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Micromachines, Volume 11, Issue 7 (July 2020) – 82 articles

Cover Story (view full-size image): Reservoir-based drug delivery microsystems have enabled novel and effective drug delivery concepts in recent decades. These systems typically incorporate integrated storing and pumping components. This article presents a stand-alone, 3D-printed, thin, and refillable microreservoir platform to be used as a storage component of these microsystems. This modular and readily scalable platform enables integration to various pumping mechanisms with minimal design changes, for implantable and transdermal drug delivery in animal models and human patients. View this paper
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Article
Analytical Guidelines for Designing Curvature-Induced Dielectrophoretic Particle Manipulation Systems
Micromachines 2020, 11(7), 707; https://doi.org/10.3390/mi11070707 - 21 Jul 2020
Cited by 5 | Viewed by 1538
Abstract
Curvature-induced dielectrophoresis (C-iDEP) is an established method of applying electrical energy gradients across curved microchannels to obtain a label-free manipulation of particles and cells. This method offers several advantages over the other DEP-based methods, such as increased chip area utilisation, simple fabrication, reduced [...] Read more.
Curvature-induced dielectrophoresis (C-iDEP) is an established method of applying electrical energy gradients across curved microchannels to obtain a label-free manipulation of particles and cells. This method offers several advantages over the other DEP-based methods, such as increased chip area utilisation, simple fabrication, reduced susceptibility to Joule heating and reduced risk of electrolysis in the active region. Although C-iDEP systems have been extensively demonstrated to achieve focusing and separation of particles, a detailed mathematical analysis of the particle dynamics has not been reported yet. This work computationally confirms a fully analytical dimensionless study of the electric field-induced particle motion inside a circular arc microchannel, the simplest design of a C-iDEP system. Specifically, the analysis reveals that the design of a circular arc microchannel geometry for manipulating particles using an applied voltage is fully determined by three dimensionless parameters. Simple equations are established and numerically confirmed to predict the mutual relationships of the parameters for a comprehensive range of their practically relevant values, while ensuring design for safety. This work aims to serve as a starting point for microfluidics engineers and researchers to have a simple calculator-based guideline to develop C-iDEP particle manipulation systems specific to their applications. Full article
(This article belongs to the Special Issue Micromachines for Dielectrophoresis)
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Article
Numerical Investigation of a Short Polarization Beam Splitter Based on Dual-Core Photonic Crystal Fiber with As2S3 Layer
Micromachines 2020, 11(7), 706; https://doi.org/10.3390/mi11070706 - 21 Jul 2020
Cited by 7 | Viewed by 1141
Abstract
A polarization beam splitter is an important component of modern optical system, especially a splitter that combines the structural flexibility of photonic crystal fiber and the optical modulation of functional material. Thus, this paper presents a compact dual-core photonic crystal fiber polarization beam [...] Read more.
A polarization beam splitter is an important component of modern optical system, especially a splitter that combines the structural flexibility of photonic crystal fiber and the optical modulation of functional material. Thus, this paper presents a compact dual-core photonic crystal fiber polarization beam splitter based on thin layer As2S3. The mature finite element method was utilized to simulate the performance of the proposed splitter. Numerical simulation results indicated that at 1.55 μm, when the fiber device length was 1.0 mm, the x- and y-polarized lights could be split out, the extinction ratio could reach −83.6 dB, of which the bandwidth for extinction ratio better than −20 dB was 280 nm. It also had a low insertion loss of 0.18 dB for the x-polarized light. In addition, it can be completely fabricated using existing processes. The proposed compact polarization beam splitter is a promising candidate that can be used in various optical fields. Full article
(This article belongs to the Section E:Engineering and Technology)
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Article
Preliminary Study on Fluidized Bed Chemical Mechanical Polishing (FB-CMP) Process for Stainless Steel 304 (SS304)
Micromachines 2020, 11(7), 705; https://doi.org/10.3390/mi11070705 - 21 Jul 2020
Cited by 3 | Viewed by 963
Abstract
Fluidized bed machining (FBM) is used for the surface finishing or cleaning of complex 3D machine parts. FBM is a process of injecting air into a chamber to encourage particles into a fluid-like state. Subsequently, FBM involves rotating the specimen at high speed [...] Read more.
Fluidized bed machining (FBM) is used for the surface finishing or cleaning of complex 3D machine parts. FBM is a process of injecting air into a chamber to encourage particles into a fluid-like state. Subsequently, FBM involves rotating the specimen at high speed to process the surface of the material. However, owing to the long processing time involved in FBM, there is a limit to its application in various industries. In this paper, we propose a fluidized bed chemical mechanical polishing (FB-CMP) process, wherein the material removal mechanism of chemical mechanical polishing (CMP) is applied to FBM to improve the processing efficiency of FBM. An FB-CMP system was prepared, and preliminary experiments on the chemical solution were conducted using stainless steel 304 (SS304) plates. In the experiment, hydrogen peroxide (H2O2) was used as the oxidant, oxalic acid (C2H2O4) was used as the complexing agent and alumina (Al2O3) was used as the abrasive particle. The material removal rate (MRR) and roughness reduction rate during the FB-CMP of SS304 were dependent on the composition of the chemical solution. The experimental results revealed the highest MRR and roughness reduction rate at 0.33 wt % H2O2 and 0.2 wt % oxalic acid. To stabilize the proposed FB-CMP process, it is necessary to examine the chemical solutions of various materials. Full article
(This article belongs to the Special Issue Ultra Precision Technologies for Micromachining)
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Article
A Customized Two Photon Fluorescence Imaging Probe Based on 2D scanning MEMS Mirror Including Electrothermal Two-Level-Ladder Dual S-Shaped Actuators
Micromachines 2020, 11(7), 704; https://doi.org/10.3390/mi11070704 - 21 Jul 2020
Cited by 2 | Viewed by 1177
Abstract
We report the design and characterization of a two-photon fluorescence imaging miniature probe. This customized two-axis scanning probe is dedicated for intraoperative two-photon fluorescence imaging endomicroscopic use and is based on a micro-electro-mechanical system (MEMS) mirror with a high reflectivity plate and two-level-ladder [...] Read more.
