Micromachines

3461 KiB

Open AccessFeature PaperArticle

Flexible Holographic Fabrication of 3D Photonic Crystal Templates with Polarization Control through a 3D Printed Reflective Optical Element

by David Lowell, David George, Jeffrey Lutkenhaus, Chris Tian, Murthada Adewole, Usha Philipose, Hualiang Zhang and Yuankun Lin

Micromachines 2016, 7(7), 128; https://doi.org/10.3390/mi7070128 - 21 Jul 2016

Cited by 12 | Viewed by 7376

Abstract

In this paper, we have systematically studied the holographic fabrication of three-dimensional (3D) structures using a single 3D printed reflective optical element (ROE), taking advantage of the ease of design and 3D printing of the ROE. The reflective surface was setup at non-Brewster [...] Read more.

In this paper, we have systematically studied the holographic fabrication of three-dimensional (3D) structures using a single 3D printed reflective optical element (ROE), taking advantage of the ease of design and 3D printing of the ROE. The reflective surface was setup at non-Brewster angles to reflect both s- and p-polarized beams for the interference. The wide selection of reflective surface materials and interference angles allow control of the ratio of s- and p-polarizations, and intensity ratio of side-beam to central beam for interference lithography. Photonic bandgap simulations have also indicated that both s and p-polarized waves are sometimes needed in the reflected side beams for maximum photonic bandgap size and certain filling fractions of dielectric inside the photonic crystals. The flexibility of single ROE and single exposure based holographic fabrication of 3D structures was demonstrated with reflective surfaces of ROEs at non-Brewster angles, highlighting the capability of the ROE technique of producing umbrella configurations of side beams with arbitrary angles and polarizations and paving the way for the rapid throughput of various photonic crystal templates. Full article

(This article belongs to the Special Issue Laser Micromachining and Microfabrication)

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(a) Model of the lab-designed ROE in the 4 + 1 configuration, designed using CAD software. The reflective surfaces are mounted on the support structures to reflect a single circularly polarized laser beam; (b) schematic of wave vector configuration for four side beams and one central beam in the 4 + 1 configuration; (c) schematic of an aperture for beam selection; (d) photonic band structure for one of holographic photonic crystals; and (e) plot of maximum bandgap size and filling fraction of dielectric that produces maximum bandgap for the PhCs that can be fabricated using a reflective surface with refractive index n and angle of incidence 67°. Full article ">Figure 2
(a) Cross-section view SEM of over-exposed sample formed with 4 + 1 configuration ROE; (b,c) Top-view SEM of holographically fabricated, well-developed 3D structures with 4 + 1 configuration ROE with large areas showing no diffraction pattern (b) and enlarged view (c); Fabricated (d) and (e) simulated cross-sectional view of 3D structure formed with 4 + 1 configuration. The structure is not uniform as was expected due to a designed shift in the angle of incidence of a side beam. The dark-red solid line is in parallel with the sample surface and the yellow dashed line indicates the orientation of the holographic structures. Full article ">Figure 3
(a) Simulated top view of the 5 + 1 interference pattern and (b) atomic force micrograph (AFM) of fabricated quasi-crystals in DPHPA using a 5 + 1 configuration ROE. Five-circle clusters, pentagons, sun-like shapes of ten lines and decagons are drawn for eye guidance; (c) simulated interference patterns showing the front and back sides of a cubic volume; (d–f) cross-section SEM images of fabricated 3D quasicrystals in SU-8 cut in different orientation revealing various structural information; and (g) a side view of simulated 3D interference pattern due to 5 + 1 beams. Full article ">Figure 4
(a) SEM of cross-section of not fully developed 3D PhCs in SU-8 but cut in an orientation where layer-by-layer pattern can be seen; (b) SEM of top-view of fabricated structures with six-fold symmetry in SU-8. Yellow lines indicate the orientation of structures in different layers. The hexagonal structure and the lattice constant Λ are indicated by the green hexagon and red arrow, respectively, for eye guidance; (c) SEM of the cross section of fabricated 3D PhCs in SU-8 and (d) the simulated interference pattern. Yellow lines indicate analogous fabricated and simulated structures; (e) measured FTIR reflection spectra from SU-8 PhCs and overexposed SU-8 film without any structures. Full article ">Figure 5
(a) Diffraction pattern from fabricated 3D photonic crystal template in SU-8 using 532 nm laser; (b) top-view of simulated interference among pure s-wave side beams plus the central circularly polarized beam; (c) among pure p-wave side beams plus the central circularly polarized beam; (d) among side beams with both s- and p-waves plus the central circularly polarized beam. Interference patterns generated with 4 + 1 and 6 + 1 configurations are shown in top and bottom row in (b,c,d), respectively. Circles indicate the corresponding locations of high intensity spots. Dotted circles indicate the spots located at the bottom as shown in the side view in the insert in (c). Full article ">

3388 KiB

Open AccessArticle

Quantification of Vortex Generation Due to Non-Equilibrium Electrokinetics at the Micro/Nanochannel Interface: Particle Tracking Velocimetry

by Seung Jun Lee, Kilsung Kwon, Tae-Joon Jeon, Sun Min Kim and Daejoong Kim

Micromachines 2016, 7(7), 127; https://doi.org/10.3390/mi7070127 - 21 Jul 2016

Cited by 4 | Viewed by 4752

Abstract

We describe a quantitative study of vortex generation due to non-equilibrium electrokinetics near a micro/nanochannel interface. The microfluidic device is comprised of a microchannel with a set of nanochannels. These perm-selective nanochannels induce flow instability and thereby produce strong vortex generation. We performed [...] Read more.

We describe a quantitative study of vortex generation due to non-equilibrium electrokinetics near a micro/nanochannel interface. The microfluidic device is comprised of a microchannel with a set of nanochannels. These perm-selective nanochannels induce flow instability and thereby produce strong vortex generation. We performed tracking visualization of fluorescent microparticles to obtain velocity fields. Particle tracking enables the calculation of an averaged velocity field and the velocity fluctuations. We characterized the effect of applied voltages and electrolyte concentrations on vortex formation. The experimental results show that an increasing voltage or decreasing concentration results in a larger vortex region and a strong velocity fluctuation. We calculate the normalized velocity fluctuation—whose meaning is comparable to turbulent intensity—and we found that it is as high as 0.12. This value is indicative of very efficient mixing, albeit with a small Reynolds number. Full article

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Schematic of the microfluidic device. The red rectangle indicates the region for the results in <a href="#micromachines-07-00127-f003" class="html-fig">Figure 3</a>, <a href="#micromachines-07-00127-f004" class="html-fig">Figure 4</a> and <a href="#micromachines-07-00127-f006" class="html-fig">Figure 6</a>. The black rectangles indicate the region for the results in <a href="#micromachines-07-00127-f005" class="html-fig">Figure 5</a>. Full article ">Figure 2
(a) Particle path lines with no voltage and (b) particle path lines with an applied voltage of 150 V. Full article ">Figure 3
Velocity field particle tracking with (a) no applied voltage; (b) 50 V; (c) 100 V; and (d) 150 V. Full article ">Figure 4
Region of influence of vortex generation versus (a) applied voltage and (b) KCl concentration. Full article ">Figure 5
Speed distribution in (a) a non-vortex region and (b) a vortex region (see <a href="#micromachines-07-00127-f001" class="html-fig">Figure 1</a>). Full article ">Figure 6
Normalized velocity fluctuation versus (a) applied voltage and (b) KCl concentration. Full article ">

3508 KiB

Open AccessReview

Mimicking the Kidney: A Key Role in Organ-on-Chip Development

by Roberto Paoli and Josep Samitier

Micromachines 2016, 7(7), 126; https://doi.org/10.3390/mi7070126 - 20 Jul 2016

Cited by 35 | Viewed by 20722

Abstract

Pharmaceutical drug screening and research into diseases call for significant improvement in the effectiveness of current in vitro models. Better models would reduce the likelihood of costly failures at later drug development stages, while limiting or possibly even avoiding the use of animal [...] Read more.

