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Micromachines, Volume 8, Issue 4 (April 2017)

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Cover Story A fanciful ball design has been used to demonstrate the 4D printing abilities of entrapped enzymes [...] Read more.
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Editorial

Jump to: Research, Review

Open AccessEditorial Opportunities and Challenges in Flexible and Stretchable Electronics: A Panel Discussion at ISFSE2016
Micromachines 2017, 8(4), 129; doi:10.3390/mi8040129
Received: 10 April 2017 / Revised: 10 April 2017 / Accepted: 12 April 2017 / Published: 18 April 2017
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(This article belongs to the Special Issue Flexible and Stretchable Electronics)

Research

Jump to: Editorial, Review

Open AccessArticle Red Blood Cell Responses during a Long-Standing Load in a Microfluidic Constriction
Micromachines 2017, 8(4), 100; doi:10.3390/mi8040100
Received: 25 January 2017 / Revised: 7 March 2017 / Accepted: 22 March 2017 / Published: 26 March 2017
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Abstract
Red blood cell responses during a long-standing load were experimentally investigated. With a high-speed camera and a high-speed actuator, we were able to manipulate cells staying inside a microfluidic constriction, and each cell was compressed due to the geometric constraints. During the load
[...] Read more.
Red blood cell responses during a long-standing load were experimentally investigated. With a high-speed camera and a high-speed actuator, we were able to manipulate cells staying inside a microfluidic constriction, and each cell was compressed due to the geometric constraints. During the load inside the constriction, the color of the cells was found to gradually darken, while the cell lengths became shorter and shorter. According to the analysis results of a 5 min load, the average increase of the cell darkness was 60.9 in 8-bit color resolution, and the average shrinkage of the cell length was 15% of the initial length. The same tendency was consistently observed from cell to cell. A correlation between the changes of the color and the length were established based on the experimental results. The changes are believed partially due to the viscoelastic properties of the cells that the cells’ configurations change with time for adapting to the confined space inside the constriction. Full article
(This article belongs to the Special Issue Biomedical Microfluidic Devices)
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Open AccessArticle 3D–4D Printed Objects: New Bioactive Material Opportunities
Micromachines 2017, 8(4), 102; doi:10.3390/mi8040102
Received: 8 February 2017 / Revised: 16 March 2017 / Accepted: 21 March 2017 / Published: 27 March 2017
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Abstract
One of the main objectives of 3D printing in health science is to mimic biological functions. To reach this goal, a 4D printing might be added to 3D-printed objects which will be characterized by their abilities to evolve over time and under external
[...] Read more.
One of the main objectives of 3D printing in health science is to mimic biological functions. To reach this goal, a 4D printing might be added to 3D-printed objects which will be characterized by their abilities to evolve over time and under external stimulus by modifying their shape, properties or composition. Such abilities are the promise of great opportunities for biosensing and biomimetic systems to progress towards more physiological mimicking systems. Herein are presented two 4D printing examples for biosensing and biomimetic applications using 3D-printed enzymes. The first one is based on the printing of the enzymatic couple glucose oxidase/peroxidase for the chemiluminescent detection of glucose, and the second uses printed alkaline phosphatase to generate in situ programmed and localized calcification of the printed object. Full article
(This article belongs to the Special Issue 3D Printing: Microfabrication and Emerging Concepts)
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Open AccessArticle Design and Construction of a Micro-Tribotester for Precise In-Situ Wear Measurements
Micromachines 2017, 8(4), 103; doi:10.3390/mi8040103
Received: 1 February 2017 / Revised: 9 March 2017 / Accepted: 25 March 2017 / Published: 28 March 2017
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Abstract
Extensive research efforts have been devoted to understand the complex mechanisms of wear with the aim to minimize wear in sliding systems. Improvements in the instruments used for the characterization of the wear phenomenon are required to enhance the effectiveness of research method.
[...] Read more.
Extensive research efforts have been devoted to understand the complex mechanisms of wear with the aim to minimize wear in sliding systems. Improvements in the instruments used for the characterization of the wear phenomenon are required to enhance the effectiveness of research method. In this paper, we report the design of an experimental platform that enables in-situ observation of the surface topography evolution during the evaluation of the tribological behavior of surfaces in dry and lubricated conditions. Use of state-of-the-art components for surface topography measurement, planar positioning, and force sensing allowed for the improvement of sensitivity and resolution compared with the previously reported systems. The effectiveness of the tribotester was demonstrated through friction and wear tests performed using a stainless-steel ball and a silicon wafer coated with SiO2. It was found that transition of the wear mechanism from adhesive to abrasive wear took place when a significant amount of wear debris was formed as evidenced by the in-situ observation of removal of the coating and exposure of the Si substrate. The in-situ observation of wear phenomena enabled a robust and in-depth elucidation of wear mechanisms. Full article
(This article belongs to the Special Issue Microtribology, Adhesion and Surface Engineering)
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Open AccessArticle Paper-Based Colorimetric Biosensor for Tear Glucose Measurements
Micromachines 2017, 8(4), 104; doi:10.3390/mi8040104
Received: 8 February 2017 / Revised: 15 March 2017 / Accepted: 22 March 2017 / Published: 29 March 2017
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Abstract
This paper describes a paper-based colorimetric biosensor for measuring glucose concentration levels in human tear samples. Colorimetric biosensors were wax printed on paper platforms and modified with chitosan previously prepared in acetic acid. The proposed device was explored to measure the glucose levels
[...] Read more.
This paper describes a paper-based colorimetric biosensor for measuring glucose concentration levels in human tear samples. Colorimetric biosensors were wax printed on paper platforms and modified with chitosan previously prepared in acetic acid. The proposed device was explored to measure the glucose levels in human tear samples using 3,3′,5,5′-tetramethylbenzydine (TMB) as the chromogenic reagent. The paper-based colorimetric biosensor exhibited a linear behavior for the glucose concentration range between 0.1 and 1.0 mM. The achieved analytical sensitivity and limit of detection (LOD) were 84 AU/mM and 50 µM, respectively. Moreover, the device provided analytical reliability and no statistical difference when compared to the data recorded with a commercial glucometer. The proof-of-concept of our device was successfully demonstrated by measuring the glucose levels in six tear samples from nondiabetic subjects. In general, the results showed that the colorimetric biosensor has noticeable potential to be used as a powerful tool for tear glucose monitoring, since this fluid offers lower potential interferences, non-invasive sample collection and is pain-free. Furthermore, the proposed device could facilitate the treatment of diabetic patients who need constant control of glucose levels and cannot tolerate multiple finger sticks per day. Full article
(This article belongs to the Special Issue Paper Microfluidics: Fundamental Studies and Applications)
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Open AccessArticle Two-Dimensional Magnetic Field Sensor Based on Silicon Magnetic Sensitive Transistors with Differential Structure
Micromachines 2017, 8(4), 95; doi:10.3390/mi8040095
Received: 10 December 2016 / Revised: 16 February 2017 / Accepted: 17 March 2017 / Published: 23 March 2017
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Abstract
A two-dimensional (2D) magnetic field sensor consisting of four silicon magnetic sensitive transistors (SMSTs) with similar characteristics is presented in this paper. By use of micro-electromechanical systems (MEMS) and integrated packaging technology, this sensor fabricated by using the silicon wafer with a <100>
[...] Read more.
