insufficient dean and inertial lift forces, so particles are not focused nor separated. At 1.7 m/s, the lateral Dean forces are slightly less than inertial lift forces, and this supports particle focusing and fractionation. At 2.6 m/s, Dean forces dominate, and particle streams are defocused due to lateral mixing.</p> Full article ">Figure 6
<p>Blood cell separation efficiency, (<b>a</b>) using only white blood cells at 100× dilution while varying flow rate, an (<b>b</b>) using only red blood cells at 1.9 mL/min while varying concentration.</p> Full article ">
24 pages, 4470 KiB  
Review
Determination of Dielectric Properties of Cells using AC Electrokinetic-based Microfluidic Platform: A Review of Recent Advances
by Wenfeng Liang, Xieliu Yang, Junhai Wang, Yuechao Wang, Wenguang Yang and Lianqing Liu
Micromachines 2020, 11(5), 513; https://doi.org/10.3390/mi11050513 - 19 May 2020
Cited by 32 | Viewed by 4725
Abstract
Cell dielectric properties, a type of intrinsic property of cells, can be used as electrophysiological biomarkers that offer a label-free way to characterize cell phenotypes and states, purify clinical samples, and identify target cancer cells. Here, we present a review of the determination [...] Read more.
Cell dielectric properties, a type of intrinsic property of cells, can be used as electrophysiological biomarkers that offer a label-free way to characterize cell phenotypes and states, purify clinical samples, and identify target cancer cells. Here, we present a review of the determination of cell dielectric properties using alternating current (AC) electrokinetic-based microfluidic mechanisms, including electro-rotation (ROT) and dielectrophoresis (DEP). The review covers theoretically how ROT and DEP work to extract cell dielectric properties. We also dive into the details of differently structured ROT chips, followed by a discussion on the determination of cell dielectric properties and the use of these properties in bio-related applications. Additionally, the review offers a look at the future challenges facing the AC electrokinetic-based microfluidic platform in terms of acquiring cell dielectric parameters. Our conclusion is that this platform will bring biomedical and bioengineering sciences to the next level and ultimately achieve the shift from lab-oriented research to real-world applications. Full article
(This article belongs to the Special Issue Electrokinetics in Micro-/nanofluidic Devices)
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<p>Typical schematic illustration of an electro-rotation (ROT) chip. Reproduced with permission from Bahrieh et al., RSC Adv. <b>4</b>, 44879 (2014). Copyright 2014 RSC Publishing.</p> Full article ">Figure 2
<p>Picture of a real dielectrophoresis (DEP) chip and experimentally captured images of DEP electrodes and trapped cells using DEP. Reproduced with permission from Flanagan et al., Stem Cells <b>26</b>, 656 (2008). Copyright 2008 Wiley Publishing.</p> Full article ">Figure 3
<p>Schematic illustration of a ROT chip. (<b>a</b>) Two glass substrates coated with interdigitated array electrodes were arranged orthogonally and face-to-face; (<b>b</b>) a rotating electric field was produced by applying an electrical connection with a π/2 phase difference between adjacent electrodes; (<b>c</b>) overview of the ROT chip; (<b>d</b>) enlarged view of the ROT chip. Reproduced with permission from Ino et al., Sensors Actuators B Chem. <b>153</b>, 468 (2011). Copyright 2011 Elsevier Publishing.</p> Full article ">Figure 4
<p>Working principle of a 3D cell ROT chip. (<b>a</b>) One single cell hydrodynamically trapped by a SU-8-based unit; (<b>b</b>) a trapped single cell was released by back flow and stayed in the rotation chamber after a negative DEP force was applied from the two electrodes; (<b>c</b>) simulation result of the negative DEP force; (<b>d</b>–<b>f</b>) are AC signals for cell rotation along the Z-axis, Y-axis, and X-axis, respectively. Reproduced with permission from Huang et al., Lab Chip <b>18</b>, 2359 (2018). Copyright 2018 RSC Publishing.</p> Full article ">Figure 5
