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Micromachines
Volume 4
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Micromachines, Volume 4, Issue 2 (June 2013) – 12 articles , Pages 128-285

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921 KiB  
Article
On-Chip Enucleation of Bovine Oocytes using Microrobot-Assisted Flow-Speed Control
by Lin Feng, Masaya Hagiwara, Akihiko Ichikawa and Fumihito Arai
Micromachines 2013, 4(2), 272-285; https://doi.org/10.3390/mi4020272 - 21 Jun 2013
Cited by 44 | Viewed by 8870
Abstract
In this study, we developed a microfluidic chip with a magnetically driven microrobot for oocyte enucleation. A microfluidic system was specially designed for enucleation, and the microrobot actively controls the local flow-speed distribution in the microfluidic chip. The microrobot can adjust fluid resistances [...] Read more.
In this study, we developed a microfluidic chip with a magnetically driven microrobot for oocyte enucleation. A microfluidic system was specially designed for enucleation, and the microrobot actively controls the local flow-speed distribution in the microfluidic chip. The microrobot can adjust fluid resistances in a channel and can open or close the channel to control the flow distribution. Analytical modeling was conducted to control the fluid speed distribution using the microrobot, and the model was experimentally validated. The novelties of the developed microfluidic system are as follows: (1) the cutting speed improved significantly owing to the local fluid flow control; (2) the cutting volume of the oocyte can be adjusted so that the oocyte undergoes less damage; and (3) the nucleus can be removed properly using the combination of a microrobot and hydrodynamic forces. Using this device, we achieved a minimally invasive enucleation process. The average enucleation time was 2.5 s and the average removal volume ratio was 20%. The proposed new system has the advantages of better operation speed, greater cutting precision, and potential for repeatable enucleation. Full article
(This article belongs to the Special Issue Micro/Nanofluidic Devices for Single Cell Analysis)
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<p>(<b>a</b>) Overview of the enucleation microchip. (<b>b</b>–<b>e</b>) Concept of the oocyte enucleation process by the use of magnetically driven microtools (MMTs) in a microfluidic chip. Blue arrows show the flow direction. (<b>f</b>) Height differences in the microchannel design. The white arrow shows the movement of the MMT.</p> Full article ">Figure 2
<p>Electric circuit analogy of the enucleation chip.</p> Full article ">Figure 3
<p>Theoretical and experimental values of the fluid velocity changes at three points in the channel. The velocity of the outflow is set to 3.5 mm/s. (<b>a</b>) In case that the MMT is near the right-side corner, (<b>b</b>) In case that the MMT is the left-side corner.</p> Full article ">Figure 4
<p>Correlations of the volume sucked into the outlet microchannel with respect to the time under the fixed position of the MMT. The velocity of the outflow is set to 3.5 mm/s. (<b>a</b>) The definition of volume ratio, (<b>b</b>) the experimental result.</p> Full article ">Figure 5
<p>FEM results of the velocity distribution and the surface traction of oocytes in the Y-direction. Object surface: y component of surface traction (force/area) (Pa). Arrow: Velocity field, Slice: y component of velocity field (m/s).</p> Full article ">Figure 6
<p>Fabrication process of the MMT and a fabricated chip with a magnified figure of the MMT.</p> Full article ">Figure 7
<p>Components of experimental system: (<b>a</b>) experimental setup for the enucleation of oocytes including the linear stage for magnet actuation, a microfluidic chip, and a piezoceramic for generating vibrations on the microfluidic chip and (<b>b</b>) system architecture.</p> Full article ">Figure 8
<p>(<b>a</b>–<b>d</b>) Experimental results of the oocyte enucleation process with an MMT. (<b>e</b>) Nucleus after being removed from the oocyte. The incision of the enucleated oocyte is smooth and the remaining oocyte is remains smooth; the enucleated nucleus is also shown in this figure with a removal volume of 17.8% from the original volume. (Supplemental Video file available online).</p> Full article ">Figure 9
<p>(<b>a</b>) Enucleation processing time for 15 samples; the average enucleation time is 2.5 s for one oocyte. (<b>b</b>) Removal proportion of the nucleus from the original oocyte for 15 samples; the average removal proportion is 20%.</p> Full article ">
1411 KiB  
Article
Microfluidic Platform for Enzyme-Linked and Magnetic Particle-Based Immunoassay
by Nikhil Bhalla, Danny Wen Yaw Chung, Yaw-Jen Chang, Kimberly Jane S. Uy, Yi Ying Ye, Ting-Yu Chin, Hao Chun Yang and Dorota G. Pijanowska
Micromachines 2013, 4(2), 257-271; https://doi.org/10.3390/mi4020257 - 18 Jun 2013
Cited by 19 | Viewed by 9230
Abstract
This article presents design and testing of a microfluidic platform for immunoassay. The method is based on sandwiched ELISA, whereby the primary antibody is immobilized on nitrocelluose and, subsequently, magnetic beads are used as a label to detect the analyte. The chip takes [...] Read more.