A two-dimensional (2D) magnetic field sensor consisting of four silicon magnetic sensitive transistors (SMSTs) with similar characteristics is presented in this paper. By use of micro-electromechanical systems (MEMS) and integrated packaging technology, this sensor fabricated by using the silicon wafer with a <100> orientation and high resistivity, was packaged on printed circuit boards (PCBs). In order to detect the magnetic fields in the x and y axes directions, two of the four SMSTs with opposite magnetic sensitive directions were located along the x and −x axes directions, symmetrically, and the others were located along the y and −y axes directions. The experimental results show that when the VCE = 10.0 V and IB = 6.0 mA, the magnetic sensitivities of the sensor in the x and y axes directions are 366.0 mV/T and 365.0 mV/T, respectively. It is possible to measure the 2D magnetic field and improve the magnetic sensitivity, significantly. Full article
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Open AccessArticle A Novel Electroosmotic Micromixer with Asymmetric Lateral Structures and DC Electrode Arrays
Micromachines 2017, 8(4), 105; doi:10.3390/mi8040105
Received: 28 February 2017 / Revised: 21 March 2017 / Accepted: 27 March 2017 / Published: 29 March 2017
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Abstract
We present a novel electroosmotic micromixer that consists of arrays of direct current (DC) asymmetric electrode and asymmetric lateral structures. By embedding asymmetric electrode arrays on the top and bottom walls of a rectangular microchannel appropriately, the flow perturbations and vortexes can be
[...] Read more.
We present a novel electroosmotic micromixer that consists of arrays of direct current (DC) asymmetric electrode and asymmetric lateral structures. By embedding asymmetric electrode arrays on the top and bottom walls of a rectangular microchannel appropriately, the flow perturbations and vortexes can be induced when a DC electric field is imposed. An efficient lateral structure is then sequentially combined with the rectangular microchannel, which enhances the mixing effect significantly. The effects of operational parameters such as the Reynolds number, the applied potential, and the Peclet number on the mixing performance are analyzed in detail by numerical simulations. The results indicate that an enhanced mixing performance can be achieved with low applied potential. The novel method proposed in this paper provides a simple solution for mixing in the field of 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 Effects of Doping Elements on the Friction and Wear of SUJ2 Steel Sliding against Aluminum Alloys
Micromachines 2017, 8(4), 96; doi:10.3390/mi8040096
Received: 7 February 2017 / Revised: 14 March 2017 / Accepted: 17 March 2017 / Published: 23 March 2017
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Abstract
Damage to mechanical components caused by wear is considered to be an important issue for mechanical engineers. For the purpose of wear resistance, it is necessary to improve the material properties of the mechanical elements. Furthermore, low friction plays an important role in
[...] Read more.
Damage to mechanical components caused by wear is considered to be an important issue for mechanical engineers. For the purpose of wear resistance, it is necessary to improve the material properties of the mechanical elements. Furthermore, low friction plays an important role in saving energy. Hence, it is important to establish a key technology for wear resistance and low friction through appropriate materials science for related industries. In general, the tribological properties of aluminum alloys are very different from those of steels. Hence, aluminum alloys should be specially considered and clarified for their tribological properties before being applied industrially. This paper therefore aims to further investigate the effects of the content of doping elements on the friction and wear of the selected aluminum alloys. From the experimental results, it can be concluded that the higher the Si content, the smaller the friction coefficient, and the milder the variation. The higher the content of iron and copper, the more materials are removed, showing better machinability. Moreover, three frictional models and wear mechanisms that describe the effects of the content of doping elements on the friction and wear are proposed. The wear mechanisms change as the silicon content increases, from the junction growth to the wedge and the ploughing particles. As a result, better choices of aluminum alloys with regards to friction and wear can then be made. These results have great practical importance. Full article
(This article belongs to the Special Issue Microtribology, Adhesion and Surface Engineering)
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Open AccessArticle Preparing of Interdigitated Microelectrode Arrays for AC Electrokinetic Devices Using Inkjet Printing of Silver Nanoparticles Ink
Micromachines 2017, 8(4), 106; doi:10.3390/mi8040106
Received: 27 February 2017 / Revised: 21 March 2017 / Accepted: 27 March 2017 / Published: 1 April 2017
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Abstract
The surge in popularity of lab-on-chip applications has set a new challenge for the fabrication of prototyping devices, such as electrokinetic devices. In such devices, a micro-electrode is the key component. Currently, microelectromechanical systems (MEMS) processes such as lift-off and etching techniques are
[...] Read more.
The surge in popularity of lab-on-chip applications has set a new challenge for the fabrication of prototyping devices, such as electrokinetic devices. In such devices, a micro-electrode is the key component. Currently, microelectromechanical systems (MEMS) processes such as lift-off and etching techniques are employed to prepare the micro-sized conductive patterns. These processes are time-consuming, require a material removal step, clean-room facilities, and the utilisation of harmful chemicals. On the other hand, rapid fabrication is required by researchers designing such devices to test their functionality. Additive manufacturing technology such as the inkjet printing of conductive material is one potential solution to achieve that objective. In this study, we report the utilisation of inkjet printing for the rapid prototyping of alternating current (AC) electrokinetic devices on a rigid glass substrate. The non-lithographical and vacuum-free process for the fabrication of a microfluidic device was demonstrated. The smallest feature size of 60 μm was successfully printed. The crystalline structure of the printed material under different curing temperatures was characterised. It was found that these treatment conditions affect electrical conductivity. Although a low-temperature sintering process was applied, low resistivity was obtained. An AC electrokinetics device for the manipulation of microparticles has been prepared to illustrate such printed silver micro-patterns. The results strongly support the idea that inkjet printing is a powerful and cost-effective prototyping tool for researchers who work with electrokinetic devices. Full article
(This article belongs to the Special Issue Bioprinting and 3D Printing in MEMS Technology)
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Open AccessArticle Large-Area Piezoelectric PVDF Fibers Fabricated by Near-Field Electrospinning with Multi-Spinneret Structures
Micromachines 2017, 8(4), 97; doi:10.3390/mi8040097
Received: 16 January 2017 / Revised: 10 March 2017 / Accepted: 17 March 2017 / Published: 24 March 2017
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Abstract
In the study, we improved the near-field electrospinning (NFES) by multi-spinnerets with a cylindrical collector to fabricate a large area permanent piezoelectric of polyvinylidene fluoride (PVDF) fibers array. We designed multi-spinnerets by using printed circuit board (PCB) and drilled spinnerets on the solder
[...] Read more.
In the study, we improved the near-field electrospinning (NFES) by multi-spinnerets with a cylindrical collector to fabricate a large area permanent piezoelectric of polyvinylidene fluoride (PVDF) fibers array. We designed multi-spinnerets by using printed circuit board (PCB) and drilled spinnerets on the solder balls. With different process parameters, we can obtain different diameters of PVDF fibers. By using the Taguchi method analysis, we found that the optimum sample of PVDF fiber arrays were manufactured by an electrical field of 1.6 × 107 V/m. The cylindrical collector with high tangential velocity of 1779.9 mm/s and the heat treatment temperature of 65 °C for one hour. In addition, we used X-ray diffraction (XRD) and scanning electron microscopy (SEM) to analyze β-phase crystal quality and the surface character of PVDF fibers, respectively. From the observation of XRD, it revealed a high diffraction peak at 2θ = 20.6° of piezoelectric crystal β-phase structure. As PVDF solution with concentration of 18 wt % and the conductivity of 44.2 μS/cm was electrospun via NFES with multi-spinneret structure, we obtained a smooth manufacturing process. When the periodical tapping frequency was applied with 9 Hz, the maximum peak voltage of 86.9 mV was generated. In a cicada’s wing test, when the tapping frequency input was applied during 10–50 Hz, the maximum output voltage signals of 6.2 mV were generated. Full article
(This article belongs to the Special Issue Microtribology, Adhesion and Surface Engineering)
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Open AccessArticle Multi-Response Optimization of Electrothermal Micromirror Using Desirability Function-Based Response Surface Methodology
Micromachines 2017, 8(4), 107; doi:10.3390/mi8040107
Received: 20 December 2016 / Revised: 20 March 2017 / Accepted: 23 March 2017 / Published: 1 April 2017
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Abstract
The design of a micromirror for biomedical applications requires multiple output responses to be optimized, given a set of performance parameters and constraints. This paper presents the parametric design optimization of an electrothermally actuated micromirror for the deflection angle, input power, and micromirror
[...] Read more.
