Editorial

3 pages, 174 KiB

Open AccessEditorial

Editorial for the Special Issue of 10th Anniversary of Micromachines

by Ai Qun Liu, Nam-Trung Nguyen and Yi Zhang

Micromachines 2021, 12(1), 9; https://0-doi-org.brum.beds.ac.uk/10.3390/mi12010009 - 24 Dec 2020

Cited by 1 | Viewed by 1313

Micromachines published its inaugural issue in 2010; it has experienced a tremendous growth in both the quantity and quality of its scientific papers [...] Full article

(This article belongs to the Special Issue 10th Anniversary of Micromachines)

Research

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11 pages, 2460 KiB

Open AccessArticle

Photoacoustic Detection of H₂ and NH₃ Using Plasmonic Signal Enhancement in GaN Microcantilevers

by Digangana Khan, Hongmei Li, Ferhat Bayram, Durga Gajula and Goutam Koley

Micromachines 2020, 11(7), 680; https://0-doi-org.brum.beds.ac.uk/10.3390/mi11070680 - 13 Jul 2020

Cited by 3 | Viewed by 2110

Abstract

Photoacoustic (PA) detection of H₂ and NH₃ using plasmonic excitation in Pt- and Pd-decorated GaN piezotransistive microcantilevers were investigated using pulsed 520-nm laser illumination. The sensing performances of 1-nm Pt and Pd nanoparticle (NP) deposited cantilever devices were compared, of which [...] Read more.

Photoacoustic (PA) detection of H₂ and NH₃ using plasmonic excitation in Pt- and Pd-decorated GaN piezotransistive microcantilevers were investigated using pulsed 520-nm laser illumination. The sensing performances of 1-nm Pt and Pd nanoparticle (NP) deposited cantilever devices were compared, of which the Pd-coated sensor devices exhibited consistently better sensing performance, with lower limit of detection and superior signal-to-noise ratio (SNR) values, compared to the Pt-coated devices. Among the two functionalization layers, Pd-coated devices were found to respond only to H₂ exposure and not to NH₃, while Pt-coated devices exhibited repeatable response to both H₂ and NH₃ exposures, highlighting the potential of the former in performing selective detection between these reducing gases. Optimization of the device-biasing conditions were found to enhance the detection sensitivity of the sensors. Full article

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13 pages, 4728 KiB

Open AccessArticle

Experimental Characterization and Simulation of Thermoplastic Polymer Flow Hesitation in Thin-Wall Injection Molding Using Direct In-Mold Visualization Technique

by Francesco Regi, Patrick Guerrier, Yang Zhang and Guido Tosello

Micromachines 2020, 11(4), 428; https://0-doi-org.brum.beds.ac.uk/10.3390/mi11040428 - 19 Apr 2020

Cited by 11 | Viewed by 3244

Abstract

A special mold provided with a glass window was used in order to directly evaluate the flow progression during the filling phase of the injection molding process in a thin-wall cavity and to validate the simulation of the process with particular focus on [...] Read more.

A special mold provided with a glass window was used in order to directly evaluate the flow progression during the filling phase of the injection molding process in a thin-wall cavity and to validate the simulation of the process with particular focus on the hesitation effect. The flow of the polymer was recorded at 500 frames per second using a high-speed camera (HSC). Two unfilled thermoplastic polymers, acrylonitrile butadiene styrene (ABS), and polypropylene (PP), were used to fill two different 50 mm × 18 mm staircase geometry cavities, which were specifically designed to evaluate the hesitation effect with thicknesses of 1500, 1250, 1000, 750, 500 µm (cavity insert no. 1) and 1500, 1200, 900, 600, 300 µm (cavity insert no. 2). In addition to the video recordings, the simulations were validated using the timings and the data obtained by three pressure sensors and two thermocouples located in the cavity. For each injection cycle recorded on camera the machine data were collected to carefully implement the correct boundary conditions in the simulations. The analysis of the video recordings highlighted that flow progression and hesitation were mainly influenced not only by the thickness, but also by the velocity and the material type. The simulation results were in relatively good agreement with the experiments in terms of flow pattern and progression. Filling times were predicted with an average relative error deviation of 2.5% throughout all the section thicknesses of the cavity. Lower accuracies in terms of both filling times and injection pressure were observed at increasingly thinner sections. Full article

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14 pages, 3261 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

A Microfluidic-Based Investigation of Bacterial Attachment in Ureteral Stents

by Antonio De Grazia, Gareth LuTheryn, Alireza Meghdadi, Ali Mosayyebi, Erika J. Espinosa-Ortiz, Robin Gerlach and Dario Carugo

Micromachines 2020, 11(4), 408; https://0-doi-org.brum.beds.ac.uk/10.3390/mi11040408 - 13 Apr 2020

Cited by 23 | Viewed by 5139

Abstract

Obstructions of the ureter lumen can originate from intrinsic or extrinsic factors, such as kidney stones, tumours, or strictures. These can affect the physiological flow of urine from the kidneys to the bladder, potentially causing infection, pain, and kidney failure. To overcome these [...] Read more.

Obstructions of the ureter lumen can originate from intrinsic or extrinsic factors, such as kidney stones, tumours, or strictures. These can affect the physiological flow of urine from the kidneys to the bladder, potentially causing infection, pain, and kidney failure. To overcome these complications, ureteral stents are often deployed clinically in order to temporarily re-establish urinary flow. Despite their clinical benefits, stents are prone to encrustation and biofilm formation that lead to reduced quality of life for patients; however, the mechanisms underlying the formation of crystalline biofilms in stents are not yet fully understood. In this study, we developed microfluidic-based devices replicating the urodynamic field within different configurations of an occluded and stented ureter. We employed computational fluid dynamic simulations to characterise the flow dynamic field within these models and investigated bacterial attachment (Pseudomonas fluorescens) by means of crystal violet staining and fluorescence microscopy. We identified the presence of hydrodynamic cavities in the vicinity of a ureteric occlusion, which were characterised by low levels of wall shear stress (WSS < 40 mPa), and observed that initiation of bacterial attachment occurred in these specific regions of the stented ureter. Notably, the bacterial coverage area was directly proportional to the number of cavities present in the model. Fluorescence microscopy confirmed that the number density of bacteria was greater within cavities (3 bacteria·mm⁻²) when compared to side-holes of the stent (1 bacterium·mm⁻²) or its luminal surface (0.12 bacteria·mm⁻²). These findings informed the design of a novel technological solution against bacterial attachment, which reduces the extent of cavity flow and increases wall shear stress over the stent’s surface. Full article

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13 pages, 3248 KiB

Open AccessFeature PaperArticle

Metabolic Switching of Tumor Cells under Hypoxic Conditions in a Tumor-on-a-chip Model

by Valentina Palacio-Castañeda, Lucas Kooijman, Bastien Venzac, Wouter P.R. Verdurmen and Séverine Le Gac

Micromachines 2020, 11(4), 382; https://0-doi-org.brum.beds.ac.uk/10.3390/mi11040382 - 04 Apr 2020

Cited by 32 | Viewed by 5034

Abstract

Hypoxia switches the metabolism of tumor cells and induces drug resistance. Currently, no therapeutic exists that effectively and specifically targets hypoxic cells in tumors. Development of such therapeutics critically depends on the availability of in vitro models that accurately recapitulate hypoxia as found [...] Read more.

Hypoxia switches the metabolism of tumor cells and induces drug resistance. Currently, no therapeutic exists that effectively and specifically targets hypoxic cells in tumors. Development of such therapeutics critically depends on the availability of in vitro models that accurately recapitulate hypoxia as found in the tumor microenvironment. Here, we report on the design and validation of an easy-to-fabricate tumor-on-a-chip microfluidic platform that robustly emulates the hypoxic tumor microenvironment. The tumor-on-a-chip model consists of a central chamber for 3D tumor cell culture and two side channels for medium perfusion. The microfluidic device is fabricated from polydimethylsiloxane (PDMS), and oxygen diffusion in the device is blocked by an embedded sheet of polymethyl methacrylate (PMMA). Hypoxia was confirmed using oxygen-sensitive probes and the effect on the 3D tumor cell culture investigated by a pH-sensitive dual-labeled fluorescent dextran and a fluorescently labeled glucose analogue. In contrast to control devices without PMMA, PMMA-containing devices gave rise to decreases in oxygen and pH levels as well as an increased consumption of glucose after two days of culture, indicating a rapid metabolic switch of the tumor cells under hypoxic conditions towards increased glycolysis. This platform will open new avenues for testing anti-cancer therapies targeting hypoxic areas. Full article

(This article belongs to the Special Issue 10th Anniversary of Micromachines)

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13 pages, 5724 KiB

Open AccessArticle

Step-Wise Deposition Process for Dielectrophoretic Formation of Conductive 50-Micron-Long Carbon Nanotube Bridges

by Tuo Zhou, Ethan Kropp, Jingyuan Chen and Lawrence Kulinsky

Micromachines 2020, 11(4), 371; https://0-doi-org.brum.beds.ac.uk/10.3390/mi11040371 - 01 Apr 2020

Cited by 12 | Viewed by 2686

Abstract

Carbon Nanotube (CNT) agglomerates can be aligned along field lines between adjacent electrodes to form conductive bridges. This study discusses the step-wise process of dielectrophoretic deposition of CNTs to form conducting bridges between adjacent electrodes. For the first time, the creation of conductive [...] Read more.

Carbon Nanotube (CNT) agglomerates can be aligned along field lines between adjacent electrodes to form conductive bridges. This study discusses the step-wise process of dielectrophoretic deposition of CNTs to form conducting bridges between adjacent electrodes. For the first time, the creation of conductive CNT bridges spanning lengths over 50 microns is demonstrated. The CNT bridges are permanently secured using electrodeposition of the conducting polymer polypyrrole. Morphologies of the CNT bridges formed within a frequency range of 1 kHz and 10 MHz are explored and explained as a consequence of interplay between dielectrophoretic and electroosmotic forces. Postdeposition heat treatment increases the conductivity of CNT bridges, likely due to solvent evaporation and resulting surface tension inducing better contact between CNTs. Full article

(This article belongs to the Special Issue 10th Anniversary of Micromachines)

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13 pages, 5470 KiB

Open AccessArticle

Bubbles Moving in Blood Flow in a Microchannel Network: The Effect on the Local Hematocrit

by David Bento, Sara Lopes, Inês Maia, Rui Lima and João M. Miranda

Micromachines 2020, 11(4), 344; https://0-doi-org.brum.beds.ac.uk/10.3390/mi11040344 - 26 Mar 2020

Cited by 19 | Viewed by 2749

Abstract

Air inside of blood vessels is a phenomenon known as gas embolism. During the past years, studies have been performed to assess the influence of air bubbles in microcirculation. In this study, we investigated the flow of bubbles in a microchannel network with [...] Read more.

Air inside of blood vessels is a phenomenon known as gas embolism. During the past years, studies have been performed to assess the influence of air bubbles in microcirculation. In this study, we investigated the flow of bubbles in a microchannel network with several bifurcations, mimicking part of a capillary system. Thus, two working fluids were used, composed by sheep red blood cells (RBCs) suspended in a Dextran 40 solution with different hematocrits (5% and 10%). The experiments were carried out in a polydimethylsiloxane (PDMS) microchannel network fabricated by a soft lithography. A high-speed video microscopy system was used to obtain the results for a blood flow rate of 10 µL/min. This system enables the visualization of bubble formation and flow along the network. The results showed that the passage of air bubbles strongly influences the cell’s local concentration, since a higher concentration of cells was observed upstream of the bubble, whereas a lower local hematocrit was visualized at the region downstream of the bubble. In bifurcations, bubbles may split asymmetrically, leading to an uneven distribution of RBCs between the outflow branches. Full article

(This article belongs to the Special Issue 10th Anniversary of Micromachines)

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20 pages, 2548 KiB

Open AccessArticle

On the Effects of Package on the PMUTs Performances—Multiphysics Model and Frequency Analyses

by Gianluca Massimino, Alessandro Colombo, Raffaele Ardito, Fabio Quaglia and Alberto Corigliano

Micromachines 2020, 11(3), 307; https://0-doi-org.brum.beds.ac.uk/10.3390/mi11030307 - 14 Mar 2020

Cited by 10 | Viewed by 2356

Abstract

This paper deals with a multiphysics numerical modelling via finite element method (FEM) of an air-coupled array piezoelectric micromachined ultrasonic transducers (PMUTs). The proposed numerical model is fully 3D with the following features: the presence of the fabrication induced residual stresses, which determine [...] Read more.

