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Micromachines, Volume 9, Issue 4 (April 2018)

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Open AccessArticle Mode Transition of Droplet Formation in a Semi-3D Flow-Focusing Microfluidic Droplet System
Micromachines 2018, 9(4), 139; doi:10.3390/mi9040139
Received: 8 February 2018 / Revised: 7 March 2018 / Accepted: 19 March 2018 / Published: 21 March 2018
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Abstract
Uniform droplets have significant potential in many biological applications due to their higher surface area to volume ratio. This paper proposed a semi-three-dimensional (sime-3D) flow-focusing microfluidic system, which was fabricated using the multi-layer soft lithography method. Based on the semi-3D structure, we focus
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Uniform droplets have significant potential in many biological applications due to their higher surface area to volume ratio. This paper proposed a semi-three-dimensional (sime-3D) flow-focusing microfluidic system, which was fabricated using the multi-layer soft lithography method. Based on the semi-3D structure, we focus on droplets formation modes and droplet uniformity at different bulk concentration of surfactant. The relationships between droplets uniformity, droplets breakup processes (jetting mode, dripping mode and tip-streaming mode) and surfactant concentration was investigated. It was found that three droplet generation modes occur through adjusting the pressure ratio in two inlet channels and the concentration of surfactant in continuous phase liquid. The jetting mode would transform to the dripping mode or the tip-streaming mode as the pressure ratio in different surfactant concentrations increased. Furthermore, the uniformity of droplets could be improved through the transition of jetting to dripping mode. We assumed that the uniformity declined through the transition of jetting to tip-streaming, and explored the specific transitions from jetting to dripping mode and tip-streaming mode. Dripping mode leads to high droplet uniformity, and generation frequency decreases with increasing pressure ratio. Tip-streaming mode is considered as an extreme state of jetting mode, leading to higher formation frequency and smaller droplet size at low uniformity. Full article
(This article belongs to the Special Issue Droplet Microfluidics: Techniques and Technologies, Volume II)
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Open AccessArticle A Microfluidic Lab-on-a-Disc (LOD) for Antioxidant Activities of Plant Extracts
Micromachines 2018, 9(4), 140; doi:10.3390/mi9040140
Received: 13 January 2018 / Revised: 15 March 2018 / Accepted: 19 March 2018 / Published: 21 March 2018
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Abstract
Antioxidants are an important substance that can fight the deterioration of free radicals and can easily oxidize when exposed to light. There are many methods to measure the antioxidant activity in a biological sample, for example 2,2-diphenyl-1-picrylhydrazyl (DPPH) antioxidant activity test, which is
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Antioxidants are an important substance that can fight the deterioration of free radicals and can easily oxidize when exposed to light. There are many methods to measure the antioxidant activity in a biological sample, for example 2,2-diphenyl-1-picrylhydrazyl (DPPH) antioxidant activity test, which is one of the simplest methods used. Despite its simplicity, the organic solvent that has been used to dilute DPPH is easily evaporated and degraded with respect to light exposure and time. Thus, it needs to be used at the earliest convenient time prior to the experiment. To overcome this issue, a rapid and close system for antioxidant activity is required. In this paper, we introduced the Lab-on-a-Disc (LoD) method that integrates the DPPH antioxidant activity test on a microfluidic compact disc (CD). We used ascorbic acid, quercetin, Areca catechu, Polygonum minus, and Syzygium polyanthum plant extracts to compare the results of our proposed LoD method with the conventional method. Contrasted to the arduous laborious conventional method, our proposed method offer rapid analysis and simple determination of antioxidant. This proposed LoD method for antioxidant activity in plants would be a platform for the further development of antioxidant assay. Full article
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Open AccessArticle Robotic Cell Rotation Based on Optimal Poking Direction
Micromachines 2018, 9(4), 141; doi:10.3390/mi9040141
Received: 31 January 2018 / Revised: 9 March 2018 / Accepted: 20 March 2018 / Published: 22 March 2018
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Abstract
It is essential to have three-dimensional orientation of cells under a microscope for biological manipulation. Conventional manual cell manipulation is highly dependent on the operator’s experience. It has some problems of low repeatability, low efficiency, and contamination. The current popular robotic method uses
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It is essential to have three-dimensional orientation of cells under a microscope for biological manipulation. Conventional manual cell manipulation is highly dependent on the operator’s experience. It has some problems of low repeatability, low efficiency, and contamination. The current popular robotic method uses an injection micropipette to rotate cells. However, the optimal poking direction of the injection micropipette has not been established. In this paper, a strategy of robotic cell rotation based on optimal poking direction is proposed to move the specific structure of the cell to the desired orientation. First, analysis of the force applied to the cell during rotation was done to find the optimal poking direction, where we had the biggest moment of force. Then, the moving trajectory of the injection micropipette was designed to exert rotation force based on optimal poking direction. Finally, the strategy was applied to oocyte rotation in nuclear transfer. Experimental results show that the average completion time was up to 23.6 s and the success rate was 93.3% when the moving speed of the injection micropipette was 100 μm/s, which demonstrates that our strategy could overcome slippage effectively and with high efficiency. Full article
(This article belongs to the Special Issue Micro/Nano Robotics, Volume II)
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Open AccessArticle Matrix Effect Study and Immunoassay Detection Using Electrolyte-Gated Graphene Biosensor
Micromachines 2018, 9(4), 142; doi:10.3390/mi9040142
Received: 12 February 2018 / Revised: 8 March 2018 / Accepted: 21 March 2018 / Published: 23 March 2018
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Abstract
Significant progress has been made on the development of electrolyte-gated graphene field effect transistor (EGGFET) biosensors over the last decade, yet they are still in the stage of proof-of-concept. In this work, we studied the electrolyte matrix effects, including its composition, pH and
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Significant progress has been made on the development of electrolyte-gated graphene field effect transistor (EGGFET) biosensors over the last decade, yet they are still in the stage of proof-of-concept. In this work, we studied the electrolyte matrix effects, including its composition, pH and ionic strength, and demonstrate that variations in electrolyte matrices have a significant impact on the Fermi level of the graphene channel and the sensitivity of the EGGFET biosensors. This is attributed to the polarization-induced interaction between the electrolyte and the graphene at the interface which can lead to considerable modulation of the Fermi level of the graphene channel. As a result, the response of the EGGFET biosensors is susceptible to the matrix effect which might lead to high uncertainty or even false results. Then, an EGGFET immunoassay is presented which aims to allow good regulation of the matrix effect. The multichannel design allows in-situ calibration with negative control, as well as statistical validation of the measurement results. Its performance is demonstrated by the detection of human immunoglobulin G (IgG) from serum. The detection range is estimated to be around 2–50 nM with a coefficient of variation (CV) of less than 20% and the recovery rate for IgG detection is around 85–95%. Compared with traditional immunoassay techniques, the EGGFET immunoassay is label-free and ready to be integrated with microfluidics sensor platforms, suggesting its great prospect for point-of-care applications. Full article
(This article belongs to the Special Issue Biomedical Applications of Nanotechnology and Nanomaterials)
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Open AccessArticle Improving Electrophoretic Particle Motion Control in Electrophoretic Displays by Eliminating the Fringing Effect via Driving Waveform Design
Micromachines 2018, 9(4), 143; doi:10.3390/mi9040143
Received: 31 January 2018 / Revised: 19 March 2018 / Accepted: 20 March 2018 / Published: 23 March 2018
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Abstract
Electrophoretic display is realized by controlling colored nanoparticles moving in micrometer spaces via electrophoresis. The quality of information display is therefore affected by the unsynchronized particle moving speed and the mismatched electric signal according to the crosstalk of the electric field and inhomogeneous
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Electrophoretic display is realized by controlling colored nanoparticles moving in micrometer spaces via electrophoresis. The quality of information display is therefore affected by the unsynchronized particle moving speed and the mismatched electric signal according to the crosstalk of the electric field and inhomogeneous material distribution. In this work, we analyzed the mechanism of a fringe phenomenon that affected the information display quality of electrophoretic displays (EPDs). Electrical driving waveforms (voltage signals) are designed to reduce the fringe phenomenon. By using the optimizing driving waveform, we proposed that the fringe phenomenon is quantified as gray value that can be diminished by 25.5, while keeping a response time of 200 ms. Full article
(This article belongs to the Special Issue Micro/Nano-Chip Electrokinetics, Volume II)
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Open AccessArticle A Magnetic-Field-Assisted Milli-Scale Robotic Assembly Machine: An Approach to Parallel Robotic Automation Systems
Micromachines 2018, 9(4), 144; doi:10.3390/mi9040144
Received: 5 February 2018 / Revised: 18 March 2018 / Accepted: 21 March 2018 / Published: 23 March 2018
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Abstract
Utilizing large numbers of microrobots to heterogeneously integrate small devices to build advanced structures has long been a goal in the field of manufacturing automation. In this paper, we demonstrate a novel milli-scale robotic assembly machine with highly parallel capabilities and assisted with
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Utilizing large numbers of microrobots to heterogeneously integrate small devices to build advanced structures has long been a goal in the field of manufacturing automation. In this paper, we demonstrate a novel milli-scale robotic assembly machine with highly parallel capabilities and assisted with a programmable magnetic field. The prototype machine consists of a 16 × 16 array of electromagnets. Using this machine, we have successfully demonstrated the manipulation of up to nine milli-scale robots simultaneously. Moreover, two microrobots have been operated to demonstrate the proof of concept of two simultaneous pick-and-place light-emitting diodes (LEDs). The design and modeling of the microrobots is discussed. Full article
(This article belongs to the Special Issue Micro/Nano Robotics, Volume II)
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Open AccessArticle Investigation on Surface Integrity of Rapidly Solidified Aluminum RSA 905 by Magnetic Field-Assisted Finishing
Micromachines 2018, 9(4), 146; doi:10.3390/mi9040146
Received: 31 January 2018 / Revised: 20 March 2018 / Accepted: 20 March 2018 / Published: 25 March 2018
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Abstract
RSA 905, a rapidly solidified aluminum alloy, has been widely utilized in optical, automotive, and aerospace industries owing to its superior mechanical properties such as hardness and strength compared to conventional aluminum alloys. However, the surface finishing of RSA 905 to achieve submicron
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RSA 905, a rapidly solidified aluminum alloy, has been widely utilized in optical, automotive, and aerospace industries owing to its superior mechanical properties such as hardness and strength compared to conventional aluminum alloys. However, the surface finishing of RSA 905 to achieve submicron surface roughness is quite challenging and was rarely addressed. This paper presents an experimental and analytical study on magnetic field-assisted finishing (MFAF) of RSA 905 through a systematic investigation on surface integrity in relation to the MFAF process parameters. The effect of abrasive and polishing speed conditions on material removal and surface roughness was quantitatively investigated. The surface and subsurface quality were evaluated by optical microscope and scanning electron microscope (SEM) observations, residual stress measurement, surface microhardness and tribology test. The results show that relatively high material removal and low surface roughness were obtained under conditions using the SiC abrasive with a grit size of 12 µm at polishing speed of 400 rpm or using the Al2O3 abrasive with a grit size of 5 µm at polishing speed of 800 rpm. Heat melt layer caused by wire electrical discharge machining (EDM) during the sample preparation was removed by MFAF without inducing new subsurface damage. The MFAF process also helps release the surface residual stress and improve the tribological performance although the surface microhardness was slightly reduced. Full article
(This article belongs to the Special Issue Micro-Machining: Challenges and Opportunities)
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Open AccessArticle A DLC-Punch Array to Fabricate the Micro-Textured Aluminum Sheet for Boiling Heat Transfer Control
