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Micromachines, Volume 7, Issue 7 (July 2016) – 22 articles

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Open AccessFeature PaperArticle
Flexible Holographic Fabrication of 3D Photonic Crystal Templates with Polarization Control through a 3D Printed Reflective Optical Element
Micromachines 2016, 7(7), 128; https://doi.org/10.3390/mi7070128 - 21 Jul 2016
Cited by 7 | Viewed by 3232
Abstract
In this paper, we have systematically studied the holographic fabrication of three-dimensional (3D) structures using a single 3D printed reflective optical element (ROE), taking advantage of the ease of design and 3D printing of the ROE. The reflective surface was setup at non-Brewster [...] Read more.
In this paper, we have systematically studied the holographic fabrication of three-dimensional (3D) structures using a single 3D printed reflective optical element (ROE), taking advantage of the ease of design and 3D printing of the ROE. The reflective surface was setup at non-Brewster angles to reflect both s- and p-polarized beams for the interference. The wide selection of reflective surface materials and interference angles allow control of the ratio of s- and p-polarizations, and intensity ratio of side-beam to central beam for interference lithography. Photonic bandgap simulations have also indicated that both s and p-polarized waves are sometimes needed in the reflected side beams for maximum photonic bandgap size and certain filling fractions of dielectric inside the photonic crystals. The flexibility of single ROE and single exposure based holographic fabrication of 3D structures was demonstrated with reflective surfaces of ROEs at non-Brewster angles, highlighting the capability of the ROE technique of producing umbrella configurations of side beams with arbitrary angles and polarizations and paving the way for the rapid throughput of various photonic crystal templates. Full article
(This article belongs to the collection Laser Micromachining and Microfabrication)
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Open AccessArticle
Quantification of Vortex Generation Due to Non-Equilibrium Electrokinetics at the Micro/Nanochannel Interface: Particle Tracking Velocimetry
Micromachines 2016, 7(7), 127; https://doi.org/10.3390/mi7070127 - 21 Jul 2016
Cited by 3 | Viewed by 2076
Abstract
We describe a quantitative study of vortex generation due to non-equilibrium electrokinetics near a micro/nanochannel interface. The microfluidic device is comprised of a microchannel with a set of nanochannels. These perm-selective nanochannels induce flow instability and thereby produce strong vortex generation. We performed [...] Read more.
We describe a quantitative study of vortex generation due to non-equilibrium electrokinetics near a micro/nanochannel interface. The microfluidic device is comprised of a microchannel with a set of nanochannels. These perm-selective nanochannels induce flow instability and thereby produce strong vortex generation. We performed tracking visualization of fluorescent microparticles to obtain velocity fields. Particle tracking enables the calculation of an averaged velocity field and the velocity fluctuations. We characterized the effect of applied voltages and electrolyte concentrations on vortex formation. The experimental results show that an increasing voltage or decreasing concentration results in a larger vortex region and a strong velocity fluctuation. We calculate the normalized velocity fluctuation—whose meaning is comparable to turbulent intensity—and we found that it is as high as 0.12. This value is indicative of very efficient mixing, albeit with a small Reynolds number. Full article
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Open AccessReview
Mimicking the Kidney: A Key Role in Organ-on-Chip Development
Micromachines 2016, 7(7), 126; https://doi.org/10.3390/mi7070126 - 20 Jul 2016
Cited by 10 | Viewed by 10327
Abstract
Pharmaceutical drug screening and research into diseases call for significant improvement in the effectiveness of current in vitro models. Better models would reduce the likelihood of costly failures at later drug development stages, while limiting or possibly even avoiding the use of animal [...] Read more.