This article presents design and testing of a microfluidic platform for immunoassay. The method is based on sandwiched ELISA, whereby the primary antibody is immobilized on nitrocelluose and, subsequently, magnetic beads are used as a label to detect the analyte. The chip takes approximately 2 h and 15 min to complete the assay. A Hall Effect sensor using 0.35-μm BioMEMS TSMC technology (Taiwan Semiconductor Manufacturing Company Bio-Micro-Electro-Mechanical Systems) was fabricated to sense the magnetic field from the beads. Furthermore, florescence detection and absorbance measurements from the chip demonstrate successful immunoassay on the chip. In addition, investigation also covers the Hall Effect simulations, mechanical modeling of the bead–protein complex, testing of the microfluidic platform with magnetic beads averaging 10 nm, and measurements with an inductor-based system. Full article
(This article belongs to the Special Issue Bioinspired Microsensors and Micromachines)
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<p>Mechanical model of a superparamagnetic nanoparticle–protein complex.</p> Full article ">Figure 2
<p>(<b>a</b>) scheme for microfluidic platform design (<b>b</b>) fabricated microfluidic platform (white color depicts the nitrocellulose coating at the reaction chamber).</p> Full article ">Figure 3
<p>Layout of Hall sensor area (yellow) and induction coil (red).</p> Full article ">Figure 4
<p>Fabrication process (<b>a</b>) after-standard TSMC 0.35-μm CMOS process (<b>b</b>) removal of passivation layer (<b>c</b>) RLS etch (<b>d</b>) gold coating.</p> Full article ">Figure 5
<p>Total deformation of the bio-complex.</p> Full article ">Figure 6
<p>Von Mises stress distribution plot of bio-complex.</p> Full article ">Figure 7
<p>Testing platform with pump and sensor to perform immunoassay.</p> Full article ">Figure 8
<p>Fluorescent intensity on nitrocellulose <span class="html-italic">vs</span>. wavelength.</p> Full article ">Figure 9
<p>Average fluorescence values from the microfluidic chip.</p> Full article ">Figure 10
<p>Controls for ELISA using florescence detection (one-way ANOVA analysis; “*” denotes the significant result within <span class="html-italic">p</span> &lt; 0.05).</p> Full article ">Figure 11
<p>Analyte concentration <span class="html-italic">vs</span>. florescence (off-chip and on-chip).</p> Full article ">Figure 12
<p>Differential pair of inductors measuring signal from magnetic beads on microfluidic platform.</p> Full article ">Figure 13
<p>Graph indicating linearity of the magnetic field measurements from different sets of magnetic beads.</p> Full article ">Figure 14
<p>Magnetic flux (Input) <span class="html-italic">vs</span>. voltage (Output) curve.</p> Full article ">Figure 15
<p>Top view of Hall’s voltage distribution.</p> Full article ">
3124 KiB  
Article
Analysis of Electric Fields inside Microchannels and Single Cell Electrical Lysis with a Microfluidic Device
by Bashir I. Morshed, Maitham Shams and Tofy Mussivand
Micromachines 2013, 4(2), 243-256; https://doi.org/10.3390/mi4020243 - 7 Jun 2013
Cited by 11 | Viewed by 10861
Abstract
Analysis of electric fields generated inside the microchannels of a microfluidic device for electrical lysis of biological cells along with experimental verification are presented. Electrical lysis is the complete disintegration of cell membranes, due to a critical level of electric fields applied for [...] Read more.
Analysis of electric fields generated inside the microchannels of a microfluidic device for electrical lysis of biological cells along with experimental verification are presented. Electrical lysis is the complete disintegration of cell membranes, due to a critical level of electric fields applied for a critical duration on a biological cell. Generating an electric field inside a microchannel of a microfluidic device has many advantages, including the efficient utilization of energy and low-current requirement. An ideal microchannel model was compared with a practical microchannel model using a finite element analysis tool that suggests that the overestimation error can be over 10%, from 2.5 mm or smaller, in the length of a microchannel. Two analytical forms are proposed to reduce this overestimation error. Experimental results showed that the high electric field is confined only inside the microchannel that is in agreement with the simulation results. Single cell electrical lysis was conducted with a fabricated microfluidic device. An average of 800 V for seven seconds across an 8 mm-long microchannel with the dimension of 100 μm × 20 μm was required for lysis, with electric fields exceeding 100 kV/m and consuming 300 mW. Full article
(This article belongs to the Special Issue Micro/Nanofluidic Devices for Single Cell Analysis)
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<p>Finite element method (FEM) simulations (<b>a</b>) without and (<b>b</b>) with microchannel structures (microchannels of 100 μm-wide and 20 μm-deep) that depict high electric field distributions inside the microchannel structure, in the latter case away from the electrodes inside the reservoirs with normalized excitation (1 V). A 3D view of a reservoir is shown in the inset. Electric field distributions and electric potentials with the microchannel structure are plotted for five different electrode locations (1 to 5) inside the reservoirs. Note: Electric field distributions inside the fluidic subdomain are only shown in (<b>b</b>).</p> Full article ">Figure 2
<p>(<b>a</b>) A schematic diagram of the experimental setup of the microfluidic device; (<b>b</b>) a photograph of the experimental setup showing the Pexiglass platform, microfluidic device (MFD), spirit level meter and the electrical connections of the platinum (Pt) electrodes inside the access holes.</p> Full article ">Figure 3
<p>Sample cells from a fingerprint observed under (<b>a</b>) 10X and (<b>b</b>) 40X lens with an optical microscope in phase-contrast mode; (<b>c</b>) stained cell-sample with haematoxylin dye clearly showing the cellular structures.</p> Full article ">Figure 4
<p>Cell debris, labeled with Alexa Flour 488 V florescence dye, collected from a fingerprint sample, is positioned inside a microchannel and is observed under a fluorescence microscope. (<b>a</b>) Image of the cell with optical microscope with phase-contrast mode; (<b>b</b>) image of the cell with 488 nm laser in a fluorescence microscope.</p> Full article ">Figure 5
<p>SEM photographs of (<b>a</b>) a microchannel and (<b>b</b>) an exposed trench (top glass slide removed) detailing the surface topography and roughness of the chemically etched microchannels.</p> Full article ">Figure 6
<p>Temporal sequence of images of electrical lysis of a single sample cell under a high electric field inside a microchannel captured using an optical microscope. Here, (<b>a</b>) is a sample cell inside the microchannel, (<b>b</b>) is a cell inside the reservoir, (<b>c</b>) is the boundary of the reservoir on the top glass slide, (<b>d</b>) is the edge of the microchannel and (<b>e</b>) is the boundary of the etching on the bottom glass slide. Eight-hundred volts are applied to the microchannel of 9 mm length. The cell is observed to disappear between 6 and 6.5 s.</p> Full article ">Figure 7
<p>An optical microscope image of a microchannel showing damage of the microchannel surface from electric arcs generated with an applied voltage of 1800 V (electric field over 225 kV/m).</p> Full article ">
1176 KiB  
Article
Fabrication of Nanopillar Micropatterns by Hybrid Mask Lithography for Surface-Directed Liquid Flow
by Shinya Sakuma, Masakuni Sugita and Fumihito Arai
Micromachines 2013, 4(2), 232-242; https://doi.org/10.3390/mi4020232 - 5 Jun 2013
Cited by 6 | Viewed by 7526
Abstract
This paper presents a novel method for fabricating nanopillar micropatterns for surface-directed liquid flows. It employs hybrid mask lithography, which uses a mask consisting of a combination of a photoresist and nanoparticles in the photolithography process. The nanopillar density is controlled by varying [...] Read more.