Micromachines 2018, 9(4), 147; doi:10.3390/mi9040147
Received: 31 December 2017 / Revised: 21 March 2018 / Accepted: 23 March 2018 / Published: 25 March 2018
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Abstract
A diamond-like carbon (DLC) film, coated on an SKD11 (alloy tool steel) substrate, was shaped by plasma oxidation to form an assembly of DLC macro-pillars and to be used as a DLC-punch array that is micro-embossed into aluminum sheets. First, the SKD11 steel
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A diamond-like carbon (DLC) film, coated on an SKD11 (alloy tool steel) substrate, was shaped by plasma oxidation to form an assembly of DLC macro-pillars and to be used as a DLC-punch array that is micro-embossed into aluminum sheets. First, the SKD11 steel die substrate was prepared and DLC-coated to have a film thickness of 10 μm. This DLC coating worked as a punch material. The two-dimensional micro-patterns were printed onto this DLC film by maskless lithography. The unprinted DLC films were selectively removed by plasma oxidation to leave the three-dimensional DLC-punch array on the SKD11 substrate. Each DLC punch had a head of 3.5 μm × 3.5 μm and a height of 8 μm. This DLC-punch array was fixed into the cassette die set for a micro-embossing process using a table-top servo-stamper. Furthermore, through numerically controlled micro-embossing, an alignment of rectangular punches was transcribed into a micro-cavity array in the aluminum sheet. The single micro-cavity had a bottom surface of 3.2 μm × 3.2 μm and an average depth of 7.5 μm. A heat-transfer experiment in boiling water was also performed to investigate the effect of micro-cavity texture on bubbling behavior and the boiling curve. Full article
(This article belongs to the Special Issue Carbon Based Materials for MEMS/NEMS)
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Open AccessArticle Advanced Fabrication of Single-Crystal Diamond Membranes for Quantum Technologies
Micromachines 2018, 9(4), 148; doi:10.3390/mi9040148
Received: 20 February 2018 / Revised: 21 March 2018 / Accepted: 22 March 2018 / Published: 25 March 2018
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Abstract
Many promising applications of single crystal diamond and its color centers as sensor platform and in photonics require free-standing membranes with a thickness ranging from several micrometers to the few 100 nm range. In this work, we present an approach to conveniently fabricate
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Many promising applications of single crystal diamond and its color centers as sensor platform and in photonics require free-standing membranes with a thickness ranging from several micrometers to the few 100 nm range. In this work, we present an approach to conveniently fabricate such thin membranes with up to about one millimeter in size. We use commercially available diamond plates (thickness 50 μ m) in an inductively coupled reactive ion etching process which is based on argon, oxygen and SF 6 . We thus avoid using toxic, corrosive feed gases and add an alternative to previously presented recipes involving chlorine-based etching steps. Our membranes are smooth (RMS roughness <1 nm) and show moderate thickness variation (central part: <1 μ m over ≈200 × 200 μ m 2 ). Due to an improved etch mask geometry, our membranes stay reliably attached to the diamond plate in our chlorine-based as well as SF 6 -based processes. Our results thus open the route towards higher reliability in diamond device fabrication and up-scaling. Full article
(This article belongs to the Special Issue Color Centers in Diamond: Fabrication, Devices and Applications)
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Open AccessArticle Paper-Based Sensor Chip for Heavy Metal Ion Detection by SWSV
Micromachines 2018, 9(4), 150; doi:10.3390/mi9040150
Received: 26 February 2018 / Revised: 24 March 2018 / Accepted: 26 March 2018 / Published: 27 March 2018
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Abstract
Heavy metal ion pollution problems have had a terrible influence on human health and the environment. Therefore, the monitoring of heavy metal ions is of great practical significance. In this paper, an electrochemical three-electrode system was fabricated and integrated on nitrocellulose membrane (NC)
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Heavy metal ion pollution problems have had a terrible influence on human health and the environment. Therefore, the monitoring of heavy metal ions is of great practical significance. In this paper, an electrochemical three-electrode system was fabricated and integrated on nitrocellulose membrane (NC) by the use of magnetron sputtering technology, which exhibited a uniform arrangement of porous structure without further film modification. This paper-based sensor chip was used for Cu2+ detection by square-wave stripping voltammetry (SWSV). Within the ranges of 5~200 μg·L−1 and 200~1000 μg·L−1, it showed good linearity of 99.58% and 98.87%, respectively. The limit of detection was 2 μg·L−1. On the basis of satisfying the detection requirements (10 μg·L−1), the integrated sensor was small in size and inexpensive in cost. Zn2+, Cd2+, Pb2+ and Bi3+ were also detected by this paper-based sensor chip with good linearity. Full article
(This article belongs to the Special Issue Paper-Based Transducers and Electronics)
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Open AccessArticle A Control and Detecting System of Micro-Near-Infrared Spectrometer Based on a MOEMS Scanning Grating Mirror
Micromachines 2018, 9(4), 152; doi:10.3390/mi9040152
Received: 3 February 2018 / Revised: 23 March 2018 / Accepted: 26 March 2018 / Published: 27 March 2018
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Abstract
Based on the scanning grating mirror we developed, this paper presents a method of the precise control of a scanning grating mirror and of high-speed spectrum data detection. In addition, the system circuit of the scanning grating mirror control and spectrum signal detecting
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Based on the scanning grating mirror we developed, this paper presents a method of the precise control of a scanning grating mirror and of high-speed spectrum data detection. In addition, the system circuit of the scanning grating mirror control and spectrum signal detecting is designed and manufactured in this paper. The mirror control system includes a drive generator module, an amplitude detection module, a feedback control module, and a variable gain amplification (VGA) module; the detecting system includes a field programmable gate array (FPGA) main control module, a synchronous trigger module, an analog-digital conversion (ADC) module, and a universal serial bus (USB) interface module. The final results of the experiment show that the control system has successfully realized the precision control of the swing of the scanning grating mirror and that the detecting system has successfully realized the high-speed acquisition and transmission of the spectral signal and the angle signals. The spectrum has been reconstructed according to the mathematical relationship between the wavelength λ and the angle β of the mirror. The resolution of the spectrometer reaches 10 nm in the wavelength range of 800–1800 nm, the signal-to-noise ratio (SNR) of the spectrometer is 4562 at full scale, the spectrum data drift is 0.9% in 24 h, and the precision of the closed loop control is 0.06%. Full article
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Open AccessArticle Capillary Rise of Nanostructured Microwicks
Micromachines 2018, 9(4), 153; doi:10.3390/mi9040153
Received: 10 February 2018 / Revised: 21 March 2018 / Accepted: 26 March 2018 / Published: 28 March 2018
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Abstract
Capillarity refers to the driving force to propel liquid through small gaps in the absence of external forces, and hence enhanced capillary force has been pursued for various applications. In this study, flower like ZnO nanostructures are successfully deposited to enhance capillarity of
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Capillarity refers to the driving force to propel liquid through small gaps in the absence of external forces, and hence enhanced capillary force has been pursued for various applications. In this study, flower like ZnO nanostructures are successfully deposited to enhance capillarity of microwick structures that are specially designed to augment boiling heat transfer performance. Microreactor-assisted nanomaterial deposition, MANDTM, is employed with a flow cell to deposit the ZnO nanostructures on a large sized microwick (4.3 cm × 10.7 cm) with dual-channel configuration. A capillary rise experiment based on the mass gain method is first performed using water and ethanol (EtOH) as the working liquids to demonstrate the enhanced capillary force induced by the ZnO nanostructure on the microwick structure. It is found that the coating of ZnO nanostructure effectively propels the working fluids through the nano- or micro pores created from the ZnO nanostructure and consequently improves the capillary force. In order to investigate the wicking mechanism of the ZnO coated microwick structure, the capillary rise result based on height measurement was compared with analytical models. It is found that the gravity effect and viscous force play an important role in wicking rise of the coated wick structure. This study aims at demonstrating the capability of the integrated MAND process with a flow cell for producing a large scaled nanostructured surface, which eventually has a great potential for enhanced boiling heat transfer. Full article
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Open AccessArticle DC-25 GHz and Low-Loss MEMS Thermoelectric Power Sensors with Floating Thermal Slug and Reliable Back Cavity Based on GaAs MMIC Technology
Micromachines 2018, 9(4), 154; doi:10.3390/mi9040154
Received: 22 February 2018 / Revised: 26 March 2018 / Accepted: 27 March 2018 / Published: 29 March 2018
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Abstract
Wideband and low-loss microwave power measurements are becoming increasingly important for microwave communication and radar systems. To achieve such a power measurement, this paper presents the design and measurement of wideband DC-25 GHz and low-loss MEMS thermoelectric power sensors with a floating thermal
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Wideband and low-loss microwave power measurements are becoming increasingly important for microwave communication and radar systems. To achieve such a power measurement, this paper presents the design and measurement of wideband DC-25 GHz and low-loss MEMS thermoelectric power sensors with a floating thermal slug and a reliable back cavity. In the sensors, the microwave power is converted to thermovoltages via heat. The collaborative design of the thermal slug and the back cavity, i.e., two thermal flow paths, is utilized to improve the efficiency of heat transfer and to ensure reliable applications. These sensors are required to operate up to 25 GHz. In order to achieve low microwave losses at the bandwidth, the floating thermal slug is designed instead of the grounded one. The effects of the floating slug on the reflection losses are analyzed by the simulation. The fabrication of these sensors is completed by GaAs monolithic microwave integrated circuits (MMIC) and micro-electro-mechanical systems (MEMS) technology. Measured reflection losses are less than −25.6 dB up to 12 GHz and −18.6 dB up to 25 GHz. The design of the floating thermal slug reduces the losses, which is equivalent to improving the sensitivity. At 10 and 25 GHz, experiments exhibit that the sensors result in sensitivities of about 51.13 and 35.28 μV/mW for the floating slug and 81.68 and 55.20 μV/mW for the floating slug and the cavity. Full article
(This article belongs to the Special Issue MEMS/NEMS Sensors: Fabrication and Application)
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Open AccessArticle Electroosmotic Flow of Viscoelastic Fluid in a Nanoslit
Micromachines 2018, 9(4), 155; doi:10.3390/mi9040155
Received: 7 March 2018 / Revised: 22 March 2018 / Accepted: 26 March 2018 / Published: 29 March 2018
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Abstract
The electroosmotic flow (EOF) of viscoelastic fluid in a long nanoslit is numerically studied to investigate the rheological property effect of Linear Phan-Thien-Tanner (LPTT) fluid on the fully developed EOF. The non-linear Poisson-Nernst-Planck equations governing the electric potential and the ionic concentration distribution
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The electroosmotic flow (EOF) of viscoelastic fluid in a long nanoslit is numerically studied to investigate the rheological property effect of Linear Phan-Thien-Tanner (LPTT) fluid on the fully developed EOF. The non-linear Poisson-Nernst-Planck equations governing the electric potential and the ionic concentration distribution within the channel are adopted to take into account the effect of the electrical double layer (EDL), including the EDL overlap. When the EDL is not overlapped, the velocity profiles for both Newtonian and viscoelastic fluids are plug-like and increase sharply near the charged wall. The velocity profile resembles that of pressure-driven flow when the EDL is overlapped. Regardless of the EDL thickness, apparent increase of velocity is obtained for viscoelastic fluid of larger Weissenberg number compared to the Newtonian fluid, indicating the shear thinning behavior of the LPTT fluid. The effect of the Weissenberg number on the velocity distribution is less significant as the degree of EDL overlapping increases, due to the overall decrease of the shear rate. The increase (decrease) of polymer extensibility (viscosity ratio) also enhances the EOF of viscoelastic fluid. Full article
(This article belongs to the Special Issue Micro/Nano-Chip Electrokinetics, Volume II)
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Open AccessArticle An FEP Microfluidic Reactor for Photochemical Reactions
Micromachines 2018, 9(4), 156; doi:10.3390/mi9040156
Received: 28 February 2018 / Revised: 23 March 2018 / Accepted: 28 March 2018 / Published: 30 March 2018
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Abstract
