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Editor’s Choice Articles

Editor’s Choice articles are based on recommendations by the scientific editors of MDPI journals from around the world. Editors select a small number of articles recently published in the journal that they believe will be particularly interesting to readers, or important in the respective research area. The aim is to provide a snapshot of some of the most exciting work published in the various research areas of the journal.

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12 pages, 3173 KiB  
Article
Microfluidic Viscometer Using a Suspending Micromembrane for Measurement of Biosamples
by Lelin Liu, Dinglong Hu and Raymond H. W. Lam
Micromachines 2020, 11(10), 934; https://doi.org/10.3390/mi11100934 - 14 Oct 2020
Cited by 19 | Viewed by 3545
Abstract
The viscosity of biofluids such as blood and saliva can reflect an individual’s health conditions, and viscosity measurements are therefore considered in health monitoring and disease diagnosis. However, conventional viscometers can only handle a larger liquid volume beyond the quantity that can be [...] Read more.
The viscosity of biofluids such as blood and saliva can reflect an individual’s health conditions, and viscosity measurements are therefore considered in health monitoring and disease diagnosis. However, conventional viscometers can only handle a larger liquid volume beyond the quantity that can be extracted from a person. Though very effective, micro-sensors based on electrokinetic, ultrasonic, or other principles often have strict requirements for the supporting equipment and complicated procedures and signal processing. Sample contamination is always an important issue. In this paper, we report a microfluidic viscometer requiring a small volume of biosamples (<50 µL) and straightforward operation procedures. It is fabricated with low-cost and biocompatible polymeric materials as one-time-use devices, such that contamination is no longer the concern. It contains a suspending micromembrane located along a microchannel. Under a steady driving pressure, the membrane displacement is a function of viscosity of the liquid sample being tested. We derived a simple analytical relation and perform a simulation for converting the membrane displacement to the sample viscosity. We conducted experiments with liquids (water and mineral oil) with defined properties to verify such a relation. We further applied the micro-viscometer to measure bovine blood samples with different hematocrit levels. It can be concluded that the microfluidic viscometer has a high compatibility with a broad range of biomedical applications. Full article
(This article belongs to the Section E：Engineering and Technology)
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42 pages, 14997 KiB  
Review
MEMS Ultrasound Transducers for Endoscopic Photoacoustic Imaging Applications
by Haoran Wang, Yifei Ma, Hao Yang, Huabei Jiang, Yingtao Ding and Huikai Xie
Micromachines 2020, 11(10), 928; https://doi.org/10.3390/mi11100928 - 12 Oct 2020
Cited by 33 | Viewed by 9854
Abstract
Photoacoustic imaging (PAI) is drawing extensive attention and gaining rapid development as an emerging biomedical imaging technology because of its high spatial resolution, large imaging depth, and rich optical contrast. PAI has great potential applications in endoscopy, but the progress of endoscopic PAI [...] Read more.
Photoacoustic imaging (PAI) is drawing extensive attention and gaining rapid development as an emerging biomedical imaging technology because of its high spatial resolution, large imaging depth, and rich optical contrast. PAI has great potential applications in endoscopy, but the progress of endoscopic PAI was hindered by the challenges of manufacturing and assembling miniature imaging components. Over the last decade, microelectromechanical systems (MEMS) technology has greatly facilitated the development of photoacoustic endoscopes and extended the realm of applicability of the PAI. As the key component of photoacoustic endoscopes, micromachined ultrasound transducers (MUTs), including piezoelectric MUTs (pMUTs) and capacitive MUTs (cMUTs), have been developed and explored for endoscopic PAI applications. In this article, the recent progress of pMUTs (thickness extension mode and flexural vibration mode) and cMUTs are reviewed and discussed with their applications in endoscopic PAI. Current PAI endoscopes based on pMUTs and cMUTs are also introduced and compared. Finally, the remaining challenges and future directions of MEMS ultrasound transducers for endoscopic PAI applications are given. Full article
(This article belongs to the Special Issue MEMS for Ultrasound)
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15 pages, 4573 KiB  
Article
A Scalable and Low Stress Post-CMOS Processing Technique for Implantable Microsensors
by Ah-Hyoung Lee, Jihun Lee, Farah Laiwalla, Vincent Leung, Jiannan Huang, Arto Nurmikko and Yoon-Kyu Song
Micromachines 2020, 11(10), 925; https://doi.org/10.3390/mi11100925 - 5 Oct 2020
Cited by 14 | Viewed by 5315
Abstract
Implantable active electronic microchips are being developed as multinode in-body sensors and actuators. There is a need to develop high throughput microfabrication techniques applicable to complementary metal–oxide–semiconductor (CMOS)-based silicon electronics in order to process bare dies from a foundry to physiologically compatible implant [...] Read more.
Implantable active electronic microchips are being developed as multinode in-body sensors and actuators. There is a need to develop high throughput microfabrication techniques applicable to complementary metal–oxide–semiconductor (CMOS)-based silicon electronics in order to process bare dies from a foundry to physiologically compatible implant ensembles. Post-processing of a miniature CMOS chip by usual methods is challenging as the typically sub-mm size small dies are hard to handle and not readily compatible with the standard microfabrication, e.g., photolithography. Here, we present a soft material-based, low chemical and mechanical stress, scalable microchip post-CMOS processing method that enables photolithography and electron-beam deposition on hundreds of micrometers scale dies. The technique builds on the use of a polydimethylsiloxane (PDMS) carrier substrate, in which the CMOS chips were embedded and precisely aligned, thereby enabling batch post-processing without complication from additional micromachining or chip treatments. We have demonstrated our technique with 650 μm × 650 μm and 280 μm × 280 μm chips, designed for electrophysiological neural recording and microstimulation implants by monolithic integration of patterned gold and PEDOT:PSS electrodes on the chips and assessed their electrical properties. The functionality of the post-processed chips was verified in saline, and ex vivo experiments using wireless power and data link, to demonstrate the recording and stimulation performance of the microscale electrode interfaces. Full article
(This article belongs to the Special Issue Implantable Neural Sensors for the Brain Machine Interface)
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10 pages, 4545 KiB  
Article
Micropillar/Microwell Chip Assessment for Detoxification of Bisphenol A with Korean Pear (Pyrus pyrifolia)
by Dong Woo Lee, Moo-Yeal Lee, Sukkil Koh and Mihi Yang
Micromachines 2020, 11(10), 922; https://doi.org/10.3390/mi11100922 - 3 Oct 2020
Cited by 7 | Viewed by 4056
Abstract
A micropillar/microwell chip platform with 3D cultured liver cells has been used for HTP screening of hepatotoxicity of bisphenol A (BPA), an endocrine-disrupting chemical. We previously found the hepatotoxicity of BPA is alleviated by alcohol dehydrogenase (ADH) and aldehyde dehydrogenase 2 (ALDH2). In [...] Read more.
A micropillar/microwell chip platform with 3D cultured liver cells has been used for HTP screening of hepatotoxicity of bisphenol A (BPA), an endocrine-disrupting chemical. We previously found the hepatotoxicity of BPA is alleviated by alcohol dehydrogenase (ADH) and aldehyde dehydrogenase 2 (ALDH2). In this study, we have tested potential BPA detoxification with Korean pear (Pyrus pyrifolia) extract, stimulators of ADH and ALDH, as well as arbutin, a reference compound in the pears, on the micropillar/microwell chip platform with human liver cells. Surprisingly, the toxicity of BPA was reduced in the presence of Korean pear extract, indicated by significantly increased IC50 values. The IC50 value of BPA with Korean pear extract tested against HepG2 cells was shifted from 151 to 451 μM, whereas those tested against Hep3B cells was shifted from 110 to 204 μM. Among the tested various concentrations, 1.25, 2.5, and 5 mg/mL of the extract significantly reduced BPA toxicity (Ps < 0.05). However, there was no such detoxification effects with arbutin. This result was supported by changes in protein levels of ADH in the liver cells. Full article
(This article belongs to the Special Issue Lab-on-a-Chip Systems for Toxicology)
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21 pages, 5429 KiB  
Review
Acoustic Microfluidic Separation Techniques and Bioapplications: A Review
by Yuan Gao, Mengren Wu, Yang Lin and Jie Xu
Micromachines 2020, 11(10), 921; https://doi.org/10.3390/mi11100921 - 2 Oct 2020
Cited by 80 | Viewed by 9376
Abstract
Microfluidic separation technology has garnered significant attention over the past decade where particles are being separated at a micro/nanoscale in a rapid, low-cost, and simple manner. Amongst a myriad of separation technologies that have emerged thus far, acoustic microfluidic separation techniques are extremely [...] Read more.
Microfluidic separation technology has garnered significant attention over the past decade where particles are being separated at a micro/nanoscale in a rapid, low-cost, and simple manner. Amongst a myriad of separation technologies that have emerged thus far, acoustic microfluidic separation techniques are extremely apt to applications involving biological samples attributed to various advantages, including high controllability, biocompatibility, and non-invasive, label-free features. With that being said, downsides such as low throughput and dependence on external equipment still impede successful commercialization from laboratory-based prototypes. Here, we present a comprehensive review of recent advances in acoustic microfluidic separation techniques, along with exemplary applications. Specifically, an inclusive overview of fundamental theory and background is presented, then two sets of mechanisms underlying acoustic separation, bulk acoustic wave and surface acoustic wave, are introduced and discussed. Upon these summaries, we present a variety of applications based on acoustic separation. The primary focus is given to those associated with biological samples such as blood cells, cancer cells, proteins, bacteria, viruses, and DNA/RNA. Finally, we highlight the benefits and challenges behind burgeoning developments in the field and discuss the future perspectives and an outlook towards robust, integrated, and commercialized devices based on acoustic microfluidic separation. Full article
(This article belongs to the Special Issue Microfluidic Sensors II)
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14 pages, 2188 KiB  
Article
Graphene-Based Contacts for Optoelectronic Devices
by Susana Fernández, Antonio Molinero, David Sanz, José Pablo González, Marina de la Cruz, José Javier Gandía and Julio Cárabe
Micromachines 2020, 11(10), 919; https://doi.org/10.3390/mi11100919 - 1 Oct 2020
Cited by 12 | Viewed by 3661
Abstract
Hybrid transparent contacts based on combinations of a transparent conductive oxide and a few graphene monolayers were developed in order to evaluate their optical and electrical performance with the main aim to use them as front contacts in optoelectronic devices. The assessment of [...] Read more.
Hybrid transparent contacts based on combinations of a transparent conductive oxide and a few graphene monolayers were developed in order to evaluate their optical and electrical performance with the main aim to use them as front contacts in optoelectronic devices. The assessment of the most suitable strategies for their fabrication was performed by testing different protocols addressing such issues as the protection of the device structure underneath, the limitation of sample temperature during the graphene-monolayer transfer process and the determination of the most suitable stacking structure. Suitable metal ohmic electrodes were also evaluated. Among a number of options tested, the metal contact based on Ti + Ag showed the highest reproducibility and the lowest contact resistivity. Finally, with the objective of extracting the current generated from optoelectronic devices to the output pins of an external package, focusing on a near future commercial application, the electrical properties of the connections made with an ultrasonic bonding machine (sonic welding) between the optimized Ti + Ag metal contacts and Al or Au micro-wires were also evaluated. All these results have an enormous potential as hybrid electrodes based on graphene to be used in novel designs of a future generation of optoelectronic devices, such as solar cells. Full article
(This article belongs to the Special Issue Graphene based Electronic Devices)
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13 pages, 3601 KiB  
Article
Toward Vasculature in Skeletal Muscle-on-a-Chip through Thermo-Responsive Sacrificial Templates
by Li Wan, James Flegle, Burak Ozdoganlar and Philip R. LeDuc
Micromachines 2020, 11(10), 907; https://doi.org/10.3390/mi11100907 - 30 Sep 2020
Cited by 17 | Viewed by 4811
Abstract
Developing new approaches for vascularizing synthetic tissue systems will have a tremendous impact in diverse areas. One area where this is particularly important is developing new skeletal muscle tissue systems, which could be utilized in physiological model studies and tissue regeneration. To develop [...] Read more.
