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Micromachines, Volume 8, Issue 1 (January 2017) – 30 articles

Cover Story (view full-size image): In this communication, we demonstrate how a heat-sensitive adhesive material can be exploited to rapidly produce microfluidic devices for the three key stages of human profiling: DNA extraction, polymerase chain reaction, and DNA separation. These exemplary devices are equipped with the high levels of durability and resilience now expected by the end user in many applications, while the fabrication methodology itself presents characteristics which make it attractive as a prototyping tool. View this paper.
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Open AccessArticle
Glass Imprint Templates by Spark Assisted Chemical Engraving for Microfabrication by Hot Embossing
Micromachines 2017, 8(1), 29; https://doi.org/10.3390/mi8010029 - 23 Jan 2017
Cited by 7 | Viewed by 2978
Abstract
As the field of microelectromechanical systems (MEMS) matures, new demands are being placed on the microfabrication of complex architectures in robust materials, such as hard plastics. Iterative design optimization in a timely manner—rapid prototyping—places challenges on template fabrication, for methods such as injection [...] Read more.
As the field of microelectromechanical systems (MEMS) matures, new demands are being placed on the microfabrication of complex architectures in robust materials, such as hard plastics. Iterative design optimization in a timely manner—rapid prototyping—places challenges on template fabrication, for methods such as injection moulding and hot embossing. In this paper, we demonstrate the possibility of using spark assisted chemical engraving (SACE) to produce micro patterned glass templates. The direct, write-based approach enabled the facile fabrication of smooth microfeatures with variations in all three-dimensions, which could be replicated by hot embossing different thermoplastics. As a proof of principle, we demonstrated the technique for a high glass transition temperature polycarbonate. Good fidelity over more than 10 cycles provides evidence that the approach is viable for rapid prototyping and has the potential to satisfy commercial-grade production at medium-level output volumes. Glass imprint templates showed no degradation after use, but care must be taken due to brittleness. The technique has the potential to advance microfabrication needs in academia and could be used by MEMS product developers. Full article
(This article belongs to the Special Issue Glass Micromachining)
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Open AccessCommunication
Organic Solvent and Surfactant Resistant Paper-Fluidic Devices Fabricated by One-Step Embossing of Nonwoven Polypropylene Sheet
Micromachines 2017, 8(1), 30; https://doi.org/10.3390/mi8010030 - 22 Jan 2017
Cited by 5 | Viewed by 2764
Abstract
In this communication, we report a physical method for the fabrication of organic solvent and surfactant-resistant barriers on paper-based fluidic devices. When nonwoven polypropylene sheet is embossed with a steel mold, the embossed region acts as a physical barrier that can prevent the [...] Read more.
In this communication, we report a physical method for the fabrication of organic solvent and surfactant-resistant barriers on paper-based fluidic devices. When nonwoven polypropylene sheet is embossed with a steel mold, the embossed region acts as a physical barrier that can prevent the flow of liquids. Embossed polypropylene barriers not only block water, but also block organic solvents and surfactants, which are known to be difficult to handle on previous paper-based devices. Various amounts of embossing pressures were tested to determine the minimum embossing pressure required for leakproof barrier formation. The compatibility of the barrier was also investigated with several surfactants and organic solvents. As a demonstration, a lysis buffer, which was known to leak through wax-printed barriers, was used to detect Escherichia coli (E. coli) O157:H7. To the best of our knowledge, this paper is the first to report a one-step fabrication method of paper-fluidic devices capable of handling surfactants and organic solvents, including alcohols. Full article
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Open AccessArticle
Microfluidic Techniques for Analytes Concentration
Micromachines 2017, 8(1), 28; https://doi.org/10.3390/mi8010028 - 22 Jan 2017
Cited by 25 | Viewed by 2665
Abstract
Microfluidics has been undergoing fast development in the past two decades due to its promising applications in biotechnology, medicine, and chemistry. Towards these applications, enhancing concentration sensitivity and detection resolution are indispensable to meet the detection limits because of the dilute sample concentrations, [...] Read more.
Microfluidics has been undergoing fast development in the past two decades due to its promising applications in biotechnology, medicine, and chemistry. Towards these applications, enhancing concentration sensitivity and detection resolution are indispensable to meet the detection limits because of the dilute sample concentrations, ultra-small sample volumes and short detection lengths in microfluidic devices. A variety of microfluidic techniques for concentrating analytes have been developed. This article presents an overview of analyte concentration techniques in microfluidics. We focus on discussing the physical mechanism of each concentration technique with its representative advancements and applications. Finally, the article is concluded by highlighting and discussing advantages and disadvantages of the reviewed techniques. Full article
(This article belongs to the Special Issue Micro/Nano-Chip Electrokinetics)
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Open AccessArticle
Human Liver Sinusoid on a Chip for Hepatitis B Virus Replication Study
Micromachines 2017, 8(1), 27; https://doi.org/10.3390/mi8010027 - 20 Jan 2017
Cited by 9 | Viewed by 2801
Abstract
We have developed a miniature human liver (liver-sinusoid-on-a-chip) model using a dual microchannel separated by a porous membrane. Primary human hepatocytes and immortalized bovine aortic endothelial cells were co-cultured on opposite sides of a microporous membrane in a dual microchannel with [...] Read more.