This paper deals with a multiphysics numerical modelling via finite element method (FEM) of an air-coupled array piezoelectric micromachined ultrasonic transducers (PMUTs). The proposed numerical model is fully 3D with the following features: the presence of the fabrication induced residual stresses, which determine a geometrically non-linear initial deformed configuration of the diaphragms and a remarkable shift of the fundamental frequency; the multiple coupling between different physics, namely electro-mechanical-coupling for the piezo-electric model, acoustic-structure interaction at the acoustic-structure interface and pressure acoustics in the surrounding air. The model takes into account the complete set of PMUTs belonging to the silicon die in a 4 × 4 array configuration and the protective package, as well. The results have been validated by experimental data, in terms of initial static pre-deflected configuration of the diaphragms and frequency response function of the PMUT. The numerical procedure was applied, to analyze different package configurations of the device, to study the influence of the holes on the acoustic transmission in terms of SPL and propagation pattern and consequently extract a set of design guidelines. Full article

(This article belongs to the Special Issue 10th Anniversary of Micromachines)

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17 pages, 4274 KiB

Open AccessArticle

Microfluidic Device for Microinjection of Caenorhabditis elegans

by Reza Ghaemi, Justin Tong, Bhagwati P. Gupta and P. Ravi Selvaganapathy

Micromachines 2020, 11(3), 295; https://0-doi-org.brum.beds.ac.uk/10.3390/mi11030295 - 11 Mar 2020

Cited by 6 | Viewed by 4639

Abstract

Microinjection is an established and reliable method to deliver transgenic constructs and other reagents to specific locations in C. elegans worms. Specifically, microinjection of a desired DNA construct into the distal gonad is the most widely used method to generate germ-line transformation of [...] Read more.

Microinjection is an established and reliable method to deliver transgenic constructs and other reagents to specific locations in C. elegans worms. Specifically, microinjection of a desired DNA construct into the distal gonad is the most widely used method to generate germ-line transformation of C. elegans. Although, current C. elegans microinjection method is effective to produce transgenic worms, it requires expensive multi degree of freedom (DOF) micromanipulator, careful injection alignment procedure and skilled operator, all of which make it slow and not suitable for scaling to high throughput. A few microfabricated microinjectors have been developed recently to address these issues. However, none of them are capable of immobilizing a freely mobile animal such as C. elegans worm using a passive immobilization mechanism. Here, a microfluidic microinjector was developed to passively immobilize a freely mobile animal such as C. elegans and simultaneously perform microinjection by using a simple and fast mechanism for needle actuation. The entire process of the microinjection takes ~30 s which includes 10 s for worm loading and aligning, 5 s needle penetration, 5 s reagent injection and 5 s worm unloading. The device is suitable for high-throughput and can be potentially used for creating transgenic C. elegans. Full article

(This article belongs to the Special Issue 10th Anniversary of Micromachines)

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13 pages, 4270 KiB

Open AccessArticle

High-Throughput White Blood Cell (Leukocyte) Enrichment from Whole Blood Using Hydrodynamic and Inertial Forces

by Batzorig Lombodorj, Horas Cendana Tseng, Hwan-You Chang, Yen-Wen Lu, Namnan Tumurpurev, Chun-Wei Lee, Batdemberel Ganbat, Ren-Guei Wu and Fan-Gang Tseng

Micromachines 2020, 11(3), 275; https://0-doi-org.brum.beds.ac.uk/10.3390/mi11030275 - 06 Mar 2020

Cited by 12 | Viewed by 4162

Abstract

A microfluidic chip, which can separate and enrich leukocytes from whole blood, is proposed. The chip has 10 switchback curve channels, which are connected by straight channels. The straight channels are designed to permit the inertial migration effect and to concentrate the blood [...] Read more.

A microfluidic chip, which can separate and enrich leukocytes from whole blood, is proposed. The chip has 10 switchback curve channels, which are connected by straight channels. The straight channels are designed to permit the inertial migration effect and to concentrate the blood cells, while the curve channels allow the Dean flow to further classify the blood cells based on the cell sizes. Hydrodynamic suction is also utilized to remove smaller blood cells (e.g., red blood cell (RBC)) in the curve channels for higher separation purity. By employing the inertial migration, Dean flow force, and hydrodynamic suction in a continuous flow system, our chip successfully separates large white blood cells (WBCs) from the whole blood with the processing rates as high as 1 × 10⁸ cells/sec at a high recovery rate at 93.2% and very few RBCs (~0.1%). Full article

(This article belongs to the Special Issue 10th Anniversary of Micromachines)

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14 pages, 1241 KiB

Open AccessArticle

Dipolophoresis and Travelling-Wave Dipolophoresis of Metal Microparticles

by Jose Eladio Flores-Mena, Pablo García-Sánchez and Antonio Ramos

Micromachines 2020, 11(3), 259; https://0-doi-org.brum.beds.ac.uk/10.3390/mi11030259 - 28 Feb 2020

Cited by 4 | Viewed by 2225

Abstract

We study theoretically and numerically the electrokinetic behavior of metal microparticles immersed in aqueous electrolytes. We consider small particles subjected to non-homogeneous ac electric fields and we describe their motion as arising from the combination of electrical forces (dielectrophoresis) and the electroosmotic flows [...] Read more.

We study theoretically and numerically the electrokinetic behavior of metal microparticles immersed in aqueous electrolytes. We consider small particles subjected to non-homogeneous ac electric fields and we describe their motion as arising from the combination of electrical forces (dielectrophoresis) and the electroosmotic flows on the particle surface (induced-charge electrophoresis). The net particle motion is known as dipolophoresis. We also study the particle motion induced by travelling electric fields. We find analytical expressions for the dielectrophoresis and induced-charge electrophoresis of metal spheres and we compare them with numerical solutions. This validates our numerical method, which we also use to study the dipolophoresis of metal cylinders. Full article

(This article belongs to the Special Issue 10th Anniversary of Micromachines)

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8 pages, 5639 KiB

Open AccessArticle

Design and Fabrication of Microscale, Thin-Film Silicon Solid Immersion Lenses for Mid-Infrared Application

by Gil Ju Lee, Hyun Myung Kim and Young Min Song

Micromachines 2020, 11(3), 250; https://0-doi-org.brum.beds.ac.uk/10.3390/mi11030250 - 27 Feb 2020

Cited by 13 | Viewed by 3296

Abstract

Lens-based optical microscopes cannot resolve the sub-wavelength objects overpass diffraction limit. Recently, research on super-resolution imaging has been conducted to overcome this limitation in visible wavelength using solid immersion lenses. However, IR imaging, which is useful for chemical imaging, bio-imaging, and thermal imaging, [...] Read more.

Lens-based optical microscopes cannot resolve the sub-wavelength objects overpass diffraction limit. Recently, research on super-resolution imaging has been conducted to overcome this limitation in visible wavelength using solid immersion lenses. However, IR imaging, which is useful for chemical imaging, bio-imaging, and thermal imaging, has not been studied much in optical super-resolution by solid immersion lens owing to material limitations. Herein, we present the design and fabrication schemes of microscale silicon solid immersion lenses (µ-SIL) based on thin-film geometry for mid-infrared (MIR) applications. Compared with geometrical optics, a rigorous finite-difference time-domain (FDTD) calculation of proposed silicon microlenses at MIR wavelengths shows that the outstanding short focal lengths result in enhanced magnification, which allows resolving objects beyond the diffraction limit. In addition, the theoretical analyses evaluate the influences of various structural parameters, such as radius of curvature (RoC), refractive index, and substrate thickness, in µ-SIL. In particular, the high refractive index of µ-SIL is beneficial to implement the outstanding near-field focusing, which corresponds to a high numerical aperture. On the basis of this theoretical background, novel methods are developed for the fabrication of a printable, thin-film silicon microlens array and its integration with a specimen substrate. From the result, we provide a physical understanding of near-field focusing phenomena and offer a promising tool for super-resolution far-field imaging in the MIR range. Full article

(This article belongs to the Special Issue 10th Anniversary of Micromachines)

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13 pages, 2678 KiB

Open AccessArticle

The Research on Multi-Material 3D Vascularized Network Integrated Printing Technology

by Shuai Yang, Hao Tang, Chunmei Feng, Jianping Shi and Jiquan Yang

Micromachines 2020, 11(3), 237; https://0-doi-org.brum.beds.ac.uk/10.3390/mi11030237 - 25 Feb 2020

Cited by 12 | Viewed by 2957

Abstract

Three-dimensional bioprinting has emerged as one of the manufacturing approaches that could potentially fabricate vascularized channels, which is helpful to culture tissues in vitro. In this paper, we report a novel approach to fabricate 3D perfusable channels by using the combination of extrusion [...] Read more.

Three-dimensional bioprinting has emerged as one of the manufacturing approaches that could potentially fabricate vascularized channels, which is helpful to culture tissues in vitro. In this paper, we report a novel approach to fabricate 3D perfusable channels by using the combination of extrusion and inkjet techniques in an integrated manufacture process. To achieve this, firstly we investigate the theoretical model to analyze influencing factors of structural dimensions of the printed parts like the printing speed, pressure, dispensing time, and voltage. In the experiment, photocurable hydrogel was printed to form a self-supporting structure with internal channel grooves. When the desired height of hydrogel was reached, the dual print-head was switched to the piezoelectric nozzle immediately, and the sacrificial material was printed by the changed nozzle on the printed hydrogel layer. Then, the extrusion nozzle was switched to print the next hydrogel layer. Once the printing of the internal construct was finished, hydrogel was extruded to wrap the entire structure, and the construct was immersed in a CaCl₂ solution to crosslink. After that, the channel was formed by removing the sacrificial material. This approach can potentially provide a strategy for fabricating 3D vascularized channels and advance the development of culturing thick tissues in vitro. Full article

(This article belongs to the Special Issue 10th Anniversary of Micromachines)

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17 pages, 3663 KiB

Open AccessArticle

Effects of Top-hat Laser Beam Processing and Scanning Strategies in Laser Micro-Structuring

by Hoang Le, Pavel Penchev, Anne Henrottin, David Bruneel, Vahid Nasrollahi, Jose A. Ramos-de-Campos and Stefan Dimov

Micromachines 2020, 11(2), 221; https://0-doi-org.brum.beds.ac.uk/10.3390/mi11020221 - 20 Feb 2020

Cited by 26 | Viewed by 5571

Abstract

The uniform energy distribution of top-hat laser beams is a very attractive property that can offer some advantages compared to Gaussian beams. Especially, the desired intensity distribution can be achieved at the laser spot through energy redistribution across the beam spatial profile and, [...] Read more.

The uniform energy distribution of top-hat laser beams is a very attractive property that can offer some advantages compared to Gaussian beams. Especially, the desired intensity distribution can be achieved at the laser spot through energy redistribution across the beam spatial profile and, thus, to minimize and even eliminate some inherent shortcomings in laser micro-processing. This paper reports an empirical study that investigates the effects of top-hat beam processing in micro-structuring and compares the results with those obtainable with a conventional Gaussian beam. In particular, a refractive field mapping beam shaper was used to obtain a top-hat profile and the effects of different scanning strategies, pulse energy settings, and accumulated fluence, i.e., hatch and pulse distances, were investigated. In general, the top-hat laser processing led to improvements in surface and structuring quality. Especially, the taper angle was reduced while the surface roughness and edge definition were also improved compared to structures produced with Gaussian beams. A further decrease of the taper angle was achieved by combining hatching with some outlining beam passes. The scanning strategies with only outlining beam passes led to very high ablation rates but in expense of structuring quality. Improvements in surface roughness were obtained with a wide range of pulse energies and pulse and hatch distances when top-hat laser processing was used. Full article

(This article belongs to the Special Issue 10th Anniversary of Micromachines)

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10 pages, 1550 KiB

Open AccessArticle

Light Gradient-Based Screening of Arabidopsis thaliana on a 384-Well Type Plant Array Chip

by Youn-Hee Park and Je-Kyun Park

Micromachines 2020, 11(2), 191; https://0-doi-org.brum.beds.ac.uk/10.3390/mi11020191 - 12 Feb 2020

Cited by 1 | Viewed by 2984

Abstract

Arabidopsis thaliana (Arabidopsis), as a model for plant research, is widely used for various aspects of plant science. To provide a more sophisticated and microscopic environment for the germination and growth of Arabidopsis, we report a 384-well type plant array [...] Read more.