Developing new approaches for vascularizing synthetic tissue systems will have a tremendous impact in diverse areas. One area where this is particularly important is developing new skeletal muscle tissue systems, which could be utilized in physiological model studies and tissue regeneration. To develop vascularized approaches a microfluidic on-chip design for creating channels in polymer systems can be pursued. Current microfluidic tissue engineering methods include soft lithography, rapid prototyping, and cell printing; however, these have limitations such as having their scaffolding being inorganic, less desirable planar vasculature geometry, low fabrication efficiency, and limited resolution. Here we successfully developed a circular microfluidic channel embedded in a 3D extracellular matrix scaffolding with 3D myogenesis. We used a thermo-responsive polymer approach with micromilling-molding and designed a mixture of polyester wax and paraffin wax to fabricate the sacrificial template for microfluidic channel generation in the scaffolding. These findings will impact a number of fields including biomaterials, biomimetic structures, and personalized medicine in the future. Full article
(This article belongs to the Special Issue Microengineered Physiological Systems for Disease Modeling and Drug Testing)
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15 pages, 12024 KiB  
Article
A Capacitive Pressure Sensor Interface IC with Wireless Power and Data Transfer
by Chaoping Zhang, Robert Gallichan, David M. Budgett and Daniel McCormick
Micromachines 2020, 11(10), 897; https://doi.org/10.3390/mi11100897 - 27 Sep 2020
Cited by 13 | Viewed by 4222
Abstract
This paper presents a capacitive pressure sensor interface circuit design in 180 nm XH018 CMOS technology for an implantable capacitive pressure sensor, which has a wireless power supply and wireless data transfer function. It integrates full-bridge rectifiers, shorting control switches, low-dropout regulators, bandgap [...] Read more.
This paper presents a capacitive pressure sensor interface circuit design in 180 nm XH018 CMOS technology for an implantable capacitive pressure sensor, which has a wireless power supply and wireless data transfer function. It integrates full-bridge rectifiers, shorting control switches, low-dropout regulators, bandgap references, analog front end, single slope analog to digital converter (ADC), I2C, and an RC oscillator. The low-dropout regulators regulate the wireless power supply coming from the rectifier and provide a stable and accurate 1.8 V DC voltage to other blocks. The capacitance of the pressure sensor is sampled to a discrete voltage by the analog front end. The single slope ADC converts the discrete voltage into 11 bits of digital data, which is then converted into 1 kbps serial data out by the I2C block. The “1” of serial data is modulated to a 500 kHz digital signal that is used to control the shorting switch for wireless data transfer via inductive back scatter. This capacitive pressure sensor interface IC has a resolution of 0.98 mmHg (1.4 fF), average total power consumption of 7.8 mW, and ±3.2% accuracy at the worst case under a −20 to 80 °C temperature range, which improves to ±0.86% when operated between 20 and 60 °C. Full article
(This article belongs to the Special Issue Power Electronics and Sensors)
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41 pages, 4549 KiB  
Review
Recent Advances of Wearable Antennas in Materials, Fabrication Methods, Designs, and Their Applications: State-of-the-Art
by Shahid M. Ali, Cheab Sovuthy, Muhammad A. Imran, Soeung Socheatra, Qammer H. Abbasi and Zuhairiah Zainal Abidin
Micromachines 2020, 11(10), 888; https://doi.org/10.3390/mi11100888 - 24 Sep 2020
Cited by 77 | Viewed by 8947
Abstract
The demand for wearable technologies has grown tremendously in recent years. Wearable antennas are used for various applications, in many cases within the context of wireless body area networks (WBAN). In WBAN, the presence of the human body poses a significant challenge to [...] Read more.
The demand for wearable technologies has grown tremendously in recent years. Wearable antennas are used for various applications, in many cases within the context of wireless body area networks (WBAN). In WBAN, the presence of the human body poses a significant challenge to the wearable antennas. Specifically, such requirements are required to be considered on a priority basis in the wearable antennas, such as structural deformation, precision, and accuracy in fabrication methods and their size. Various researchers are active in this field and, accordingly, some significant progress has been achieved recently. This article attempts to critically review the wearable antennas especially in light of new materials and fabrication methods, and novel designs, such as miniaturized button antennas and miniaturized single and multi-band antennas, and their unique smart applications in WBAN. Finally, the conclusion has been drawn with respect to some future directions. Full article
(This article belongs to the Special Issue Future Wearable and Implants)
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21 pages, 3226 KiB  
Review
Advances in Label-Free Detections for Nanofluidic Analytical Devices
by Thu Hac Huong Le, Hisashi Shimizu and Kyojiro Morikawa
Micromachines 2020, 11(10), 885; https://doi.org/10.3390/mi11100885 - 23 Sep 2020
Cited by 19 | Viewed by 4284
Abstract
Nanofluidics, a discipline of science and engineering of fluids confined to structures at the 1–1000 nm scale, has experienced significant growth over the past decade. Nanofluidics have offered fascinating platforms for chemical and biological analyses by exploiting the unique characteristics of liquids and [...] Read more.
Nanofluidics, a discipline of science and engineering of fluids confined to structures at the 1–1000 nm scale, has experienced significant growth over the past decade. Nanofluidics have offered fascinating platforms for chemical and biological analyses by exploiting the unique characteristics of liquids and molecules confined in nanospaces; however, the difficulty to detect molecules in extremely small spaces hampers the practical applications of nanofluidic devices. Laser-induced fluorescence microscopy with single-molecule sensitivity has been so far a major detection method in nanofluidics, but issues arising from labeling and photobleaching limit its application. Recently, numerous label-free detection methods have been developed to identify and determine the number of molecules, as well as provide chemical, conformational, and kinetic information of molecules. This review focuses on label-free detection techniques designed for nanofluidics; these techniques are divided into two groups: optical and electrical/electrochemical detection methods. In this review, we discuss on the developed nanofluidic device architectures, elucidate the mechanisms by which the utilization of nanofluidics in manipulating molecules and controlling light–matter interactions enhances the capabilities of biological and chemical analyses, and highlight new research directions in the field of detections in nanofluidics. Full article
(This article belongs to the Special Issue Advances in Nanofluidics)
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13 pages, 1848 KiB  
Article
Single-Cell Elasticity Measurement with an Optically Actuated Microrobot
by István Grexa, Tamás Fekete, Judit Molnár, Kinga Molnár, Gaszton Vizsnyiczai, Pál Ormos and Lóránd Kelemen
Micromachines 2020, 11(9), 882; https://doi.org/10.3390/mi11090882 - 22 Sep 2020
Cited by 18 | Viewed by 3594
Abstract
A cell elasticity measurement method is introduced that uses polymer microtools actuated by holographic optical tweezers. The microtools were prepared with two-photon polymerization. Their shape enables the approach of the cells in any lateral direction. In the presented case, endothelial cells grown on [...] Read more.
A cell elasticity measurement method is introduced that uses polymer microtools actuated by holographic optical tweezers. The microtools were prepared with two-photon polymerization. Their shape enables the approach of the cells in any lateral direction. In the presented case, endothelial cells grown on vertical polymer walls were probed by the tools in a lateral direction. The use of specially shaped microtools prevents the target cells from photodamage that may arise during optical trapping. The position of the tools was recorded simply with video microscopy and analyzed with image processing methods. We critically compare the resulting Young’s modulus values to those in the literature obtained by other methods. The application of optical tweezers extends the force range available for cell indentations measurements down to the fN regime. Our approach demonstrates a feasible alternative to the usual vertical indentation experiments. Full article
(This article belongs to the Special Issue New Trends and Applications in Femtosecond Laser Micromachining)
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12 pages, 3021 KiB  
Article
Fused Deposition Modeling of Microfluidic Chips in Polymethylmethacrylate
by Frederik Kotz, Markus Mader, Nils Dellen, Patrick Risch, Andrea Kick, Dorothea Helmer and Bastian E. Rapp
Micromachines 2020, 11(9), 873; https://doi.org/10.3390/mi11090873 - 19 Sep 2020
Cited by 64 | Viewed by 7166
Abstract
Polymethylmethacrylate (PMMA) is one of the most important thermoplastic materials and is a widely used material in microfluidics. However, PMMA is usually structured using industrial scale replication processes, such as hot embossing or injection molding, not compatible with rapid prototyping. In this work, [...] Read more.
Polymethylmethacrylate (PMMA) is one of the most important thermoplastic materials and is a widely used material in microfluidics. However, PMMA is usually structured using industrial scale replication processes, such as hot embossing or injection molding, not compatible with rapid prototyping. In this work, we demonstrate that microfluidic chips made from PMMA can be 3D printed using fused deposition modeling (FDM). We demonstrate that using FDM microfluidic chips with a minimum channel cross-section of ~300 µm can be printed and a variety of different channel geometries and mixer structures are shown. The optical transparency of the chips is shown to be significantly enhanced by printing onto commercial PMMA substrates. The use of such commercial PMMA substrates also enables the integration of PMMA microstructures into the printed chips, by first generating a microstructure on the PMMA substrates, and subsequently printing the PMMA chip around the microstructure. We further demonstrate that protein patterns can be generated within previously printed microfluidic chips by employing a method of photobleaching. The FDM printing of microfluidic chips in PMMA allows the use of one of microfluidics’ most used industrial materials on the laboratory scale and thus significantly simplifies the transfer from results gained in the lab to an industrial product. Full article
(This article belongs to the Special Issue 3D Printing of MEMS Technology)
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21 pages, 5529 KiB  
Review
A Review and Perspective for the Development of Triboelectric Nanogenerator (TENG)-Based Self-Powered Neuroprosthetics
by Hao Wang, Tianzhun Wu, Qi Zeng and Chengkuo Lee
Micromachines 2020, 11(9), 865; https://doi.org/10.3390/mi11090865 - 18 Sep 2020
Cited by 28 | Viewed by 6467
Abstract
Neuroprosthetics have become a powerful toolkit for clinical interventions of various diseases that affect the central nervous or peripheral nervous systems, such as deep brain stimulation (DBS), functional electrical stimulation (FES), and vagus nerve stimulation (VNS), by electrically stimulating different neuronal structures. To [...] Read more.