Pharmaceutical drug screening and research into diseases call for significant improvement in the effectiveness of current in vitro models. Better models would reduce the likelihood of costly failures at later drug development stages, while limiting or possibly even avoiding the use of animal models. In this regard, promising advances have recently been made by the so-called “organ-on-chip” (OOC) technology. By combining cell culture with microfluidics, biomedical researchers have started to develop microengineered models of the functional units of human organs. With the capacity to mimic physiological microenvironments and vascular perfusion, OOC devices allow the reproduction of tissue- and organ-level functions. When considering drug testing, nephrotoxicity is a major cause of attrition during pre-clinical, clinical, and post-approval stages. Renal toxicity accounts for 19% of total dropouts during phase III drug evaluation—more than half the drugs abandoned because of safety concerns. Mimicking the functional unit of the kidney, namely the nephron, is therefore a crucial objective. Here we provide an extensive review of the studies focused on the development of a nephron-on-chip device. Full article
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Open AccessFeature PaperArticle
Wide Field-of-View Fluorescence Imaging with Optical-Quality Curved Microfluidic Chamber for Absolute Cell Counting
Micromachines 2016, 7(7), 125; https://doi.org/10.3390/mi7070125 - 20 Jul 2016
Cited by 4 | Viewed by 2688
Abstract
Field curvature and other aberrations are encountered inevitably when designing a compact fluorescence imaging system with a simple lens. Although multiple lens elements can be used to correct most such aberrations, doing so increases system cost and complexity. Herein, we propose a wide [...] Read more.
Field curvature and other aberrations are encountered inevitably when designing a compact fluorescence imaging system with a simple lens. Although multiple lens elements can be used to correct most such aberrations, doing so increases system cost and complexity. Herein, we propose a wide field-of-view (FOV) fluorescence imaging method with an unconventional optical-quality curved sample chamber that corrects the field curvature caused by a simple lens. Our optics simulations and proof-of-concept experiments demonstrate that a curved substrate with lens-dependent curvature can reduce greatly the distortion in an image taken with a conventional planar detector. Following the validation study, we designed a curved sample chamber that can contain a known amount of sample volume and fabricated it at reasonable cost using plastic injection molding. At a magnification factor of approximately 0.6, the curved chamber provides a clear view of approximately 119 mm2, which is approximately two times larger than the aberration-free area of a planar chamber. Remarkably, a fluorescence image of microbeads in the curved chamber exhibits almost uniform intensity over the entire field even with a simple lens imaging system, whereas the distorted boundary region has much lower brightness than the central area in the planar chamber. The absolute count of white blood cells stained with a fluorescence dye was in good agreement with that obtained by a commercially available conventional microscopy system. Hence, a wide FOV imaging system with the proposed curved sample chamber would enable us to acquire an undistorted image of a large sample volume without requiring a time-consuming scanning process in point-of-care diagnostic applications. Full article
(This article belongs to the Special Issue MEMS/NEMS for Biomedical Imaging and Sensing)
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Open AccessArticle
Locally-Actuated Graphene-Based Nano-Electro-Mechanical Switch
Micromachines 2016, 7(7), 124; https://doi.org/10.3390/mi7070124 - 19 Jul 2016
Cited by 13 | Viewed by 2448
Abstract
The graphene nano-electro-mechanical switches are promising components due to their outstanding switching performance. However, most of the reported devices suffered from a large actuation voltages, hindering them from the integration in the conventional complementary metal-oxide-semiconductor (CMOS) circuit. In this work, we demonstrated the [...] Read more.
The graphene nano-electro-mechanical switches are promising components due to their outstanding switching performance. However, most of the reported devices suffered from a large actuation voltages, hindering them from the integration in the conventional complementary metal-oxide-semiconductor (CMOS) circuit. In this work, we demonstrated the graphene nano-electro-mechanical switches with the local actuation electrode via conventional nanofabrication techniques. Both cantilever-type and double-clamped beam switches were fabricated. These devices exhibited the sharp switching, reversible operation cycles, high on/off ratio, and a low actuation voltage of below 5 V, which were compatible with the CMOS circuit requirements. Full article
(This article belongs to the Special Issue Graphene Nano-Electro-Mechanical (NEM) Devices and Applications)
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Open AccessReview
Microfluidic Approaches for Manipulating, Imaging, and Screening C. elegans
Micromachines 2016, 7(7), 123; https://doi.org/10.3390/mi7070123 - 19 Jul 2016
Cited by 35 | Viewed by 3131
Abstract
The nematode C. elegans (worm) is a small invertebrate animal widely used in studies related to fundamental biological processes, disease modelling, and drug discovery. Due to their small size and transparent body, these worms are highly suitable for experimental manipulations. In recent years [...] Read more.