Arabidopsis thaliana (Arabidopsis), as a model for plant research, is widely used for various aspects of plant science. To provide a more sophisticated and microscopic environment for the germination and growth of Arabidopsis, we report a 384-well type plant array chip in which each Arabidopsis seed is independently seeded in a solid medium. The plant array chip is made of a poly(methyl methacrylate) (PMMA) acrylic material and is assembled with a home-made light gradient module to investigate the light effects that significantly affect the germination and growth of Arabidopsis. The light gradient module was used to observe the growth pattern of seedlings according to the intensity of the white light and to efficiently screen for the influence of the white light. To investigate the response to red light (600 nm), which stimulates seed germination, the light gradient module was also applied to the germination test. As a result, the germination results showed that the plant array chip can be used to simultaneously screen wild type seeds and phytochrome B mutant seeds on a single array chip according to the eight red light intensities. Full article

(This article belongs to the Special Issue 10th Anniversary of Micromachines)

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13 pages, 2348 KiB

Open AccessFeature PaperArticle

A Quantitative Study of the Secondary Acoustic Radiation Force on Biological Cells during Acoustophoresis

by Davood Saeidi, Mohsen Saghafian, Shaghayegh Haghjooy Javanmard and Martin Wiklund

Micromachines 2020, 11(2), 152; https://0-doi-org.brum.beds.ac.uk/10.3390/mi11020152 - 30 Jan 2020

Cited by 21 | Viewed by 3828

Abstract

We investigate cell-particle secondary acoustic radiation forces in a plain ultrasonic standing wave field inside a microfluidic channel. The effect of secondary acoustic radiation forces on biological cells is measured in a location between a pressure node and a pressure anti-node and the [...] Read more.

We investigate cell-particle secondary acoustic radiation forces in a plain ultrasonic standing wave field inside a microfluidic channel. The effect of secondary acoustic radiation forces on biological cells is measured in a location between a pressure node and a pressure anti-node and the result is compared with theory by considering both compressibility and density dependent effects. The secondary acoustic force between motile red blood cells (RBCs) and MCF-7 cells and fixed 20 µm silica beads is investigated in a half-wavelength wide microchannel actuated at 2 MHz ultrasonic frequency. Our study shows that the secondary acoustic force between cells in acoustofluidic devices could play an important role for cell separation, sorting, and trapping purposes. Our results also demonstrate the possibility to isolate individual cells at trapping positions provided by silica beads immobilized and adhered to the microchannel bottom. We conclude that during certain experimental conditions, the secondary acoustic force acting on biological cells can dominate over the primary acoustic radiation force, which could open up for new microscale acoustofluidic methods. Full article

(This article belongs to the Special Issue 10th Anniversary of Micromachines)

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12 pages, 2903 KiB

Open AccessArticle

Durability and Recoverability of Soft Lithographically Patterned Hydrogel Molds for the Formation of Phase Separation Membranes

by Asad Asad, Masoud Rastgar, Hadi Nazaripoor, Mohtada Sadrzadeh and Dan Sameoto

Micromachines 2020, 11(1), 108; https://0-doi-org.brum.beds.ac.uk/10.3390/mi11010108 - 19 Jan 2020

Cited by 5 | Viewed by 3688

Abstract

Hydrogel-facilitated phase separation (HFPS) has recently been applied to make microstructured porous membranes by modified phase separation processes. In HFPS, a soft lithographically patterned hydrogel mold is used as a water content source that initiates the phase separation process in membrane fabrication. However, [...] Read more.

Hydrogel-facilitated phase separation (HFPS) has recently been applied to make microstructured porous membranes by modified phase separation processes. In HFPS, a soft lithographically patterned hydrogel mold is used as a water content source that initiates the phase separation process in membrane fabrication. However, after each membrane casting, the hydrogel content changes due to the diffusion of organic solvent into the hydrogel from the original membrane solution. The absorption of solvent into the hydrogel mold limits the continuous use of the mold in repeated membrane casts. In this study, we investigated a simple treatment process for hydrogel mold recovery, consisting of warm and cold treatment steps to provide solvent extraction without changing the hydrogel mold integrity. The best recovery result was 96%, which was obtained by placing the hydrogel in a warm water bath (50 °C) for 10 min followed by immersing in a cold bath (23 °C) for 4 min and finally 4 min drying in air. This recovery was attributed to nearly complete solvent extraction without any deformation of the hydrogel structure. The reusability of hydrogel can assist in the development of a continuous membrane fabrication process using HFPS. Full article

(This article belongs to the Special Issue 10th Anniversary of Micromachines)

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10 pages, 4721 KiB

Open AccessFeature PaperArticle

Paper-Supported High-Throughput 3D Culturing, Trapping, and Monitoring of Caenorhabditis Elegans

by Mehdi Tahernia, Maedeh Mohammadifar and Seokheun Choi

Micromachines 2020, 11(1), 99; https://0-doi-org.brum.beds.ac.uk/10.3390/mi11010099 - 17 Jan 2020

Cited by 9 | Viewed by 3887

Abstract

We developed an innovative paper-based platform for high-throughput culturing, trapping, and monitoring of C. elegans. A 96-well array was readily fabricated by placing a nutrient-replenished paper substrate on a micromachined 96-well plastic frame, providing high-throughput 3D culturing environments and in situ analysis [...] Read more.

We developed an innovative paper-based platform for high-throughput culturing, trapping, and monitoring of C. elegans. A 96-well array was readily fabricated by placing a nutrient-replenished paper substrate on a micromachined 96-well plastic frame, providing high-throughput 3D culturing environments and in situ analysis of the worms. The paper allows C. elegans to pass through the porous and aquatic paper matrix until the worms grow and reach the next developmental stages with the increased body size comparable to the paper pores. When the diameter of C. elegans becomes larger than the pore size of the paper substrate, the worms are trapped and immobilized for further high-throughput imaging and analysis. This work will offer a simple yet powerful technique for high-throughput sorting and monitoring of C. elegans at a different larval stage by controlling and choosing different pore sizes of paper. Furthermore, we developed another type of 3D culturing system by using paper-like transparent polycarbonate substrates for higher resolution imaging. The device used the multi-laminate structure of the polycarbonate layers as a scaffold to mimic the worm’s 3D natural habitats. Since the substrate is thin, mechanically strong, and largely porous, the layered structure allowed C. elegans to move and behave freely in 3D and promoted the efficient growth of both C. elegans and their primary food, E. coli. The transparency of the structure facilitated visualization of the worms under a microscope. Development, fertility, and dynamic behavior of C. elegans in the 3D culture platform outperformed those of the standard 2D cultivation technique. Full article

(This article belongs to the Special Issue 10th Anniversary of Micromachines)

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12 pages, 6293 KiB

Open AccessArticle

Low-Concentration Ammonia Gas Sensors Manufactured Using the CMOS–MEMS Technique

by Wei-Chun Shen, Po-Jen Shih, Yao-Chuan Tsai, Cheng-Chih Hsu and Ching-Liang Dai

Micromachines 2020, 11(1), 92; https://0-doi-org.brum.beds.ac.uk/10.3390/mi11010092 - 15 Jan 2020

Cited by 31 | Viewed by 3837

Abstract

This study describes the fabrication of an ammonia gas sensor (AGS) using a complementary metal oxide semiconductor (CMOS)–microelectromechanical system (MEMS) technique. The structure of the AGS features interdigitated electrodes (IDEs) and a sensing material on a silicon substrate. The IDEs are the stacked [...] Read more.

This study describes the fabrication of an ammonia gas sensor (AGS) using a complementary metal oxide semiconductor (CMOS)–microelectromechanical system (MEMS) technique. The structure of the AGS features interdigitated electrodes (IDEs) and a sensing material on a silicon substrate. The IDEs are the stacked aluminum layers that are made using the CMOS process. The sensing material; polypyrrole/reduced graphene oxide (PPy/RGO), is synthesized using the oxidation–reduction method; and the material is characterized using an electron spectroscope for chemical analysis (ESCA), a scanning electron microscope (SEM), and high-resolution X-ray diffraction (XRD). After the CMOS process; the AGS needs post-processing to etch an oxide layer and to deposit the sensing material. The resistance of the AGS changes when it is exposed to ammonia. A non-inverting amplifier circuit converts the resistance of the AGS into a voltage signal. The AGS operates at room temperature. Experiments show that the AGS response is 4.5% at a concentration of 1 ppm NH₃; and it exhibits good repeatability. The lowest concentration that the AGS can detect is 0.1 ppm NH₃ Full article

(This article belongs to the Special Issue 10th Anniversary of Micromachines)

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16 pages, 8781 KiB

Open AccessArticle

Experimental Study on Machinability of Zr-Based Bulk Metallic Glass during Micro Milling

by Tao Wang, Xiaoyu Wu, Guoqing Zhang, Bin Xu, Yinghua Chen and Shuangchen Ruan

Micromachines 2020, 11(1), 86; https://0-doi-org.brum.beds.ac.uk/10.3390/mi11010086 - 13 Jan 2020

Cited by 11 | Viewed by 2923

Abstract

The micro machinability of Zr_41.2Ti_13.8Cu_12.5Ni₁₀Be_22.5 bulk metallic glass (BMG) was investigated by micro milling with coated cemented carbide tools. The corresponding micro milling tests on Al6061 were conducted for comparison. The results showed that [...] Read more.

The micro machinability of Zr_41.2Ti_13.8Cu_12.5Ni₁₀Be_22.5 bulk metallic glass (BMG) was investigated by micro milling with coated cemented carbide tools. The corresponding micro milling tests on Al6061 were conducted for comparison. The results showed that the tool was still in stable wear stage after milling 300 mm, and the surface roughness Ra could be maintained around 0.06 μm. The tool experienced only slight chipping and rubbing wear after milling the BMG, while a built-up edge and the coating peeling off occurred severely when milling Al6061. The influence of rotation speed on surface roughness was insignificant, while surface roughness decreased with the reduction of feed rate, and then increased dramatically when the feed rate was below 2 μm/tooth. The surface roughness increased gradually with the axial depth of cut (DOC). Milling force decreased slightly with the increase in rotation speed, while it increased with the increase in axial DOC, and the size effect on milling force occurred when the feed rate decreased below 1 μm/tooth. The results of X-ray diffraction (XRD) showed that all milled surfaces were still dominated by an amorphous structure. This study could pave a solid foundation for structural and functional applications. Full article

(This article belongs to the Special Issue 10th Anniversary of Micromachines)

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10 pages, 3955 KiB

Open AccessArticle

Application of a Terahertz System Combined with an X-Shaped Metamaterial Microfluidic Cartridge

by Shih-Ting Huang, Shen-Fu Hsu, Kai-Yuan Tang, Ta-Jen Yen and Da-Jeng Yao

Micromachines 2020, 11(1), 74; https://0-doi-org.brum.beds.ac.uk/10.3390/mi11010074 - 09 Jan 2020

Cited by 9 | Viewed by 2672

Abstract

Terahertz (THz) radiation has attracted wide attention for its ability to sense molecular structure and chemical matter because of a label-free molecular fingerprint and nondestructive properties. When it comes to molecular recognition with terahertz radiation, our attention goes first towards the absorption spectrum, [...] Read more.