Neuroprosthetics have become a powerful toolkit for clinical interventions of various diseases that affect the central nervous or peripheral nervous systems, such as deep brain stimulation (DBS), functional electrical stimulation (FES), and vagus nerve stimulation (VNS), by electrically stimulating different neuronal structures. To prolong the lifetime of implanted devices, researchers have developed power sources with different approaches. Among them, the triboelectric nanogenerator (TENG) is the only one to achieve direct nerve stimulations, showing great potential in the realization of a self-powered neuroprosthetic system in the future. In this review, the current development and progress of the TENG-based stimulation of various kinds of nervous systems are systematically summarized. Then, based on the requirements of the neuroprosthetic system in a real application and the development of current techniques, a perspective of a more sophisticated neuroprosthetic system is proposed, which includes components of a thin-film TENG device with a biocompatible package, an amplification circuit to enhance the output, and a self-powered high-frequency switch to generate high-frequency current pulses for nerve stimulations. Then, we review and evaluate the recent development and progress of each part. Full article
(This article belongs to the Special Issue Implantable Microdevices, Volume II)
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24 pages, 3665 KiB  
Review
Microphysiological Systems for Neurodegenerative Diseases in Central Nervous System
by Mihyeon Bae, Hee-Gyeong Yi, Jinah Jang and Dong-Woo Cho
Micromachines 2020, 11(9), 855; https://doi.org/10.3390/mi11090855 - 16 Sep 2020
Cited by 11 | Viewed by 5684
Abstract
Neurodegenerative diseases are among the most severe problems in aging societies. Various conventional experimental models, including 2D and animal models, have been used to investigate the pathogenesis of (and therapeutic mechanisms for) neurodegenerative diseases. However, the physiological gap between humans and the current [...] Read more.
Neurodegenerative diseases are among the most severe problems in aging societies. Various conventional experimental models, including 2D and animal models, have been used to investigate the pathogenesis of (and therapeutic mechanisms for) neurodegenerative diseases. However, the physiological gap between humans and the current models remains a hurdle to determining the complexity of an irreversible dysfunction in a neurodegenerative disease. Therefore, preclinical research requires advanced experimental models, i.e., those more physiologically relevant to the native nervous system, to bridge the gap between preclinical stages and patients. The neural microphysiological system (neural MPS) has emerged as an approach to summarizing the anatomical, biochemical, and pathological physiology of the nervous system for investigation of neurodegenerative diseases. This review introduces the components (such as cells and materials) and fabrication methods for designing a neural MPS. Moreover, the review discusses future perspectives for improving the physiological relevance to native neural systems. Full article
(This article belongs to the Special Issue Microengineered Physiological Systems for Disease Modeling and Drug Testing)
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12 pages, 8357 KiB  
Communication
Single-Cell Electroporation with Real-Time Impedance Assessment Using a Constriction Microchannel
by Yifei Ye, Xiaofeng Luan, Lingqian Zhang, Wenjie Zhao, Jie Cheng, Mingxiao Li, Yang Zhao and Chengjun Huang
Micromachines 2020, 11(9), 856; https://doi.org/10.3390/mi11090856 - 16 Sep 2020
Cited by 10 | Viewed by 4252
Abstract
The electroporation system can serve as a tool for the intracellular delivery of foreign cargos. However, this technique is presently limited by the inaccurate electric field applied to the single cells and lack of a real-time electroporation metrics subsystem. Here, we reported a [...] Read more.
The electroporation system can serve as a tool for the intracellular delivery of foreign cargos. However, this technique is presently limited by the inaccurate electric field applied to the single cells and lack of a real-time electroporation metrics subsystem. Here, we reported a microfluidic system for precise and rapid single-cell electroporation and simultaneous impedance monitoring in a constriction microchannel. When single cells (A549) were continuously passing through the constriction microchannel, a localized high electric field was applied on the cell membrane, which resulted in highly efficient (up to 96.6%) electroporation. During a single cell entering the constriction channel, an abrupt impedance drop was noticed and demonstrated to be correlated with the occurrence of electroporation. Besides, while the cell was moving in the constriction channel, the stabilized impedance showed the capability to quantify the electroporation extent. The correspondence of the impedance variation and electroporation was validated by the intracellular delivery of the fluorescence indicator (propidium iodide). Based on the obtained results, this system is capable of precise control of electroporation and real-time, label-free impedance assessment, providing a potential tool for intracellular delivery and other biomedical applications. Full article
(This article belongs to the Special Issue Microfluidics for Cells and Other Organisms, Volume II)
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25 pages, 2719 KiB  
Review
Immune Organs and Immune Cells on a Chip: An Overview of Biomedical Applications
by Margaretha A. J. Morsink, Niels G. A. Willemen, Jeroen Leijten, Ruchi Bansal and Su Ryon Shin
Micromachines 2020, 11(9), 849; https://doi.org/10.3390/mi11090849 - 12 Sep 2020
Cited by 45 | Viewed by 11556
Abstract
Understanding the immune system is of great importance for the development of drugs and the design of medical implants. Traditionally, two-dimensional static cultures have been used to investigate the immune system in vitro, while animal models have been used to study the immune [...] Read more.
Understanding the immune system is of great importance for the development of drugs and the design of medical implants. Traditionally, two-dimensional static cultures have been used to investigate the immune system in vitro, while animal models have been used to study the immune system’s function and behavior in vivo. However, these conventional models do not fully emulate the complexity of the human immune system or the human in vivo microenvironment. Consequently, many promising preclinical findings have not been reproduced in human clinical trials. Organ-on-a-chip platforms can provide a solution to bridge this gap by offering human micro-(patho)physiological systems in which the immune system can be studied. This review provides an overview of the existing immune-organs-on-a-chip platforms, with a special emphasis on interorgan communication. In addition, future challenges to develop a comprehensive immune system-on-chip model are discussed. Full article
(This article belongs to the Special Issue Microengineered Physiological Systems for Disease Modeling and Drug Testing)
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14 pages, 8218 KiB  
Article
Single-Cell Mechanophenotyping in Microfluidics to Evaluate Behavior of U87 Glioma Cells
by Esra Sengul and Meltem Elitas
Micromachines 2020, 11(9), 845; https://doi.org/10.3390/mi11090845 - 11 Sep 2020
Cited by 10 | Viewed by 4281
Abstract
Integration of microfabricated, single-cell resolution and traditional, population-level biological assays will be the future of modern techniques in biology that will enroll in the evolution of biology into a precision scientific discipline. In this study, we developed a microfabricated cell culture platform to [...] Read more.
Integration of microfabricated, single-cell resolution and traditional, population-level biological assays will be the future of modern techniques in biology that will enroll in the evolution of biology into a precision scientific discipline. In this study, we developed a microfabricated cell culture platform to investigate the indirect influence of macrophages on glioma cell behavior. We quantified proliferation, morphology, motility, migration, and deformation properties of glioma cells at single-cell level and compared these results with population-level data. Our results showed that glioma cells obtained slightly slower proliferation, higher motility, and extremely significant deformation capability when cultured with 50% regular growth medium and 50% macrophage-depleted medium. When the expression levels of E-cadherin and Vimentin proteins were measured, it was verified that observed mechanophenotypic alterations in glioma cells were not due to epithelium to mesenchymal transition. Our results were consistent with previously reported enormous heterogeneity of U87 glioma cell line. Herein, for the first time, we quantified the change of deformation indexes of U87 glioma cells using microfluidic devices for single-cells analysis. Full article
(This article belongs to the Special Issue Micro/Nanofluidic Devices for Single Cell Analysis, Volume II)
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10 pages, 18929 KiB  
Article
Microfluidic Separation of Blood Cells Based on the Negative Dielectrophoresis Operated by Three Dimensional Microband Electrodes
by Tomoyuki Yasukawa, Junko Yamada, Hitoshi Shiku, Tomokazu Matsue and Masato Suzuki
Micromachines 2020, 11(9), 833; https://doi.org/10.3390/mi11090833 - 31 Aug 2020
Cited by 9 | Viewed by 3366
Abstract
A microfluidic device is presented for the continuous separation of red blood cells (RBCs) and white blood cells (WBCs) in a label-free manner based on negative dielectrophoresis (n-DEP). An alteration of the electric field, generated by pairs of slanted electrodes (separators) that is [...] Read more.
A microfluidic device is presented for the continuous separation of red blood cells (RBCs) and white blood cells (WBCs) in a label-free manner based on negative dielectrophoresis (n-DEP). An alteration of the electric field, generated by pairs of slanted electrodes (separators) that is fabricated by covering parts of single slanted electrodes with an insulating layer is used to separate cells by their sizes. The repulsive force of n-DEP formed by slanted electrodes prepared on both the top and bottom substrates led to the deflection of the cell flow in lateral directions. The presence of gaps covered with an insulating layer for the electric field on the electrodes allows the passing of RBCs through gaps, while relatively large WBCs (cultured cultured human acute monocytic leukemia cell line (THP-1 cells)) flowed along the slanted separator without passing through the gaps and arrived at an edge in the channel. The passage efficiency for RBCs through the gaps and the arrival efficiency for THP-1 cells to the upper edge in the channel were estimated and found to be 91% and 93%, respectively. Full article
(This article belongs to the Special Issue Micro and Nano Devices for Cell Analysis)
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25 pages, 3154 KiB  
Review
Electrical Impedance Spectroscopy for Monitoring Chemoresistance of Cancer Cells
by Lexi L. Crowell, Juan S. Yakisich, Brian Aufderheide and Tayloria N. G. Adams
Micromachines 2020, 11(9), 832; https://doi.org/10.3390/mi11090832 - 31 Aug 2020
Cited by 37 | Viewed by 6295
Abstract
Electrical impedance spectroscopy (EIS) is an electrokinetic method that allows for the characterization of intrinsic dielectric properties of cells. EIS has emerged in the last decade as a promising method for the characterization of cancerous cells, providing information on inductance, capacitance, and impedance [...] Read more.
Electrical impedance spectroscopy (EIS) is an electrokinetic method that allows for the characterization of intrinsic dielectric properties of cells. EIS has emerged in the last decade as a promising method for the characterization of cancerous cells, providing information on inductance, capacitance, and impedance of cells. The individual cell behavior can be quantified using its characteristic phase angle, amplitude, and frequency measurements obtained by fitting the input frequency-dependent cellular response to a resistor–capacitor circuit model. These electrical properties will provide important information about unique biomarkers related to the behavior of these cancerous cells, especially monitoring their chemoresistivity and sensitivity to chemotherapeutics. There are currently few methods to assess drug resistant cancer cells, and therefore it is difficult to identify and eliminate drug-resistant cancer cells found in static and metastatic tumors. Establishing techniques for the real-time monitoring of changes in cancer cell phenotypes is, therefore, important for understanding cancer cell dynamics and their plastic properties. EIS can be used to monitor these changes. In this review, we will cover the theory behind EIS, other impedance techniques, and how EIS can be used to monitor cell behavior and phenotype changes within cancerous cells. Full article
(This article belongs to the Special Issue Microfluidic Devices for Biosensing)
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11 pages, 3103 KiB  
Article
Understanding of the Mechanism for Laser Ablation-Assisted Patterning of Graphene/ITO Double Layers: Role of Effective Thermal Energy Transfer
by Hyung Seok Ryu, Hong-Seok Kim, Daeyoon Kim, Sang Jun Lee, Wonjoon Choi, Sang Jik Kwon, Jae-Hee Han and Eou-Sik Cho
Micromachines 2020, 11(9), 821; https://doi.org/10.3390/mi11090821 - 29 Aug 2020
Cited by 6 | Viewed by 3963
Abstract
Demand for the fabrication of high-performance, transparent electronic devices with improved electronic and mechanical properties is significantly increasing for various applications. In this context, it is essential to develop highly transparent and conductive electrodes for the realization of such devices. To this end, [...] Read more.