<p>(<b>a</b>) A conventional four-electrode ROT chip; (<b>b</b>) the proposed ROT chip consisting of two electrodes and induced cell electrodes; (<b>c</b>) 3D structure of the proposed ROT chip; (<b>d</b>) operation mode of the cell electrodes and the trapped cells rotating on an insulating layer. Reproduced with permission from Huang et al., Electrophoresis <b>40</b>, 784 (2019). Copyright 2019 Wiley Publishing.</p> Full article ">Figure 6
<p>ROT spectra of B-lymphocytes (▲), T-lymphocytes (Δ), monocytes (○), and granulocytes (●) in an isotonic solution. Reproduced with permission from Yang et al., Biophys. J. <b>76</b>, 3307 (1999). Copyright 1999 Elsevier Publishing.</p> Full article ">Figure 7
<p>ROT spectra of the B16F10 (<b>a</b>) and Jurkat (<b>b</b>) cell lines before and after the application of a pulsed electric field. Reproduced with permission from Trainito et al., Electrophoresis <b>36</b>, 1115 (2015). Copyright 2015 Wiley Publishing.</p> Full article ">Figure 8
<p>(<b>a</b>) ROT spectra of four cell types; (<b>b</b>) evaluation of the differences between peak frequencies before and after 5 minutes of exposure to the rotating electric field. Reproduced with permission from Keim et al., Electrophoresis <b>40</b>, 1830 (2019). Copyright 2019 Wiley Publishing.</p> Full article ">Figure 9
<p>ROT spectra of the three sequentially-staged mouse ovarian surface epithelial (MOSE) cells. Reproduced with permission from Trainito et al., PLoS One <b>40</b>, e0222289 (2019). Copyright 2019 PLoS Publishing.</p> Full article ">Figure 10
<p>(<b>a</b>) The real part of the Clausius–Mossotti (CM) factor of MDA-MB231, THP-1, PC1, and RBCs; (<b>b</b>) DEP forces exerted on MDA-MB231, THP-1, PC1, and RBCs with respect to AC frequency; (<b>c</b>) difference in CM factor between MDA-MB231 (solid), THP-1 (dotted), PC1 (dash-dot), and red blood cells (RBCs) (broken lines). Reproduced with permission from Sano et al., Electrophoresis <b>32</b>, 3164 (2011). Copyright 2011 Wiley Publishing.</p> Full article ">Figure 11
<p>(<b>a</b>) Crossover frequencies divided by the liquid conductivity and (<b>b</b>) specific membrane capacitances measured for MOSE-E, MOSE-E/I, MOSE-I, and MOSE-L. *, **, and *** indicate <span class="html-italic">p</span> &lt; 0.001, 0.01, and 0.05, respectively (n = 3). Reproduced with permission from Salmanzadeh et al., Biomicrofluidics <b>7</b>, 011809 (2013). Copyright 2013 American Institute of Physics Publishing.</p> Full article ">Figure 12
<p>Membrane capacitance of Raji cells with respect to the diameter of these cells. Reproduced with permission from Liang et al., Biomicrofluidics <b>9</b>, 014121 (2015). Copyright 2015 American Institute of Physics Publishing.</p> Full article ">Figure 13
<p>DEP profiles of (<b>a</b>) 0.00 mM (native), (<b>b</b>) 0.07 mM, (<b>c</b>) 0.11 mM, and (<b>d</b>) 0.17 mM Triton X-100-treated RBCs with respect to AC frequency (300 to 700 kHz). Reproduced with permission from Habibi et al., Biomicrofluidics <b>13</b>, 054101 (2019). Copyright 2019 American Institute of Physics Publishing.</p> Full article ">Figure 14
<p>(<b>a</b>) Membrane capacitances, (<b>b</b>) cytoplasm conductivities, and (<b>c</b>) radii extracted for Hela, MCF-7, Jurkat, and GM 12878 cells. Significant difference: *<span class="html-italic">p</span> &lt; 0.01, **<span class="html-italic">p</span> &lt; 0.05. Distribution percentages of (<b>d</b>) membrane capacitance, (<b>e</b>) cytoplasm conductivity, and (<b>f</b>) radius for Hela, MCF-7, Jurkat, and GM 12878 cells. Reproduced with permission from Zhang et al., Sensors Actuators B Chem. <b>304</b>, 127326 (2020). Copyright 2020 Elsevier Publishing.</p> Full article ">
12 pages, 4147 KiB   20 MHz) Ultrasonic Array Transducer Applications" data-journal="micromachines">
Article
Micromachining of High Quality PMN–31%PT Single Crystals for High-Frequency (>20 MHz) Ultrasonic Array Transducer Applications
by Zhihong Lei, Yan Chen, Guisheng Xu, Jinfeng Liu, Maodan Yuan, Lvming Zeng, Xuanrong Ji and Dawei Wu