Terahertz (THz) radiation has attracted wide attention for its ability to sense molecular structure and chemical matter because of a label-free molecular fingerprint and nondestructive properties. When it comes to molecular recognition with terahertz radiation, our attention goes first towards the absorption spectrum, which is beyond the far infrared region. To enhance the sensitivity for similar species, however, it is necessary to apply an artificially designed metamaterial sensor for detection, which confines an electromagnetic field in an extremely sub-wavelength space and hence receives an electromagnetic response through resonance. Once the resonance is caused through the interaction between the THz radiation and the metamaterial, a minute variation might be observed in the frequency domain. For a geometric structure of a metamaterial, a novel design called an X-shaped plasmonic sensor (XPS) can create a quadrupole resonance and lead to sensitivity greater than in the dipole mode. A microfluidic system is able to consume reagents in small volumes for detection, to diminish noise from the environment, and to concentrate the sample into detection spots. A microfluidic device integrated with an X-shaped plasmonic sensor might thus achieve an effective and highly sensitive detection cartridge. Our tests involved not only measurements of liquid samples, but also the performance of a dry bio-sample coated on an XPS. Full article

(This article belongs to the Special Issue 10th Anniversary of Micromachines)

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14 pages, 4697 KiB

Open AccessArticle

Electrothermally Driven Hydrogel-on-Flex-Circuit Actuator for Smart Steerable Catheters

by Madeshwaran Selvaraj and Kenichi Takahata

Micromachines 2020, 11(1), 68; https://0-doi-org.brum.beds.ac.uk/10.3390/mi11010068 - 08 Jan 2020

Cited by 13 | Viewed by 4450

Abstract

This paper reports an active catheter-tip device functionalized by integrating a temperature-responsive smart polymer onto a microfabricated flexible heater strip, targeting at enabling the controlled steering of catheters through complex vascular networks. A bimorph-like strip structure is enabled by photo-polymerizing a layer of [...] Read more.

This paper reports an active catheter-tip device functionalized by integrating a temperature-responsive smart polymer onto a microfabricated flexible heater strip, targeting at enabling the controlled steering of catheters through complex vascular networks. A bimorph-like strip structure is enabled by photo-polymerizing a layer of poly(N-isopropylacrylamide) hydrogel (PNIPAM), on top of a 20 × 3.5 mm² flexible polyimide film that embeds a micropatterned heater fabricated using a low-cost flex-circuit manufacturing process. The heater activation stimulates the PNIPAM layer to shrink and bend the tip structure. The bending angle is shown to be adjustable with the amount of power fed to the device, proving the device’s feasibility to provide the integrated catheter with a controlled steering ability for a wide range of navigation angles. The powered device exhibits uniform heat distribution across the entire PNIPAM layer, with a temperature variation of <2 °C. The operation of fabricated prototypes assembled on commercial catheter tubes demonstrates their bending angles of up to 200°, significantly larger than those reported with other smart-material-based steerable catheters. The temporal responses and bending forces of their actuations are also characterized to reveal consistent and reproducible behaviors. This proof-of-concept study verifies the promising features of the prototyped approach to the targeted application area. Full article

(This article belongs to the Special Issue 10th Anniversary of Micromachines)

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20 pages, 6936 KiB

Open AccessArticle

Anti-Symmetric Mode Vibration of Electrostatically Actuated Clamped–Clamped Microbeams for Mass Sensing

by Lei Li, Yin-ping Zhang, Chi-cheng Ma, Can-chang Liu and Bo Peng

Micromachines 2020, 11(1), 12; https://0-doi-org.brum.beds.ac.uk/10.3390/mi11010012 - 19 Dec 2019

Cited by 11 | Viewed by 2239

Abstract

This paper details study of the anti-symmetric response to the symmetrical electrostatic excitation of a Micro-electro-mechanical-systems (MEMS) resonant mass sensor. Under higher order mode excitation, two nonlinear coupled flexural modes to describe MEMS mass sensors are obtained by using Hamilton’s principle and Galerkin [...] Read more.

This paper details study of the anti-symmetric response to the symmetrical electrostatic excitation of a Micro-electro-mechanical-systems (MEMS) resonant mass sensor. Under higher order mode excitation, two nonlinear coupled flexural modes to describe MEMS mass sensors are obtained by using Hamilton’s principle and Galerkin method. Static analysis is introduced to investigate the effect of added mass on the natural frequency of the resonant sensor. Then, the perturbation method is applied to determine the response and stability of the system for small amplitude vibration. Through bifurcation analysis, the physical conditions of the anti-symmetric mode vibration are obtained. The corresponding stability analysis is carried out. Results show that the added mass can change the bifurcation behaviors of the anti-symmetric mode and affect the voltage and frequency of the bifurcation jump point. Typically, we propose a mass parameter identification method based on the dynamic jump motion of the anti-symmetric mode. Numerical studies are introduced to verify the validity of mass detection method. Finally, the influence of physical parameters on the sensitivity of mass sensor is analyzed. It is found that the DC voltage and mass adsorption position are critical to the sensitivity of the sensor. The results of this paper can be potentially useful in nonlinear mass sensors. Full article

(This article belongs to the Special Issue 10th Anniversary of Micromachines)

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12 pages, 2270 KiB

Open AccessFeature PaperArticle

Microfluidic Array Chip for Parallel Detection of Waterborne Bacteria

by Lena Gorgannezhad, Kamalalayam Rajan Sreejith, Jun Zhang, Gregor Kijanka, Melody Christie, Helen Stratton and Nam-Trung Nguyen

Micromachines 2019, 10(12), 883; https://0-doi-org.brum.beds.ac.uk/10.3390/mi10120883 - 16 Dec 2019

Cited by 11 | Viewed by 4013

Abstract

The polymerase chain reaction (PCR) is a robust technique used to make multiple copies of a segment of DNA. However, the available PCR platforms require elaborate and time-consuming operations or costly instruments, hindering their application. Herein, we introduce a sandwiched glass–polydimethylsiloxane (PDMS)–glass microchip [...] Read more.

The polymerase chain reaction (PCR) is a robust technique used to make multiple copies of a segment of DNA. However, the available PCR platforms require elaborate and time-consuming operations or costly instruments, hindering their application. Herein, we introduce a sandwiched glass–polydimethylsiloxane (PDMS)–glass microchip containing an array of reactors for the real-time PCR-based detection of multiple waterborne bacteria. The PCR solution was loaded into the array of reactors in a single step utilising capillary filling, eliminating the need for pumps, valves, and liquid handling instruments. Issues of generating and trapping bubbles during the loading chip step were addressed by creating smooth internal reactor surfaces. Triton X-100 was used to enhance PCR compatibility in the chip by minimising the nonspecific adsorption of enzymes. A custom-made real-time PCR instrument was also fabricated to provide thermal cycling to the array chip. The microfluidic device was successfully demonstrated for microbial faecal source tracking (MST) in water. Full article

(This article belongs to the Special Issue 10th Anniversary of Micromachines)

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12 pages, 4825 KiB

Open AccessArticle

Rapid Design and Analysis of Microtube Pneumatic Actuators Using Line-Segment and Multi-Segment Euler–Bernoulli Beam Models

by Myunggi Ji, Qiang Li, In Ho Cho and Jaeyoun Kim

Micromachines 2019, 10(11), 780; https://0-doi-org.brum.beds.ac.uk/10.3390/mi10110780 - 14 Nov 2019

Cited by 3 | Viewed by 2775

Abstract

Soft material-based pneumatic microtube actuators are attracting intense interest, since their bending motion is potentially useful for the safe manipulation of delicate biological objects. To increase their utility in biomedicine, researchers have begun to apply shape-engineering to the microtubes to diversify their bending [...] Read more.

Soft material-based pneumatic microtube actuators are attracting intense interest, since their bending motion is potentially useful for the safe manipulation of delicate biological objects. To increase their utility in biomedicine, researchers have begun to apply shape-engineering to the microtubes to diversify their bending patterns. However, design and analysis of such microtube actuators are challenging in general, due to their continuum natures and small dimensions. In this paper, we establish two methods for rapid design, analysis, and optimization of such complex, shape-engineered microtube actuators that are based on the line-segment model and the multi-segment Euler–Bernoulli’s beam model, respectively, and are less computation-intensive than the more conventional method based on finite element analysis. To validate the models, we first realized multi-segment microtube actuators physically, then compared their experimentally observed motions against those obtained from the models. We obtained good agreements between the three sets of results with their maximum bending-angle errors falling within ±11%. In terms of computational efficiency, our models decreased the simulation time significantly, down to a few seconds, in contrast with the finite element analysis that sometimes can take hours. The models reported in this paper exhibit great potential for rapid and facile design and optimization of shape-engineered soft actuators. Full article

(This article belongs to the Special Issue 10th Anniversary of Micromachines)

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15 pages, 21430 KiB

Open AccessFeature PaperArticle

Performance Evaluation of a Dense MEMS-Based Seismic Sensor Array Deployed in the Sichuan-Yunnan Border Region for Earthquake Early Warning

by Chaoyong Peng, Peng Jiang, Quansheng Chen, Qiang Ma and Jiansi Yang

Micromachines 2019, 10(11), 735; https://0-doi-org.brum.beds.ac.uk/10.3390/mi10110735 - 29 Oct 2019

Cited by 23 | Viewed by 3992

Abstract

With the last decades of development, earthquake early warning (EEW) has proven to be one of the potential means for disaster mitigation. Usually, the density of the EEW network determines the performance of the EEW system. For reducing the cost of sensors and [...] Read more.

With the last decades of development, earthquake early warning (EEW) has proven to be one of the potential means for disaster mitigation. Usually, the density of the EEW network determines the performance of the EEW system. For reducing the cost of sensors and building a dense EEW network, an upgraded low-cost Micro Electro Mechanical System (MEMS)-based sensor named GL-P2B was developed in this research. This device uses a new high-performance CPU board and is built on a custom-tailored Linux 3.6.9 operating system integrating with seismological processing. Approximately 170 GL-P2Bs were installed and tested in the Sichuan-Yunnan border region from January 2017 to December 2018. We evaluated its performance on noise-level, dynamic range (DR), useful resolution (NU), collocated recording comparison, and shake map generation. The results proved that GL-P2B can be classified as a type of Class-B sensor. The records obtained are consistent with the data obtained by the collocated traditional force-balanced accelerometers even for stations with an epicenter distance of more than 150 km, and most of the relative percentage difference of peak ground acceleration (PGA) values is smaller than 10%. In addition, with the current density of the GL-P2B seismic network, near-real-time refined shake maps without using values derived for virtual stations could be directly generated, which will significantly improve the capability for earthquake emergency response. Overall, this MEMS-based sensor can meet the requirements of dense EEW purpose and lower the total investment of the National System for Fast Seismic Intensity Report and Earthquake Early Warning project. Full article

(This article belongs to the Special Issue 10th Anniversary of Micromachines)

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10 pages, 2836 KiB

Open AccessFeature PaperArticle

Reliable Nanofabrication of Single-Crystal Diamond Photonic Nanostructures for Nanoscale Sensing

by Mariusz Radtke, Richard Nelz, Abdallah Slablab and Elke Neu

Micromachines 2019, 10(11), 718; https://0-doi-org.brum.beds.ac.uk/10.3390/mi10110718 - 24 Oct 2019

Cited by 11 | Viewed by 4530

Abstract

In this manuscript, we outline a reliable procedure to manufacture photonic nanostructures from single-crystal diamond (SCD). Photonic nanostructures, in our case SCD nanopillars on thin (<1

μ

m) platforms, are highly relevant for nanoscale sensing. The presented top-down procedure includes electron beam lithography [...] Read more.

In this manuscript, we outline a reliable procedure to manufacture photonic nanostructures from single-crystal diamond (SCD). Photonic nanostructures, in our case SCD nanopillars on thin (<1

μ

m) platforms, are highly relevant for nanoscale sensing. The presented top-down procedure includes electron beam lithography (EBL) as well as reactive ion etching (RIE). Our method introduces a novel type of inter-layer, namely silicon, that significantly enhances the adhesion of hydrogen silsesquioxane (HSQ) electron beam resist to SCD and avoids sample charging during EBL. In contrast to previously used adhesion layers, our silicon layer can be removed using a highly-selective RIE step, which is not damaging HSQ mask structures. We thus refine published nanofabrication processes to ease a higher process reliability especially in the light of the advancing commercialization of SCD sensor devices. Full article

(This article belongs to the Special Issue 10th Anniversary of Micromachines)

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10 pages, 5970 KiB

Open AccessArticle

Fabrication and Characterization of Flexible Thermoelectric Generators Using Micromachining and Electroplating Techniques

by Wnag-Lin Lee, Po-Jen Shih, Cheng-Chih Hsu and Ching-Liang Dai

Micromachines 2019, 10(10), 660; https://0-doi-org.brum.beds.ac.uk/10.3390/mi10100660 - 30 Sep 2019

Cited by 8 | Viewed by 3404

Abstract

This study involves the fabrication and measurement of a flexible thermoelectric generator (FTG) using micromachining and electroplating processes. The area of the FTG is 46 × 17 mm², and it is composed of 39 thermocouples in series. The thermoelectric materials that [...] Read more.