We report the design and characterization of a two-photon fluorescence imaging miniature probe. This customized two-axis scanning probe is dedicated for intraoperative two-photon fluorescence imaging endomicroscopic use and is based on a micro-electro-mechanical system (MEMS) mirror with a high reflectivity plate and two-level-ladder double S-shaped electrothermal bimorph actuators. The fully assembled probe has a total outer diameter of 4 mm including all elements. With a two-lens configuration and a small aperture MEMS mirror, this probe can generate a large optical scan angle of 24° with 4 V drive voltage and can achieve a 450 µm FOV with a 2-fps frame rate. A uniform Pixel Dwell Time and a stable scanning speed along a raster pattern were demonstrated while a 57-fs pulse duration of the excitation beam was measured at the exit of the probe head. This miniature imaging probe will be coupled to a two-photon fluorescence endomicroscope oriented towards clinical use. Full article
(This article belongs to the Special Issue Optical MEMS, Volume II)
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Article
Enhancement of the Start-Up Time for Microliter-Scale Microbial Fuel Cells (µMFCs) via the Surface Modification of Gold Electrodes
Micromachines 2020, 11(7), 703; https://doi.org/10.3390/mi11070703 - 21 Jul 2020
Cited by 3 | Viewed by 1198
Abstract
Microbial Fuel Cells (MFCs) are biological fuel cells based on the oxidation of fuels by electrogenic bacteria to generate an electric current in electrochemical cells. There are several methods that can be employed to improve their performance. In this study, the effects of [...] Read more.
Microbial Fuel Cells (MFCs) are biological fuel cells based on the oxidation of fuels by electrogenic bacteria to generate an electric current in electrochemical cells. There are several methods that can be employed to improve their performance. In this study, the effects of gold surface modification with different thiol molecules were investigated for their implementation as anode electrodes in micro-scale MFCs (µMFCs). Several double-chamber µMFCs with 10.4 µL anode and cathode chambers were fabricated using silicon-microelectromechanical systems (MEMS) fabrication technology. µMFC systems assembled with modified gold anodes were operated under anaerobic conditions with the continuous feeding of anolyte and catholyte to compare the effect of different thiol molecules on the biofilm formation of Shewanella oneidensis MR-1. Performances were evaluated using polarization curves, Electrochemical Impedance Spectroscopy (EIS), and Scanning Electron Microcopy (SEM). The results showed that µMFCs modified with thiol self-assembled monolayers (SAMs) (cysteamine and 11-MUA) resulted in more than a 50% reduction in start-up times due to better bacterial attachment on the anode surface. Both 11-MUA and cysteamine modifications resulted in dense biofilms, as observed in SEM images. The power output was found to be similar in cysteamine-modified and bare gold µMFCs. The power and current densities obtained in this study were comparable to those reported in similar studies in the literature. Full article
(This article belongs to the Special Issue Biosensors and MEMS-based Diagnostic Applications)
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Article
Oil Conductivity, Electric-Field-Induced Interfacial Charge Effects, and Their Influence on the Electro-Optical Response of Electrowetting Display Devices
Micromachines 2020, 11(7), 702; https://doi.org/10.3390/mi11070702 - 20 Jul 2020
Cited by 4 | Viewed by 837
Abstract
A pixel in an electrowetting display (EWD) can be viewed as a confined water/oil two-phase microfluidic system that can be manipulated by applying an electric field. The phenomenon of charge trapping in the protective dielectric and conductivity of the oil phase reduce the [...] Read more.
A pixel in an electrowetting display (EWD) can be viewed as a confined water/oil two-phase microfluidic system that can be manipulated by applying an electric field. The phenomenon of charge trapping in the protective dielectric and conductivity of the oil phase reduce the effective electric field that is required to keep the three-phase contact line (TCL) in place. This probably leads to an oil-backflow effect which deteriorates the electro-optical performance of EWD devices. In order to investigate charge trapping and conduction effects on the device electro-optical response, an EWD device was studied, which was fabricated with a black oil, aiming for a high-contrast ratio and color-filter display. For comparison, we also prepared a device containing a purple oil, which had a lower electrical conductivity. As anticipated, the black-oil device showed faster backflow than the purple-oil device. A simple model was proposed to explain the role of oil conductivity in the backflow effect. In addition, the rebound and reopening effects were also observed after the voltage was switched to zero. The above observations were strongly dependent on polarity. By combining observations of the polarity dependence of the oil conductivity and assuming that negative charges trap more strongly in the dielectric than positive charges, our experimental results on rebound and reopening can be explained. In the AC optical response, the pixel closing speed decreased in time for intermediate frequencies. This is likely related to the phenomenon of charge trapping. It was also found that the periodic driving method could not suppress the backflow effect when the driving frequency was above ~10 kHz. Our findings confirm the significance of the above charge-related effects of EWD devices, which need to be investigated further for better understanding in order to properly design/use materials and driving schemes to suppress them. Full article
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Article
Microfluidic Formation of Honeycomb-Patterned Droplets Bounded by Interface Bilayers via Bimodal Molecular Adsorption
Micromachines 2020, 11(7), 701; https://doi.org/10.3390/mi11070701 - 20 Jul 2020
Cited by 6 | Viewed by 1926
Abstract
Assembled water-in-oil droplets bounded by lipid bilayers are used in synthetic biology as minimal models of cell tissue. Microfluidic devices successfully generate monodispersed droplets and assemble them via droplet interface bilayesr (DIB) formation. However, a honeycomb pattern of DIB-bounded droplets, similar to epithelial [...] Read more.
