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Micromachines, Volume 9, Issue 3 (March 2018)

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Cover Story (view full-size image) Circulating tumor cells (CTCs) are regarded as a strong biomarker which includes clinically [...] Read more.
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Editorial

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Open AccessEditorial Editorial for the Special Issue on MEMS Mirrors
Micromachines 2018, 9(3), 99; doi:10.3390/mi9030099
Received: 22 February 2018 / Revised: 22 February 2018 / Accepted: 23 February 2018 / Published: 27 February 2018
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Abstract
MEMS mirrors can steer, modulate, and switch light, as well as control the wavefront for focusing or phase modulation.[...] Full article
(This article belongs to the Special Issue MEMS Mirrors)
Open AccessEditorial Editorial for the Special Issue on Wireless Microdevices and Systems for Biomedical Applications
Micromachines 2018, 9(3), 112; doi:10.3390/mi9030112
Received: 27 February 2018 / Accepted: 27 February 2018 / Published: 5 March 2018
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Abstract
Wireless microdevices are getting smaller and smaller, and in this special issue seven papers address a few miniaturization challenges in the biomedical field, which are common across different applications. Kargaran et al. [1] proposes a new ultra-low-voltage ultra-low-power LNA, where the reduced current
[...] Read more.
Wireless microdevices are getting smaller and smaller, and in this special issue seven papers address a few miniaturization challenges in the biomedical field, which are common across different applications. Kargaran et al. [1] proposes a new ultra-low-voltage ultra-low-power LNA, where the reduced current consumption of only 160 A, on a supply as low as 0.18 V, has potential to enable future RF receivers for ultra-low-power implantable devices [...]
Full article
(This article belongs to the Special Issue Wireless Microdevices and Systems for Biomedical Applications)

Research

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Open AccessArticle Electrowetting Using a Microfluidic Kelvin Water Dropper
Micromachines 2018, 9(3), 92; doi:10.3390/mi9030092
Received: 16 December 2017 / Revised: 15 February 2018 / Accepted: 22 February 2018 / Published: 25 February 2018
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Abstract
The Kelvin water dropper is an electrostatic generator that can generate high voltage electricity through water dripping. A conventional Kelvin water dropper converts the gravitational potential energy of water into electricity. Due to its low current output, Kelvin water droppers can only be
[...] Read more.
The Kelvin water dropper is an electrostatic generator that can generate high voltage electricity through water dripping. A conventional Kelvin water dropper converts the gravitational potential energy of water into electricity. Due to its low current output, Kelvin water droppers can only be used in limited cases that demand high voltage. In the present study, microfluidic Kelvin water droppers (MKWDs) were built in house to demonstrate a low-cost but accurately controlled miniature device for high voltage generation. The performance of the MKWDs was characterized using different channel diameters and flow rates. The best performed MKWD was then used to conduct experiments of the electrowetting of liquid on dielectric surfaces. Electrowetting is a process that has been widely used in manipulating the wetting properties of a surface using an external electric field. Usually electrowetting requires an expensive DC power supply that outputs high voltage. However, in this research, it was demonstrated that electrowetting can be conducted by simply using an MKWD. Additionally, an analytic model was developed to simulate the electrowetting process. Finally, the model’s ability to well predict the liquid deformation during electrowetting using MKWDs was validated. Full article
(This article belongs to the Special Issue Micro/Nano-Chip Electrokinetics, Volume II)
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Open AccessArticle Wafer-Level Packaging Method for RF MEMS Applications Using Pre-Patterned BCB Polymer
Micromachines 2018, 9(3), 93; doi:10.3390/mi9030093
Received: 21 January 2018 / Revised: 19 February 2018 / Accepted: 21 February 2018 / Published: 25 February 2018
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Abstract
A radio-frequency micro-electro-mechanical system (RF MEMS) wafer-level packaging (WLP) method using pre-patterned benzo-cyclo-butene (BCB) polymers with a high-resistivity silicon cap is proposed to achieve high bonding quality and excellent RF performance. In this process, the BCB polymer was pre-defined to form the sealing
[...] Read more.
A radio-frequency micro-electro-mechanical system (RF MEMS) wafer-level packaging (WLP) method using pre-patterned benzo-cyclo-butene (BCB) polymers with a high-resistivity silicon cap is proposed to achieve high bonding quality and excellent RF performance. In this process, the BCB polymer was pre-defined to form the sealing ring and bonding layer by the spin-coating and patterning of photosensitive BCB before the cavity formation. During anisotropic wet etching of the silicon wafer to generate the housing cavity, the BCB sealing ring was protected by a sputtered Cr/Au (chromium/gold) layer. The average measured thickness of the BCB layer was 5.9 μm. In contrast to the conventional methods of spin-coating BCB after fabricating cavities, the pre-patterned BCB method presented BCB bonding layers with better quality on severe topography surfaces in terms of increased uniformity of thickness and better surface flatness. The observation of the bonded layer showed that no void or gap formed on the protruding coplanar waveguide (CPW) lines. A shear strength test was experimentally implemented as a function of the BCB widths in the range of 100–400 μm. The average shear strength of the packaged device was higher than 21.58 MPa. A RF MEMS switch was successfully packaged using this process with a negligible impact on the microwave characteristics and a significant improvement in the lifetime from below 10 million to over 1 billion. The measured insertion loss of the packaged RF MEMS switch was 0.779 dB and the insertion loss deterioration caused by the package structure was less than 0.2 dB at 30 GHz. Full article
(This article belongs to the Special Issue Wafer Level Packaging of MEMS)
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Open AccessArticle Prediction of Necrotic Core and Hypoxic Zone of Multicellular Spheroids in a Microbioreactor with a U-Shaped Barrier
Micromachines 2018, 9(3), 94; doi:10.3390/mi9030094
Received: 30 December 2017 / Revised: 6 February 2018 / Accepted: 22 February 2018 / Published: 25 February 2018
Cited by 1 | PDF Full-text (3996 KB) | HTML Full-text | XML Full-text
Abstract
Microfluidic devices have been widely used for biological and cellular studies. Microbioreactors for three-dimensional (3D) multicellular spheroid culture are now considered as the next generation in in vitro diagnostic tools. The feasibility of using 3D cell aggregates to form multicellular spheroids in a
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Microfluidic devices have been widely used for biological and cellular studies. Microbioreactors for three-dimensional (3D) multicellular spheroid culture are now considered as the next generation in in vitro diagnostic tools. The feasibility of using 3D cell aggregates to form multicellular spheroids in a microbioreactor with U-shaped barriers has been demonstrated experimentally. A barrier array is an alternative to commonly used microwell traps. The present study investigates oxygen and glucose concentration distributions as key parameters in a U-shaped array microbioreactor using finite element simulation. The effect of spheroid diameter, inlet concentration and flow rate of the medium are systematically studied. In all cases, the channel walls are considered to be permeable to oxygen. Necrotic and hypoxic or quiescent regions corresponding to both oxygen and glucose concentration distributions are identified for various conditions. The results show that the entire quiescent and necrotic regions become larger with increasing spheroid diameter and decreasing inlet and wall concentration. The shear stress (0.5–9 mPa) imposed on the spheroid surface by the fluid flow was compared with the critical values to predict possible damage to the cells. Finally, optimum range of medium inlet concentration (0.13–0.2 mM for oxygen and 3–11 mM for glucose) and flow rate (5–20 μL/min) are found to form the largest possible multicellular spheroid (500 μm), without any quiescent and necrotic regions with an acceptable shear stress. The effect of cell-trap types on the oxygen and glucose concentration inside the spheroid was also investigated. The levels of oxygen and glucose concentration for the microwell are much lower than those for the other two traps. The U-shaped barrier created with microposts allows for a continuous flow of culture medium, and so improves the glucose concentration compared to that in the integrated U-shaped barrier. Oxygen concentration for both types of U-shaped barriers is nearly the same. Due to the advantage of using U-shaped barriers to culture multicellular spheroids, the results of this paper can help to choose the experimental and design parameters of the microbioreactor. Full article
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Open AccessArticle Theoretical Studies of the Spin-Dependent Electronic Transport Properties in Ethynyl-Terminated Ferrocene Molecular Junctions
Micromachines 2018, 9(3), 95; doi:10.3390/mi9030095
Received: 17 January 2018 / Revised: 8 February 2018 / Accepted: 14 February 2018 / Published: 26 February 2018
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Abstract
The spin-dependent electron transport in the ferrocene-based molecular junctions, in which the molecules are 1,3-substituted and 1,3′-substituted ethynyl ferrocenes, respectively, is studied by the theoretical simulation with nonequilibrium Green’s function and density functional theory. The calculated results suggest that the substitution position of
[...] Read more.
The spin-dependent electron transport in the ferrocene-based molecular junctions, in which the molecules are 1,3-substituted and 1,3′-substituted ethynyl ferrocenes, respectively, is studied by the theoretical simulation with nonequilibrium Green’s function and density functional theory. The calculated results suggest that the substitution position of the terminal ethynyl groups has a great effect on the spin-dependent current-voltage properties and the spin filtering efficiency of the molecular junctions. At the lower bias, high spin filtering efficiency is found in 1,3′-substituted ethynyl ferrocene junction, which suggests that the spin filtering efficiency is also dependent on the bias voltage. The different spin-dependent transport properties for the two molecular junctions originate from their different evolutions of spin-up and spin-down energy levels. Full article
(This article belongs to the Special Issue Atomic and Molecular Junction for Molecular Electronic Devices)
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Open AccessArticle Fabrication of a Micro-Lens Array Mold by Micro Ball End-Milling and Its Hot Embossing
Micromachines 2018, 9(3), 96; doi:10.3390/mi9030096
Received: 24 January 2018 / Revised: 12 February 2018 / Accepted: 15 February 2018 / Published: 26 February 2018
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Abstract
Hot embossing is an efficient technique for manufacturing high-quality micro-lens arrays. The machining quality is significant for hot embossing the micro-lens array mold. This study investigates the effects of micro ball end-milling on the machining quality of AISI H13 tool steel used in
[...] Read more.