The nematode C. elegans (worm) is a small invertebrate animal widely used in studies related to fundamental biological processes, disease modelling, and drug discovery. Due to their small size and transparent body, these worms are highly suitable for experimental manipulations. In recent years several microfluidic devices and platforms have been developed to accelerate worm handling, phenotypic studies and screens. Here we review major tools and briefly discuss their usage in C. elegans research. Full article
(This article belongs to the Special Issue Micro/Nano Devices for Chemical Analysis) Printed Edition available
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Open AccessArticle
High-Throughput Assessment of Drug Cardiac Safety Using a High-Speed Impedance Detection Technology-Based Heart-on-a-Chip
Micromachines 2016, 7(7), 122; https://doi.org/10.3390/mi7070122 - 19 Jul 2016
Cited by 15 | Viewed by 2379
Abstract
Drug cardiac safety assessments play a significant role in drug discovery. Drug-induced cardiotoxicity is one of the main reasons for drug attrition, even when antiarrhythmic drugs can otherwise effectively treat the arrhythmias. Consequently, efficient drug preclinical assessments are needed in the drug industry. [...] Read more.
Drug cardiac safety assessments play a significant role in drug discovery. Drug-induced cardiotoxicity is one of the main reasons for drug attrition, even when antiarrhythmic drugs can otherwise effectively treat the arrhythmias. Consequently, efficient drug preclinical assessments are needed in the drug industry. However, most drug efficacy assessments are performed based on electrophysiological tests of cardiomyocytes in vitro and cannot effectively provide information on drug-induced dysfunction of cardiomyocyte beating. Here we present a heart-on-a-chip device for evaluating the drug cardiac efficacy using a high-speed impedance detection technology. Verapamil and doxorubicin were utilized to test this heart-on-a-chip, and multiple parameters of cardiomyocyte beating status are used to reveal the effects of drugs. The results show that drug efficacy or cardiotoxicity can be determined by this heart-on-a-chip. We believe this heart-on-a-chip will be a promising tool for the preclinical assessment of drug cardiac efficacy. Full article
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Open AccessArticle
Cytostretch, an Organ-on-Chip Platform
Micromachines 2016, 7(7), 120; https://doi.org/10.3390/mi7070120 - 14 Jul 2016
Cited by 16 | Viewed by 3189
Abstract
Organ-on-Chips (OOCs) are micro-fabricated devices which are used to culture cells in order to mimic functional units of human organs. The devices are designed to simulate the physiological environment of tissues in vivo. Cells in some types of OOCs can be stimulated in [...] Read more.
Organ-on-Chips (OOCs) are micro-fabricated devices which are used to culture cells in order to mimic functional units of human organs. The devices are designed to simulate the physiological environment of tissues in vivo. Cells in some types of OOCs can be stimulated in situ by electrical and/or mechanical actuators. These actuations can mimic physiological conditions in real tissue and may include fluid or air flow, or cyclic stretch and strain as they occur in the lung and heart. These conditions similarly affect cultured cells and may influence their ability to respond appropriately to physiological or pathological stimuli. To date, most focus has been on devices specifically designed to culture just one functional unit of a specific organ: lung alveoli, kidney nephrons or blood vessels, for example. In contrast, the modular Cytostretch membrane platform described here allows OOCs to be customized to different OOC applications. The platform utilizes silicon-based micro-fabrication techniques that allow low-cost, high-volume manufacturing. We describe the platform concept and its modules developed to date. Membrane variants include membranes with (i) through-membrane pores that allow biological signaling molecules to pass between two different tissue compartments; (ii) a stretchable micro-electrode array for electrical monitoring and stimulation; (iii) micro-patterning to promote cell alignment; and (iv) strain gauges to measure changes in substrate stress. This paper presents the fabrication and the proof of functionality for each module of the Cytostretch membrane. The assessment of each additional module demonstrate that a wide range of OOCs can be achieved. Full article
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Open AccessArticle
Combining Electro-Osmotic Flow and FTA® Paper for DNA Analysis on Microfluidic Devices
Micromachines 2016, 7(7), 119; https://doi.org/10.3390/mi7070119 - 14 Jul 2016
Cited by 6 | Viewed by 2230
Abstract
FTA® paper can be used to protect a variety of biological samples prior to analysis, facilitating ease-of-transport to laboratories or long-term archive storage. The use of FTA® paper as a solid phase eradicates the need to elute the nucleic acids from [...] Read more.