Micromachines 2020, 11(5), 512; https://doi.org/10.3390/mi11050512 - 19 May 2020
Cited by 8 | Viewed by 3241
Abstract
A decrease of piezoelectric properties in the fabrication of ultra-small Pb(Mg1/3Nb2/3)–x%PbTiO3 (PMN–x%PT) for high-frequency (>20 MHz) ultrasonic array transducers remains an urgent problem. Here, PMN–31%PT with micron-sized kerfs and high piezoelectric performance was micromachined using [...] Read more.
A decrease of piezoelectric properties in the fabrication of ultra-small Pb(Mg1/3Nb2/3)–x%PbTiO3 (PMN–x%PT) for high-frequency (>20 MHz) ultrasonic array transducers remains an urgent problem. Here, PMN–31%PT with micron-sized kerfs and high piezoelectric performance was micromachined using a 355 nm laser. We studied the kerf profile as a function of laser parameters, revealing that micron-sized kerfs with designated profiles and fewer micro-cracks can be obtained by optimizing the laser parameters. The domain morphology of micromachined PMN–31%PT was thoroughly analyzed to validate the superior piezoelectric performance maintained near the kerfs. A high piezoresponse of the samples after micromachining was also successfully demonstrated by determining the effective piezoelectric coefficient (d33*~1200 pm/V). Our results are promising for fabricating superior PMN–31%PT and other piezoelectric high-frequency (>20 MHz) ultrasonic array transducers. Full article
(This article belongs to the Special Issue Pulsed Laser Micromachining)
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<p>Piezoelectric coefficient d<sub>33</sub> (<b>a</b>) and dielectric permittivity (<b>b</b>) of the Pb(Mg<sub>1/3</sub>Nb<sub>2/3</sub>)–<span class="html-italic">x</span>%PbTiO<sub>3</sub> (PMN–PT) samples.</p> Full article ">Figure 2
<p>Optical microscope images (<b>a</b>,<b>b</b>) and scanning electron microscope image (<b>c</b>) of laser micromachined PMN–31%PT under 1.0 W, 50 kHz, 500 mm/s, and 20 scanning cycles.</p> Full article ">Figure 3
<p>Variation of laser power (<b>a</b>,<b>b</b>) and frequency (<b>c</b>,<b>d</b>) with respect to ablated depth (<span class="html-italic">z</span>) and width (<span class="html-italic">r</span>).</p> Full article ">Figure 4
<p>Dependence of the number of scanning cycles (<b>a</b>,<b>b</b>) and speed (<b>c</b>,<b>d</b>) on ablated depth (<span class="html-italic">z</span>) and width (<span class="html-italic">r</span>).</p> Full article ">Figure 5
<p>Polarized light microscope images of ferroelectric domains for the PMN–31%PT micromachined at different powers (<b>a</b>–<b>c</b>) and the scanning electron microscope images of micromachined kerfs (<b>d</b>,<b>e</b>). Initial domain morphology of the sample without micromachining (<b>a</b>) and those micromachined at 0.5 W (<b>b</b>,<b>d</b>) and 1.0 W (<b>c</b>,<b>e</b>).</p> Full article ">Figure 6
<p>Schematic of the experiment conducted using the piezoresponse force microscope (PFM) (<b>a</b>,<b>d</b>,<b>g</b>), PFM phase (<b>b</b>,<b>e</b>,<b>h</b>), and amplitude (<b>c</b>,<b>f</b>,<b>i</b>) images of ferroelectric domains. The sample without micromachining (<b>a</b>–<b>c</b>), and those micromachined at 0.5 W (<b>d</b>–<b>f</b>) and 1.0 W (<b>g</b>–<b>i</b>).</p> Full article ">Figure 7
<p>Amplitude–voltage butterfly loops, phase–voltage hysteresis loops, and piezoelectric hysteresis loops of PMN–31%PT samples. The sample without micromachining (<b>a</b>,<b>d</b>), and those micromachined at 0.5 W (<b>b</b>,<b>e</b>) and 1.0 W (<b>c</b>,<b>f</b>).</p> Full article ">
16 pages, 7039 KiB  
Article
AC/DC Fields Demodulation Methods of Resonant Electric Field Microsensor
by Pengfei Yang, Xiaolong Wen, Zhaozhi Chu, Xiaoming Ni and Chunrong Peng
Micromachines 2020, 11(5), 511; https://doi.org/10.3390/mi11050511 - 19 May 2020
Cited by 10 | Viewed by 3126
Abstract
Electric field microsensors have the advantages of a small size, a low power consumption, of avoiding wear, and of measuring both direct-current (DC) and alternating-current (AC) fields, which are especially suited to applications in power systems. However, previous reports were chiefly concerned with [...] Read more.