Assembled water-in-oil droplets bounded by lipid bilayers are used in synthetic biology as minimal models of cell tissue. Microfluidic devices successfully generate monodispersed droplets and assemble them via droplet interface bilayesr (DIB) formation. However, a honeycomb pattern of DIB-bounded droplets, similar to epithelial tissues, remains unrealized because the rapid DIB formation between the droplets hinders their ability to form the honeycomb pattern. In this paper, we demonstrate the microfluidic formation of a honeycomb pattern of DIB-bounded droplets using two surfactants with different adsorption rates on the droplet surface. A non-DIB forming surfactant (sorbitan monooleate, Span 80) was mixed with a lipid (1,2-dioleoyl-sn-glycero-3-phosphocholine, PC), whose adsorption rate on the droplet surface and saturated interfacial tension were lower than those of Span 80. By changing the surfactant composition, we established the conditions under which the droplets initially form a honeycomb pattern and subsequently adhere to each other via DIB formation to minimize the interfacial energy. In addition, the reconstituted membrane protein nanopores at the DIBs were able to transport molecules. This new method, using the difference in the adsorption rates of two surfactants, allows the formation of a honeycomb pattern of DIB-bounded droplets in a single step, and thus facilitates research using DIB-bounded droplet assemblies. Full article
(This article belongs to the Special Issue Recent Advances of Molecular Machines and Molecular Robots)
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Article
Dielectrophoretic Separation of Particles Using Microfluidic Chip with Composite Three-Dimensional Electrode
Micromachines 2020, 11(7), 700; https://doi.org/10.3390/mi11070700 - 20 Jul 2020
Cited by 13 | Viewed by 1161
Abstract
Integrating three-dimensional (3D) microelectrodes on microfluidic chips based on polydimethylsiloxane (PDMS) has been a challenge. This paper introduces a composite 3D electrode composed of Ag powder (particle size of 10 nm) and PDMS. Ethyl acetate is added as an auxiliary dispersant during the [...] Read more.
Integrating three-dimensional (3D) microelectrodes on microfluidic chips based on polydimethylsiloxane (PDMS) has been a challenge. This paper introduces a composite 3D electrode composed of Ag powder (particle size of 10 nm) and PDMS. Ethyl acetate is added as an auxiliary dispersant during the compounding process. A micromachining technique for processing 3D microelectrodes of any shape and size was developed to allow the electrodes to be firmly bonded to the PDMS chip. Through theoretical calculations, numerical simulations, and experimental verification, the role of the composite 3D microelectrodes in separating polystyrene particles of three different sizes via dielectrophoresis was systematically studied. This microfluidic device separated 20-, 10-, and 5-μm polystyrene particles nondestructively, efficiently, and accurately. Full article
(This article belongs to the Special Issue Electrokinetics in Micro-/nanofluidic Devices)
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Article
Design and Simulation of an Integrated Centrifugal Microfluidic Device for CTCs Separation and Cell Lysis
Micromachines 2020, 11(7), 699; https://doi.org/10.3390/mi11070699 - 20 Jul 2020
Cited by 17 | Viewed by 2157
Abstract
Separation of circulating tumor cells (CTCs) from blood samples and subsequent DNA extraction from these cells play a crucial role in cancer research and drug discovery. Microfluidics is a versatile technology that has been applied to create niche solutions to biomedical applications, such [...] Read more.
Separation of circulating tumor cells (CTCs) from blood samples and subsequent DNA extraction from these cells play a crucial role in cancer research and drug discovery. Microfluidics is a versatile technology that has been applied to create niche solutions to biomedical applications, such as cell separation and mixing, droplet generation, bioprinting, and organs on a chip. Centrifugal microfluidic biochips created on compact disks show great potential in processing biological samples for point of care diagnostics. This study investigates the design and numerical simulation of an integrated microfluidic device, including a cell separation unit for isolating CTCs from a blood sample and a micromixer unit for cell lysis on a rotating disk platform. For this purpose, an inertial microfluidic device was designed for the separation of target cells by using contraction–expansion microchannel arrays. Additionally, a micromixer was incorporated to mix separated target cells with the cell lysis chemical reagent to dissolve their membranes to facilitate further assays. Our numerical simulation approach was validated for both cell separation and micromixer units and corroborates existing experimental results. In the first compartment of the proposed device (cell separation unit), several simulations were performed at different angular velocities from 500 rpm to 3000 rpm to find the optimum angular velocity for maximum separation efficiency. By using the proposed inertial separation approach, CTCs, were successfully separated from white blood cells (WBCs) with high efficiency (~90%) at an angular velocity of 2000 rpm. Furthermore, a serpentine channel with rectangular obstacles was designed to achieve a highly efficient micromixer unit with high mixing quality (~98%) for isolated CTCs lysis at 2000 rpm. Full article
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Article
Improving Machining Localization and Surface Roughness in Wire Electrochemical Micromachining Using a Rotating Ultrasonic Helix Electrode
Micromachines 2020, 11(7), 698; https://doi.org/10.3390/mi11070698 - 19 Jul 2020
Cited by 4 | Viewed by 1098
Abstract
Wire electrochemical micromachining (WECMM) technology is regarded a promising method to fabricate high aspect ratio microstructures on hard-to-machining materials, however, the by-product accumulation in the machining gap limits its application. In this paper, a new method called ultrasonic-assisted wire electrochemical micromachining (UA-WECMM) is [...] Read more.