FTA® paper can be used to protect a variety of biological samples prior to analysis, facilitating ease-of-transport to laboratories or long-term archive storage. The use of FTA® paper as a solid phase eradicates the need to elute the nucleic acids from the matrix prior to DNA amplification, enabling both DNA purification and polymerase chain reaction (PCR)-based DNA amplification to be performed in a single chamber on the microfluidic device. A disc of FTA® paper, containing a biological sample, was placed within the microfluidic device on top of wax-encapsulated DNA amplification reagents. The disc containing the biological sample was then cleaned up using Tris-EDTA (TE) buffer, which was passed over the disc, via electro-osmotic flow, in order to remove any potential inhibitors of downstream processes. DNA amplification was successfully performed (from buccal cells, whole blood and semen) using a Peltier thermal cycling system, whereupon the stored PCR reagents were released during the initial denaturing step due to the wax barrier melting between the FTA® disc and PCR reagents. Such a system offers advantages in terms of a simple sample introduction interface and the ability to process archived samples in an integrated microfluidic environment with minimal risk of contamination. Full article
(This article belongs to the Special Issue Application of Microfluidic Methodology for the Analysis of DNA)
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Open AccessReview
Plasmonic Structures, Materials and Lenses for Optical Lithography beyond the Diffraction Limit: A Review
Micromachines 2016, 7(7), 118; https://doi.org/10.3390/mi7070118 - 13 Jul 2016
Cited by 19 | Viewed by 3862
Abstract
The rapid development of nanotechnologies and sciences has led to the great demand for novel lithography methods allowing large area, low cost and high resolution nano fabrications. Characterized by unique sub-diffraction optical features like propagation with an ultra-short wavelength and great field enhancement [...] Read more.
The rapid development of nanotechnologies and sciences has led to the great demand for novel lithography methods allowing large area, low cost and high resolution nano fabrications. Characterized by unique sub-diffraction optical features like propagation with an ultra-short wavelength and great field enhancement in subwavelength regions, surface plasmon polaritons (SPPs), including surface plasmon waves, bulk plasmon polaritons (BPPs) and localized surface plasmons (LSPs), have become potentially promising candidates for nano lithography. In this paper, investigations into plasmonic lithography in the manner of point-to-point writing, interference and imaging were reviewed in detail. Theoretical simulations and experiments have demonstrated plasmonic lithography resolution far beyond the conventional diffraction limit, even with ultraviolet light sources and single exposure performances. Half-pitch resolution as high as 22 nm (~1/17 light wavelength) was observed in plasmonic lens imaging lithography. Moreover, not only the overview of state-of-the-art results, but also the physics behind them and future research suggestions are discussed as well. Full article
(This article belongs to the Special Issue Micro/Nano Photonic Devices and Systems)
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Open AccessArticle
Synthesis and Electro-Magneto-Mechanical Properties of Graphene Aerogels Functionalized with Co-Fe-P Amorphous Alloys
Micromachines 2016, 7(7), 117; https://doi.org/10.3390/mi7070117 - 12 Jul 2016
Cited by 4 | Viewed by 2125
Abstract
Graphene aerogels (GAs) are functionalized with Fe-Co-P alloy using an electro-deposition method. The Fe-Co-P alloy coated on the graphene nanosheets is found to possess an amorphous structure and a nanoporous architecture of GAs. The electro-mechanical properties of GAs are significantly affected by the [...] Read more.
Graphene aerogels (GAs) are functionalized with Fe-Co-P alloy using an electro-deposition method. The Fe-Co-P alloy coated on the graphene nanosheets is found to possess an amorphous structure and a nanoporous architecture of GAs. The electro-mechanical properties of GAs are significantly affected by the Fe-Co-P nanoparticles embedded inside GAs. The electro-mechanical responses of GA/Fe-Co-P nanoporous hybrid structures are sensitive to an applied magnetic field, demonstrating that they are promising for electro-magneto-mechanical applications. The light-weight, high-strength and nanoporous GAs functionalized with Fe-Co-P amorphous alloys are desirable sensors, actuators, and nano-electro-mechanical systems that could be controlled or manipulated by mechanical, electric and magnetic fields. Full article
(This article belongs to the Special Issue Graphene Nano-Electro-Mechanical (NEM) Devices and Applications)
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Open AccessArticle
Gravity-Based Precise Cell Manipulation System Enhanced by In-Phase Mechanism
Micromachines 2016, 7(7), 116; https://doi.org/10.3390/mi7070116 - 09 Jul 2016
Cited by 5 | Viewed by 2435
Abstract
This paper proposes a gravity-based system capable of generating high-resolution pressure for precise cell manipulation or evaluation in a microfluidic channel. While the pressure resolution of conventional pumps for microfluidic applications is usually about hundreds of pascals as the resolution of their feedback [...] Read more.