Electric field microsensors have the advantages of a small size, a low power consumption, of avoiding wear, and of measuring both direct-current (DC) and alternating-current (AC) fields, which are especially suited to applications in power systems. However, previous reports were chiefly concerned with proposing new structures or improving the resolution, and there are no systematic studies on the signal characteristics of the microsensor output and the demodulation methods under different electric fields. In this paper, the use of an improved resonant microsensor with coplanar electrodes, and the signal characteristics under a DC field, power frequency field, and AC/DC hybrid fields were thoroughly analyzed respectively, and matching demodulation methods derived from synchronous detection were proposed. We theoretically obtained that the frequencies of the detectable electric fields should be less than half of the resonant frequency of the microsensor, and that the sensitivities of the microsensor were identical for AC/DC hybrid fields with different frequencies. Experiments were conducted to verify the proposed demodulation methods. Within electric field ranges of 0–667 kV/m, the uncertainties were 2.4% and 1.5% for the most common DC and 50 Hz power frequency fields, respectively. The frequency characteristic test results of the microsensor were in agreement with those of the theoretical analysis in the range of 0–1 kHz. Full article
(This article belongs to the Special Issue Power Electronics and Sensors)
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<p>Operating principle of the resonant electric field microsensor (EFM) with coplanar electrodes.</p> Full article ">Figure 2
<p>Electric field line distribution of the shutter (s) at different positions: (<b>a</b>) Proximity to sensing electrode (+); (<b>b</b>) Proximity to sensing electrode (−).</p> Full article ">Figure 3
<p>Scanning electron micrograph (SEM) photo of the fabricated EFM.</p> Full article ">Figure 4
<p>Block diagram of a synchronous demodulator.</p> Full article ">Figure 5
<p>Spectrum of the microsensor output signal under the power frequency field.</p> Full article ">Figure 6
<p>Block diagram of the high-pass-orthogonal-correlation-band-pass detection method.</p> Full article ">Figure 7
<p>Normalized simulation results of <span class="html-italic">X</span>(<span class="html-italic">t</span>) under different initial phase <span class="html-italic">φ</span> values, <span class="html-italic">ω<sub>e</sub></span> = 2π·50 rad/s, <span class="html-italic">ω<sub>s</sub></span> = 2π·3050 rad/s.</p> Full article ">Figure 8
<p>Normalized simulation results of <span class="html-italic">R</span>(<span class="html-italic">t</span>) under different initial phase <span class="html-italic">φ</span> values, <span class="html-italic">ω<sub>e</sub></span> = 2π·50 rad/s, <span class="html-italic">ω<sub>s</sub></span> = 2π·3050 rad/s.</p> Full article ">Figure 9
<p>Normalized simulation results of <span class="html-italic">R<sub>i</sub></span>(<span class="html-italic">t</span>) at different measured field frequencies, <span class="html-italic">ω<sub>s</sub></span> = 2π·3050 rad/s, <span class="html-italic">φ<sub>i</sub></span> = 0.</p> Full article ">Figure 10
<p>Verification test system for the AC/DC electric fields demodulation methods: (<b>a</b>) The schematic diagram; (<b>b</b>) The test setup; (<b>c</b>) A cross-section of the packaged EFM.</p> Full article ">Figure 11
<p>Raw voltage signal of the microsensor output and AC drive signal.</p> Full article ">Figure 12
<p>Spectrum of the microsensor output voltage: (<b>a</b>) under a DC electric field; (<b>b</b>) under a 50 Hz power frequency field; and (<b>c</b>) under a 500 Hz AC field.</p> Full article ">Figure 13
