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Micromachines, Volume 8, Issue 4 (April 2017)

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Cover Story (view full-size image) A fanciful ball design has been used to demonstrate the 4D printing abilities of entrapped enzymes [...] Read more.
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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; https://doi.org/10.3390/mi8040132
Received: 4 February 2017 / Revised: 31 March 2017 / Accepted: 16 April 2017 / Published: 19 April 2017
Cited by 2 | PDF Full-text (10842 KB) | HTML Full-text | XML Full-text
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
[...] Read more.
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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Open AccessReview Stencil Lithography for Scalable Micro- and Nanomanufacturing
Micromachines 2017, 8(4), 131; https://doi.org/10.3390/mi8040131
Received: 14 March 2017 / Revised: 7 April 2017 / Accepted: 13 April 2017 / Published: 19 April 2017
Cited by 7 | PDF Full-text (6213 KB) | HTML Full-text | XML Full-text
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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Open AccessArticle A Micromanipulator and Transporter Based on Vibrating Bubbles in an Open Chip Environment
Micromachines 2017, 8(4), 130; https://doi.org/10.3390/mi8040130
Received: 13 January 2017 / Revised: 22 March 2017 / Accepted: 7 April 2017 / Published: 18 April 2017
Cited by 1 | PDF Full-text (12379 KB) | HTML Full-text | XML Full-text
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
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Open AccessEditorial Opportunities and Challenges in Flexible and Stretchable Electronics: A Panel Discussion at ISFSE2016
Micromachines 2017, 8(4), 129; https://doi.org/10.3390/mi8040129
Received: 10 April 2017 / Revised: 10 April 2017 / Accepted: 12 April 2017 / Published: 18 April 2017
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Abstract
The 2016 International Symposium of Flexible and Stretchable Electronics (ISFSE2016), co-sponsored by the Flexible Electronics Research Center, Huazhong University of Science and Technology (HUST) & State Key Laboratory of Digital Manufacturing and Equipment Technology, National Natural Science and Engineering (NSFC), was successfully held
[...] Read more.
The 2016 International Symposium of Flexible and Stretchable Electronics (ISFSE2016), co-sponsored by the Flexible Electronics Research Center, Huazhong University of Science and Technology (HUST) & State Key Laboratory of Digital Manufacturing and Equipment Technology, National Natural Science and Engineering (NSFC), was successfully held in Wuhan, China, 29–30 June 2016.[...] Full article
(This article belongs to the Special Issue Flexible and Stretchable Electronics) Printed Edition available
Open AccessReview Ultrahigh-Throughput Improvement and Discovery of Enzymes Using Droplet-Based Microfluidic Screening
Micromachines 2017, 8(4), 128; https://doi.org/10.3390/mi8040128
Received: 21 January 2017 / Revised: 11 April 2017 / Accepted: 13 April 2017 / Published: 18 April 2017
Cited by 4 | PDF Full-text (2385 KB) | HTML Full-text | XML Full-text
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 AccessArticle Paper-Based Analytical Device for Zinc Ion Quantification in Water Samples with Power-Free Analyte Concentration
Micromachines 2017, 8(4), 127; https://doi.org/10.3390/mi8040127
Received: 25 March 2017 / Revised: 11 April 2017 / Accepted: 13 April 2017 / Published: 18 April 2017
Cited by 5 | PDF Full-text (2400 KB) | HTML Full-text | XML Full-text | Supplementary Files
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 The Exploration for an Appropriate Vacuum Level for Performance Enhancement of a Comb-Drive Microscanner
Micromachines 2017, 8(4), 126; https://doi.org/10.3390/mi8040126
Received: 17 February 2017 / Revised: 7 April 2017 / Accepted: 11 April 2017 / Published: 16 April 2017
Cited by 2 | PDF Full-text (10567 KB) | HTML Full-text | XML Full-text
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
[...] Read more.
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) Printed Edition available
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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; https://doi.org/10.3390/mi8040125
Received: 25 February 2017 / Revised: 6 April 2017 / Accepted: 9 April 2017 / Published: 14 April 2017
Cited by 4 | PDF Full-text (7845 KB) | HTML Full-text | XML Full-text
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 AccessArticle Surface Roughness of Z-Cut Quartz Etched by Ammonium Bifluoride and Ammonium Bifluoride Mixed with Isopropyl Alcohol Solutions
Micromachines 2017, 8(4), 122; https://doi.org/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
[...] Read more.
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 AccessFeature PaperReview The Use of Microfluidics in Cytotoxicity and Nanotoxicity Experiments
Micromachines 2017, 8(4), 124; https://doi.org/10.3390/mi8040124
Received: 28 February 2017 / Revised: 6 April 2017 / Accepted: 7 April 2017 / Published: 12 April 2017
Cited by 1 | PDF Full-text (3123 KB) | HTML Full-text | XML Full-text
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) Printed Edition available
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Open AccessReview The Self-Propulsion of the Spherical Pt–SiO2 Janus Micro-Motor
Micromachines 2017, 8(4), 123; https://doi.org/10.3390/mi8040123
Received: 22 February 2017 / Revised: 5 April 2017 / Accepted: 5 April 2017 / Published: 12 April 2017
Cited by 3 | PDF Full-text (4337 KB) | HTML Full-text | XML Full-text | Supplementary Files
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) Printed Edition available
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Open AccessArticle Localized Single-Cell Lysis and Manipulation Using Optothermally-Induced Bubbles
Micromachines 2017, 8(4), 121; https://doi.org/10.3390/mi8040121
Received: 3 March 2017 / Revised: 30 March 2017 / Accepted: 7 April 2017 / Published: 11 April 2017
Cited by 1 | PDF Full-text (5536 KB) | HTML Full-text | XML Full-text
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
[...] Read more.
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
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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; https://doi.org/10.3390/mi8040120
Received: 2 March 2017 / Revised: 6 April 2017 / Accepted: 7 April 2017 / Published: 10 April 2017
Cited by 4 | PDF Full-text (5736 KB) | HTML Full-text | XML Full-text
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
[...] Read more.
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) Printed Edition available
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Open AccessArticle Fluid Flow and Mixing Induced by AC Continuous Electrowetting of Liquid Metal Droplet
Micromachines 2017, 8(4), 119; https://doi.org/10.3390/mi8040119
Received: 11 March 2017 / Revised: 27 March 2017 / Accepted: 6 April 2017 / Published: 9 April 2017
Cited by 2 | PDF Full-text (2478 KB) | HTML Full-text | XML Full-text | Supplementary Files
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
[...] Read more.
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 A Suspended Six-Port Transformer-Based Power Divider for 2.4 GHz Applications
Micromachines 2017, 8(4), 118; https://doi.org/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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