This paper presents a novel method for fabricating nanopillar micropatterns for surface-directed liquid flows. It employs hybrid mask lithography, which uses a mask consisting of a combination of a photoresist and nanoparticles in the photolithography process. The nanopillar density is controlled by varying the weight ratio of nanoparticles in the composite mask. Hybrid mask lithography was used to fabricate a surface-directed liquid flow. The effect of the surface-directed liquid flow, which was formed by the air-liquid interface due to nanopillar micropatterns, was evaluated, and the results show that the oscillation of microparticles, when the micro-tool was actuated, was dramatically reduced by using a surface-directed liquid flow. Moreover, the target particle was manipulated individually without non-oscillating ambient particles. Full article
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<p>Surface-directed liquid flow for on-chip cell manipulation: (<b>a</b>) conventional microchannel and (<b>b</b>) surface-directed liquid flow.</p> Full article ">Figure 2
<p>Concept and demonstration of hybrid mask lithography: (<b>a</b>) spin coating of composite; (<b>b</b>) patterning of composite; (<b>c</b>) deep reactive ion etching (DRIE); and (<b>d</b>) removal of composite.</p> Full article ">Figure 3
<p>SEM images of fabricated structure by hybrid mask lithography: (<b>a</b>) perspective view; and (<b>b</b>) cross-sectional image of fabricated nanopillar micropattern.</p> Full article ">Figure 4
<p>SEM images of the top of the nanopillar and measured density of the nanopillar as a function of the weight ratio of the nanoparticle. (<b>a</b>) 0.10%; (<b>b</b>) 0.20 %; (<b>c</b>) 0.40%; (<b>d</b>) measured density of the nanopillar of the fabricated chip; and (<b>e</b>) measured diameter of the nanopillar of the fabricated chip.</p> Full article ">Figure 5
<p>Evaluation of the contact angle: (<b>a</b>) analytical model of contact angle and (<b>b</b>) measured contact angle of water droplet as a function of the density of the nanopillars and the photographs of the droplet of the typical results.</p> Full article ">Figure 6
<p>Fabrication of surface-directed liquid flow. (<b>a</b>) Patterning of OFPR as the sacrifice layer, (<b>b</b>) deposition of fluorocarbon, (<b>c</b>) removal of OFPR and (<b>d</b>) packaging and introduction of water.</p> Full article ">Figure 7
<p>Demonstration of surface-directed liquid flow. (<b>a</b>) Introduction of water, (<b>b</b>) forming of air-liquid interface and (<b>c</b>) transportation of microparticles.</p> Full article ">Figure 8
<p>Photographs of insertion of a probe tip of magnetically driven micro-tools (MMTs) into (<b>a</b>) the previous microchannel and (<b>b</b>) surface-directed liquid flow.</p> Full article ">Figure 9
<p>Measured oscillation velocity of the microparticle. (<b>a</b>) Previous microchannel and (<b>b</b>) surface-directed liquid flow.</p> Full article ">
2296 KiB  
Review
Automated Ultrafiltration Device for Environmental Nanoparticle Research and Implications: A Review
by Tsung M. Tsao, Ya N. Wang, Yue M. Chen, Yu M. Chou and Ming K. Wang
Micromachines 2013, 4(2), 215-231; https://doi.org/10.3390/mi4020215 - 3 Jun 2013
Cited by 2 | Viewed by 7201
Abstract
Nanoparticle research and development have brought significant breakthroughs in many areas of basic and applied sciences. However, efficiently collecting nanoparticles in large quantities in pure and natural systems is a major challenge in nanoscience. This review article has focused on experimental investigation and [...] Read more.