This paper proposes a gravity-based system capable of generating high-resolution pressure for precise cell manipulation or evaluation in a microfluidic channel. While the pressure resolution of conventional pumps for microfluidic applications is usually about hundreds of pascals as the resolution of their feedback sensors, precise cell manipulation at the pascal level cannot be done. The proposed system successfully achieves a resolution of 100 millipascals using water head pressure with an in-phase noise cancelation mechanism. The in-phase mechanism aims to suppress the noises from ambient vibrations to the system. The proposed pressure system is tested with a microfluidic platform for pressure validation. The experimental results show that the in-phase mechanism effectively reduces the pressure turbulence, and the pressure-driven cell movement matches the theoretical simulations. Preliminary experiments on deformability evaluation with red blood cells under incremental pressures of one pascal are successfully performed. Different deformation patterns are observed from cell to cell under precise pressure control. Full article
(This article belongs to the Special Issue Advances in Microfluidic Devices for Cell Handling and Analysis)
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Open AccessArticle
A New Method of Fixing High-Aspect-Ratio Microstructures by Gel
Micromachines 2016, 7(7), 115; https://doi.org/10.3390/mi7070115 - 09 Jul 2016
Cited by 3 | Viewed by 2191
Abstract
In the microfabrication processes, it is necessary to examine the quality of the structures to ensure the whole process runs smoothly. However, the examination process of pattern defects is interrupted during the fabrication of high-aspect-ratio microstructures. The inevitable pattern defects arise from capillary [...] Read more.
In the microfabrication processes, it is necessary to examine the quality of the structures to ensure the whole process runs smoothly. However, the examination process of pattern defects is interrupted during the fabrication of high-aspect-ratio microstructures. The inevitable pattern defects arise from capillary forces which occur during the liquid drying process. In this paper, a new method that enables us to fix the microstructures with gel to restrict deformations before the rinsed liquid drying process has been proposed. It is effective to avoid the capillary forces by preventing the formation of the liquid level. The process parameters, types of gel, gel time and observation time were discussed and the flatness and thickness of the gel layer could be controlled. A series of high-aspect-ratio microstructures were fixed in good condition by gel. Full article
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Open AccessFeature PaperArticle
A Microchip for High-Throughput Axon Growth Drug Screening
Micromachines 2016, 7(7), 114; https://doi.org/10.3390/mi7070114 - 07 Jul 2016
Cited by 7 | Viewed by 2972
Abstract
It has been recently known that not only the presence of inhibitory molecules associated with myelin but also the reduced growth capability of the axons limit mature central nervous system (CNS) axonal regeneration after injury. Conventional axon growth studies are typically conducted using [...] Read more.
It has been recently known that not only the presence of inhibitory molecules associated with myelin but also the reduced growth capability of the axons limit mature central nervous system (CNS) axonal regeneration after injury. Conventional axon growth studies are typically conducted using multi-well cell culture plates that are very difficult to use for investigating localized effects of drugs and limited to low throughput. Unfortunately, there is currently no other in vitro tool that allows investigating localized axonal responses to biomolecules in high-throughput for screening potential drugs that might promote axonal growth. We have developed a compartmentalized neuron culture platform enabling localized biomolecular treatments in parallel to axons that are physically and fluidically isolated from their neuronal somata. The 24 axon compartments in the developed platform are designed to perform four sets of six different localized biomolecular treatments simultaneously on a single device. In addition, the novel microfluidic configuration allows culture medium of 24 axon compartments to be replenished altogether by a single aspiration process, making high-throughput drug screening a reality. Full article
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Open AccessCommunication
Microfluidic Autologous Serum Eye-Drops Preparation as a Potential Dry Eye Treatment
Micromachines 2016, 7(7), 113; https://doi.org/10.3390/mi7070113 - 04 Jul 2016
Cited by 1 | Viewed by 2363
Abstract
Dry eye is a problem in tearing quality and/or quantity and it afflicts millions of persons worldwide. An autologous serum eye-drop is a good candidate for dry eye treatment; however, the eye-drop preparation procedures take a long time and are relatively troublesome. Here [...] Read more.