Pharmaceutical drug screening and research into diseases call for significant improvement in the effectiveness of current in vitro models. Better models would reduce the likelihood of costly failures at later drug development stages, while limiting or possibly even avoiding the use of animal models. In this regard, promising advances have recently been made by the so-called “organ-on-chip” (OOC) technology. By combining cell culture with microfluidics, biomedical researchers have started to develop microengineered models of the functional units of human organs. With the capacity to mimic physiological microenvironments and vascular perfusion, OOC devices allow the reproduction of tissue- and organ-level functions. When considering drug testing, nephrotoxicity is a major cause of attrition during pre-clinical, clinical, and post-approval stages. Renal toxicity accounts for 19% of total dropouts during phase III drug evaluation—more than half the drugs abandoned because of safety concerns. Mimicking the functional unit of the kidney, namely the nephron, is therefore a crucial objective. Here we provide an extensive review of the studies focused on the development of a nephron-on-chip device. Full article

(This article belongs to the Special Issue Microfluidic Bioreactors and Organ-on-Chip Devices for Drug Screening and Disease Modeling)

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5476 KiB

Open AccessFeature PaperArticle

Wide Field-of-View Fluorescence Imaging with Optical-Quality Curved Microfluidic Chamber for Absolute Cell Counting

by Mohiuddin Khan Shourav, Kyunghoon Kim, Subin Kim and Jung Kyung Kim

Micromachines 2016, 7(7), 125; https://doi.org/10.3390/mi7070125 - 20 Jul 2016

Cited by 5 | Viewed by 6420

Abstract

Field curvature and other aberrations are encountered inevitably when designing a compact fluorescence imaging system with a simple lens. Although multiple lens elements can be used to correct most such aberrations, doing so increases system cost and complexity. Herein, we propose a wide [...] Read more.

Field curvature and other aberrations are encountered inevitably when designing a compact fluorescence imaging system with a simple lens. Although multiple lens elements can be used to correct most such aberrations, doing so increases system cost and complexity. Herein, we propose a wide field-of-view (FOV) fluorescence imaging method with an unconventional optical-quality curved sample chamber that corrects the field curvature caused by a simple lens. Our optics simulations and proof-of-concept experiments demonstrate that a curved substrate with lens-dependent curvature can reduce greatly the distortion in an image taken with a conventional planar detector. Following the validation study, we designed a curved sample chamber that can contain a known amount of sample volume and fabricated it at reasonable cost using plastic injection molding. At a magnification factor of approximately 0.6, the curved chamber provides a clear view of approximately 119 mm², which is approximately two times larger than the aberration-free area of a planar chamber. Remarkably, a fluorescence image of microbeads in the curved chamber exhibits almost uniform intensity over the entire field even with a simple lens imaging system, whereas the distorted boundary region has much lower brightness than the central area in the planar chamber. The absolute count of white blood cells stained with a fluorescence dye was in good agreement with that obtained by a commercially available conventional microscopy system. Hence, a wide FOV imaging system with the proposed curved sample chamber would enable us to acquire an undistorted image of a large sample volume without requiring a time-consuming scanning process in point-of-care diagnostic applications. Full article

(This article belongs to the Special Issue MEMS/NEMS for Biomedical Imaging and Sensing)

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1637 KiB

Open AccessArticle

Locally-Actuated Graphene-Based Nano-Electro-Mechanical Switch

by Jian Sun, Manoharan Muruganathan, Nozomu Kanetake and Hiroshi Mizuta

Micromachines 2016, 7(7), 124; https://doi.org/10.3390/mi7070124 - 19 Jul 2016

Cited by 22 | Viewed by 5612

Abstract

The graphene nano-electro-mechanical switches are promising components due to their outstanding switching performance. However, most of the reported devices suffered from a large actuation voltages, hindering them from the integration in the conventional complementary metal-oxide-semiconductor (CMOS) circuit. In this work, we demonstrated the [...] Read more.

The graphene nano-electro-mechanical switches are promising components due to their outstanding switching performance. However, most of the reported devices suffered from a large actuation voltages, hindering them from the integration in the conventional complementary metal-oxide-semiconductor (CMOS) circuit. In this work, we demonstrated the graphene nano-electro-mechanical switches with the local actuation electrode via conventional nanofabrication techniques. Both cantilever-type and double-clamped beam switches were fabricated. These devices exhibited the sharp switching, reversible operation cycles, high on/off ratio, and a low actuation voltage of below 5 V, which were compatible with the CMOS circuit requirements. Full article

(This article belongs to the Special Issue Graphene Nano-Electro-Mechanical (NEM) Devices and Applications)

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(a) Exfoliated graphene flake, black and red dots indicate the monolayer and bilayer regions, respectively; and (b) Raman spectra probed at locations marked as two color dots in (a). Green lines are the sub-peaks obtained from Lorentzian peak fitting. The arrow indicates the location of D band. Full article ">Figure 2
Schematics of fabrication procedure of the graphene NEM switch with local top actuation electrode. T and B denote top and bottom electrodes, respectively. (a) Graphene exfoliation and bottom electrodes definition; (b) HSQ spin coating and pattering; (c) graphene etching in oxygen plasma; (d) definition of SiO2 sacrificial layer; (e) definition of top electrode; (f) releasing graphene in HF. Full article ">Figure 3
False color SEM image of a double-clamped beam graphene switch as-fabricated. T and B denote top and bottom electrodes, respectively. Full article ">Figure 4
Electrical characterization of the switching performance of a double-clamped beam switch. The inset shows the two-terminal measurement configuration. Full article ">Figure 5
SEM images of a graphene cantilever-type switch with a local top actuation electrode (a) before and (b) after the switching operation. The initial air gap g0 between the graphene and the top electrode is about 140 nm. The graphene cantilever is artificially colored in light blue. The scale bars are 500 nm. Full article ">Figure 6
Electrical characterization of the switching performance of a cantilever-type switch. Inset: (Lower) two-terminal configuration and switch-off status, (Right upper) switch-on status, and (Left upper) I-V response after device failure. Full article ">

8583 KiB

Open AccessReview

Microfluidic Approaches for Manipulating, Imaging, and Screening C. elegans

by Bhagwati P. Gupta and Pouya Rezai

Micromachines 2016, 7(7), 123; https://doi.org/10.3390/mi7070123 - 19 Jul 2016

Cited by 57 | Viewed by 10275

Abstract

The nematode C. elegans (worm) is a small invertebrate animal widely used in studies related to fundamental biological processes, disease modelling, and drug discovery. Due to their small size and transparent body, these worms are highly suitable for experimental manipulations. In recent years [...] Read more.