Nanoparticle research and development have brought significant breakthroughs in many areas of basic and applied sciences. However, efficiently collecting nanoparticles in large quantities in pure and natural systems is a major challenge in nanoscience. This review article has focused on experimental investigation and implications of nanoparticles in soil, clay, geological and environmental sciences. An automated ultrafiltration device (AUD) apparatus was used to demonstrate efficient collection and separation of nanoparticles in highly weathering red soils, black soils, and gouge of earthquake fault, as well as zeolite. The kaolinite, illite, goethite, and hematite were identified in highly weathering red soils. Transmission electron microscopic (TEM) images showed the presence of hematite nanoparticles on the surface coating of kaolinite nanoparticles and aggregated hematite nanoparticles overlapping the edge of a kaolinite flake in a size range from 4 to 7 nm. The maximum crystal violet (CV) and methylene blue (MB) adsorption amount of smectite nanoparticles (<100 nm) separated by black soils were about two to three times higher than those of bulk sample (<2000 nm). The smectite nanoparticles adsorb both CV and MB dyes efficiently and could be employed as a low-cost alternative to remove cationic dyes in wastewater treatment. Quartz grain of <50 nm was found in the gouge of fault by X-ray diffraction (XRD) analysis and TEM observation. Separated quartz could be used as the index mineral associated with earthquake fracture and the finest grain size was around 25 nm. Comparing the various particle-size fractions of zeolite showed significant differences in surface area, Si to Al molar ratio, morphology, crystallinity, framework structure, and surface atomic structure of nanoparticles from those of the bulk sample prior to particle-size fractionations. The AUD apparatus has the characteristics of automation, easy operation, and high efficiency in the separation of nanoparticles and would, thus, facilitate future nanoparticle research and developments in basic and applied sciences. Full article
(This article belongs to the Special Issue Micromachined Tools for Nanoscale Science and Technology)
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<p>Photograph showing the second-generation automated ultrafiltration device (AUD) apparatus for separation of nanoparticles. The sampling suspensions were gathered in a bottle of 10 L (<a href="#micromachines-04-00215-f001" class="html-fig">Figure 1</a>a). One large Teflon container (diameter 12 cm, length 9 cm, volume 1018 mL) was set up in central part of the third plate (<a href="#micromachines-04-00215-f001" class="html-fig">Figure 1</a>b). The power system (<a href="#micromachines-04-00215-f001" class="html-fig">Figure 1</a>c) included a cylinder, flow and pressure valves, hydraulic valves, oil tank (volume 5 L), pump (output flow 1.5 cc rev<sup>−</sup><sup>1</sup>), and motor (output power 1/2 HP, 4 poles, 1720 rpm). The functions of button switches were: stop (<a href="#micromachines-04-00215-f001" class="html-fig">Figure 1</a>d), power (<a href="#micromachines-04-00215-f001" class="html-fig">Figure 1</a>e), human machine interface (<a href="#micromachines-04-00215-f001" class="html-fig">Figure 1</a>f), and collecting bottle (<a href="#micromachines-04-00215-f001" class="html-fig">Figure 1</a>g). The human machine interface included control functions of manual or automatic operation, counter, working timer, and stopping timer. In <a href="#micromachines-04-00215-f001" class="html-fig">Figure 1</a>h, stirring filtration device (diameter 5 cm, length 12 cm, volume 236 mL) included two filter holder in lift and right sides, stirring fan rod within device, and motor (output power 6 W, 175 rpm). Filtrates were gathering in collecting bottle (2000 mL × 2) (<a href="#micromachines-04-00215-f001" class="html-fig">Figure 1</a>g). The teflon container, in which suspensions from the suspension bottlewere installed, had one male luer installed under the barrel bottom to connect the stirring filtration device in order to allow the suspensions to flow to the membrane filters in its left and light sides, where the nanoparticles were collected into a collecting bottle.</p> Full article ">Figure 2
<p>Schematic diagram of the second-generation AUD apparatus to show a flowing suspension of particles in the system.</p> Full article ">Figure 3
<p>X-ray diffractograms of the (<b>a</b>) 1–25, (<b>b</b>) 25–100, (<b>c</b>) 100–450, (<b>d</b>) 450–2000 nm size fractions, and (<b>e</b>) bulk sample (&lt;2000 nm) prior to particle-size fractionation. With decrease in particle size, nanoparticles of 25–100 and 1–25 nm are XRD noncrystalline, indicating its structural transformation from well crystalline to short-range-ordered (SRO) particles [<a href="#B12-micromachines-04-00215" class="html-bibr">12</a>].</p> Full article ">Figure 4
<p>TEM images of the (<b>a</b>) kaolinite nanoparticles aggregated hematite nanoparticles overlapping the edge of a kaolinite flake and (<b>b</b>) illite nanoparticles with aggregated hematite nanoparticles. I: illite; K: kaolinite; G: goethite; H: hematite [<a href="#B50-micromachines-04-00215" class="html-bibr">50</a>].</p> Full article ">Figure 5
<p>Photograph showing the (<b>a</b>) bulk sample (&lt;2000 nm) prior to particle-size fractionations, (<b>b</b>) smectite nanoparticles with 1–100 nm size fraction.</p> Full article ">
1234 KiB  
Article
Photomasks Fabrication Based on Optical Reduction for Microfluidic Applications
by Emanuele Orabona, Alessandro Caliò, Ivo Rendina, Luca De Stefano and Mario Medugno
Micromachines 2013, 4(2), 206-214; https://doi.org/10.3390/mi4020206 - 28 May 2013
Cited by 6 | Viewed by 8494
Abstract
A procedure for fabrication of photomasks on photographic films with minimum feature achievable of about 20 μm, which are particularly suitable for the fast prototyping of microfluidic devices, has been improved. We used a commercial photographic enlarger in reverse mode obtaining 10:1 reduction [...] Read more.
A procedure for fabrication of photomasks on photographic films with minimum feature achievable of about 20 μm, which are particularly suitable for the fast prototyping of microfluidic devices, has been improved. We used a commercial photographic enlarger in reverse mode obtaining 10:1 reduction factor with error less than 1%. Masks have been characterized by optical transmission measurement and contact profilometry: the exposed region completely absorbs light in the wavelength region explored, while the non-exposed region is transparent from 350 nm on; the average film thickness is of 410 nm and its roughness is about 120 nm. A PDMS microfluidic device has been realized and tested in order to prove the effectiveness of designed photomasks used with the common UV light box. Full article
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Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>(<b>a</b>) Computer aided designed (CAD) design of mask patterns; (<b>b</b>) Scaled print (typically 10:1) of the mask patterns on a paper sheet; (<b>c</b>) Mask patterns optical reduction and transfer from paper to film by reversal use of an enlarger; (<b>d</b>) The film photomask after the development process.</p> Full article ">Figure 2
<p>(<b>a</b>) Test pattern used for optimize the reduction parameter. It contains lines and dots in black and white with dimensions from 10 µm to 100 µm. (<b>b</b>) Photo of the impressed photographic film. (<b>c</b>) Optical image of test pattern lines.</p> Full article ">Figure 3
<p>Transmittance of photomask in the transparent and dark regions.</p> Full article ">Figure 4
<p>(<b>a</b>) Optical photograph and (<b>b</b>) thickness profiles measured by the profilometer of the transition from dark exposed region to transparent unexposed region on the photographic film.</p> Full article ">Figure 5
<p>SU-8 Y-shape channel impressed with the same mask using (<b>a</b>) the mask aligner and (<b>b</b>) the UV Box (SU-8, thickness: 10µm).</p> Full article ">Figure 6
<p>Microscope images of microchannel cross sections with three different widths, (<b>a</b>) 107 µm; (<b>b</b>) 35 µm; (<b>c</b>) 19 µm, realized in SU-8 on a silicon wafer (white zone).</p> Full article ">Figure 7
<p>Optical image of laminar flow in a y-shaped microchannel.</p> Full article ">
1636 KiB  
Article
Active and Precise Control of Microdroplet Division Using Horizontal Pneumatic Valves in Bifurcating Microchannel
by Dong Hyun Yoon, Junichi Ito, Tetsushi Sekiguchi and Shuichi Shoji
Micromachines 2013, 4(2), 197-205; https://doi.org/10.3390/mi4020197 - 7 May 2013
Cited by 21 | Viewed by 8479
Abstract
This paper presents a microfluidic system for the active and precise control of microdroplet division in a micro device. Using two horizontal pneumatic valves formed at downstream of bifurcating microchannel, flow resistances of downstream channels were variably controlled. With the resistance control, volumetric [...] Read more.