We have developed a miniature human liver (liver-sinusoid-on-a-chip) model using a dual microchannel separated by a porous membrane. Primary human hepatocytes and immortalized bovine aortic endothelial cells were co-cultured on opposite sides of a microporous membrane in a dual microchannel with continuous perfusion. Primary human hepatocytes in this system retained their polygonal morphology for up to 26 days, while hepatocytes cultured in the absence of bovine aortic endothelial cells lost their morphology within a week. In order to demonstrate the utility of our human-liver-sinusoid-on-a-chip, human hepatocytes in this system were directly infected by Hepatitis B Virus (HBV). Expression of the HBV core antigen was detected in human hepatocytes in the microchannel system. HBV replication, measured by the presence of cell-secreted HBV DNA, was also detected. Importantly, HBV is hepatotropic, and expression of HBV RNA transcripts is dependent upon expression of hepatocyte-specific factors. Moreover, HBV infection requires expression of the human-hepatocyte-specific HBV cell surface receptor. Therefore, the ability to detect HBV replication and Hepatitis B core Antigen (HBcAg) expression in our microfluidic platform confirmed that hepatocyte differentiation and functions were retained throughout the time course of our studies. We believe that our human-liver-sinusoid-on-a-chip could have many applications in liver-related research and drug development. Full article
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Open AccessArticle
Three-Dimensional Interaction of a Large Number of Dense DEP Particles on a Plane Perpendicular to an AC Electrical Field
Micromachines 2017, 8(1), 26; https://doi.org/10.3390/mi8010026 - 20 Jan 2017
Cited by 4 | Viewed by 2087
Abstract
The interaction of dielectrophoresis (DEP) particles in an electric field has been observed in many experiments, known as the “particle chains phenomenon”. However, the study in 3D models (spherical particles) is rarely reported due to its complexity and significant computational cost. In this [...] Read more.
The interaction of dielectrophoresis (DEP) particles in an electric field has been observed in many experiments, known as the “particle chains phenomenon”. However, the study in 3D models (spherical particles) is rarely reported due to its complexity and significant computational cost. In this paper, we employed the iterative dipole moment (IDM) method to study the 3D interaction of a large number of dense DEP particles randomly distributed on a plane perpendicular to a uniform alternating current (AC) electric field in a bounded or unbounded space. The numerical results indicated that the particles cannot move out of the initial plane. The similar particles (either all positive or all negative DEP particles) always repelled each other, and did not form a chain. The dissimilar particles (a mixture of positive and negative DEP particles) always attracted each other, and formed particle chains consisting of alternately arranged positive and negative DEP particles. The particle chain patterns can be randomly multitudinous depending on the initial particle distribution, the electric properties of particles/fluid, the particle sizes and the number of particles. It is also found that the particle chain patterns can be effectively manipulated via tuning the frequency of the AC field and an almost uniform distribution of particles in a bounded plane chip can be achieved when all of the particles are similar, which may have potential applications in the particle manipulation of microfluidics. Full article
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Open AccessArticle
All-Semiconductor Plasmonic Resonator for Surface-Enhanced Infrared Absorption Spectroscopy
Micromachines 2017, 8(1), 6; https://doi.org/10.3390/mi8010006 - 19 Jan 2017
Cited by 7 | Viewed by 2525
Abstract
Infrared absorption spectroscopy remains a challenge due to the weak light-matter interaction between micron-wavelengthed infrared light and nano-sized molecules. A highly doped semiconductor supports intrinsic plasmon modes at infrared frequencies, and is compatible with the current epitaxial growth processing, which makes it promising [...] Read more.
Infrared absorption spectroscopy remains a challenge due to the weak light-matter interaction between micron-wavelengthed infrared light and nano-sized molecules. A highly doped semiconductor supports intrinsic plasmon modes at infrared frequencies, and is compatible with the current epitaxial growth processing, which makes it promising for various applications. Here, we propose an all-semiconductor plasmonic resonator to enhance the infrared absorption of the adsorbed molecules. An optical model is employed to investigate the effect of structural parameters on the spectral features of the resonator and the enhanced infrared absorption characteristics are further discussed. When a molecular layer is deposited upon the resonator, the weak molecular absorption signal can be significantly enhanced. A high enhancement factor of 470 can be achieved once the resonance wavelength of the resonator is overlapped with the desired vibrational mode of the molecules. Our study offers a promising approach to engineering semiconductor optics devices for mid-infrared sensing applications. Full article
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Open AccessArticle
A Sensitivity-Enhanced Film Bulk Acoustic Resonator Gas Sensor with an Oscillator Circuit and Its Detection Application
Micromachines 2017, 8(1), 25; https://doi.org/10.3390/mi8010025 - 19 Jan 2017
Cited by 9 | Viewed by 2425
Abstract
This paper presents a sensitivity-enhanced gas sensor based on a film bulk acoustic resonator (FBAR). It was designed and fabricated with micro through-holes in its top electrode for sensitivity enhancement. The sensor was driven by a Colpitts oscillator circuit, and the output signal [...] Read more.