The nematode C. elegans (worm) is a small invertebrate animal widely used in studies related to fundamental biological processes, disease modelling, and drug discovery. Due to their small size and transparent body, these worms are highly suitable for experimental manipulations. In recent years several microfluidic devices and platforms have been developed to accelerate worm handling, phenotypic studies and screens. Here we review major tools and briefly discuss their usage in C. elegans research. Full article

(This article belongs to the Special Issue Micro/Nano Devices for Chemical Analysis)

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1933 KiB

Open AccessArticle

High-Throughput Assessment of Drug Cardiac Safety Using a High-Speed Impedance Detection Technology-Based Heart-on-a-Chip

by Xi Zhang, Tianxing Wang, Ping Wang and Ning Hu

Micromachines 2016, 7(7), 122; https://doi.org/10.3390/mi7070122 - 19 Jul 2016

Cited by 42 | Viewed by 6808

Abstract

Drug cardiac safety assessments play a significant role in drug discovery. Drug-induced cardiotoxicity is one of the main reasons for drug attrition, even when antiarrhythmic drugs can otherwise effectively treat the arrhythmias. Consequently, efficient drug preclinical assessments are needed in the drug industry. [...] Read more.

Drug cardiac safety assessments play a significant role in drug discovery. Drug-induced cardiotoxicity is one of the main reasons for drug attrition, even when antiarrhythmic drugs can otherwise effectively treat the arrhythmias. Consequently, efficient drug preclinical assessments are needed in the drug industry. However, most drug efficacy assessments are performed based on electrophysiological tests of cardiomyocytes in vitro and cannot effectively provide information on drug-induced dysfunction of cardiomyocyte beating. Here we present a heart-on-a-chip device for evaluating the drug cardiac efficacy using a high-speed impedance detection technology. Verapamil and doxorubicin were utilized to test this heart-on-a-chip, and multiple parameters of cardiomyocyte beating status are used to reveal the effects of drugs. The results show that drug efficacy or cardiotoxicity can be determined by this heart-on-a-chip. We believe this heart-on-a-chip will be a promising tool for the preclinical assessment of drug cardiac efficacy. Full article

(This article belongs to the Special Issue Microfluidic Bioreactors and Organ-on-Chip Devices for Drug Screening and Disease Modeling)

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Establishment of heart-on-a-chip for drug assessment. (a) The fabrication of interdigitated electrodes (IDEs); (b) The IDEs layout and image of device; (c) Schematics of heart-on-a-chip with IDEs and impedance detection method; (d) The Diff-Quik staining images of cardiomyocytes on the device; (e) High-throughput impedance detection system for drug assessment using beating characteristics. Full article ">Figure 2
Heart-on-a-chip for verapamil test. (a) The beating signals before and after the verapamil with different concentrations are administered on the cardiomyocytes; (b) Statistical beating rate within 60 min in the presence of verapamil; (c) Statistical beating rate within 60 min in the presence of verapamil. Full article ">Figure 3
Heart-on-a-chip for doxorubicin test. (a) The beating signals before and after the doxorubicin with different concentrations are administered on the cardiomyocytes; (b) Statistical beating rate within 60 min in the presence of doxorubicin; (c) Statistical beating rate within 60 min in the presence of doxorubicin. Full article ">Figure 4
Cell viability test by the impedance detection method. (a) Cell growth curves in the absence and presence of verapamil; (b) Cell growth curves in the absence and presence of doxorubicin. Black arrows show the initial time of drug treatment. Full article ">Figure 5
Long-term monitoring (24 h) after drug treatment. Full article ">

8270 KiB

Open AccessArticle

Cytostretch, an Organ-on-Chip Platform

by Nikolas Gaio, Berend Van Meer, William Quirós Solano, Lambert Bergers, Anja Van de Stolpe, Christine Mummery, Pasqualina M. Sarro and Ronald Dekker

Micromachines 2016, 7(7), 120; https://doi.org/10.3390/mi7070120 - 14 Jul 2016

Cited by 37 | Viewed by 8398

Abstract

Organ-on-Chips (OOCs) are micro-fabricated devices which are used to culture cells in order to mimic functional units of human organs. The devices are designed to simulate the physiological environment of tissues in vivo. Cells in some types of OOCs can be stimulated in [...] Read more.

Organ-on-Chips (OOCs) are micro-fabricated devices which are used to culture cells in order to mimic functional units of human organs. The devices are designed to simulate the physiological environment of tissues in vivo. Cells in some types of OOCs can be stimulated in situ by electrical and/or mechanical actuators. These actuations can mimic physiological conditions in real tissue and may include fluid or air flow, or cyclic stretch and strain as they occur in the lung and heart. These conditions similarly affect cultured cells and may influence their ability to respond appropriately to physiological or pathological stimuli. To date, most focus has been on devices specifically designed to culture just one functional unit of a specific organ: lung alveoli, kidney nephrons or blood vessels, for example. In contrast, the modular Cytostretch membrane platform described here allows OOCs to be customized to different OOC applications. The platform utilizes silicon-based micro-fabrication techniques that allow low-cost, high-volume manufacturing. We describe the platform concept and its modules developed to date. Membrane variants include membranes with (i) through-membrane pores that allow biological signaling molecules to pass between two different tissue compartments; (ii) a stretchable micro-electrode array for electrical monitoring and stimulation; (iii) micro-patterning to promote cell alignment; and (iv) strain gauges to measure changes in substrate stress. This paper presents the fabrication and the proof of functionality for each module of the Cytostretch membrane. The assessment of each additional module demonstrate that a wide range of OOCs can be achieved. Full article

(This article belongs to the Special Issue Microfluidic Bioreactors and Organ-on-Chip Devices for Drug Screening and Disease Modeling)

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2175 KiB

Open AccessArticle

Combining Electro-Osmotic Flow and FTA^® Paper for DNA Analysis on Microfluidic Devices

by Ryan Wimbles, Louise M. Melling and Kirsty J. Shaw

Micromachines 2016, 7(7), 119; https://doi.org/10.3390/mi7070119 - 14 Jul 2016

Cited by 7 | Viewed by 5331

Abstract

FTA^® paper can be used to protect a variety of biological samples prior to analysis, facilitating ease-of-transport to laboratories or long-term archive storage. The use of FTA^® paper as a solid phase eradicates the need to elute the nucleic acids from [...] Read more.

FTA^® paper can be used to protect a variety of biological samples prior to analysis, facilitating ease-of-transport to laboratories or long-term archive storage. The use of FTA^® paper as a solid phase eradicates the need to elute the nucleic acids from the matrix prior to DNA amplification, enabling both DNA purification and polymerase chain reaction (PCR)-based DNA amplification to be performed in a single chamber on the microfluidic device. A disc of FTA^® paper, containing a biological sample, was placed within the microfluidic device on top of wax-encapsulated DNA amplification reagents. The disc containing the biological sample was then cleaned up using Tris-EDTA (TE) buffer, which was passed over the disc, via electro-osmotic flow, in order to remove any potential inhibitors of downstream processes. DNA amplification was successfully performed (from buccal cells, whole blood and semen) using a Peltier thermal cycling system, whereupon the stored PCR reagents were released during the initial denaturing step due to the wax barrier melting between the FTA^® disc and PCR reagents. Such a system offers advantages in terms of a simple sample introduction interface and the ability to process archived samples in an integrated microfluidic environment with minimal risk of contamination. Full article

(This article belongs to the Special Issue Application of Microfluidic Methodology for the Analysis of DNA)