Wire electrochemical micromachining (WECMM) technology is regarded a promising method to fabricate high aspect ratio microstructures on hard-to-machining materials, however, the by-product accumulation in the machining gap limits its application. In this paper, a new method called ultrasonic-assisted wire electrochemical micromachining (UA-WECMM) is proposed to improve the machining performance of WECMM. Firstly, a flow-field simulation in the machining gap was carried out; the results showed that the ultrasonic vibration of electrode can remarkably enhance the mass transport in the machining gap and improve the machining condition. Secondly, experiments were performed to confirm the effect of ultrasonic vibration, which illustrated that the vibration with proper amplitude can reduce the slit width and improve the morphology of machined surface. Moreover, the influence of other machining parameters were also discussed. Finally, a T-type micro connector with good surface roughness (Ra 0.286 μm) was fabricated on a 300-μm-thick 304 stainless steel workpiece and a micro gear (diameter: 3.362 mm; Ra: 0.271 μm) with an aspect ratio of 7 was fabricated on a 2-mm-thick workpiece. It is proved that the proposed ultrasonic-assisted wire electrochemical micromachining method has considerable potential and broad application prospects. Full article
(This article belongs to the Section D:Materials and Processing)
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Article
Magnetically Guided Micromanipulation of Magnetic Microrobots for Accurate Creation of Artistic Patterns in Liquid Environment
Micromachines 2020, 11(7), 697; https://doi.org/10.3390/mi11070697 - 18 Jul 2020
Cited by 5 | Viewed by 1421
Abstract
In this paper, a magnetically guided micromanipulation method is proposed to accurately create artistic patterns with magnetic microrobots in a liquid environment for tissue engineering. A magnetically guided device is developed depend on symmetrical combination of square permanent magnets and array layout of [...] Read more.
In this paper, a magnetically guided micromanipulation method is proposed to accurately create artistic patterns with magnetic microrobots in a liquid environment for tissue engineering. A magnetically guided device is developed depend on symmetrical combination of square permanent magnets and array layout of soft magnetic wires, which changed the space distribution of magnetic field of conventional permanent magnet and generated powerful magnetic flux density and high magnetic field gradient. Furthermore, the morphological structure of the magnetic microrobot is flexibly adjusted via precise control of the volumetric flow rates inside the microfluidic device and the magnetic nanoparticles are taken along to enable its controllability by rapid magnetic response. And then, the spatial posture of the magnetic microrobot is contactless controlled by the magnetically guided manipulator and it is released under the influence of surface tension and gravity. Subsequently, the artistic fashions of the magnetic microrobots are precisely distributed via the dot-matrix magnetic flux density of the magnetically guided device. Finally, the experimental results herein demonstrate the accuracy and diversity of the pattern structures in the water and the developed method will be providing a new way for personalized functional scaffold construction. Full article
(This article belongs to the Special Issue Magnetic Microrobots)
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Article
Novel Decomposition Technique on Rational-Based Neuro-Transfer Function for Modeling of Microwave Components
Micromachines 2020, 11(7), 696; https://doi.org/10.3390/mi11070696 - 17 Jul 2020
Cited by 1 | Viewed by 929
Abstract
The rational-based neuro-transfer function (neuro-TF) method is a popular method for parametric modeling of electromagnetic (EM) behavior of microwave components. However, when the order in the neuro-TF becomes high, the sensitivities of the model response with respect to the coefficients of the transfer [...] Read more.
The rational-based neuro-transfer function (neuro-TF) method is a popular method for parametric modeling of electromagnetic (EM) behavior of microwave components. However, when the order in the neuro-TF becomes high, the sensitivities of the model response with respect to the coefficients of the transfer function become high. Due to this high-sensitivity issue, small training errors in the coefficients of the transfer function will result in large errors in the model output, leading to the difficulty in training of the neuro-TF model. This paper proposes a new decomposition technique to address this high-sensitivity issue. In the proposed technique, we decompose the original neuro-TF model with high order of transfer function into multiple sub-neuro-TF models with much lower order of transfer function. We then reformulate the overall model as the combination of the sub-neuro-TF models. New formulations are derived to determine the number of sub-models and the order of transfer function for each sub-model. Using the proposed decomposition technique, we can decrease the sensitivities of the overall model response with respect to the coefficients of the transfer function in each sub-model. Therefore, the modeling approach using the proposed decomposition technique can increase the modeling accuracy. Two EM parametric modeling examples are used to demonstrate the proposed decomposition technique. Full article
(This article belongs to the Section A:Physics)
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Article
A 3D Printed Jet Mixer for Centrifugal Microfluidic Platforms
Micromachines 2020, 11(7), 695; https://doi.org/10.3390/mi11070695 - 17 Jul 2020
Cited by 6 | Viewed by 1271
Abstract
Homogeneous mixing of microscopic volume fluids at low Reynolds number is of great significance for a wide range of chemical, biological, and medical applications. An efficient jet mixer with arrays of micronozzles was designed and fabricated using additive manufacturing (three-dimensional (3D) printing) technology [...] Read more.