Dry eye is a problem in tearing quality and/or quantity and it afflicts millions of persons worldwide. An autologous serum eye-drop is a good candidate for dry eye treatment; however, the eye-drop preparation procedures take a long time and are relatively troublesome. Here we use spiral microchannels to demonstrate a strategy for the preparation of autologous serum eye-drops, which provide benefits for all dry eye patients; 100% and 90% removal efficiencies are achieved for 10 μm microbeads and whole human blood cells, respectively. Since our strategy allows researchers to integrate other functional microchannels into one device, such a microfluidic device will be able to offer a new one-step preparation system for autologous serum eye-drops. Full article
(This article belongs to the Special Issue Micro/Nano Devices for Chemical Analysis) Printed Edition available
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Open AccessArticle
Light-Addressable Potentiometric Sensor as a Sensing Element in Plug-Based Microfluidic Devices
Micromachines 2016, 7(7), 111; https://doi.org/10.3390/mi7070111 - 01 Jul 2016
Cited by 10 | Viewed by 2689
Abstract
A plug-based microfluidic system based on the principle of the light-addressable potentiometric sensor (LAPS) is proposed. The LAPS is a semiconductor-based chemical sensor, which has a free addressability of the measurement point on the sensing surface. By combining a microfluidic device and LAPS, [...] Read more.
A plug-based microfluidic system based on the principle of the light-addressable potentiometric sensor (LAPS) is proposed. The LAPS is a semiconductor-based chemical sensor, which has a free addressability of the measurement point on the sensing surface. By combining a microfluidic device and LAPS, ion sensing can be performed anywhere inside the microfluidic channel. In this study, the sample solution to be measured was introduced into the channel in a form of a plug with a volume in the range of microliters. Taking advantage of the light-addressability, the position of the plug could be monitored and pneumatically controlled. With the developed system, the pH value of a plug with a volume down to 400 nL could be measured. As an example of plug-based operation, two plugs were merged in the channel, and the pH change was detected by differential measurement. Full article
(This article belongs to the Special Issue Micro/Nano Devices for Chemical Analysis) Printed Edition available
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Open AccessArticle
Design and Experiment of a Solder Paste Jetting System Driven by a Piezoelectric Stack
Micromachines 2016, 7(7), 112; https://doi.org/10.3390/mi7070112 - 30 Jun 2016
Cited by 11 | Viewed by 3087
Abstract
To compensate for the insufficiency and instability of solder paste dispensing and printing that are used in the SMT (Surface Mount Technology) production process, a noncontact solder paste jetting system driven by a piezoelectric stack based on the principle of the nozzle-needle-system is [...] Read more.
To compensate for the insufficiency and instability of solder paste dispensing and printing that are used in the SMT (Surface Mount Technology) production process, a noncontact solder paste jetting system driven by a piezoelectric stack based on the principle of the nozzle-needle-system is introduced in this paper, in which a miniscule gap exists between the nozzle and needle during the jetting process. Here, the critical jet ejection velocity is discussed through theoretical analysis. The relations between ejection velocity and needle structure, needle velocity, and nozzle diameter were obtained by FLUENT software. Then, the prototype of the solder paste jetting system was fabricated, and the performance was verified by experiments. The effects of the gap between nozzle and needle, the driving voltage, and the nozzle diameter on the jetting performance and droplet diameter were obtained. Solder paste droplets 0.85 mm in diameter were produced when the gap between the nozzle and needle was adjusted to 10 μm, the driving voltage to 80 V, the nozzle diameter to 0.1 mm, and the variation of the droplet diameter was within ±3%. Full article
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Open AccessArticle
A Multithread Nested Neural Network Architecture to Model Surface Plasmon Polaritons Propagation
Micromachines 2016, 7(7), 110; https://doi.org/10.3390/mi7070110 - 30 Jun 2016
Cited by 19 | Viewed by 2179
Abstract
Surface Plasmon Polaritons are collective oscillations of electrons occurring at the interface between a metal and a dielectric. The propagation phenomena in plasmonic nanostructures is not fully understood and the interdependence between propagation and metal thickness requires further investigation. We propose an ad-hoc [...] Read more.