Demand for the fabrication of high-performance, transparent electronic devices with improved electronic and mechanical properties is significantly increasing for various applications. In this context, it is essential to develop highly transparent and conductive electrodes for the realization of such devices. To this end, in this work, a chemical vapor deposition (CVD)-grown graphene was transferred to both glass and polyethylene terephthalate (PET) substrates that had been pre-coated with an indium tin oxide (ITO) layer and then subsequently patterned by using a laser-ablation method for a low-cost, simple, and high-throughput process. A comparison of the results of the laser ablation of such a graphene/ITO double layer with those of the ITO single-layered films reveals that a larger amount of effective thermal energy of the laser used is transferred in the lateral direction along the graphene upper layer in the graphene/ITO double-layered structure, attributable to the high thermal conductivity of graphene. The transferred thermal energy is expected to melt and evaporate the lower ITO layer at a relatively lower threshold energy of laser ablation. The transient analysis of the temperature profiles indicates that the graphene layers can act as both an effective thermal diffuser and converter for the planar heat transfer. Raman spectroscopy was used to investigate the graphite peak on the ITO layer where the graphene upper layer was selectively removed because of the incomplete heating and removal process for the ITO layer by the laterally transferred effective thermal energy of the laser beam. Our approach could have broad implications for designing highly transparent and conductive electrodes as well as a new way of nanoscale patterning for other optoelectronic-device applications using laser-ablation methods. Full article
(This article belongs to the Special Issue Advanced Techniques for Ultrafast Laser Nano/Micro Patterning)
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11 pages, 8315 KiB  
Article
Improved High-Yield PMMA/Graphene Pressure Sensor and Sealed Gas Effect Analysis
by Ying Liu, Yong Zhang, Xin Lin, Ke-hong Lv, Peng Yang, Jing Qiu and Guan-jun Liu
Micromachines 2020, 11(9), 786; https://doi.org/10.3390/mi11090786 - 19 Aug 2020
Cited by 8 | Viewed by 3081
Abstract
Graphene with atomic thickness possesses excellent mechanical and electrical properties, which hold great potential for high performance pressure sensing. The exposed electron of graphene is always cross-sensitive to any pollution absorbed or desorbed on the surface, from which the long-term stability of the [...] Read more.
Graphene with atomic thickness possesses excellent mechanical and electrical properties, which hold great potential for high performance pressure sensing. The exposed electron of graphene is always cross-sensitive to any pollution absorbed or desorbed on the surface, from which the long-term stability of the graphene pressure sensor suffers a lot. This is one of the main obstacles towards graphene commercial applications. In this paper, we utilized polymethylmethacrylate (PMMA)/graphene heterostructure to isolate graphene from the ambient environment and enhance its strength simultaneously. PMMA/graphene pressure sensors, with the finite-depth cavities and the through-hole cavities separately, were made for comparative study. The through-hole device obtained a comparable sensitivity per unit area to the state of the art of the bare graphene pressure sensor, since there were no leaking cracks or defects. Both the sensitivity and stability of the through-hole sensor are better than those of the sensor with 285-nm-deep cavities, which is due to the sealed gas effect in the pressure cavity. A modified piezoresistive model was derived by considering the pressure change of the sealed gas in the pressure cavity. The calculated result of the new model is consistent with the experimental results. Our findings point out a promising route for performance optimization of graphene pressure sensors. Full article
(This article belongs to the Special Issue Graphene based Electronic Devices)
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16 pages, 8383 KiB  
Article
Random Access Addressing of MEMS Electrostatic Shutter Array for Multi-Object Astronomical Spectroscopy
by Xufeng Liu, Takuya Takahashi, Masahiro Konishi, Kentaro Motohara and Hiroshi Toshiyoshi
Micromachines 2020, 11(8), 782; https://doi.org/10.3390/mi11080782 - 17 Aug 2020
Cited by 4 | Viewed by 3779
Abstract
An extended version of cross-bar type addressing technique is developed for three-port electrostatic micro shutters arranged in an arrayed format. A microelectromechanical systems (MEMS) shutter blade suspended by a pair of torsion beams works as a movable electrode that is either attracted upwards [...] Read more.
An extended version of cross-bar type addressing technique is developed for three-port electrostatic micro shutters arranged in an arrayed format. A microelectromechanical systems (MEMS) shutter blade suspended by a pair of torsion beams works as a movable electrode that is either attracted upwards to the cover plate to close the aperture or retracted downwards into the through-hole to open it. Tri-state positioning of the shutter—i.e., open, rest, and close—is controlled by the hysteresis loop of the electrostatic pull-in and release behavior using the combination of the voltages applied to the shutter, the cover, and the substrate. Random access addressing of the shutters is demonstrated by a control system composed of MATLAB-coded Arduino electronics. The shutter array developed in this work is for a sub-cluster of a reconfigurable shutter array under development for a multi-object galactic astronomy. Full article
(This article belongs to the Special Issue Optical MEMS, Volume II)
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17 pages, 4661 KiB  
Article
Development of Fully Flexible Tactile Pressure Sensor with Bilayer Interlaced Bumps for Robotic Grasping Applications
by Lingfeng Zhu, Yancheng Wang, Deqing Mei and Chengpeng Jiang
Micromachines 2020, 11(8), 770; https://doi.org/10.3390/mi11080770 - 12 Aug 2020
Cited by 21 | Viewed by 5658
Abstract
Flexible tactile sensors have been utilized in intelligent robotics for human-machine interaction and healthcare monitoring. The relatively low flexibility, unbalanced sensitivity and sensing range of the tactile sensors are hindering the accurate tactile information perception during robotic hand grasping of different objects. This [...] Read more.
Flexible tactile sensors have been utilized in intelligent robotics for human-machine interaction and healthcare monitoring. The relatively low flexibility, unbalanced sensitivity and sensing range of the tactile sensors are hindering the accurate tactile information perception during robotic hand grasping of different objects. This paper developed a fully flexible tactile pressure sensor, using the flexible graphene and silver composites as the sensing element and stretchable electrodes, respectively. As for the structural design of the tactile sensor, the proposed bilayer interlaced bumps can be used to convert external pressure into the stretching of graphene composites. The fabricated tactile sensor exhibits a high sensing performance, including relatively high sensitivity (up to 3.40% kPa−1), wide sensing range (200 kPa), good dynamic response, and considerable repeatability. Then, the tactile sensor has been integrated with the robotic hand finger, and the grasping results have indicated the capability of using the tactile sensor to detect the distributed pressure during grasping applications. The grasping motions, properties of the objects can be further analyzed through the acquired tactile information in time and spatial domains, demonstrating the potential applications of the tactile sensor in intelligent robotics and human-machine interfaces. Full article
(This article belongs to the Special Issue Graphene based Electronic Devices)
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12 pages, 1376 KiB  
Article
Parallel-Channel Electrotaxis and Neuron Screening of Caenorhabditis elegans
by Khaled Youssef, Daphne Archonta, Terrance Kubiseski, Anurag Tandon and Pouya Rezai
Micromachines 2020, 11(8), 756; https://doi.org/10.3390/mi11080756 - 4 Aug 2020
Cited by 8 | Viewed by 3620
Abstract
In this paper, we report a novel microfluidic method to conduct a Caenorhabditis elegans electrotaxis movement assay and neuronal imaging on up to 16 worms in parallel. C. elegans is a model organism for neurodegenerative disease and movement disorders such as Parkinson’s disease [...] Read more.
In this paper, we report a novel microfluidic method to conduct a Caenorhabditis elegans electrotaxis movement assay and neuronal imaging on up to 16 worms in parallel. C. elegans is a model organism for neurodegenerative disease and movement disorders such as Parkinson’s disease (PD), and for screening chemicals that alleviate protein aggregation, neuronal death, and movement impairment in PD. Electrotaxis of C. elegans in microfluidic channels has led to the development of neurobehavioral screening platforms, but enhancing the throughput of the electrotactic behavioral assay has remained a challenge. Our device consisted of a hierarchy of tree-like channels for worm loading into 16 parallel electrotaxis screening channels with equivalent electric fields. Tapered channels at the ends of electrotaxis channels were used for worm immobilization and fluorescent imaging of neurons. Parallel electrotaxis of worms was first validated against established single-worm electrotaxis phenotypes. Then, mutant screening was demonstrated using the NL5901 strain, carrying human α-synuclein in the muscle cells, by showing the associated electrotaxis defects in the average speed, body bend frequency (BBF), and electrotaxis time index (ETI). Moreover, chemical screening of a PD worm model was shown by exposing the BZ555 strain, expressing green fluorescence protein (GFP) in the dopaminergic neurons (DNs), to 6-hydroxydopamine neurotoxin. The neurotoxin-treated worms exhibited a reduction in electrotaxis swimming speed, BBF, ETI, and DNs fluorescence intensity. We envision our technique to be used widely in C. elegans-based movement disorder assays to accelerate behavioral and cellular phenotypic investigations. Full article
(This article belongs to the Special Issue Organisms-on-Chips)
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14 pages, 5613 KiB  
Article
Facile Fabrication of Thin-Bottom Round-Well Plates Using the Deformation of PDMS Molds and Their Application for Single-Cell PCR
by Shinya Yamahira and Yuji Heike
Micromachines 2020, 11(8), 748; https://doi.org/10.3390/mi11080748 - 31 Jul 2020
Cited by 2 | Viewed by 5859
Abstract
Recently, microdevices made of resins have been strongly supporting cell analysis in a range of fields, from fundamental life science research to medical applications. Many microdevices are fabricated by molding resin to a mold made precisely from rigid materials. However, because dimensional errors [...] Read more.
Recently, microdevices made of resins have been strongly supporting cell analysis in a range of fields, from fundamental life science research to medical applications. Many microdevices are fabricated by molding resin to a mold made precisely from rigid materials. However, because dimensional errors in the mold are also accurately printed to the products, the accuracy of the product is limited to less than the accuracy of the rigid mold. Therefore, we hypothesized that if dimensional errors could be self-corrected by elastic molds, microdevices could be facilely fabricated with precision beyond that of molds. In this paper, we report a novel processing strategy in which an elastic mold made of polymethylsiloxane (PDMS) deforms to compensate for the dimensional error on the products. By heat-press molding a polycarbonate plate using a mold that has 384 PDMS convexes with a large dimensional error of height of ± 15.6 µm in standard deviation, a 384-round-well plate with a bottom thickness 13.3 ± 2.3 µm (n = 384) was easily fabricated. Finally, single-cell observation and polymerase chain reactions (PCRs) demonstrated the application of the products made by elastic PDMS molds. Therefore, this processing method is a promising strategy for facile, low-cost, and higher precision microfabrication. Full article
(This article belongs to the Special Issue Micro and Nano Devices for Cell Analysis)
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12 pages, 2972 KiB  
Article
Curved Structure of Si by Improving Etching Direction Controllability in Magnetically Guided Metal-Assisted Chemical Etching
by Tae Kyoung Kim, Jee-Hwan Bae, Juyoung Kim, Min Kyung Cho, Yu-Chan Kim, Sungho Jin and Dongwon Chun
Micromachines 2020, 11(8), 744; https://doi.org/10.3390/mi11080744 - 30 Jul 2020
Cited by 7 | Viewed by 4060
Abstract
Metal-assisted chemical etching (MACE) is widely used to fabricate micro-/nano-structured Si owing to its simplicity and cost-effectiveness. The technique of magnetically guided MACE, involving MACE with a tri-layer metal catalyst, was developed to improve etching speed as well as to adjust the etching [...] Read more.
