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Micromachines, Volume 10, Issue 6 (June 2019)

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Cover Story (view full-size image) Tailor-made polymer scaffolds are excellent biomimetic platforms for tissue engineering. Yet [...] Read more.
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Open AccessArticle
Lift-Off Assisted Patterning of Few Layers Graphene
Micromachines 2019, 10(6), 426; https://doi.org/10.3390/mi10060426
Received: 29 May 2019 / Revised: 20 June 2019 / Accepted: 21 June 2019 / Published: 25 June 2019
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Abstract
Graphene and 2D materials have been exploited in a growing number of applications and the quality of the deposited layer has been found to be a critical issue for the functionality of the developed devices. Particularly, Chemical Vapor Deposition (CVD) of high quality [...] Read more.
Graphene and 2D materials have been exploited in a growing number of applications and the quality of the deposited layer has been found to be a critical issue for the functionality of the developed devices. Particularly, Chemical Vapor Deposition (CVD) of high quality graphene should be preserved without defects also in the subsequent processes of transferring and patterning. In this work, a lift-off assisted patterning process of Few Layer Graphene (FLG) has been developed to obtain a significant simplification of the whole transferring method and a conformal growth on micrometre size features. The process is based on the lift-off of the catalyst seed layer prior to the FLG deposition. Starting from a SiO2 finished Silicon substrate, a photolithographic step has been carried out to define the micro patterns, then an evaporation of Pt thin film on Al2O3 adhesion layer has been performed. Subsequently, the Pt/Al2O3 lift-off step has been attained using a dimethyl sulfoxide (DMSO) bath. The FLG was grown directly on the patterned Pt seed layer by Chemical Vapor Deposition (CVD). Raman spectroscopy was applied on the patterned area in order to investigate the quality of the obtained graphene. Following the novel lift-off assisted patterning technique a minimization of the de-wetting phenomenon for temperatures up to 1000 °C was achieved and micropatterns, down to 10 µm, were easily covered with a high quality FLG. Full article
(This article belongs to the Special Issue 2D Nanomaterials Processing and Integration in Miniaturized Devices)
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Open AccessArticle
Hydrodynamic Microparticle Separation Mechanism Using Three-Dimensional Flow Profiles in Dual-Depth and Asymmetric Lattice-Shaped Microchannel Networks
Micromachines 2019, 10(6), 425; https://doi.org/10.3390/mi10060425
Received: 6 June 2019 / Revised: 20 June 2019 / Accepted: 21 June 2019 / Published: 25 June 2019
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Abstract
We herein propose a new hydrodynamic mechanism of particle separation using dual-depth, lattice-patterned asymmetric microchannel networks. This mechanism utilizes three-dimensional (3D) laminar flow profiles formed at intersections of lattice channels. Large particles, primarily flowing near the bottom surface, frequently enter the shallower channels [...] Read more.
We herein propose a new hydrodynamic mechanism of particle separation using dual-depth, lattice-patterned asymmetric microchannel networks. This mechanism utilizes three-dimensional (3D) laminar flow profiles formed at intersections of lattice channels. Large particles, primarily flowing near the bottom surface, frequently enter the shallower channels (separation channels), whereas smaller particles flowing near the microchannel ceiling primarily flow along the deeper channels (main channels). Consequently, size-based continuous particle separation was achieved in the lateral direction in the lattice area. We confirmed that the depth of the main channel was a critical factor dominating the particle separation efficiencies, and the combination of 15-μm-deep separation channels and 40-μm-deep main channels demonstrated the good separation ability for 3–10-μm particles. We prepared several types of microchannels and successfully tuned the particle separation size. Furthermore, the input position of the particle suspension was controlled by adjusting the input flow rates and/or using a Y-shaped inlet connector that resulted in a significant improvement in the separation precision. The presented concept is a good example of a new type of microfluidic particle separation mechanism using 3D flows and may potentially be applicable to the sorting of various types of micrometer-sized objects, including living cells and synthetic microparticles. Full article
(This article belongs to the Special Issue Particles Separation in Microfluidic Devices)
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Open AccessArticle
Design and Investigation of the High Performance Doping-Less TFET with Ge/Si0.6Ge0.4/Si Heterojunction
Micromachines 2019, 10(6), 424; https://doi.org/10.3390/mi10060424
Received: 10 June 2019 / Revised: 20 June 2019 / Accepted: 24 June 2019 / Published: 24 June 2019
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Abstract
A high performance doping-less tunneling field effect transistor with Ge/Si0.6Ge0.4/Si heterojunction (H-DLTFET) is proposed in this paper. Compared to the conventional doping-less tunneling field effect transistor (DLTFET), the source and channel regions of H-DLTFET respectively use the germanium and [...] Read more.
A high performance doping-less tunneling field effect transistor with Ge/Si0.6Ge0.4/Si heterojunction (H-DLTFET) is proposed in this paper. Compared to the conventional doping-less tunneling field effect transistor (DLTFET), the source and channel regions of H-DLTFET respectively use the germanium and Si0.6Ge0.4 materials to get the steeper energy band, which can also increase the electric field of source/channel tunneling junction. Meanwhile, the double-gate process is used to improve the gate-to-channel control. In addition, the effects of Ge content, electrode work functions, and device structure parameters on the performance of H-DLTFET are researched in detail, and then the above optimal device structure parameters can be obtained. Compared to the DLTFET, the simulation results show that the maximum on-state current, trans-conductance, and output current of H-DLTFET are all increased by one order of magnitude, whereas the off-state current is reduced by two orders of magnitude, so the switching ratio increase by three orders of magnitude. At the same time, the cut-off frequency and gain bandwidth product of H-DLTFET increase from 1.75 GHz and 0.23 GHz to 23.6 GHz and 4.69 GHz, respectively. Therefore, the H-DLTFET is more suitable for the ultra-low power integrated circuits. Full article
(This article belongs to the Special Issue Extremely-Low-Power Devices and Their Applications)
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Open AccessReview
DEP-on-a-Chip: Dielectrophoresis Applied to Microfluidic Platforms
Micromachines 2019, 10(6), 423; https://doi.org/10.3390/mi10060423
Received: 17 May 2019 / Revised: 15 June 2019 / Accepted: 19 June 2019 / Published: 24 June 2019
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Abstract
Dielectric particles in a non-uniform electric field are subject to a force caused by a phenomenon called dielectrophoresis (DEP). DEP is a commonly used technique in microfluidics for particle or cell separation. In comparison with other separation methods, DEP has the unique advantage [...] Read more.