Homogeneous mixing of microscopic volume fluids at low Reynolds number is of great significance for a wide range of chemical, biological, and medical applications. An efficient jet mixer with arrays of micronozzles was designed and fabricated using additive manufacturing (three-dimensional (3D) printing) technology for applications in centrifugal microfluidic platforms. The contact surface of miscible liquids was enhanced significantly by impinging plumes from two opposite arrays of micronozzles to improve mixing performance. The mixing efficiency was evaluated and compared with the commonly used Y-shaped micromixer. Effective mixing in the jet mixer was achieved within a very short timescale (3s). This 3D printed jet mixer has great potential to be implemented in applications by being incorporated into multifarious 3D printing devices in microfluidic platforms. Full article
(This article belongs to the Special Issue Analysis, Design and Fabrication of Micromixers)
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Review
Research Status and Development Trend of MEMS Switches: A Review
Micromachines 2020, 11(7), 694; https://doi.org/10.3390/mi11070694 - 17 Jul 2020
Cited by 14 | Viewed by 1750
Abstract
MEMS switch is a movable device manufactured by means of semiconductor technology, possessing many incomparable advantages such as a small volume, low power consumption, high integration, etc. This paper reviews recent research of MEMS switches, pointing out the important performance indexes and systematically [...] Read more.
MEMS switch is a movable device manufactured by means of semiconductor technology, possessing many incomparable advantages such as a small volume, low power consumption, high integration, etc. This paper reviews recent research of MEMS switches, pointing out the important performance indexes and systematically summarizing the classification according to driving principles. Then, a comparative study of current MEMS switches stressing their strengths and drawbacks is presented, based on performance requirements such as driven voltage, power consumption, and reliability. The efforts of teams to optimize MEMS switches are introduced and the applications of switches with different driving principles are also briefly reviewed. Furthermore, the development trend of MEMS switch and the research gaps are discussed. Finally, a summary and forecast about MEMS switches is given with the aim of providing a reference for future research in this domain. Full article
(This article belongs to the Special Issue Micro-Manufacturing and Applications)
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Review
Thermal and Photo Sensing Capabilities of Mono- and Few-Layer Thick Transition Metal Dichalcogenides
Micromachines 2020, 11(7), 693; https://doi.org/10.3390/mi11070693 - 17 Jul 2020
Cited by 4 | Viewed by 1228
Abstract
Two-dimensional (2D) materials have shown promise in various optical and electrical applications. Among these materials, semiconducting transition metal dichalcogenides (TMDs) have been heavily studied recently for their photodetection and thermoelectric properties. The recent progress in fabrication, defect engineering, doping, and heterostructure design has [...] Read more.
Two-dimensional (2D) materials have shown promise in various optical and electrical applications. Among these materials, semiconducting transition metal dichalcogenides (TMDs) have been heavily studied recently for their photodetection and thermoelectric properties. The recent progress in fabrication, defect engineering, doping, and heterostructure design has shown vast improvements in response time and sensitivity, which can be applied to both contact-based (thermocouple), and non-contact (photodetector) thermal sensing applications. These improvements have allowed the possibility of cost-effective and tunable thermal sensors for novel applications, such as broadband photodetectors, ultrafast detectors, and high thermoelectric figures of merit. In this review, we summarize the properties arisen in works that focus on the respective qualities of TMD-based photodetectors and thermocouples, with a focus on their optical, electrical, and thermoelectric capabilities for using them in sensing and detection. Full article
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Review
Overview of Ultrasound Detection Technologies for Photoacoustic Imaging
Micromachines 2020, 11(7), 692; https://doi.org/10.3390/mi11070692 - 17 Jul 2020
Cited by 27 | Viewed by 2624
Abstract
Ultrasound detection is one of the major components of photoacoustic imaging systems. Advancement in ultrasound transducer technology has a significant impact on the translation of photoacoustic imaging to the clinic. Here, we present an overview on various ultrasound transducer technologies including conventional piezoelectric [...] Read more.
Ultrasound detection is one of the major components of photoacoustic imaging systems. Advancement in ultrasound transducer technology has a significant impact on the translation of photoacoustic imaging to the clinic. Here, we present an overview on various ultrasound transducer technologies including conventional piezoelectric and micromachined transducers, as well as optical ultrasound detection technology. We explain the core components of each technology, their working principle, and describe their manufacturing process. We then quantitatively compare their performance when they are used in the receive mode of a photoacoustic imaging system. Full article
(This article belongs to the Special Issue Semiconductor Infrared Devices and Applications)
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Article
A Microfluidic Probe Integrated Device for Spatiotemporal 3D Chemical Stimulation in Cells
Micromachines 2020, 11(7), 691; https://doi.org/10.3390/mi11070691 - 16 Jul 2020
Viewed by 1107
Abstract
Numerous in vitro studies have been conducted in conventional static cell culture systems. However, most of the results represent an average response from a population of cells regardless of their local microenvironment. A microfluidic probe is a non-contact technology that has been widely [...] Read more.
Numerous in vitro studies have been conducted in conventional static cell culture systems. However, most of the results represent an average response from a population of cells regardless of their local microenvironment. A microfluidic probe is a non-contact technology that has been widely used to perform local chemical stimulation within a restricted space, providing elaborated modulation and analysis of cellular responses within the microenvironment. Although microfluidic probes developed earlier have various potential applications, the two-dimensional structure can compromise their functionality and flexibility for practical use. In this study, we developed a three-dimensional microfluidic probe integrated device equipped with vertically oriented microchannels to overcome crucial challenges and tested the potential utility of the device in biological research. We demonstrated that the device tightly regulated spatial diffusion of a fluorescent molecule, and the flow profile predicted by simulation replicated the experimental results. Additionally, the device modulated the physiological Ca2+ response of cells within the restricted area by altering the local and temporal concentrations of biomolecules such as ATP. The novel device developed in this study may provide various applications for biological studies and contribute to further understanding of molecular mechanisms underlying cellular physiology. Full article
(This article belongs to the Special Issue Cell Microarrays)
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Article
Study on Functionality and Surface Modification of a Stair-Step Liquid-Triggered Valve for On-Chip Flow Control
Micromachines 2020, 11(7), 690; https://doi.org/10.3390/mi11070690 - 16 Jul 2020
Cited by 1 | Viewed by 892
Abstract
Distinctive from other forms of microfluidic system, capillary microfluidics is of great interest in autonomous micro-systems due to its well-engineered fluidic control based on capillary force. As an essential component of fluidic control in capillaric circuits, micro-valves enable sequential fluidic operations by performing [...] Read more.