Metal-assisted chemical etching (MACE) is widely used to fabricate micro-/nano-structured Si owing to its simplicity and cost-effectiveness. The technique of magnetically guided MACE, involving MACE with a tri-layer metal catalyst, was developed to improve etching speed as well as to adjust the etching direction using an external magnetic field. However, the controllability of the etching direction diminishes with an increase in the etching dimension, owing to the corrosion of Fe due to the etching solution; this impedes the wider application of this approach for the fabrication of complex micro Si structures. In this study, we modified a tri-layer metal catalyst (Au/Fe/Au), wherein the Fe layer was encapsulated to improve direction controllability; this improved controllability was achieved by protecting Fe against the corrosion caused by the etching solution. We demonstrated curved Si microgroove arrays via magnetically guided MACE with Fe encapsulated in the tri-layer catalyst. Furthermore, the curvature in the curved Si microarrays could be modulated via an external magnetic field, indicating that direction controllability could be maintained even for the magnetically guided MACE of bulk Si. The proposed fabrication method developed for producing curved Si microgroove arrays can be applied to electronic devices and micro-electromechanical systems. Full article
(This article belongs to the Special Issue Micro- and Nano-Fabrication by Metal Assisted Chemical Etching)
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12 pages, 5457 KiB  
Article
Single-Grain Gate-All-Around Si Nanowire FET Using Low-Thermal-Budget Processes for Monolithic Three-Dimensional Integrated Circuits
by Tung-Ying Hsieh, Ping-Yi Hsieh, Chih-Chao Yang, Chang-Hong Shen, Jia-Min Shieh, Wen-Kuan Yeh and Meng-Chyi Wu
Micromachines 2020, 11(8), 741; https://doi.org/10.3390/mi11080741 - 30 Jul 2020
Cited by 5 | Viewed by 4710
Abstract
We introduce a single-grain gate-all-around (GAA) Si nanowire (NW) FET using the location-controlled-grain technique and several innovative low-thermal budget processes, including green nanosecond laser crystallization, far-infrared laser annealing, and hybrid laser-assisted salicidation, that keep the substrate temperature (Tsub) lower than 400 [...] Read more.
We introduce a single-grain gate-all-around (GAA) Si nanowire (NW) FET using the location-controlled-grain technique and several innovative low-thermal budget processes, including green nanosecond laser crystallization, far-infrared laser annealing, and hybrid laser-assisted salicidation, that keep the substrate temperature (Tsub) lower than 400 °C for monolithic three-dimensional integrated circuits (3D-ICs). The detailed process verification of a low-defect GAA nanowire and electrical characteristics were investigated in this article. The GAA Si NW FETs, which were intentionally fabricated within the controlled Si grain, exhibit a steeper subthreshold swing (S.S.) of about 65 mV/dec., higher driving currents of 327 µA/µm (n-type) and 297 µA/µm (p-type) @ Vth ± 0.8 V, and higher Ion/Ioff (>105 @|Vd| = 1 V) and have a narrower electrical property distribution. In addition, the proposed Si NW FETs with a GAA structure were found to be less sensitive to Vth roll-off and S.S. degradation compared to the omega(Ω)-gate Si FETs. It enables ultrahigh-density sequentially stackable integrated circuits with superior performance and low power consumption for future mobile and neuromorphic applications. Full article
(This article belongs to the Special Issue Monolithic 3D Chips)
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13 pages, 1633 KiB  
Article
RhoA and Rac1 in Liver Cancer Cells: Induction of Overexpression Using Mechanical Stimulation
by Sharda Yadav, Navid Kashaninejad and Nam-Trung Nguyen
Micromachines 2020, 11(8), 729; https://doi.org/10.3390/mi11080729 - 28 Jul 2020
Cited by 16 | Viewed by 3146
Abstract
Liver cancer, especially hepatocellular carcinoma (HCC), is an aggressive disease with an extremely high mortality rate. Unfortunately, no promising markers are currently available for the early diagnosis of this disease. Thus, a reliable biomarker reflecting the early behaviour of the tumour will be [...] Read more.
Liver cancer, especially hepatocellular carcinoma (HCC), is an aggressive disease with an extremely high mortality rate. Unfortunately, no promising markers are currently available for the early diagnosis of this disease. Thus, a reliable biomarker reflecting the early behaviour of the tumour will be valuable for diagnosis and treatment. The Ras homologous (Rho) GTPases, which belong to the small guanosine triphosphate (GTP) binding proteins, have been reported to play an important role in mediating liver cancer based on their important function in cytoskeletal reorganisation. These proteins can be either oncogenic or tumour suppressors. They are also associated with the acquirement of malignant features by cancer cells. The overexpression of RhoA and Rac1, members of the Rho GTPases, have been linked with carcinogenesis and the progression of different types of cancer. In the quest of elucidating the role of mechanical stimulation in the mechanobiology of liver cancer cells, this paper evaluates the effect of stretching on the expression levels of RhoA and Rac1 in different types of liver cancers. It is shown that that stretching liver cancer cells significantly increases the expression levels of RhoA and Rac1 in HCC and cholangiocarcinoma cell lines. We hypothesise that this relatively simple and sensitive method could be helpful for screening biological features and provide suitable treatment guidance for liver cancer patients. Full article
(This article belongs to the Special Issue Mechanobiology and Biologically Inspired Engineering)
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20 pages, 4522 KiB  
Review
Recent Advances in Vertically Aligned Nanowires for Photonics Applications
by Sehui Chang, Gil Ju Lee and Young Min Song
Micromachines 2020, 11(8), 726; https://doi.org/10.3390/mi11080726 - 26 Jul 2020
Cited by 13 | Viewed by 5576
Abstract
Over the past few decades, nanowires have arisen as a centerpiece in various fields of application from electronics to photonics, and, recently, even in bio-devices. Vertically aligned nanowires are a particularly decent example of commercially manufacturable nanostructures with regard to its packing fraction [...] Read more.
Over the past few decades, nanowires have arisen as a centerpiece in various fields of application from electronics to photonics, and, recently, even in bio-devices. Vertically aligned nanowires are a particularly decent example of commercially manufacturable nanostructures with regard to its packing fraction and matured fabrication techniques, which is promising for mass-production and low fabrication cost. Here, we track recent advances in vertically aligned nanowires focused in the area of photonics applications. Begin with the core optical properties in nanowires, this review mainly highlights the photonics applications such as light-emitting diodes, lasers, spectral filters, structural coloration and artificial retina using vertically aligned nanowires with the essential fabrication methods based on top-down and bottom-up approaches. Finally, the remaining challenges will be briefly discussed to provide future directions. Full article
(This article belongs to the Special Issue Nanowires and Nanoprobes – Functionalized Arrays)
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14 pages, 14832 KiB  
Article
The Robot Selection Problem for Mini-Parallel Kinematic Machines: A Task-Driven Approach to the Selection Attributes Identification
by Cinzia Amici, Nicola Pellegrini and Monica Tiboni
Micromachines 2020, 11(8), 711; https://doi.org/10.3390/mi11080711 - 22 Jul 2020
Cited by 14 | Viewed by 2986
Abstract
In the last decades, the Robot Selection Problem (RSP) has been widely investigated, and the importance of properly structuring the decision problem has been stated. Crucial aspect in this process is the correct identification of the robot attributes, which should be limited in [...] Read more.
In the last decades, the Robot Selection Problem (RSP) has been widely investigated, and the importance of properly structuring the decision problem has been stated. Crucial aspect in this process is the correct identification of the robot attributes, which should be limited in number as much as possible, but should be also able to detect at best the peculiar requirements of specific applications. Literature describes several attributes examples, but mainly dedicated to traditional industrial tasks, and applied to the selection of conventional industrial robots. After a synthetic review of the robot attributes depicted in the RSP literature, presented with a custom taxonomy, this paper proposes a set of possible requirements for the selection problem of small scale parallel kinematic machines (PKMs). The RSP is based on a task-driven approach: two mini-manipulators are compared as equivalent linear actuators to be integrated within a more complex system, for the application in both an industrial and a biomedical environment. The set of identified criteria for the two environments is proposed in the results and investigated with respect to working conditions and context in the discussion, emphasizing limits and strength points of this approach; finally, the conclusions synthesizes the main results. Full article
(This article belongs to the Special Issue Sustainable and Reconfigurable Machines for Mini and Micro-Applications)
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12 pages, 2629 KiB  
Article
Safe Coated Microneedles with Reduced Puncture Occurrence after Administration
by Hye-Rin Jeong, Hyesun Jun, Hye-Ran Cha, Jae Myun Lee and Jung-Hwan Park
Micromachines 2020, 11(8), 710; https://doi.org/10.3390/mi11080710 - 22 Jul 2020
Cited by 17 | Viewed by 3904
Abstract
The goal of this study is the preparation of safer coated microneedles so that tips remaining after the initial use are less likely to be reinserted on a second use. Twelve groups of uncoated microneedles (u-MNs) were prepared from the combination of three [...] Read more.
The goal of this study is the preparation of safer coated microneedles so that tips remaining after the initial use are less likely to be reinserted on a second use. Twelve groups of uncoated microneedles (u-MNs) were prepared from the combination of three different aspect ratios (height to base width) and four kinds of polymer (polyethylene (PE), polypropylene (PP), nylon and polylactic acid (PLA)). After coating the u-MNs with polyvinyl alcohol formulation to make coated MNs (c-MNs), the force displacement of the u-MNs and the c-MNs was measured. The aspect ratio was reduced from 2.2, 2.5 and 3.0 with u-MNs to 1.3, 1.4 and 1.6 with c-MNs, respectively, after the coating formulation was applied to the MNs. All PLA MNs had a puncture performance of more than 95%. However, the puncture performance of u-MNs made of PE and of PP with a 3.0 aspect ratio was only 8% and 53%, respectively, whereas the rates of c-MNs made of PE and of PP were 82% and 95%, respectively. In animal experiments with PP MNs with a 3.0 aspect ratio, the 59% rate of puncture performance with u-MNs increased to above 96% with c-MNs and fell to 13% for r-MNs. Safe c-MNs can overcome the disadvantages of standard c-MNs by reducing the probable contamination of remaining tips after use. Safe c-MNs have advantages over standard c-MNs in terms of humidity resistance, reasonable cost, sterilization process and short processing time through the separate process of u-MN preparation and simple dip-coating. Full article
(This article belongs to the Special Issue Microneedles)
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17 pages, 5201 KiB  
Article
Design and Characterization of an EEG-Hat for Reliable EEG Measurements
by Takumi Kawana, Yuri Yoshida, Yuta Kudo, Chiho Iwatani and Norihisa Miki
Micromachines 2020, 11(7), 635; https://doi.org/10.3390/mi11070635 - 28 Jun 2020
Cited by 11 | Viewed by 4408
Abstract
In this study, a new hat-type electroencephalogram (EEG) device with candle-like microneedle electrodes (CMEs), called an EEG-Hat, was designed and fabricated. CMEs are dry EEG electrodes that can measure high-quality EEG signals without skin treatment or conductive gels. One of the challenges in [...] Read more.