Dielectric particles in a non-uniform electric field are subject to a force caused by a phenomenon called dielectrophoresis (DEP). DEP is a commonly used technique in microfluidics for particle or cell separation. In comparison with other separation methods, DEP has the unique advantage of being label-free, fast, and accurate. It has been widely applied in microfluidics for bio-molecular diagnostics and medical and polymer research. This review introduces the basic theory of DEP, its advantages compared with other separation methods, and its applications in recent years, in particular, focusing on the different electrode types integrated into microfluidic chips, fabrication techniques, and operation principles. Full article
(This article belongs to the Special Issue Nanoparticles on Microfluidic Platforms)
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Open AccessReview
Research Progress of Near-Infrared Fluorescence Immunoassay
Micromachines 2019, 10(6), 422; https://doi.org/10.3390/mi10060422
Received: 4 April 2019 / Revised: 16 June 2019 / Accepted: 17 June 2019 / Published: 24 June 2019
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Abstract
Near-infrared fluorescence probes (NIFPs) have been widely used in immunoassay, bio-imaging and medical diagnosis. We review the basic principles of near-infrared fluorescence and near-infrared detection technology, and summarize structures, properties and characteristics of NIFPs (i.e., cyanines, xanthenes fluorescent dyes, phthalocyanines, porphyrin derivates, single-walled [...] Read more.
Near-infrared fluorescence probes (NIFPs) have been widely used in immunoassay, bio-imaging and medical diagnosis. We review the basic principles of near-infrared fluorescence and near-infrared detection technology, and summarize structures, properties and characteristics of NIFPs (i.e., cyanines, xanthenes fluorescent dyes, phthalocyanines, porphyrin derivates, single-walled carbon nanotubes (SWCNTs), quantum dots and rare earth compounds). We next analyze applications of NIFPs in immunoassays, and prospect the application potential of lateral flow assay (LFA) in rapid detection of pathogens. At present, our team intends to establish a new platform that has highly sensitive NIFPs combined with portable and simple immunochromatographic test strips (ICTSs) for rapid detection of food-borne viruses. This will provide technical support for rapid detection on the port. Full article
(This article belongs to the Special Issue Biosensors for Pathogen Detection)
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Open AccessArticle
A Shear-Mode Piezoelectric Heterostructure for Electric Current Sensing in Electric Power Grids
Micromachines 2019, 10(6), 421; https://doi.org/10.3390/mi10060421
Received: 1 June 2019 / Revised: 18 June 2019 / Accepted: 21 June 2019 / Published: 23 June 2019
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Abstract
This paper presents a shear-mode piezoelectric current sensing device for two-wire power cords in electric power grids. The piezoelectric heterostructure consists of a cymbal structure and a permalloy plate. The cymbal structure is constructed from a permanent magnet, a brass cap, and shear-mode [...] Read more.
This paper presents a shear-mode piezoelectric current sensing device for two-wire power cords in electric power grids. The piezoelectric heterostructure consists of a cymbal structure and a permalloy plate. The cymbal structure is constructed from a permanent magnet, a brass cap, and shear-mode piezoelectric materials. The permalloy plate concentrates the magnetic field generated by the two-wire power cord on the magnet. Under the force amplification effect of the cymbal structure, the response of the device is improved. A prototype has been fabricated to conduct the experiments. The experimental average sensitivity of the device is 12.74 mV/A in the current range of 1–10 A with a separating distance of d = 0 mm, and the resolution reaches 0.04 A. The accuracy is calculated to be ±0.0177 mV at 1.5 A according to the experimental voltage distribution. The current-to-voltage results demonstrate that the proposed heterostructure can also be used as a magnetoelectric device without bias. Full article
(This article belongs to the Special Issue Piezoelectric Transducers: Materials, Devices and Applications)
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Open AccessArticle
Research on the Protrusions Near Silicon-Glass Interface during Cavity Fabrication
Micromachines 2019, 10(6), 420; https://doi.org/10.3390/mi10060420
Received: 30 May 2019 / Revised: 14 June 2019 / Accepted: 19 June 2019 / Published: 23 June 2019
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Abstract
Taking advantage of good hermeticity, tiny parasitic capacitance, batch mode fabrication, and compatibility with multiple bonding techniques, the glass-silicon composite substrate manufactured by the glass reflow process has great potential to achieve 3D wafer-level packaging for high performance. However, the difference in etching [...] Read more.
Taking advantage of good hermeticity, tiny parasitic capacitance, batch mode fabrication, and compatibility with multiple bonding techniques, the glass-silicon composite substrate manufactured by the glass reflow process has great potential to achieve 3D wafer-level packaging for high performance. However, the difference in etching characteristics between silicon and glass inevitably leads to the formation of the undesired micro-protrusions near the silicon-glass interface when preparing a shallow cavity etched around a few microns in the composite substrate. The micro-protrusions have a comparable height with the depth of the cavity, which increases the risks of damages to sensitive structures and may even trigger electrical breakdown, resulting in thorough device failure. In this paper, we studied the characteristics of the chemical composition and etching mechanisms at the interface carefully and proposed the corresponding optimized solutions that utilized plasma accumulation at the interface to accelerate etching and bridge the gap in etching rates between different chemical compositions. Finally, a smooth transition of 131.1 nm was achieved at the interface, obtaining an ideal etching cavity surface and experimentally demonstrating the feasibility of our proposal. The micromachining solution is beneficial for improving the yield and structural design flexibility of higher performance micro-electromechanical systems (MEMS) devices. Full article
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Open AccessReview
Micro/Nano Technologies for High-Density Retinal Implant
Micromachines 2019, 10(6), 419; https://doi.org/10.3390/mi10060419
Received: 22 May 2019 / Revised: 14 June 2019 / Accepted: 21 June 2019 / Published: 22 June 2019
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Abstract
During the past decades, there have been leaps in the development of micro/nano retinal implant technologies, which is one of the emerging applications in neural interfaces to restore vision. However, higher feedthroughs within a limited space are needed for more complex electronic systems [...] Read more.