This paper presents a microfluidic system for the active and precise control of microdroplet division in a micro device. Using two horizontal pneumatic valves formed at downstream of bifurcating microchannel, flow resistances of downstream channels were variably controlled. With the resistance control, volumetric ratio of downstream flows was changed and water-in-oil microdroplets were divided into two daughter droplets of different volume corresponding to the ratio. The microfluidic channels and pneumatic valves were fabricated by single-step soft lithography process of PDMS (polydimethylsiloxane) using SU-8 mold. A wide range control of the daughter droplets’ volume ratio was achieved by the simple channel structure. Volumetric ratio between large and small daughter droplets are ranged from 1 to 70, and the smallest droplet volume of 14 pL was obtained. The proposed microfluidic device is applicable for precise and high throughput droplet based digital synthesis. Full article
(This article belongs to the Special Issue Selected Papers from the 1st International Conference on Microfluidic Handling Systems)
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<p>Controllable microdroplet division in bifurcating microchannel using a change in flow resistance of downstream.</p> Full article ">Figure 2
<p>Schematic view of a total device and division part for droplet division utilizing horizontal pneumatic valves.</p> Full article ">Figure 3
<p>Total design of the droplet division device and detailed sizes of each part.</p> Full article ">Figure 4
<p>(<b>a</b>) Fabrication process of the droplet division device. (<b>b</b>) SEM images of the SU-8 mold of each part.</p> Full article ">Figure 5
<p>Visualization of droplet division with operation of pneumatic valves (Q<sub>water</sub> = Q<sub>oil</sub> = 2 μL/min).</p> Full article ">Figure 6
<p>Ratios of divided droplet volume with applied pressure to lower valve.</p> Full article ">Figure 7
<p>(<b>a</b>) Size change of division part for an effective use of the valve deformation. (<b>b</b>) Division results of large volume ratio with applied high pressure and cross section views.</p> Full article ">Figure 8
<p>A change in original microdroplets’ volume in upstream due to valve deformation with applied pressure to each valve.</p> Full article ">
11999 KiB  
Article
Review on Electrodynamic Energy Harvesters—A Classification Approach
by Clemens Cepnik, Roland Lausecker and Ulrike Wallrabe
Micromachines 2013, 4(2), 168-196; https://doi.org/10.3390/mi4020168 - 29 Apr 2013
Cited by 81 | Viewed by 10716
Abstract
Beginning with a short historical sketch, electrodynamic energy harvesters with focus on vibration generators and volumes below 1dm3 are reviewed. The current challenges to generate up to several milliwatts of power from practically relevant flows and vibrations are addressed, and the variety of [...] Read more.
Beginning with a short historical sketch, electrodynamic energy harvesters with focus on vibration generators and volumes below 1dm3 are reviewed. The current challenges to generate up to several milliwatts of power from practically relevant flows and vibrations are addressed, and the variety of available solutions is sketched. Sixty-seven different harvester concepts from more than 130 publications are classified with respect to excitation, additional boundary conditions, design and fabrication. A chronological list of the harvester concepts with corresponding references provides an impression about the developments. Besides resonant harvester concepts, the review includes broadband approaches and mechanisms to harvest from flow. Finally, a short overview of harvesters in applications and first market ready concepts is given. Full article
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<p>Electrodynamic harvester prototypes (1)–(6) reprinted from [<a href="#B26-micromachines-04-00168" class="html-bibr">26</a>,<a href="#B27-micromachines-04-00168" class="html-bibr">27</a>,<a href="#B28-micromachines-04-00168" class="html-bibr">28</a>,<a href="#B29-micromachines-04-00168" class="html-bibr">29</a>,<a href="#B30-micromachines-04-00168" class="html-bibr">30</a>,<a href="#B31-micromachines-04-00168" class="html-bibr">31</a>].</p> Full article ">Figure 2
<p>Electrodynamic harvester prototypes (7)–(11) reprinted from [<a href="#B37-micromachines-04-00168" class="html-bibr">37</a>,<a href="#B38-micromachines-04-00168" class="html-bibr">38</a>,<a href="#B39-micromachines-04-00168" class="html-bibr">39</a>,<a href="#B40-micromachines-04-00168" class="html-bibr">40</a>,<a href="#B41-micromachines-04-00168" class="html-bibr">41</a>].</p> Full article ">Figure 3
<p>Electrodynamic harvester prototypes (12)–(17) reprinted from [<a href="#B45-micromachines-04-00168" class="html-bibr">45</a>,<a href="#B46-micromachines-04-00168" class="html-bibr">46</a>,<a href="#B47-micromachines-04-00168" class="html-bibr">47</a>,<a href="#B48-micromachines-04-00168" class="html-bibr">48</a>,<a href="#B49-micromachines-04-00168" class="html-bibr">49</a>].</p> Full article ">Figure 4