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(a) Photograph showing the design of the microfluidic device used to perform integrated DNA purification and amplification experiments. The buffer wells are connected to the central chamber via 250-µm channels; (b) Schematic top-view showing the location of the channels, central chamber and reservoirs at the end of each channel. The dashed red line also indicates the cross-section view though which (c) occurs; (c) Schematic cross-section showing how the FTA® paper discs are placed in the central chamber on top of a layer of wax-encapsulated PCR reagents. Full article ">Figure 2
Graph showing the EOF velocity of the TE buffer used in the DNA purification process. Error bars represent the standard deviation of the triplicate analysis performed on three separate microfluidic devices. Full article ">Figure 3
PCR product intensity compared to the voltage applied during the purification procedure on the microfluidic device (n = 3). Peak area refers to the band intensity/peak area of the PCR products on the gel. Conventional off-chip positive and negative controls produced peak areas of 4768 (±780) and 93 (±93), respectively. Error bars represent the standard deviation from triplicate analysis. Full article ">Figure 4
Results from direct analysis of semen samples on FTA® paper using a variety of treatment conditions for disulphide bond reduction (n = 3). A range of treatment options were tested: (1) semen added to FTA® paper and dried; (2) semen added to FTA® paper, dried, 40 µL of 1 M DTT added and dried; (3) semen and 1 M DTT mixed 50:50 (v/v), added to FTA® paper and dried; (4) 40 µL of 1 M DTT added to FTA® paper, dried, semen added and dried. Error bars represent the standard deviation from triplicate analysis. Full article ">

18878 KiB

Open AccessReview

Plasmonic Structures, Materials and Lenses for Optical Lithography beyond the Diffraction Limit: A Review

by Changtao Wang, Wei Zhang, Zeyu Zhao, Yanqin Wang, Ping Gao, Yunfei Luo and Xiangang Luo

Micromachines 2016, 7(7), 118; https://doi.org/10.3390/mi7070118 - 13 Jul 2016

Cited by 50 | Viewed by 11955

Abstract

The rapid development of nanotechnologies and sciences has led to the great demand for novel lithography methods allowing large area, low cost and high resolution nano fabrications. Characterized by unique sub-diffraction optical features like propagation with an ultra-short wavelength and great field enhancement [...] Read more.

The rapid development of nanotechnologies and sciences has led to the great demand for novel lithography methods allowing large area, low cost and high resolution nano fabrications. Characterized by unique sub-diffraction optical features like propagation with an ultra-short wavelength and great field enhancement in subwavelength regions, surface plasmon polaritons (SPPs), including surface plasmon waves, bulk plasmon polaritons (BPPs) and localized surface plasmons (LSPs), have become potentially promising candidates for nano lithography. In this paper, investigations into plasmonic lithography in the manner of point-to-point writing, interference and imaging were reviewed in detail. Theoretical simulations and experiments have demonstrated plasmonic lithography resolution far beyond the conventional diffraction limit, even with ultraviolet light sources and single exposure performances. Half-pitch resolution as high as 22 nm (~1/17 light wavelength) was observed in plasmonic lens imaging lithography. Moreover, not only the overview of state-of-the-art results, but also the physics behind them and future research suggestions are discussed as well. Full article

(This article belongs to the Special Issue Micro/Nano Photonic Devices and Systems)

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14556 KiB

Open AccessArticle

Synthesis and Electro-Magneto-Mechanical Properties of Graphene Aerogels Functionalized with Co-Fe-P Amorphous Alloys

by Guang-Ping Zheng, Xi Lu and Zhuo Han

Micromachines 2016, 7(7), 117; https://doi.org/10.3390/mi7070117 - 12 Jul 2016

Cited by 6 | Viewed by 4790

Abstract

Graphene aerogels (GAs) are functionalized with Fe-Co-P alloy using an electro-deposition method. The Fe-Co-P alloy coated on the graphene nanosheets is found to possess an amorphous structure and a nanoporous architecture of GAs. The electro-mechanical properties of GAs are significantly affected by the [...] Read more.

Graphene aerogels (GAs) are functionalized with Fe-Co-P alloy using an electro-deposition method. The Fe-Co-P alloy coated on the graphene nanosheets is found to possess an amorphous structure and a nanoporous architecture of GAs. The electro-mechanical properties of GAs are significantly affected by the Fe-Co-P nanoparticles embedded inside GAs. The electro-mechanical responses of GA/Fe-Co-P nanoporous hybrid structures are sensitive to an applied magnetic field, demonstrating that they are promising for electro-magneto-mechanical applications. The light-weight, high-strength and nanoporous GAs functionalized with Fe-Co-P amorphous alloys are desirable sensors, actuators, and nano-electro-mechanical systems that could be controlled or manipulated by mechanical, electric and magnetic fields. Full article

(This article belongs to the Special Issue Graphene Nano-Electro-Mechanical (NEM) Devices and Applications)

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SEM images of GA (a) and GA/Co-Fe-P (Sample-h14) (b). The inset in (b) shows the typical size and shape of GA and GA/Co-Fe-P samples. Full article ">Figure 2
SEM images of GA/Co-Fe-P samples: (a) Sample-h2; (b) Sample-h4; (c) Sample-h8; (d) Sample-h14. Full article ">Figure 3
XRD patterns of GA and GA/Co-Fe-P samples: (a) Sample-h2, Sample-h4 and Sample-h8; (b) GA, Co-Fe-P foils and Sample-h14. Full article ">Figure 4
Raman spectra of GA and GA/Co-Fe-P samples. Id/Ig is the ratio of intensities of D- and G-bands. Full article ">Figure 5
The relative changes of resistances of GA and GA/Co-Fe-P samples under compressive strains in a loading (from 0 to εm) and un-loading (from εm to 0) cycle. εm denotes the maximum applied strain. Full article ">Figure 6
(a) Magnetic hysteresis loop of the GA/Co-Fe-P sample; (b) The relative changes of resistances of GA/Co-Fe-P samples under compressive strains in a loading (from 0 to εm) and un-loading (after εm to 0) cycle, with and without an applied magnetic field H. εm denotes the maximum applied strain. Full article ">

6862 KiB

Open AccessArticle

Gravity-Based Precise Cell Manipulation System Enhanced by In-Phase Mechanism

by Koji Mizoue, Manh Hao Phan, Chia-Hung Dylan Tsai, Makoto Kaneko, Junsu Kang and Wan Kyun Chung

Micromachines 2016, 7(7), 116; https://doi.org/10.3390/mi7070116 - 9 Jul 2016

Cited by 8 | Viewed by 5389

Abstract

This paper proposes a gravity-based system capable of generating high-resolution pressure for precise cell manipulation or evaluation in a microfluidic channel. While the pressure resolution of conventional pumps for microfluidic applications is usually about hundreds of pascals as the resolution of their feedback [...] Read more.

This paper proposes a gravity-based system capable of generating high-resolution pressure for precise cell manipulation or evaluation in a microfluidic channel. While the pressure resolution of conventional pumps for microfluidic applications is usually about hundreds of pascals as the resolution of their feedback sensors, precise cell manipulation at the pascal level cannot be done. The proposed system successfully achieves a resolution of 100 millipascals using water head pressure with an in-phase noise cancelation mechanism. The in-phase mechanism aims to suppress the noises from ambient vibrations to the system. The proposed pressure system is tested with a microfluidic platform for pressure validation. The experimental results show that the in-phase mechanism effectively reduces the pressure turbulence, and the pressure-driven cell movement matches the theoretical simulations. Preliminary experiments on deformability evaluation with red blood cells under incremental pressures of one pascal are successfully performed. Different deformation patterns are observed from cell to cell under precise pressure control. Full article

(This article belongs to the Special Issue Advances in Microfluidic Devices for Cell Handling and Analysis)

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1733 KiB

Open AccessArticle

A New Method of Fixing High-Aspect-Ratio Microstructures by Gel

by Nan Chen, Xiangyu Chen, Penghui Xiong, Shuangyue Hou, Xiaobo Zhang, Ying Xiong, Gang Liu and Yangchao Tian

Micromachines 2016, 7(7), 115; https://doi.org/10.3390/mi7070115 - 9 Jul 2016

Cited by 3 | Viewed by 5048

Abstract

In the microfabrication processes, it is necessary to examine the quality of the structures to ensure the whole process runs smoothly. However, the examination process of pattern defects is interrupted during the fabrication of high-aspect-ratio microstructures. The inevitable pattern defects arise from capillary [...] Read more.