In this study, a new hat-type electroencephalogram (EEG) device with candle-like microneedle electrodes (CMEs), called an EEG-Hat, was designed and fabricated. CMEs are dry EEG electrodes that can measure high-quality EEG signals without skin treatment or conductive gels. One of the challenges in the measurement of high-quality EEG signals is the fixation of electrodes to the skin, i.e., the design of a good EEG headset. The CMEs were able to achieve good contact with the scalp for heads of different sizes and shapes, and the EEG-Hat has a shutter mechanism to separate the hair and ensure good contact between the CMEs and the scalp. Simultaneous measurement of EEG signals from five measurement points on the scalp was successfully conducted after a simple and brief setup process. The EEG-Hat is expected to contribute to the advancement of EEG research. Full article
(This article belongs to the Special Issue Selected Papers from the 10th Symposium on Micro-Nano Science and Technology on Micromachines)
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14 pages, 4999 KiB  
Article
Closable Valves and Channels for Polymeric Microfluidic Devices
by Charles P. Clark, M. Shane Woolf, Sarah L. Karstens, Hannah M. Lewis, Aeren Q. Nauman and James P. Landers
Micromachines 2020, 11(7), 627; https://doi.org/10.3390/mi11070627 - 27 Jun 2020
Cited by 7 | Viewed by 4027
Abstract
This study explores three unique approaches for closing valves and channels within microfluidic systems, specifically multilayer, centrifugally driven polymeric devices. Precise control over the cessation of liquid movement is achieved through either the introduction of expanding polyurethane foam, the application of direct contact [...] Read more.
This study explores three unique approaches for closing valves and channels within microfluidic systems, specifically multilayer, centrifugally driven polymeric devices. Precise control over the cessation of liquid movement is achieved through either the introduction of expanding polyurethane foam, the application of direct contact heating, or the redeposition of xerographic toner via chloroform solvation and evaporation. Each of these techniques modifies the substrate of the microdevice in a different way. All three are effective at closing a previously open fluidic pathway after a desired unit operation has taken place, i.e., sample metering, chemical reaction, or analytical measurement. Closing previously open valves and channels imparts stringent fluidic control—preventing backflow, maintaining pressurized chambers within the microdevice, and facilitating sample fractionation without cross-contamination. As such, a variety of microfluidic bioanalytical systems would benefit from the integration of these valving approaches. Full article
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17 pages, 6565 KiB  
Article
A mm-Sized Free-Floating Wireless Implantable Opto-Electro Stimulation Device
by Yaoyao Jia, Yan Gong, Arthur Weber, Wen Li and Maysam Ghovanloo
Micromachines 2020, 11(6), 621; https://doi.org/10.3390/mi11060621 - 25 Jun 2020
Cited by 4 | Viewed by 5783
Abstract
Towards a distributed neural interface, consisting of multiple miniaturized implants, for interfacing with large-scale neuronal ensembles over large brain areas, this paper presents a mm-sized free-floating wirelessly-powered implantable opto-electro stimulation (FF-WIOS2) device equipped with 16-ch optical and 4-ch electrical stimulation for reconfigurable neuromodulation. [...] Read more.
Towards a distributed neural interface, consisting of multiple miniaturized implants, for interfacing with large-scale neuronal ensembles over large brain areas, this paper presents a mm-sized free-floating wirelessly-powered implantable opto-electro stimulation (FF-WIOS2) device equipped with 16-ch optical and 4-ch electrical stimulation for reconfigurable neuromodulation. The FF-WIOS2 is wirelessly powered and controlled through a 3-coil inductive link at 60 MHz. The FF-WIOS2 receives stimulation parameters via on-off keying (OOK) while sending its rectified voltage information to an external headstage for closed-loop power control (CLPC) via load-shift-keying (LSK). The FF-WIOS2 system-on-chip (SoC), fabricated in a 0.35-µm standard CMOS process, employs switched-capacitor-based stimulation (SCS) architecture to provide large instantaneous current needed for surpassing the optical stimulation threshold. The SCS charger charges an off-chip capacitor up to 5 V at 37% efficiency. At the onset of stimulation, the capacitor delivers charge with peak current in 1.7–12 mA range to a micro-LED (µLED) array for optical stimulation or 100–700 μA range to a micro-electrode array (MEA) for biphasic electrical stimulation. Active and passive charge balancing circuits are activated in electrical stimulation mode to ensure stimulation safety. In vivo experiments conducted on three anesthetized rats verified the efficacy of the two stimulation mechanisms. The proposed FF-WIOS2 is potentially a reconfigurable tool for performing untethered neuromodulation. Full article
(This article belongs to the Special Issue Implantable Microdevices, Volume II)
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33 pages, 2680 KiB  
Review
Tissue-Engineered Models for Glaucoma Research
by Renhao Lu, Paul A. Soden and Esak Lee
Micromachines 2020, 11(6), 612; https://doi.org/10.3390/mi11060612 - 24 Jun 2020
Cited by 10 | Viewed by 5915
Abstract
Glaucoma is a group of optic neuropathies characterized by the progressive degeneration of retinal ganglion cells (RGCs). Patients with glaucoma generally experience elevations in intraocular pressure (IOP), followed by RGC death, peripheral vision loss and eventually blindness. However, despite the substantial economic and [...] Read more.
Glaucoma is a group of optic neuropathies characterized by the progressive degeneration of retinal ganglion cells (RGCs). Patients with glaucoma generally experience elevations in intraocular pressure (IOP), followed by RGC death, peripheral vision loss and eventually blindness. However, despite the substantial economic and health-related impact of glaucoma-related morbidity worldwide, the surgical and pharmacological management of glaucoma is still limited to maintaining IOP within a normal range. This is in large part because the underlying molecular and biophysical mechanisms by which glaucomatous changes occur are still unclear. In the present review article, we describe current tissue-engineered models of the intraocular space that aim to advance the state of glaucoma research. Specifically, we critically evaluate and compare both 2D and 3D-culture models of the trabecular meshwork and nerve fiber layer, both of which are key players in glaucoma pathophysiology. Finally, we point out the need for novel organ-on-a-chip models of glaucoma that functionally integrate currently available 3D models of the retina and the trabecular outflow pathway. Full article
(This article belongs to the Special Issue Mechanobiology and Biologically Inspired Engineering)
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17 pages, 5749 KiB  
Article
3D Printed Monolithic Microreactors for Real-Time Detection of Klebsiella pneumoniae and the Resistance Gene blaNDM-1 by Recombinase Polymerase Amplification
by Ole Behrmann, Matthias Hügle, Franz Eckardt, Iris Bachmann, Cecilia Heller, Marina Schramm, Carrie Turner, Frank T. Hufert and Gregory Dame
Micromachines 2020, 11(6), 595; https://doi.org/10.3390/mi11060595 - 17 Jun 2020
Cited by 7 | Viewed by 3846
Abstract
We investigate the compatibility of three 3D printing materials towards real-time recombinase polymerase amplification (rtRPA). Both the general ability of the rtRPA reaction to occur while in contact with the cured 3D printing materials as well as the residual autofluorescence and fluorescence drift [...] Read more.
We investigate the compatibility of three 3D printing materials towards real-time recombinase polymerase amplification (rtRPA). Both the general ability of the rtRPA reaction to occur while in contact with the cured 3D printing materials as well as the residual autofluorescence and fluorescence drift in dependence on post curing of the materials is characterized. We 3D printed monolithic rtRPA microreactors and subjected the devices to different post curing protocols. Residual autofluorescence and drift, as well as rtRPA kinetics, were then measured in a custom-made mobile temperature-controlled fluorescence reader (mTFR). Furthermore, we investigated the effects of storage on the devices over a 30-day period. Finally, we present the single- and duplex rtRPA detection of both the organism-specific Klebsiella haemolysin (khe) gene and the New Delhi metallo-β-lactamase 1 (blaNDM-1) gene from Klebsiella pneumoniae. Results: No combination of 3D printing resin and post curing protocol completely inhibited the rtRPA reaction. The autofluorescence and fluorescence drift measured were found to be highly dependent on printing material and wavelength. Storage had the effect of decreasing the autofluorescence of the investigated materials. Both khe and blaNDM-1 were successfully detected by single- and duplex-rtRPA inside monolithic rtRPA microreactors printed from NextDent Ortho Clear (NXOC). The reaction kinetics were found to be close to those observed for rtRPA performed in a microcentrifuge tube without the need for mixing during amplification. Singleplex assays for both khe and blaNDM-1 achieved a limit of detection of 2.5 × 101 DNA copies while the duplex assay achieved 2.5 × 101 DNA copies for khe and 2.5 × 102 DNA copies for blaNDM-1. Impact: We expand on the state of the art by demonstrating a technology that can manufacture monolithic microfluidic devices that are readily suitable for rtRPA. The devices exhibit very low autofluorescence and fluorescence drift and are compatible with RPA chemistry without the need for any surface pre-treatment such as blocking with, e.g., BSA or PEG. Full article
(This article belongs to the Section B：Biology and Biomedicine)
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17 pages, 2249 KiB  
Article
Optimal Control of Colloidal Trajectories in Inertial Microfluidics Using the Saffman Effect
by Felix Rühle, Christian Schaaf and Holger Stark
Micromachines 2020, 11(6), 592; https://doi.org/10.3390/mi11060592 - 15 Jun 2020
Cited by 5 | Viewed by 3422
Abstract
In inertial microfluidics colloidal particles in a Poiseuille flow experience the Segré-Silberberg lift force, which drives them to specific positions in the channel cross section. An external force applied along the microchannel induces a cross-streamline migration to a new equilibrium position because of [...] Read more.
In inertial microfluidics colloidal particles in a Poiseuille flow experience the Segré-Silberberg lift force, which drives them to specific positions in the channel cross section. An external force applied along the microchannel induces a cross-streamline migration to a new equilibrium position because of the Saffman effect. We apply optimal control theory to design the time protocol of the axial control force in order to steer a single particle as precisely as possible from a channel inlet to an outlet at a chosen target position. We discuss the influence of particle radius and channel length and show that optimal steering is cheaper than using a constant control force. Using a single optimized control-force protocol, we demonstrate that even a pulse of particles spread along the channel axis can be steered to a target and that particles of different radii can be separarted most efficiently. Full article
(This article belongs to the Special Issue Inertial Microfluidics)
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19 pages, 6235 KiB  
Article
Droplet-Based Screening for the Investigation of Microbial Nonlinear Dose–Response Characteristics System, Background and Examples
by Jialan Cao, Felix Richter, Michael Kastl, Jonny Erdmann, Christian Burgold, David Dittrich, Steffen Schneider, J. Michael Köhler and G. Alexander Groß
Micromachines 2020, 11(6), 577; https://doi.org/10.3390/mi11060577 - 8 Jun 2020
Cited by 9 | Viewed by 3335
Abstract
Droplet-based microfluidics is a versatile tool to reveal the dose–response relationship of different effectors on the microbial proliferation. Traditional readout parameter is the temporal development of the cell density for different effector concentrations. To determine nonlinear or unconventional dose–response relationships, data with high [...] Read more.
Droplet-based microfluidics is a versatile tool to reveal the dose–response relationship of different effectors on the microbial proliferation. Traditional readout parameter is the temporal development of the cell density for different effector concentrations. To determine nonlinear or unconventional dose–response relationships, data with high temporal resolution and dense concentration graduation are essential. If microorganisms with slow microbial growth kinetics are investigated, a sterile and evaporation-free long-term incubation technique is required. Here, we present a modular droplet-based screening system which was developed to solve these issues. Beside relevant technical aspects of the developed modules, the procedural workflow, and exemplary dose–response data for 1D and 2D dose–response screenings are presented. Full article
(This article belongs to the Special Issue Microfluidic for High-Throughput Screening)
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12 pages, 1836 KiB  
Article
Novel Design Approaches in the Fabrication of Polymeric Microarray Patches via Micromoulding
by Inken K. Ramöller, Emma McAlister, Abigail Bogan, Ana S. Cordeiro and Ryan F. Donnelly
Micromachines 2020, 11(6), 554; https://doi.org/10.3390/mi11060554 - 30 May 2020
Cited by 30 | Viewed by 4790
Abstract
The focus on novel systems for transdermal delivery of therapeutic agents has increased considerably over recent years, as this administration route comes with many advantages. Polymeric microarray patches (MAPs) are minimally invasive devices that enable systemic delivery of a wide range of drugs [...] Read more.