Hot embossing is an efficient technique for manufacturing high-quality micro-lens arrays. The machining quality is significant for hot embossing the micro-lens array mold. This study investigates the effects of micro ball end-milling on the machining quality of AISI H13 tool steel used in the micro-lens array mold. The micro ball end-milling experiments were performed under different machining strategies, and the surface roughness and scallop height of the machined micro-lens array mold are measured. The experimental results showed that a three-dimensional (3D) offset spiral strategy could achieve a higher machining quality in comparison with other strategies assessed in this study. Moreover, the 3D offset spiral strategy is more appropriate for machining the micro-lens array mold. With an increase of the cutting speed and feed rate, the surface roughness of the micro-lens array mold slightly increases, while a small step-over can greatly reduce the surface roughness. In addition, a hot embossing experiment was undertaken, and the obtained results indicated higher-quality production of the micro-lens array mold by the 3D offset spiral strategy. Full article
(This article belongs to the Special Issue Micro-Machining: Challenges and Opportunities)
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Open AccessArticle The Design of Rare-Earth Giant Magnetostrictive Ultrasonic Transducer and Experimental Study on Its Application of Ultrasonic Surface Strengthening
Micromachines 2018, 9(3), 98; doi:10.3390/mi9030098
Received: 16 January 2018 / Revised: 10 February 2018 / Accepted: 24 February 2018 / Published: 27 February 2018
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Abstract
Ultrasonic transducer based on rare-earth giant magnetostrictive materials was designed in accordance with the technical requirements of ultrasonic surface strengthening. The whole structure of the transducer was designed. Modal analysis is made to get the natural frequency of the compound oscillator. The working
[...] Read more.
Ultrasonic transducer based on rare-earth giant magnetostrictive materials was designed in accordance with the technical requirements of ultrasonic surface strengthening. The whole structure of the transducer was designed. Modal analysis is made to get the natural frequency of the compound oscillator. The working frequency of the transducer should be guaranteed at about 15.2 kHz and the composite oscillator should have relatively better vibration mode. The magnetic field of the transducer is well sealed and the transducer will not show obvious magnetic flux leakage phenomenon. Which shows the rationality of structural design. Based on this transducer, the ultrasonic surface strengthening experiment on 40 steel was conducted. The surface roughness and hardness of the parts were analyzed after the experiment. The results show that the surface of the parts reach the mirror surface result after the ultrasonic strengthening. When compared to the previous process, the roughness decreases by about 75%, and the surface hardness increases by more than 20%. Full article
(This article belongs to the Special Issue Micro-Machining: Challenges and Opportunities)
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Open AccessArticle Fabrication of 3D Capillary Vessel Models with Circulatory Connection Ports
Micromachines 2018, 9(3), 101; doi:10.3390/mi9030101
Received: 29 December 2017 / Revised: 6 February 2018 / Accepted: 22 February 2018 / Published: 28 February 2018
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Abstract
Bionic microscopic vessel models can contribute to the development of vascular treatment skills and techniques for clinical training. Most microscopic vessel models are limited to two dimensions, but three-dimensional (3D) models are important for surgery, such as on retina microscopic vessels, for the
[...] Read more.
Bionic microscopic vessel models can contribute to the development of vascular treatment skills and techniques for clinical training. Most microscopic vessel models are limited to two dimensions, but three-dimensional (3D) models are important for surgery, such as on retina microscopic vessels, for the observation of colon microvessels, for measuring the deformability of red blood cell (RBC), and so on. Therefore, bionic 3D blood vessel models are increasingly in demand. For this reason, it is necessary to establish 3D fabrication techniques for microchannels. In this study, we established two fabrication methods for 3D microfluidic devices for the development of microscopic vessel models. First, we employed an exposure method using photolithographic technology. Second, we employed a 3D method using femtosecond laser and mask hybrid exposure (FMEx). Both methods made it possible to fabricate a millimeter-scale 3D structure with a submicrometer resolution and achieve an easy injection of solution. This is because it was possible to fabricate typical microfluidic channels used for model inlet and outlet ports. Furthermore, in the FMEx method, we employed an acid-diffusion effect using a chemically amplified resist to form a circular channel cross-section. The acid-diffusion effect made it realizable to fabricate a smooth surface independent of the laser scanning line width. Thus, we succeeded in establishing two methods for the fabrication of bionic 3D microfluidic devices with microfluidic channels having diameters of 15–16 µm for mimicking capillary vessels. Full article
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Open AccessArticle On AC-Field-Induced Nonlinear Electroosmosis next to the Sharp Corner-Field-Singularity of Leaky Dielectric Blocks and Its Application in on-Chip Micro-Mixing
Micromachines 2018, 9(3), 102; doi:10.3390/mi9030102
Received: 7 February 2018 / Revised: 24 February 2018 / Accepted: 24 February 2018 / Published: 28 February 2018
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Abstract
Induced-charge electroosmosis has attracted lots of attention from the microfluidic community over the past decade. Most previous researches on this subject focused on induced-charge electroosmosis (ICEO) vortex streaming actuated on ideally polarizable surfaces immersed in electrolyte solutions. Starting from this point, we conduct
[...] Read more.
Induced-charge electroosmosis has attracted lots of attention from the microfluidic community over the past decade. Most previous researches on this subject focused on induced-charge electroosmosis (ICEO) vortex streaming actuated on ideally polarizable surfaces immersed in electrolyte solutions. Starting from this point, we conduct herein a linear asymptotic analysis on nonlinear electroosmotic flow next to leaky dielectric blocks of arbitrary electrical conductivity and dielectric permittivity in harmonic AC electric fields, and theoretically demonstrate that observable ICEO fluid motion can be generated at high field frequencies in the vicinity of nearly insulating semiconductors, a very low electrical conductivity, of which can evidently increase the double-layer relaxation frequency (inversely proportional to the solid permittivity) to be much higher than the typical reciprocal RC time constant for induced double-layer charging on ideally polarizable surfaces. A computational model is developed to study the feasibility of this high-frequency vortex flow field of ICEO for sample mixing in microfluidics, in which the usage of AC voltage signal at high field frequencies may be beneficial to suppress electrochemical reactions to some extent. The influence of various parameters for developing an efficient mixer is investigated, and an integrated arrangement of semiconductor block array is suggested for achieving a reliable mixing performance at relatively high sample fluxes. Our physical demonstration with high-frequency ICEO next to leaky dielectric blocks using a simple channel structure offers valuable insights into the design of high-throughput micromixers for a variety of lab-on-a-chip applications. Full article
(This article belongs to the Special Issue Micro/Nano-Chip Electrokinetics, Volume II)
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Open AccessArticle Experimental Research on Fluid Coupling Flexible Actuator
Micromachines 2018, 9(3), 103; doi:10.3390/mi9030103
Received: 4 January 2018 / Revised: 8 February 2018 / Accepted: 22 February 2018 / Published: 28 February 2018
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Abstract
In the field of micromechanics, piezoelectric actuator has attracted great attention for its high-frequency response, high displacement resolution, and high output force. However, its prospect of practical application has been largely limited by the displacement of micrometer. A fluid coupling flexible actuator was
[...] Read more.
In the field of micromechanics, piezoelectric actuator has attracted great attention for its high-frequency response, high displacement resolution, and high output force. However, its prospect of practical application has been largely limited by the displacement of micrometer. A fluid coupling flexible actuator was proposed, which utilizes resonance to enlarge the output displacement. The actuator uses a piezoelectric oscillator as an excitation source, fluid as the transmission medium and a flexible diaphragm for the displacement output. On the condition that the fluid is inviscid and incompressible, mathematical formulation of the membrane vibration theory has been analyzed. Then, the prototype is made. The displacement is amplified 21 times to 1.106 mm when driving frequency is 127 Hz. The flexible diaphragm appears the largest displacement output when driving frequency is close to one of the system’s natural frequency. Then, the points with zero amplitude form a circle on the surface of flexible diaphragm and the movement direction of the flexible diaphragm is opposite on different sides of the circle. In fact, rather than vibrates at the first resonance frequency, the membrane in the essay is vibrating at a certain higher-order resonance frequency. The experimental results are mainly consistent with the theoretical analysis. Full article
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Open AccessArticle Design, Fabrication, and Implementation of an Array-Type MEMS Piezoresistive Intelligent Pressure Sensor System
Micromachines 2018, 9(3), 104; doi:10.3390/mi9030104
Received: 29 December 2017 / Revised: 12 February 2018 / Accepted: 26 February 2018 / Published: 28 February 2018
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Abstract
To meet the radiosonde requirement of high sensitivity and linearity, this study designs and implements a monolithically integrated array-type piezoresistive intelligent pressure sensor system which is made up of two groups of four pressure sensors with the pressure range of 0–50 kPa and
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To meet the radiosonde requirement of high sensitivity and linearity, this study designs and implements a monolithically integrated array-type piezoresistive intelligent pressure sensor system which is made up of two groups of four pressure sensors with the pressure range of 0–50 kPa and 0–100 kPa respectively. First, theoretical models and ANSYS (version 14.5, Canonsburg, PA, USA) finite element method (FEM) are adopted to optimize the parameters of array sensor structure. Combing with FEM stress distribution results, the size and material characteristics of the array-type sensor are determined according to the analysis of the sensitivity and the ratio of signal to noise (SNR). Based on the optimized parameters, the manufacture and packaging of array-type sensor chips are then realized by using the standard complementary metal-oxide-semiconductor (CMOS) and microelectromechanical system (MEMS) process. Furthermore, an intelligent acquisition and processing system for pressure and temperature signals is achieved. The S3C2440A microprocessor (Samsung, Seoul, Korea) is regarded as the core part which can be applied to collect and process data. In particular, digital signal storage, display and transmission are realized by the application of a graphical user interface (GUI) written in QT/E. Besides, for the sake of compensating the temperature drift and nonlinear error, the data fusion technique is proposed based on a wavelet neural network improved by genetic algorithm (GA-WNN) for average measuring signal. The GA-WNN model is implemented in hardware by using a S3C2440A microprocessor. Finally, the results of calibration and test experiments achieved with the temperature ranges from −20 to 20 °C show that: (1) the nonlinear error and the sensitivity of the array-type pressure sensor are 8330 × 10−4 and 0.052 mV/V/kPa in the range of 0–50 kPa, respectively; (2) the nonlinear error and the sensitivity are 8129 × 10−4 and 0.020 mV/V/kPa in the range of 50–100 kPa, respectively; (3) the overall error of the intelligent pressure sensor system is maintained at ±0.252% within the hybrid composite range (0–100 kPa). The involved results indicate that the developed array-type composite pressure sensor has good performance, which can provide a useful reference for the development of multi-range MEMS piezoresistive pressure sensor. Full article
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Open AccessArticle An Adaptable Interface Conditioning Circuit Based on Triboelectric Nanogenerators for Self-Powered Sensors
Micromachines 2018, 9(3), 105; doi:10.3390/mi9030105
Received: 29 December 2017 / Revised: 22 February 2018 / Accepted: 23 February 2018 / Published: 1 March 2018
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Abstract
In order to solve the limited life problem of typical battery power supply, a self-powered method that is based on the environmental energy harvesting has emerged as an amazing power supply approach. The Tribo-electric-Nano-generator (TENG) has been widely studied because of its high
[...] Read more.