During the past decades, there have been leaps in the development of micro/nano retinal implant technologies, which is one of the emerging applications in neural interfaces to restore vision. However, higher feedthroughs within a limited space are needed for more complex electronic systems and precise neural modulations. Active implantable medical electronics are required to have good electrical and mechanical properties, such as being small, light, and biocompatible, and with low power consumption and minimal immunological reactions during long-term implantation. For this purpose, high-density implantable packaging and flexible microelectrode arrays (fMEAs) as well as high-performance coating materials for retinal stimulation are crucial to achieve high resolution. In this review, we mainly focus on the considerations of the high-feedthrough encapsulation of implantable biomedical components to prolong working life, and fMEAs for different implant sites to deliver electrical stimulation to targeted retinal neuron cells. In addition, the functional electrode materials to achieve superior stimulation efficiency are also reviewed. The existing challenge and future research directions of micro/nano technologies for retinal implant are briefly discussed at the end of the review. Full article
(This article belongs to the Special Issue Implantable Microdevices)
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Open AccessReview
Coupling Microfluidic Platforms, Microfabrication, and Tissue Engineered Scaffolds to Investigate Tumor Cells Mechanobiology
Micromachines 2019, 10(6), 418; https://doi.org/10.3390/mi10060418
Received: 11 May 2019 / Revised: 15 June 2019 / Accepted: 19 June 2019 / Published: 22 June 2019
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Abstract
The tumor microenvironment (TME) is composed of dynamic and complex networks composed of matrix substrates, extracellular matrix (ECM), non-malignant cells, and tumor cells. The TME is in constant evolution during the disease progression, most notably through gradual stiffening of the stroma. Within the [...] Read more.
The tumor microenvironment (TME) is composed of dynamic and complex networks composed of matrix substrates, extracellular matrix (ECM), non-malignant cells, and tumor cells. The TME is in constant evolution during the disease progression, most notably through gradual stiffening of the stroma. Within the tumor, increased ECM stiffness drives tumor growth and metastatic events. However, classic in vitro strategies to study the TME in cancer lack the complexity to fully replicate the TME. The quest to understand how the mechanical, geometrical, and biochemical environment of cells impacts their behavior and fate has been a major force driving the recent development of new technologies in cell biology research. Despite rapid advances in this field, many challenges remain in order to bridge the gap between the classical culture dish and the biological reality of actual tissue. Microfabrication coupled with microfluidic approaches aim to engineer the actual complexity of the TME. Moreover, TME bioengineering allows artificial modulations with single or multiple cues to study different phenomena occurring in vivo. Some innovative cutting-edge tools and new microfluidic approaches could have an important impact on the fields of biology and medicine by bringing deeper understanding of the TME, cell behavior, and drug effects. Full article
(This article belongs to the Special Issue Microengineering Techniques for Disease Modeling and Drug Discovery)
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Open AccessArticle
Inkjet Printing of Functional Electronic Memory Cells: A Step Forward to Green Electronics
Micromachines 2019, 10(6), 417; https://doi.org/10.3390/mi10060417
Received: 21 May 2019 / Revised: 12 June 2019 / Accepted: 18 June 2019 / Published: 22 June 2019
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Abstract
Nowadays, the environmental issues surrounding the production of electronics, from the perspectives of both the materials used and the manufacturing process, are of major concern. The usage, storage, disposal protocol and volume of waste material continue to increase the environmental footprint of our [...] Read more.
Nowadays, the environmental issues surrounding the production of electronics, from the perspectives of both the materials used and the manufacturing process, are of major concern. The usage, storage, disposal protocol and volume of waste material continue to increase the environmental footprint of our increasingly “throw away society”. Almost ironically, society is increasingly involved in pollution prevention, resource consumption issues and post-consumer waste management. Clearly, a dichotomy between environmentally aware usage and consumerism exists. The current technology used to manufacture functional materials and electronic devices requires high temperatures for material deposition processes, which results in the generation of harmful chemicals and radiation. With such issues in mind, it is imperative to explore new electronic functional materials and new manufacturing pathways. Here, we explore the potential of additive layer manufacturing, inkjet printing technology which provides an innovative manufacturing pathway for functional materials (metal nanoparticles and polymers), and explore a fully printed two terminal electronic memory cell. In this work, inkjetable materials (silver (Ag) and poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) (PEDOT:PSS)) were first printed by a piezoelectric Epson Stylus P50 inkjet printer as stand-alone layers, and secondly as part of a metal (Ag)/active layer (PEDOT:PSS)/metal (Ag) crossbar architecture. The quality of the individual multi-layers of the printed Ag and PEDOT:PSS was first evaluated via optical microscopy and scanning electron microscopy (SEM). Furthermore, an electrical characterisation of the printed memory elements was performed using an HP4140B picoammeter. Full article
(This article belongs to the Special Issue Printable and Flexible Electronics for Sensors)
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Open AccessArticle
MEMS-Based Wavelength-Selective Bolometers
Micromachines 2019, 10(6), 416; https://doi.org/10.3390/mi10060416
Received: 13 May 2019 / Revised: 6 June 2019 / Accepted: 10 June 2019 / Published: 21 June 2019
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Abstract
We propose and experimentally demonstrate a compact design for membrane-supported wavelength-selective infrared (IR) bolometers. The proposed bolometer device is composed of wavelength-selective absorbers functioning as the efficient spectroscopic IR light-to-heat transducers that make the amorphous silicon (a-Si) bolometers respond at the desired resonance [...] Read more.
We propose and experimentally demonstrate a compact design for membrane-supported wavelength-selective infrared (IR) bolometers. The proposed bolometer device is composed of wavelength-selective absorbers functioning as the efficient spectroscopic IR light-to-heat transducers that make the amorphous silicon (a-Si) bolometers respond at the desired resonance wavelengths. The proposed devices with specific resonances are first numerically simulated to obtain the optimal geometrical parameters and then experimentally realized. The fabricated devices exhibit a wide resonance tunability in the mid-wavelength IR atmospheric window by changing the size of the resonator of the devices. The measured spectral response of the fabricated device wholly follows the pre-designed resonance, which obviously evidences that the concept of the proposed wavelength-selective IR bolometers is realizable. The results obtained in this work provide a new solution for on-chip MEMS-based wavelength-selective a-Si bolometers for practical applications in IR spectroscopic devices. Full article
(This article belongs to the Special Issue Infrared Nanophotonics: Materials, Devices, and Applications)
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Open AccessArticle
Driving Forces of the Bubble-Driven Tubular Micromotor Based on the Full Life-Cycle of the Bubble
Micromachines 2019, 10(6), 415; https://doi.org/10.3390/mi10060415
Received: 24 April 2019 / Revised: 10 June 2019 / Accepted: 14 June 2019 / Published: 21 June 2019
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Abstract
Micromotors show many advantages in practical applications, including small size, large push-to-weight ratio, and low power consumption. Micromotors have been widely used in a variety of applications, including cell manipulation, payload delivery, and removal of toxic components. Among them, bubble-driven micromotors have received [...] Read more.