Distinctive from other forms of microfluidic system, capillary microfluidics is of great interest in autonomous micro-systems due to its well-engineered fluidic control based on capillary force. As an essential component of fluidic control in capillaric circuits, micro-valves enable sequential fluidic operations by performing actions such as stopping and triggering. In this paper, we present a stair-step liquid-triggered valve; the functionality of the valve and its dependencies on geometry and surface modification are studied. The surface contact angle of the microfabricated valves that are coated by polyethylene glycol (PEG) or (3-Aminopropyl) triethoxysilane (APTES) is evaluated experimentally, and the corresponding reliability of the valve structure is discussed. Moreover, the variation in the surface contact angle over time is investigated, indicating the shelf time of the device. We further discuss the overall fluidic behavior in such capillary valves, which benefits the capillaric circuit designs at the initial stage. Full article
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Article
Performance Analysis of a Travelling-Wave Ultrasonic Motor under Impact Load
Micromachines 2020, 11(7), 689; https://doi.org/10.3390/mi11070689 - 16 Jul 2020
Cited by 3 | Viewed by 828
Abstract
With the increased application of ultrasonic motors, it is necessary to put forward higher demand for the adaptability to environment. Impact, as a type of extreme environment, is widespread in weapon systems, machinery and aerospace. However, there are few reports about the influence [...] Read more.
With the increased application of ultrasonic motors, it is necessary to put forward higher demand for the adaptability to environment. Impact, as a type of extreme environment, is widespread in weapon systems, machinery and aerospace. However, there are few reports about the influence of impact on an ultrasonic motor. This article aimed to study the reasons for the performance degradation and failure mechanism of an ultrasonic motor in a shock environment. First, a finite element model is established to observe the dynamic response of ultrasonic motor in a shock environment. Meanwhile, the reasons of the performance degradation in the motor are discussed. An impact experiment is carried out to test the influence of impact on an ultrasonic motor, including the influence on the mechanical characteristic of an ultrasonic motor and the vibration characteristic of a stator. In addition, the protection effect of rubber on an ultrasonic motor in a shock environment is verified via an experimental method. This article reveals the failure mechanism of ultrasonic motors in a shock environment and provides a basis for the improvement of the anti-impact property of ultrasonic motors. Full article
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Article
An Improved Passivity-based Control of Electrostatic MEMS Device
Micromachines 2020, 11(7), 688; https://doi.org/10.3390/mi11070688 - 16 Jul 2020
Cited by 4 | Viewed by 912
Abstract
It is commonly known that the performance of an electrostatic microelectromechanical system (MEMS) device is limited to a specific range of the full gap distance due to the inherited “pull-in instability” phenomenon. In this work, we design a controller to extend the stabilization [...] Read more.
It is commonly known that the performance of an electrostatic microelectromechanical system (MEMS) device is limited to a specific range of the full gap distance due to the inherited “pull-in instability” phenomenon. In this work, we design a controller to extend the stabilization range of an electrostatic MEMS device and to enhance its performance. The interconnection and damping assignment-passivity based control (IDA-PBC) method is used and the controller design involves coordinate transformations and a coupling between the mechanical and electrical subsystems of the device. The method deploys a design of a speed observer to estimate the speed, which cannot be directly measured by sensors. The effectiveness of the dynamical controller is verified via numerical simulations; it is evident by the extended travel range of the parallel plates as well as the improved performance of the plates, even with a naturally lighter damping ratio. Full article
(This article belongs to the Section E:Engineering and Technology)
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Article
Measuring Surface and Interfacial Tension In Situ in Microdripping Mode for Electrohydrodynamic Applications
Micromachines 2020, 11(7), 687; https://doi.org/10.3390/mi11070687 - 16 Jul 2020
Viewed by 1107
Abstract
Walking on water is made possible, at least for tiny insects, by molecular interaction at the interfaces of dissimilar materials. Impact of these interactions—surface tension (SFT) and, more broadly, interfacial tension (IFT)—is particularly evident at micro and nano sizescales. Thus, implications of walking [...] Read more.