The design of a micromirror for biomedical applications requires multiple output responses to be optimized, given a set of performance parameters and constraints. This paper presents the parametric design optimization of an electrothermally actuated micromirror for the deflection angle, input power, and micromirror temperature rise from the ambient for Optical Coherence Tomography (OCT) system. Initially, a screening design matrix based on the Design of Experiments (DOE) technique is developed and the corresponding output responses are obtained using coupled structural-thermal-electric Finite Element Modeling (FEM). The interaction between the significant design factors is analyzed by developing Response Surface Models (RSM) for the output responses. The output responses are optimized by combining the individual responses into a composite function using desirability function approach. A downhill simplex method, based on the heuristic search algorithm, is implemented on the RSM models to find the optimal levels of the design factors. The predicted values of output responses obtained using multi-response optimization are verified by the FEM simulations. Full article
(This article belongs to the Special Issue MEMS Mirrors)
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Open AccessFeature PaperArticle Experimental Analysis of Fabrication Parameters in the Development of Microfluidic Paper-Based Analytical Devices (µPADs)
Micromachines 2017, 8(4), 99; doi:10.3390/mi8040099
Received: 28 February 2017 / Revised: 18 March 2017 / Accepted: 21 March 2017 / Published: 25 March 2017
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Abstract
Microfluidic paper-based analytical devices (µPADs) have emerged as viable multiplexable platforms with the potential to transcend existing analytical techniques in resource-limited settings. µPADs are fabricated by patterning hydrophobic materials on hydrophilic paper. Reproducibility in fabrication is essential in a myriad of applications and
[...] Read more.
Microfluidic paper-based analytical devices (µPADs) have emerged as viable multiplexable platforms with the potential to transcend existing analytical techniques in resource-limited settings. µPADs are fabricated by patterning hydrophobic materials on hydrophilic paper. Reproducibility in fabrication is essential in a myriad of applications and particularly, in the development of point-of-care (POC) diagnostic devices that utilize paper-based platforms. A critical step in fabrication involves the wax heating process that determines the channel dimensions and the depth at which hydrophobic wax material permeates paper to create barriers. In this paper, we assess µPAD viability by examining two fabrication parameters that affect wax ink spreading and permeation using a commercial heat press: temperature and time of heating. Analysis of the µPADs revealed that functional chips could be fabricated at temperatures between 143 and 215 °C and time of heating between 50 and 135 s, while non-functioning chips were obtained at temperatures between 76 and 140 °C and time of heating between 5 and 45 s. Wax ink spread and permeated paper consistently between 143 and 215 °C. Also shown is a simple three dimensional (3D) microfluidic channel fabricated in a single sheet of cellulose paper utilizing the fabrication conditions described herein. This work demonstrates that controlling the extent of wax printing in the fabrication process of a µPAD can yield versatile and interesting devices for use in both resource-rich and -limited settings. Full article
(This article belongs to the Special Issue Paper Microfluidics: Fundamental Studies and Applications)
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Open AccessArticle Field-Dependent Resonant Behavior of Thin Nickel Film-Coated Microcantilever
Micromachines 2017, 8(4), 109; doi:10.3390/mi8040109
Received: 10 February 2017 / Revised: 27 February 2017 / Accepted: 27 March 2017 / Published: 1 April 2017
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Abstract
Herein we describe the vibration of a thin nickel film-coated microcantilever at resonance under an external magnetic field. The resonance frequency and the mechanical loss—experimentally observed while varying the magnetic field—closely follow the field-dependence of the magnetostriction coefficient, indicating the strong coupling between
[...] Read more.
Herein we describe the vibration of a thin nickel film-coated microcantilever at resonance under an external magnetic field. The resonance frequency and the mechanical loss—experimentally observed while varying the magnetic field—closely follow the field-dependence of the magnetostriction coefficient, indicating the strong coupling between the mechanical motion and the magnetostriction through the surface stress. Comparing to the surface stress model based on uniformly distributed axial load, the magnetostriction coefficient of a nickel film has been estimated, and its value is comparable to the reported one. Our study suggests that the nature of the surface stress originating from the magnetostrictive film can govern and modulate the resonant behavior of miniaturized mechanical systems. Full article
(This article belongs to the Special Issue Mechanical Systems Approaching Nanoscales and Beyond)
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Open AccessFeature PaperArticle Selective Laser-Induced Etching of 3D Precision Quartz Glass Components for Microfluidic Applications—Up-Scaling of Complexity and Speed
Micromachines 2017, 8(4), 110; doi:10.3390/mi8040110
Received: 5 March 2017 / Revised: 18 March 2017 / Accepted: 28 March 2017 / Published: 1 April 2017
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Abstract
By modification of glasses with ultrafast laser radiation and subsequent wet-chemical etching (here named SLE = selective laser-induced etching), precise 3D structures have been produced, especially in quartz glass (fused silica), for more than a decade. By the combination of a three-axis system
[...] Read more.
By modification of glasses with ultrafast laser radiation and subsequent wet-chemical etching (here named SLE = selective laser-induced etching), precise 3D structures have been produced, especially in quartz glass (fused silica), for more than a decade. By the combination of a three-axis system to move the glass sample and a fast 3D system to move the laser focus, the SLE process is now suitable to produce more complex structures in a shorter time. Here we present investigations which enabled the new possibilities. We started with investigations of the optimum laser parameters to enable high selective laser-induced etching: surprisingly, not the shortest pulse duration is best suited for the SLE process. Secondly we investigated the scaling of the writing velocity: a faster writing speed results in higher selectivity and thus higher precision of the resulting structures, so the SLE process is now even suitable for the mass production of 3D structures. Finally we programmed a printer driver for commercial CAD software enabling the automated production of complex 3D glass parts as new examples for lab-on-a-chip applications such as nested nozzles, connectors and a cell-sorting structure. Full article
(This article belongs to the Special Issue Ultrafast Laser Fabrication for Lab-on-a-Chip)
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Open AccessArticle A Programmable Digital Microfluidic Assay for the Simultaneous Detection of Multiple Anti-Microbial Resistance Genes
Micromachines 2017, 8(4), 111; doi:10.3390/mi8040111
Received: 25 January 2017 / Revised: 23 February 2017 / Accepted: 7 March 2017 / Published: 1 April 2017
PDF Full-text (3634 KB) | HTML Full-text | XML Full-text | Supplementary Files
Abstract
The rapid emergence of antimicrobial resistant bacteria requires the development of new diagnostic tests. Nucleic acid-based assays determine antimicrobial susceptibility by detecting genes that encode for the resistance. In this study, we demonstrate rapid and simultaneous detection of three genes that confer resistance
[...] Read more.