Micromotors show many advantages in practical applications, including small size, large push-to-weight ratio, and low power consumption. Micromotors have been widely used in a variety of applications, including cell manipulation, payload delivery, and removal of toxic components. Among them, bubble-driven micromotors have received great attention due to their large driving force and high speed. The driving force of the bubble-driven micromotor movement comes from the four stages of the life cycle of the bubble: nucleation, growth, slip, and ejection. At present, investigators are still unclear about the driving mechanism of the bubble-driven micromotors, the source of the driving force being still especially controversial. In response to this problem, this paper combines the mass transfer model, hydrodynamic theory, and numerical simulation to explain the driving force generated by the various stages of the life-cycle of the bubble. A mass transfer model was used to calculate the driving force of the motor contributed by the bubble nucleation and slip stage. Based on equilibrium of force and conservation of energy, a theoretical model of the driving force of the tubular micromotor in the growth and ejection stage of the bubble was established. The results show that the driving force contributed by the bubble in the nucleation and the slip stage is rather small. However, the stage of bubble growth and ejection provide most of the driving force. On further evaluating the effect of the bubble driving force on the motor speed, it was found that the growth stage plays a major role in the motion of the bubble-driven micromotor. The micromotor velocity based on the driving forces of the full life-cycle of bubbles agrees well with the experimental results. Full article
(This article belongs to the Special Issue Microswimmer)
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Open AccessFeature PaperReview
Evaluating Nanoparticles in Preclinical Research Using Microfluidic Systems
Micromachines 2019, 10(6), 414; https://doi.org/10.3390/mi10060414
Received: 26 May 2019 / Revised: 14 June 2019 / Accepted: 17 June 2019 / Published: 21 June 2019
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Abstract
Nanoparticles (NPs) have found a wide range of applications in clinical therapeutic and diagnostic fields. However, currently most NPs are still in the preclinical evaluation phase with few approved for clinical use. Microfluidic systems can simulate dynamic fluid flows, chemical gradients, partitioning of [...] Read more.
Nanoparticles (NPs) have found a wide range of applications in clinical therapeutic and diagnostic fields. However, currently most NPs are still in the preclinical evaluation phase with few approved for clinical use. Microfluidic systems can simulate dynamic fluid flows, chemical gradients, partitioning of multi-organs as well as local microenvironment controls, offering an efficient and cost-effective opportunity to fast screen NPs in physiologically relevant conditions. Here, in this review, we are focusing on summarizing key microfluidic platforms promising to mimic in vivo situations and test the performance of fabricated nanoparticles. Firstly, we summarize the key evaluation parameters of NPs which can affect their delivery efficacy, followed by highlighting the importance of microfluidic-based NP evaluation. Next, we will summarize main microfluidic systems effective in evaluating NP haemocompatibility, transport, uptake and toxicity, targeted accumulation and general efficacy respectively, and discuss the future directions for NP evaluation in microfluidic systems. The combination of nanoparticles and microfluidic technologies could greatly facilitate the development of drug delivery strategies and provide novel treatments and diagnostic techniques for clinically challenging diseases. Full article
(This article belongs to the Special Issue Nanoparticles on Microfluidic Platforms)
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Open AccessArticle
A MEMS-Based Quad-Wavelength Hybrid Plasmonic–Pyroelectric Infrared Detector
Micromachines 2019, 10(6), 413; https://doi.org/10.3390/mi10060413
Received: 3 March 2019 / Revised: 28 March 2019 / Accepted: 29 March 2019 / Published: 21 June 2019
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Abstract
Spectrally selective detection is of crucial importance for diverse modern spectroscopic applications such as multi-wavelength pyrometry, non-dispersive infrared gas sensing, biomedical analysis, flame detection, and thermal imaging. This paper reports a quad-wavelength hybrid plasmonic–pyroelectric detector that exhibited spectrally selective infrared detection at four [...] Read more.
Spectrally selective detection is of crucial importance for diverse modern spectroscopic applications such as multi-wavelength pyrometry, non-dispersive infrared gas sensing, biomedical analysis, flame detection, and thermal imaging. This paper reports a quad-wavelength hybrid plasmonic–pyroelectric detector that exhibited spectrally selective infrared detection at four wavelengths—3.3, 3.7, 4.1, and 4.5 μm. The narrowband detection was achieved by coupling the incident infrared light to the resonant modes of the four different plasmonic perfect absorbers based on Al-disk-array placed on a Al2O3–Al bilayer. These absorbers were directly integrated on top of a zinc oxide thin film functioning as a pyroelectric transducer. The device was fabricated using micro-electromechanical system (MEMS) technology to optimize the spectral responsivity. The proposed detector operated at room temperature and exhibited a responsivity of approximately 100–140 mV/W with a full width at half maximum of about 0.9–1.2 μm. The wavelength tunability, high spectral resolution, compactness and robust MEMS-based platform of the hybrid device demonstrated a great advantage over conventional photodetectors with bandpass filters, and exhibited impressive possibilities for miniature multi-wavelength spectroscopic devices. Full article
(This article belongs to the Special Issue Infrared Nanophotonics: Materials, Devices, and Applications)
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Open AccessReview
Recent Advances in Droplet-based Microfluidic Technologies for Biochemistry and Molecular Biology
Micromachines 2019, 10(6), 412; https://doi.org/10.3390/mi10060412
Received: 2 May 2019 / Revised: 16 June 2019 / Accepted: 18 June 2019 / Published: 20 June 2019
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Abstract
Recently, droplet-based microfluidic systems have been widely used in various biochemical and molecular biological assays. Since this platform technique allows manipulation of large amounts of data and also provides absolute accuracy in comparison to conventional bioanalytical approaches, over the last decade a range [...] Read more.