In order to solve the limited life problem of typical battery power supply, a self-powered method that is based on the environmental energy harvesting has emerged as an amazing power supply approach. The Tribo-electric-Nano-generator (TENG) has been widely studied because of its high efficiency, low fabrication cost, and high output voltage. However, low output power conversion efficiency has restricted its practical application because of its own extremely high output impedance. In order to match the high output impedance of TENG and increase the output power, this paper presents an adaptable interface conditioning circuit, which is composed of an impedance matching circuit, a synchronous rectifier bridge, a control circuit, and an energy storage device. In the impedance matching circuit, the energy loss of coupling inductance could be reduced by using the bi-directional switch to increase the frequency, and impedance matching circuit can be used to increase the output efficiency of TENG. Experimental results show that, in about 3.6 s, the storing capacitor voltage was basically stable at 5.5 V by using the proposed adapted interface conditioning circuit in this paper. The charging efficiency has increased by 50%. Full article
(This article belongs to the Special Issue Interface Circuits for Microsensor Integrated Systems)
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Open AccessArticle Deterministic Capture of Individual Circulating Tumor Cells Using a Flow-Restricted Microfluidic Trap Array
Micromachines 2018, 9(3), 106; doi:10.3390/mi9030106
Received: 31 January 2018 / Revised: 27 February 2018 / Accepted: 27 February 2018 / Published: 2 March 2018
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Abstract
Circulating tumor cells (CTCs) are regarded as a strong biomarker which includes clinically valuable information. However, CTCs are very rare and require precise separation and detection for effective clinical applications. Furthermore, downstream analysis has become necessary to identify the distinct sub-population of CTCs
[...] Read more.
Circulating tumor cells (CTCs) are regarded as a strong biomarker which includes clinically valuable information. However, CTCs are very rare and require precise separation and detection for effective clinical applications. Furthermore, downstream analysis has become necessary to identify the distinct sub-population of CTCs that causes metastasis. Here, we report a flow-restricted microfluidic trap array capable of deterministic single-cell capture of CTCs. The extent of flow restriction, correlating with the device geometry, was then optimized using a highly invasive breast cancer cell line (LM2 MDA-MB-231) to achieve 97% capture efficiency with a single-cell capture rate of 99%. Single-cell capture of CTCs from mice with full-blown metastasis was also demonstrated. The single-CTC capturing ability of the flow-restricted trap array not only showed cell enumerating ability but also high prospects for application in future automated downstream analysis. Full article
(This article belongs to the Special Issue Microfluidics for Circulating Biomarkers)
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Open AccessArticle Mixing Enhancement in Serpentine Micromixers with a Non-Rectangular Cross-Section
Micromachines 2018, 9(3), 107; doi:10.3390/mi9030107
Received: 31 January 2018 / Revised: 16 February 2018 / Accepted: 28 February 2018 / Published: 2 March 2018
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Abstract
In this numerical study, a new type of serpentine micromixer involving mixing units with a non-rectangular cross-section is investigated. Similar to other serpentine/spiral shaped micromixers, the design exploits the formation of transversal vortices (Dean flows) in pressure-driven systems, associated with the centrifugal forces
[...] Read more.
In this numerical study, a new type of serpentine micromixer involving mixing units with a non-rectangular cross-section is investigated. Similar to other serpentine/spiral shaped micromixers, the design exploits the formation of transversal vortices (Dean flows) in pressure-driven systems, associated with the centrifugal forces experienced by the fluid as it is confined to move along curved geometries. In contrast with other previous designs, though, the use of non-rectangular cross-sections that change orientation between mixing units is exploited to control the center of rotation of the transversal flows formed. The associated extensional flows that thus develop between the mixing segments complement the existent rotational flows, leading to a more complex fluid motion. The fluid flow characteristics and associated mixing are determined numerically from computational solutions to Navier–Stokes equations and the concentration-diffusion equation. It is found that the performance of the investigated mixers exceeds that of simple serpentine channels with a more consistent behavior at low and high Reynolds numbers. An analysis of the mixing quality using an entropic mixing index indicates that maximum mixing can be achieved at Reynolds numbers as small as 20 in less than four serpentine mixing units. Full article
(This article belongs to the Special Issue Passive Micromixers)
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Open AccessArticle Analytical, Numerical and Experimental Study of a Horizontal Electrothermal MEMS Microgripper for the Deformability Characterisation of Human Red Blood Cells
Micromachines 2018, 9(3), 108; doi:10.3390/mi9030108
Received: 5 February 2018 / Revised: 23 February 2018 / Accepted: 27 February 2018 / Published: 2 March 2018
Cited by 1 | PDF Full-text (4584 KB) | HTML Full-text | XML Full-text
Abstract
Microgrippers are typical microelectromechanical systems (MEMS) that are widely used for micromanipulation and microassembly in both biological and micromanufacturing fields. This paper presents the design, modelling, fabrication and experimental testing of an electrothermal microgripper based on a ‘hot and cold arm’ actuator design
[...] Read more.
Microgrippers are typical microelectromechanical systems (MEMS) that are widely used for micromanipulation and microassembly in both biological and micromanufacturing fields. This paper presents the design, modelling, fabrication and experimental testing of an electrothermal microgripper based on a ‘hot and cold arm’ actuator design that is suitable for the deformability characterisation of human red blood cells (RBCs). The analysis of the mechanical properties of human RBCs is of great interest in the field of medicine as pathological alterations in the deformability characteristics of RBCs have been linked to a number of diseases. The study of the microgripper’s steady-state performance is initially carried out by the development of a lumped analytical model, followed by a numerical model established in CoventorWare® (Coventor, Inc., Cary, NC, USA) using multiphysics finite element analysis. Both analytical and numerical models are based on an electothermomechanical analysis, and take into account the internal heat generation due to the applied potential, as well as conduction heat losses through both the anchor pads and the air gap to the substrate. The models are used to investigate key factors of the actuator’s performance including temperature distribution, deflection and stresses based on an elastic analysis of structures. Results show that analytical and numerical values for temperature and deflection are in good agreement. The analytical and computational models are then validated experimentally using a polysilicon microgripper fabricated by the standard surface micromachining process, PolyMUMPs™ (Durham, NC, USA). The microgripper’s actuation is characterised at atmospheric pressure by optical microscopy studies. Experimental results for the deflection of the microgripper arm tips are found to be in good agreement with the analytical and numerical results, with process-induced variations and the non-linear temperature dependence of the material properties accounting for the slight discrepancies observed. The microgripper is shown to actuate to a maximum opening displacement of 9 μ m at an applied voltage of 3 V, thus being in line with the design requirement of an approximate opening of 8 μ m for securing and characterising a RBC. Full article
(This article belongs to the Special Issue Silicon-based Micro/Nanofabrication for Biomedical Applications)
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Open AccessArticle Turing Instability-Driven Biofabrication of Branching Tissue Structures: A Dynamic Simulation and Analysis Based on the Reaction–Diffusion Mechanism
Micromachines 2018, 9(3), 109; doi:10.3390/mi9030109
Received: 1 January 2018 / Revised: 20 February 2018 / Accepted: 1 March 2018 / Published: 2 March 2018
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Abstract
Four-dimensional (4D) biofabrication techniques aim to dynamically produce and control three-dimensional (3D) biological structures that would transform their shapes or functionalities with time, when a stimulus is imposed or cell post-printing self-assembly occurs. The evolution of 3D branching patterns via self-assembly of cells
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Four-dimensional (4D) biofabrication techniques aim to dynamically produce and control three-dimensional (3D) biological structures that would transform their shapes or functionalities with time, when a stimulus is imposed or cell post-printing self-assembly occurs. The evolution of 3D branching patterns via self-assembly of cells is critical for the 4D biofabrication of artificial organs or tissues with branched geometry. However, it is still unclear how the formation and evolution of these branching patterns are biologically encoded. Here, we study the biofabrication of lung branching structures utilizing a simulation model based on Turing instability that raises a dynamic reaction–diffusion (RD) process of the biomolecules and cells. The simulation model incorporates partial differential equations of four variables, describing the tempo-spatial distribution of the variables in 3D over time. The simulation results present the formation and evolution process of 3D branching patterns over time and also interpret both the behaviors of side-branching and tip-splitting as the stalk grows and the fabrication style under an external concentration gradient of morphogen, through 3D visualization. This provides a theoretical framework for rationally guiding the 4D biofabrication of lung airway grafts via cellular self-organization, which would potentially reduce the complexity of future experimental research and number of trials. Full article
(This article belongs to the Special Issue Selected Papers from ICMEAS 2017)
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Open AccessArticle Multi-Objective Optimizations of a Serpentine Micromixer with Crossing Channels at Low and High Reynolds Numbers
Micromachines 2018, 9(3), 110; doi:10.3390/mi9030110
Received: 24 January 2018 / Revised: 26 February 2018 / Accepted: 1 March 2018 / Published: 4 March 2018
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Abstract
In order to maximize the mixing performance of a micromixer with an integrated three-dimensional serpentine and split-and-recombination configuration, multi-objective optimizations were performed at two different Reynolds numbers, 1 and 120, based on numerical simulation. Numerical analyses of fluid flow and mixing in the