The focus on novel systems for transdermal delivery of therapeutic agents has increased considerably over recent years, as this administration route comes with many advantages. Polymeric microarray patches (MAPs) are minimally invasive devices that enable systemic delivery of a wide range of drugs by overcoming the outer skin barrier. Conventionally, MAPs fabricated by micromoulding have a low needle density. In this study, the performance of hydrogel-forming MAPs cast using novel industrially manufactured micromoulds with a high needle density (600 needles/0.75 cm2) was compared to that of MAPs obtained using conventional moulds with a lower density (196 needles/0.89 cm2). Surrounding holders for micromoulds were designed for time-efficient fabrication of MAPs. The influence of needle densities on mechanical strength, insertion efficiency and in vitro permeation of ibuprofen sodium (IBU) was analysed. Insertion of both MAPs into an artificial skin model and neonatal porcine skin was comparable. No significant difference was observed in permeation studies of IBU (p > 0.05), with a delivery of 8.7 ± 1.7 mg for low-density and 9.5 ± 0.1 mg for high-density MAPs within 24 h. This highlights the potential of these novel micromoulds for manufacturing polymeric MAPs with a higher needle density for future applications. Full article
(This article belongs to the Special Issue Microneedles)
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17 pages, 8494 KiB  
Review
Sperm Cell Driven Microrobots—Emerging Opportunities and Challenges for Biologically Inspired Robotic Design
by Ajay Vikram Singh, Mohammad Hasan Dad Ansari, Mihir Mahajan, Shubhangi Srivastava, Shubham Kashyap, Prajjwal Dwivedi, Vaibhav Pandit and Uma Katha
Micromachines 2020, 11(4), 448; https://doi.org/10.3390/mi11040448 - 23 Apr 2020
Cited by 77 | Viewed by 13618
Abstract
With the advent of small-scale robotics, several exciting new applications like Targeted Drug Delivery, single cell manipulation and so forth, are being discussed. However, some challenges remain to be overcome before any such technology becomes medically usable; among which propulsion and biocompatibility are [...] Read more.
With the advent of small-scale robotics, several exciting new applications like Targeted Drug Delivery, single cell manipulation and so forth, are being discussed. However, some challenges remain to be overcome before any such technology becomes medically usable; among which propulsion and biocompatibility are the main challenges. Propulsion at micro-scale where the Reynolds number is very low is difficult. To overcome this, nature has developed flagella which have evolved over millions of years to work as a micromotor. Among the microscopic cells that exhibit this mode of propulsion, sperm cells are considered to be fast paced. Here, we give a brief review of the state-of-the-art of Spermbots—a new class of microrobots created by coupling sperm cells to mechanical loads. Spermbots utilize the flagellar movement of the sperm cells for propulsion and as such do not require any toxic fuel in their environment. They are also naturally biocompatible and show considerable speed of motion thereby giving us an option to overcome the two challenges of propulsion and biocompatibility. The coupling mechanisms of physical load to the sperm cells are discussed along with the advantages and challenges associated with the spermbot. A few most promising applications of spermbots are also discussed in detail. A brief discussion of the future outlook of this extremely promising category of microrobots is given at the end. Full article
(This article belongs to the Special Issue Advances in Microswimmers)
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14 pages, 3263 KiB  
Article
High-Throughput Particle Concentration Using Complex Cross-Section Microchannels
by Asma Mihandoust, Sajad Razavi Bazaz, Nahid Maleki-Jirsaraei, Majid Alizadeh, Robert A. Taylor and Majid Ebrahimi Warkiani
Micromachines 2020, 11(4), 440; https://doi.org/10.3390/mi11040440 - 22 Apr 2020
Cited by 25 | Viewed by 4547
Abstract
High throughput particle/cell concentration is crucial for a wide variety of biomedical, clinical, and environmental applications. In this work, we have proposed a passive spiral microfluidic concentrator with a complex cross-sectional shape, i.e., a combination of rectangle and trapezoid, for high separation efficiency [...] Read more.
High throughput particle/cell concentration is crucial for a wide variety of biomedical, clinical, and environmental applications. In this work, we have proposed a passive spiral microfluidic concentrator with a complex cross-sectional shape, i.e., a combination of rectangle and trapezoid, for high separation efficiency and a confinement ratio less than 0.07. Particle focusing in our microfluidic system was observed in a single, tight focusing line, in which higher particle concentration is possible, as compared with simple rectangular or trapezoidal cross-sections with similar flow area. The sharper focusing stems from the confinement of Dean vortices in the trapezoidal region of the complex cross-section. To quantify this effect, we introduce a new parameter, complex focusing number or CFN, which is indicative of the enhancement of inertial focusing of particles in these channels. Three spiral microchannels with various widths of 400 µm, 500 µm, and 600 µm, with the corresponding CFNs of 4.3, 4.5, and 6, respectively, were used. The device with the total width of 600 µm was shown to have a separation efficiency of ~98%, and by recirculating, the output concentration of the sample was 500 times higher than the initial input. Finally, the investigation of results showed that the magnitude of CFN relies entirely on the microchannel geometry, and it is independent of the overall width of the channel cross-section. We envision that this concept of particle focusing through complex cross-sections will prove useful in paving the way towards more efficient inertial microfluidic devices. Full article
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14 pages, 3062 KiB  
Perspective
3D Printed MEMS Technology—Recent Developments and Applications
by Tomasz Blachowicz and Andrea Ehrmann
Micromachines 2020, 11(4), 434; https://doi.org/10.3390/mi11040434 - 20 Apr 2020
Cited by 58 | Viewed by 12541
Abstract
Microelectromechanical systems (MEMS) are of high interest for recent electronic applications. Their applications range from medicine to measurement technology, from microfluidics to the Internet of Things (IoT). In many cases, MEMS elements serve as sensors or actuators, e.g., in recent mobile phones, but [...] Read more.
Microelectromechanical systems (MEMS) are of high interest for recent electronic applications. Their applications range from medicine to measurement technology, from microfluidics to the Internet of Things (IoT). In many cases, MEMS elements serve as sensors or actuators, e.g., in recent mobile phones, but also in future autonomously driving cars. Most MEMS elements are based on silicon, which is not deformed plastically under a load, as opposed to metals. While highly sophisticated solutions were already found for diverse MEMS sensors, actuators, and other elements, MEMS fabrication is less standardized than pure microelectronics, which sometimes blocks new ideas. One of the possibilities to overcome this problem may be the 3D printing approach. While most 3D printing technologies do not offer sufficient resolution for MEMS production, and many of the common 3D printing materials cannot be used for this application, there are still niches in which the 3D printing of MEMS enables producing new structures and thus creating elements for new applications, or the faster and less expensive production of common systems. Here, we give an overview of the most recent developments and applications in 3D printing of MEMS. Full article
(This article belongs to the Special Issue 3D Printing of MEMS Technology)
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14 pages, 3261 KiB  
Article
A Microfluidic-Based Investigation of Bacterial Attachment in Ureteral Stents
by Antonio De Grazia, Gareth LuTheryn, Alireza Meghdadi, Ali Mosayyebi, Erika J. Espinosa-Ortiz, Robin Gerlach and Dario Carugo
Micromachines 2020, 11(4), 408; https://doi.org/10.3390/mi11040408 - 13 Apr 2020
Cited by 25 | Viewed by 5732
Abstract
Obstructions of the ureter lumen can originate from intrinsic or extrinsic factors, such as kidney stones, tumours, or strictures. These can affect the physiological flow of urine from the kidneys to the bladder, potentially causing infection, pain, and kidney failure. To overcome these [...] Read more.
Obstructions of the ureter lumen can originate from intrinsic or extrinsic factors, such as kidney stones, tumours, or strictures. These can affect the physiological flow of urine from the kidneys to the bladder, potentially causing infection, pain, and kidney failure. To overcome these complications, ureteral stents are often deployed clinically in order to temporarily re-establish urinary flow. Despite their clinical benefits, stents are prone to encrustation and biofilm formation that lead to reduced quality of life for patients; however, the mechanisms underlying the formation of crystalline biofilms in stents are not yet fully understood. In this study, we developed microfluidic-based devices replicating the urodynamic field within different configurations of an occluded and stented ureter. We employed computational fluid dynamic simulations to characterise the flow dynamic field within these models and investigated bacterial attachment (Pseudomonas fluorescens) by means of crystal violet staining and fluorescence microscopy. We identified the presence of hydrodynamic cavities in the vicinity of a ureteric occlusion, which were characterised by low levels of wall shear stress (WSS < 40 mPa), and observed that initiation of bacterial attachment occurred in these specific regions of the stented ureter. Notably, the bacterial coverage area was directly proportional to the number of cavities present in the model. Fluorescence microscopy confirmed that the number density of bacteria was greater within cavities (3 bacteria·mm−2) when compared to side-holes of the stent (1 bacterium·mm−2) or its luminal surface (0.12 bacteria·mm−2). These findings informed the design of a novel technological solution against bacterial attachment, which reduces the extent of cavity flow and increases wall shear stress over the stent’s surface. Full article
(This article belongs to the Special Issue 10th Anniversary of Micromachines)
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15 pages, 3964 KiB  
Article
Controllable pH Manipulations in Micro/Nanofluidic Device Using Nanoscale Electrokinetics
by Jae Suk Park, Jeewhan Oh and Sung Jae Kim
Micromachines 2020, 11(4), 400; https://doi.org/10.3390/mi11040400 - 10 Apr 2020
Cited by 6 | Viewed by 3226
Abstract
Recently introduced nanoscale electrokinetic phenomenon called ion concentration polarization (ICP) has been suffered from serious pH changes to the sample fluid. A number of studies have focused on the origin of pH changes and strategies for regulating it. Instead of avoiding pH changes, [...] Read more.
Recently introduced nanoscale electrokinetic phenomenon called ion concentration polarization (ICP) has been suffered from serious pH changes to the sample fluid. A number of studies have focused on the origin of pH changes and strategies for regulating it. Instead of avoiding pH changes, in this work, we tried to demonstrate new ways to utilize this inevitable pH change. First, one can obtain a well-defined pH gradient in proton-received microchannel by applying a fixed electric current through a proton exchange membrane. Furthermore, one can tune the pH gradient on demand by adjusting the proton mass transportation (i.e., adjusting electric current). Secondly, we demonstrated that the occurrence of ICP can be examined by sensing a surrounding pH of electrolyte solution. When pH > threshold pH, patterned pH-responsive hydrogel inside a straight microchannel acted as a nanojunction to block the microchannel, while it did as a microjunction when pH < threshold pH. In case of forming a nanojunction, electrical current significantly dropped compared to the case of a microjunction. The strategies that presented in this work would be a basis for useful engineering applications such as a localized pH stimulation to biomolecules using tunable pH gradient generation and portable pH sensor with pH-sensitive hydrogel. Full article
(This article belongs to the Special Issue Electrokinetics in Micro-/nanofluidic Devices)
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17 pages, 10037 KiB  
Article
Construction of a CQDs/Ag3PO4/BiPO4 Heterostructure Photocatalyst with Enhanced Photocatalytic Degradation of Rhodamine B under Simulated Solar Irradiation
by Huajing Gao, Chengxiang Zheng, Hua Yang, Xiaowei Niu and Shifa Wang
Micromachines 2019, 10(9), 557; https://doi.org/10.3390/mi10090557 - 23 Aug 2019
Cited by 57 | Viewed by 5266
Abstract
A carbon quantum dot (CQDs)/Ag3PO4/BiPO4 heterostructure photocatalyst was constructed by a simple hydrothermal synthesis method. The as-prepared CQDs/Ag3PO4/BiPO4 photocatalyst has been characterized in detail by X-ray diffraction, field-emission scanning electron microscopy, transmission electron [...] Read more.