Walking on water is made possible, at least for tiny insects, by molecular interaction at the interfaces of dissimilar materials. Impact of these interactions—surface tension (SFT) and, more broadly, interfacial tension (IFT)—is particularly evident at micro and nano sizescales. Thus, implications of walking on water can be significant for SFT or IFT (S/IFT)-driven nanofabrication technologies, such as electrohydrodynamic atomization (EHDA), in developing next generation biomimetic microphysiological systems (MPS) and drug delivery systems (DDS). However, current methods for estimating S/IFT, based on sessile drops or new surface formation on a ring or plate, are unsuitable for integration with EHDA assemblies used in electrospinning and electrospraying. Here, we show an in situ method for estimating S/IFT specifically devised for EHDA applications using signal processing algorithms that correlate the frequency and periodicity of liquid dispensed in EHDA microdripping mode with numerical solutions from computational fluid dynamics (CFD). Estimated S/IFT was generally in agreement with published ranges for water–air, 70% ethanol–air, chloroform–air, and chloroform–water. SFT for solutions with surfactants decreased with increasing concentrations of surfactant, but at relatively higher than published values. This was anticipated, considering that established methods measure SFT at boundaries with asymmetrically high concentrations of surfactants which lower SFT. Full article
(This article belongs to the Special Issue Microfluidics: Tissue Chips and Microphysiological Systems)
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Article
High-Fidelity Harmonic Generation in Optical Micro-Resonators Using BFGS Algorithm
Micromachines 2020, 11(7), 686; https://doi.org/10.3390/mi11070686 - 15 Jul 2020
Cited by 3 | Viewed by 906
Abstract
Harmonic generation is an attractive research field that finds a variety of application areas. However, harmonic generation within a medium of micron-scale interaction length limits the magnitude of nonlinear coupling and leads to poor harmonic generation efficiency. In this study, we present a [...] Read more.
Harmonic generation is an attractive research field that finds a variety of application areas. However, harmonic generation within a medium of micron-scale interaction length limits the magnitude of nonlinear coupling and leads to poor harmonic generation efficiency. In this study, we present a constrained non-linear programming approach based on the Quasi-Newton Broyden–Fletcher–Goldfarb–Shanno (BFGS) algorithm to obtain high-fidelity harmonic generation in optical micro-resonators. Using this approach, one can achieve high-intensity harmonic generation in a simple Fabry–Perot type optical micro-resonator. The generation of super-intense harmonics at a typical ultraviolet (UV)-ablation frequency of 820 THz and at pure yellow-light (515 THz) is investigated in particular. Moreover, we achieved more than 98% accuracy compared to well-known theoretical results. Our approach enables the design of highly efficient microscale harmonic generators to be used in integrated photonic devices. Full article
(This article belongs to the Special Issue Micro-Resonators: The Quest for Superior Performance, II)
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Article
Mixing Performance of a Cross-Channel Split-and-Recombine Micro-Mixer Combined with Mixing Cell
Micromachines 2020, 11(7), 685; https://doi.org/10.3390/mi11070685 - 15 Jul 2020
Cited by 8 | Viewed by 1144
Abstract
A new cross-channel split-and-recombine (CC-SAR) micro-mixer was proposed, and its performance was demonstrated numerically. A numerical study was carried out over a wide range of volume flow rates from 3.1 μL/min to 826.8 μL/min. The corresponding Reynolds number ranges from 0.3 to 80. [...] Read more.
A new cross-channel split-and-recombine (CC-SAR) micro-mixer was proposed, and its performance was demonstrated numerically. A numerical study was carried out over a wide range of volume flow rates from 3.1 μL/min to 826.8 μL/min. The corresponding Reynolds number ranges from 0.3 to 80. The present micro-mixer consists of four mixing units. Each mixing unit is constructed by combining one split-and-recombine (SAR) unit with a mixing cell. The mixing performance was analyzed in terms of the degree of mixing and relative mixing cost. All numerical results show that the present micro-mixer performs better than other micro-mixers based on SARs over a wide range of volume flow rate. The mixing enhancement is realized by a particular motion of vortex flow: the Dean vortex in the circular sub-channel and another vortex inside the mixing cell. The two vortex flows are generated on the different planes perpendicular to each other. They cause the two fluids to change their relative position as the fluids flow into the circular sub-channel of the SAR, eventually promoting violent mixing. High vorticity in the mixing cell elongates the flow interface between two fluids, and promotes mixing in the flow regime of molecular diffusion dominance. Full article
(This article belongs to the Special Issue Micro Process-Devices)
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Editorial
Editorial for the Special Issue on IMCO 2019
Micromachines 2020, 11(7), 684; https://doi.org/10.3390/mi11070684 - 15 Jul 2020
Viewed by 661
Abstract
This special issue is a collection of 12 technical papers and two reviews that are expanded into full-length articles from the conference abstracts of the 9th International Multidisciplinary Conference on Optofluidics (IMCO 2019) held in Hong Kong in 14–17 June 2019 [...] Full article
(This article belongs to the Special Issue IMCO 2019)
Editorial
Editorial for the Special Issue on Printable and Flexible Electronics for Sensors
Micromachines 2020, 11(7), 683; https://doi.org/10.3390/mi11070683 - 15 Jul 2020
Viewed by 787
Abstract
Printable and flexible electronic materials have gained a tremendous amount of interest both in academia and in industry, due to their potential impact in many areas, including advanced manufacturing, healthcare, diagnostics, wearables, renewable energy, and defense, to name a few [...] Full article
(This article belongs to the Special Issue Printable and Flexible Electronics for Sensors)
Article
Facile Fabrication of Self-Similar Hierarchical Micro-Nano Structures for Multifunctional Surfaces via Solvent-Assisted UV-Lasering
Micromachines 2020, 11(7), 682; https://doi.org/10.3390/mi11070682 - 14 Jul 2020
Cited by 6 | Viewed by 1291
Abstract
Cross-scale self-similar hierarchical micro–nano structures in living systems often provide unique features on surfaces and serve as inspiration sources for artificial materials or devices. For instance, a highly self-similar structure often has a higher fractal dimension and, consequently, a larger active surface area; [...] Read more.