This study involves the fabrication and measurement of a flexible thermoelectric generator (FTG) using micromachining and electroplating processes. The area of the FTG is 46 × 17 mm², and it is composed of 39 thermocouples in series. The thermoelectric materials that are used for the FTG are copper and nickel. The fabrication process involves patterning a silver seed layer on the polymethyl methacrylate (PMMA) substrate using a computer numerical control (CNC) micro-milling machine. Thermoelectric materials, copper and nickel, are deposited on the PMMA substrate using an electroplating process. An epoxy polymer is then coated onto the PMMA substrate. Acetone solution is then used to etch the PMMA substrate and to transfer the thermocouples to the flexible epoxy film. The FTG generates an output voltage (OV) as the thermocouples have a temperature difference (ΔT) between the cold and hot parts. The experiments show that the OV of the FTG is 4.2 mV at ΔT of 5.3 K and the output power is 429 nW at ΔT of 5.3 K. The FTG has a voltage factor of 1 μV/mm²K and a power factor of 19.5 pW/mm²K². The FTG reaches a curvature of 20 m⁻¹. Full article

(This article belongs to the Special Issue 10th Anniversary of Micromachines)

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11 pages, 1015 KiB

Open AccessArticle

Cord-Based Microfluidic Chips as A Platform for ELISA and Glucose Assays

by Jenny Elomaa, Laura Gallegos and Frank A. Gomez

Micromachines 2019, 10(9), 614; https://0-doi-org.brum.beds.ac.uk/10.3390/mi10090614 - 15 Sep 2019

Cited by 5 | Viewed by 3032

Abstract

This paper describes the development and application of microfluidic cord-based analytical devices (µCADs) in two enzyme-linked immunosorbent assays (ELISAs) and glucose assay. In this study, biotinylated goat anti-mouse immunoglobulin (IgG) antibody, rabbit IgG antibody, and glucose are quantitatively detected. In the ELISA systems, [...] Read more.

This paper describes the development and application of microfluidic cord-based analytical devices (µCADs) in two enzyme-linked immunosorbent assays (ELISAs) and glucose assay. In this study, biotinylated goat anti-mouse immunoglobulin (IgG) antibody, rabbit IgG antibody, and glucose are quantitatively detected. In the ELISA systems, the antibody is spotted on the cord at the detection site and a series of washes, followed by streptavidin-alkaline phosphatase (Strep-ALP) or alkaline phosphatase (ALP)-conjugated secondary antibody and colorimetric substrate, completing the experiment. The devices are subsequently scanned and analyzed yielding a correlation between inverse yellow or inverse blue intensity and antibody concentration. For the first ELISA, a linear range of detection was observed at lower concentrations (2.50 × 10⁻⁴–1.75 × 10⁻³ mg/mL) of Strep-ALP with saturation of the enzyme achieved at higher concentrations (>2.50 × 10⁻⁴). For the second ELISA, the L₅₀ was demonstrated to be 167.6 fmol/zone. The glucose assay consisted of spotting increasing concentrations of glucose on the analysis sites and transporting, via capillary action, a solution containing glucose oxidase (GOx), horseradish peroxidase (HRP), and potassium iodide (KI) to the detection sites realizing a yellow-brown color indicating oxidation of iodide to iodine. The device was then dried, scanned, and analyzed to show the correlation between yellow inverse intensity and glucose. Glucose in artificial urine showed good correlation using the devices. Full article

(This article belongs to the Special Issue 10th Anniversary of Micromachines)

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9 pages, 2404 KiB

Open AccessFeature PaperArticle

Three-Dimensional Laser Printing of Macro-Scale Glass Objects at a Micro-Scale Resolution

by Peng Wang, Wei Chu, Wenbo Li, Yuanxin Tan, Fang Liu, Min Wang, Jia Qi, Jintian Lin, Fangbo Zhang, Zhanshan Wang and Ya Cheng

Micromachines 2019, 10(9), 565; https://0-doi-org.brum.beds.ac.uk/10.3390/mi10090565 - 26 Aug 2019

Cited by 29 | Viewed by 4412

Abstract

Three-dimensional (3D) printing has allowed for the production of geometrically complex 3D objects with extreme flexibility, which is currently undergoing rapid expansion in terms of materials, functionalities, as well as areas of application. When attempting to print 3D microstructures in glass, femtosecond laser-induced [...] Read more.

Three-dimensional (3D) printing has allowed for the production of geometrically complex 3D objects with extreme flexibility, which is currently undergoing rapid expansion in terms of materials, functionalities, as well as areas of application. When attempting to print 3D microstructures in glass, femtosecond laser-induced chemical etching (FLICE)—which is a subtractive 3D printing technique—has proved itself a powerful approach. Here, we demonstrate the fabrication of macro-scale 3D glass objects of large heights up to ~3.8 cm with an identical lateral and longitudinal feature size of ~20 μm. The remarkable accomplishment is achieved by revealing an unexplored regime in the interaction of ultrafast laser pulses with fused silica, which results in depth-insensitive focusing of the laser pulses inside fused silica. Full article

(This article belongs to the Special Issue 10th Anniversary of Micromachines)

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17 pages, 8753 KiB

Open AccessArticle

Towards a Miniaturized 3D Receiver WPT System for Capsule Endoscopy

by Sadeque Reza Khan and Marc P.Y. Desmulliez

Micromachines 2019, 10(8), 545; https://0-doi-org.brum.beds.ac.uk/10.3390/mi10080545 - 17 Aug 2019

Cited by 14 | Viewed by 4225

Abstract

The optimization, manufacturing, and performance characterization of a miniaturized 3D receiver (RX)-based wireless power transfer (WPT) system fed by a multi-transmitter (multi-TX) array is presented in this study for applications in capsule endoscopy (CE). The 200 mm outer diameter, 35 μm thick printed [...] Read more.

The optimization, manufacturing, and performance characterization of a miniaturized 3D receiver (RX)-based wireless power transfer (WPT) system fed by a multi-transmitter (multi-TX) array is presented in this study for applications in capsule endoscopy (CE). The 200 mm outer diameter, 35 μm thick printed spiral TX coils of 2.8 g weight, is manufactured on a flexible substrate to enable bendability and portability of the transmitters by the patients. The 8.9 mm diameter—4.8 mm long, miniaturized 3D RX—includes a 4 mm diameter ferrite road to increase power transfer efficiency (PTE) and is dimensionally compatible for insertion into current endoscopic capsules. The multi-TX is activated using a custom-made high-efficiency dual class-E power amplifier operated in subnominal condition. A resulting link and system PTE of 1% and 0.7%, respectively, inside a phantom tissue is demonstrated for the proposed 3D WPT system. The specific absorption rate (SAR) is simulated using the HFSS^TM software (15.0) at 0.66 W/kg at 1 MHz operation frequency, which is below the IEEE guidelines for tissue safety. The maximum variation in temperature was also measured as 1.9 °C for the typical duration of the capsule’s travel in the gastrointestinal tract to demonstrate the patients’ tissues safety. Full article

(This article belongs to the Special Issue 10th Anniversary of Micromachines)

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12 pages, 3950 KiB

Open AccessArticle

Fabrication of Different Microchannels by Adjusting the Extrusion Parameters for Sacrificial Molds

by Wenlai Tang, Hao Liu, Liya Zhu, Jianping Shi, Zongan Li, Nan Xiang and Jiquan Yang

Micromachines 2019, 10(8), 544; https://0-doi-org.brum.beds.ac.uk/10.3390/mi10080544 - 17 Aug 2019

Cited by 14 | Viewed by 4542

Abstract

Using the 3D printed mold-removal method to fabricate microchannel has become a promising alternative to the conventional soft lithography technique, due to the convenience in printing channel mold and the compatibility with PDMS material. Although having great potential, the use of single filament [...] Read more.

Using the 3D printed mold-removal method to fabricate microchannel has become a promising alternative to the conventional soft lithography technique, due to the convenience in printing channel mold and the compatibility with PDMS material. Although having great potential, the use of single filament extruded by fused deposition modeling (FDM) as the sacrificial channel mold has not been elaborately studied. In this paper, we demonstrate the fabrication of microchannels with different structure and size by controllably extruding the sacrificial channel molds. The influences of the main processing parameters including working distance, extrusion amount and printing speed on the printed microchannels are systematically investigated. The results show that, the circular and low-aspect-ratio straight microchannels with different sizes can be fabricated by adjusting the extrusion amounts. The sinusoidal, 3D curved and cross-linked curved microchannels along straight path can be fabricated, either independently or in combination, by the combined control of the working distance, extrusion amount and printing speed. The complex microchannels with different structural features can also be printed along curved serpentine, rectangular serpentine, and spiral paths. This paper presents a simple and powerful method to fabricate the complex microchannels with different structure and size by just controlling the processing parameters for extruding channel molds. Full article

(This article belongs to the Special Issue 10th Anniversary of Micromachines)

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15 pages, 2866 KiB

Open AccessFeature PaperArticle

On a Robust, Sensitive Cell-Free Method for Pseudomonas Sensing and Quantification in Microfluidic Templated Hydrogels

by Jong Seto

Micromachines 2019, 10(8), 506; https://0-doi-org.brum.beds.ac.uk/10.3390/mi10080506 - 31 Jul 2019

Cited by 6 | Viewed by 3474

Abstract

Through the use of droplet microfluidics to integrate cell-free activity into inert hydrogel beads, we have developed a platform that can perform biologically relevant functions without the need for cells. Specifically, cell-free lysates serve a utility in performing cellular functions and providing biologically [...] Read more.

Through the use of droplet microfluidics to integrate cell-free activity into inert hydrogel beads, we have developed a platform that can perform biologically relevant functions without the need for cells. Specifically, cell-free lysates serve a utility in performing cellular functions and providing biologically relevant metabolic products without requiring the optimal biological conditions for cell growth and proliferation. By teasing out specific biological components that enable transcription and translation to occur, these cell-like functions can be reconstituted in vitro without requiring the entire cell and milieu of cellular organelles. This enables the optimization of synthetic biological circuits, either by concentration or logic switches, simply through the addition or removal of genetic components (plasmids, inducers, or repressors) of regulatory elements. Here, we demonstrate an application of cell-free processes that is robust and portable, independent of a substrate, to apply for sensing and reporting functions of a quorum-sensing molecule N-3-oxododecanoyl homoserine lactone (3OC12HSL) found crucial for pathological Pseudomonas aeruginosa infection. We develop an agarose bead platform that is easily adaptable and simply programmable to fit a variety of biological and chemical sensing applications for the utility of ease of delivery and activation in remote environments—even in conditions with very little hydration. Full article

(This article belongs to the Special Issue 10th Anniversary of Micromachines)

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13 pages, 2033 KiB

Open AccessArticle

Single-Cell Point Constrictions for Reagent-Free High-Throughput Mechanical Lysis and Intact Nuclei Isolation

by Xiaomin Huang, Xiaoxing Xing, Chun Ning Ng and Levent Yobas

Micromachines 2019, 10(7), 488; https://0-doi-org.brum.beds.ac.uk/10.3390/mi10070488 - 19 Jul 2019

Cited by 9 | Viewed by 4150

Abstract

Highly localized (point) constrictions featuring a round geometry with ultra-sharp edges in silicon have been demonstrated for the reagent-free continuous-flow rapid mechanical lysis of mammalian cells on a single-cell basis. Silicon point constrictions, robust structures formed by a single-step dry etching process, are [...] Read more.