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In order to maximize the mixing performance of a micromixer with an integrated three-dimensional serpentine and split-and-recombination configuration, multi-objective optimizations were performed at two different Reynolds numbers, 1 and 120, based on numerical simulation. Numerical analyses of fluid flow and mixing in the micromixer were performed using three-dimensional Navier-Stokes equations and convection-diffusion equation. Three dimensionless design variables that were related to the geometry of the micromixer were selected as design variables for optimization. Mixing index at the exit and pressure drop through the micromixer were employed as two objective functions. A parametric study was carried out to explore the effects of the design variables on the objective functions. Latin hypercube sampling method as a design-of-experiment technique has been used to select design points in the design space. Surrogate modeling of the objective functions was performed by using radial basis neural network. Concave Pareto-optimal curves comprising of Pareto-optimal solutions that represents the trade-off between the objective functions were obtained using a multi-objective genetic algorithm at Re = 1 and 120. Through the optimizations, maximum enhancements of 18.8% and 6.0% in mixing index were achieved at Re = 1 and 120, respectively. Full article
(This article belongs to the Special Issue Passive Micromixers)
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Open AccessArticle Modeling and Closed Loop Flight Testing of a Fixed Wing Micro Air Vehicle
Micromachines 2018, 9(3), 111; doi:10.3390/mi9030111
Received: 6 February 2018 / Revised: 28 February 2018 / Accepted: 1 March 2018 / Published: 4 March 2018
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Abstract
This paper presents the nonlinear six degrees of freedom dynamic modeling of a fixed wing micro air vehicle. The static derivatives of the micro air vehicle are obtained through the wind tunnel testing. The propeller effects on the lift, drag, pitching moment and
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This paper presents the nonlinear six degrees of freedom dynamic modeling of a fixed wing micro air vehicle. The static derivatives of the micro air vehicle are obtained through the wind tunnel testing. The propeller effects on the lift, drag, pitching moment and side force are quantified through wind tunnel testing. The dynamic derivatives are obtained through empirical relations available in the literature. The trim conditions are computed for a straight and constant altitude flight condition. The linearized longitudinal and lateral state space models are obtained about trim conditions. The variations in short period mode, phugoid mode, Dutch roll mode, roll subsidence mode and spiral mode with respect to different trim operating conditions is presented. A stabilizing static output feedback controller is designed using the obtained model. Successful closed loop flight trials are conducted with the static output feedback controller. Full article
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Open AccessArticle Adaptive Absolute Ego-Motion Estimation Using Wearable Visual-Inertial Sensors for Indoor Positioning
Micromachines 2018, 9(3), 113; doi:10.3390/mi9030113
Received: 29 December 2017 / Revised: 2 March 2018 / Accepted: 3 March 2018 / Published: 6 March 2018
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Abstract
This paper proposes an adaptive absolute ego-motion estimation method using wearable visual-inertial sensors for indoor positioning. We introduce a wearable visual-inertial device to estimate not only the camera ego-motion, but also the 3D motion of the moving object in dynamic environments. Firstly, a
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This paper proposes an adaptive absolute ego-motion estimation method using wearable visual-inertial sensors for indoor positioning. We introduce a wearable visual-inertial device to estimate not only the camera ego-motion, but also the 3D motion of the moving object in dynamic environments. Firstly, a novel method dynamic scene segmentation is proposed using two visual geometry constraints with the help of inertial sensors. Moreover, this paper introduces a concept of “virtual camera” to consider the motion area related to each moving object as if a static object were viewed by a “virtual camera”. We therefore derive the 3D moving object’s motion from the motions for the real and virtual camera because the virtual camera’s motion is actually the combined motion of both the real camera and the moving object. In addition, a multi-rate linear Kalman-filter (MR-LKF) as our previous work was selected to solve both the problem of scale ambiguity in monocular camera tracking and the different sampling frequencies of visual and inertial sensors. The performance of the proposed method is evaluated by simulation studies and practical experiments performed in both static and dynamic environments. The results show the method’s robustness and effectiveness compared with the results from a Pioneer robot as the ground truth. Full article
(This article belongs to the Special Issue MEMS Technology for Biomedical Imaging Applications)
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Open AccessArticle Design, Preparation and Performance Study of On-Chip Flow-Through Amperometric Sensors with an Integrated Ag/AgCl Reference Electrode
Micromachines 2018, 9(3), 114; doi:10.3390/mi9030114
Received: 23 January 2018 / Revised: 27 February 2018 / Accepted: 28 February 2018 / Published: 7 March 2018
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Abstract
To improve the reference potential stability of on-chip amperometric sensors, we propose a novel integrated Ag/AgCl reference electrode structure. This structure can refresh the saturated potassium chloride filling solution surrounding the Ag/AgCl electrode. We then designed a flow-through amperometric sensor and a multilayer
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To improve the reference potential stability of on-chip amperometric sensors, we propose a novel integrated Ag/AgCl reference electrode structure. This structure can refresh the saturated potassium chloride filling solution surrounding the Ag/AgCl electrode. We then designed a flow-through amperometric sensor and a multilayer microfluidic chip based on the integrated reference electrode. In order to improve the detection signal strength of the flow-through sensor, a numerical simulation model was established. The simulation results showed that a combination of (1) using a step-type detection cell structure that maintains micro-channel width while reducing micro-channel height, and (2) controlling the sample flow rate to limit the mass transfer of the sensor surface effectively, improves the detection signal strength. The step-type detection cell structure had dimensions of 200 μm × 200 μm × 100 μm (length × width × height), and the electroosmotic flow driving voltage was 120 V/cm. Finally, successful trace detection of Mg2+ and Pb2+ in the water was achieved using the amperometric sensor and microfluidic chip: detection limits were 5 μmol/L and 84 μmol/L. The preparation of an on-chip flow-through amperometric sensor with an integrated Ag/AgCl reference electrode will facilitate improved portability of microfluidic detection technology. Full article
(This article belongs to the Special Issue Microfluidic Sensors)
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Open AccessArticle Highly Fluorinated Methacrylates for Optical 3D Printing of Microfluidic Devices
Micromachines 2018, 9(3), 115; doi:10.3390/mi9030115
Received: 31 January 2018 / Revised: 27 February 2018 / Accepted: 7 March 2018 / Published: 8 March 2018
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Abstract
Highly fluorinated perfluoropolyether (PFPE) methacrylates are of great interest for transparent and chemically resistant microfluidic chips. However, so far only a few examples of material formulations for three-dimensional (3D) printing of these polymers have been demonstrated. In this paper we show that microfluidic
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Highly fluorinated perfluoropolyether (PFPE) methacrylates are of great interest for transparent and chemically resistant microfluidic chips. However, so far only a few examples of material formulations for three-dimensional (3D) printing of these polymers have been demonstrated. In this paper we show that microfluidic chips can be printed using these highly fluorinated polymers by 3D stereolithography printing. We developed photocurable resin formulations that can be printed in commercial benchtop stereolithography printers. We demonstrate that the developed formulations can be printed with minimal cross-sectional area of 600 µm for monolithic embedded microfluidic channels and 200 µm for open structures. The printed and polymerized PFPE methacrylates show a good transmittance above 70% at wavelengths between 520–900 nm and a high chemical resistance when being exposed to organic solvents. Microfluidic mixers were printed to demonstrate the great variability of different designs that can be printed using stereolithography. Full article
(This article belongs to the Special Issue 3D Printed Microfluidic Devices)
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Open AccessArticle Monitoring of Non-Ferrous Wear Debris in Hydraulic Oil by Detecting the Equivalent Resistance of Inductive Sensors
Micromachines 2018, 9(3), 117; doi:10.3390/mi9030117
Received: 29 December 2017 / Revised: 3 March 2018 / Accepted: 5 March 2018 / Published: 8 March 2018
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Abstract
Wear debris in hydraulic oil contains important information on the operation of equipment, which is important for condition monitoring and fault diagnosis in mechanical equipment. A micro inductive sensor based on the inductive coulter principle is presented in this work. It consists of
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Wear debris in hydraulic oil contains important information on the operation of equipment, which is important for condition monitoring and fault diagnosis in mechanical equipment. A micro inductive sensor based on the inductive coulter principle is presented in this work. It consists of a straight micro-channel and a 3-D solenoid coil wound on the micro-channel. Instead of detecting the inductance change of the inductive sensor, the equivalent resistance change of the inductive sensor is detected for non-ferrous particle (copper particle) monitoring. The simulation results show that the resistance change rate caused by the presence of copper particles is greater than the inductance change rate. Copper particles with sizes ranging from 48 μm to 150 μm were used in the experiment, and the experimental results are in good agreement with the simulation results. By detecting the inductive change of the micro inductive sensor, the detection limit of the copper particles only reaches 70 μm. However, the detection limit can be improved to 48 μm by detecting the equivalent resistance of the inductive sensor. The equivalent resistance method was demonstrated to have a higher detection accuracy than conventional inductive detection methods for non-ferrous particle detection in hydraulic oil. Full article
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Open AccessArticle Determination of the Three-Dimensional Rate of Cancer Cell Rotation in an Optically-Induced Electrokinetics Chip Using an Optical Flow Algorithm
Micromachines 2018, 9(3), 118; doi:10.3390/mi9030118
Received: 28 January 2018 / Revised: 21 February 2018 / Accepted: 1 March 2018 / Published: 8 March 2018
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Abstract
Our group has reported that Melan-A cells and lymphocytes undergo self-rotation in a homogeneous AC electric field, and found that the rotation velocity of these cells is a key indicator to characterize their physical properties. However, the determination of the rotation properties of
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Our group has reported that Melan-A cells and lymphocytes undergo self-rotation in a homogeneous AC electric field, and found that the rotation velocity of these cells is a key indicator to characterize their physical properties. However, the determination of the rotation properties of a cell by human eyes is both gruesome and time consuming, and not always accurate. In this paper, a method is presented to more accurately determine the 3D cell rotation velocity and axis from a 2D image sequence captured by a single camera. Using the optical flow method, we obtained the 2D motion field data from the image sequence and back-project it onto a 3D sphere model, and then the rotation axis and velocity of the cell were calculated. After testing the algorithm on animated image sequences, experiments were also performed on image sequences of real rotating cells. All of these results indicate that this method is accurate, practical, and useful. Furthermore, the method presented there can also be used to determine the 3D rotation velocity of other types of spherical objects that are commonly used in microfluidic applications, such as beads and microparticles. Full article