Surface Plasmon Polaritons are collective oscillations of electrons occurring at the interface between a metal and a dielectric. The propagation phenomena in plasmonic nanostructures is not fully understood and the interdependence between propagation and metal thickness requires further investigation. We propose an ad-hoc neural network topology assisting the study of the said propagation when several parameters, such as wavelengths, propagation length and metal thickness are considered. This approach is novel and can be considered a first attempt at fully automating such a numerical computation. For the proposed neural network topology, an advanced training procedure has been devised in order to shun the possibility of accumulating errors. The provided results can be useful, e.g., to improve the efficiency of photocells, for photon harvesting, and for improving the accuracy of models for solid state devices. Full article
(This article belongs to the Special Issue Micro/Nano Photonic Devices and Systems)
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Open AccessArticle
3D Printed Paper-Based Microfluidic Analytical Devices
Micromachines 2016, 7(7), 108; https://doi.org/10.3390/mi7070108 - 28 Jun 2016
Cited by 31 | Viewed by 5445
Abstract
As a pump-free and lightweight analytical tool, paper-based microfluidic analytical devices (μPADs) attract more and more interest. If the flow speed of μPAD can be programmed, the analytical sequences could be designed and they will be more popular. This reports presents a novel [...] Read more.
As a pump-free and lightweight analytical tool, paper-based microfluidic analytical devices (μPADs) attract more and more interest. If the flow speed of μPAD can be programmed, the analytical sequences could be designed and they will be more popular. This reports presents a novel μPAD, driven by the capillary force of cellulose powder, printed by a desktop three-dimensional (3D) printer, which has some promising features, such as easy fabrication and programmable flow speed. First, a suitable size-scale substrate with open microchannels on its surface is printed. Next, the surface of the substrate is covered with a thin layer of polydimethylsiloxane (PDMS) to seal the micro gap caused by 3D printing. Then, the microchannels are filled with a mixture of cellulose powder and deionized water in an appropriate proportion. After drying in an oven at 60 °C for 30 min, it is ready for use. As the different channel depths can be easily printed, which can be used to achieve the programmable capillary flow speed of cellulose powder in the microchannels. A series of microfluidic analytical experiments, including quantitative analysis of nitrite ion and fabrication of T-sensor were used to demonstrate its capability. As the desktop 3D printer (D3DP) is very cheap and accessible, this device can be rapidly printed at the test field with a low cost and has a promising potential in the point-of-care (POC) system or as a lightweight platform for analytical chemistry. Full article
(This article belongs to the Special Issue 3D Printing: Microfabrication and Emerging Concepts)
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Open AccessArticle
Quantification of Vortex Generation Due to Non-Equilibrium Electrokinetics at the Micro/Nanochannel Interface: Spectral Analysis
Micromachines 2016, 7(7), 109; https://doi.org/10.3390/mi7070109 - 27 Jun 2016
Cited by 3 | Viewed by 2245
Abstract
We report on our investigation of a low Reynolds number non-equilibrium electrokinetic flow in a micro/nanochannel platform. Non-equilibrium electrokinetic phenomena include so-called concentration polarization in a moderate electric field and vortex formation in a high electric field. We conducted a spectral analysis of [...] Read more.
We report on our investigation of a low Reynolds number non-equilibrium electrokinetic flow in a micro/nanochannel platform. Non-equilibrium electrokinetic phenomena include so-called concentration polarization in a moderate electric field and vortex formation in a high electric field. We conducted a spectral analysis of non-equilibrium electrokinetic vortices at a micro/nanochannel interface. We found that periodic vortices are formed while the frequency varies with the applied voltages and solution concentrations. At a frequency as high as 60 Hz, vortex generation was obtained with the strongest electric field and the lowest concentration. The power spectra show increasing frequency with increasing voltage or decreasing concentration. We expect that our spectral analysis results will be useful for micromixer developers in the micromachine research field. Full article
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Open AccessReview
Farewell to Animal Testing: Innovations on Human Intestinal Microphysiological Systems
Micromachines 2016, 7(7), 107; https://doi.org/10.3390/mi7070107 - 27 Jun 2016
Cited by 11 | Viewed by 4789
Abstract
The human intestine is a dynamic organ where the complex host-microbe interactions that orchestrate intestinal homeostasis occur. Major contributing factors associated with intestinal health and diseases include metabolically-active gut microbiota, intestinal epithelium, immune components, and rhythmical bowel movement known as peristalsis. Human intestinal [...] Read more.