The rapid emergence of antimicrobial resistant bacteria requires the development of new diagnostic tests. Nucleic acid-based assays determine antimicrobial susceptibility by detecting genes that encode for the resistance. In this study, we demonstrate rapid and simultaneous detection of three genes that confer resistance in bacteria to extended spectrum β-lactam and carbapenem antibiotics; CTX-M-15, KPC and NDM-1. The assay uses isothermal DNA amplification (recombinase polymerase amplification, RPA) implemented on a programmable digital microfluidics (DMF) platform. Automated dispensing protocols are used to simultaneously manipulate 45 droplets of nL volume containing sample DNA, reagents, and controls. The droplets are processed and mixed under electronic control on the DMF devices with positive amplification measured by fluorescence. The assay on these devices is significantly improved with a Time to Positivity (TTP) half that of the benchtop assay. Full article
(This article belongs to the Special Issue Application of Microfluidic Methodology for the Analysis of DNA)
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Open AccessArticle A Feasibility Study on the Simultaneous Sensing of Turbidity and Chlorophyll a Concentration Using a Simple Optical Measurement Method
Micromachines 2017, 8(4), 112; doi:10.3390/mi8040112
Received: 31 December 2016 / Revised: 10 March 2017 / Accepted: 23 March 2017 / Published: 1 April 2017
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Abstract
We have been developing a wireless sensor network system to monitor the quality of lake water in real time. It consists of a sensor module and a system module, which includes communication and power modules. We have focused on pH, turbidity and chlorophyll
[...] Read more.
We have been developing a wireless sensor network system to monitor the quality of lake water in real time. It consists of a sensor module and a system module, which includes communication and power modules. We have focused on pH, turbidity and chlorophyll a concentration as the criteria for qualifying lake water quality. These parameters will be detected by a microfluidic device based sensor module embedded in the wireless sensor network system. In order to detect the turbidity and the chlorophyll a concentration simultaneously, we propose a simple optical measurement method using LED and photodiode in this paper. Before integrating a turbidity and chlorophyll a concentration sensor into the microfluidic device based pH sensor, we performed feasibility studies such as confirmation of the working principle and experiments using environmental water samples. As a result, we successfully verified our simultaneous sensing method by using a simple optical setup of the turbidity and the chlorophyll a concentration. Full article
(This article belongs to the Special Issue Optofluidics 2016)
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Open AccessArticle Modeling and Identification of the Rate-Dependent Hysteresis of Piezoelectric Actuator Using a Modified Prandtl-Ishlinskii Model
Micromachines 2017, 8(4), 114; doi:10.3390/mi8040114
Received: 20 December 2016 / Revised: 21 March 2017 / Accepted: 29 March 2017 / Published: 4 April 2017
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Abstract
Piezoelectric actuator (PEA) is an ideal microscale and nanoscale actuator because of its ultra-precision positioning resolution. However, the inherent hysteretic nonlinearity significantly degrades the PEA’s accuracy. The measured hysteresis of PEA exhibits strong rate-dependence and saturation phenomena, increasing the difficulty in the hysteresis
[...] Read more.
Piezoelectric actuator (PEA) is an ideal microscale and nanoscale actuator because of its ultra-precision positioning resolution. However, the inherent hysteretic nonlinearity significantly degrades the PEA’s accuracy. The measured hysteresis of PEA exhibits strong rate-dependence and saturation phenomena, increasing the difficulty in the hysteresis modeling and identification. In this paper, a modified Prandtl-Ishlinskii (PI) hysteresis model is proposed. The weights of the backlash operators are updated according to the input rates so as to account for the rate-dependence property. Subsequently, the saturation property is realized by cascading a polynomial operator with only odd powers. In order to improve the efficiency of the parameter identification, a special control input consisting of a superimposition of multiple sinusoidal signals is utilized. Because the input rate of such a control input covers a wide range, all the parameters of the hysteresis model can be identified through only one set of experimental data, and no additional curve-fitting is required. The effectiveness of the hysteresis modeling and identification methodology is verified on a PEA-driven flexure mechanism. Experimental results show that the modeling accuracy is on the same order of the noise level of the overall system. Full article
(This article belongs to the Special Issue Piezoelectric MEMS)
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Open AccessArticle Helical Piezoelectric Energy Harvester and Its Application to Energy Harvesting Garments
Micromachines 2017, 8(4), 115; doi:10.3390/mi8040115
Received: 18 January 2017 / Revised: 31 March 2017 / Accepted: 31 March 2017 / Published: 4 April 2017
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Abstract
In this paper, we propose a helical piezoelectric energy harvester, examine its application to clothes in the form of an energy harvesting garment, and analyze its design and characteristics. The helical harvester is composed of an elastic core and a polymer piezoelectric strap
[...] Read more.
In this paper, we propose a helical piezoelectric energy harvester, examine its application to clothes in the form of an energy harvesting garment, and analyze its design and characteristics. The helical harvester is composed of an elastic core and a polymer piezoelectric strap twining the core. The fabricated harvester is highly elastic and can be stretched up to 158% of its initial length. Following the experiments using three different designs, the maximum output power is measured as 1.42 mW at a 3 MΩ load resistance and 1 Hz motional frequency. The proposed helical harvesters are applied at four positions of stretchable tight-fitting sportswear, namely shoulder, arm joint, knee, and hip. The maximum output voltage is measured as more than 20 V from the harvester at the knee position during intended body motions. In addition, electric power is also generated from this energy harvesting garment during daily human motions, which is about 3.9 V at the elbow, 3.1 V at the knee, and 4.4 V at the knee during push-up, walking, and squatting motions, respectively. Full article
(This article belongs to the Special Issue MEMS Energy Harvesters)
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Open AccessArticle A Highly Sensitive Humidity Sensor Based on Ultrahigh-Frequency Microelectromechanical Resonator Coated with Nano-Assembled Polyelectrolyte Thin Films
Micromachines 2017, 8(4), 116; doi:10.3390/mi8040116
Received: 10 March 2017 / Revised: 23 March 2017 / Accepted: 27 March 2017 / Published: 5 April 2017
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Abstract
We developed a highly sensitive humidity sensor based on the combination of ultrahigh-frequency film bulk acoustic resonator (FBAR) and nano-assembled polyelectrolyte (PET) thin films. The water molecule absorption efficiency was optimized by forming loosely-packed PET nanostructures. Then, the humidity sensing characteristics were analyzed
[...] Read more.
We developed a highly sensitive humidity sensor based on the combination of ultrahigh-frequency film bulk acoustic resonator (FBAR) and nano-assembled polyelectrolyte (PET) thin films. The water molecule absorption efficiency was optimized by forming loosely-packed PET nanostructures. Then, the humidity sensing characteristics were analyzed in terms of sensitivity, linearity, reversibility, stability and detection limit. As a result, PET-coated FBAR exhibits excellent humidity sensitivity of 2202.20 Hz/ppm, which is five orders of magnitude higher than quartz crystal microbalance (QCM). Additionally, temperature dependence was investigated with the result that PET-coated FBAR possessed a higher sensitivity at low temperature. Furthermore, we realized the selective detection of water vapor from volatile organic compounds (VOCs) with respect to the polarity property. Owing to the high sensitivity, miniaturized size and ultrahigh operating frequency, PET-coated FBAR is uniquely favorable as a wireless humidity sensor node to integrate into wireless sensor networks (WSNs). Full article
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Open AccessArticle A Suspended Six-Port Transformer-Based Power Divider for 2.4 GHz Applications
Micromachines 2017, 8(4), 118; doi:10.3390/mi8040118
Received: 25 January 2017 / Revised: 31 March 2017 / Accepted: 5 April 2017 / Published: 8 April 2017
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Abstract
This paper presents a transformer-based power divider with six-port suspending structure for 2.4 GHz wireless applications. The proposed power divider, which is featured with chip size (2.9 mm × 2.8 mm × 21 μm), was constructed by an 8-μm-thick Cu bottom electrode, a
[...] Read more.