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Open AccessArticle Study of the Operational Safety of a Vascular Interventional Surgical Robotic System
Micromachines 2018, 9(3), 119; doi:10.3390/mi9030119
Received: 29 December 2017 / Revised: 1 March 2018 / Accepted: 6 March 2018 / Published: 8 March 2018
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Abstract
This paper proposes an operation safety early warning system based on LabView (2014, National Instruments Corporation, Austin, TX, USA) for vascular interventional surgery (VIS) robotic system. The system not only provides intuitive visual feedback information for the surgeon, but also has a safety
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This paper proposes an operation safety early warning system based on LabView (2014, National Instruments Corporation, Austin, TX, USA) for vascular interventional surgery (VIS) robotic system. The system not only provides intuitive visual feedback information for the surgeon, but also has a safety early warning function. It is well known that blood vessels differ in their ability to withstand stress in different age groups, therefore, the operation safety early warning system based on LabView has a vascular safety threshold function that changes in real-time, which can be oriented to different age groups of patients and a broader applicable scope. In addition, the tracing performance of the slave manipulator to the master manipulator is also an important index for operation safety. Therefore, we also transformed the slave manipulator and integrated the displacement error compensation algorithm in order to improve the tracking ability of the slave manipulator to the master manipulator and reduce master–slave tracking errors. We performed experiments “in vitro” to validate the proposed system. According to previous studies, 0.12 N is the maximum force when the blood vessel wall has been penetrated. Experimental results showed that the proposed operation safety early warning system based on LabView combined with operating force feedback can effectively avoid excessive collisions between the surgical catheter and vessel wall to avoid vascular puncture. The force feedback error of the proposed system is maintained between ±20 mN, which is within the allowable safety range and meets our design requirements. Therefore, the proposed system can ensure the safety of surgery. Full article
(This article belongs to the Special Issue Biomedical Microdevices: Design, Fabrication and Application)
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Open AccessArticle Design, Fabrication, and Performance Characterization of LTCC-Based Capacitive Accelerometers
Micromachines 2018, 9(3), 120; doi:10.3390/mi9030120
Received: 28 December 2017 / Revised: 28 February 2018 / Accepted: 7 March 2018 / Published: 9 March 2018
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Abstract
In this paper, two versions of capacitive accelerometers based on low-temperature co-fired ceramic (LTCC) technology are developed, different with respect to the detection technique, as well as the mechanical structure. Fabrication of the key structure, a heavy proof mass with thin beams embedded
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In this paper, two versions of capacitive accelerometers based on low-temperature co-fired ceramic (LTCC) technology are developed, different with respect to the detection technique, as well as the mechanical structure. Fabrication of the key structure, a heavy proof mass with thin beams embedded in a large cavity, which is extremely difficult for the conventional LTCC process, is successfully completed by the optimized process. The LC resonant accelerometer, using coupling resonance frequency sensing which is first applied to LTCC accelerometer and may facilitate application in harsh environments, demonstrates a sensitivity of 375 KHz/g over the full scale range 1 g, with nonlinearity less than 6%, and the telemetry distance is 5 mm. The differential capacitive accelerometer adopting differential capacitive sensing presents a larger full scale range 10 g and lower nonlinearity less than 1%, and the sensitivity is 30.27 mV/g. Full article
(This article belongs to the Special Issue MEMS Accelerometers)
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Open AccessArticle A Novel High-Precision Digital Tunneling Magnetic Resistance-Type Sensor for the Nanosatellites’ Space Application
Micromachines 2018, 9(3), 121; doi:10.3390/mi9030121
Received: 16 January 2018 / Revised: 21 February 2018 / Accepted: 6 March 2018 / Published: 9 March 2018
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Abstract
Micro-electromechanical system (MEMS) magnetic sensors are widely used in the nanosatellites field. We proposed a novel high-precision miniaturized three-axis digital tunneling magnetic resistance-type (TMR) sensor. The design of the three-axis digital magnetic sensor includes a low-noise sensitive element and high-performance interface circuit. The
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Micro-electromechanical system (MEMS) magnetic sensors are widely used in the nanosatellites field. We proposed a novel high-precision miniaturized three-axis digital tunneling magnetic resistance-type (TMR) sensor. The design of the three-axis digital magnetic sensor includes a low-noise sensitive element and high-performance interface circuit. The TMR sensor element can achieve a background noise of 150 pT/Hz1/2 by the vertical modulation film at a modulation frequency of 5 kHz. The interface circuit is mainly composed of an analog front-end current feedback instrumentation amplifier (CFIA) with chopper structure and a fully differential 4th-order Sigma-Delta (ΣΔ) analog to digital converter (ADC). The low-frequency 1/f noise of the TMR magnetic sensor are reduced by the input-stage and system-stage chopper. The dynamic element matching (DEM) is applied to average out the mismatch between the input and feedback transconductor so as to improve the gain accuracy and gain drift. The digital output is achieved by a switched-capacitor ΣΔ ADC. The interface circuit is implemented by a 0.35 μm CMOS technology. The performance test of the TMR magnetic sensor system shows that: at a 5 V operating voltage, the sensor can achieve a power consumption of 120 mW, a full scale of ±1 Guass, a bias error of 0.01% full scale (FS), a nonlinearity of x-axis 0.13% FS, y-axis 0.11% FS, z-axis 0.15% FS and a noise density of x-axis 250 pT/Hz1/2 (at 1 Hz), y-axis 240 pT/Hz1/2 (at 1 Hz), z-axis 250 pT/Hz1/2 (at 1 Hz), respectively. This work has a less power consumption, a smaller size, and higher resolution than other miniaturized magnetometers by comparison. Full article
(This article belongs to the Special Issue Development of CMOS-MEMS/NEMS Devices)
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Open AccessArticle Three-Dimensional Reservoir-Based Dielectrophoresis (rDEP) for Enhanced Particle Enrichment
Micromachines 2018, 9(3), 123; doi:10.3390/mi9030123
Received: 25 January 2018 / Revised: 24 February 2018 / Accepted: 9 March 2018 / Published: 10 March 2018
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Abstract
Selective enrichment of target species is crucial for a wide variety of engineering systems for improved performance of subsequent processes. Dielectrophoresis (DEP) is a powerful electrokinetic method that can be used to focus, trap, concentrate, and separate a variety of species in a
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Selective enrichment of target species is crucial for a wide variety of engineering systems for improved performance of subsequent processes. Dielectrophoresis (DEP) is a powerful electrokinetic method that can be used to focus, trap, concentrate, and separate a variety of species in a label-free manner. The commonly employed methods for DEP suffer from limitations such as electrode fouling and high susceptibility to Joule heating effects. Recently, our group has demonstrated DEP-based manipulations of particles and cells using a novel method of reservoir-based dielectrophoresis (rDEP) which exploits the naturally produced electric field gradients at the reservoir-microchannel junction. Although this method reasonably addresses the limitations mentioned above while maintaining a high simplicity of fabrication, all of our demonstrations so far have used a two-dimensional rDEP, which limits the performance of the devices. This work aims to improve their performance further by making the DEP three-dimensional. Through detailed experimental and numerical analysis, we demonstrate a six-fold increase in the enrichment performance of latex beads and a significant reduction in the power consumption for the new devices, which would allow a more reliable integration of the same into micro-total analysis systems. Full article
(This article belongs to the Special Issue Micro/Nano-Chip Electrokinetics, Volume II)
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Open AccessArticle Microstructure Formation of Functional Polymers by Evaporative Self-Assembly under Flexible Geometric Confinement
Micromachines 2018, 9(3), 124; doi:10.3390/mi9030124
Received: 30 January 2018 / Revised: 2 March 2018 / Accepted: 8 March 2018 / Published: 12 March 2018
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Abstract
Polymer microstructures are widely used in optics, flexible electronics, and so forth. We demonstrate a cost-effective bottom-up manner for patterning polymer microstructures by evaporative self-assembly under a flexible geometric confinement at a high temperature. Two-parallel-plates confinement would become curve-to-flat shape geometric confinement as
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Polymer microstructures are widely used in optics, flexible electronics, and so forth. We demonstrate a cost-effective bottom-up manner for patterning polymer microstructures by evaporative self-assembly under a flexible geometric confinement at a high temperature. Two-parallel-plates confinement would become curve-to-flat shape geometric confinement as the polydimethylsiloxane (PDMS) cover plate deformed during solvent swelling. We found that a flexible cover plate would be favorable for the formation of gradient microstructures, with various periodicities and widths obtained at varied heights of clearance. After thermal annealing, the edge of the PMMA (Poly-methylmethacrylate) microstructures would become smooth, while the RR-P3HT (regioregular-poly(3-hexylthiophene)) might generate nanocrystals. The morphologies of RR-P3HT structures included thick films, straight lines, hierarchical stripes, incomplete stripes, and regular dots. Finally, a simple field-effect transistor (FET) device was demonstrated with the RR-P3HT micropattern as an active layer. Full article
(This article belongs to the Special Issue Self-Assembly of Polymers)
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Open AccessFeature PaperCommunication Digital Manufacturing of Selective Porous Barriers in Microchannels Using Multi-Material Stereolithography
Micromachines 2018, 9(3), 125; doi:10.3390/mi9030125
Received: 1 February 2018 / Revised: 9 March 2018 / Accepted: 13 March 2018 / Published: 14 March 2018
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Abstract
We have developed a sequential stereolithographic co-printing process using two different resins for fabricating porous barriers in microfluidic devices. We 3D-printed microfluidic channels with a resin made of poly(ethylene glycol) diacrylate (MW = 258) (PEG-DA-258), a UV photoinitiator, and a UV sensitizer. The