<p>Electrodynamic harvester prototypes (18)–(23) reprinted from [<a href="#B50-micromachines-04-00168" class="html-bibr">50</a>,<a href="#B51-micromachines-04-00168" class="html-bibr">51</a>,<a href="#B52-micromachines-04-00168" class="html-bibr">52</a>,<a href="#B53-micromachines-04-00168" class="html-bibr">53</a>,<a href="#B54-micromachines-04-00168" class="html-bibr">54</a>,<a href="#B55-micromachines-04-00168" class="html-bibr">55</a>].</p> Full article ">Figure 5
<p>Electrodynamic harvester prototypes (24)–(27) reprinted from [<a href="#B57-micromachines-04-00168" class="html-bibr">57</a>,<a href="#B58-micromachines-04-00168" class="html-bibr">58</a>,<a href="#B59-micromachines-04-00168" class="html-bibr">59</a>,<a href="#B60-micromachines-04-00168" class="html-bibr">60</a>].</p> Full article ">Figure 6
<p>Electrodynamic harvester prototypes (28)–(30) according to [<a href="#B88-micromachines-04-00168" class="html-bibr">88</a>,<a href="#B89-micromachines-04-00168" class="html-bibr">89</a>,<a href="#B90-micromachines-04-00168" class="html-bibr">90</a>]-</p> Full article ">
714 KiB  
Article
Fabrication of a Polymer High-Aspect-Ratio Pillar Array Using UV Imprinting
by Hidetoshi Shinohara, Hiroshi Goto, Takashi Kasahara and Jun Mizuno
Micromachines 2013, 4(2), 157-167; https://doi.org/10.3390/mi4020157 - 17 Apr 2013
Cited by 8 | Viewed by 9832
Abstract
This paper presents UV imprinting methods for fabricating a high-aspect-ratio pillar array. A polydimethylsiloxane (PDMS) mold was selected as the UV imprinting mold. The pillar pattern was formed on a 50 × 50 mm2 area on a polyethylene terephthalate (PET) film without [...] Read more.
This paper presents UV imprinting methods for fabricating a high-aspect-ratio pillar array. A polydimethylsiloxane (PDMS) mold was selected as the UV imprinting mold. The pillar pattern was formed on a 50 × 50 mm2 area on a polyethylene terephthalate (PET) film without remarkable deformation. The aspect ratios of the pillar and space were about four and ten, respectively. The mold was placed into contact with a UV-curable resin under a reduced pressure, and the resin was cured by UV light irradiation after exposure to atmospheric pressure. The PDMS mold showed good mold releasability and high flexibility. By moderately pressing the mold before UV-curing, the thickness of the residual layer of the imprinted resin was reduced and the pattern was precisely imprinted. Both batch pressing and roll pressing are available. Full article
(This article belongs to the Special Issue Micromachined Tools for Nanoscale Science and Technology)
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Figure 1
<p>Design of sample having high-aspect-ratio pillar array.</p> Full article ">Figure 2
<p>Outline of fabrication process: (<b>a</b>) silicon master fabrication by deep-reactive ion etching (DRIE); (<b>b</b>) polydimethylsiloxane (PDMS) mold fabrication by casting; (<b>c</b>) sample fabrication by UV imprinting.</p> Full article ">Figure 3
<p>UV imprinting process: (<b>a</b>) placing PDMS mold and UV-curable resin-coated polyethylene terephthalate (PET) in a vacuum chamber; (<b>b</b>) moving mold and resin into contact under reduced pressure; (<b>c</b>) pressing by rotating roll; (<b>d</b>) UV irradiation; (<b>e</b>) peeling off mold along roll; (<b>f</b>) pressing mold and resin under reduced pressure; (<b>g</b>) UV irradiation and pressing. The roll press method includes (<b>a</b>), (<b>b</b>), (<b>c</b>), (<b>d</b>) and (<b>e</b>), and the batch press method includes (<b>a</b>), (<b>f</b>), (<b>g</b>) and (<b>e</b>).</p> Full article ">Figure 4
<p>(<b>a</b>) Five measurement points for the silicon master and imprinted sample; (<b>b</b>) two base points for measuring pillar height; (<b>c</b>) definition of location from edge of pattern area (<span class="html-italic">x</span>) on the imprinted sample.</p> Full article ">Figure 5
<p>(<b>a</b>) Photograph and (<b>b</b>) Bird’s-eye SIM image of the UV-imprinted sample.</p> Full article ">Figure 6
<p>Bird’s-eye SIM images of the sample molded without evacuation.</p> Full article ">Figure 7
<p>Photomicrograph of the sample imprinted at <span class="html-italic">F</span><sub>1</sub> = <span class="html-italic">F</span><sub>2</sub> = 0.50 kN.</p> Full article ">Figure 8
<p>Cross-sectional SIM images of samples: (<b>a</b>) without pressing (with mold and resin simply in contact); with batch pressing at (<b>b</b>) <span class="html-italic">F</span><sub>1</sub> = 0.01 kN and (<b>c</b>) <span class="html-italic">F</span><sub>1</sub> = 0.45 kN; and (<b>d</b>) with roll pressing.</p> Full article ">Figure 9
<p>(<b>a</b>) Definitions of two types of residual layer thicknesses (RLTs) and (<b>b</b>) RLTs within the roll-pressed sample.</p> Full article ">
1395 KiB  
Article
Freeform Fabrication of Magnetophotonic Crystals with Diamond Lattices of Oxide and Metallic Glasses for Terahertz Wave Control by Micro Patterning Stereolithography and Low Temperature Sintering
by Soshu Kirihara and Maasa Nakano
Micromachines 2013, 4(2), 149-156; https://doi.org/10.3390/mi4020149 - 2 Apr 2013
Cited by 4 | Viewed by 6764
Abstract
Micrometer order magnetophotonic crystals with periodic arranged metallic glass and oxide glass composite materials were fabricated by stereolithographic method to reflect electromagnetic waves in terahertz frequency ranges through Bragg diffraction. In the fabrication process, the photo sensitive acrylic resin paste mixed with micrometer [...] Read more.