Organic syntheses based on photochemical reactions play an important role in the medical, pharmaceutical, and polymeric chemistry. For years, photochemistry was performed using high-pressure mercury lamps and immersion-wells. However, due to excellent yield, control of temperature, selectivity, low consumption of reagents and safety,
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Organic syntheses based on photochemical reactions play an important role in the medical, pharmaceutical, and polymeric chemistry. For years, photochemistry was performed using high-pressure mercury lamps and immersion-wells. However, due to excellent yield, control of temperature, selectivity, low consumption of reagents and safety, the microreactors made of fluorinated ethylene propylene (FEP) tubings have recently been used more frequently. Fluoropolymers are the material of choice for many types of syntheses due to their chemical compatibility and low surface energy. The use of tubing restricts the freedom in designing 2D and 3D geometries of the sections of the microreactors, mixing sections, etc., that are easily achievable in the format of a planar chip. A chip microreactor made of FEP is impracticable to develop due to its high chemical inertness and high melting temperature, both of which make it difficult (or impossible) to bond two plates of polymer. Here, we demonstrate a ‘click’ system, where the two plates of FEP are joined together mechanically using a tenon and a mortise. The concept was presented by us previously for a preparation polytetrafluoroethylene (PTFE) microreactor (Szymborski et al. Sensors Actuators, B Chem. 2017, doi:10.1016/j.snb.2017.09.035). Here, we use the same strategy for FEP plates, test the use of the chips in photochemistry and also describe a custom-designed non-transparent polyethylene (PE) mask-holder with a circular opening to guide and focus the ultraviolet (UV) illumination. The solutions that we describe offer tight microreactor chips, preventing any leakage either of the liquid reagents or of UV light outside the reactor. This allows for conducting photochemical synthesis without a fume hood and without special protection against UV radiation. Full article
(This article belongs to the Special Issue Integrated Microfluidics for Chemical Synthesis and Analysis)
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Open AccessArticle A Microfluidic Chip with Double-Slit Arrays for Enhanced Capture of Single Cells
Micromachines 2018, 9(4), 157; doi:10.3390/mi9040157
Received: 5 March 2018 / Revised: 27 March 2018 / Accepted: 29 March 2018 / Published: 1 April 2018
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Abstract
The application of microfluidic technology to manipulate cells or biological particles is becoming one of the rapidly growing areas, and various microarray trapping devices have recently been designed for high throughput single-cell analysis and manipulation. In this paper, we design a double-slit microfluidic
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The application of microfluidic technology to manipulate cells or biological particles is becoming one of the rapidly growing areas, and various microarray trapping devices have recently been designed for high throughput single-cell analysis and manipulation. In this paper, we design a double-slit microfluidic chip for hydrodynamic cell trapping at the single-cell level, which maintains a high capture ability. The geometric effects on flow behaviour are investigated in detail for optimizing chip architecture, including the flow velocity, the fluid pressure, and the equivalent stress of cells. Based on the geometrical parameters optimized, the double-slit chip enhances the capture of HeLa cells and the drug experiment verifies the feasibility of the drug delivery. Full article
(This article belongs to the Special Issue Microfluidics for Cell-Based Assays)
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Open AccessArticle Electric Power Self-Supply Module for WSN Sensor Node Based on MEMS Vibration Energy Harvester
Micromachines 2018, 9(4), 161; doi:10.3390/mi9040161
Received: 15 January 2018 / Revised: 21 March 2018 / Accepted: 28 March 2018 / Published: 1 April 2018
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Abstract
This paper proposes an electric power self-supply module for the wireless sensor network (WSN) sensor node. The module includes an electromagnetic vibration energy harvester based on micro-electro-mechanical system (MEMS) technology and a processing circuit. The vibration energy harvester presented in this paper is
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This paper proposes an electric power self-supply module for the wireless sensor network (WSN) sensor node. The module includes an electromagnetic vibration energy harvester based on micro-electro-mechanical system (MEMS) technology and a processing circuit. The vibration energy harvester presented in this paper is fabricated by an integrated microfabrication process and consists of four similar and relatively independent beam vibration elements. The main functions of the processing circuit are to convert the output of the harvester from unstable alternating current (AC) to stable direct current (DC), charge the super capacitor, and ensure the stable output of the super capacitor. The preliminary test results of the harvester chip show that the chip can output discontinuous pulse voltage, and the range of the voltage value is from tens to hundreds of millivolts in the vibration frequency range of 10–90 Hz. The maximum value that can be reached is 563 mV (at the vibration frequency of 18 Hz). The results of the test show that the harvester can output a relatively high voltage, which can meet the general electric power demand of a WSN sensor node. Full article
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Open AccessArticle SF6 Optimized O2 Plasma Etching of Parylene C
Micromachines 2018, 9(4), 162; doi:10.3390/mi9040162
Received: 3 February 2018 / Revised: 23 March 2018 / Accepted: 27 March 2018 / Published: 2 April 2018
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Abstract
Parylene C is a widely used polymer material in microfabrication because of its excellent properties such as chemical inertness, biocompatibility and flexibility. It has been commonly adopted as a structural material for a variety of microfluidics and bio-MEMS (micro-electro-mechanical system) applications. However, it
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Parylene C is a widely used polymer material in microfabrication because of its excellent properties such as chemical inertness, biocompatibility and flexibility. It has been commonly adopted as a structural material for a variety of microfluidics and bio-MEMS (micro-electro-mechanical system) applications. However, it is still difficult to achieve a controllable Parylene C pattern, especially on film thicker than a couple of micrometers. Here, we proposed an SF6 optimized O2 plasma etching (SOOE) of Parylene C, with titanium as the etching mask. Without the SF6, noticeable nanoforest residuals were found on the O2 plasma etched Parylene C film, which was supposed to arise from the micro-masking effect of the sputtered titanium metal mask. By introducing a 5-sccm SF6 flow, the residuals were effectively removed during the O2 plasma etching. This optimized etching strategy achieved a 10 μm-thick Parylene C etching with the feature size down to 2 μm. The advanced SOOE recipes will further facilitate the controllable fabrication of Parylene C microstructures for broader applications. Full article
(This article belongs to the Special Issue Polymer Based MEMS and Microfabrication)
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Open AccessArticle PDMS-PDMS Micro Channels Filled with Phase-Change Material for Chip Cooling
Micromachines 2018, 9(4), 165; doi:10.3390/mi9040165
Received: 24 February 2018 / Revised: 30 March 2018 / Accepted: 1 April 2018 / Published: 2 April 2018
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Abstract
This paper reports on a chip cooling solution using polydimethylsiloxane (PDMS) based microfluidic devices filled with n-Octadecane. A thick SU-8 layer of 150 µm is used as the master mold for patterning PDMS fabrication. With the SU-8 mold, patterns with straight lines
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This paper reports on a chip cooling solution using polydimethylsiloxane (PDMS) based microfluidic devices filled with n-Octadecane. A thick SU-8 layer of 150 µm is used as the master mold for patterning PDMS fabrication. With the SU-8 mold, patterns with straight lines at microscale have been fabricated with standard micro-electro-mechanical system (MEMS) technology. Thermal polymer bonding technique is used to bond the PDMS pattern directly to a flat polydimethylsiloxane (PDMS) film which results in the sealed microchannels. n-Octadecane as a phase-change material has been successfully filled in the microchannels using a dispensing machine. Infrared thermal image shows a sharp contrast of the temperature distribution between the chip with n-Octadecane and the empty chip during the same heating process. This result indicates an efficient cooling performance of the microchannel device with phase-change material. A thermal stimulation test demonstrates that a 16 °C-lower temperature difference can be achieved. This microchannel device, benefited from the flexibility of PDMS substrate, shows specific advantages in meeting the need for the heat dissipation of flexible electronics such as flexible displays, electronic skins, and wearable electronics. Latent heat of the phase-change material can keep the temperature of devices relatively lower over a period of time, which shows potential application values on discontinuously active flexible electronic devices. Full article
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Open AccessArticle Manufacturing of a Compact Micro Air Bearing Device for Power Micro Electro Mechanical System (MEMS) Applications Using Silica Film Assisted Processing
Micromachines 2018, 9(4), 166; doi:10.3390/mi9040166
Received: 11 January 2018 / Revised: 25 March 2018 / Accepted: 29 March 2018 / Published: 2 April 2018
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Abstract
The focus of this study is on the manufacturing of micro air bearings (MABs) using silica film assisted processing. Structure of the three-layer micro air bearing is described in detail and the salient process flow of etching and bonding is illustrated. The main
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The focus of this study is on the manufacturing of micro air bearings (MABs) using silica film assisted processing. Structure of the three-layer micro air bearing is described in detail and the salient process flow of etching and bonding is illustrated. The main manufacturing challenges and the methods adopted to overcome them are also presented. The uniformity of wet etching for nozzles with 20 μm in diameter to silica film is improved by adopting an ultrasound assisted method. Particular attention is given to the novel fabrication procedures for the second layer of MAB (with three depths on aft side). This paper develops new applications of silica film in Micro Electro Mechanical System (MEMS) processing for MABs to realize the etching of multi-depth on the same side and efficient three-layer bonding with increased bonding areas. A silica etch mask is proven to achieve a higher accuracy in surface topography when compared to a photoresist mask for multi-depth etching, resulting in precise depth and vertical control. The bonding rate of three-layer direct bonding for MAB is increased by 50% from 0.05 to 0.1 with the novel silica film protection method. Full article
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Open AccessArticle A Visualization Technique of a Unique pH Distribution around an Ion Depletion Zone in a Microchannel by Using a Dual-Excitation Ratiometric Method
Micromachines 2018, 9(4), 167; doi:10.3390/mi9040167
Received: 8 March 2018 / Revised: 25 March 2018 / Accepted: 27 March 2018 / Published: 2 April 2018
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Abstract
The ion depletion zone of ion concentration polarization has a strong potential to act as an immaterial barrier, separating delicate submicron substances, including biomolecules, without causing physical damage. However, the detailed mechanisms of the barrier effect remain incompletely understood because it is difficult
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The ion depletion zone of ion concentration polarization has a strong potential to act as an immaterial barrier, separating delicate submicron substances, including biomolecules, without causing physical damage. However, the detailed mechanisms of the barrier effect remain incompletely understood because it is difficult to visualize the linked behavior of protons, cations, anions, and charged molecules in the thin ion depletion zone. In this study, pH distribution in an ion depletion zone was measured to estimate the role of proton behavior. This was done in order to use it as a tool with good controllability for biomolecule handling in the future. As a result, a unique pH peak was observed at several micrometers distance from the microchannel wall. The position of the peak appeared to be in agreement with the boundary of the ion depletion zone. From this agreement, it is expected that the pH peak has a causal connection to the barrier effect of the ion depletion zone. Full article
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Open AccessArticle Analytical Model and Experimental Evaluation of the Micro-Scale Thermal Property Sensor for Single-Sided Measurement
Micromachines 2018, 9(4), 168; doi:10.3390/mi9040168
Received: 13 March 2018 / Revised: 29 March 2018 / Accepted: 2 April 2018 / Published: 5 April 2018
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Abstract
We report a new analytical model of the MEMS-based thermal property sensor for samples which are difficult to handle and susceptible to damage by thermal stimulus, such as living cells. Many sensor designs had been reported for thermal property measurements, but only a