Recently, droplet-based microfluidic systems have been widely used in various biochemical and molecular biological assays. Since this platform technique allows manipulation of large amounts of data and also provides absolute accuracy in comparison to conventional bioanalytical approaches, over the last decade a range of basic biochemical and molecular biological operations have been transferred to drop-based microfluidic formats. In this review, we introduce recent advances and examples of droplet-based microfluidic techniques that have been applied in biochemistry and molecular biology research including genomics, proteomics and cellomics. Their advantages and weaknesses in various applications are also comprehensively discussed here. The purpose of this review is to provide a new point of view and current status in droplet-based microfluidics to biochemists and molecular biologists. We hope that this review will accelerate communications between researchers who are working in droplet-based microfluidics, biochemistry and molecular biology. Full article
(This article belongs to the Special Issue Microfluidics for Soft Matter and Mechanobiology)
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Open AccessArticle
Fine-Grained Power Gating Using an MRAM-CMOS Non-Volatile Flip-Flop
Micromachines 2019, 10(6), 411; https://doi.org/10.3390/mi10060411
Received: 28 April 2019 / Revised: 15 June 2019 / Accepted: 17 June 2019 / Published: 20 June 2019
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Abstract
An area-efficient non-volatile flip flop (NVFF) is proposed. Two minimum-sized Metal-Oxide-Semiconductor Field-Effect Transistor (MOSFET) and two magnetic tunnel junction (MTJ) devices are added on top of a conventional D flip-flop for temporary storage during the power-down. An area overhead of the temporary storage [...] Read more.
An area-efficient non-volatile flip flop (NVFF) is proposed. Two minimum-sized Metal-Oxide-Semiconductor Field-Effect Transistor (MOSFET) and two magnetic tunnel junction (MTJ) devices are added on top of a conventional D flip-flop for temporary storage during the power-down. An area overhead of the temporary storage is minimized by reusing a part of the D flip-flop and an energy overhead is reduced by a current-reuse technique. In addition, two optimization strategies of the use of the proposed NVFF are proposed: (1) A module-based placement in a design phase for minimizing the area overhead; and (2) a dynamic write pulse modulation at runtime for reducing the energy overhead. We evaluated the proposed NVFF circuit using a compact MTJ model targeting an implementation in a 10 nm technology node. Results indicate that area overhead is 6.9 % normalized to the conventional flip flop. Compared to the best previously known NVFFs, the proposed circuit succeeded in reducing the area by 4.1 × and the energy by 1.5 × . The proposed placement strategy of the NVFF shows an improvement of nearly a factor of 2–18 in terms of area and energy, and the pulse duration modulation provides a further energy reduction depending on fault tolerance of programs. Full article
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Open AccessArticle
Single Drive Multi-Axis Gyroscope with High Dynamic Range, High Linearity and Wide Bandwidth
Micromachines 2019, 10(6), 410; https://doi.org/10.3390/mi10060410
Received: 23 May 2019 / Revised: 10 June 2019 / Accepted: 17 June 2019 / Published: 20 June 2019
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Abstract
This paper presents the design, fabrication, and characterization of a highly sensitive, single drive multi-axis gyroscope. The multi-axis gyroscope allows for a wide bandwidth in all three axes (X, Y, Z) and exhibits high linearity. The fabricated multi-axis gyroscope was fabricated with a [...] Read more.
This paper presents the design, fabrication, and characterization of a highly sensitive, single drive multi-axis gyroscope. The multi-axis gyroscope allows for a wide bandwidth in all three axes (X, Y, Z) and exhibits high linearity. The fabricated multi-axis gyroscope was fabricated with a structural thickness of 30 µm and packaged at 100 mtorr using wafer level packaging. The fabricated multi-axis gyroscope has a small footprint of 1426 × 1426 µm2, making it one of the smallest multi-axis gyroscopes. A custom printed circuit board (PCB) was designed for the evaluation of the multi-axis gyroscope. The experimental results demonstrate that the gyroscope has a high sensitivity of 12.56   μ V / dps ,   17.13   μ V / dps and 25.79   μ V / dps in the roll (X-sense), pitch (Y-sense) and yaw (Z-sense) modes respectively. The scale-factor non-linearity of the gyroscope is less than 0.2 % for roll and pitch mode and 0.001 % for the yaw mode, in the full-scale range of ± 1500   deg / s . The multi-axis gyroscope demonstrates an angle random walk of 2.79   dps / Hz , 2.14   dps / Hz , and   1.42   dps / Hz , for the roll, pitch and yaw rate with the in-run bias stability 1.62   deg / s , 1.14   deg / s and 0.84   deg / s respectively. Full article
(This article belongs to the Special Issue MEMS/NEMS Sensors: Fabrication and Application, Volume II)
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Open AccessArticle
Microfluidic Cell Trapping for Single-Cell Analysis
Micromachines 2019, 10(6), 409; https://doi.org/10.3390/mi10060409
Received: 22 May 2019 / Revised: 10 June 2019 / Accepted: 18 June 2019 / Published: 19 June 2019
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Abstract
The single-cell capture microfluidic chip has many advantages, including low cost, high throughput, easy manufacturing, integration, non-toxicity and good stability. Because of these characteristics, the cell capture microfluidic chip is increasingly becoming an important carrier on the study of life science and pharmaceutical [...] Read more.