<p>Demodulation results of a 50 Hz power frequency field using the HOCBM: (<b>a</b>) The output of <span class="html-italic">X</span>(<span class="html-italic">t</span>); (<b>b</b>) The output of <span class="html-italic">R</span>(<span class="html-italic">t</span>).</p> Full article ">Figure 14
<p>The response characteristics of the EFM: (<b>a</b>) The uncertainty of 2.4% for DC fields; (<b>b</b>) The uncertainty of 1.5% for 50 Hz power frequency fields.</p> Full article ">Figure 14 Cont.
<p>The response characteristics of the EFM: (<b>a</b>) The uncertainty of 2.4% for DC fields; (<b>b</b>) The uncertainty of 1.5% for 50 Hz power frequency fields.</p> Full article ">Figure 15
<p>The frequency characteristics of the EFM.</p> Full article ">
13 pages, 3845 KiB  
Article
Experiments on Liquid Flow through Non-Circular Micro-Orifices
by Stefano Cassineri, Andrea Cioncolini, Liam Smith, Michele Curioni and Fabio Scenini
Micromachines 2020, 11(5), 510; https://doi.org/10.3390/mi11050510 - 19 May 2020
Cited by 3 | Viewed by 3292
Abstract
Microfluidics is an active research area in modern fluid mechanics, with several applications in science and engineering. Despite their importance in microfluidic systems, micro-orifices with non-circular cross-sections have not been extensively investigated. In this study, micro-orifice discharge with single-phase liquid flow was experimentally [...] Read more.
Microfluidics is an active research area in modern fluid mechanics, with several applications in science and engineering. Despite their importance in microfluidic systems, micro-orifices with non-circular cross-sections have not been extensively investigated. In this study, micro-orifice discharge with single-phase liquid flow was experimentally investigated for seven square and rectangular cross-section micro-orifices with a hydraulic diameter in the range of 326–510 µm. The discharge measurements were carried out in pressurized water (12 MPa) at ambient temperature (298 K) and high temperature (503 K). During the tests, the Reynolds number varied between 5883 and 212,030, significantly extending the range in which data are currently available in the literature on non-circular micro-orifices. The results indicate that the cross-sectional shape of the micro-orifice has little, if any, effect on the hydrodynamic behavior. Thus, existing methods for the prediction of turbulent flow behavior in circular micro-orifices can be used to predict the flow behavior in non-circular micro-orifices, provided that the flow geometry of the non-circular micro-orifice is described using a hydraulic diameter. Full article
(This article belongs to the Section A：Physics)
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<p>SEM images (front and back) of all the discs containing the micro-orifice.</p> Full article ">Figure 2
<p>Schematic representation of the flow loop (<b>left</b>) and 3D representation and drawing of the flow cell test section (<b>right</b>).</p> Full article ">Figure 3
<p>Discharge characteristics of the micro-orifices tested.</p> Full article ">Figure 4
<p>Dimensionless pressure drop as a function of Reynolds number for the micro-orifices tested.</p> Full article ">Figure 5
<p>(<b>a</b>) Dimensionless pressure drop as a function of Reynolds number for the micro-orifices tested in this study and from the literature; (<b>b</b>) parity plot of measured dimensionless pressure drop vs. prediction of Equation (3) (the dashed lines are ±30% bounds).</p> Full article ">
13 pages, 5572 KiB  
Article
Hybrid Process Chain for the Integration of Direct Ink Writing and Polymer Injection Molding
by Dario Loaldi, Leonardo Piccolo, Eric Brown, Guido Tosello, Corey Shemelya and Davide Masato
Micromachines 2020, 11(5), 509; https://doi.org/10.3390/mi11050509 - 18 May 2020
Cited by 11 | Viewed by 3872
Abstract
The integration of additive manufacturing direct-writing technologies with injection molding provides a novel method to combine functional features into plastic products, and could enable mass-manufacturing of custom-molded plastic parts. In this work, direct-write technology is used to deposit conductive ink traces on the [...] Read more.