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We report a new analytical model of the MEMS-based thermal property sensor for samples which are difficult to handle and susceptible to damage by thermal stimulus, such as living cells. Many sensor designs had been reported for thermal property measurements, but only a few of them have considered the analytical model of the single-sided measurement in which a measurement sample is placed on the sensor substrate. Even in the few designs that have considered the analytical model, their applicable limits are restricted to more than 1 mm length in practical situations. Our new model considers both the sample and the sensor substrate thermal properties and is applicable to a sensor length less than 1 µm. In order to minimize the influence of the heat stimulus to the sample, the model formulates the required heat dissipating time for different sensor geometries. We propose fast and precise detection circuit architecture to realize our model, and we discuss the sensor performance for a number of different designs. Full article
(This article belongs to the Special Issue State-of-the-Art Lab-on-a-Chip Technology in Japan)
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Open AccessArticle Effect of Substrate Support on Dynamic Graphene/Metal Electrical Contacts
Micromachines 2018, 9(4), 169; doi:10.3390/mi9040169
Received: 22 March 2018 / Revised: 5 April 2018 / Accepted: 6 April 2018 / Published: 7 April 2018
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Abstract
Recent advances in graphene and other two-dimensional (2D) material synthesis and characterization have led to their use in emerging technologies, including flexible electronics. However, a major challenge is electrical contact stability, especially under mechanical straining or dynamic loading, which can be important for
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Recent advances in graphene and other two-dimensional (2D) material synthesis and characterization have led to their use in emerging technologies, including flexible electronics. However, a major challenge is electrical contact stability, especially under mechanical straining or dynamic loading, which can be important for 2D material use in microelectromechanical systems. In this letter, we investigate the stability of dynamic electrical contacts at a graphene/metal interface using atomic force microscopy (AFM), under static conditions with variable normal loads and under sliding conditions with variable speeds. Our results demonstrate that contact resistance depends on the nature of the graphene support, specifically whether the graphene is free-standing or supported by a substrate, as well as on the contact load and sliding velocity. The results of the dynamic AFM experiments are corroborated by simulations, which show that the presence of a stiff substrate, increased load, and reduced sliding velocity lead to a more stable low-resistance contact. Full article
(This article belongs to the Special Issue Carbon Based Materials for MEMS/NEMS)
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Open AccessArticle Stretchable Tattoo-Like Heater with On-Site Temperature Feedback Control
Micromachines 2018, 9(4), 170; doi:10.3390/mi9040170
Received: 20 February 2018 / Revised: 20 March 2018 / Accepted: 27 March 2018 / Published: 8 April 2018
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Abstract
Wearable tissue heaters can play many important roles in the medical field. They may be used for heat therapy, perioperative warming and controlled transdermal drug delivery, among other applications. State-of-the-art heaters are too bulky, rigid, or difficult to control to be able to
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Wearable tissue heaters can play many important roles in the medical field. They may be used for heat therapy, perioperative warming and controlled transdermal drug delivery, among other applications. State-of-the-art heaters are too bulky, rigid, or difficult to control to be able to maintain long-term wearability and safety. Recently, there has been progress in the development of stretchable heaters that may be attached directly to the skin surface, but they often use expensive materials or processes and take significant time to fabricate. Moreover, they lack continuously active, on-site, unobstructive temperature feedback control, which is critical for accommodating the dynamic temperatures required for most medical applications. We have developed, fabricated and tested a cost-effective, large area, ultra-thin and ultra-soft tattoo-like heater that has autonomous proportional-integral-derivative (PID) temperature control. The device comprises a stretchable aluminum heater and a stretchable gold resistance temperature detector (RTD) on a soft medical tape as fabricated using the cost and time effective “cut-and-paste” method. It can be noninvasively laminated onto human skin and can follow skin deformation during flexure without imposing any constraint. We demonstrate the device’s ability to maintain a target temperature typical of medical uses over extended durations of time and to accurately adjust to a new set point in process. The cost of the device is low enough to justify disposable use. Full article
(This article belongs to the Special Issue Flexible Electronics: Fabrication and Ubiquitous Integration)
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Open AccessArticle Spiral Microchannels with Trapezoidal Cross Section Fabricated by Femtosecond Laser Ablation in Glass for the Inertial Separation of Microparticles
Micromachines 2018, 9(4), 171; doi:10.3390/mi9040171
Received: 16 February 2018 / Revised: 18 March 2018 / Accepted: 20 March 2018 / Published: 9 April 2018
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Abstract
The fabrication and testing of spiral microchannels with a trapezoidal cross section for the passive separation of microparticles is reported in this article. In contrast to previously reported fabrication methods, the fabrication of trapezoidal spiral channels in glass substrates using a femtosecond laser
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The fabrication and testing of spiral microchannels with a trapezoidal cross section for the passive separation of microparticles is reported in this article. In contrast to previously reported fabrication methods, the fabrication of trapezoidal spiral channels in glass substrates using a femtosecond laser is reported for the first time in this paper. Femtosecond laser ablation has been proposed as an accurate and fast prototyping method with the ability to create 3D features such as slanted-base channels. Moreover, the fabrication in borosilicate glass substrates can provide high optical transparency, thermal resistance, dimensional stability, and chemical inertness. Post-processing steps of the laser engraved glass substrate are also detailed in this paper including hydrogen fluoride (HF) dipping, chemical cleaning, surface activation, and thermal bonding. Optical 3D images of the fabricated chips confirmed a good fabrication accuracy and acceptable surface roughness. To evaluate the particle separation function of the microfluidic chip, 5 μm, 10 μm, and 15 μm particles were focused and recovered from the two outlets of the spiral channel. In conclusion, the new chemically inert separation chip can be utilized in biological or chemical processes where different sizes of cells or particles must be separated, i.e., red blood cells, circulating tumor cells, and technical particle suspensions. Full article
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Open AccessArticle Millimeter-Wave Substrate Integrated Waveguide Using Micromachined Tungsten-Coated Through Glass Silicon Via Structures
Micromachines 2018, 9(4), 172; doi:10.3390/mi9040172
Received: 27 February 2018 / Revised: 21 March 2018 / Accepted: 5 April 2018 / Published: 9 April 2018
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Abstract
A millimeter-wave substrate integrated waveguide (SIW) has been demonstrated using micromachined tungsten-coated through glass silicon via (TGSV) structures. Two-step deep reactive ion etching (DRIE) of silicon vias and selective tungsten coating onto them using a shadow mask are combined with glass reflow techniques
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A millimeter-wave substrate integrated waveguide (SIW) has been demonstrated using micromachined tungsten-coated through glass silicon via (TGSV) structures. Two-step deep reactive ion etching (DRIE) of silicon vias and selective tungsten coating onto them using a shadow mask are combined with glass reflow techniques to realize a glass substrate with metal-coated TGSVs for millimeter-wave applications. The proposed metal-coated TGSV structures effectively replace the metallic vias in conventional through glass via (TGV) substrates, in which an additional individual glass machining process to form micro holes in the glass substrate as well as a time-consuming metal-filling process are required. This metal-coated TGSV substrate is applied to fabricate a SIW operating at Ka-band as a test vehicle. The fabricated SIW shows an average insertion loss of 0.69 ± 0.18 dB and a return loss better than 10 dB in a frequency range from 20 GHz to 45 GHz. Full article
(This article belongs to the Special Issue Wafer Level Packaging of MEMS)
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Open AccessArticle A Study on Measurement Variations in Resonant Characteristics of Electrostatically Actuated MEMS Resonators
Micromachines 2018, 9(4), 173; doi:10.3390/mi9040173
Received: 12 February 2018 / Revised: 28 March 2018 / Accepted: 6 April 2018 / Published: 9 April 2018
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Abstract
Microelectromechanical systems (MEMS) resonators require fast, accurate, and cost-effective testing for mass production. Among the different test methods, frequency domain analysis is one of the easiest and fastest. This paper presents the measurement uncertainties in electrostatically actuated MEMS resonators, using frequency domain analysis.
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Microelectromechanical systems (MEMS) resonators require fast, accurate, and cost-effective testing for mass production. Among the different test methods, frequency domain analysis is one of the easiest and fastest. This paper presents the measurement uncertainties in electrostatically actuated MEMS resonators, using frequency domain analysis. The influence of the applied driving force was studied to evaluate the measurement variations in resonant characteristics, such as the natural frequency and the quality factor of the resonator. To quantify the measurement results, measurement system analysis (MSA) was performed using the analysis of variance (ANOVA) method. The results demonstrate that the resonant frequency ( f r ) is mostly affected by systematic error. However, the quality (Q) factor strongly depends on the applied driving force. To reduce the measurement variations in Q factor, experiments were carried out to study the influence of DC and/or AC driving voltages on the resonator. The results reveal that measurement uncertainties in the quality factor were high for a small electrostatic force. Full article
(This article belongs to the Section Micro-/Nano-system and Technology)
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Open AccessArticle Comprehensive Die Shear Test of Silicon Packages Bonded by Thermocompression of Al Layers with Thin Sn Capping or Insertions
Micromachines 2018, 9(4), 174; doi:10.3390/mi9040174
Received: 15 March 2018 / Revised: 5 April 2018 / Accepted: 8 April 2018 / Published: 11 April 2018
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Abstract
Thermocompression bonding for wafer-level hermetic packaging was demonstrated at the lowest temperature of 370 to 390 °C ever reported using Al films with thin Sn capping or insertions as bonding layer. For shrinking the chip size of MEMS (micro electro mechanical systems), a
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Thermocompression bonding for wafer-level hermetic packaging was demonstrated at the lowest temperature of 370 to 390 °C ever reported using Al films with thin Sn capping or insertions as bonding layer. For shrinking the chip size of MEMS (micro electro mechanical systems), a smaller size of wafer-level packaging and MEMS–ASIC (application specific integrated circuit) integration are of great importance. Metal-based bonding under the temperature of CMOS (complementary metal-oxide-semiconductor) backend process is a key technology, and Al is one of the best candidates for bonding metal in terms of CMOS compatibility. In this study, after the thermocompression bonding of two substrates, the shear fracture strength of dies was measured by a bonding tester, and the shear-fractured surfaces were observed by SEM (scanning electron microscope), EDX (energy dispersive X-ray spectrometry), and a surface profiler to clarify where the shear fracture took place. We confirmed two kinds of fracture mode. One mode is Si bulk fracture mode, where the die shear strength is 41.6 to 209 MPa, proportionally depending on the area of Si fracture. The other mode is bonding interface fracture mode, where the die shear strength is 32.8 to 97.4 MPa. Regardless of the fracture modes, the minimum die shear strength is practical for wafer-level MEMS packaging. Full article
(This article belongs to the Special Issue Wafer Level Packaging of MEMS)
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Open AccessArticle Microfabricated Vapor Cells with Reflective Sidewalls for Chip Scale Atomic Sensors
Micromachines 2018, 9(4), 175; doi:10.3390/mi9040175
Received: 13 December 2017 / Revised: 1 April 2018 / Accepted: 9 April 2018 / Published: 11 April 2018
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Abstract
We investigate the architecture of microfabricated vapor cells with reflective sidewalls for applications in chip scale atomic sensors. The optical configuration in operation is suitable for both one-beam and two-beam (pump & probe) schemes. In the miniaturized vapor cells, the laser beam is