Highly localized (point) constrictions featuring a round geometry with ultra-sharp edges in silicon have been demonstrated for the reagent-free continuous-flow rapid mechanical lysis of mammalian cells on a single-cell basis. Silicon point constrictions, robust structures formed by a single-step dry etching process, are arranged in a cascade along microfluidic channels and can effectively rupture cells delivered in a pressure-driven flow. The influence of the constriction size and count on the lysis performance is presented for fibroblasts in reference to total protein, DNA, and intact nuclei levels in the lysates evaluated by biochemical and fluoremetric assays and flow-cytometric analyses. Protein and DNA levels obtained from an eight-constriction treatment match or surpass those from a chemical method. More importantly, many intact nuclei are found in the lysates with a relatively high nuclei-isolation efficiency from a four-constriction treatment. Point constrictions and their role in rapid reagent-free disruption of the plasma membrane could have implications for integrated sample preparation in future lab-on-a-chip systems. Full article

(This article belongs to the Special Issue 10th Anniversary of Micromachines)

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11 pages, 1919 KiB

Open AccessFeature PaperArticle

Thread as a Low-Cost Material for Microfluidic Assays on Intact Tumor Slices

by Maxwell Rumaner, Lisa Horowitz, Avital Ovadya and Albert Folch

Micromachines 2019, 10(7), 481; https://0-doi-org.brum.beds.ac.uk/10.3390/mi10070481 - 17 Jul 2019

Cited by 8 | Viewed by 4015

Abstract

In this paper we describe the use of thread as a low-cost material for a microfluidic chemosensitivity assay that uses intact tumor tissue ex vivo. Today, the need for new and effective cancer treatments is greater than ever, but unfortunately, the cost of [...] Read more.

In this paper we describe the use of thread as a low-cost material for a microfluidic chemosensitivity assay that uses intact tumor tissue ex vivo. Today, the need for new and effective cancer treatments is greater than ever, but unfortunately, the cost of developing new chemotherapy drugs has never been higher. Implementation of low-cost microfluidic techniques into drug screening devices could potentially mitigate some of the immense cost of drug development. Thread is an ideal material for use in drug screening as it is inexpensive, widely available, and can transport liquid without external pumping hardware, i.e., via capillary action. We have developed an inexpensive microfluidic delivery prototype that uses silk threads to selectively deliver fluids onto subregions of living xenograft tumor slices. Our device can be fabricated completely for less than $0.25 in materials and requires no external equipment to operate. We found that by varying thread materials, we could optimize device characteristics, such as flow rate; we specifically explored the behavior of silk, nylon, cotton, and polyester. The incremental cost of our device is insignificant compared to the tissue culture supplies. The use of thread as a microfluidic material has the potential to produce inexpensive, accessible, and user-friendly devices for drug testing that are especially suited for low-resource settings. Full article

(This article belongs to the Special Issue 10th Anniversary of Micromachines)

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12 pages, 2873 KiB

Open AccessArticle

The Actuation Mechanism of 3D Printed Flexure-Based Robotic Microtweezers

by Alexander Almeida, George Andrews, Devina Jaiswal and Kazunori Hoshino

Micromachines 2019, 10(7), 470; https://0-doi-org.brum.beds.ac.uk/10.3390/mi10070470 - 14 Jul 2019

Cited by 15 | Viewed by 4536

Abstract

We report on the design and the modeling of a three-dimensional (3D) printed flexure-based actuation mechanism for robotic microtweezers, the main body of which is a single piece of nylon. Our design aims to fill a void in sample manipulation between two classes [...] Read more.

We report on the design and the modeling of a three-dimensional (3D) printed flexure-based actuation mechanism for robotic microtweezers, the main body of which is a single piece of nylon. Our design aims to fill a void in sample manipulation between two classes of widely used instruments: nano-scale and macro-scale robotic manipulators. The key component is a uniquely designed cam flexure system, which linearly translates the bending of a piezoelectric bimorph actuator into angular displacement. The 3D printing made it possible to realize the fabrication of the cam with a specifically calculated curve, which would otherwise be costly using conventional milling techniques. We first characterized 3D printed nylon by studying sets of simple cantilevers, which provided fundamental characteristics that could be used for further designs. The finite element method analysis based on the obtained material data matched well with the experimental data. The tweezers showed angular displacement from 0° to 10° linearly to the deflection of the piezo actuator (0–1.74 mm) with the linearity error of 0.1°. Resonant frequency of the system with/without working tweezer tips was discovered as 101 Hz and 127 Hz, respectively. Our design provides simple and low-cost construction of a versatile manipulator system for samples in the micro/meso-scale (0.1–1 mm). Full article

(This article belongs to the Special Issue 10th Anniversary of Micromachines)

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12 pages, 3788 KiB

Open AccessArticle

Design, Fabrication and Mass-spectrometric Studies of a Micro Ion Source for High-Field Asymmetric Waveform Ion Mobility Spectrometry

by Hua Li, Hongmei Yun, Xiaoxia Du, Chaoqun Guo, Ruosheng Zeng, Yongrong Jiang and Zhencheng Chen

Micromachines 2019, 10(5), 286; https://0-doi-org.brum.beds.ac.uk/10.3390/mi10050286 - 27 Apr 2019

Cited by 8 | Viewed by 3213

Abstract

A needle-to-cylinder electrode, adopted as an ion source for high-field asymmetric ion mobility spectrometry (FAIMS), is designed and fabricated by lithographie, galvanoformung and abformung (LIGA) technology. The needle, with a tip diameter of 20 μm and thickness of 20 μm, and a cylinder, [...] Read more.

A needle-to-cylinder electrode, adopted as an ion source for high-field asymmetric ion mobility spectrometry (FAIMS), is designed and fabricated by lithographie, galvanoformung and abformung (LIGA) technology. The needle, with a tip diameter of 20 μm and thickness of 20 μm, and a cylinder, with a diameter of 400 μm, were connected to the negative high voltage and ground, respectively. A negative corona and glow discharge were realized. For acetone with a density of 99.7 ppm, ethanol with a density of 300 ppm, and acetic ether with a density of 99.3 ppm, the sample gas was ionized by the needle-to-cylinder chip and the ions were detected by an LTQ XL™ (Thermo Scientific Corp.) mass spectrometer. The mass spectra show that the ions are mainly the protonated monomer, the proton bound dimer, and an ion-H₂O molecule cluster. In tandem with a FAIMS system, the FAIMS spectra show that the resolving power increases with an increase in the RF voltage. The obtained experimental results showed that the micro needle-to-cylinder chip may serve as a miniature, low cost and non-radioactive ion source for FAIMS. Full article

(This article belongs to the Special Issue 10th Anniversary of Micromachines)

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26 pages, 8133 KiB

Open AccessArticle

Design Optimization and FE Analysis of 3D Printed Carbon PEEK Based Mono Leaf Spring

by Amir Kessentini, Gulam Mohammed Sayeed Ahmed and Jamel Madiouli

Micromachines 2019, 10(5), 279; https://0-doi-org.brum.beds.ac.uk/10.3390/mi10050279 - 26 Apr 2019

Cited by 8 | Viewed by 5358

Abstract

In this research work, design optimization and static analysis of a 3D printed based carbon PEEK (poly ether ether ketone, reinforced with carbon) polymer composite mono leaf spring was done using finite element analysis. Comparative study of leaf springs of a Dodge SUV [...] Read more.

In this research work, design optimization and static analysis of a 3D printed based carbon PEEK (poly ether ether ketone, reinforced with carbon) polymer composite mono leaf spring was done using finite element analysis. Comparative study of leaf springs of a Dodge SUV car has been made by using 3D printed carbon PEEK. The main objective of this work is to optimize the design and material parameters, such as fiber diameter, fiber length, percentage volume of fibers and orientation angle of fibers in 3D printed based material with a mono polymer composite leaf spring. The effects of these parameters were studied to evaluate the deflection, bending stress, spring rate, stiffness and von Mises stress under different loading conditions. Furthermore investigation has been done to reduce the weight of leaf springs and claimed the 3D printed based leaf springs have better load carrying capacity. Thus an attempt has been made in this regard and we selected the 3D printed carbon PEEK in developing product design and material selection for minimum deflection and bending stress by means of response surface optimization methodology for an efficient leaf spring suspension system. The 3D printed carbon fiber polymer composite has three different percentage volume fractions such as 30%, 50%, and 60%. The selected carbon PEEK has 0°, 45°, and 90° fiber orientations. Finite element based analysis has been performed on 3D printed carbon PEEK material to conclude the optimized design parameters and best possible combination of factors affecting the leaf spring performance. Full article

(This article belongs to the Special Issue 10th Anniversary of Micromachines)

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11 pages, 6081 KiB

Open AccessArticle

Design, Fabrication, and Testing of a Monolithically Integrated Tri-Axis High-Shock Accelerometer in Single (111)-Silicon Wafer

by Shengran Cai, Wei Li, Hongshuo Zou, Haifei Bao, Kun Zhang, Jiachou Wang, Zhaohui Song and Xinxin Li

Micromachines 2019, 10(4), 227; https://0-doi-org.brum.beds.ac.uk/10.3390/mi10040227 - 29 Mar 2019

Cited by 10 | Viewed by 2838

Abstract

In this paper, a monolithic tri-axis piezoresistive high-shock accelerometer has been proposed that has been single-sided fabricated in a single (111)-silicon wafer. A single-cantilever structure and two dual-cantilever structures are designed and micromachined in one (111)-silicon chip to detect Z-axis and X-/Y-axis high-shock [...] Read more.

In this paper, a monolithic tri-axis piezoresistive high-shock accelerometer has been proposed that has been single-sided fabricated in a single (111)-silicon wafer. A single-cantilever structure and two dual-cantilever structures are designed and micromachined in one (111)-silicon chip to detect Z-axis and X-/Y-axis high-shock accelerations, respectively. Unlike the previous tri-axis sensors where the X-/Y-axis structure was different from the Z-axis one, the herein used similar cantilever sensing structures for tri-axis sensing facilitates design of uniform performance among the three elements for different sensing axes and simplifies micro-fabrication for the multi-axis sensing structure. Attributed to the tri-axis sensors formed by using the single-wafer single-sided fabrication process, the sensor is mechanically robust enough to endure the harsh high-g shocking environment and can be compatibly batch-fabricated in standard semiconductor foundries. After the single-sided process to form the sensor, the untouched chip backside facilitates simple and reliable die-bond packaging. The high-shock testing results of the fabricated sensor show linear sensing outputs along X-/Y-axis and Z-axis, with the sensitivities (under DC 5 V supply) as about 0.80–0.88 μV/g and 1.36 μV/g, respectively. Being advantageous in single-chip compact integration of the tri-axis accelerometers, the proposed monolithic tri-axis sensors are promising to be embedded into detection micro-systems for high-shock measurement applications. Full article

(This article belongs to the Special Issue 10th Anniversary of Micromachines)

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11 pages, 7065 KiB

Open AccessArticle

Rapid Prototyping of Soft Lithography Masters for Microfluidic Devices Using Dry Film Photoresist in a Non-Cleanroom Setting

by Prithviraj Mukherjee, Federico Nebuloni, Hua Gao, Jian Zhou and Ian Papautsky

Micromachines 2019, 10(3), 192; https://0-doi-org.brum.beds.ac.uk/10.3390/mi10030192 - 15 Mar 2019

Cited by 41 | Viewed by 7564

Abstract

Fabrication of microfluidic devices by soft lithography is by far the most popular approach due to simplicity and low cost. In this approach PDMS (polydimethylsiloxane) is cast on a photoresist master to generate replicas that are then sealed against glass slides using oxygen [...] Read more.

Fabrication of microfluidic devices by soft lithography is by far the most popular approach due to simplicity and low cost. In this approach PDMS (polydimethylsiloxane) is cast on a photoresist master to generate replicas that are then sealed against glass slides using oxygen plasma. In this work, we demonstrated fabrication of soft photolithography masters using lamination of ADEX dry film as an alternative to the now classic SU-8 resist masters formed by spin coating. Advantages of using ADEX dry film include the easily-achievable uniform thickness without edge bead; simplicity of the process with significant time savings due to non-sticky nature of the film; and fewer health concerns due to less toxic developing solution and antimony-free composition. As we demonstrate, the process can be performed in a low-cost improvised fabrication room in ambient light, in place of a conventional yellow-light cleanroom environment. We believe this approach holds the promise of delivering state-of-the-art microfluidic techniques to the broad field of biomedical and pharmaceutical research. Full article

(This article belongs to the Special Issue 10th Anniversary of Micromachines)

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18 pages, 7865 KiB

Open AccessArticle

The Effects of Cold Arm Width and Metal Deposition on the Performance of a U-Beam Electrothermal MEMS Microgripper for Biomedical Applications

by Marija Cauchi, Ivan Grech, Bertram Mallia, Pierluigi Mollicone and Nicholas Sammut

Micromachines 2019, 10(3), 167; https://0-doi-org.brum.beds.ac.uk/10.3390/mi10030167 - 28 Feb 2019

Cited by 27 | Viewed by 3173

Abstract

Microelectromechanical systems (MEMS) have established themselves within various fields dominated by high-precision micromanipulation, with the most distinguished sectors being the microassembly, micromanufacturing and biomedical ones. This paper presents a horizontal electrothermally actuated ‘hot and cold arm’ microgripper design to be used for the [...] Read more.