The integration of additive manufacturing direct-writing technologies with injection molding provides a novel method to combine functional features into plastic products, and could enable mass-manufacturing of custom-molded plastic parts. In this work, direct-write technology is used to deposit conductive ink traces on the surface of an injection mold. After curing on the mold surface, the printed trace is transferred into the plastic part by exploiting the high temperature and pressure of a thermoplastic polymer melt flow. The transfer of the traces is controlled by interlocking with the polymer system, which creates strong plastic/ink interfacial bonding. The hybrid process chain uses designed mold/ink surface interactions to manufacture stable ink/polymer interfaces. Here, the process chain is proposed and validated through systematic interfacial analysis including feature fidelity, mechanical properties, adhesion, mold topography, surface energy, and hot polymer contact angle. Full article
(This article belongs to the Special Issue Latest Advancements in Micro Nano Molding Technologies – Process Developments and Optimization, Materials, Applications, Key Enabling Technologies)
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<p>Steps of the process chain developed to manufacture molded interconnect devices.</p> Full article ">Figure 2
<p>Ink dispensing system before printing over the injection mold surface.</p> Full article ">Figure 3
<p>(<b>a</b>) Characterization of the mold before injection and the plastic replica after transfer. (<b>b</b>) Cross-section of the plastic part with the embedded traces, and (<b>c</b>) high magnification of the ink embedded in the printed traces.</p> Full article ">Figure 4
<p>3D view of the analyzed surface topographies: (<b>a</b>) 3D printed ink on the mold before injection molding, (<b>b</b>) coating on the mold before injection molding, (<b>c</b>) polished mold surface, (<b>d</b>) plastic part surface after demolding, (<b>e</b>) embedded ink on the plastic part.</p> Full article ">Figure 5
<p>SEM micrographs at different magnification (500× (<b>a</b>) –3000× (<b>b</b>) –12000× (<b>c</b>)) of the sintered ink surface before injection molding. Micrographs were taken with an E beam power of 5 kV.</p> Full article ">Figure 6
<p>SEM micrographs at different magnification (500× (<b>a</b>) –3000× (<b>b</b>) –12000× (<b>c</b>)) of the sintered ink surface embedded in the injection molded part. Micrographs were taken with an E beam power of 5 kV.</p> Full article ">Figure 7
<p>(<b>a</b>) Contact angle measurements for polar (H<sub>2</sub>O) and a-polar (CH<sub>2</sub>I<sub>2</sub>) liquids: (<b>b</b>) surface energy for different surfaces; (<b>c</b>) percentage of dispersion and polar content for the analyzed surfaces.</p> Full article ">Figure 8
<p>Contact angle measurements using (<b>a</b>) liquid ink and (<b>b</b>) ABS melt at 260 °C on different surfaces.</p> Full article ">Figure 9
<p>(<b>a</b>) Elastic modulus and (<b>b</b>) Ultimate Tensile Strength for samples with embedded printed electronics and bulk parts.</p> Full article ">Figure 10
<p>Optical images of the embedded traces after the peeling test for a trace with a nominal width of (<b>a</b>) 250 µm and (<b>b</b>) 2000 µm.</p> Full article ">
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