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We investigate the architecture of microfabricated vapor cells with reflective sidewalls for applications in chip scale atomic sensors. The optical configuration in operation is suitable for both one-beam and two-beam (pump & probe) schemes. In the miniaturized vapor cells, the laser beam is reflected twice by the aluminum reflectors on the wet etched 54.7° sidewalls to prolong the optical length significantly, thus resulting in a return reflectance that is three times that of bare silicon sidewalls. To avoid limitations faced in the fabrication process, a simpler, more universal and less constrained fabrication process of microfabricated vapor cells for chip scale atomic sensors with uncompromised performance is implemented, which also decreases the fabrication costs and procedures. Characterization measurements show that with effective sidewall reflectors, mm3 level volume and feasible hermeticity, the elongated miniature vapor cells demonstrate a linear absorption contrast improvement by 10 times over the conventional micro-electro-mechanical system (MEMS) vapor cells at ~50 °C in the rubidium D1 absorption spectroscopy experiments. At the operating temperature of ~90 °C for chip scale atomic sensors, a 50% linear absorption contrast enhancement is obtained with the reflective cell architecture. This leads to a potential improvement in the clock stability and magnetometer sensitivity. Besides, the coherent population trapping spectroscopy is applied to characterize the microfabricated vacuum cells with 46.3 kHz linewidth in the through cell configuration, demonstrating the effectiveness in chip scale atomic sensors. Full article
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Open AccessArticle Mechanical Response of MEMS Inductor with Auxiliary Pillar under High-g Shock
Micromachines 2018, 9(4), 176; doi:10.3390/mi9040176
Received: 14 March 2018 / Revised: 7 April 2018 / Accepted: 8 April 2018 / Published: 11 April 2018
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Abstract
Micro-electromechanical system (MEMS) suspended inductors have excellent radio-frequency (RF) performance, but poor mechanical properties. To improve their reliability, auxiliary pillars have been used. However, few studies have been carried out on the response of a suspended inductor with auxiliary pillars under high mechanical
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Micro-electromechanical system (MEMS) suspended inductors have excellent radio-frequency (RF) performance, but poor mechanical properties. To improve their reliability, auxiliary pillars have been used. However, few studies have been carried out on the response of a suspended inductor with auxiliary pillars under high mechanical shock. In this paper, a theoretical method is proposed that combines a single-degree-of-freedom (SDOF) model and a method for solving statically indeterminate structures. The calculated results obtained by this proposed method were verified by finite-element analysis (ANSYS). The calculated results obtained by the proposed method were found to agree well with the results of ANSYS simulation. Finally, this method was extended to a suspended inductor with double auxiliary pillars. The method proposed in this paper provides a theoretical reference for mechanical performance evaluation and reliability optimization design for MEMS suspended inductors with auxiliary pillars. Full article
(This article belongs to the Section Micro-/Nano-system and Technology)
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Open AccessArticle Microfluidic Line-Free Mass Sensor Based on an Antibody-Modified Mechanical Resonator
Micromachines 2018, 9(4), 177; doi:10.3390/mi9040177
Received: 27 February 2018 / Revised: 3 April 2018 / Accepted: 10 April 2018 / Published: 12 April 2018
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Abstract
This research proposes a mass sensor based on mechanical resonance that is free from power supply lines (line-free) and incorporates both microfluidic mechanisms and label-free techniques to improve its sensitivity and reusability. The microfluidic line-free mass sensor comprises a disk-shaped mechanical resonator, a
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This research proposes a mass sensor based on mechanical resonance that is free from power supply lines (line-free) and incorporates both microfluidic mechanisms and label-free techniques to improve its sensitivity and reusability. The microfluidic line-free mass sensor comprises a disk-shaped mechanical resonator, a separate piezoelectric element used to excite vibrations in the resonator, and a microfluidic mechanism. Electrical power is used to actuate the piezoelectric element, leaving the resonator free from power lines. The microfluidic mechanism allows for rapid, repeat washings to remove impurities from a sample. The microfluidic line-free mass sensor is designed as a label-free sensor to enable high-throughput by modifying and dissociating an antibody on the resonator. The resonator was fabricated by photolithography and the diameter and thickness were 4 mm and 0.5 mm, respectively. The line-free mass sensor enabled a high Q-factor and resonance frequency of 7748 MHz and 1.402 MHz, respectively, to be achieved even in liquids, facilitating the analysis of human salivary cortisol. The line-free mass sensor could be used for repeated measurements with the microfluidic mechanism, and the resonator could be fully washed out. It was concluded that the microfluidic line-free mass sensor was suitable to analyze the concentration of a salivary hormone, cortisol, in human saliva samples, and that it provided high-throughput suitable for point-of-care testing. Full article
(This article belongs to the Special Issue Microfluidic Sensors)
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Open AccessArticle Fabrication Technology and Characteristics Research of the Acceleration Sensor Based on Li-Doped ZnO Piezoelectric Thin Films
Micromachines 2018, 9(4), 178; doi:10.3390/mi9040178
Received: 25 January 2018 / Revised: 2 April 2018 / Accepted: 9 April 2018 / Published: 12 April 2018
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Abstract
An acceleration sensor based on piezoelectric thin films is proposed in this paper, which comprises the elastic element of a silicon cantilever beam and a piezoelectric structure with Li-doped ZnO piezoelectric thin films. The Li-doped ZnO piezoelectric thin films were prepared on SiO
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An acceleration sensor based on piezoelectric thin films is proposed in this paper, which comprises the elastic element of a silicon cantilever beam and a piezoelectric structure with Li-doped ZnO piezoelectric thin films. The Li-doped ZnO piezoelectric thin films were prepared on SiO2/Si by radio frequency (RF) magnetron sputtering method. The microstructure and micrograph of ZnO piezoelectric thin films is analysed by a X-ray diffractometer (XRD), scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), and piezoresponse force microscopy (PFM), respectively. When the sputtering power of 220 W and Li-doped concentration of 5%, ZnO piezoelectric thin films have a preferred (002) orientation. The chips of the sensor were fabricated on the <100> silicon substrate by micro-electromechanical systems (MEMS) technology, meanwhile, the proposed sensor was packaged on the printed circuit board (PCB). The experimental results show the sensitivity of the proposed sensor is 29.48 mV/g at resonant frequency (1479.8 Hz). Full article
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Open AccessArticle On Developing Field-Effect-Tunable Nanofluidic Ion Diodes with Bipolar, Induced-Charge Electrokinetics
Micromachines 2018, 9(4), 179; doi:10.3390/mi9040179
Received: 10 March 2018 / Revised: 7 April 2018 / Accepted: 10 April 2018 / Published: 12 April 2018
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Abstract
We introduce herein the induced-charge electrokinetic phenomenon to nanometer fluidic systems; the design of the nanofluidic ion diode for field-effect ionic current control of the nanometer dimension is developed by enhancing internal ion concentration polarization through electrochemical transport of inhomogeneous inducing-counterions resulting from
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We introduce herein the induced-charge electrokinetic phenomenon to nanometer fluidic systems; the design of the nanofluidic ion diode for field-effect ionic current control of the nanometer dimension is developed by enhancing internal ion concentration polarization through electrochemical transport of inhomogeneous inducing-counterions resulting from double gate terminals mounted on top of a thin dielectric layer, which covers the nanochannel connected to microfluidic reservoirs on both sides. A mathematical model based on the fully-coupled Poisson-Nernst-Plank-Navier-Stokes equations is developed to study the feasibility of this structural configuration causing effective ionic current rectification. The effect of various physiochemical and geometrical parameters, such as the native surface charge density on the nanochannel sidewalls, the number of gate electrodes (GE), the gate voltage magnitude, and the solution conductivity, permittivity, and thickness of the dielectric coating, as well as the size and position of the GE pair of opposite gate polarity, on the resulted rectification performance of the presented nanoscale ionic device is numerically analyzed by using a commercial software package, COMSOL Multiphysics (version 5.2). Three types of electrohydrodynamic flow, including electroosmosis of 1st kind, induced-charge electroosmosis, and electroosmosis of 2nd kind that were originated by the Coulomb force within three distinct charge layers coexist in the micro/nanofluidic hybrid network and are shown to simultaneously influence the output current flux in a complex manner. The rectification factor of a contrast between the ‘on’ and ‘off’ working states can even exceed one thousand-fold in the case of choosing a suitable combination of several key parameters. Our demonstration of field-effect-tunable nanofluidic ion diodes of double external gate electrodes proves invaluable for the construction of a flexible electrokinetic platform for ionic current control and may help transform the field of smart, on-chip, integrated circuits. Full article
(This article belongs to the Special Issue Micro/Nano-Chip Electrokinetics, Volume II)
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Open AccessArticle Quantitative Evaluation of Dielectric Breakdown of Silicon Micro- and Nanofluidic Devices for Electrophoretic Transport of a Single DNA Molecule
Micromachines 2018, 9(4), 180; doi:10.3390/mi9040180
Received: 8 March 2018 / Revised: 9 April 2018 / Accepted: 11 April 2018 / Published: 13 April 2018
PDF Full-text (10648 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
In the present study, we quantitatively evaluated dielectric breakdown in silicon-based micro- and nanofluidic devices under practical electrophoretic conditions by changing the thickness of the insulating layer. At higher buffer concentration, a silicon nanofluidic device with a 100 nm or 250 nm silicon
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In the present study, we quantitatively evaluated dielectric breakdown in silicon-based micro- and nanofluidic devices under practical electrophoretic conditions by changing the thickness of the insulating layer. At higher buffer concentration, a silicon nanofluidic device with a 100 nm or 250 nm silicon dioxide layer tolerated dielectric breakdown up to ca. 10 V/cm, thereby allowing successful electrophoretic migration of a single DNA molecule through a nanochannel. The observed DNA migration behavior suggested that parameters, such as thickness of the insulating layer, tolerance of dielectric breakdown, and bonding status of silicon and glass substrate, should be optimized to achieve successful electrophoretic transport of a DNA molecule through a nanopore for nanopore-based DNA sequencing applications. Full article
(This article belongs to the Special Issue State-of-the-Art Lab-on-a-Chip Technology in Japan)
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Open AccessArticle Bonding-Based Wafer-Level Vacuum Packaging Using Atomic Hydrogen Pre-Treated Cu Bonding Frames
Micromachines 2018, 9(4), 181; doi:10.3390/mi9040181
Received: 15 March 2018 / Revised: 3 April 2018 / Accepted: 10 April 2018 / Published: 13 April 2018
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Abstract
A novel surface activation technology for Cu-Cu bonding-based wafer-level vacuum packaging using hot-wire-generated atomic hydrogen treatment was developed. Vacuum sealing temperature at 300 °C was achieved by atomic hydrogen pre-treatment for Cu native oxide reduction, while 350 °C was needed by the conventional
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A novel surface activation technology for Cu-Cu bonding-based wafer-level vacuum packaging using hot-wire-generated atomic hydrogen treatment was developed. Vacuum sealing temperature at 300 °C was achieved by atomic hydrogen pre-treatment for Cu native oxide reduction, while 350 °C was needed by the conventional wet chemical oxide reduction procedure. A remote-type hot-wire tool was employed to minimize substrate overheating by thermal emission from the hot-wire. The maximum substrate temperature during the pre-treatment is lower than the temperature of Cu nano-grain re-crystallization, which enhances Cu atomic diffusion during the bonding process. Even after 24 h wafer storage in atmospheric conditions after atomic hydrogen irradiation, low-temperature vacuum sealing was achieved because surface hydrogen species grown by the atomic hydrogen treatment suppressed re-oxidation. Vacuum sealing yield, pressure in the sealed cavity and bonding shear strength by atomic hydrogen pre-treated Cu-Cu bonding are 90%, 5 kPa and 100 MPa, respectively, which are equivalent to conventional Cu-Cu bonding at higher temperature. Leak rate of the bonded device is less than 10−14 Pa m3 s−1 order, which is applicable for practical use. The developed technology can contribute to low-temperature hermetic packaging. Full article
(This article belongs to the Special Issue Wafer Level Packaging of MEMS)
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Open AccessCommunication Photopatternable Magnetic Hollowbots by Nd-Fe-B Nanocomposite for Potential Targeted Drug Delivery Applications
Micromachines 2018, 9(4), 182; doi:10.3390/mi9040182
Received: 23 January 2018 / Revised: 3 April 2018 / Accepted: 5 April 2018 / Published: 13 April 2018
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Abstract
In contrast to traditional drug administration, targeted drug delivery can prolong, localize, target and have a protected drug interaction with the diseased tissue. Drug delivery carriers, such as polymeric micelles, liposomes, dendrimers, nanotubes, and so on, are hard to scale-up, costly, and have