Micrometer order magnetophotonic crystals with periodic arranged metallic glass and oxide glass composite materials were fabricated by stereolithographic method to reflect electromagnetic waves in terahertz frequency ranges through Bragg diffraction. In the fabrication process, the photo sensitive acrylic resin paste mixed with micrometer sized metallic glass of Fe72B14.4Si9.6Nb4 and oxide glass of B2O3·Bi2O3 particles was spread on a metal substrate, and cross sectional images of ultra violet ray were exposed. Through the layer by layer stacking, micro lattice structures with a diamond type periodic arrangement were successfully formed. The composite structures could be obtained through the dewaxing and sintering process with the lower temperature under the transition point of metallic glass. Transmission spectra of the terahertz waves through the magnetophotonic crystals were measured by using a terahertz time domain spectroscopy. Full article
(This article belongs to the Special Issue Glass Micromachining and Applications of Glass)
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Figure 1
<p>A schematic illustrated a magnetophotonic crystal sensor device (<b>a</b>) and transmission spectra of terahertz waves including various water solvents without (<b>b</b>) or with (<b>c</b>) absorption properties.</p> Full article ">Figure 2
<p>Schematic illustrations of a stereolithographic method. A three dimensional model was sliced into two dimensional cross sections by computer graphic technique (<b>a</b>). A micrometer order component could be created successfully through layer by layer smoothly slurry spreading and finely pattern exposing (<b>b</b>).</p> Full article ">Figure 3
<p>A graphic model of test specimen to optimize the stereolithographic process parameters (<b>a</b>). Layer thicknesses of photo polymerization depths (<b>b</b>) and size tolerances of exposure right scattering (<b>c</b>) were measured.</p> Full article ">Figure 4
<p>An acryl diamond lattice with metallic glass (Fe<sub>72</sub>B<sub>14.4</sub>Si<sub>9.6</sub>Nb<sub>4</sub>) and oxide glass (B<sub>2</sub>O<sub>3</sub>·Bi<sub>2</sub>O<sub>3</sub>) particles dispersion fabricated by the stereolithography (<b>a</b>) and a magnetophotonic crystal after dewaxing and sintering (<b>b</b>).</p> Full article ">Figure 5
<p>A microstructure of the oxide glass lattice with the metallic glass particles dispersion observed by a scanning electron microscopy.</p> Full article ">Figure 6
<p>A X-ray diffraction patterns of the metallic glass particles before and after the dewaxing and sintering heat treatments under the transition temperature from the amorphous structure for the crystal phase.</p> Full article ">Figure 7
<p>An electromagnetic band gap formation in a transmission spectrum of the terahertz wave through the magnetophotonic crystal with the diamond lattice structure. The black and gray lines show the measured and calculated results, respectively.</p> Full article ">Figure 8
<p>The magnetophotonic crystal with a structural defect in the periodic lattice of the diamond structure. The round hole was opened as the defect cavity for the perpendicularly direction toward the crystal face.</p> Full article ">Figure 9
<p>Localized modes formation in the electromagnetic band gap. The terahertz waves with the selected wavelengths can resonate with the defect cavity and transmit the crystal. The black and gray lines show the measured and calculated results, respectively.</p> Full article ">
1223 KiB  
Article
Pushing the Limits of Electrical Detection of Ultralow Flows in Nanofluidic Channels
by Klaus Mathwig and Serge G. Lemay
Micromachines 2013, 4(2), 138-148; https://doi.org/10.3390/mi4020138 - 2 Apr 2013
Cited by 21 | Viewed by 14560
Abstract
This paper presents improvements in flow detection by electrical cross-correlation spectroscopy. This new technique detects molecular number fluctuations of electrochemically active analyte molecules as they are transported by liquid flow through a nanochannel. The fluctuations are used as a marker of liquid flow [...] Read more.
This paper presents improvements in flow detection by electrical cross-correlation spectroscopy. This new technique detects molecular number fluctuations of electrochemically active analyte molecules as they are transported by liquid flow through a nanochannel. The fluctuations are used as a marker of liquid flow as their time of flight in between two consecutive transducers is determined, thereby allowing for the measurement of liquid flow rates in the picoliter-per-minute regime. Here we show an enhanced record-low sensitivity below 1 pL/min by capitalizing on improved electrical instrumentation, an optimized sensor geometry and a smaller channel cross section. We further discuss the impact of sensor geometry on the cross-correlation functions. Full article
(This article belongs to the Special Issue Selected Papers from the 1st International Conference on Microfluidic Handling Systems)
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Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>Schematic of the experimental setup. Fluctuations in the number density of electroactive molecules are used as tracers of liquid flow as solution is transported through a nanochannel. The fluctuations are detected electrically by redox cycling and their time of flight between the detectors—or, equivalently, the flow velocity—is then determined by cross correlation analysis of current-time traces (curves in the insets are a schematic illustration).</p> Full article ">Figure 2
<p>(<b>a</b>) Schematic cross section of the device along the longitudinal (top) and lateral axis (bottom). (<b>b</b>) Top view micrograph of a 202 μm long nanofluidic device bonded to a polydimethylsiloxane (PDMS) microchannel layer (only two out of four microchannels running in parallel to the device are shown). (<b>c</b>) Micrograph of the overall chip structure. (<b>d</b>) Photography of a chip bonded to PDMS connected to tubing; electrical contact pads are visible on the right.</p> Full article ">Figure 3