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We have developed a sequential stereolithographic co-printing process using two different resins for fabricating porous barriers in microfluidic devices. We 3D-printed microfluidic channels with a resin made of poly(ethylene glycol) diacrylate (MW = 258) (PEG-DA-258), a UV photoinitiator, and a UV sensitizer. The porous barriers were created within the microchannels in a different resin made of either PEG-DA (MW = 575) (PEG-DA-575) or 40% (w/w in water) PEG-DA (MW = 700) (40% PEG-DA-700). We showed selective hydrogen ion diffusion across a 3D-printed PEG-DA-575 porous barrier in a cross-channel diffusion chip by observing color changes in phenol red, a pH indicator. We also demonstrated the diffusion of fluorescein across a 3D-printed 40% PEG-DA-700 porous barrier in a symmetric-channel diffusion chip by measuring fluorescence intensity changes across the porous barrier. Creating microfluidic chips with integrated porous barriers using a semi-automated 3D printing process shortens the design and processing time, avoids assembly and bonding complications, and reduces manufacturing costs compared to micromolding processes. We believe that our digital manufacturing method for fabricating selective porous barriers provides an inexpensive, simple, convenient and reproducible route to molecule delivery in the fields of molecular filtration and cell-based microdevices. Full article
(This article belongs to the Special Issue 3D Printed Microfluidic Devices)
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Open AccessArticle Micro-UFO (Untethered Floating Object): A Highly Accurate Microrobot Manipulation Technique
Micromachines 2018, 9(3), 126; doi:10.3390/mi9030126
Received: 2 February 2018 / Revised: 3 March 2018 / Accepted: 12 March 2018 / Published: 14 March 2018
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Abstract
A new microrobot manipulation technique with high precision (nano level) positional accuracy to move in a liquid environment with diamagnetic levitation is presented. Untethered manipulation of microrobots by means of externally applied magnetic forces has been emerging as a promising field of research,
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A new microrobot manipulation technique with high precision (nano level) positional accuracy to move in a liquid environment with diamagnetic levitation is presented. Untethered manipulation of microrobots by means of externally applied magnetic forces has been emerging as a promising field of research, particularly due to its potential for medical and biological applications. The purpose of the presented method is to eliminate friction force between the surface of the substrate and microrobot. In an effort to achieve high accuracy motion, required magnetic force for the levitation of the microrobot was determined by finite element method (FEM) simulations in COMSOL (version 5.3, COMSOL Inc., Stockholm, Sweden) and verified by experimental results. According to position of the lifter magnet, the levitation height of the microrobot in the liquid was found analytically, and compared with the experimental results head-to-head. The stable working range of the microrobot is between 30 µm to 330 µm, and it was confirmed in both simulations and experimental results. It can follow the given trajectory with high accuracy (<1 µm error avg.) at varied speeds and levitation heights. Due to the nano-level positioning accuracy, desired locomotion can be achieved in pre-specified trajectories (sinusoidal or circular). During its locomotion, phase difference between lifter magnet and carrier magnet has been observed, and relation with drag force effect has been discussed. Without using strong electromagnets or bulky permanent magnets, our manipulation approach can move the microrobot in three dimensions in a liquid environment. Full article
(This article belongs to the Special Issue Micro/Nano Robotics, Volume II)
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Open AccessArticle Experimental Investigation on Ductile Mode Micro-Milling of ZrO2 Ceramics with Diamond-Coated End Mills
Micromachines 2018, 9(3), 127; doi:10.3390/mi9030127
Received: 12 February 2018 / Revised: 4 March 2018 / Accepted: 12 March 2018 / Published: 14 March 2018
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Abstract
ZrO2 ceramics are currently used in a broad range of industrial applications. However, the machining of post-sintered ZrO2 ceramic is a difficult task, due to its high hardness and brittleness. In this study, micro-milling of ZrO2 with two kinds of
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ZrO2 ceramics are currently used in a broad range of industrial applications. However, the machining of post-sintered ZrO2 ceramic is a difficult task, due to its high hardness and brittleness. In this study, micro-milling of ZrO2 with two kinds of diamond-coated end mills has been conducted on a Kern MMP 2522 micro-milling center (Kern Microtechnik GmbH, Eschenlohe, Germany). To achieve a ductile mode machining of ZrO2, the feed per tooth and depth of cut was set in the range of a few micrometers. Cutting force and machined surface roughness have been measured by a Kistler MiniDynamometer (Kistler Group, Winterthur, Switzerland) and a Talysurf 120 L profilometer (Taylor Hobson Ltd., Leicester, UK), respectively. Machined surface topography and tool wear have been examined under SEM. Experiment results show that the material can be removed in ductile mode, and mirror quality surface with Ra low as 0.02 μm can be achieved. Curled and smooth chips have been collected and observed. The axial cutting force Fz is always bigger than Fx and Fy, and presents a rising trend with increasing of milling length. Tool wear includes delamination of diamond coating and wear of tungsten carbide substrate. Without the protection of diamond coating, the tungsten carbide substrate was worn out quickly, resulting a change of tool tip geometry. Full article
(This article belongs to the Special Issue Micro-Machining: Challenges and Opportunities)
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Open AccessArticle Method of Measuring the Mismatch of Parasitic Capacitance in MEMS Accelerometer Based on Regulating Electrostatic Stiffness
Micromachines 2018, 9(3), 128; doi:10.3390/mi9030128
Received: 29 January 2018 / Revised: 25 February 2018 / Accepted: 2 March 2018 / Published: 15 March 2018
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Abstract
For the MEMS capacitive accelerometer, parasitic capacitance is a serious problem. Its mismatch will deteriorate the performance of accelerometer. Obtaining the mismatch of the parasitic capacitance precisely is helpful for improving the performance of bias and scale. Currently, the method of measuring the
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For the MEMS capacitive accelerometer, parasitic capacitance is a serious problem. Its mismatch will deteriorate the performance of accelerometer. Obtaining the mismatch of the parasitic capacitance precisely is helpful for improving the performance of bias and scale. Currently, the method of measuring the mismatch is limited in the direct measuring using the instrument. This traditional method has low accuracy for it would lead in extra parasitic capacitive and have other problems. This paper presents a novel method based on the mechanism of a closed-loop accelerometer. The strongly linear relationship between the output of electric force and the square of pre-load voltage is obtained through theoretical derivation and validated by experiment. Based on this relationship, the mismatch of parasitic capacitance can be obtained precisely through regulating electrostatic stiffness without other equipment. The results can be applied in the design of decreasing the mismatch and electrical adjusting for eliminating the influence of the mismatch. Full article
(This article belongs to the Special Issue MEMS Accelerometers)
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Open AccessArticle A Label Free Disposable Device for Rapid Isolation of Rare Tumor Cells from Blood by Ultrasounds
Micromachines 2018, 9(3), 129; doi:10.3390/mi9030129
Received: 7 February 2018 / Revised: 4 March 2018 / Accepted: 12 March 2018 / Published: 15 March 2018
PDF Full-text (2765 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
The use of blood samples as liquid biopsy is a label-free method for cancer diagnosis that offers benefits over traditional invasive biopsy techniques. Cell sorting by acoustic waves offers a means to separate rare cells from blood samples based on their physical properties
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The use of blood samples as liquid biopsy is a label-free method for cancer diagnosis that offers benefits over traditional invasive biopsy techniques. Cell sorting by acoustic waves offers a means to separate rare cells from blood samples based on their physical properties in a label-free, contactless and biocompatible manner. Herein, we describe a flow-through separation approach that provides an efficient separation of tumor cells (TCs) from white blood cells (WBCs) in a microfluidic device, “THINUS-Chip” (Thin-Ultrasonic-Separator-Chip), actuated by ultrasounds. We introduce for the first time the concept of plate acoustic waves (PAW) applied to acoustophoresis as a new strategy. It lies in the geometrical chip design: different to other microseparators based on either bulk acoustic waves (BAW) or surface waves (SAW, SSAW and tSAW), it allows the use of polymeric materials without restrictions in the frequency of work. We demonstrate its ability to perform high-throughput isolation of TCs from WBCs, allowing a recovery rate of 84% ± 8% of TCs with a purity higher than 80% and combined viability of 85% at a flow rate of 80 μL/min (4.8 mL/h). The THINUS-Chip performs cell fractionation with low-cost manufacturing processes, opening the door to possible easy printing fabrication. Full article
(This article belongs to the Special Issue Microfluidics for Circulating Biomarkers)
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Open AccessArticle Crack-Configuration Analysis of Metal Conductive Track Embedded in Stretchable Elastomer
Micromachines 2018, 9(3), 130; doi:10.3390/mi9030130
Received: 28 February 2018 / Revised: 9 March 2018 / Accepted: 9 March 2018 / Published: 15 March 2018
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Abstract
This paper reports the analysis of the crack configuration of a stretched metal conductive track that is embedded in a stretchable elastomer. The factor determining the crack configurations is analyzed by modeling as well as experiments. The modeling analysis indicates that the crack
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This paper reports the analysis of the crack configuration of a stretched metal conductive track that is embedded in a stretchable elastomer. The factor determining the crack configurations is analyzed by modeling as well as experiments. The modeling analysis indicates that the crack configuration is determined by the ratio of the elongation stiffness of the track and elastomer, and is classified into two types: multiple-crack growth and single-crack growth. When the track stiffness is considerably lower than the elastomer stiffness, multiple-crack growth type occurs; in the opposite case, single-crack growth type occurs. Hence, to verify the modeling analysis, metal conductive tracks with different thicknesses are fabricated, and the cracks are studied with respect to the crack width, number of cracks, and crack propagation speed. In this study, two conventional metal-track shapes are studied: straight-shaped tracks with track thickness of 0.04–1.17 µm, and wave-shaped tracks with track thickness of 2–10 µm. For straight-shaped tracks, multiple-crack growth type occurred, when the track thickness was 0.04 µm, and the crack configuration gradually changed to a single crack, with the increase in the track thickness. For wave-shaped tracks with track thickness of 2–10 µm, only single-crack growth type occurred; however, the crack propagation speed decreased and the maximum stretchability of the track increased, with the increase in the track thickness. Full article