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In contrast to traditional drug administration, targeted drug delivery can prolong, localize, target and have a protected drug interaction with the diseased tissue. Drug delivery carriers, such as polymeric micelles, liposomes, dendrimers, nanotubes, and so on, are hard to scale-up, costly, and have short shelf life. Here we show the novel fabrication and characterization of photopatternable magnetic hollow microrobots that can potentially be utilized in microfluidics and drug delivery applications. These magnetic hollowbots can be fabricated using standard ultraviolet (UV) lithography with low cost and easily accessible equipment, which results in them being easy to scale up, and inexpensive to fabricate. Contact-free actuation of freestanding magnetic hollowbots were demonstrated by using an applied 900 G external magnetic field to achieve the movement control in an aqueous environment. According to the movement clip, the average speed of the magnetic hollowbots was estimated to be 1.9 mm/s. Full article
(This article belongs to the Special Issue Locomotion at Small Scales: From Biology to Artificial Systems)
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Open AccessArticle Topology Optimization of Spatially Compliant Mechanisms with an Isomorphic Matrix of a 3-UPC Type Parallel Prototype Manipulator
Micromachines 2018, 9(4), 184; doi:10.3390/mi9040184
Received: 25 February 2018 / Revised: 9 April 2018 / Accepted: 11 April 2018 / Published: 14 April 2018
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Abstract
A novel topology optimization approach is proposed in this paper for the design of three rotational degree-of-freedom (DOF) spatially compliant mechanisms, combining the Jacobian isomorphic mapping matrix with the solid isotropic material with penalization (SIMP) topological method. In this approach, the isomorphic Jacobian
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A novel topology optimization approach is proposed in this paper for the design of three rotational degree-of-freedom (DOF) spatially compliant mechanisms, combining the Jacobian isomorphic mapping matrix with the solid isotropic material with penalization (SIMP) topological method. In this approach, the isomorphic Jacobian matrix of a 3-UPC (U: universal joint, P: prismatic joint, C: cylindrical joint) type parallel prototype manipulator is formulated. Subsequently, the orthogonal triangular decomposition and differential kinematic method is applied to uncouple the Jacobian matrix to construct a constraint for topology optimization. Firstly, with respect to the 3-UPC type parallel prototype manipulator, the Jacobian matrix is derived to map the inputs and outputs to be used for initializing the topology optimization process. Secondly, the orthogonal triangular decomposition with the differential kinematic method is used to reconstruct the uncoupled mapping matrix to derive the 3-UPC type parallel prototype manipulator. Finally, a combination of the solid isotropic material with penalization (SIMP) method and the isomorphic mapping matrix is applied to construct the topological model. A typical three rotational DOF spatially compliant mechanism is reported as a numerical example to demonstrate the effectiveness of the proposed method. Full article
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Open AccessArticle Fabrication of an Anti-Reflective and Super-Hydrophobic Structure by Vacuum Ultraviolet Light-Assisted Bonding and Nanoscale Pattern Transfer
Micromachines 2018, 9(4), 186; doi:10.3390/mi9040186
Received: 13 March 2018 / Revised: 11 April 2018 / Accepted: 13 April 2018 / Published: 15 April 2018
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Abstract
The application of subwavelength, textured structures to glass surfaces has been shown to reduce reflectivity and also results in self-cleaning due to super-hydrophobicity. However, current methods of producing such textures are typically either expensive or difficult to scale up. Based on prior work
[...] Read more.
The application of subwavelength, textured structures to glass surfaces has been shown to reduce reflectivity and also results in self-cleaning due to super-hydrophobicity. However, current methods of producing such textures are typically either expensive or difficult to scale up. Based on prior work by the authors, the present study employed a combination of vacuum ultraviolet (VUV) light-assisted bonding and release agent-free pattern transfer to fabricate a moth-eye texture on a glass substrate. This was accomplished by forming a cyclic olefin polymer mold master with a moth-eye pattern, transferring this pattern to a polydimethylsiloxane (PDMS) spin coating, activating both the PDMS and a glass substrate with VUV light, and then bonding the PDMS to the glass before releasing the mold. Atomic force microscopy demonstrated that the desired pattern was successfully replicated on the PDMS surface with a high degree of accuracy, and the textured glass specimen exhibited approximately 3% higher transmittance than untreated glass. Contact angle measurements also showed that the hydrophobicity of the textured surface was significantly increased. These results confirm that this new technique is a viable means of fabricating optical nanostructures via a simple, inexpensive process. Full article
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Open AccessArticle Progress on the Use of Commercial Digital Optical Disc Units for Low-Power Laser Micromachining in Biomedical Applications
Micromachines 2018, 9(4), 187; doi:10.3390/mi9040187
Received: 23 March 2018 / Revised: 2 April 2018 / Accepted: 3 April 2018 / Published: 16 April 2018
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Abstract
The development of organ-on-chip and biological scaffolds is currently requiring simpler methods for microstructure biocompatible materials in three dimensions, to fabricate structural and functional elements in biomaterials, or modify the physicochemical properties of desired substrates. Aiming at addressing this need, a low-power CD-DVD-Blu-ray
[...] Read more.
The development of organ-on-chip and biological scaffolds is currently requiring simpler methods for microstructure biocompatible materials in three dimensions, to fabricate structural and functional elements in biomaterials, or modify the physicochemical properties of desired substrates. Aiming at addressing this need, a low-power CD-DVD-Blu-ray laser pickup head was mounted on a programmable three-axis micro-displacement system in order to modify the surface of polymeric materials in a local fashion. Thanks to a specially-designed method using a strongly absorbing additive coating the materials of interest, it has been possible to establish and precisely control processes useful in microtechnology for biomedical applications. The system was upgraded with Blu-ray laser for additive manufacturing and ablation on a single platform. In this work, we present the application of these fabrication techniques to the development of biomimetic cellular culture platforms thanks to the simple integration of several features typically achieved with traditional, less cost-effective microtechnology methods in one step or through replica-molding. Our straightforward approach indeed enables great control of local laser microablation or polymerization for true on-demand biomimetic micropatterned designs in transparent polymers and hydrogels and is allowing integration of microfluidics, microelectronics, surface microstructuring, and transfer of superficial protein micropatterns on a variety of biocompatible materials. Full article
(This article belongs to the Special Issue Micro-Machining: Challenges and Opportunities)
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Open AccessArticle A Horizontal Magnetic Tweezers and Its Use for Studying Single DNA Molecules
Micromachines 2018, 9(4), 188; doi:10.3390/mi9040188
Received: 29 January 2018 / Revised: 11 April 2018 / Accepted: 12 April 2018 / Published: 17 April 2018
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Abstract
We report the development of a magnetic tweezers that can be used to micromanipulate single DNA molecules by applying picoNewton (pN)-scale forces in the horizontal plane. The resulting force–extension data from our experiments show high-resolution detection of changes in the DNA tether’s extension:
[...] Read more.
We report the development of a magnetic tweezers that can be used to micromanipulate single DNA molecules by applying picoNewton (pN)-scale forces in the horizontal plane. The resulting force–extension data from our experiments show high-resolution detection of changes in the DNA tether’s extension: ~0.5 pN in the force and <10 nm change in extension. We calibrate our instrument using multiple orthogonal techniques including the well-characterized DNA overstretching transition. We also quantify the repeatability of force and extension measurements, and present data on the behavior of the overstretching transition under varying salt conditions. The design and experimental protocols are described in detail, which should enable straightforward reproduction of the tweezers. Full article
(This article belongs to the Special Issue Micro Technologies for Single Molecule Manipulation and Detection)
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Open AccessArticle Position-Space-Based Design of a Symmetric Spatial Translational Compliant Mechanism for Micro-/Nano-Manipulation
Micromachines 2018, 9(4), 189; doi:10.3390/mi9040189
Received: 19 March 2018 / Revised: 8 April 2018 / Accepted: 13 April 2018 / Published: 17 April 2018
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Abstract
Symmetry enables excellent motion performance of compliant mechanisms, such as minimized parasitic motion, reduced cross-axis coupling, mitigated buckling, and decreased thermal sensitivity. However, most existing symmetric compliant mechanisms are heavily over-constrained due to the fact that they are usually obtained by directly adding
[...] Read more.
Symmetry enables excellent motion performance of compliant mechanisms, such as minimized parasitic motion, reduced cross-axis coupling, mitigated buckling, and decreased thermal sensitivity. However, most existing symmetric compliant mechanisms are heavily over-constrained due to the fact that they are usually obtained by directly adding over-constraints to the associated non-symmetric compliant mechanisms. Therefore, existing symmetric compliant mechanisms usually have relatively complex structures and relatively large actuation stiffness. This paper presents a position-space-based approach to the design of symmetric compliant mechanisms. Using this position-space-based approach, a non-symmetric compliant mechanism can be reconfigured into a symmetric compliant mechanism by rearranging the compliant modules and adding minimal over-constraints. A symmetric spatial translational compliant parallel mechanism (symmetric XYZ compliant parallel mechanism (CPM)) is designed using the position-space-based design approach in this paper. Furthermore, the actuation forces of the symmetric XYZ CPM are nonlinearly and analytically modelled, which are represented by the given primary translations and the geometrical parameters. The maximum difference, between the nonlinear analytical results and the nonlinear finite element analysis (FEA) results, is less than 2.58%. Additionally, a physical prototype of the symmetric XYZ CPM is fabricated, and the desirable motion characteristics such as minimized cross-axis coupling are also verified by FEA simulations and experimental testing. Full article
(This article belongs to the Section Micro-/Nano-system and Technology)
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Open AccessArticle Electrostatically Driven In-Plane Silicon Micropump for Modular Configuration
Micromachines 2018, 9(4), 190; doi:10.3390/mi9040190
Received: 6 February 2018 / Revised: 6 April 2018 / Accepted: 12 April 2018 / Published: 18 April 2018
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Abstract
In this paper, an in-plane reciprocating displacement micropump for liquids and gases which is actuated by a new class of electrostatic bending actuators is reported. The so-called “Nano Electrostatic Drive” is capable of deflecting beyond the electrode gap distance, enabling large generated forces
[...] Read more.
In this paper, an in-plane reciprocating displacement micropump for liquids and gases which is actuated by a new class of electrostatic bending actuators is reported. The so-called “Nano Electrostatic Drive” is capable of deflecting beyond the electrode gap distance, enabling large generated forces and deflections. Depending on the requirements of the targeted system, the micropump can be modularly designed to meet the specified differential pressures and flow rates by a serial and parallel arrangement of equally working pumping base units. Two selected, medium specific micropump test structure devices for pumping air and isopropanol were designed and investigated. An analytical approach of the driving unit is presented and two-way Fluid-Structure Interaction (FSI) simulations of the micropump were carried out to determine the dynamic behavior. The simulation showed that the test structure device designed for air expected to overcome a total differential pressure of 130 kPa and deliver a flow rate of 0.11 sccm at a 265 Hz driving frequency. The isopropanol design is expected to generate 210 kPa and pump 0.01 sccm at 21 Hz. The device is monolithically fabricated by CMOS-compatible bulk micromachining processes under the use of standard materials only, such as crystalline silicon, silicon dioxide and alumina. Full article
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Open AccessArticle Open Design 3D-Printable Adjustable Micropipette that Meets the ISO Standard for Accuracy
Micromachines 2018, 9(4), 191; doi:10.3390/mi9040191
Received: 30 March 2018 / Revised: 16 April 2018 / Accepted: 17 April 2018 / Published: 18 April 2018
PDF Full-text (3483 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Scientific communities are drawn to the open source model as an increasingly utilitarian method to produce and share work. Initially used as a means to develop freely-available software, open source projects have been applied to hardware including scientific tools. Increasing convenience of 3D
[...] Read more.