<p>(<b>a</b>) Cross-correlation functions for different syringe pump flow rates determined from current-time traces recorded at both 100 μm long top electrodes of a 202 μm long nanofluidic device. (<b>b</b>) Analytically derived cross-correlation functions for different molecular drift velocities <span class="html-italic">v</span> for the same device geometry and an effective diffusion coefficient of <span class="html-italic">D</span> = 3.4 × 10<sup>−10</sup> m<sup>2</sup>/s.</p> Full article ">Figure 4
<p>Nanofluidic flow rates as a function of syringe flow. The adjusted experimental data points are corrected for the shift of the peak times as well as for dynamic adsorption. The dashed line’s slope corresponds to the ratio of the micro- and nanochannels’ resistances of 1/400,000.</p> Full article ">Figure 5
<p>(<b>a</b>) Analytically determined deviation of the cross-correlation function’s peak time <span class="html-fig-inline" id="micromachines-04-00138-i012"> <img alt="Micromachines 04 00138 i012" src="/micromachines/micromachines-04-00138/article_deploy/html/images/micromachines-04-00138-i012.png"/></span> from the time of flight as a function of flow velocity. The blue curve is corrected for an effectively slower diffusion of the molecules due to dynamic adsorption. Experimental flow rates range from 15 μm/s to 50 μm/s. (<b>b</b>) Cross-correlation functions for a constant time of flight of 4 s but with different molecular velocities <span class="html-italic">v</span> (and corresponding different electrode lengths <span class="html-italic">L</span> or flight paths, respectively).</p> Full article ">Figure 6
<p>Analytical cross-correlations function as a function of electrode length <span class="html-italic">L</span> for symmetric transducers for a constant velocity <span class="html-italic">v</span> = 100 μm/s, <span class="html-italic">D</span> = 5 × 10<sup>−10</sup> m<sup>2</sup>/s and no gap in between the consecutive sensors. The cross-correlation peaks are more pronounced with increasing <span class="html-italic">L</span> and shift to longer <span class="html-fig-inline" id="micromachines-04-00138-i012"> <img alt="Micromachines 04 00138 i012" src="/micromachines/micromachines-04-00138/article_deploy/html/images/micromachines-04-00138-i012.png"/></span>.</p> Full article ">Figure 7
<p>Analytical correlation functions for a varying separation distance <span class="html-italic">L</span><sub>2</sub> - <span class="html-italic">L</span><sub>1</sub> in between consecutive electrodes for <span class="html-italic">v</span> = 100 μm/s, <span class="html-italic">D</span> = 5 × 10<sup>−10</sup> m<sup>2</sup>/s, <span class="html-fig-inline" id="micromachines-04-00138-i033"> <img alt="Micromachines 04 00138 i033" src="/micromachines/micromachines-04-00138/article_deploy/html/images/micromachines-04-00138-i033.png"/></span> 100 μm. Green curve: Autocorrelation, which corresponds to <span class="html-italic">L</span><sub>2</sub> = 0; blue curves: intermediate auto-cross-correlation for a gap length <span class="html-italic">L</span><sub>2</sub> - <span class="html-italic">L</span><sub>1</sub> = −75 μm, −50 μm, −25 μm; red, orange, purple curves: cross-correlation with <span class="html-italic">L</span><sub>2</sub> - <span class="html-italic">L</span><sub>1</sub> = 0 μm…1000 μm.</p> Full article ">
2331 KiB  
Article
Photomechanical Bending of Azobenzene-Based Photochromic Molecular Fibers
by Hideyuki Nakano, Ryoji Ichikawa and Riku Matsui
Micromachines 2013, 4(2), 128-137; https://doi.org/10.3390/mi4020128 - 27 Mar 2013
Cited by 17 | Viewed by 7402
Abstract
Microfibers composed of azobenzene-based photochromic amorphous molecular materials, namely low molecular-mass photochromic materials with a glass-forming property, could be fabricated. These fibers were found to exhibit mechanical bending motion upon irradiation with a laser beam. In addition, the bending direction could be controlled [...] Read more.
Microfibers composed of azobenzene-based photochromic amorphous molecular materials, namely low molecular-mass photochromic materials with a glass-forming property, could be fabricated. These fibers were found to exhibit mechanical bending motion upon irradiation with a laser beam. In addition, the bending direction could be controlled by altering the polarization direction of the irradiated light without changing the position of the light source or the wavelength of the light. In-situ fluorescence observation of mass transport induced at the surface of the fiber doped with CdSe quantum dots suggested that the bending motions were related with the photoinduced mass transport taking place near the irradiated surface of the fiber. Full article
(This article belongs to the Special Issue Glass Micromachining and Applications of Glass)
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Graphical abstract

Graphical abstract
Full article ">Figure 1
<p>Chemical structures of the materials used in the present study. (<b>a</b>) BFlAB; (<b>b</b>) BMAB; (<b>c</b>) DBAB; (<b>d</b>) NO<sub>2</sub>-BFlAB.</p> Full article ">Figure 2
<p>Schematic experimental set-up for photoirradiation of the molecular fibers.</p> Full article ">Figure 3
<p>Photomechanical bending motions of DBAB and NO<sub>2</sub>-BFlAB molecular fibers upon irradiation with (<b>a</b>) H-polarized laser beam (<b>b</b>) V-polarized one. Interval of grid lines: 1 mm.</p> Full article ">Figure 4
<p>(<b>a</b>) Photographs of fluorescence patterns of quantum dots (QDs)-doped BFlAB fiber upon angled irradiation using H-polarized laser beam. Scale bar: 10 µm. (<b>b</b>,<b>c</b>) Schematic illustration for plausible mechanism of the bending motion in the positive direction upon H-polarized laser beam. See text.</p> Full article ">Figure 5
<p>(<b>a</b>) Photographs of fluorescence patterns of QDs-doped BFlAB fiber upon irradiation using V-polarized laser beam viewed from the back of the irradiated surface. Scale bar: 10 µm. (<b>b</b>,<b>c</b>) Schematic illustration for plausible mechanism of the bending motion in the negative direction upon V-polarized laser beam. See text.</p> Full article ">
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