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Open AccessArticle Silicon-Based Microfabrication of Free-Floating Neural Probes and Insertion Tool for Chronic Applications
Micromachines 2018, 9(3), 131; doi:10.3390/mi9030131
Received: 8 January 2018 / Revised: 6 March 2018 / Accepted: 14 March 2018 / Published: 16 March 2018
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Abstract
Bidirectional neural interfaces for multi-channel, high-density recording and electrical stimulation of neural activity in the central nervous system are fundamental tools for neuroscience and medical applications. Especially for clinical use, these electrical interfaces must be stable over several years, which is still a
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Bidirectional neural interfaces for multi-channel, high-density recording and electrical stimulation of neural activity in the central nervous system are fundamental tools for neuroscience and medical applications. Especially for clinical use, these electrical interfaces must be stable over several years, which is still a major challenge due to the foreign body response of neural tissue. A feasible solution to reduce this inflammatory response is to enable a free-floating implantation of high-density, silicon-based neural probes to avoid mechanical coupling between the skull and the cortex during brain micromotion. This paper presents our latest development of a reproducible microfabrication process, which allows a monolithic integration of a highly-flexible, polyimide-based cable with a silicon-stiffened neural probe at a high resolution of 1 µm. For a precise and complete insertion of the free-floating probes into the cortex, a new silicon-based, vacuum-actuated insertion tool is presented, which can be attached to commercially available electrode drives. To reduce the electrode impedance and enable safe and stable microstimulation an additional coating with the electrical conductive polymer PEDOT:PSS is used. The long-term stability of the presented free-floating neural probes is demonstrated in vitro and in vivo. The promising results suggest the feasibility of these neural probes for chronic applications. Full article
(This article belongs to the Special Issue Silicon-based Micro/Nanofabrication for Biomedical Applications)
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Open AccessArticle Single-Wall Carbon Nanotube-Coated Cotton Yarn for Electrocardiography Transmission
Micromachines 2018, 9(3), 132; doi:10.3390/mi9030132
Received: 21 July 2017 / Revised: 1 March 2018 / Accepted: 14 March 2018 / Published: 19 March 2018
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Abstract
We fabricated a type of conductive fabric, specifically single-wall carbon nanotube-coated cotton yarns (SWNT-CYs), for electrocardiography (ECG) signal transmission utilizing a “dipping and drying” method. The conductive cotton yarns were prepared by dipping cotton yarns in SWNTs (single-wall carbon nanotubes) solutions and then
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We fabricated a type of conductive fabric, specifically single-wall carbon nanotube-coated cotton yarns (SWNT-CYs), for electrocardiography (ECG) signal transmission utilizing a “dipping and drying” method. The conductive cotton yarns were prepared by dipping cotton yarns in SWNTs (single-wall carbon nanotubes) solutions and then drying them at room temperature—a simple process that shows consistency in successfully coating cotton yarns with conductive carbon nanotubes (CNTs). The influence of fabrication conditions on the conductivity properties of SWNT-CYs was investigated. The results demonstrate that our conductive yarns can transmit weak bio-electrical (i.e., ECG) signals without significant attenuation and distortion. Our conductive cotton yarns, which combine the flexibility of conventional fabrics and the good conductivity of SWNTs, are promising materials for wearable electronics and sensor applications in the future. Full article
(This article belongs to the Special Issue Carbon Based Materials for MEMS/NEMS)
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Open AccessArticle Fabrication and Study of Micro Monolithic Tungsten Ball Tips for Micro/Nano-CMM Probes
Micromachines 2018, 9(3), 133; doi:10.3390/mi9030133
Received: 2 February 2018 / Revised: 12 March 2018 / Accepted: 13 March 2018 / Published: 19 March 2018
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Abstract
Micro ball tips with high precision, small diameter, and high stiffness stems are required to measure microstructures with high aspect ratio. Existing ball tips cannot meet such demands because of their weak qualities. This study used an arc-discharge melting method to fabricate a
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Micro ball tips with high precision, small diameter, and high stiffness stems are required to measure microstructures with high aspect ratio. Existing ball tips cannot meet such demands because of their weak qualities. This study used an arc-discharge melting method to fabricate a micro monolithic tungsten ball tip on a tungsten stylus. The principles of arc discharge and surface tension phenomenon were introduced. The experimental setup was designed and established. Appropriate process parameters, such as impulse voltage, electro discharge time, and discharge gap were determined. Experimental results showed that a ball tip of approximately 60 µm in diameter with less than 0.6 µm roundness error and 0.6 µm center offset could be realized on a 100 µm-diameter tungsten wire. The fabricated micro ball tip was installed on a homemade probe, touched by high-precision gauge blocks in different directions. A repeatability of 41 nm (K = 2) was obtained. Several interesting phenomena in the ball-forming process were also discussed. The proposed method could be used to fabricate a monolithic probe ball tip, which is necessary for measuring microstructures. Full article
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Open AccessArticle Modeling and Analysis of an Opto-Fluidic Sensor for Lab-on-a-Chip Applications
Micromachines 2018, 9(3), 134; doi:10.3390/mi9030134
Received: 27 February 2018 / Revised: 15 March 2018 / Accepted: 15 March 2018 / Published: 19 March 2018
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Abstract
In this work modeling and analysis of an integrated opto-fluidic sensor, with a focus on achievement of single mode optical confinement and continuous flow of microparticles in the microfluidic channel for lab-on-a-chip (LOC) sensing application is presented. This sensor consists of integrated optical
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In this work modeling and analysis of an integrated opto-fluidic sensor, with a focus on achievement of single mode optical confinement and continuous flow of microparticles in the microfluidic channel for lab-on-a-chip (LOC) sensing application is presented. This sensor consists of integrated optical waveguides, microfluidic channel among other integrated optical components. A continuous flow of microparticles in a narrow fluidic channel is achieved by maintaining the two sealed chambers at different temperatures and by maintaining a constant pressure of 1 Pa at the centroid of narrow fluidic channel geometry. The analysis of silicon on insulator (SOI) integrated optical waveguide at an infrared wavelength of 1550 nm for single mode sensing operation is presented. The optical loss is found to be 5.7 × 10−4 dB/cm with an effective index of 2.3. The model presented in this work can be effectively used to detect the nature of microparticles and continuous monitoring of pathological parameters for sensing applications. Full article
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Open AccessArticle Dielectrophoretic Microfluidic Device for in Vitro Fertilization
Micromachines 2018, 9(3), 135; doi:10.3390/mi9030135
Received: 30 December 2017 / Revised: 14 March 2018 / Accepted: 15 March 2018 / Published: 20 March 2018
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Abstract
The aim of this work was to create a microfluidic platform that uses in vitro fertilization (IVF) and avoids unnecessary damage to oocytes due to the dielectrophoretic force manipulation of the sperms and oocytes that occurs in a traditional IVF operation. The device
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The aim of this work was to create a microfluidic platform that uses in vitro fertilization (IVF) and avoids unnecessary damage to oocytes due to the dielectrophoretic force manipulation of the sperms and oocytes that occurs in a traditional IVF operation. The device from this research can serve also to decrease medium volumes, as well as the cost of cell culture under evaporation, and to prevent unnecessary risk in intracytoplasmic sperm injection (ICSI). To decrease the impact and destruction of the oocyte and the sperm, we adopted a positive dielectrophoretic force to manipulate both the sperms and the oocyte. The mouse oocytes were trapped with a positive dielectrophoretic (p-DEP) force by using Indium Tin Oxide (ITO)-glass electrodes; the ITO-glass electrode chip was fabricated by wet etching the ITO-glass. The polydimethylsiloxane (PDMS) flow-focusing microfluidic device was used to generate microdroplets of micrometer size to contain the zygotes. The volume of the microdroplets was controlled by adjusting the flow rates of both inlets for oil and the DEP buffer. As a result, the rate of fertilization was increased by about 5% beyond that of the DEP treatment in traditional IVF, and more than 20% developed to the blastocyst stage with a low sperm-oocyte ratio. Full article
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Open AccessArticle Topology Optimization of Passive Micromixers Based on Lagrangian Mapping Method
Micromachines 2018, 9(3), 137; doi:10.3390/mi9030137
Received: 26 January 2018 / Revised: 17 March 2018 / Accepted: 18 March 2018 / Published: 20 March 2018
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Abstract
This paper presents an optimization-based design method of passive micromixers for immiscible fluids, which means that the Peclet number infinitely large. Based on topology optimization method, an optimization model is constructed to find the optimal layout of the passive micromixers. Being different from
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This paper presents an optimization-based design method of passive micromixers for immiscible fluids, which means that the Peclet number infinitely large. Based on topology optimization method, an optimization model is constructed to find the optimal layout of the passive micromixers. Being different from the topology optimization methods with Eulerian description of the convection-diffusion dynamics, this proposed method considers the extreme case, where the mixing is dominated completely by the convection with negligible diffusion. In this method, the mixing dynamics is modeled by the mapping method, a Lagrangian description that can deal with the case with convection-dominance. Several numerical examples have been presented to demonstrate the validity of the proposed method. Full article
(This article belongs to the Special Issue Passive Micromixers)
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Open AccessFeature PaperArticle Fabrication of Through via Holes in Ultra-Thin Fused Silica Wafers for Microwave and Millimeter-Wave Applications
Micromachines 2018, 9(3), 138; doi:10.3390/mi9030138
Received: 14 February 2018 / Revised: 8 March 2018 / Accepted: 16 March 2018 / Published: 20 March 2018
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Abstract
Through via holes in fused silica are a key infrastructure element of microwave and millimeter-wave circuits and 3D integration. In this work, etching through via holes in ultra-thin fused silica wafers using deep reactive-ion etching (DRIE) and laser ablation was developed and analyzed.