This paper presents a sensitivity-enhanced gas sensor based on a film bulk acoustic resonator (FBAR). It was designed and fabricated with micro through-holes in its top electrode for sensitivity enhancement. The sensor was driven by a Colpitts oscillator circuit, and the output signal had characteristics of a power of −2.6 [email protected] V and a phase noise of −90 dBc/[email protected] kHz. In order to test the performance of the sensor, it was used for the detection of relative humidity (RH) and ethanol. When the relative humidity ranged from 25% to 88%, the frequency shift of the sensor was 733 kHz, which was 3.2 times higher than that of the existing FBAR sensor with a complete top electrode. Fitting results of the frequency shift and the relative humidity indicated that the measurement error was within ±0.8% RH. When the ethanol concentration ranged from 0 to 0.2355 g/L, the frequency shift of the sensor was 365 kHz. The effect of the oscillator circuit on the adsorption reaction and temperature response of the FBAR sensor device was analyzed to optimize its detection application. Full article
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Open AccessArticle
Frequency-Dependent Electroformation of Giant Unilamellar Vesicles in 3D and 2D Microelectrode Systems
Micromachines 2017, 8(1), 24; https://doi.org/10.3390/mi8010024 - 16 Jan 2017
Cited by 5 | Viewed by 2262
Abstract
A giant unilamellar vesicle (GUV), with similar properties to cellular membrane, has been widely studied. Electroformation with its simplicity and accessibility has become the most common method for GUV production. In this work, GUV electroformation in devices with traditional 3D and new 2D [...] Read more.
A giant unilamellar vesicle (GUV), with similar properties to cellular membrane, has been widely studied. Electroformation with its simplicity and accessibility has become the most common method for GUV production. In this work, GUV electroformation in devices with traditional 3D and new 2D electrode structures were studied with respect to the applied electric field. An optimal frequency (10 kHz in the 3D and 1 kHz in the 2D systems) was found in each system. A positive correlation was found between GUV formation and applied voltage in the 3D electrode system from 1 to 10 V. In the 2D electrode system, the yield of the generated GUV increased first but decreased later as voltage increased. These phenomena were further confirmed by numerically calculating the load that the lipid film experienced from the generated electroosmotic flow (EOF). The discrepancy between the experimental and numerical results of the 3D electrode system may be because the parameters that were adopted in the simulations are quite different from those of the lipid film in experiments. The lipid film was not involved in the simulation of the 2D system, and the numerical results matched well with the experiments. Full article
(This article belongs to the Special Issue Micro/Nano-Chip Electrokinetics)
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Open AccessArticle
Effects of Process Conditions on the Mechanical Behavior of Aluminium Wrought Alloy EN AW-2219 (AlCu6Mn) Additively Manufactured by Laser Beam Melting in Powder Bed
Micromachines 2017, 8(1), 23; https://doi.org/10.3390/mi8010023 - 16 Jan 2017
Cited by 30 | Viewed by 4140
Abstract
Additive manufacturing is especially suitable for complex-shaped 3D parts with integrated and optimized functionality realized by filigree geometries. Such designs benefit from low safety factors in mechanical layout. This demands ductile materials that reduce stress peaks by predictable plastic deformation instead of failure. [...] Read more.
Additive manufacturing is especially suitable for complex-shaped 3D parts with integrated and optimized functionality realized by filigree geometries. Such designs benefit from low safety factors in mechanical layout. This demands ductile materials that reduce stress peaks by predictable plastic deformation instead of failure. Al–Cu wrought alloys are established materials meeting this requirement. Additionally, they provide high specific strengths. As the designation “Wrought Alloys” implies, they are intended for manufacturing by hot or cold working. When cast or welded, they are prone to solidification cracks. Al–Si fillers can alleviate this, but impair ductility. Being closely related to welding, Laser Beam Melting in Powder Bed (LBM) of Al–Cu wrought alloys like EN AW-2219 can be considered challenging. In LBM of aluminium alloys, only easily-weldable Al–Si casting alloys have succeeded commercially today. This article discusses the influences of boundary conditions during LBM of EN AW-2219 on sample porosity and tensile test results, supported by metallographic microsections and fractography. Load direction was varied relative to LBM build-up direction. T6 heat treatment was applied to half of the samples. Pronounced anisotropy was observed. Remarkably, elongation at break of T6 specimens loaded along the build-up direction exceeded the values from literature for conventionally manufactured EN AW-2219 by a factor of two. Full article
(This article belongs to the Special Issue Laser Micromachining and Microfabrication)
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Open AccessReview
Droplet Microfluidics for the Production of Microparticles and Nanoparticles
Micromachines 2017, 8(1), 22; https://doi.org/10.3390/mi8010022 - 14 Jan 2017
Cited by 55 | Viewed by 5691
Abstract
Droplet microfluidics technology is recently a highly interesting platform in material fabrication. Droplets can precisely monitor and control entire material fabrication processes and are superior to conventional bulk techniques. Droplet production is controlled by regulating the channel geometry and flow rates of each [...] Read more.
Droplet microfluidics technology is recently a highly interesting platform in material fabrication. Droplets can precisely monitor and control entire material fabrication processes and are superior to conventional bulk techniques. Droplet production is controlled by regulating the channel geometry and flow rates of each fluid. The micro-scale size of droplets results in rapid heat and mass-transfer rates. When used as templates, droplets can be used to develop reproducible and scalable microparticles with tailored sizes, shapes and morphologies, which are difficult to obtain using traditional bulk methods. This technology can revolutionize material processing and application platforms. Generally, microparticle preparation methods involve three steps: (1) the formation of micro-droplets using a microfluidics generator; (2) shaping the droplets in micro-channels; and (3) solidifying the droplets to form microparticles. This review discusses the production of microparticles produced by droplet microfluidics according to their morphological categories, which generally determine their physicochemical properties and applications. Full article
(This article belongs to the Special Issue Insights and Advancements in Microfluidics)
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Open AccessArticle
Comparative Influences of Fluid and Shell on Modeled Ejection Performance of a Piezoelectric Micro-Jet
Micromachines 2017, 8(1), 21; https://doi.org/10.3390/mi8010021 - 13 Jan 2017
Cited by 3 | Viewed by 2129
Abstract
The piezoelectric micro-jet, which can achieve the drop-on-demand requirement, is based on ink-jet technology and small droplets can be ejected out by precise control. The droplets are driven out of the nozzle by the acoustic pressure waves which are generated by the piezoelectric [...] Read more.