Microelectromechanical systems (MEMS) have established themselves within various fields dominated by high-precision micromanipulation, with the most distinguished sectors being the microassembly, micromanufacturing and biomedical ones. This paper presents a horizontal electrothermally actuated ‘hot and cold arm’ microgripper design to be used for the deformability study of human red blood cells (RBCs). In this study, the width and layer composition of the cold arm are varied to investigate the effects of dimensional and material variation of the cold arm on the resulting temperature distribution, and ultimately on the achieved lateral displacement at the microgripper arm tips. The cold arm widths investigated are 14

μ

m, 30

μ

m, 55

μ

m, 70

μ

m and 100

μ

m. A gold layer with a thin chromium adhesion promoter layer is deposited on the top surface of each of these cold arms to study its effect on the performance of the microgripper. The resultant ten microgripper design variants are fabricated using a commercially available MEMS fabrication technology known as a silicon-on-insulator multi-user MEMS process (SOIMUMPs)™. This process results in an overhanging 25

μ

m thick single crystal silicon microgripper structure having a low aspect ratio (width:thickness) value compared to surface micromachined structures where structural thicknesses are of the order of 2

μ

m. Finite element analysis was used to numerically model the microgripper structures and coupled electrothermomechanical simulations were implemented in CoventorWare

^{®}

. The numerical simulations took into account the temperature dependency of the coefficient of thermal expansion, the thermal conductivity and the electrical conductivity properties in order to achieve more reliable results. The fabricated microgrippers were actuated under atmospheric pressure and the experimental results achieved through optical microscopy studies conformed with those predicted by the numerical models. The gap opening and the temperature rise at the cell gripping zone were also compared for the different microgripper structures in this work, with the aim of identifying an optimal microgripper design for the deformability characterisation of RBCs. Full article

(This article belongs to the Special Issue 10th Anniversary of Micromachines)

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13 pages, 7461 KiB

Open AccessFeature PaperArticle

Piezoelectric MEMS Resonators for Cigarette Particle Detection

by Javier Toledo, Víctor Ruiz-Díez, Maik Bertke, Hutomo Suryo Wasisto, Erwin Peiner and José Luis Sánchez-Rojas

Micromachines 2019, 10(2), 145; https://0-doi-org.brum.beds.ac.uk/10.3390/mi10020145 - 21 Feb 2019

Cited by 25 | Viewed by 5421

Abstract

In this work, we demonstrate the potential of a piezoelectric resonator for developing a low-cost sensor system to detect microscopic particles in real-time, which can be present in a wide variety of environments and workplaces. The sensor working principle is based on the [...] Read more.

In this work, we demonstrate the potential of a piezoelectric resonator for developing a low-cost sensor system to detect microscopic particles in real-time, which can be present in a wide variety of environments and workplaces. The sensor working principle is based on the resonance frequency shift caused by particles collected on the resonator surface. To test the sensor sensitivity obtained from mass-loading effects, an Aluminum Nitride-based piezoelectric resonator was exposed to cigarette particles in a sealed chamber. In order to determine the resonance parameters of interest, an interface circuit was implemented and included within both open-loop and closed-loop schemes for comparison. The system was capable of tracking the resonance frequency with a mass sensitivity of 8.8 Hz/ng. Although the tests shown here were proven by collecting particles from a cigarette, the results obtained in this application may have interest and can be extended towards other applications, such as monitoring of nanoparticles in a workplace environment. Full article

(This article belongs to the Special Issue 10th Anniversary of Micromachines)

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12 pages, 4066 KiB

Open AccessFeature PaperArticle

Heterogeneous Immunoassay Using Channels and Droplets in a Digital Microfluidic Platform

by Yuguang Liu and Ian Papautsky

Micromachines 2019, 10(2), 107; https://0-doi-org.brum.beds.ac.uk/10.3390/mi10020107 - 05 Feb 2019

Cited by 17 | Viewed by 3881

Abstract

This work presents a heterogeneous immunoassay using the integrated functionalities of a channel and droplets in a digital microfluidic (DMF) platform. Droplet functionality in DMF allows for the programmable manipulation of discrete sample and reagent droplets in the range of nanoliters. Pressure-driven channels [...] Read more.

This work presents a heterogeneous immunoassay using the integrated functionalities of a channel and droplets in a digital microfluidic (DMF) platform. Droplet functionality in DMF allows for the programmable manipulation of discrete sample and reagent droplets in the range of nanoliters. Pressure-driven channels become advantageous over droplets when sample must be washed, as the supernatant can be thoroughly removed in a convenient and rapid manner while the sample is immobilized. Herein, we demonstrate a magnetic bead-based, enzyme-linked immunosorbent assay (ELISA) using ~60 nL of human interleukin-6 (IL-6) sample. The wash buffer was introduced in the form of a wall-less virtual electrowetting channel by a syringe pump at the flow rate of 10 μL/min with ~100% bead retention rate. Critical parameters such as sample wash flow rate and bead retention rate were optimized for reliable assay results. A colorimetric readout was analyzed in the International Commission on Illumination (CIE) color space without the need for costly equipment. The concepts presented in this work are potentially applicable in rapid neonatal disease screening using a finger prick blood sample in a DMF platform. Full article

(This article belongs to the Special Issue 10th Anniversary of Micromachines)

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Review

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37 pages, 6155 KiB

Open AccessReview

Powder-Based 3D Printing for the Fabrication of Device with Micro and Mesoscale Features

by Seow Yong Chin, Vishwesh Dikshit, Balasankar Meera Priyadarshini and Yi Zhang

Micromachines 2020, 11(7), 658; https://0-doi-org.brum.beds.ac.uk/10.3390/mi11070658 - 30 Jun 2020

Cited by 58 | Viewed by 11075

Abstract

Customized manufacturing of a miniaturized device with micro and mesoscale features is a key requirement of mechanical, electrical, electronic and medical devices. Powder-based 3D-printing processes offer a strong candidate for micromanufacturing due to the wide range of materials, fast production and high accuracy. [...] Read more.

Customized manufacturing of a miniaturized device with micro and mesoscale features is a key requirement of mechanical, electrical, electronic and medical devices. Powder-based 3D-printing processes offer a strong candidate for micromanufacturing due to the wide range of materials, fast production and high accuracy. This study presents a comprehensive review of the powder-based three-dimensional (3D)-printing processes and how these processes impact the creation of devices with micro and mesoscale features. This review also focuses on applications of devices with micro and mesoscale size features that are created by powder-based 3D-printing technology. Full article

(This article belongs to the Special Issue 10th Anniversary of Micromachines)

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23 pages, 6542 KiB

Open AccessReview

A Review of Secondary Flow in Inertial Microfluidics

by Qianbin Zhao, Dan Yuan, Jun Zhang and Weihua Li

Micromachines 2020, 11(5), 461; https://0-doi-org.brum.beds.ac.uk/10.3390/mi11050461 - 28 Apr 2020

Cited by 79 | Viewed by 7503

Abstract

Inertial microfluidic technology, which can manipulate the target particle entirely relying on the microchannel characteristic geometry and intrinsic hydrodynamic effect, has attracted great attention due to its fascinating advantages of high throughput, simplicity, high resolution and low cost. As a passive microfluidic technology, [...] Read more.

Inertial microfluidic technology, which can manipulate the target particle entirely relying on the microchannel characteristic geometry and intrinsic hydrodynamic effect, has attracted great attention due to its fascinating advantages of high throughput, simplicity, high resolution and low cost. As a passive microfluidic technology, inertial microfluidics can precisely focus, separate, mix or trap target particles in a continuous and high-flow-speed manner without any extra external force field. Therefore, it is promising and has great potential for a wide range of industrial, biomedical and clinical applications. In the regime of inertial microfluidics, particle migration due to inertial effects forms multiple equilibrium positions in straight channels. However, this is not promising for particle detection and separation. Secondary flow, which is a relatively minor flow perpendicular to the primary flow, may reduce the number of equilibrium positions as well as modify the location of particles focusing within channel cross sections by applying an additional hydrodynamic drag. For secondary flow, the pattern and magnitude can be controlled by the well-designed channel structure, such as curvature or disturbance obstacle. The magnitude and form of generated secondary flow are greatly dependent on the disturbing microstructure. Therefore, many inventive and delicate applications of secondary flow in inertial microfluidics have been reported. In this review, we comprehensively summarize the usage of the secondary flow in inertial microfluidics. Full article

(This article belongs to the Special Issue 10th Anniversary of Micromachines)

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32 pages, 7506 KiB

Open AccessReview

Recent Progress in Optical Sensors for Biomedical Diagnostics

by Muqsit Pirzada and Zeynep Altintas

Micromachines 2020, 11(4), 356; https://0-doi-org.brum.beds.ac.uk/10.3390/mi11040356 - 30 Mar 2020

Cited by 78 | Viewed by 7797

Abstract

In recent years, several types of optical sensors have been probed for their aptitude in healthcare biosensing, making their applications in biomedical diagnostics a rapidly evolving subject. Optical sensors show versatility amongst different receptor types and even permit the integration of different detection [...] Read more.

In recent years, several types of optical sensors have been probed for their aptitude in healthcare biosensing, making their applications in biomedical diagnostics a rapidly evolving subject. Optical sensors show versatility amongst different receptor types and even permit the integration of different detection mechanisms. Such conjugated sensing platforms facilitate the exploitation of their neoteric synergistic characteristics for sensor fabrication. This paper covers nearly 250 research articles since 2016 representing the emerging interest in rapid, reproducible and ultrasensitive assays in clinical analysis. Therefore, we present an elaborate review of biomedical diagnostics with the help of optical sensors working on varied principles such as surface plasmon resonance, localised surface plasmon resonance, evanescent wave fluorescence, bioluminescence and several others. These sensors are capable of investigating toxins, proteins, pathogens, disease biomarkers and whole cells in varied sensing media ranging from water to buffer to more complex environments such as serum, blood or urine. Hence, the recent trends discussed in this review hold enormous potential for the widespread use of optical sensors in early-stage disease prediction and point-of-care testing devices. Full article

(This article belongs to the Special Issue 10th Anniversary of Micromachines)

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25 pages, 5034 KiB

Open AccessReview

Photonic Crystal Stimuli-Responsive Chromatic Sensors: A Short Review

by Andrea Chiappini, Lam Thi Ngoc Tran, Pablo Marco Trejo-García, Lidia Zur, Anna Lukowiak, Maurizio Ferrari and Giancarlo C. Righini

Micromachines 2020, 11(3), 290; https://0-doi-org.brum.beds.ac.uk/10.3390/mi11030290 - 10 Mar 2020

Cited by 31 | Viewed by 6722

Abstract

Photonic crystals (PhC) are spatially ordered structures with lattice parameters comparable to the wavelength of propagating light. Their geometrical and refractive index features lead to an energy band structure for photons, which may allow or forbid the propagation of electromagnetic waves in a [...] Read more.