Scientific communities are drawn to the open source model as an increasingly utilitarian method to produce and share work. Initially used as a means to develop freely-available software, open source projects have been applied to hardware including scientific tools. Increasing convenience of 3D printing has fueled the proliferation of open labware projects aiming to develop and share designs for scientific tools that can be produced in-house as inexpensive alternatives to commercial products. We present our design of a micropipette that is assembled from 3D-printable parts and some hardware that works by actuating a disposable syringe to a user-adjustable limit. Graduations on the syringe are used to accurately adjust the set point to the desired volume. Our open design printed micropipette is assessed in comparison with a commercial pipette and meets the ISO 8655 standards. Full article
(This article belongs to the Special Issue 3D Printed Microfluidic Devices)
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Open AccessArticle Multiple Electrohydrodynamic Effects on the Morphology and Running Behavior of Tiny Liquid Metal Motors
Micromachines 2018, 9(4), 192; doi:10.3390/mi9040192
Received: 20 March 2018 / Revised: 11 April 2018 / Accepted: 13 April 2018 / Published: 18 April 2018
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Abstract
Minimized motors can harvest different types of energy and transfer them into kinetic power to carry out complex operations, such as targeted drug delivery, health care, sensing and so on. In recent years, the liquid metal motor is emerging as a very promising
[...] Read more.
Minimized motors can harvest different types of energy and transfer them into kinetic power to carry out complex operations, such as targeted drug delivery, health care, sensing and so on. In recent years, the liquid metal motor is emerging as a very promising tiny machine. This work is dedicated to investigate the motion characteristics of self-powered liquid metal droplet machines under external electric field, after engulfing a small amount of aluminum. Two new non-dimensional parameters, named Ä and Ö , are put forward for the first time to evaluate the ratio of the forces resulting from the electric field to the fluidic viscous force and the ratio of the friction force to the fluidic viscous force. Forces exerted on liquid metal droplets, the viscosity between the droplet and the surrounding fluid, the pressure difference on both ends, the friction between the bottom of the droplet and the sink base, and bubble propulsion force are evaluated and estimated regarding whether they are impetus or resistance. Effects of electric field intensity, droplet size, solution concentration and surface roughness etc. on the morphology and running behavior of such tiny liquid metal motors are clarified in detail. This work sheds light on the moving mechanism of the liquid metal droplet in aqueous solutions, preparing for more precise and complicated control of liquid metal soft machines. Full article
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Open AccessArticle Parametric Excitation of Optomechanical Resonators by Periodical Modulation
Micromachines 2018, 9(4), 193; doi:10.3390/mi9040193
Received: 26 February 2018 / Revised: 4 April 2018 / Accepted: 17 April 2018 / Published: 18 April 2018
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Abstract
Optical excitation of mechanical resonators has long been a research interest, since it has great applications in the physical and engineering field. Previous optomechanical methods rely on the wavelength-dependent, optical anti-damping effects, with the working range limited to the blue-detuning range. In this
[...] Read more.
Optical excitation of mechanical resonators has long been a research interest, since it has great applications in the physical and engineering field. Previous optomechanical methods rely on the wavelength-dependent, optical anti-damping effects, with the working range limited to the blue-detuning range. In this study, we experimentally demonstrated the excitation of optomechanical resonators by periodical modulation. The wavelength working range was extended from the blue-detuning to red-detuning range. This demonstration will provide a new way to excite mechanical resonators and benefit practical applications, such as optical mass sensors and gyroscopes with an extended working range. Full article
(This article belongs to the Special Issue Optofluidics: From Fundamental Research to Applications)
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Open AccessArticle Particle-Based Microfluidic Quartz Crystal Microbalance (QCM) Biosensing Utilizing Mass Amplification and Magnetic Bead Convection
Micromachines 2018, 9(4), 194; doi:10.3390/mi9040194
Received: 14 March 2018 / Revised: 3 April 2018 / Accepted: 13 April 2018 / Published: 18 April 2018
PDF Full-text (4608 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
Microfluidic quartz crystal microbalances (QCM) can be used as powerful biosensors that not only allow quantifying a target analyte, but also provide kinetic information about the surface processes of binding and release. Nevertheless, their practical use as point-of-care devices is restricted by a
[...] Read more.
Microfluidic quartz crystal microbalances (QCM) can be used as powerful biosensors that not only allow quantifying a target analyte, but also provide kinetic information about the surface processes of binding and release. Nevertheless, their practical use as point-of-care devices is restricted by a limit of detection (LoD) of some ng/cm². It prohibits the measurement of small molecules in low concentrations within the initial sample. Here, two concepts based on superparamagnetic particles are presented that allow enhancing the LoD of a QCM. First, a particle-enhanced C-reactive protein (CRP) measurement on a QCM is shown. The signal response could be increased by a factor of up to five by utilizing the particles for mass amplification. Further, a scheme for sample pre-preparation utilizing convective up-concentration involving magnetic bead manipulation is investigated. These experiments are carried out with a glass device that is fabricated by utilizing a femtosecond laser. Operation regimes for the magnetic manipulation of particles within the microfluidic channel with integrated pole pieces that are activated by external permanent magnets are described. Finally, the potential combination of the concepts of mass amplification and up-concentration within an integrated lab-on-a chip device is discussed. Full article
(This article belongs to the Special Issue Microfluidic Sensors)
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Open AccessArticle Maskless Surface Modification of Polyurethane Films by an Atmospheric Pressure He/O2 Plasma Microjet for Gelatin Immobilization
Micromachines 2018, 9(4), 195; doi:10.3390/mi9040195 (registering DOI)
Received: 1 February 2018 / Revised: 1 April 2018 / Accepted: 17 April 2018 / Published: 20 April 2018
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Abstract
A localized maskless modification method of polyurethane (PU) films through an atmospheric pressure He/O2 plasma microjet (APPμJ) was proposed. The APPμJ system combines an atmospheric pressure plasma jet (APPJ) with a microfabricated silicon micronozzle with dimension of 30 μm, which has advantages
[...] Read more.
A localized maskless modification method of polyurethane (PU) films through an atmospheric pressure He/O2 plasma microjet (APPμJ) was proposed. The APPμJ system combines an atmospheric pressure plasma jet (APPJ) with a microfabricated silicon micronozzle with dimension of 30 μm, which has advantages of simple structure and low cost. The possibility of APPμJ in functionalizing PU films with hydroxyl (–OH) groups and covalent grafting of gelatin for improving its biocompatibility was demonstrated. The morphologies and chemical compositions of the modified surface were analyzed by scanning electronic microscopy (SEM), Raman spectroscopy, and X-ray photoelectron spectroscopy (XPS). The fluorescent images show the modified surface can be divided into four areas with different fluorescence intensity from the center to the outside domain. The distribution of the rings could be controlled by plasma process parameters, such as the treatment time and the flow rate of O2. When the treatment time is 4 to 5 min with the oxygen percentage of 0.6%, the PU film can be effectively local functionalized with the diameter of 170 μm. In addition, the modification mechanism of PU films by the APPμJ is investigated. The localized polymer modified by APPμJ has potential applications in the field of tissue engineering. Full article
(This article belongs to the Special Issue Plasma-Based Surface Engineering)
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Review

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Open AccessReview Optofluidics in Microstructured Optical Fibers
Micromachines 2018, 9(4), 145; doi:10.3390/mi9040145
Received: 27 January 2018 / Revised: 10 March 2018 / Accepted: 21 March 2018 / Published: 24 March 2018
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Abstract
In this paper, we review the development and applications of optofluidics investigated based on the platform of microstructured optical fibers (MOFs) that have miniature air channels along the light propagating direction. The flexibility of the customizable air channels of MOFs provides enough space
[...] Read more.
In this paper, we review the development and applications of optofluidics investigated based on the platform of microstructured optical fibers (MOFs) that have miniature air channels along the light propagating direction. The flexibility of the customizable air channels of MOFs provides enough space to implement light-matter interaction, as fluids and light can be guided simultaneously along a single strand of fiber. Different techniques employed to achieve the fluidic inlet/outlet as well as different applications for biochemical analysis are presented. This kind of miniature platform based on MOFs is easy to fabricate, free of lithography, and only needs a tiny volume of the sample. Compared to optofluidics on the chip, no additional waveguide is necessary to guide the light since the core is already designed in MOFs. The measurements of flow rate, refractive index of the filled fluids, and chemical reactions can be carried out based on this platform. Furthermore, it can also demonstrate some physical phenomena. Such devices show good potential and prospects for applications in bio-detection as well as material analysis. Full article
(This article belongs to the Special Issue Advances in Optofluidics)
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Open AccessReview Microfluidic Devices Developed for and Inspired by Thermotaxis and Chemotaxis
Micromachines 2018, 9(4), 149; doi:10.3390/mi9040149
Received: 31 January 2018 / Revised: 7 March 2018 / Accepted: 22 March 2018 / Published: 26 March 2018
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Abstract
Taxis has been reported in many cells and microorganisms, due to their tendency to migrate toward favorable physical situations and avoid damage and death. Thermotaxis and chemotaxis are two of the major types of taxis that naturally occur on a daily basis. Understanding
[...] Read more.
Taxis has been reported in many cells and microorganisms, due to their tendency to migrate toward favorable physical situations and avoid damage and death. Thermotaxis and chemotaxis are two of the major types of taxis that naturally occur on a daily basis. Understanding the details of the thermo- and chemotactic behavioral response of cells and microorganisms is necessary to reveal the body function, diagnosing diseases and developing therapeutic treatments. Considering the length-scale and range of effectiveness of these phenomena, advances in microfluidics have facilitated taxis experiments and enhanced the precision of controlling and capturing microscale samples. Microfabrication of fluidic chips could bridge the gap between in vitro and in situ biological assays, specifically in taxis experiments. Numerous efforts have been made to develop, fabricate and implement novel microchips to conduct taxis experiments and increase the accuracy of the results. The concepts originated from thermo- and chemotaxis, inspired novel ideas applicable to microfluidics as well, more specifically, thermocapillarity and chemocapillarity (or solutocapillarity) for the manipulation of single- and multi-phase fluid flows in microscale and fluidic control elements such as valves, pumps, mixers, traps, etc. This paper starts with a brief biological overview of the concept of thermo- and chemotaxis followed by the most recent developments in microchips used for thermo- and chemotaxis experiments. The last section of this review focuses on the microfluidic devices inspired by the concept of thermo- and chemotaxis. Various microfluidic devices that have either been used for, or inspired by thermo- and chemotaxis are reviewed categorically. Full article
(This article belongs to the Special Issue Bio-Inspired Micro/Nano Devices and Systems)
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Open AccessReview Deformation of Red Blood Cells, Air Bubbles, and Droplets in Microfluidic Devices: Flow Visualizations and Measurements
Micromachines 2018, 9(4), 151; doi:10.3390/mi9040151
Received: 10 February 2018 / Revised: 21 March 2018 / Accepted: 21 March 2018 / Published: 27 March 2018
PDF Full-text (6602 KB) | HTML Full-text | XML Full-text
Abstract
Techniques, such as micropipette aspiration and optical tweezers, are widely used to measure cell mechanical properties, but are generally labor-intensive and time-consuming, typically involving a difficult process of manipulation. In the past two decades, a large number of microfluidic devices have been developed
[...] Read more.