The piezoelectric micro-jet, which can achieve the drop-on-demand requirement, is based on ink-jet technology and small droplets can be ejected out by precise control. The droplets are driven out of the nozzle by the acoustic pressure waves which are generated by the piezoelectric vibrator. The propagation processes of the acoustic pressure waves are affected by the acoustic properties of the fluid and the shell material of the micro-jet, as well as the excitations and the structure sizes. The influences of the fluid density and acoustic velocity in the fluid on the nozzle pressure and support reaction force of the vibrator are analyzed in this paper. The effects of the shell material on the ejection performance are studied as well. In order to improve the ejection performance of the micro-jet, for ejecting a given fluid, the recommended methods of selecting the shell material and adjusting excitations are provided based on the results, and the influences of the factors on working frequencies are obtained as well. Full article
(This article belongs to the Special Issue Piezoelectric MEMS)
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Open AccessFeature PaperReview
Scalable Nanomanufacturing—A Review
Micromachines 2017, 8(1), 20; https://doi.org/10.3390/mi8010020 - 11 Jan 2017
Cited by 16 | Viewed by 2476
Abstract
This article describes the field of scalable nanomanufacturing, its importance and need, its research activities and achievements. The National Science Foundation is taking a leading role in fostering basic research in scalable nanomanufacturing (SNM). From this effort several novel nanomanufacturing approaches have been [...] Read more.
This article describes the field of scalable nanomanufacturing, its importance and need, its research activities and achievements. The National Science Foundation is taking a leading role in fostering basic research in scalable nanomanufacturing (SNM). From this effort several novel nanomanufacturing approaches have been proposed, studied and demonstrated, including scalable nanopatterning. This paper will discuss SNM research areas in materials, processes and applications, scale-up methods with project examples, and manufacturing challenges that need to be addressed to move nanotechnology discoveries closer to the marketplace. Full article
(This article belongs to the Special Issue Scalable Micro/Nano Patterning)
Open AccessEditorial
Acknowledgement to Reviewers of Micromachines in 2016
Micromachines 2017, 8(1), 19; https://doi.org/10.3390/mi8010019 - 11 Jan 2017
Viewed by 1264
Abstract
The editors of Micromachines would like to express their sincere gratitude to the following reviewers for assessing manuscripts in 2016.[...] Full article
Open AccessArticle
Solvent-Free Patterning of Colloidal Quantum Dot Films Utilizing Shape Memory Polymers
Micromachines 2017, 8(1), 18; https://doi.org/10.3390/mi8010018 - 10 Jan 2017
Cited by 5 | Viewed by 2824
Abstract
Colloidal quantum dots (QDs) with properties that can be tuned by size, shape, and composition are promising for the next generation of photonic and electronic devices. However, utilization of these materials in such devices is hindered by the limited compatibility of established semiconductor [...] Read more.
Colloidal quantum dots (QDs) with properties that can be tuned by size, shape, and composition are promising for the next generation of photonic and electronic devices. However, utilization of these materials in such devices is hindered by the limited compatibility of established semiconductor processing techniques. In this context, patterning of QD films formed from colloidal solutions is a critical challenge and alternative methods are currently being developed for the broader adoption of colloidal QDs in functional devices. Here, we present a solvent-free approach to patterning QD films by utilizing a shape memory polymer (SMP). The high pull-off force of the SMP below glass transition temperature (Tg) in conjunction with the conformal contact at elevated temperatures (above Tg) enables large-area, rate-independent, fine patterning while preserving desired properties of QDs. Full article
(This article belongs to the Special Issue Scalable Micro/Nano Patterning)
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Open AccessCommunication
Rapid Fabrication of Electrophoretic Microfluidic Devices from Polyester, Adhesives and Gold Leaf
Micromachines 2017, 8(1), 17; https://doi.org/10.3390/mi8010017 - 09 Jan 2017
Cited by 7 | Viewed by 2661
Abstract
In the last decade, the microfluidic community has witnessed an evolution in fabrication methodologies that deviate from using conventional glass and polymer-based materials. A leading example within this group is the print, cut and laminate (PCL) approach, which entails the laser cutting of [...] Read more.
In the last decade, the microfluidic community has witnessed an evolution in fabrication methodologies that deviate from using conventional glass and polymer-based materials. A leading example within this group is the print, cut and laminate (PCL) approach, which entails the laser cutting of microfluidic architecture into ink toner-laden polyester sheets, followed by the lamination of these layers for device assembly. Recent success when applying this method to human genetic fingerprinting has highlighted that it is now ripe for the refinements necessary to render it amenable to mass-manufacture. In this communication, we detail those modifications by identifying and implementing a suitable heat-sensitive adhesive (HSA) material to equip the devices with the durability and resilience required for commercialization and fieldwork. Importantly, this augmentation is achieved without sacrificing any of the characteristics which make the PCL approach attractive for prototyping. Exemplary HSA-devices performed DNA extraction, amplification and separation which, when combined, constitute the complete sequence necessary for human profiling and other DNA-based analyses. Full article
(This article belongs to the Special Issue Application of Microfluidic Methodology for the Analysis of DNA)
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Open AccessCommunication
Complete Procedure for Fabrication of a Fused Silica Ultrarapid Microfluidic Mixer Used in Biophysical Measurements
Micromachines 2017, 8(1), 16; https://doi.org/10.3390/mi8010016 - 07 Jan 2017
Cited by 7 | Viewed by 2839
Abstract
In this paper we present a method to fabricate a fused silica microfluidic device by employing low viscosity KMPR photoresists. The resulting device is a continuous-flow microfluidic mixer based on hydrodynamic focusing. The advantages of this new fabrication method compared to the traditional [...] Read more.