In the microfabrication processes, it is necessary to examine the quality of the structures to ensure the whole process runs smoothly. However, the examination process of pattern defects is interrupted during the fabrication of high-aspect-ratio microstructures. The inevitable pattern defects arise from capillary forces which occur during the liquid drying process. In this paper, a new method that enables us to fix the microstructures with gel to restrict deformations before the rinsed liquid drying process has been proposed. It is effective to avoid the capillary forces by preventing the formation of the liquid level. The process parameters, types of gel, gel time and observation time were discussed and the flatness and thickness of the gel layer could be controlled. A series of high-aspect-ratio microstructures were fixed in good condition by gel. Full article

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(a) Evaporation of liquid during conventional drying process; (b) Deformation of the microstructures during conventional drying process; (c) The microstructures fixed by gel. Full article ">Figure 2
The processes of fabricating metal microstructures with the new method: (a) Adding the sol and forming gel; (b) Examination of fixing photoresist microstructures under the microscope; (c) Loading the sample on the holder; (d) Dissolving the gel in the warm water; (e) Electroplating process. Full article ">Figure 3
The stereoscopic microscopy images of the gratings (side views): (a) After the conventional drying process, some structures deformed or adhered together (width: 24 μm; height: 240 μm); (b) The structures were fixed by gellan gum gel (width: 24 μm; height: 240 μm); (c) After the liquid drying process, the top of the structures adhered to each other (width: 15 μm; height: 240 μm); (d) The structures were fixed by gellan gum gel (width: 15 μm; height: 240 μm). Full article ">Figure 4
Images of SU-8 beams (width: 20 μm; height: 240 μm). (a) Traditional drying process; (b) Addition of agarose sol before the drying process; (c) Addition of gellan gum sol before the drying process. Full article ">Figure 5
Gellan gum spin speed versus thickness. Full article ">Figure 6
The gel time and observation time versus the concentration of the gellan gum sol. Full article ">Figure 7
The optical microscopy images of the micro-gratings (width: 20 μm; height: 240 μm): (a) Within observation time; (b) 10 min later. Full article ">

7860 KiB

Open AccessFeature PaperArticle

A Microchip for High-Throughput Axon Growth Drug Screening

by Hyun Soo Kim, Sehoon Jeong, Chiwan Koo, Arum Han and Jaewon Park

Micromachines 2016, 7(7), 114; https://doi.org/10.3390/mi7070114 - 7 Jul 2016

Cited by 14 | Viewed by 8042

Abstract

It has been recently known that not only the presence of inhibitory molecules associated with myelin but also the reduced growth capability of the axons limit mature central nervous system (CNS) axonal regeneration after injury. Conventional axon growth studies are typically conducted using [...] Read more.

It has been recently known that not only the presence of inhibitory molecules associated with myelin but also the reduced growth capability of the axons limit mature central nervous system (CNS) axonal regeneration after injury. Conventional axon growth studies are typically conducted using multi-well cell culture plates that are very difficult to use for investigating localized effects of drugs and limited to low throughput. Unfortunately, there is currently no other in vitro tool that allows investigating localized axonal responses to biomolecules in high-throughput for screening potential drugs that might promote axonal growth. We have developed a compartmentalized neuron culture platform enabling localized biomolecular treatments in parallel to axons that are physically and fluidically isolated from their neuronal somata. The 24 axon compartments in the developed platform are designed to perform four sets of six different localized biomolecular treatments simultaneously on a single device. In addition, the novel microfluidic configuration allows culture medium of 24 axon compartments to be replenished altogether by a single aspiration process, making high-throughput drug screening a reality. Full article

(This article belongs to the Special Issue Microfluidic Bioreactors and Organ-on-Chip Devices for Drug Screening and Disease Modeling)

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Illustrations of the high-throughput compartmentalized neuron culture platform: (A) three layers (i.e., culture medium reservoir layer, compartment layer with two through-holes at each axon compartment, cell culture substrate layer with the ridge structure) composing the platform; (B) an illustration showing the axon isolation from the neuronal somata by the shallow height of the microchannels connecting the soma compartment and the axon compartment; and (C) schematic illustrations of the assembled device showing cross-sections. Inset: A close-up view of the axon compartments showing the fluidic flow during the one-step culture medium replenishment process. Blue dotted circle indicates a branch channel that connects the outflow hole with the medium outflow channel. Full article ">Figure 2
Fabrication processes of the high-throughput compartmentalized neuron culture platform; (A) substrate layer, (B) compartment layer, (C) reservoir layer. Full article ">Figure 3
SEM images of the fabricated devices: (A,B) PMMA master showing precisely patterned microchannel array by the hot-embossing process; (C–E) bottom-side of the final PDMS layer showing 3 μm deep and 20 μm wide microchannels connecting the soma compartment and the axon compartments; (F) axon compartment of the PDMS master, in which the round pillar-like structures allows pre-defined holes to be made on the final PDMS layer; and (G,H) pre-defined through-holes on the axon compartments of the final PDMS layer. Full article ">Figure 4
Numerical simulation results of the culture medium flow profiles during the replenishment process. (A) 3D illustration of the culture medium outflow channel connected to the axon compartments and the reservoirs as well as the culture medium exchange port. (B) Normalized culture medium flow streamline showing the flow direction from the reservoirs to the culture medium exchange port. (C) y-z cross-sectional view at the center of branch channel part of which enlarged views show the design used for matching the fluidic resistance at each axon compartments. Table illustrates the dimensions of each branch channel used. (D) x-y cross-sectional view at the culture medium outflow channel. (E) x-z cross-sectional view across the center of 12th branch channel part. Both (D) and (E) clearly show the culture medium flow profile collected at the medium exchange port through axon compartments and the culture medium outflow channel under a negative pressure applied condition. Full article ">Figure 5
(A,B) Axons being isolated from the neuronal somata by the shallow microchannels connecting the soma compartment and the axon compartment. Red dotted lines indicate compartment boundaries. (C) Isolated axonal layer inside the soma compartment at DIV 12. Cells were stained with Calcein-AM for visualization. Scale bars: 50 µm. Full article ">Figure 6
Cross-sections of the high-throughput compartmentalized neuron culture platform showing the fluidic isolation scheme during: (A) the culture medium replenishment process; and (B) localized biomolecular treatment. Full article ">Figure 7
(A) Image of the high-throughput compartmentalized neuron culture platform with reservoirs filled with inks for visualization. Isolated axon (B) without the CSPG treatment (control) and (C) with the CSPG treatment inside the axon compartments. Cells were stained with Calcein-AM for visualization. Scale bars: 50 µm. Full article ">

2214 KiB

Open AccessCommunication

Microfluidic Autologous Serum Eye-Drops Preparation as a Potential Dry Eye Treatment

by Takao Yasui, Jumpei Morikawa, Noritada Kaji, Manabu Tokeshi, Kazuo Tsubota and Yoshinobu Baba

Micromachines 2016, 7(7), 113; https://doi.org/10.3390/mi7070113 - 4 Jul 2016

Cited by 1 | Viewed by 5440

Abstract

Dry eye is a problem in tearing quality and/or quantity and it afflicts millions of persons worldwide. An autologous serum eye-drop is a good candidate for dry eye treatment; however, the eye-drop preparation procedures take a long time and are relatively troublesome. Here [...] Read more.