This paper presents a transformer-based power divider with six-port suspending structure for 2.4 GHz wireless applications. The proposed power divider, which is featured with chip size (2.9 mm × 2.8 mm × 21 μm), was constructed by an 8-μm-thick Cu bottom electrode, a 5 μm-height supporting copper post, and an 8-μm-thick suspended spiral copper conducting layer with a 13 μm air gap. The main structure included two transformers and six input/output matching capacitors for simultaneously achieving two single-to-differential paths so that the chip size of the complex multiple-ports transceiver could be reduced. According to the results, the proposed divider has characteristics of the radio frequency (RF), and its input return losses are around −10 dB, output return losses are beneath −10 dB, and minimum amplitude imbalance is below 1.5 dB and less than 1° phase imbalance at 2.4 GHz operating frequency. Full article
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Open AccessArticle Fluid Flow and Mixing Induced by AC Continuous Electrowetting of Liquid Metal Droplet
Micromachines 2017, 8(4), 119; doi:10.3390/mi8040119
Received: 11 March 2017 / Revised: 27 March 2017 / Accepted: 6 April 2017 / Published: 9 April 2017
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Abstract
In this work, we proposed a novel design of a microfluidic mixer utilizing the amplified Marangoni chaotic advection induced by alternating current (AC) continuous electrowetting of a metal droplet situated in electrolyte solution, due to the linear and quadratic voltage-dependence of flow velocity
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In this work, we proposed a novel design of a microfluidic mixer utilizing the amplified Marangoni chaotic advection induced by alternating current (AC) continuous electrowetting of a metal droplet situated in electrolyte solution, due to the linear and quadratic voltage-dependence of flow velocity at small or large voltages, respectively. Unlike previous researchers exploiting the unidirectional surface stress with direct current (DC) bias at droplet/medium interface for pumping of electrolytes where the resulting flow rate is linearly proportional to the field intensity, dominance of another kind of dipolar flow pattern caused by local Marangoni stress at the drop surface in a sufficiently intense AC electric field is demonstrated by both theoretical analysis and experimental observation, which exhibits a quadratic growth trend as a function of the applied voltage. The dipolar shear stress merely appears at larger voltages and greatly enhances the mixing performance by inducing chaotic advection between the neighboring laminar flow. The mixer design developed herein, on the basis of amplified Marangoni chaotic advection around a liquid metal droplet at larger AC voltages, has great potential for chemical reaction and microelectromechanical systems (MEMS) actuator applications because of generating high-throughput and excellent mixing performance at the same time. Full article
(This article belongs to the Special Issue Micro/Nano-Chip Electrokinetics, Volume II)
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Open AccessArticle Large-Aperture kHz Operating Frequency Ti-alloy Based Optical Micro Scanning Mirror for LiDAR Application
Micromachines 2017, 8(4), 120; doi:10.3390/mi8040120
Received: 2 March 2017 / Revised: 6 April 2017 / Accepted: 7 April 2017 / Published: 10 April 2017
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Abstract
A micro scanning mirror is an optical device used to scan laser beams which can be used for Light Detection and Ranging (LiDAR) in applications like unmanned driving or Unmanned Aerial Vehicle (UAV). The MEMS scanning mirror’s light-weight and low-power make it a
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A micro scanning mirror is an optical device used to scan laser beams which can be used for Light Detection and Ranging (LiDAR) in applications like unmanned driving or Unmanned Aerial Vehicle (UAV). The MEMS scanning mirror’s light-weight and low-power make it a useful device in LiDAR applications. However, the MEMS scanning mirror’s small aperture limits its application because it is too small to deflect faint receiving light. In this paper, we present a Ti-alloy-based electromagnetic micro scanning mirror with very large-aperture (12 mm) and rapid scanning frequency (1.24 kHz). The size of micro-scanner’s mirror plate reached 12 mm, which is much larger than familiar MEMS scanning mirror. The scanner is designed using MEMS design method and fabricated by electro-sparking manufacture method. As the experimental results show, the resonant frequency of the micro scanning mirror is 1240 Hz and the optical scanning angle can reach 26 degrees at resonance frequency when the actuation current is 250 mApp. Full article
(This article belongs to the Special Issue MEMS Mirrors)
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Open AccessArticle Localized Single-Cell Lysis and Manipulation Using Optothermally-Induced Bubbles
Micromachines 2017, 8(4), 121; doi:10.3390/mi8040121
Received: 3 March 2017 / Revised: 30 March 2017 / Accepted: 7 April 2017 / Published: 11 April 2017
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Abstract
Localized single cells can be lysed precisely and selectively using microbubbles optothermally generated by microsecond laser pulses. The shear stress from the microstreaming surrounding laser-induced microbubbles and direct contact with the surface of expanding bubbles cause the rupture of targeted cell membranes. High-resolution
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Localized single cells can be lysed precisely and selectively using microbubbles optothermally generated by microsecond laser pulses. The shear stress from the microstreaming surrounding laser-induced microbubbles and direct contact with the surface of expanding bubbles cause the rupture of targeted cell membranes. High-resolution single-cell lysis is demonstrated: cells adjacent to targeted cells are not lysed. It is also shown that only a portion of the cell membrane can be punctured using this method. Both suspension and adherent cell types can be lysed in this system, and cell manipulation can be integrated for cell–cell interaction studies. Full article
(This article belongs to the Special Issue Microdevices and Microsystems for Cell Manipulation)
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Open AccessArticle Surface Roughness of Z-Cut Quartz Etched by Ammonium Bifluoride and Ammonium Bifluoride Mixed with Isopropyl Alcohol Solutions
Micromachines 2017, 8(4), 122; doi:10.3390/mi8040122
Received: 7 March 2017 / Revised: 30 March 2017 / Accepted: 7 April 2017 / Published: 13 April 2017
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Abstract
It is meaningful to study the surface morphology of monocrystalline material, but there are few studies on the surface roughness of quartz. So, surface roughness of Z-cut quartz etched by pure ammonium bifluoride and ammonium bifluoride mixed with isopropyl alcohol (IPA) solution was
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It is meaningful to study the surface morphology of monocrystalline material, but there are few studies on the surface roughness of quartz. So, surface roughness of Z-cut quartz etched by pure ammonium bifluoride and ammonium bifluoride mixed with isopropyl alcohol (IPA) solution was investigated for the first time in this paper. Firstly, when etching in pure ammonium bifluoride solutions, the surface roughness change with etching time, etching temperature, and solution concentration were studied. Then, the surface roughness improvement given by isopropyl alcohol solution was analyzed carefully. The experimental results indicated that: the surface roughness of Z-cut quartz (0001) plane increased with etching time, but decreased with etching temperature and solution concentration; the adding of isopropyl alcohol in ammonium bifluoride solution could decrease the roughness and improve the surface quality. This is the first systemic research of the evolution of quartz surface roughness when etching in ammonium bifluoride solution, and will benefit the future design and manufacture of quartz MEMS devices. Full article
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Open AccessArticle The Exploration for an Appropriate Vacuum Level for Performance Enhancement of a Comb-Drive Microscanner
Micromachines 2017, 8(4), 126; doi:10.3390/mi8040126
Received: 17 February 2017 / Revised: 7 April 2017 / Accepted: 11 April 2017 / Published: 16 April 2017
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Abstract
In order to identify the influence of the vacuum environment on the performance of a comb-drive microscanner, and indicate the optimum pressure for enhancing its performance, a comb-drive microscanner fabricated on silicon-on-insulator (SOI) substrate was prepared and tested at different pressures, and the
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In order to identify the influence of the vacuum environment on the performance of a comb-drive microscanner, and indicate the optimum pressure for enhancing its performance, a comb-drive microscanner fabricated on silicon-on-insulator (SOI) substrate was prepared and tested at different pressures, and the characteristics in vacuum were obtained. The test results revealed that the vacuum environment enhanced the performance in the optical scanning angle, and decreased the actuation voltage. With a 30 V driving voltage applied, the microscanner can reach an optical scanning angle of 44.3° at a pressure of 500 Pa. To obtain an enhancement in its properties, only a vacuum range from 100 to 1000 Pa is needed, which can be very readily and economically realized and maintained in a vacuum package. Full article
(This article belongs to the Special Issue MEMS Mirrors)
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Open AccessArticle Paper-Based Analytical Device for Zinc Ion Quantification in Water Samples with Power-Free Analyte Concentration
Micromachines 2017, 8(4), 127; doi:10.3390/mi8040127
Received: 25 March 2017 / Revised: 11 April 2017 / Accepted: 13 April 2017 / Published: 18 April 2017
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Abstract
Insufficient sensitivity is a general issue of colorimetric paper-based analytical devices (PADs) for trace analyte detection, such as metal ions, in environmental water. This paper demonstrates the colorimetric detection of zinc ions (Zn2+) on a paper-based analytical device with an integrated
[...] Read more.