In this paper we present a method to fabricate a fused silica microfluidic device by employing low viscosity KMPR photoresists. The resulting device is a continuous-flow microfluidic mixer based on hydrodynamic focusing. The advantages of this new fabrication method compared to the traditional approach using a poly-silicon mask are simplification, and time and cost reduction, while still preserving the quality and the performance of the mixers. This process results in devices in which the focusing channel has an aspect ratio of 10:1. The newly-fabricated mixer is successfully used to observe the folding of the Pin1 WW domain at the microsecond time scale. Full article
(This article belongs to the Collection Lab-on-a-Chip)
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Open AccessArticle
Continuous Jetting of Alginate Microfiber in Atmosphere Based on a Microfluidic Chip
Micromachines 2017, 8(1), 8; https://doi.org/10.3390/mi8010008 - 04 Jan 2017
Cited by 4 | Viewed by 2466
Abstract
We present a method based on a microfluidic chip that produces continuous jetting of alginate microfiber in the atmosphere to facilitate its collection and assembly. Through the analysis of the factors influencing the microfiber jetting, the principle and some microfluidic chip design criteria [...] Read more.
We present a method based on a microfluidic chip that produces continuous jetting of alginate microfiber in the atmosphere to facilitate its collection and assembly. Through the analysis of the factors influencing the microfiber jetting, the principle and some microfluidic chip design criteria are discussed. A special nozzle is designed near the chip outlet, and deionized water is introduced into the microchannel through the nozzle to increase the flux and thus to prevent drop formation around the outlet which impedes the continuous jetting of microfiber. The experiments have reported the effectiveness of the proposed structure and shown that the introduction of sheath flow promotes the stability of the flow field in the microchannel and does not affect the morphology of microfiber. Simulations of velocity and pressure distribution in the microchannel are also conducted. Further, the jetting microfibers are collected and assembled into various 3D complex fiber-based macroscopic structures through patterning or reeling. Since the proposed structure is rather simple and can be easily integrated into other complex structures without adding more soft-lithographical steps, microfibers with various morphology and function can be synthesized and collected in a single chip, which can be applied to various fields, such as tissue engineering, biotechnology, and drug discovery. Full article
(This article belongs to the Special Issue Optofluidics 2016)
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Open AccessReview
Microfluidic Platform for Cell Isolation and Manipulation Based on Cell Properties
Micromachines 2017, 8(1), 15; https://doi.org/10.3390/mi8010015 - 04 Jan 2017
Cited by 29 | Viewed by 3723
Abstract
In molecular and cellular biological research, cell isolation and sorting are required for accurate investigation of a specific cell types. By employing unique cell properties to distinguish between cell types, rapid and accurate sorting with high efficiency is possible. Though conventional methods can [...] Read more.
In molecular and cellular biological research, cell isolation and sorting are required for accurate investigation of a specific cell types. By employing unique cell properties to distinguish between cell types, rapid and accurate sorting with high efficiency is possible. Though conventional methods can provide high efficiency sorting using the specific properties of cell, microfluidics systems pave the way to utilize multiple cell properties in a single pass. This improves the selectivity of target cells from multiple cell types with increased purity and recovery rate while maintaining higher throughput comparable to conventional systems. This review covers the breadth of microfluidic platforms for isolation of cellular subtypes based on their intrinsic (e.g., electrical, magnetic, and compressibility) and extrinsic properties (e.g., size, shape, morphology and surface markers). The review concludes by highlighting the advantages and limitations of the reviewed techniques which then suggests future research directions. Addressing these challenges will lead to improved purity, throughput, viability and recovery of cells and be an enabler for novel downstream analysis of cells. Full article
(This article belongs to the Special Issue Microdevices and Microsystems for Cell Manipulation)
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Open AccessArticle
Tunable Clamped–Guided Arch Resonators Using Electrostatically Induced Axial Loads
Micromachines 2017, 8(1), 14; https://doi.org/10.3390/mi8010014 - 04 Jan 2017
Cited by 20 | Viewed by 2133
Abstract
We present a simulation and experimental investigation of bi-directional tunable in-plane clamped–guided arch microbeam resonators. Tensile and compressive axial forces are generated from a bi-directional electrostatic actuator, which modulates the microbeam stiffness, and hence changes its natural frequency to lower or higher values [...] Read more.
We present a simulation and experimental investigation of bi-directional tunable in-plane clamped–guided arch microbeam resonators. Tensile and compressive axial forces are generated from a bi-directional electrostatic actuator, which modulates the microbeam stiffness, and hence changes its natural frequency to lower or higher values from its as-fabricated value. Several devices of various anchor designs and geometries are fabricated. We found that for the fabricated shallow arches, the effect of the curvature of the arch is less important compared to the induced axial stress from the axial load. We have shown that the first mode resonance frequency can be increased up to twice its initial value. Additionally, the third mode resonance frequency can be increased up to 30% of its initial value. These results can be promising as a proof-of-concept for the realization of wide-range tunable microresonators. The experimental results have been compared to finite-element simulations, showing good agreement among them. Full article
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Open AccessArticle
Time-Efficient High-Resolution Large-Area Nano-Patterning of Silicon Dioxide
Micromachines 2017, 8(1), 13; https://doi.org/10.3390/mi8010013 - 04 Jan 2017
Cited by 2 | Viewed by 2338
Abstract
A nano-patterning approach on silicon dioxide (SiO2) material, which could be used for the selective growth of III-V nanowires in photovoltaic applications, is demonstrated. In this process, a silicon (Si) stamp with nanopillar structures was first fabricated using electron-beam lithography (EBL) [...] Read more.