Cross-scale self-similar hierarchical micro–nano structures in living systems often provide unique features on surfaces and serve as inspiration sources for artificial materials or devices. For instance, a highly self-similar structure often has a higher fractal dimension and, consequently, a larger active surface area; hence, it would have a super surface performance compared to its peer. However, artificial self-similar surfaces with hierarchical micro–nano structures and their application development have not yet received enough attention. Here, by introducing solvent-assisted UV-lasering, we establish an elegant approach to fabricate self-similar hierarchical micro–nano structures on silicon. The self-similar structure exhibits a super hydrophilicity, a high light absorbance (>90%) in an ultra-broad spectrum (200–2500 nm), and an extraordinarily high efficiency in heat transfer. Through further combinations with other techniques, such surfaces can be used for capillary assembling soft electronics, surface self-cleaning, and so on. Furthermore, such an approach can be transferred to other materials with minor modifications. For instance, by doping carbon in polymer matrix, a silicone surface with hierarchical micro–nano structures can be obtained. By selectively patterning such hierarchical structures, we obtained an ultra-high sensitivity bending sensor. We believe that such a fabrication technique of self-similar hierarchical micro–nano structures may encourage researchers to deeply explore the unique features of functional surfaces with such structures and to further discover their potentials in various applications in diverse directions. Full article
(This article belongs to the Special Issue Pulsed Laser Micromachining)
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Article
Fabrication of Microspheres from High-Viscosity Bioink Using a Novel Microfluidic-Based 3D Bioprinting Nozzle
Micromachines 2020, 11(7), 681; https://doi.org/10.3390/mi11070681 - 14 Jul 2020
Cited by 5 | Viewed by 1539
Abstract
Three-dimensional (3D) bioprinting is a novel technology utilizing biocompatible materials, cells, drugs, etc. as basic microcomponents to form 3D artificial structures and is believed as a promising method for regenerative medicine. Droplet-based bioprinting can precisely generate microspheres and manipulate them into organized structures [...] Read more.
Three-dimensional (3D) bioprinting is a novel technology utilizing biocompatible materials, cells, drugs, etc. as basic microcomponents to form 3D artificial structures and is believed as a promising method for regenerative medicine. Droplet-based bioprinting can precisely generate microspheres and manipulate them into organized structures with high fidelity. Biocompatible hydrogels are usually used as bioinks in 3D bioprinting, however, the viscosity of the bioink could be increased due to the additives such as cells, drugs, nutrient factors and other functional polymers in some particular applications, making it difficult to form monodispersed microspheres from high-viscosity bioink at the orifice of the nozzle. In this work, we reported a novel microfluidic-based printing nozzle to prepare monodispersed microspheres from high-viscosity bioink using the phase-inversion method. Different flowing conditions can be achieved by changing the flow rates of the fluids to form monodispersed solid and hollow microspheres using the same nozzle. The diameter of the microspheres can be tuned by changing the flow rate ratio and the size distribution of the microspheres is narrow. The prepared calcium alginate microspheres could also act as micro-carriers in drug delivery. Full article
(This article belongs to the Special Issue Ultra Precision Technologies for Micromachining)
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Article
Photoacoustic Detection of H2 and NH3 Using Plasmonic Signal Enhancement in GaN Microcantilevers
Micromachines 2020, 11(7), 680; https://doi.org/10.3390/mi11070680 - 13 Jul 2020
Cited by 2 | Viewed by 892
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
(This article belongs to the Special Issue 10th Anniversary of Micromachines)
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Article
Fabrication of Hollow Structures in Photodegradable Hydrogels Using a Multi-Photon Excitation Process for Blood Vessel Tissue Engineering
Micromachines 2020, 11(7), 679; https://doi.org/10.3390/mi11070679 - 13 Jul 2020
Cited by 2 | Viewed by 1224
Abstract
Engineered blood vessels generally recapitulate vascular function in vitro and can be utilized in drug discovery as a novel microphysiological system. Recently, various methods to fabricate vascular models in hydrogels have been reported to study the blood vessel functions in vitro; however, [...] Read more.
Engineered blood vessels generally recapitulate vascular function in vitro and can be utilized in drug discovery as a novel microphysiological system. Recently, various methods to fabricate vascular models in hydrogels have been reported to study the blood vessel functions in vitro; however, in general, it is difficult to fabricate hollow structures with a designed size and structure with a tens of micrometers scale for blood vessel tissue engineering. This study reports a method to fabricate the hollow structures in photodegradable hydrogels prepared in a microfluidic device. An infrared femtosecond pulsed laser, employed to induce photodegradation via multi-photon excitation, was scanned in the hydrogel in a program-controlled manner for fabricating the designed hollow structures. The photodegradable hydrogel was prepared by a crosslinking reaction between an azide-modified gelatin solution and a dibenzocyclooctyl-terminated photocleavable tetra-arm polyethylene glycol crosslinker solution. After assessing the composition of the photodegradable hydrogel in terms of swelling and cell adhesion, the hydrogel prepared in the microfluidic device was processed by laser scanning to fabricate linear and branched hollow structures present in it. We introduced a microsphere suspension into the fabricated structure in photodegradable hydrogels, and confirmed the fabrication of perfusable hollow structures of designed patterns via the multi-photon excitation process. Full article
(This article belongs to the Special Issue Cell Microarrays)
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Editorial
Editorial of Special Issue “Piezoelectric Transducers: Materials, Devices and Applications”
Micromachines 2020, 11(7), 678; https://doi.org/10.3390/mi11070678 - 13 Jul 2020
Viewed by 707
Abstract
Advances in miniaturization of sensors, actuators, and smart systems are receiving substantial industrial attention, and a wide variety of transducers are commercially available or possess high potential to impact emerging markets [...] Full article
(This article belongs to the Special Issue Piezoelectric Transducers: Materials, Devices and Applications)
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