Insufficient sensitivity is a general issue of colorimetric paper-based analytical devices (PADs) for trace analyte detection, such as metal ions, in environmental water. This paper demonstrates the colorimetric detection of zinc ions (Zn2+) on a paper-based analytical device with an integrated analyte concentration system. Concentration of Zn2+ ions from an enlarged sample volume (1 mL) has been achieved with the aid of a colorimetric Zn2+ indicator (Zincon) electrostatically immobilized onto a filter paper substrate in combination with highly water-absorbent materials. Analyte concentration as well as sample pretreatment, including pH adjustment and interferent masking, has been elaborated. The resulting device enables colorimetric quantification of Zn2+ in environmental water samples (tap water, river water) from a single sample application. The achieved detection limit of 0.53 μM is a significant improvement over that of a commercial colorimetric Zn2+ test paper (9.7 μM), demonstrating the efficiency of the developed analyte concentration system not requiring any equipment. Full article
(This article belongs to the Special Issue Paper Microfluidics: Fundamental Studies and Applications)
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Open AccessArticle A Micromanipulator and Transporter Based on Vibrating Bubbles in an Open Chip Environment
Micromachines 2017, 8(4), 130; doi:10.3390/mi8040130
Received: 13 January 2017 / Revised: 22 March 2017 / Accepted: 7 April 2017 / Published: 18 April 2017
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Abstract
A novel micromanipulation technique of multi-objectives based on vibrating bubbles in an open chip environment is described in this paper. Bubbles were created in an aqueous medium by the thermal energy converted from a laser. When the piezoelectric stack fixed under the chip
[...] Read more.
A novel micromanipulation technique of multi-objectives based on vibrating bubbles in an open chip environment is described in this paper. Bubbles were created in an aqueous medium by the thermal energy converted from a laser. When the piezoelectric stack fixed under the chip vibrated the bubbles, micro-objects (microparticles, cells, etc.) rapidly moved towards the bubbles. Results from numerical simulation demonstrate that convective flow around the bubbles can provide forces to capture objects. Since bubbles can be generated at arbitrary destinations in the open chip environment, they can act as both micromanipulators and transporters. As a result, micro- and bio-objects could be collected and transported effectively as masses in the open chip environment. This makes it possible for scientific instruments, such as atomic force microscopy (AFM) and scanning ion conductive microscopy (SICM), to operate the micro-objects directly in an open chip environment. Full article
(This article belongs to the Special Issue Microdevices and Microsystems for Cell Manipulation)
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Open AccessArticle Hydrodynamic Simulation of an Orbital Shaking Test for the Degradation Assessment of Blood-Contact Biomedical Coatings
Micromachines 2017, 8(4), 132; doi:10.3390/mi8040132
Received: 4 February 2017 / Revised: 31 March 2017 / Accepted: 16 April 2017 / Published: 19 April 2017
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Abstract
Biomedical coatings are used to promote the wear resistance and the biocompatibility of a mechanical heart valve. An orbital shaking test was proposed to assess the durability of the coatings by the amount material eroded by the surrounding fluid. However, there is still
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Biomedical coatings are used to promote the wear resistance and the biocompatibility of a mechanical heart valve. An orbital shaking test was proposed to assess the durability of the coatings by the amount material eroded by the surrounding fluid. However, there is still a lack of understanding with regards to the shaker’s rotating conditions and the corresponding physiological condition. This study implemented numerical simulations by establishing a fluid dynamic model to evaluate the intensity of the shear stress under various rotating speeds and diameters of the shaker. The results are valuable to conduct in vitro tests for estimating the performance of biomedical coatings under real hemodynamic conditions and can be applied to other fluid-contact implants. Full article
(This article belongs to the Special Issue Microtribology, Adhesion and Surface Engineering)
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Review

Jump to: Editorial, Research

Open AccessReview Two-Photon Polymerization Metrology: Characterization Methods of Mechanisms and Microstructures
Micromachines 2017, 8(4), 101; doi:10.3390/mi8040101
Received: 28 February 2017 / Revised: 18 March 2017 / Accepted: 21 March 2017 / Published: 27 March 2017
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Abstract
The ability to create complex three-dimensional microstructures has reached an unprecedented level of sophistication in the last 15 years. For the most part, this is the result of a steady development of the additive manufacturing technique named two-photon polymerization (TPP). In a short
[...] Read more.