Dry eye is a problem in tearing quality and/or quantity and it afflicts millions of persons worldwide. An autologous serum eye-drop is a good candidate for dry eye treatment; however, the eye-drop preparation procedures take a long time and are relatively troublesome. Here we use spiral microchannels to demonstrate a strategy for the preparation of autologous serum eye-drops, which provide benefits for all dry eye patients; 100% and 90% removal efficiencies are achieved for 10 μm microbeads and whole human blood cells, respectively. Since our strategy allows researchers to integrate other functional microchannels into one device, such a microfluidic device will be able to offer a new one-step preparation system for autologous serum eye-drops. Full article

(This article belongs to the Special Issue Micro/Nano Devices for Chemical Analysis)

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Full article ">Figure 1
A spiral microfluidic device. (a) Photograph of a spiral microfluidic device; scale bar, 10 mm. Microchannels are highlighted by Trypan blue dye solution. Channel width and height are 707 and 70.7 μm, respectively. Distance between two adjacent microchannels is 303 μm; (b) A magnified micrograph of part of a spiral microchannel, enclosed by the red dotted box in <a href="#micromachines-07-00113-f001" class="html-fig">Figure 1</a>a; scale bar, 100 μm. Ten-fold diluted microbeads (10 μm diameter) in phosphate buffered saline were focused at an equilibrium position close to the inner wall of the microchannel. Full article ">Figure 2
Collection efficiency of 10 μm particles. Cross-sectional area was 50,000 μm2. Ten-fold diluted microbeads (10 μm diameter) in phosphate buffered saline were used. Error bars are the standard deviation for a series of measurements (N = 3). (a) Collection efficiency vs. aspect ratio of spiral microchannels. The aspect ratio is the ratio of channel height to width. The number of microchannel spirals was 7.5, and flow rate was 1000 μL/min; (b) Photographs of fabricated spiral microchannels with 0.5 to 7.5 circles. One circle is one spiral. The microchannels are highlighted by Trypan blue dye solution; (c) Collection efficiency vs. number of microchannel spirals. The aspect ratio of the microchannels was 0.1, and flow rate was 1000 μL/min; (d) Collection efficiency vs. flow rate. The aspect ratio of the microchannels was 0.1, and the number of microchannel spirals was 7.5. Full article ">Figure 3
Collection efficiency of whole human blood cells. Cross-sectional area was 50,000 μm2, the aspect ratio was 0.1, and the number of microchannel spirals was 7.5. (a) Collection efficiency vs. flow rate. Initial hematocrit of blood samples was 0.25%; (b) Collection efficiency vs. whole blood concentration. Flow rate was 5000 μm/min; (c) Photographs of collected samples from inner and outer outlets after centrifugation. Flow rate was 5000 μm/min, and initial hematocrit of blood samples was 0.25%. Hemolyzed blood was not observed. Full article ">

1718 KiB

Open AccessArticle

Light-Addressable Potentiometric Sensor as a Sensing Element in Plug-Based Microfluidic Devices

by Ko-Ichiro Miyamoto, Takuya Sato, Minami Abe, Torsten Wagner, Michael J. Schöning and Tatsuo Yoshinobu

Micromachines 2016, 7(7), 111; https://doi.org/10.3390/mi7070111 - 1 Jul 2016

Cited by 18 | Viewed by 5553

Abstract

A plug-based microfluidic system based on the principle of the light-addressable potentiometric sensor (LAPS) is proposed. The LAPS is a semiconductor-based chemical sensor, which has a free addressability of the measurement point on the sensing surface. By combining a microfluidic device and LAPS, [...] Read more.

A plug-based microfluidic system based on the principle of the light-addressable potentiometric sensor (LAPS) is proposed. The LAPS is a semiconductor-based chemical sensor, which has a free addressability of the measurement point on the sensing surface. By combining a microfluidic device and LAPS, ion sensing can be performed anywhere inside the microfluidic channel. In this study, the sample solution to be measured was introduced into the channel in a form of a plug with a volume in the range of microliters. Taking advantage of the light-addressability, the position of the plug could be monitored and pneumatically controlled. With the developed system, the pH value of a plug with a volume down to 400 nL could be measured. As an example of plug-based operation, two plugs were merged in the channel, and the pH change was detected by differential measurement. Full article

(This article belongs to the Special Issue Micro/Nano Devices for Chemical Analysis)

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(a) Test structure of the microfluidic device combined with LAPS; (b) Channel design with a chamber for merging and differential measurement; (c) Channel design to generate plugs on chip; (d) Test structure with two sample chambers, one merging chamber, and one sensing area. Full article ">Figure 2
Schematic view of the measurement system. Full article ">Figure 3
Detection of the plug by the photocurrent signal. Full article ">Figure 4
(a) I-V curves measured for plugs with different pH values; (b) Inflection points of I-V curves plotted as a function of pH. Full article ">Figure 5
(a) I-V curves for the second plug measured in the upstream before merging; (b) I-V curves for the merged plug measured in the downstream. Full article ">Figure 6
Effect of fluorine treatment of channel on the variation of plug volume. Full article ">Figure 7
(a) Temporal change of photocurrent after merging a plug of urea solution and that of urease solution. The photocurrent response varied depending on concentrations of urea; (b) Initial slope of photocurrent change as a function of the urea concentration. Full article ">

4027 KiB

Open AccessArticle

Design and Experiment of a Solder Paste Jetting System Driven by a Piezoelectric Stack

by Shoudong Gu, Xiaoyang Jiao, Jianfang Liu, Zhigang Yang, Hai Jiang and Qingqing Lv

Micromachines 2016, 7(7), 112; https://doi.org/10.3390/mi7070112 - 30 Jun 2016

Cited by 18 | Viewed by 7840

Abstract

To compensate for the insufficiency and instability of solder paste dispensing and printing that are used in the SMT (Surface Mount Technology) production process, a noncontact solder paste jetting system driven by a piezoelectric stack based on the principle of the nozzle-needle-system is [...] Read more.

To compensate for the insufficiency and instability of solder paste dispensing and printing that are used in the SMT (Surface Mount Technology) production process, a noncontact solder paste jetting system driven by a piezoelectric stack based on the principle of the nozzle-needle-system is introduced in this paper, in which a miniscule gap exists between the nozzle and needle during the jetting process. Here, the critical jet ejection velocity is discussed through theoretical analysis. The relations between ejection velocity and needle structure, needle velocity, and nozzle diameter were obtained by FLUENT software. Then, the prototype of the solder paste jetting system was fabricated, and the performance was verified by experiments. The effects of the gap between nozzle and needle, the driving voltage, and the nozzle diameter on the jetting performance and droplet diameter were obtained. Solder paste droplets 0.85 mm in diameter were produced when the gap between the nozzle and needle was adjusted to 10 μm, the driving voltage to 80 V, the nozzle diameter to 0.1 mm, and the variation of the droplet diameter was within ±3%. Full article

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945 KiB

Open AccessArticle

A Multithread Nested Neural Network Architecture to Model Surface Plasmon Polaritons Propagation

by Giacomo Capizzi, Grazia Lo Sciuto, Christian Napoli and Emiliano Tramontana

Micromachines 2016, 7(7), 110; https://doi.org/10.3390/mi7070110 - 30 Jun 2016

Cited by 41 | Viewed by 5017

Abstract

Surface Plasmon Polaritons are collective oscillations of electrons occurring at the interface between a metal and a dielectric. The propagation phenomena in plasmonic nanostructures is not fully understood and the interdependence between propagation and metal thickness requires further investigation. We propose an ad-hoc [...] Read more.