Photonic crystals (PhC) are spatially ordered structures with lattice parameters comparable to the wavelength of propagating light. Their geometrical and refractive index features lead to an energy band structure for photons, which may allow or forbid the propagation of electromagnetic waves in a limited frequency range. These unique properties have attracted much attention for both theoretical and applied research. Devices such as high-reflection omnidirectional mirrors, low-loss waveguides, and high- and low-reflection coatings have been demonstrated, and several application areas have been explored, from optical communications and color displays to energy harvest and sensors. In this latter area, photonic crystal fibers (PCF) have proven to be very suitable for the development of highly performing sensors, but one-dimensional (1D), two-dimensional (2D) and three-dimensional (3D) PhCs have been successfully employed, too. The working principle of most PhC sensors is based on the fact that any physical phenomenon which affects the periodicity and the refractive index of the PhC structure induces changes in the intensity and spectral characteristics of the reflected, transmitted or diffracted light; thus, optical measurements allow one to sense, for instance, temperature, pressure, strain, chemical parameters, like pH and ionic strength, and the presence of chemical or biological elements. In the present article, after a brief general introduction, we present a review of the state of the art of PhC sensors, with particular reference to our own results in the field of mechanochromic sensors. We believe that PhC sensors based on changes of structural color and mechanochromic effect are able to provide a promising, technologically simple, low-cost platform for further developing devices and functionalities. Full article

(This article belongs to the Special Issue 10th Anniversary of Micromachines)

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30 pages, 8897 KiB

Open AccessReview

Development Trends and Perspectives of Future Sensors and MEMS/NEMS

by Jianxiong Zhu, Xinmiao Liu, Qiongfeng Shi, Tianyiyi He, Zhongda Sun, Xinge Guo, Weixin Liu, Othman Bin Sulaiman, Bowei Dong and Chengkuo Lee

Micromachines 2020, 11(1), 7; https://0-doi-org.brum.beds.ac.uk/10.3390/mi11010007 - 18 Dec 2019

Cited by 240 | Viewed by 24072

Abstract

With the fast development of the fifth-generation cellular network technology (5G), the future sensors and microelectromechanical systems (MEMS)/nanoelectromechanical systems (NEMS) are presenting a more and more critical role to provide information in our daily life. This review paper introduces the development trends and [...] Read more.

With the fast development of the fifth-generation cellular network technology (5G), the future sensors and microelectromechanical systems (MEMS)/nanoelectromechanical systems (NEMS) are presenting a more and more critical role to provide information in our daily life. This review paper introduces the development trends and perspectives of the future sensors and MEMS/NEMS. Starting from the issues of the MEMS fabrication, we introduced typical MEMS sensors for their applications in the Internet of Things (IoTs), such as MEMS physical sensor, MEMS acoustic sensor, and MEMS gas sensor. Toward the trends in intelligence and less power consumption, MEMS components including MEMS/NEMS switch, piezoelectric micromachined ultrasonic transducer (PMUT), and MEMS energy harvesting were investigated to assist the future sensors, such as event-based or almost zero-power. Furthermore, MEMS rigid substrate toward NEMS flexible-based for flexibility and interface was discussed as another important development trend for next-generation wearable or multi-functional sensors. Around the issues about the big data and human-machine realization for human beings’ manipulation, artificial intelligence (AI) and virtual reality (VR) technologies were finally realized using sensor nodes and its wave identification as future trends for various scenarios. Full article

(This article belongs to the Special Issue 10th Anniversary of Micromachines)

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26 pages, 3383 KiB

Open AccessReview

Flexible Microfluidics: Fundamentals, Recent Developments, and Applications

by Hedieh Fallahi, Jun Zhang, Hoang-Phuong Phan and Nam-Trung Nguyen

Micromachines 2019, 10(12), 830; https://0-doi-org.brum.beds.ac.uk/10.3390/mi10120830 - 29 Nov 2019

Cited by 129 | Viewed by 10309

Abstract

Miniaturization has been the driving force of scientific and technological advances over recent decades. Recently, flexibility has gained significant interest, particularly in miniaturization approaches for biomedical devices, wearable sensing technologies, and drug delivery. Flexible microfluidics is an emerging area that impacts upon a [...] Read more.

Miniaturization has been the driving force of scientific and technological advances over recent decades. Recently, flexibility has gained significant interest, particularly in miniaturization approaches for biomedical devices, wearable sensing technologies, and drug delivery. Flexible microfluidics is an emerging area that impacts upon a range of research areas including chemistry, electronics, biology, and medicine. Various materials with flexibility and stretchability have been used in flexible microfluidics. Flexible microchannels allow for strong fluid-structure interactions. Thus, they behave in a different way from rigid microchannels with fluid passing through them. This unique behaviour introduces new characteristics that can be deployed in microfluidic applications and functions such as valving, pumping, mixing, and separation. To date, a specialised review of flexible microfluidics that considers both the fundamentals and applications is missing in the literature. This review aims to provide a comprehensive summary including: (i) Materials used for fabrication of flexible microfluidics, (ii) basics and roles of flexibility on microfluidic functions, (iii) applications of flexible microfluidics in wearable electronics and biology, and (iv) future perspectives of flexible microfluidics. The review provides researchers and engineers with an extensive and updated understanding of the principles and applications of flexible microfluidics. Full article

(This article belongs to the Special Issue 10th Anniversary of Micromachines)

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35 pages, 8403 KiB

Open AccessReview

Recent Advances in Continuous-Flow Particle Manipulations Using Magnetic Fluids

by Xiangchun Xuan

Micromachines 2019, 10(11), 744; https://0-doi-org.brum.beds.ac.uk/10.3390/mi10110744 - 31 Oct 2019

Cited by 38 | Viewed by 7581

Abstract

Magnetic field-induced particle manipulation is simple and economic as compared to other techniques (e.g., electric, acoustic, and optical) for lab-on-a-chip applications. However, traditional magnetic controls require the particles to be manipulated being magnetizable, which renders it necessary to magnetically label particles that are [...] Read more.

Magnetic field-induced particle manipulation is simple and economic as compared to other techniques (e.g., electric, acoustic, and optical) for lab-on-a-chip applications. However, traditional magnetic controls require the particles to be manipulated being magnetizable, which renders it necessary to magnetically label particles that are almost exclusively diamagnetic in nature. In the past decade, magnetic fluids including paramagnetic solutions and ferrofluids have been increasingly used in microfluidic devices to implement label-free manipulations of various types of particles (both synthetic and biological). We review herein the recent advances in this field with focus upon the continuous-flow particle manipulations. Specifically, we review the reported studies on the negative magnetophoresis-induced deflection, focusing, enrichment, separation, and medium exchange of diamagnetic particles in the continuous flow of magnetic fluids through microchannels. Full article

(This article belongs to the Special Issue 10th Anniversary of Micromachines)

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23 pages, 3189 KiB

Open AccessReview

Microfluidic Magnetic Mixing at Low Reynolds Numbers and in Stagnant Fluids

by Eriola-Sophia Shanko, Yoeri van de Burgt, Patrick D. Anderson and Jaap M. J. den Toonder

Micromachines 2019, 10(11), 731; https://0-doi-org.brum.beds.ac.uk/10.3390/mi10110731 - 29 Oct 2019

Cited by 61 | Viewed by 8677

Abstract

Microfluidic mixing becomes a necessity when thorough sample homogenization is required in small volumes of fluid, such as in lab-on-a-chip devices. For example, efficient mixing is extraordinarily challenging in capillary-filling microfluidic devices and in microchambers with stagnant fluids. To address this issue, specifically [...] Read more.

Microfluidic mixing becomes a necessity when thorough sample homogenization is required in small volumes of fluid, such as in lab-on-a-chip devices. For example, efficient mixing is extraordinarily challenging in capillary-filling microfluidic devices and in microchambers with stagnant fluids. To address this issue, specifically designed geometrical features can enhance the effect of diffusion and provide efficient mixing by inducing chaotic fluid flow. This scheme is known as “passive” mixing. In addition, when rapid and global mixing is essential, “active” mixing can be applied by exploiting an external source. In particular, magnetic mixing (where a magnetic field acts to stimulate mixing) shows great potential for high mixing efficiency. This method generally involves magnetic beads and external (or integrated) magnets for the creation of chaotic motion in the device. However, there is still plenty of room for exploiting the potential of magnetic beads for mixing applications. Therefore, this review article focuses on the advantages of magnetic bead mixing along with recommendations on improving mixing in low Reynolds number flows (Re ≤ 1) and in stagnant fluids. Full article

(This article belongs to the Special Issue 10th Anniversary of Micromachines)

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24 pages, 5781 KiB

Open AccessFeature PaperReview

Micro-LEGO for MEMS

by Seok Kim

Micromachines 2019, 10(4), 267; https://0-doi-org.brum.beds.ac.uk/10.3390/mi10040267 - 21 Apr 2019

Cited by 14 | Viewed by 6198

Abstract

The recently developed transfer printing-based microassembly called micro-LEGO has been exploited to enable microelectromechanical systems (MEMS) applications which are difficult to achieve using conventional microfabrication. Micro-LEGO involves transfer printing and thermal processing of prefabricated micro/nanoscale materials to assemble structures and devices in a [...] Read more.

The recently developed transfer printing-based microassembly called micro-LEGO has been exploited to enable microelectromechanical systems (MEMS) applications which are difficult to achieve using conventional microfabrication. Micro-LEGO involves transfer printing and thermal processing of prefabricated micro/nanoscale materials to assemble structures and devices in a 3D manner without requiring any wet or vacuum processes. Therefore, it complements existing microfabrication and other micro-assembly methods. In this paper, the process components of micro-LEGO, including transfer printing with polymer stamps, material preparation and joining, are summarized. Moreover, recent progress of micro-LEGO within MEMS applications are reviewed by investigating several example devices which are partially or fully assembled via micro-LEGO. Full article

(This article belongs to the Special Issue 10th Anniversary of Micromachines)

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Other

Jump to: Editorial, Research, Review

11 pages, 2076 KiB

Open AccessFeature PaperBrief Report

A New Microfluidic Platform for Studying Natural Killer Cell and Dendritic Cell Interactions

by Jolly Hipolito, Hagit Peretz-Soroka, Manli Zhang, Ke Yang, Soheila Karimi-Abdolrezaee, Francis Lin and Sam K.P. Kung

Micromachines 2019, 10(12), 851; https://0-doi-org.brum.beds.ac.uk/10.3390/mi10120851 - 05 Dec 2019

Cited by 7 | Viewed by 2951

Abstract

The importance of the bi-directional natural killer–dendritic cell crosstalk in coordinating anti-tumour and anti-microbial responses in vivo has been well established. However, physical parameters associated with natural killer–dendritic cell interactions have not been fully elucidated. We have previously used a simple “Y” shaped [...] Read more.

The importance of the bi-directional natural killer–dendritic cell crosstalk in coordinating anti-tumour and anti-microbial responses in vivo has been well established. However, physical parameters associated with natural killer–dendritic cell interactions have not been fully elucidated. We have previously used a simple “Y” shaped microfluidic device to study natural killer cell-migratory responses toward chemical gradients from a conditioned medium of dendritic cells. There are, however, limitations of the Y-shaped microfluidic devices that could not support higher throughput analyses and studies of cell–cell interactions. Here, we report two novel microfluidic devices (D³-Chip, T²-Chip) we applied in advanced studies of natural killer-cell migrations and their interactions with dendritic cells in vitro. The D³-Chip is an improved version of the previously published Y-shaped device that supports high-throughput analyses and docking of the cells of interest in the migration assay before they are exposed to a chemical gradient. The T²-Chip is created to support analyses of natural killer–dendritic cell cell–cell interactions without the requirement of promoting a natural killer cell to migrate long distances to find a loaded dendritic cell in the device. Using these two microfluidic platforms, we observe quantitative differences in the abilities of the immature and lipopolysaccharide-activated mature dendritic cells to interact with activated natural killer cells. The contact time between the activated natural killer cells and immature dendritic cells is significantly longer than that of the mature dendritic cells. There is a significantly higher frequency of an immature dendritic cell coming into contact with multiple natural killer cells and/or making multiple simultaneous contacts with multiple natural killer cells. To contrast, an activated natural killer cell has a significantly higher frequency of coming into contact with the mature dendritic cells than immature dendritic cells. Collectively, these differences in natural killer–dendritic cell interactions may underlie the differential maturation of immature dendritic cells by activated natural killer cells. Further applications of these microfluidic devices in studying natural killer–dendritic cell crosstalk under defined microenvironments shall enrich our understanding of the functional regulations of natural killer cells and dendritic cells in the natural killer–dendritic cell crosstalk. Full article

(This article belongs to the Special Issue 10th Anniversary of Micromachines)

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