A nano-patterning approach on silicon dioxide (SiO2) material, which could be used for the selective growth of III-V nanowires in photovoltaic applications, is demonstrated. In this process, a silicon (Si) stamp with nanopillar structures was first fabricated using electron-beam lithography (EBL) followed by a dry etching process. Afterwards, the Si stamp was employed in nanoimprint lithography (NIL) assisted with a dry etching process to produce nanoholes on the SiO2 layer. The demonstrated approach has advantages such as a high resolution in nanoscale by EBL and good reproducibility by NIL. In addition, high time efficiency can be realized by one-spot electron-beam exposure in the EBL process combined with NIL for mass production. Furthermore, the one-spot exposure enables the scalability of the nanostructures for different application requirements by tuning only the exposure dose. The size variation of the nanostructures resulting from exposure parameters in EBL, the pattern transfer during nanoimprint in NIL, and subsequent etching processes of SiO2 were also studied quantitatively. By this method, a hexagonal arranged hole array in SiO2 with a hole diameter ranging from 45 to 75 nm and a pitch of 600 nm was demonstrated on a four-inch wafer. Full article
(This article belongs to the Special Issue Scalable Micro/Nano Patterning)
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Open AccessReview
Towards Flexible Transparent Electrodes Based on Carbon and Metallic Materials
Micromachines 2017, 8(1), 12; https://doi.org/10.3390/mi8010012 - 04 Jan 2017
Cited by 31 | Viewed by 3661
Abstract
Flexible transparent electrodes (FTEs) with high stability and scalability are in high demand for the extremely widespread applications in flexible optoelectronic devices. Traditionally, thin films of indium thin oxide (ITO) served the role of FTEs, but film brittleness and scarcity of materials limit [...] Read more.
Flexible transparent electrodes (FTEs) with high stability and scalability are in high demand for the extremely widespread applications in flexible optoelectronic devices. Traditionally, thin films of indium thin oxide (ITO) served the role of FTEs, but film brittleness and scarcity of materials limit its further application. This review provides a summary of recent advances in emerging transparent electrodes and related flexible devices (e.g., touch panels, organic light-emitting diodes, sensors, supercapacitors, and solar cells). Mainly focusing on the FTEs based on carbon nanomaterials (e.g., carbon nanotubes and graphene) and metal materials (e.g., metal grid and metal nanowires), we discuss the fabrication techniques, the performance improvement, and the representative applications of these highly transparent and flexible electrodes. Finally, the challenges and prospects of flexible transparent electrodes will be summarized. Full article
(This article belongs to the Special Issue Flexible and Stretchable Electronics)
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Open AccessArticle
Design and Analysis of a Silicon-Based Pattern Reconfigurable Antenna Employing an Active Element Pattern Method
Micromachines 2017, 8(1), 11; https://doi.org/10.3390/mi8010011 - 04 Jan 2017
Viewed by 2094
Abstract
In this paper, a silicon-based radio frequency micro-electromechanical systems (RF MEMS) pattern reconfigurable antenna for a Ka-band application was designed, analyzed, fabricated, and measured. The proposed antenna can steer the beam among three radiating patterns (with main lobe directions of −20°, 0°, and [...] Read more.
In this paper, a silicon-based radio frequency micro-electromechanical systems (RF MEMS) pattern reconfigurable antenna for a Ka-band application was designed, analyzed, fabricated, and measured. The proposed antenna can steer the beam among three radiating patterns (with main lobe directions of −20°, 0°, and +20° approximately) at 35 GHz by switching RF MEMS operating modes. The antenna has a low profile with a small size of 3.7 mm × 4.4 mm × 0.4 mm, and consists of one driven patch, four parasitic patches, two assistant patches, and two RF MEMS switches. The active element pattern method integrated with signal flow diagram was employed to analyze the performances of the proposed antenna. Comparing the measured results with analytical and simulated ones, good agreements are obtained. Full article
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Open AccessArticle
Preparation of Protein Nanoparticles Using NTA End Functionalized Polystyrenes on the Interface of a Multi-Laminated Flow Formed in a Microchannel
Micromachines 2017, 8(1), 10; https://doi.org/10.3390/mi8010010 - 03 Jan 2017
Cited by 1 | Viewed by 2456
Abstract
This paper challenges the production of the protein nanoparticles using the conjugation of Ni2+ complexed nitrilotriacetic acid end-functionalized polystyrene (Ni-NTA-PS) and histidine tagged GFP (His-GFP) hybrid. The microfluidic synthesis of the protein nanoparticle with the advantages of a uniform size, a fast [...] Read more.