The ability to create complex three-dimensional microstructures has reached an unprecedented level of sophistication in the last 15 years. For the most part, this is the result of a steady development of the additive manufacturing technique named two-photon polymerization (TPP). In a short amount of time, TPP has gone from being a microfabrication novelty employed largely by laser specialists to a useful tool in the hands of scientists and engineers working in a wide range of research fields including microfluidics. When used in combination with traditional microfabrication processes, TPP can be employed to add unique three-dimensional components to planar platforms, thus enabling the realization of lab-on-a-chip solutions otherwise impossible to create. To take full advantage of TPP, an in-depth understanding is required of the materials photochemistry and the fabricated microstructures’ mechanical and chemical properties. Thus, we review methods developed so far to investigate the underling mechanism involved during TPP and analytical methods employed to characterize TPP microstructures. Furthermore, we will discuss potential opportunities for using optofluidics and lab-on-a-chip systems for TPP metrology. Full article
(This article belongs to the Special Issue Ultrafast Laser Fabrication for Lab-on-a-Chip)
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Open AccessReview Microfluidic Technology for the Generation of Cell Spheroids and Their Applications
Micromachines 2017, 8(4), 94; doi:10.3390/mi8040094
Received: 11 January 2017 / Revised: 13 March 2017 / Accepted: 15 March 2017 / Published: 23 March 2017
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Abstract
A three-dimensional (3D) tissue model has significant advantages over the conventional two-dimensional (2D) model. A 3D model mimics the relevant in-vivo physiological conditions, allowing a cell culture to serve as an effective tool for drug discovery, tissue engineering, and the investigation of disease
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A three-dimensional (3D) tissue model has significant advantages over the conventional two-dimensional (2D) model. A 3D model mimics the relevant in-vivo physiological conditions, allowing a cell culture to serve as an effective tool for drug discovery, tissue engineering, and the investigation of disease pathology. The present reviews highlight the recent advances and the development of microfluidics based methods for the generation of cell spheroids. The paper emphasizes on the application of microfluidic technology for tissue engineering including the formation of multicellular spheroids (MCS). Further, the paper discusses the recent technical advances in the integration of microfluidic devices for MCS-based high-throughput drug screening. The review compares the various microfluidic techniques and finally provides a perspective for the future opportunities in this research area. Full article
(This article belongs to the Special Issue Microdevices and Microsystems for Cell Manipulation)
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Open AccessReview Aerogels for Optofluidic Waveguides
Micromachines 2017, 8(4), 98; doi:10.3390/mi8040098
Received: 7 January 2017 / Revised: 16 March 2017 / Accepted: 17 March 2017 / Published: 29 March 2017
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Abstract
Aerogels—solid materials keeping their internal structure of interconnected submicron-sized pores intact upon exchanging the pore liquid with a gas—were first synthesized in 1932 by Samuel Kistler. Overall, an aerogel is a special form of a highly porous material with a very low solid
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Aerogels—solid materials keeping their internal structure of interconnected submicron-sized pores intact upon exchanging the pore liquid with a gas—were first synthesized in 1932 by Samuel Kistler. Overall, an aerogel is a special form of a highly porous material with a very low solid density and it is composed of individual nano-sized particles or fibers that are connected to form a three-dimensional network. The unique properties of these materials, such as open pores and high surface areas, are attributed to their high porosity and irregular solid structure, which can be tuned through proper selection of the preparation conditions. Moreover, their low refractive index makes them a remarkable solid-cladding material for developing liquid-core optofluidic waveguides based on total internal reflection of light. This paper is a comprehensive review of the literature on the use of aerogels for optofluidic waveguide applications. First, an overview of different types of aerogels and their physicochemical properties is presented. Subsequently, possible techniques to fabricate channels in aerogel monoliths are discussed and methods to make the channel surfaces hydrophobic are described in detail. Studies in the literature on the characterization of light propagation in liquid-filled channels within aerogel monoliths as well as their light-guiding characteristics are discussed. Finally, possible applications of aerogel-based optofluidic waveguides are described. Full article
(This article belongs to the Special Issue Optofluidics 2016)
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Open AccessReview Nanomechanical Motion Transducers for Miniaturized Mechanical Systems
Micromachines 2017, 8(4), 108; doi:10.3390/mi8040108
Received: 18 February 2017 / Revised: 20 March 2017 / Accepted: 27 March 2017 / Published: 1 April 2017
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Abstract
Reliable operation of a miniaturized mechanical system requires that nanomechanical motion be transduced into electrical signals (and vice versa) with high fidelity and in a robust manner. Progress in transducer technologies is expected to impact numerous emerging and future applications of micro- and,
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Reliable operation of a miniaturized mechanical system requires that nanomechanical motion be transduced into electrical signals (and vice versa) with high fidelity and in a robust manner. Progress in transducer technologies is expected to impact numerous emerging and future applications of micro- and, especially, nanoelectromechanical systems (MEMS and NEMS); furthermore, high-precision measurements of nanomechanical motion are broadly used to study fundamental phenomena in physics and biology. Therefore, development of nanomechanical motion transducers with high sensitivity and bandwidth has been a central research thrust in the fields of MEMS and NEMS. Here, we will review recent progress in this rapidly-advancing area. Full article
(This article belongs to the Special Issue Mechanical Systems Approaching Nanoscales and Beyond)
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Open AccessReview The Emerging Frontiers and Applications of High-Resolution 3D Printing
Micromachines 2017, 8(4), 113; doi:10.3390/mi8040113
Received: 1 March 2017 / Revised: 27 March 2017 / Accepted: 28 March 2017 / Published: 1 April 2017
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Abstract
Over the past few decades, there has been an increasing interest in the fabrication of complex high-resolution three-dimensional (3D) architectures at micro/nanoscale. These architectures can be obtained through conventional microfabrication methods including photolithography, electron-beam lithography, femtosecond laser lithography, nanoimprint lithography, etc. However, the
[...] Read more.
Over the past few decades, there has been an increasing interest in the fabrication of complex high-resolution three-dimensional (3D) architectures at micro/nanoscale. These architectures can be obtained through conventional microfabrication methods including photolithography, electron-beam lithography, femtosecond laser lithography, nanoimprint lithography, etc. However, the applications of these fabrication methods are limited by their high costs, the generation of various chemical wastes, and their insufficient ability to create high-aspect-ratio 3D structures. High-resolution 3D printing has recently emerged as a promising solution, as it is capable of building multifunctional 3D constructs with optimal properties. Here we present a review on the principles and the recent advances of high-resolution 3D printing techniques, including two-photon polymerization (TPP), projection microstereoLithography (PµSL), direct ink writing (DIW) and electrohydrodynamic printing (EHDP). We also highlight their typical applications in various fields such as metamaterials, energy storage, flexible electronics, microscale tissue engineering scaffolds and organ-on-chips. Finally, we discuss the challenge and perspective of these high-resolution 3D printing techniques in technical and application aspects. We believe that high-resolution 3D printing will eventually revolutionize the microfabrication processes of 3D architectures with high product quality and diversified materials. It will also find applications in a wide scope. Full article
(This article belongs to the Special Issue Bioprinting and 3D Printing in MEMS Technology)
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Open AccessReview Microplasma Field Effect Transistors
Micromachines 2017, 8(4), 117; doi:10.3390/mi8040117
Received: 16 February 2017 / Revised: 10 March 2017 / Accepted: 21 March 2017 / Published: 5 April 2017
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Abstract
Micro plasma devices (MPD) with power gains are of interest in applications involving operations in the presence of ionizing radiations, in propulsion, in control, amplification of high power electromagnetic waves, and in metamaterials for energy management. Here, we review and discuss MPDs with
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Micro plasma devices (MPD) with power gains are of interest in applications involving operations in the presence of ionizing radiations, in propulsion, in control, amplification of high power electromagnetic waves, and in metamaterials for energy management. Here, we review and discuss MPDs with an emphasis on new architectures that have evolved during the past seven years. Devices with programmable impact ionization rates and programmable boundaries are developed to control the plasma ignition voltage and current to achieve power gain. Plasma devices with 1–10 μm gaps are shown to operate in the sub-Paschen regime in atmospheric pressures where ion-assisted field emission results in a breakdown voltage that linearly depends on the gap distance in contrast to the exponential dependence dictated by the Paschen curve. Small gap devices offer higher operation frequencies at low operation voltages with applications in metamaterial skins for energy management and in harsh environment inside nuclear reactors and in space. In addition to analog plasma devices, logic gates, digital circuits, and distributed amplifiers are also discussed. Full article
(This article belongs to the Special Issue Microplasma Devices)
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Open AccessReview The Self-Propulsion of the Spherical Pt–SiO2 Janus Micro-Motor
Micromachines 2017, 8(4), 123; doi:10.3390/mi8040123
Received: 22 February 2017 / Revised: 5 April 2017 / Accepted: 5 April 2017 / Published: 12 April 2017
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Abstract
The double-faced Janus micro-motor, which utilizes the heterogeneity between its two hemispheres to generate self-propulsion, has shown great potential in water cleaning, drug delivery in micro/nanofluidics, and provision of power for a novel micro-robot. In this paper, we focus on the self-propulsion of
[...] Read more.