The single-cell capture microfluidic chip has many advantages, including low cost, high throughput, easy manufacturing, integration, non-toxicity and good stability. Because of these characteristics, the cell capture microfluidic chip is increasingly becoming an important carrier on the study of life science and pharmaceutical analysis. Important promises of single-cell analysis are the paring, fusion, disruption and analysis of intracellular components for capturing a single cell. The capture, which is based on the fluid dynamics method in the field of micro fluidic chips is an important way to achieve and realize the operations mentioned above. The aim of this study was to compare the ability of three fluid dynamics-based microfluidic chip structures to capture cells. The effects of cell growth and distribution after being captured by different structural chips and the subsequent observation and analysis of single cells on the chip were compared. It can be seen from the experimental results that the microfluidic chip structure most suitable for single-cell capture is a U-shaped structure. It enables single-cell capture as well as long-term continuous culture and the single-cell observation of captured cells. Compared to the U-shaped structure, the cells captured by the microcavity structure easily overlapped during the culture process and affected the subsequent analysis of single cells. The flow shortcut structure can also be used to capture and observe single cells, however, the shearing force of the fluid caused by the chip structure is likely to cause deformation of the cultured cells. By comparing the cell capture efficiency of the three chips, the reagent loss during the culture process and the cell growth state of the captured cells, we are provided with a theoretical support for the design of a single-cell capture microfluidic chip and a reference for the study of single-cell capture in the future. Full article
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Open AccessFeature PaperReview
Microfluidic-Based Nucleic Acid Amplification Systems in Microbiology
Micromachines 2019, 10(6), 408; https://doi.org/10.3390/mi10060408
Received: 27 May 2019 / Revised: 14 June 2019 / Accepted: 17 June 2019 / Published: 19 June 2019
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Abstract
Rapid, sensitive, and selective bacterial detection is a hot topic, because the progress in this research area has had a broad range of applications. Novel and innovative strategies for detection and identification of bacterial nucleic acids are important for practical applications. Microfluidics is [...] Read more.
Rapid, sensitive, and selective bacterial detection is a hot topic, because the progress in this research area has had a broad range of applications. Novel and innovative strategies for detection and identification of bacterial nucleic acids are important for practical applications. Microfluidics is an emerging technology that only requires small amounts of liquid samples. Microfluidic devices allow for rapid advances in microbiology, enabling access to methods of amplifying nucleic acid molecules and overcoming difficulties faced by conventional. In this review, we summarize the recent progress in microfluidics-based polymerase chain reaction devices for the detection of nucleic acid biomarkers. The paper also discusses the recent development of isothermal nucleic acid amplification and droplet-based microfluidics devices. We discuss recent microfluidic techniques for sample preparation prior to the amplification process. Full article
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Open AccessArticle
Research on an On-Chip MEMS Based Safety and Arming Device with a Mechanical Encryption System
Micromachines 2019, 10(6), 407; https://doi.org/10.3390/mi10060407
Received: 8 May 2019 / Revised: 14 June 2019 / Accepted: 17 June 2019 / Published: 19 June 2019
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Abstract
The design and characterization of microelectromechanical systems (MEMS) based on-chip SAD (Safety and Arming Device) are proposed. An encryption system has been integrated into the device to enhance its reliability during the electromagnetic interference. The conversion between safe status and arm status is [...] Read more.
The design and characterization of microelectromechanical systems (MEMS) based on-chip SAD (Safety and Arming Device) are proposed. An encryption system has been integrated into the device to enhance its reliability during the electromagnetic interference. The conversion between safe status and arm status is reversible due to the bidirectional actuation design of the slider and pawl on the SOI (Silicon on Insulator) chip, being driven by the chevron electrothermal actuators. The width of each tooth on the slider, which contains coding information, is different from that of its adjacent neighbor. Additionally, the different teeth width, respectively 32 μm, 82 μm, requiring different decoding displacement of 100 μm and 150 μm, corresponds to the different decoding voltage of 13.5 V and 14.8 V. The travel range of interrupter in the SAD will only be limited by the chip dimension and be able to cover the motion of ±1 mm in the present research, due to the capability of motion retention. Finally, the SAD is integrated with a copper azide exploding chip to measure the average velocity of the titanium flyer for the application feasibility validation. Full article
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Open AccessReview
Silicon Carbide Converters and MEMS Devices for High-temperature Power Electronics: A Critical Review
Micromachines 2019, 10(6), 406; https://doi.org/10.3390/mi10060406
Received: 14 April 2019 / Revised: 4 June 2019 / Accepted: 17 June 2019 / Published: 19 June 2019
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Abstract
The significant advance of power electronics in today’s market is calling for high-performance power conversion systems and MEMS devices that can operate reliably in harsh environments, such as high working temperature. Silicon-carbide (SiC) power electronic devices are featured by the high junction temperature, [...] Read more.
The significant advance of power electronics in today’s market is calling for high-performance power conversion systems and MEMS devices that can operate reliably in harsh environments, such as high working temperature. Silicon-carbide (SiC) power electronic devices are featured by the high junction temperature, low power losses, and excellent thermal stability, and thus are attractive to converters and MEMS devices applied in a high-temperature environment. This paper conducts an overview of high-temperature power electronics, with a focus on high-temperature converters and MEMS devices. The critical components, namely SiC power devices and modules, gate drives, and passive components, are introduced and comparatively analyzed regarding composition material, physical structure, and packaging technology. Then, the research and development directions of SiC-based high-temperature converters in the fields of motor drives, rectifier units, DC–DC converters are discussed, as well as MEMS devices. Finally, the existing technical challenges facing high-temperature power electronics are identified, including gate drives, current measurement, parameters matching between each component, and packaging technology. Full article
(This article belongs to the Special Issue SiC based Miniaturized Devices)
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Open AccessReview
Micro-optical Components for Bioimaging on Tissues, Cells and Subcellular Structures
Micromachines 2019, 10(6), 405; https://doi.org/10.3390/mi10060405
Received: 19 April 2019 / Revised: 27 May 2019 / Accepted: 14 June 2019 / Published: 19 June 2019
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Abstract
Bioimaging generally indicates imaging techniques that acquire biological information from living forms. Among different imaging techniques, optical microscopy plays a predominant role in observing tissues, cells and biomolecules. Along with the fast development of microtechnology, developing miniaturized and integrated optical imaging systems has [...] Read more.
Bioimaging generally indicates imaging techniques that acquire biological information from living forms. Among different imaging techniques, optical microscopy plays a predominant role in observing tissues, cells and biomolecules. Along with the fast development of microtechnology, developing miniaturized and integrated optical imaging systems has become essential to provide new imaging solutions for point-of-care applications. In this review, we will introduce the basic micro-optical components and their fabrication technologies first, and further emphasize the development of integrated optical systems for in vitro and in vivo bioimaging, respectively. We will conclude by giving our perspectives on micro-optical components for bioimaging applications in the near future. Full article
(This article belongs to the Special Issue MEMS Technology for Biomedical Imaging Applications)
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Open AccessArticle
The Effect of Electrolytic Jet Orientation on Machining Characteristics in Jet Electrochemical Machining
Micromachines 2019, 10(6), 404; https://doi.org/10.3390/mi10060404
Received: 5 May 2019 / Revised: 2 June 2019 / Accepted: 14 June 2019 / Published: 17 June 2019
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Abstract
Jet electrochemical machining (Jet-ECM) is a significant prospective electrochemical machining process for the fabrication of micro-sized features. Traditionally and normally, the Jet-ECM process is carried out with its electrolytic jet being vertically impinged downstream against the workpiece. Therefore, other jet orientations, including a [...] Read more.