This paper challenges the production of the protein nanoparticles using the conjugation of Ni2+ complexed nitrilotriacetic acid end-functionalized polystyrene (Ni-NTA-PS) and histidine tagged GFP (His-GFP) hybrid. The microfluidic synthesis of the protein nanoparticle with the advantages of a uniform size, a fast reaction, and a precise control of preparation conditions is examined. The self-assembly occurs on the interfacial surface of the multi-laminated laminar flow stably formed in the microchannel. The clogging of the produced protein nanoparticles on the channel surface is solved by adding a retarding inlet channel. The size and shape of the produced protein nanoparticles are measured by the analysis of transmission electron microscopy (TEM) and scanning electron microscope (SEM) images, and the attachment of the protein is visualized with a green fluorescent image. Future research includes the encapsulation of vaccines and the coating of antigens on the protein surface. Full article
(This article belongs to the Special Issue Microfluidic Technologies for Drug Delivery)
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Open AccessArticle
Microfluidic Separation of a Soluble Substance Using Transverse Diffusion in a Layered Flow
Micromachines 2017, 8(1), 9; https://doi.org/10.3390/mi8010009 - 29 Dec 2016
Viewed by 2507
Abstract
This paper presents a practical flow-through method to separate anisole and ethyl phenylacetate, respectively, from a polystyrene mixture. The microfluidic separation uses different diffusive dynamics of the substances transverse to the lamination flow formed in a microchannel. The effect of inlet flow rates [...] Read more.
This paper presents a practical flow-through method to separate anisole and ethyl phenylacetate, respectively, from a polystyrene mixture. The microfluidic separation uses different diffusive dynamics of the substances transverse to the lamination flow formed in a microchannel. The effect of inlet flow rates and ambient temperature on separation is examined. Additionally, the possibility of the separation of the light substance from the mixture with different molecular weight is shown numerically and experimentally. The separation efficiency is explained by the facts that the relaxation time depends on the inlet flow rate and that the diffusivity depends on the ambient temperature. This method can be applied to separate monomers from aggregates. Full article
(This article belongs to the Special Issue Microfluidic Technologies for Drug Delivery)
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Open AccessFeature PaperReview
Materials, Mechanics, and Patterning Techniques for Elastomer-Based Stretchable Conductors
Micromachines 2017, 8(1), 7; https://doi.org/10.3390/mi8010007 - 27 Dec 2016
Cited by 36 | Viewed by 5791
Abstract
Stretchable electronics represent a new generation of electronics that utilize soft, deformable elastomers as the substrate or matrix instead of the traditional rigid printed circuit boards. As the most essential component of stretchable electronics, the conductors should meet the requirements for both high [...] Read more.
Stretchable electronics represent a new generation of electronics that utilize soft, deformable elastomers as the substrate or matrix instead of the traditional rigid printed circuit boards. As the most essential component of stretchable electronics, the conductors should meet the requirements for both high conductivity and the capability to maintain conductive under large deformations such as bending, twisting, stretching, and compressing. This review summarizes recent progresses in various aspects of this fascinating and challenging area, including materials for supporting elastomers and electrical conductors, unique designs and stretching mechanics, and the subtractive and additive patterning techniques. The applications are discussed along with functional devices based on these conductors. Finally, the review is concluded with the current limitations, challenges, and future directions of stretchable conductors. Full article
(This article belongs to the Special Issue Flexible and Stretchable Electronics)
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Open AccessArticle
Plasma Polymerization of SnOxCy Organic-Like Films and Grafted PNIPAAm Composite Hydrogel with Nanogold Particles for Promotion of Thermal Resistive Properties
Micromachines 2017, 8(1), 5; https://doi.org/10.3390/mi8010005 - 26 Dec 2016
Cited by 3 | Viewed by 2214
Abstract
In this study, a new type of temperature sensor device was developed. The circular electrode of the thermally sensitive sensor was modified with tetramethyltin (TMT) and O2 plasma to form a thin SnOxCy conductive layer on the electrode surface. [...] Read more.
In this study, a new type of temperature sensor device was developed. The circular electrode of the thermally sensitive sensor was modified with tetramethyltin (TMT) and O2 plasma to form a thin SnOxCy conductive layer on the electrode surface. The nano-Au particles (AuNPs) were subjected to O2 plasma pretreatment to form peroxide groups on the surface. The thermally sensitive sensor made by mixing the treated AuNPs with N-isopropylacrylamide (NIPAAm) solution and then applying UV-induced grafting polymerization of the NIPAAm-containing solution onto the electrode substrate. The composite hydrogels on the electrode introduce thermo-sensitive polymeric surface films for temperature sensing. Using the ambient environment resistance test to measure the resistance, the lower critical solution temperature (LCST) of AuNPs mixed with NIPAAm hydrogel was found to be 32 °C. In common metallic materials, the resistance increased during environmental temperature enhancement. In this study, at ambient temperatures higher than the LCST, the electrode resistance decreases linearly due to the shrinkage structure with AuNPs contacting the circuit electrode. Full article
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Open AccessFeature PaperReview
Vorticella: A Protozoan for Bio-Inspired Engineering
Micromachines 2017, 8(1), 4; https://doi.org/10.3390/mi8010004 - 26 Dec 2016
Cited by 15 | Viewed by 4040
Abstract
In this review, we introduce Vorticella as a model biological micromachine for microscale engineering systems. Vorticella has two motile organelles: the oral cilia of the zooid and the contractile spasmoneme in the stalk. The oral cilia beat periodically, generating a water flow that [...] Read more.