The human intestine is a dynamic organ where the complex host-microbe interactions that orchestrate intestinal homeostasis occur. Major contributing factors associated with intestinal health and diseases include metabolically-active gut microbiota, intestinal epithelium, immune components, and rhythmical bowel movement known as peristalsis. Human intestinal disease models have been developed; however, a considerable number of existing models often fail to reproducibly predict human intestinal pathophysiology in response to biological and chemical perturbations or clinical interventions. Intestinal organoid models have provided promising cytodifferentiation and regeneration, but the lack of luminal flow and physical bowel movements seriously hamper mimicking complex host-microbe crosstalk. Here, we discuss recent advances of human intestinal microphysiological systems, such as the biomimetic human “Gut-on-a-Chip” that can employ key intestinal components, such as villus epithelium, gut microbiota, and immune components under peristalsis-like motions and flow, to reconstitute the transmural 3D lumen-capillary tissue interface. By encompassing cutting-edge tools in microfluidics, tissue engineering, and clinical microbiology, gut-on-a-chip has been leveraged not only to recapitulate organ-level intestinal functions, but also emulate the pathophysiology of intestinal disorders, such as chronic inflammation. Finally, we provide potential perspectives of the next generation microphysiological systems as a personalized platform to validate the efficacy, safety, metabolism, and therapeutic responses of new drug compounds in the preclinical stage. Full article
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Open AccessReview
Cell Monitoring and Manipulation Systems (CMMSs) based on Glass Cell-Culture Chips (GC3s)
Micromachines 2016, 7(7), 106; https://doi.org/10.3390/mi7070106 - 24 Jun 2016
Cited by 8 | Viewed by 3304
Abstract
We developed different types of glass cell-culture chips (GC3s) for culturing cells for microscopic observation in open media-containing troughs or in microfluidic structures. Platinum sensor and manipulation structures were used to monitor physiological parameters and to allocate and permeabilize cells. Electro-thermal [...] Read more.
We developed different types of glass cell-culture chips (GC3s) for culturing cells for microscopic observation in open media-containing troughs or in microfluidic structures. Platinum sensor and manipulation structures were used to monitor physiological parameters and to allocate and permeabilize cells. Electro-thermal micro pumps distributed chemical compounds in the microfluidic systems. The integrated temperature sensors showed a linear, Pt1000-like behavior. Cell adhesion and proliferation were monitored using interdigitated electrode structures (IDESs). The cell-doubling times of primary murine embryonic neuronal cells (PNCs) were determined based on the IDES capacitance-peak shifts. The electrical activity of PNC networks was detected using multi-electrode arrays (MEAs). During seeding, the cells were dielectrophoretically allocated to individual MEAs to improve network structures. MEA pads with diameters of 15, 20, 25, and 35 µm were tested. After 3 weeks, the magnitudes of the determined action potentials were highest for pads of 25 µm in diameter and did not differ when the inter-pad distances were 100 or 170 µm. Using 25-µm diameter circular oxygen electrodes, the signal currents in the cell-culture media were found to range from approximately −0.08 nA (0% O2) to −2.35 nA (21% O2). It was observed that 60-nm thick silicon nitride-sensor layers were stable potentiometric pH sensors under cell-culture conditions for periods of days. Their sensitivity between pH 5 and 9 was as high as 45 mV per pH step. We concluded that sensorized GC3s are potential animal replacement systems for purposes such as toxicity pre-screening. For example, the effect of mefloquine, a medication used to treat malaria, on the electrical activity of neuronal cells was determined in this study using a GC3 system. Full article
(This article belongs to the Special Issue Advances in Microfluidic Devices for Cell Handling and Analysis)
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