A carbon quantum dot (CQDs)/Ag3PO4/BiPO4 heterostructure photocatalyst was constructed by a simple hydrothermal synthesis method. The as-prepared CQDs/Ag3PO4/BiPO4 photocatalyst has been characterized in detail by X-ray diffraction, field-emission scanning electron microscopy, transmission electron microscopy, X-ray photoelectron spectroscopy, ultraviolet–visible spectroscopy, and photoelectrochemical measurements. It is demonstrated that the CQDs/Ag3PO4/BiPO4 composite is constructed by assembling Ag3PO4 fine particles and CQDs on the surface of rice-like BiPO4 granules. The CQDs/Ag3PO4/BiPO4 heterostructure photocatalyst exhibits a higher photocatalytic activity for the degradation of the rhodamine B dye than that of Ag3PO4, BiPO4, and Ag3PO4/BiPO4. The synergistic effects of light absorption capacity, band edge position, separation, and utilization efficiency of photogenerated carriers play the key role for the enhanced photodegradation of the rhodamine B dye. Full article
(This article belongs to the Special Issue Nanostructures for Photocatalysis)
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15 pages, 13069 KiB  
Article
Facile Preparation of CNT/Ag2S Nanocomposites with Improved Visible and NIR Light Photocatalytic Degradation Activity and Their Catalytic Mechanism
by Lijing Di, Tao Xian, Xiaofeng Sun, Hongqin Li, Yongjie Zhou, Jun Ma and Hua Yang
Micromachines 2019, 10(8), 503; https://doi.org/10.3390/mi10080503 - 30 Jul 2019
Cited by 53 | Viewed by 4969
Abstract
In this work, a series of carbon nanotubes (CNT)/Ag2S hybrid nanocomposites were successfully prepared by a facile precipitation method. Transmission electron microscope (TEM) observation indicates that Ag2S nanoparticles with an average particle size of ~25 nm are uniformly anchored [...] Read more.
In this work, a series of carbon nanotubes (CNT)/Ag2S hybrid nanocomposites were successfully prepared by a facile precipitation method. Transmission electron microscope (TEM) observation indicates that Ag2S nanoparticles with an average particle size of ~25 nm are uniformly anchored on the surface of CNT. The photocatalytic activities of the CNT/Ag2S nanocomposites were investigated toward the degradation of rhodamine B (RhB) under visible and near-infrared (NIR) light irradiation. It is shown that the nanocomposites exhibit obviously enhanced visible and NIR light photocatalytic activities compared with bare Ag2S nanoparticles. Moreover, the recycling photocatalytic experiment demonstrates that the CNT/Ag2S nanocomposites possess excellent photocatalytic stability. The photoelectrochemical and photoluminescence measurements reveal the efficient separation of photogenerated charges in the CNT/Ag2S nanocomposites. This is the dominant reason behind the improvement of the photocatalytic activity. Based on active species trapping experiments, the possible photocatalytic mechanism of CNT/Ag2S nanocomposites for dye degradation under visible and NIR light irradiation was proposed. Full article
(This article belongs to the Section D：Materials and Processing)
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11 pages, 4881 KiB  
Article
Dual-Band Plasmonic Perfect Absorber Based on Graphene Metamaterials for Refractive Index Sensing Application
by Zao Yi, Cuiping Liang, Xifang Chen, Zigang Zhou, Yongjian Tang, Xin Ye, Yougen Yi, Junqiao Wang and Pinghui Wu
Micromachines 2019, 10(7), 443; https://doi.org/10.3390/mi10070443 - 2 Jul 2019
Cited by 103 | Viewed by 5786
Abstract
We demonstrate a dual-band plasmonic perfect absorber (PA) based on graphene metamaterials. Two absorption peaks (22.5 μm and 74.5 μm) with the maximal absorption of 99.4% and 99.9% have been achieved, respectively. We utilize this perfect absorber as a plasmonic sensor for refractive [...] Read more.
We demonstrate a dual-band plasmonic perfect absorber (PA) based on graphene metamaterials. Two absorption peaks (22.5 μm and 74.5 μm) with the maximal absorption of 99.4% and 99.9% have been achieved, respectively. We utilize this perfect absorber as a plasmonic sensor for refractive index (RI) sensing. It has the figure of merit (FOM) of 10.8 and 3.2, and sensitivities of about 5.6 and 17.2 μm/RIU, respectively. Hence, the designed dual-band PA-based RI sensor exhibits good sensing performance in the infrared regime, which offers great potential applications in various biomedical, tunable spectral detecting, environmental monitoring and medical diagnostics. Full article
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10 pages, 1831 KiB  
Article
Effects of Charge Transport Materials on Blue Fluorescent Organic Light-Emitting Diodes with a Host-Dopant System
by Neng Liu, Sijiong Mei, Dongwei Sun, Wuxing Shi, Jiahuan Feng, Yuanming Zhou, Fei Mei, Jinxia Xu, Yan Jiang and Xianan Cao
Micromachines 2019, 10(5), 344; https://doi.org/10.3390/mi10050344 - 25 May 2019
Cited by 78 | Viewed by 7184
Abstract
High efficiency blue fluorescent organic light-emitting diodes (OLEDs), based on 1,3-bis(carbazol-9-yl)benzene (mCP) doped with 4,4’-bis(9-ethyl-3-carbazovinylene)-1,1’-biphenyl (BCzVBi), were fabricated using four different hole transport layers (HTLs) and two different electron transport layers (ETLs). Fixing the electron transport material TPBi, four hole transport materials, including [...] Read more.
High efficiency blue fluorescent organic light-emitting diodes (OLEDs), based on 1,3-bis(carbazol-9-yl)benzene (mCP) doped with 4,4’-bis(9-ethyl-3-carbazovinylene)-1,1’-biphenyl (BCzVBi), were fabricated using four different hole transport layers (HTLs) and two different electron transport layers (ETLs). Fixing the electron transport material TPBi, four hole transport materials, including 1,1-Bis[(di-4-tolylamino)phenyl]cyclohexane (TAPC), N,N’-Di(1-naphthyl)-N,N’-diphenyl-(1,1’-biphenyl)-4’-diamine(NPB), 4,4’-Bis(N-carbazolyl)-1,1,-biphenyl (CBP) and molybdenum trioxide (MoO3), were selected to be HTLs, and the blue OLED with TAPC HTL exhibited a maximum luminance of 2955 cd/m2 and current efficiency (CE) of 5.75 cd/A at 50 mA/cm2, which are 68% and 62% higher, respectively, than those of the minimum values found in the device with MoO3 HTL. Fixing the hole transport material TAPC, the replacement of TPBi ETL with Bphen ETL can further improve the performance of the device, in which the maximum luminance can reach 3640 cd/m2 at 50 mA/cm2, which is 23% higher than that of the TPBi device. Furthermore, the lifetime of the device is also optimized by the change of ETL. These results indicate that the carrier mobility of transport materials and energy level alignment of different functional layers play important roles in the performance of the blue OLEDs. The findings suggest that selecting well-matched electron and hole transport materials is essential and beneficial for the device engineering of high-efficiency blue OLEDs. Full article
(This article belongs to the Special Issue Nanostructured Light-Emitters)
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16 pages, 22489 KiB  
Article
Enhanced Photocatalytic Performance and Mechanism of Au@CaTiO3 Composites with Au Nanoparticles Assembled on CaTiO3 Nanocuboids
by Yuxiang Yan, Hua Yang, Zao Yi, Ruishan Li and Xiangxian Wang
Micromachines 2019, 10(4), 254; https://doi.org/10.3390/mi10040254 - 17 Apr 2019
Cited by 73 | Viewed by 6193
Abstract
Using P25 as the titanium source and based on a hydrothermal route, we have synthesized CaTiO3 nanocuboids (NCs) with the width of 0.3–0.5 μm and length of 0.8–1.1 μm, and systematically investigated their growth process. Au nanoparticles (NPs) of 3–7 nm in [...] Read more.
Using P25 as the titanium source and based on a hydrothermal route, we have synthesized CaTiO3 nanocuboids (NCs) with the width of 0.3–0.5 μm and length of 0.8–1.1 μm, and systematically investigated their growth process. Au nanoparticles (NPs) of 3–7 nm in size were assembled on the surface of CaTiO3 NCs via a photocatalytic reduction method to achieve excellent Au@CaTiO3 composite photocatalysts. Various techniques were used to characterize the as-prepared samples, including X-ray powder diffraction (XRD), scanning/transmission electron microscopy (SEM/TEM), diffuse reflectance spectroscopy (UV-vis DRS), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). Rhodamine B (RhB) in aqueous solution was chosen as the model pollutant to assess the photocatalytic performance of the samples separately under simulated-sunlight, ultraviolet (UV) and visible-light irradiation. Under irradiation of all kinds of light sources, the Au@CaTiO3 composites, particularly the 4.3%Au@CaTiO3 composite, exhibit greatly enhanced photocatalytic performance when compared with bare CaTiO3 NCs. The main roles of Au NPs in the enhanced photocatalytic mechanism of the Au@CaTiO3 composites manifest in the following aspects: (1) Au NPs act as excellent electron sinks to capture the photoexcited electrons in CaTiO3, thus leading to an efficient separation of photoexcited electron/hole pairs in CaTiO3; (2) the electromagnetic field caused by localized surface plasmon resonance (LSPR) of Au NPs could facilitate the generation and separation of electron/hole pairs in CaTiO3; and (3) the LSPR-induced electrons in Au NPs could take part in the photocatalytic reactions. Full article
(This article belongs to the Special Issue Nanostructures for Photocatalysis)
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11 pages, 2585 KiB  
Article
Tunable Graphene-based Plasmonic Perfect Metamaterial Absorber in the THz Region
by Zao Yi, Jiajia Chen, Chunlian Cen, Xifang Chen, Zigang Zhou, Yongjian Tang, Xin Ye, Shuyuan Xiao, Wei Luo and Pinghui Wu
Micromachines 2019, 10(3), 194; https://doi.org/10.3390/mi10030194 - 18 Mar 2019
Cited by 77 | Viewed by 6679
Abstract
The optical performance of a periodically tunable plasma perfect metamaterial absorber based on a square-square-circle array we propose in the terahertz region is analyzed in this work by the finite difference time domain (FDTD) method. We not only discuss the impact of various [...] Read more.
The optical performance of a periodically tunable plasma perfect metamaterial absorber based on a square-square-circle array we propose in the terahertz region is analyzed in this work by the finite difference time domain (FDTD) method. We not only discuss the impact of various parameters such as period a, length L, radius R, and incident angle θ under transverse magnetic (TM)- and transverse electric (TE)-polarization on the absorption spectra of the absorber but also study the effect of the Fermi energy EF and relaxation time τ. Finally, we simulate the spectra as the surrounding refractive index n changes to better evaluate the sensing performance of the structure, producing a sensitivity S of the structure of up to 15006 nm/RIU. On account of this research, we find that the absorber is beneficial to sensors and detectors in the terahertz region. Full article
(This article belongs to the Special Issue Plasmonics: From Materials to Devices)
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