In this review, we introduce Vorticella as a model biological micromachine for microscale engineering systems. Vorticella has two motile organelles: the oral cilia of the zooid and the contractile spasmoneme in the stalk. The oral cilia beat periodically, generating a water flow that translates food particles toward the animal at speeds in the order of 0.1–1 mm/s. The ciliary flow of Vorticella has been characterized by experimental measurement and theoretical modeling, and tested for flow control and mixing in microfluidic systems. The spasmoneme contracts in a few milliseconds, coiling the stalk and moving the zooid at 15–90 mm/s. Because the spasmoneme generates tension in the order of 10–100 nN, powered by calcium ion binding, it serves as a model system for biomimetic actuators in microscale engineering systems. The spasmonemal contraction of Vorticella has been characterized by experimental measurement of its dynamics and energetics, and both live and extracted Vorticellae have been tested for moving microscale objects. We describe past work to elucidate the contraction mechanism of the spasmoneme, recognizing that past and continuing efforts will increase the possibilities of using the spasmoneme as a microscale actuator as well as leading towards bioinspired actuators mimicking the spasmoneme. Full article
(This article belongs to the Special Issue Bio-Inspired Micro/Nano Devices and Systems)
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Open AccessArticle
Single-Sided Digital Microfluidic (SDMF) Devices for Effective Coolant Delivery and Enhanced Two-Phase Cooling
Micromachines 2017, 8(1), 3; https://doi.org/10.3390/mi8010003 - 24 Dec 2016
Cited by 16 | Viewed by 3015
Abstract
Digital microfluidics (DMF) driven by electrowetting-on-dielectric (EWOD) has recently been attracting great attention as an effective liquid-handling platform for on-chip cooling. It enables rapid transportation of coolant liquid sandwiched between two parallel plates and drop-wise thermal rejection from a target heating source without [...] Read more.
Digital microfluidics (DMF) driven by electrowetting-on-dielectric (EWOD) has recently been attracting great attention as an effective liquid-handling platform for on-chip cooling. It enables rapid transportation of coolant liquid sandwiched between two parallel plates and drop-wise thermal rejection from a target heating source without additional mechanical components such as pumps, microchannels, and capillary wicks. However, a typical sandwiched configuration in DMF devices only allows sensible heat transfer, which seriously limits heat rejection capability, particularly for high-heat-flux thermal dissipation. In this paper, we present a single-sided digital microfluidic (SDMF) device that enables not only effective liquid handling on a single-sided surface, but also two-phase heat transfer to enhance thermal rejection performance. Several droplet manipulation functions required for two-phase cooling were demonstrated, including continuous droplet injection, rapid transportation as fast as 7.5 cm/s, and immobilization on the target hot spot where heat flux is locally concentrated. Using the SDMF platform, we experimentally demonstrated high-heat-flux cooling on the hydrophilic-coated hot spot. Coolant droplets were continuously transported to the target hot spot which was mitigated below 40 K of the superheat. The effective heat transfer coefficient was stably maintained even at a high heat flux regime over ~130 W/cm2, which will allow us to develop a reliable thermal management module. Our SDMF technology offers an effective on-chip cooling approach, particularly for high-heat-flux thermal management based on two-phase heat transfer. Full article
(This article belongs to the Special Issue Optofluidics 2016)
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Open AccessArticle
MEMS Gyroscopes Based on Acoustic Sagnac Effect
Micromachines 2017, 8(1), 2; https://doi.org/10.3390/mi8010002 - 24 Dec 2016
Cited by 6 | Viewed by 2871
Abstract
This paper reports on the design, fabrication and preliminary test results of a novel microelectromechanical systems (MEMS) device—the acoustic gyroscope. The unique operating mechanism is based on the “acoustic version” of the Sagnac effect in fiber-optic gyros. The device measures the phase difference [...] Read more.
This paper reports on the design, fabrication and preliminary test results of a novel microelectromechanical systems (MEMS) device—the acoustic gyroscope. The unique operating mechanism is based on the “acoustic version” of the Sagnac effect in fiber-optic gyros. The device measures the phase difference between two sound waves traveling in opposite directions, and correlates the signal to the angular velocity of the hosting frame. As sound travels significantly slower than light and develops a larger phase change within the same path length, the acoustic gyro can potentially outperform fiber-optic gyros in sensitivity and form factor. It also promises superior stability compared to vibratory MEMS gyros as the design contains no moving parts and is largely insensitive to mechanical stress or temperature. We have carried out systematic simulations and experiments, and developed a series of processes and design rules to implement the device. Full article
(This article belongs to the Special Issue Piezoelectric MEMS)
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Open AccessArticle
A Microfluidic Chip for Cell Patterning Utilizing Paired Microwells and Protein Patterns
Micromachines 2017, 8(1), 1; https://doi.org/10.3390/mi8010001 - 23 Dec 2016
Cited by 21 | Viewed by 5010
Abstract
Cell patterning has been widely used in research on fundamental cell biology and in applications such as tissue engineering, neuron network formation, cell based biosensor and drug screening. Although various methods have been developed, cell patterning in an enclosed microfluidic device at single [...] Read more.
Cell patterning has been widely used in research on fundamental cell biology and in applications such as tissue engineering, neuron network formation, cell based biosensor and drug screening. Although various methods have been developed, cell patterning in an enclosed microfluidic device at single cell level remains challenging. This paper describes a microfluidic device with microwells and protein patterns paired together in a single microchannel for an easy cell patterning. Cells captured in the microwells were positioned directly onto the protein patterns within 5 min and the patterning performance was successfully demonstrated using HeLa cells and human gallbladder carcinoma cells (SGC-996). Cells survived for 6 days in the microchannel. Cell attachment, migration, proliferation and cell colony formation were observed. Our device is free of topographic constraint for the patterned cells and no complex chemical modification to the substrate is needed, offering a simple, fast, and easy-to-operate way of patterning cells at single cell level in an enclosed microfluidic channel. Full article
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