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Through via holes in fused silica are a key infrastructure element of microwave and millimeter-wave circuits and 3D integration. In this work, etching through via holes in ultra-thin fused silica wafers using deep reactive-ion etching (DRIE) and laser ablation was developed and analyzed. The experimental setup and process parameters for both methods are presented and compared. For DRIE, three types of mask materials including KMPR 1035 (Nippon Kayaku, Tokyo, Japan) photoresist, amorphous silicon and chromium—with their corresponding optimized processing recipes—were tested, aiming at etching through a 100 μm fused silica wafer. From the experiments, we concluded that using chromium as the masking material is the best choice when using DRIE. However, we found that the laser ablation method with a laser pulse fluence of 2.89 J/cm2 and a pulse overlap of 91% has advantages over DRIE. The laser ablation method has a simpler process complexity, while offering a fair etching result. In particular, the sidewall profile angle is measured to be 75° to the bottom surface of the wafer, which is ideal for the subsequent metallization process. As a demonstration, a two-inch wafer with 624 via holes was processed using both technologies, and the laser ablation method showed better efficiency compared to DRIE. Full article
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Review

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Open AccessReview Optofluidic Tunable Lenses for In-Plane Light Manipulation
Micromachines 2018, 9(3), 97; doi:10.3390/mi9030097
Received: 22 January 2018 / Revised: 10 February 2018 / Accepted: 11 February 2018 / Published: 26 February 2018
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Abstract
Optofluidics incorporates optics and microfluidics together to construct novel devices for microsystems, providing flexible reconfigurability and high compatibility. Among many novel devices, a prominent one is the in-plane optofluidic lens. It manipulates the light in the plane of the substrate, upon which the
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Optofluidics incorporates optics and microfluidics together to construct novel devices for microsystems, providing flexible reconfigurability and high compatibility. Among many novel devices, a prominent one is the in-plane optofluidic lens. It manipulates the light in the plane of the substrate, upon which the liquid sample is held. Benefiting from the compatibility, the in-plane optofluidic lenses can be incorporated into a single chip without complicated manual alignment and promises high integration density. In term of the tunability, the in-plane liquid lenses can be either tuned by adjusting the fluidic interface using numerous microfluidic techniques, or by modulating the refractive index of the liquid using temperature, electric field and concentration. In this paper, the in-plane liquid lenses will be reviewed in the aspects of operation mechanisms and recent development. In addition, their applications in lab-on-a-chip systems are also discussed. Full article
(This article belongs to the Special Issue Advances in Optofluidics)
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Open AccessFeature PaperReview Liquid Biopsy in Lung Cancer: Clinical Applications of Circulating Biomarkers (CTCs and ctDNA)
Micromachines 2018, 9(3), 100; doi:10.3390/mi9030100
Received: 1 February 2018 / Revised: 18 February 2018 / Accepted: 26 February 2018 / Published: 28 February 2018
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Abstract
Lung cancer is by far the leading cause of cancer death worldwide, with non-small cell lung cancer (NSCLC) accounting for the majority of cases. Recent advances in the understanding of the biology of tumors and in highly sensitive detection technologies for molecular analysis
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Lung cancer is by far the leading cause of cancer death worldwide, with non-small cell lung cancer (NSCLC) accounting for the majority of cases. Recent advances in the understanding of the biology of tumors and in highly sensitive detection technologies for molecular analysis offer targeted therapies, such as epidermal growth factor receptor (EGFR) tyrosine kinase inhibitors. However, our understanding of an individual patient’s lung cancer is often limited by tumor accessibility because of the high risk and invasive nature of current tissue biopsy procedures. “Liquid biopsy”, the analysis of circulating biomarkers from peripheral blood, such as circulating tumor cells (CTCs) and circulating tumor DNA (ctDNA), offers a new source of cancer-derived materials that may reflect the status of the disease better and thereby contribute to more personalized treatment. In this review, we examined the clinical significance and uniqueness of CTCs and ctDNA from NSCLC patients, isolation and detection methods developed to analyze each type of circulating biomarker, and examples of clinical studies of potential applications for early diagnosis, prognosis, treatment monitoring, and prediction of resistance to therapy. We also discuss challenges that remain to be addressed before such tools are implemented for routine use in clinical settings. Full article
(This article belongs to the Special Issue Microfluidics for Circulating Biomarkers)
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Open AccessReview Advances of Optofluidic Microcavities for Microlasers and Biosensors
Micromachines 2018, 9(3), 122; doi:10.3390/mi9030122
Received: 29 January 2018 / Revised: 2 March 2018 / Accepted: 6 March 2018 / Published: 9 March 2018
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Abstract
Optofluidic microcavities with high Q factor have made rapid progress in recent years by using various micro-structures. On one hand, they are applied to microfluidic lasers with low excitation thresholds. On the other hand, they inspire the innovation of new biosensing devices with
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Optofluidic microcavities with high Q factor have made rapid progress in recent years by using various micro-structures. On one hand, they are applied to microfluidic lasers with low excitation thresholds. On the other hand, they inspire the innovation of new biosensing devices with excellent performance. In this article, the recent advances in the microlaser research and the biochemical sensing field will be reviewed. The former will be categorized based on the structures of optical resonant cavities such as the Fabry–Pérot cavity and whispering gallery mode, and the latter will be classified based on the working principles into active sensors and passive sensors. Moreover, the difficulty of single-chip integration and recent endeavors will be briefly discussed. Full article
(This article belongs to the Special Issue Advances in Optofluidics)
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Open AccessReview Optofluidics Refractometers
Micromachines 2018, 9(3), 136; doi:10.3390/mi9030136
Received: 31 January 2018 / Revised: 2 March 2018 / Accepted: 16 March 2018 / Published: 20 March 2018
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Abstract
Refractometry is a classic analytical method in analytical chemistry and biosensing. By integrating advanced micro- and nano-optical systems with well-developed microfluidics technology, optofluidics are shown to be a powerful, smart and universal platform for refractive index sensing applications. This paper reviews recent work
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Refractometry is a classic analytical method in analytical chemistry and biosensing. By integrating advanced micro- and nano-optical systems with well-developed microfluidics technology, optofluidics are shown to be a powerful, smart and universal platform for refractive index sensing applications. This paper reviews recent work on optofluidic refractometers based on different sensing mechanisms and structures (e.g., photonic crystal/photonic crystal fibers, waveguides, whisper gallery modes and surface plasmon resonance), and traces the performance enhancement due to the synergistic integration of optics and microfluidics. A brief discussion of future trends in optofluidic refractometers, namely volume sensing and resolution enhancement, are also offered. Full article
(This article belongs to the Special Issue Advances in Optofluidics)
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Other

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Open AccessTechnical Note Characterization of 3D-Printed Moulds for Soft Lithography of Millifluidic Devices
Micromachines 2018, 9(3), 116; doi:10.3390/mi9030116
Received: 2 February 2018 / Revised: 28 February 2018 / Accepted: 7 March 2018 / Published: 8 March 2018
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Abstract
Increased demand for inexpensive and rapid prototyping methods for micro- and millifluidic lab-on-a-chip (LOC) devices has stimulated considerable interest in alternative cost-effective fabrication techniques. Additive manufacturing (AM)—also called three-dimensional (3D) printing—provides an attractive alternative to conventional fabrication techniques. AM has been used to
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Increased demand for inexpensive and rapid prototyping methods for micro- and millifluidic lab-on-a-chip (LOC) devices has stimulated considerable interest in alternative cost-effective fabrication techniques. Additive manufacturing (AM)—also called three-dimensional (3D) printing—provides an attractive alternative to conventional fabrication techniques. AM has been used to produce LOC master moulds from which positive replicas are made using soft-lithography and a biocompatible elastomer, poly(dimethylsiloxane) (PDMS). Here we characterize moulds made using two AM methods—stereolithography (SLA) and material-jetting (MJ)—and the positive replicas produced by soft lithography and PDMS moulding. The results showed that SLA, more than MJ, produced finer part resolution and finer tuning of feature geometry. Furthermore, as assessed by zebrafish (Danio rerio) biotoxicity tests, there was no toxicity observed in SLA and MJ moulded PDMS replicas. We conclude that SLA, utilizing commercially available printers and resins, combined with PDMS soft-lithography, is a simple and easily accessible technique that lends its self particularly well to the fabrication of biocompatible millifluidic devices, highly suited to the in-situ analysis of small model organisms. Full article
(This article belongs to the Special Issue 3D Printed Microfluidic Devices)
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