The double-faced Janus micro-motor, which utilizes the heterogeneity between its two hemispheres to generate self-propulsion, has shown great potential in water cleaning, drug delivery in micro/nanofluidics, and provision of power for a novel micro-robot. In this paper, we focus on the self-propulsion of a platinum–silica (Pt–SiO2) spherical Janus micro-motor (JM), which is one of the simplest micro-motors, suspended in a hydrogen peroxide solution (H2O2). Due to the catalytic decomposition of H2O2 on the Pt side, the JM is propelled by the established concentration gradient known as diffusoiphoretic motion. Furthermore, as the JM size increases to O (10 μm), oxygen molecules nucleate on the Pt surface, forming microbubbles. In this case, a fast bubble propulsion is realized by the microbubble cavitation-induced jet flow. We systematically review the results of the above two distinct mechanisms: self-diffusiophoresis and microbubble propulsion. Their typical behaviors are demonstrated, based mainly on experimental observations. The theoretical description and the numerical approach are also introduced. We show that this tiny motor, though it has a very simple structure, relies on sophisticated physical principles and can be used to fulfill many novel functions. Full article
(This article belongs to the Special Issue Insights and Advancements in Microfluidics)
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Open AccessFeature PaperReview The Use of Microfluidics in Cytotoxicity and Nanotoxicity Experiments
Micromachines 2017, 8(4), 124; doi:10.3390/mi8040124
Received: 28 February 2017 / Revised: 6 April 2017 / Accepted: 7 April 2017 / Published: 12 April 2017
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Abstract
Many unique chemical compounds and nanomaterials are being developed, and each one requires a considerable range of in vitro and/or in vivo toxicity screening in order to evaluate their safety. The current methodology of in vitro toxicological screening on cells is based on
[...] Read more.
Many unique chemical compounds and nanomaterials are being developed, and each one requires a considerable range of in vitro and/or in vivo toxicity screening in order to evaluate their safety. The current methodology of in vitro toxicological screening on cells is based on well-plate assays that require time-consuming manual handling or expensive automation to gather enough meaningful toxicology data. Cost reduction; access to faster, more comprehensive toxicity data; and a robust platform capable of quantitative testing, will be essential in evaluating the safety of new chemicals and nanomaterials, and, at the same time, in securing the confidence of regulators and end-users. Microfluidic chips offer an alternative platform for toxicity screening that has the potential to transform both the rates and efficiency of nanomaterial testing, as reviewed here. The inherent advantages of microfluidic technologies offer high-throughput screening with small volumes of analytes, parallel analyses, and low-cost fabrication. Full article
(This article belongs to the Special Issue Insights and Advancements in Microfluidics)
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Open AccessReview A Review of the State of Dry Adhesives: Biomimetic Structures and the Alternative Designs They Inspire
Micromachines 2017, 8(4), 125; doi:10.3390/mi8040125
Received: 25 February 2017 / Revised: 6 April 2017 / Accepted: 9 April 2017 / Published: 14 April 2017
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Abstract
Robust and inexpensive dry adhesives would have a multitude of potential applications, but replicating the impressive adhesive organs of many small animals has proved challenging. A substantial body of work has been produced in recent years which has illuminated the many mechanical processes
[...] Read more.
Robust and inexpensive dry adhesives would have a multitude of potential applications, but replicating the impressive adhesive organs of many small animals has proved challenging. A substantial body of work has been produced in recent years which has illuminated the many mechanical processes influencing a dry adhesive interface. The especially potent footpads of the tokay gecko have inspired researchers to develop and examine an impressive and diverse collection of artificial fibrillar dry adhesives, though study of tree frogs and insects demonstrate that successful adhesive designs come in many forms. This review discusses the current theoretical understanding of dry adhesive mechanics, including the observations from biological systems and the lessons learned by recent attempts to mimic them. Attention is drawn in particular to the growing contingent of work exploring ideas which are complimentary to or an alternative for fibrillar designs. The fundamentals of compliance control form a basis for dry adhesives made of composite and “smart,” stimuli-responsive materials including shape memory polymers. An overview of fabrication and test techniques, with a sampling of performance results, is provided. Full article
(This article belongs to the Special Issue Bio-Inspired Micro/Nano Devices and Systems)
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Open AccessReview Ultrahigh-Throughput Improvement and Discovery of Enzymes Using Droplet-Based Microfluidic Screening
Micromachines 2017, 8(4), 128; doi:10.3390/mi8040128
Received: 21 January 2017 / Revised: 11 April 2017 / Accepted: 13 April 2017 / Published: 18 April 2017
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Abstract
Enzymes are extremely valuable tools for industrial, environmental, and biotechnological applications and there is a constant need for improving existing biological catalysts and for discovering new ones. Screening microbe or gene libraries is an efficient way of identifying new enzymes. In this view,
[...] Read more.
Enzymes are extremely valuable tools for industrial, environmental, and biotechnological applications and there is a constant need for improving existing biological catalysts and for discovering new ones. Screening microbe or gene libraries is an efficient way of identifying new enzymes. In this view, droplet-based microfluidics appears to be one of the most powerful approaches as it allows inexpensive screenings in well-controlled conditions and an ultrahigh-throughput regime. This review aims to introduce the main microfluidic devices and concepts to be considered for such screening before presenting and discussing the latest successful applications of the technology for enzyme discovery. Full article
(This article belongs to the Special Issue Droplet Microfluidics: Techniques and Technologies, Volume II)
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Open AccessReview Stencil Lithography for Scalable Micro- and Nanomanufacturing
Micromachines 2017, 8(4), 131; doi:10.3390/mi8040131
Received: 14 March 2017 / Revised: 7 April 2017 / Accepted: 13 April 2017 / Published: 19 April 2017
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Abstract
In this paper, we review the current development of stencil lithography for scalable micro- and nanomanufacturing as a resistless and reusable patterning technique. We first introduce the motivation and advantages of stencil lithography for large-area micro- and nanopatterning. Then we review the progress
[...] Read more.
In this paper, we review the current development of stencil lithography for scalable micro- and nanomanufacturing as a resistless and reusable patterning technique. We first introduce the motivation and advantages of stencil lithography for large-area micro- and nanopatterning. Then we review the progress of using rigid membranes such as SiNx and Si as stencil masks as well as stacking layers. We also review the current use of flexible membranes including a compliant SiNx membrane with springs, polyimide film, polydimethylsiloxane (PDMS) layer, and photoresist-based membranes as stencil lithography masks to address problems such as blurring and non-planar surface patterning. Moreover, we discuss the dynamic stencil lithography technique, which significantly improves the patterning throughput and speed by moving the stencil over the target substrate during deposition. Lastly, we discuss the future advancement of stencil lithography for a resistless, reusable, scalable, and programmable nanolithography method. Full article
(This article belongs to the Special Issue Scalable Micro/Nano Patterning)
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