Jet electrochemical machining (Jet-ECM) is a significant prospective electrochemical machining process for the fabrication of micro-sized features. Traditionally and normally, the Jet-ECM process is carried out with its electrolytic jet being vertically impinged downstream against the workpiece. Therefore, other jet orientations, including a vertically upstream orientation and a horizontal orientation, have rarely been adopted. In this study, three jet orientations were applied to electrolytic jet machining, and the effect of jet orientations on machining characteristics was systemically investigated. Horizontal jet orientation is of great benefit in achieving accurate micro-sized features with excellent surface quality with either a static jet or a scanning jet for the Jet-ECM. On the other hand, the Jet-ECM with a horizontal jet orientation has a smaller material removal rate (MMR) than the ones with vertical jet orientations, which have almost the same MMR. It was found that an enhancement of machining localization and a reduction of MMR for horizontal jet electrochemical machining primarily results from an improvement of the mass-transfer field. The horizontal orientation of the jet is beneficial for the Jet-ECM processes to improve machining accuracy. Full article
(This article belongs to the Section D:Materials and Processing)
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Open AccessArticle
Extension of the Measurable Wavelength Range for a Near-Infrared Spectrometer Using a Plasmonic Au Grating on a Si Substrate
Micromachines 2019, 10(6), 403; https://doi.org/10.3390/mi10060403
Received: 14 May 2019 / Revised: 10 June 2019 / Accepted: 13 June 2019 / Published: 17 June 2019
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Abstract
In this paper, we proposed near-infrared spectroscopy based on a Si photodetector equipped with a gold grating and extended the measurable wavelength range to cover 1200–1600 nm by improving a spectrum derivation procedure. In the spectrum derivation, photocurrent data during alteration of the [...] Read more.
In this paper, we proposed near-infrared spectroscopy based on a Si photodetector equipped with a gold grating and extended the measurable wavelength range to cover 1200–1600 nm by improving a spectrum derivation procedure. In the spectrum derivation, photocurrent data during alteration of the incidence angle of the measured light were converted using a responsivity matrix R, which determines the spectroscopic characteristics of the photodetector device. A generalized inverse matrix of R was used to obtain the spectrum and to fit a situation where multiple surface plasmon resonance (SPR) peaks appeared in the scanning range. When light composed of two wavelengths, 1250 nm and 1450 nm, was irradiated, the two wavelengths were distinctively discriminated using the improved method. Full article
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Open AccessArticle
Advanced Graphene-Based Transparent Conductive Electrodes for Photovoltaic Applications
Micromachines 2019, 10(6), 402; https://doi.org/10.3390/mi10060402
Received: 24 May 2019 / Revised: 11 June 2019 / Accepted: 11 June 2019 / Published: 17 June 2019
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Abstract
New architectures of transparent conductive electrodes (TCEs) incorporating graphene monolayers in different configurations have been explored with the aim to improve the performance of silicon-heterojunction (SHJ) cell front transparent contacts. In SHJ technology, front electrodes play an important additional role as anti-reflectance (AR) [...] Read more.
New architectures of transparent conductive electrodes (TCEs) incorporating graphene monolayers in different configurations have been explored with the aim to improve the performance of silicon-heterojunction (SHJ) cell front transparent contacts. In SHJ technology, front electrodes play an important additional role as anti-reflectance (AR) coatings. In this work, different transparent-conductive-oxide (TCO) thin films have been combined with graphene monolayers in different configurations, yielding advanced transparent electrodes specifically designed to minimize surface reflection over a wide range of wavelengths and angles of incidence and to improve electrical performance. A preliminary analysis reveals a strong dependence of the optoelectronic properties of the TCEs on (i) the order in which the different thin films are deposited or the graphene is transferred and (ii) the specific TCO material used. The results shows a clear electrical improvement when three graphene monolayers are placed on top on 80-nm-thick ITO thin film. This optimum TCE presents sheet resistances as low as 55 Ω/sq and an average conductance as high as 13.12 mS. In addition, the spectral reflectance of this TCE also shows an important reduction in its weighted reflectance value of 2–3%. Hence, the work undergone so far clearly suggests the possibility to noticeably improve transparent electrodes with this approach and therefore to further enhance silicon-heterojunction cell performance. These results achieved so far clearly open the possibility to noticeably improve TCEs and therefore to further enhance SHJ contact-technology performance. Full article
(This article belongs to the Special Issue Graphene Nanoelectronic Devices)
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Open AccessArticle
Direct Writing of Copper Micropatterns Using Near-Infrared Femtosecond Laser-Pulse-Induced Reduction of Glyoxylic Acid Copper Complex
Micromachines 2019, 10(6), 401; https://doi.org/10.3390/mi10060401
Received: 14 May 2019 / Revised: 11 June 2019 / Accepted: 13 June 2019 / Published: 17 June 2019
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Abstract
We have fabricated Cu-based micropatterns in an ambient environment using femtosecond laser direct writing to reduce a glyoxylic acid Cu complex spin-coated onto a glass substrate. To do this, we scanned a train of focused femtosecond laser pulses over the complex film in [...] Read more.