Techniques, such as micropipette aspiration and optical tweezers, are widely used to measure cell mechanical properties, but are generally labor-intensive and time-consuming, typically involving a difficult process of manipulation. In the past two decades, a large number of microfluidic devices have been developed due to the advantages they offer over other techniques, including transparency for direct optical access, lower cost, reduced space and labor, precise control, and easy manipulation of a small volume of blood samples. This review presents recent advances in the development of microfluidic devices to evaluate the mechanical response of individual red blood cells (RBCs) and microbubbles flowing in constriction microchannels. Visualizations and measurements of the deformation of RBCs flowing through hyperbolic, smooth, and sudden-contraction microchannels were evaluated and compared. In particular, we show the potential of using hyperbolic-shaped microchannels to precisely control and assess small changes in RBC deformability in both physiological and pathological situations. Moreover, deformations of air microbubbles and droplets flowing through a microfluidic constriction were also compared with RBCs deformability. Full article
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Open AccessReview Optofluidic Technology for Water Quality Monitoring
Micromachines 2018, 9(4), 158; doi:10.3390/mi9040158
Received: 25 February 2018 / Revised: 25 March 2018 / Accepted: 26 March 2018 / Published: 1 April 2018
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Abstract
Water quality-related incidents are attracting attention globally as they cause serious diseases and even threaten human lives. The current detection and monitoring methods are inadequate because of their long operation time, high cost, and complex process. In this context, there is an increasing
[...] Read more.
Water quality-related incidents are attracting attention globally as they cause serious diseases and even threaten human lives. The current detection and monitoring methods are inadequate because of their long operation time, high cost, and complex process. In this context, there is an increasing demand for low-cost, multiparameter, real-time, and continuous-monitoring methods at a higher temporal and spatial resolution. Optofluidic water quality sensors have great potential to satisfy this requirement due to their distinctive features including high throughput, small footprint, and low power consumption. This paper reviews the current development of these sensors for heavy metal, organic, and microbial pollution monitoring, which will breed new research ideas and broaden their applications. Full article
(This article belongs to the Special Issue Advances in Optofluidics)
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Open AccessReview Optofluid-Based Reflective Displays
Micromachines 2018, 9(4), 159; doi:10.3390/mi9040159
Received: 6 February 2018 / Revised: 24 March 2018 / Accepted: 27 March 2018 / Published: 1 April 2018
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Abstract
Displays can present information like text, images, or videos in a different color (visible light) by activating the materials in pixels. In a display device, pixels are typically of micrometer size and filled with displaying materials that are aligned and controlled by a
[...] Read more.
Displays can present information like text, images, or videos in a different color (visible light) by activating the materials in pixels. In a display device, pixels are typically of micrometer size and filled with displaying materials that are aligned and controlled by a display driver integrated circuit. Typical reflective displays can show designed information by manipulating ambient light via the microfluidic behavior in pixels driven by electrophoresis, electrowetting, or electromechanical forces. In this review, we describe the basic working principles and device structures of three reflective displays of electrophoresis display (EPD), electrowetting display (EWD), and interferometric modulator display (IMOD). The optofluidic behavior and controlling factors relating to the display performance are summarized. Full article
(This article belongs to the Special Issue Advances in Optofluidics)
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Open AccessReview Passive Mixing inside Microdroplets
Micromachines 2018, 9(4), 160; doi:10.3390/mi9040160
Received: 31 January 2018 / Revised: 22 March 2018 / Accepted: 23 March 2018 / Published: 1 April 2018
PDF Full-text (10351 KB) | HTML Full-text | XML Full-text
Abstract
Droplet-based micromixers are essential units in many microfluidic devices for widespread applications, such as diagnostics and synthesis. The mixers can be either passive or active. When compared to active methods, the passive mixer is widely used because it does not require extra energy
[...] Read more.
Droplet-based micromixers are essential units in many microfluidic devices for widespread applications, such as diagnostics and synthesis. The mixers can be either passive or active. When compared to active methods, the passive mixer is widely used because it does not require extra energy input apart from the pump drive. In recent years, several passive droplet-based mixers were developed, where mixing was characterized by both experiments and simulation. A unified physical understanding of both experimental processes and simulation models is beneficial for effectively developing new and efficient mixing techniques. This review covers the state-of-the-art passive droplet-based micromixers in microfluidics, which mainly focuses on three aspects: (1) Mixing parameters and analysis method; (2) Typical mixing element designs and the mixing characters in experiments; and, (3) Comprehensive introduction of numerical models used in microfluidic flow and diffusion. Full article
(This article belongs to the Special Issue Advances in Optofluidics)
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Open AccessReview Light Manipulation in Inhomogeneous Liquid Flow and Its Application in Biochemical Sensing
Micromachines 2018, 9(4), 163; doi:10.3390/mi9040163
Received: 29 January 2018 / Revised: 23 March 2018 / Accepted: 26 March 2018 / Published: 2 April 2018
PDF Full-text (4879 KB) | HTML Full-text | XML Full-text
Abstract
Light manipulation has always been the fundamental subject in the field of optics since centuries ago. Traditional optical devices are usually designed using glasses and other materials, such as semiconductors and metals. Optofluidics is the combination of microfluidics and optics, which brings a
[...] Read more.
Light manipulation has always been the fundamental subject in the field of optics since centuries ago. Traditional optical devices are usually designed using glasses and other materials, such as semiconductors and metals. Optofluidics is the combination of microfluidics and optics, which brings a host of new advantages to conventional solid systems. The capabilities of light manipulation and biochemical sensing are inherent alongside the emergence of optofluidics. This new research area promotes advancements in optics, biology, and chemistry. The development of fast, accurate, low-cost, and small-sized biochemical micro-sensors is an urgent demand for real-time monitoring. However, the fluid flow in the on-chip sensor is usually non-uniformed, which is a new and emerging challenge for the accuracy of optical detection. It is significant to reveal the principle of light propagation in an inhomogeneous liquid flow and the interaction between biochemical samples and light in flowing liquids. In this review, we summarize the current state of optofluidic lab-on-a-chip techniques from the perspective of light modulation by the unique dynamic properties of fluid in heterogeneous media, such as diffusion, heat transfer, and centrifugation etc. Furthermore, this review introduces several novel photonic phenomena in an inhomogeneous liquid flow and demonstrates their application in biochemical sensing. Full article
(This article belongs to the Special Issue Advances in Optofluidics)
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Open AccessReview High-Throughput Optofluidic Acquisition of Microdroplets in Microfluidic Systems
Micromachines 2018, 9(4), 183; doi:10.3390/mi9040183
Received: 27 February 2018 / Revised: 26 March 2018 / Accepted: 4 April 2018 / Published: 14 April 2018
PDF Full-text (2644 KB) | HTML Full-text | XML Full-text
Abstract
Droplet optofluidics technology aims at manipulating the tiny volume of fluids confined in micro-droplets with light, while exploiting their interaction to create “digital” micro-systems with highly significant scientific and technological interests. Manipulating droplets with light is particularly attractive since the latter provides wavelength
[...] Read more.
Droplet optofluidics technology aims at manipulating the tiny volume of fluids confined in micro-droplets with light, while exploiting their interaction to create “digital” micro-systems with highly significant scientific and technological interests. Manipulating droplets with light is particularly attractive since the latter provides wavelength and intensity tunability, as well as high temporal and spatial resolution. In this review study, we focus mainly on recent methods developed in order to monitor real-time analysis of droplet size and size distribution, active merging of microdroplets using light, or to use microdroplets as optical probes. Full article
(This article belongs to the Special Issue Advances in Optofluidics)
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Open AccessReview Research and Analysis of MEMS Switches in Different Frequency Bands
Micromachines 2018, 9(4), 185; doi:10.3390/mi9040185
Received: 29 January 2018 / Revised: 22 March 2018 / Accepted: 12 April 2018 / Published: 15 April 2018
PDF Full-text (2988 KB) | HTML Full-text | XML Full-text
Abstract
Due to their high isolation, low insertion loss, high linearity, and low power consumption, microelectromechanical systems (MEMS) switches have drawn much attention from researchers in recent years. In this paper, we introduce the research status of MEMS switches in different bands and several
[...] Read more.
Due to their high isolation, low insertion loss, high linearity, and low power consumption, microelectromechanical systems (MEMS) switches have drawn much attention from researchers in recent years. In this paper, we introduce the research status of MEMS switches in different bands and several reliability issues, such as dielectric charging, contact failure, and temperature instability. In this paper, some of the following methods to improve the performance of MEMS switches in high frequency are summarized: (1) utilizing combinations of several switches in series; (2) covering a float metal layer on the dielectric layer; (3) using dielectric layer materials with high dielectric constants and conductor materials with low resistance; (4) developing MEMS switches using T-match and π-match; (5) designing MEMS switches based on bipolar complementary metal–oxide–semiconductor (BiCMOS) technology and reconfigurable MEMS’ surfaces; (6) employing thermal compensation structures, circularly symmetric structures, thermal buckle-beam actuators, molybdenum membrane, and thin-film packaging; (7) selecting Ultra-NanoCrystalline diamond or aluminum nitride dielectric materials and applying a bipolar driving voltage, stoppers, and a double-dielectric-layer structure; and (8) adopting gold alloying with carbon nanotubes (CNTs), hermetic and reliable packaging, and mN-level contact. Full article
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Open AccessCorrection Correction: Athanasiou, C.-E. et al. A Monolithic Micro-Tensile Tester for Investigating Silicon Dioxide Polymorph Micromechanics, Fabricated and Operated Using a Femtosecond Laser. Micromachines, 2015, 6, 1365–1386
Micromachines 2018, 9(4), 164; doi:10.3390/mi9040164
Received: 12 March 2018 / Revised: 21 March 2018 / Accepted: 22 March 2018 / Published: 2 April 2018
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Abstract
The authors would like to make the following changes to the published paper [1]: Equation (5) should be written as follows:[...] Full article
(This article belongs to the collection Laser Micromachining and Microfabrication)
Open AccessPerspective Emerging Anti-Fouling Methods: Towards Reusability of 3D-Printed Devices for Biomedical Applications
Micromachines 2018, 9(4), 196; doi:10.3390/mi9040196 (registering DOI)
Received: 21 March 2018 / Revised: 7 April 2018 / Accepted: 19 April 2018 / Published: 20 April 2018
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Abstract
Microfluidic devices are used in a myriad of biomedical applications such as cancer screening, drug testing, and point-of-care diagnostics. Three-dimensional (3D) printing offers a low-cost, rapid prototyping, efficient fabrication method, as compared to the costly—in terms of time, labor, and resources—traditional fabrication method
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Microfluidic devices are used in a myriad of biomedical applications such as cancer screening, drug testing, and point-of-care diagnostics. Three-dimensional (3D) printing offers a low-cost, rapid prototyping, efficient fabrication method, as compared to the costly—in terms of time, labor, and resources—traditional fabrication method of soft lithography of poly(dimethylsiloxane) (PDMS). Various 3D printing methods are applicable, including fused deposition modeling, stereolithography, and photopolymer inkjet printing. Additionally, several materials are available that have low-viscosity in their raw form and, after printing and curing, exhibit high material strength, optical transparency, and biocompatibility. These features make 3D-printed microfluidic chips ideal for biomedical applications. However, for developing devices capable of long-term use, fouling—by nonspecific protein absorption and bacterial adhesion due to the intrinsic hydrophobicity of most 3D-printed materials—presents a barrier to reusability. For this reason, there is a growing interest in anti-fouling methods and materials. Traditional and emerging approaches to anti-fouling are presented in regard to their applicability to microfluidic chips, with a particular interest in approaches compatible with 3D-printed chips. Full article
(This article belongs to the Special Issue 3D Printed Microfluidic Devices)
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