Surface Plasmon Polaritons are collective oscillations of electrons occurring at the interface between a metal and a dielectric. The propagation phenomena in plasmonic nanostructures is not fully understood and the interdependence between propagation and metal thickness requires further investigation. We propose an ad-hoc neural network topology assisting the study of the said propagation when several parameters, such as wavelengths, propagation length and metal thickness are considered. This approach is novel and can be considered a first attempt at fully automating such a numerical computation. For the proposed neural network topology, an advanced training procedure has been devised in order to shun the possibility of accumulating errors. The provided results can be useful, e.g., to improve the efficiency of photocells, for photon harvesting, and for improving the accuracy of models for solid state devices. Full article

(This article belongs to the Special Issue Micro/Nano Photonic Devices and Systems)

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Full article ">Figure 1
Implemented geometry in COMSOL (left), and geometry that models Surface Plasmon Polaritons (SPP) propagation from a metal-dielectric interface (right). Full article ">Figure 2
The simulation survey coverage in the features space concerning the excitation wavelength <math display="inline"> <semantics> <msub> <mi>λ</mi> <mn>0</mn> </msub> </semantics> </math> and the adopted tickness t. Full article ">Figure 3
The real part (left) and the imaginary part (right) of the dielectric constant of various noble metals, such as Au, Ag and Mb. Full article ">Figure 4
The proposed Nested Neural Network Architecture (NNNA). Full article ">Figure 5
Global performance plot of the implemented Nested Neural Network Architecture (NNNA) (left panel), and a comparison with the performances obtained by using two separate Feed Forward Neural Networks (FFNNs) (right panel). Full article ">Figure 6
The obtained results: the model error <math display="inline"> <semantics> <msub> <mi>E</mi> <msub> <mi>λ</mi> <mrow> <mi>S</mi> <mi>P</mi> <mi>P</mi> </mrow> </msub> </msub> </semantics> </math> for the prediction of <math display="inline"> <semantics> <msub> <mi>λ</mi> <mrow> <mi>S</mi> <mi>P</mi> <mi>P</mi> </mrow> </msub> </semantics> </math> computed as in Equation (<a href="#FD11-micromachines-07-00110" class="html-disp-formula">11</a>). The (left) shows the prediction error for <math display="inline"> <semantics> <msub> <mi>λ</mi> <mrow> <mi>S</mi> <mi>P</mi> <mi>P</mi> </mrow> </msub> </semantics> </math> and the (right) shows its absolute value. Full article ">Figure 7
The obtained results: the model error <math display="inline"> <semantics> <msub> <mi>E</mi> <msub> <mi>L</mi> <mrow> <mi>S</mi> <mi>P</mi> <mi>P</mi> </mrow> </msub> </msub> </semantics> </math> for the prediction of <math display="inline"> <semantics> <msub> <mi>L</mi> <mrow> <mi>S</mi> <mi>P</mi> <mi>P</mi> </mrow> </msub> </semantics> </math> computed as in Equation (<a href="#FD11-micromachines-07-00110" class="html-disp-formula">11</a>). The (left) shows the prediction error for <math display="inline"> <semantics> <msub> <mi>L</mi> <mrow> <mi>S</mi> <mi>P</mi> <mi>P</mi> </mrow> </msub> </semantics> </math> and the (right) shows its absolute value. Full article ">

5208 KiB

Open AccessArticle

3D Printed Paper-Based Microfluidic Analytical Devices

by Yong He, Qing Gao, Wen-Bin Wu, Jing Nie and Jian-Zhong Fu

Micromachines 2016, 7(7), 108; https://doi.org/10.3390/mi7070108 - 28 Jun 2016

Cited by 59 | Viewed by 12848

Abstract

As a pump-free and lightweight analytical tool, paper-based microfluidic analytical devices (μPADs) attract more and more interest. If the flow speed of μPAD can be programmed, the analytical sequences could be designed and they will be more popular. This reports presents a novel [...] Read more.

As a pump-free and lightweight analytical tool, paper-based microfluidic analytical devices (μPADs) attract more and more interest. If the flow speed of μPAD can be programmed, the analytical sequences could be designed and they will be more popular. This reports presents a novel μPAD, driven by the capillary force of cellulose powder, printed by a desktop three-dimensional (3D) printer, which has some promising features, such as easy fabrication and programmable flow speed. First, a suitable size-scale substrate with open microchannels on its surface is printed. Next, the surface of the substrate is covered with a thin layer of polydimethylsiloxane (PDMS) to seal the micro gap caused by 3D printing. Then, the microchannels are filled with a mixture of cellulose powder and deionized water in an appropriate proportion. After drying in an oven at 60 °C for 30 min, it is ready for use. As the different channel depths can be easily printed, which can be used to achieve the programmable capillary flow speed of cellulose powder in the microchannels. A series of microfluidic analytical experiments, including quantitative analysis of nitrite ion and fabrication of T-sensor were used to demonstrate its capability. As the desktop 3D printer (D3DP) is very cheap and accessible, this device can be rapidly printed at the test field with a low cost and has a promising potential in the point-of-care (POC) system or as a lightweight platform for analytical chemistry. Full article

(This article belongs to the Special Issue 3D Printing: Microfabrication and Emerging Concepts)

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1406 KiB

Open AccessArticle

Quantification of Vortex Generation Due to Non-Equilibrium Electrokinetics at the Micro/Nanochannel Interface: Spectral Analysis

by Seung Jun Lee, Tae-Joon Jeon, Sun Min Kim and Daejoong Kim

Micromachines 2016, 7(7), 109; https://doi.org/10.3390/mi7070109 - 27 Jun 2016

Cited by 3 | Viewed by 4671

Abstract

We report on our investigation of a low Reynolds number non-equilibrium electrokinetic flow in a micro/nanochannel platform. Non-equilibrium electrokinetic phenomena include so-called concentration polarization in a moderate electric field and vortex formation in a high electric field. We conducted a spectral analysis of [...] Read more.

We report on our investigation of a low Reynolds number non-equilibrium electrokinetic flow in a micro/nanochannel platform. Non-equilibrium electrokinetic phenomena include so-called concentration polarization in a moderate electric field and vortex formation in a high electric field. We conducted a spectral analysis of non-equilibrium electrokinetic vortices at a micro/nanochannel interface. We found that periodic vortices are formed while the frequency varies with the applied voltages and solution concentrations. At a frequency as high as 60 Hz, vortex generation was obtained with the strongest electric field and the lowest concentration. The power spectra show increasing frequency with increasing voltage or decreasing concentration. We expect that our spectral analysis results will be useful for micromixer developers in the micromachine research field. Full article

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1769 KiB

Open AccessReview

Farewell to Animal Testing: Innovations on Human Intestinal Microphysiological Systems

by Tae Hyun Kang and Hyun Jung Kim

Micromachines 2016, 7(7), 107; https://doi.org/10.3390/mi7070107 - 27 Jun 2016

Cited by 29 | Viewed by 11723

Abstract

The human intestine is a dynamic organ where the complex host-microbe interactions that orchestrate intestinal homeostasis occur. Major contributing factors associated with intestinal health and diseases include metabolically-active gut microbiota, intestinal epithelium, immune components, and rhythmical bowel movement known as peristalsis. Human intestinal [...] Read more.