We have fabricated Cu-based micropatterns in an ambient environment using femtosecond laser direct writing to reduce a glyoxylic acid Cu complex spin-coated onto a glass substrate. To do this, we scanned a train of focused femtosecond laser pulses over the complex film in air, following which the non-irradiated complex was removed by rinsing the substrates with ethanol. A minimum line width of 6.1 µm was obtained at a laser-pulse energy of 0.156 nJ and scanning speeds of 500 and 1000 µm/s. This line width is significantly smaller than that obtained in previous work using a CO2 laser. In addition, the lines are electrically conducting. However, the minimum resistivity of the line pattern was 2.43 × 10−6 Ω·m, which is ~10 times greater than that of the pattern formed using the CO2 laser. An X-ray diffraction analysis suggests that the balance between reduction and re-oxidation of the glyoxylic acid Cu complex determines the nature of the highly reduced Cu patterns in the ambient air. Full article
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Open AccessFeature PaperArticle
Study Effects of Drug Treatment and Physiological Physical Stimulation on Surfactant Protein Expression of Lung Epithelial Cells Using a Biomimetic Microfluidic Cell Culture Device
Micromachines 2019, 10(6), 400; https://doi.org/10.3390/mi10060400
Received: 10 May 2019 / Revised: 4 June 2019 / Accepted: 14 June 2019 / Published: 16 June 2019
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Abstract
This paper reports a biomimetic microfluidic device capable of reconstituting physiological physical microenvironments in lungs during fetal development for cell culture. The device integrates controllability of both hydrostatic pressure and cyclic substrate deformation within a single chip to better mimic the in vivo [...] Read more.
This paper reports a biomimetic microfluidic device capable of reconstituting physiological physical microenvironments in lungs during fetal development for cell culture. The device integrates controllability of both hydrostatic pressure and cyclic substrate deformation within a single chip to better mimic the in vivo microenvironments. For demonstration, the effects of drug treatment and physical stimulations on surfactant protein C (SPC) expression of lung epithelial cells (A549) are studied using the device. The experimental results confirm the device’s capability of mimicking in vivo microenvironments with multiple physical stimulations for cell culture applications. Furthermore, the results indicate the critical roles of physical stimulations in regulating cellular behaviors. With the demonstrated functionalities and performance, the device is expected to provide a powerful tool for further lung development studies that can be translated to clinical observation in a more straightforward manner. Consequently, the device is promising for construction of more in vitro physiological microenvironments integrating multiple physical stimulations to better study organ development and its functions. Full article
(This article belongs to the Special Issue Organs-on-chips)
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Open AccessArticle
Effect of Cyclic Stretch on Tissue Maturation in Myoblast-Laden Hydrogel Fibers
Micromachines 2019, 10(6), 399; https://doi.org/10.3390/mi10060399
Received: 17 May 2019 / Revised: 9 June 2019 / Accepted: 13 June 2019 / Published: 15 June 2019
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Abstract
Engineering of the skeletal muscles has attracted attention for the restoration of damaged muscles from myopathy, injury, and extraction of malignant tumors. Reconstructing a three-dimensional muscle using living cells could be a promising approach. However, the regenerated tissue exhibits a weak construction force [...] Read more.
Engineering of the skeletal muscles has attracted attention for the restoration of damaged muscles from myopathy, injury, and extraction of malignant tumors. Reconstructing a three-dimensional muscle using living cells could be a promising approach. However, the regenerated tissue exhibits a weak construction force due to the insufficient tissue maturation. The purpose of this study is to establish the reconstruction system for the skeletal muscle. We used a cell-laden core-shell hydrogel microfiber as a three-dimensional culture to control the cellular orientation. Moreover, to mature the muscle tissue in the microfiber, we also developed a custom-made culture device for imposing cyclic stretch stimulation using a motorized stage and the fiber-grab system. As a result, the directions of the myotubes were oriented and the mature myotubes could be formed by cyclic stretch stimulation. Full article
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Open AccessArticle
Chaotic Micromixer Based on 3D Horseshoe Transformation
Micromachines 2019, 10(6), 398; https://doi.org/10.3390/mi10060398
Received: 5 May 2019 / Revised: 4 June 2019 / Accepted: 13 June 2019 / Published: 14 June 2019
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Abstract
To improve the efficiency of mixing under laminar flow with a low Reynolds number (Re), a novel three-dimensional Horseshoe Transformation (3D HT) was proposed as the basis for the design of a micromixer. Compared with the classical HT, the Lyapunov exponent of the [...] Read more.
To improve the efficiency of mixing under laminar flow with a low Reynolds number (Re), a novel three-dimensional Horseshoe Transformation (3D HT) was proposed as the basis for the design of a micromixer. Compared with the classical HT, the Lyapunov exponent of the 3D HT, which was calculated based on a symbolic dynamic system, proved the chaotic enhancement. Based on the 3D HT, a micromixer with a mixing length of 12 mm containing six mixing units was obtained by sequentially applying “squeeze”, “stretch”, “twice fold”, “inverse transformation”, and “intersection” operations. Numerical simulation and Peclet Number (Pe) calculations indicated that when the squeeze amplitude 0 < α < 1/2, 0 < β < 1/2, the stretch amplitude γ > 4, and Re ≥ 1, the mass transfer in the mixer was dominated by convective diffusion induced by chaotic flow. When Re = 10, at the outlet of the mixing chamber, the simulated mixing index was 96.4%, which was far less than the value at Re = 0.1 (σ = 0.041). Microscope images of the mixing chamber and the curve trend of pH buffer solutions obtained from a mixing experiment were both consistent with the results of the simulation. When Re = 10, the average mixing index of the pH buffer solutions was 91.75%, which proved the excellent mixing efficiency of the mixer based on the 3D HT. Full article
(This article belongs to the Special Issue Optimization of Microfluidic Devices)
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Open AccessReview
Nanomaterials-Based Electrochemical Immunosensors
Micromachines 2019, 10(6), 397; https://doi.org/10.3390/mi10060397
Received: 9 May 2019 / Revised: 11 June 2019 / Accepted: 13 June 2019 / Published: 14 June 2019
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Abstract
With the development of nanomaterials and sensor technology, nanomaterials-based electrochemical immunosensors have been widely employed in various fields. Nanomaterials for electrode modification are emerging one after another in order to improve the performance of electrochemical immunosensors. When compared with traditional detection methods, electrochemical [...] Read more.
With the development of nanomaterials and sensor technology, nanomaterials-based electrochemical immunosensors have been widely employed in various fields. Nanomaterials for electrode modification are emerging one after another in order to improve the performance of electrochemical immunosensors. When compared with traditional detection methods, electrochemical immunosensors have the advantages of simplicity, real-time analysis, high sensitivity, miniaturization, rapid detection time, and low cost. Here, we summarize recent developments in electrochemical immunosensors based on nanomaterials, including carbon nanomaterials, metal nanomaterials, and quantum dots. Additionally, we discuss research challenges and future prospects for this field of study. Full article
(This article belongs to the Special Issue Nanomaterials-Based Biosensors)
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