The human intestine is a dynamic organ where the complex host-microbe interactions that orchestrate intestinal homeostasis occur. Major contributing factors associated with intestinal health and diseases include metabolically-active gut microbiota, intestinal epithelium, immune components, and rhythmical bowel movement known as peristalsis. Human intestinal disease models have been developed; however, a considerable number of existing models often fail to reproducibly predict human intestinal pathophysiology in response to biological and chemical perturbations or clinical interventions. Intestinal organoid models have provided promising cytodifferentiation and regeneration, but the lack of luminal flow and physical bowel movements seriously hamper mimicking complex host-microbe crosstalk. Here, we discuss recent advances of human intestinal microphysiological systems, such as the biomimetic human “Gut-on-a-Chip” that can employ key intestinal components, such as villus epithelium, gut microbiota, and immune components under peristalsis-like motions and flow, to reconstitute the transmural 3D lumen-capillary tissue interface. By encompassing cutting-edge tools in microfluidics, tissue engineering, and clinical microbiology, gut-on-a-chip has been leveraged not only to recapitulate organ-level intestinal functions, but also emulate the pathophysiology of intestinal disorders, such as chronic inflammation. Finally, we provide potential perspectives of the next generation microphysiological systems as a personalized platform to validate the efficacy, safety, metabolism, and therapeutic responses of new drug compounds in the preclinical stage. Full article

(This article belongs to the Special Issue Microfluidic Bioreactors and Organ-on-Chip Devices for Drug Screening and Disease Modeling)

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Full article ">Figure 1
Schematics of static culture models using human intestinal epithelial cells: (a) an epithelial monolayer has been grown on a semipermeable insert in the Transwell; (b) a collagen membrane patterned with crypt-like topography is incorporated in replacement of the porous membrane in the Transwell [<a href="#B34-micromachines-07-00107" class="html-bibr">34</a>]. Caco-2 cells (orange) can overlay the topological collagen surface to form a monolayer; and (c) a pseudo-3D intestine model has the hydrogel-based villous microarchitecture. An inset image shows a top view of Caco-2 cells grown on villous scaffolds. Reproduced by permission of John Wiley and Sons. All rights reserved [<a href="#B35-micromachines-07-00107" class="html-bibr">35</a>]. Full article ">Figure 2
Schematic illustrations of microfluidic models mimicking human intestinal pathophysiology: (a) a microfluidic device consists of upper (AP side) and lower (BL side) layers integrated with stirrer-based micropumps and optical fibers. Caco-2 cells are cultured on a semipermeable membrane in the AP side culture chamber. Reproduced by permission of the Royal Society of Chemistry. All rights reserved [<a href="#B57-micromachines-07-00107" class="html-bibr">57</a>]; (b) a cross-section view of a microfluidic device to evaluate intestinal absorption under fluidic conditions. Reproduced by permission of The Japan Society for Analytical Chemistry. All rights reserved [<a href="#B58-micromachines-07-00107" class="html-bibr">58</a>]; and (c) a microfluidic model for the co-culture of epithelial and bacterial cells. The device provides pneumatically-actuated trapping regions for providing bacterial islands around epithelial cells. Each bacterial island (1200 mm in diameter with 1000 mm in distance) has a separate inlet and an outlet for providing nutrients and removing wastes from the island. Reproduced by permission of Royal Society of Chemistry. All rights reserved [<a href="#B62-micromachines-07-00107" class="html-bibr">62</a>]. Full article ">Figure 3
An organomimetic human gut-on-a-chip microphysiological system: (a) a photographic image of a gut-on-a-chip microdevice. Arrows indicate the direction of flow in the microchannels (blue, luminal flow; red, capillary flow); (b) a schematic of a gut-on-a-chip displaying the flexible nature to exert peristalsis-like, vacuum-driven mechanical deformations. VC, vacuum chamber; and (c) an overlaid confocal immunofluorescence image showing a horizontal cross-section view of intestinal villi co-cultured with GFP E. coli (green). Brush border membrane (F-actin, red) and nuclei (DAPI, blue) are fluorescently highlighted. Full article ">Figure 4
A simplified schematic illustration comparing the human intestinal microenvironment in healthy versus diseased conditions caused by chronic inflammation. In the diseased condition, inflamed intestinal microenvironment results in the leaky gut epithelium in accordance with the infection of pathogenic bacteria, increased level of bacterial endotoxins such as lipopolysaccharides (LPS), and recruitment of circulating immune cells. Full article ">Figure 5
A schematic diagram of the transcytosis of monoclonal antibody (mAb) drugs across the lumen-mesenchyme-capillary tissue interface. Intravenously-administered mAb drugs (blue) bind to the neonatal Fc receptor (FcRn), in which the internalized endosome functions as a vehicle to carry this complex from the capillary layer into the lamina propria (a right bottom inset with a dotted circle). Released mAb drugs capture disposed proinflammatory cytokines (secreted by activated immune cells during IBD. Orally-delivered mAb drugs (red) can also be tested in this microphysiological system in situ (a right top inset with a dotted circle). Full article ">

5404 KiB

Open AccessReview

Cell Monitoring and Manipulation Systems (CMMSs) based on Glass Cell-Culture Chips (GC³s)

by Sebastian M. Buehler, Marco Stubbe, Sebastian M. Bonk, Matthias Nissen, Kanokkan Titipornpun, Ernst-Dieter Klinkenberg, Werner Baumann and Jan Gimsa

Micromachines 2016, 7(7), 106; https://doi.org/10.3390/mi7070106 - 24 Jun 2016

Cited by 13 | Viewed by 8639

Abstract

We developed different types of glass cell-culture chips (GC³s) for culturing cells for microscopic observation in open media-containing troughs or in microfluidic structures. Platinum sensor and manipulation structures were used to monitor physiological parameters and to allocate and permeabilize cells. Electro-thermal [...] Read more.

We developed different types of glass cell-culture chips (GC³s) for culturing cells for microscopic observation in open media-containing troughs or in microfluidic structures. Platinum sensor and manipulation structures were used to monitor physiological parameters and to allocate and permeabilize cells. Electro-thermal micro pumps distributed chemical compounds in the microfluidic systems. The integrated temperature sensors showed a linear, Pt1000-like behavior. Cell adhesion and proliferation were monitored using interdigitated electrode structures (IDESs). The cell-doubling times of primary murine embryonic neuronal cells (PNCs) were determined based on the IDES capacitance-peak shifts. The electrical activity of PNC networks was detected using multi-electrode arrays (MEAs). During seeding, the cells were dielectrophoretically allocated to individual MEAs to improve network structures. MEA pads with diameters of 15, 20, 25, and 35 µm were tested. After 3 weeks, the magnitudes of the determined action potentials were highest for pads of 25 µm in diameter and did not differ when the inter-pad distances were 100 or 170 µm. Using 25-µm diameter circular oxygen electrodes, the signal currents in the cell-culture media were found to range from approximately −0.08 nA (0% O₂) to −2.35 nA (21% O₂). It was observed that 60-nm thick silicon nitride-sensor layers were stable potentiometric pH sensors under cell-culture conditions for periods of days. Their sensitivity between pH 5 and 9 was as high as 45 mV per pH step. We concluded that sensorized GC³s are potential animal replacement systems for purposes such as toxicity pre-screening. For example, the effect of mefloquine, a medication used to treat malaria, on the electrical activity of neuronal cells was determined in this study using a GC³ system. Full article

(This article belongs to the Special Issue Advances in Microfluidic Devices for Cell Handling and Analysis)

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Micromachines, Volume 7, Issue 7 (July 2016) – 22 articles

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