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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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18 pages, 8451 KiB  
Article
Biomechanical Assessment of Red Blood Cells in Pulsatile Blood Flows
by Yang Jun Kang
Micromachines 2023, 14(2), 317; https://doi.org/10.3390/mi14020317 - 26 Jan 2023
Cited by 3 | Viewed by 2511
Abstract
As rheological properties are substantially influenced by red blood cells (RBCs) and plasma, the separation of their individual contributions in blood is essential. The estimation of multiple rheological factors is a critical issue for effective early detection of diseases. In this study, three [...] Read more.
As rheological properties are substantially influenced by red blood cells (RBCs) and plasma, the separation of their individual contributions in blood is essential. The estimation of multiple rheological factors is a critical issue for effective early detection of diseases. In this study, three rheological properties (i.e., viscoelasticity, RBC aggregation, and blood junction pressure) are measured by analyzing the blood velocity and image intensity in a microfluidic device. Using a single syringe pump, the blood flow rate sets to a pulsatile flow pattern (Qb[t] = 1 + 0.5 sin(2πt/240) mL/h). Based on the discrete fluidic circuit model, the analytical formula of the time constant (λb) as viscoelasticity is derived and obtained at specific time intervals by analyzing the pulsatile blood velocity. To obtain RBC aggregation by reducing blood velocity substantially, an air compliance unit (ACU) is used to connect polyethylene tubing (i.d. = 250 µm, length = 150 mm) to the blood channel in parallel. The RBC aggregation index (AI) is obtained by analyzing the microscopic image intensity. The blood junction pressure (β) is obtained by integrating the blood velocity within the ACU. As a demonstration, the present method is then applied to detect either RBC-aggregated blood with different concentrations of dextran solution or hardened blood with thermally shocked RBCs. Thus, it can be concluded that the present method has the ability to consistently detect differences in diluent or RBCs in terms of three rheological properties. Full article
(This article belongs to the Special Issue Microfluidics and Biosensors for Point-of-Care Applications)
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20 pages, 4866 KiB  
Review
Third-Order Optical Nonlinearities of 2D Materials at Telecommunications Wavelengths
by Linnan Jia, Jiayang Wu, Yuning Zhang, Yang Qu, Baohua Jia and David J. Moss
Micromachines 2023, 14(2), 307; https://doi.org/10.3390/mi14020307 - 25 Jan 2023
Cited by 16 | Viewed by 4490
Abstract
All-optical signal processing based on nonlinear optical devices is promising for ultrafast information processing in optical communication systems. Recent advances in two-dimensional (2D) layered materials with unique structures and distinctive properties have opened up new avenues for nonlinear optics and the fabrication of [...] Read more.
All-optical signal processing based on nonlinear optical devices is promising for ultrafast information processing in optical communication systems. Recent advances in two-dimensional (2D) layered materials with unique structures and distinctive properties have opened up new avenues for nonlinear optics and the fabrication of related devices with high performance. This paper reviews the recent advances in research on third-order optical nonlinearities of 2D materials, focusing on all-optical processing applications in the optical telecommunications band near 1550 nm. First, we provide an overview of the material properties of different 2D materials. Next, we review different methods for characterizing the third-order optical nonlinearities of 2D materials, including the Z-scan technique, third-harmonic generation (THG) measurement, and hybrid device characterization, together with a summary of the measured n2 values in the telecommunications band. Finally, the current challenges and future perspectives are discussed. Full article
(This article belongs to the Special Issue Nonlinear Optics with 2D Materials)
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14 pages, 3955 KiB  
Article
Triboelectric-Electromagnetic Hybrid Wind-Energy Harvester with a Low Startup Wind Speed in Urban Self-Powered Sensing
by Gang Li, Juan Cui, Tingshan Liu, Yongqiu Zheng, Congcong Hao, Xiaojian Hao and Chenyang Xue
Micromachines 2023, 14(2), 298; https://doi.org/10.3390/mi14020298 - 23 Jan 2023
Cited by 9 | Viewed by 2784
Abstract
Wind energy as a renewable energy source is easily available and widely distributed in cities. However, current wind-energy harvesters are inadequate at capturing energy from low-speed winds in urban areas, thereby limiting their application in distributed self-powered sensor networks. A triboelectric–electromagnetic hybrid harvester [...] Read more.
Wind energy as a renewable energy source is easily available and widely distributed in cities. However, current wind-energy harvesters are inadequate at capturing energy from low-speed winds in urban areas, thereby limiting their application in distributed self-powered sensor networks. A triboelectric–electromagnetic hybrid harvester with a low startup wind speed (LSWS-TEH) is proposed that also provides output power within a wide range of wind speeds. An engineering-implementable propeller design method is developed to reduce the startup wind speed of the harvester. A mechanical analysis of the aerodynamics of the rotating propeller is performed, and optimal propeller parameter settings are found that greatly improved its aerodynamic torque. By combining the high-voltage output of the triboelectric nanogenerator under low-speed winds with the high-power output of the electromagnetic generator under high-speed winds, the harvester can maintain direct current output over a wide wind-speed range after rectification. Experiments show that the harvester activates at wind speeds as low as 1.2 m/s, powers a sensor with multiple integrated components in 1.7 m/s wind speeds, and drives a Bluetooth temperature and humidity sensor in 2.7 m/s wind speeds. The proposed small, effective, inexpensive hybrid energy harvester provides a promising way for self-powered requirements in smart city settings. Full article
(This article belongs to the Special Issue Flexible and Wearable Sensors)
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18 pages, 5562 KiB  
Article
A Simple Micromilled Microfluidic Impedance Cytometer with Vertical Parallel Electrodes for Cell Viability Analysis
by Jason Eades, Julianne F. Audiffred, Micah Fincher, Jin-Woo Choi, Steven A. Soper and William Todd Monroe
Micromachines 2023, 14(2), 283; https://doi.org/10.3390/mi14020283 - 22 Jan 2023
Cited by 2 | Viewed by 2672
Abstract
Microfluidic impedance cytometry has been demonstrated as an effective platform for single cell analysis, taking advantage of microfabricated features and dielectric cell sensing methods. In this study, we present a simple microfluidic device to improve the sensitivity, accuracy, and throughput of single suspension [...] Read more.
Microfluidic impedance cytometry has been demonstrated as an effective platform for single cell analysis, taking advantage of microfabricated features and dielectric cell sensing methods. In this study, we present a simple microfluidic device to improve the sensitivity, accuracy, and throughput of single suspension cell viability analysis using vertical sidewall electrodes fabricated by a widely accessible negative manufacturing method. A microchannel milled through a 75 µm platinum wire, which was embedded into poly-methyl-methacrylate (PMMA), created a pair of parallel vertical sidewall platinum electrodes. Jurkat cells were interrogated in a custom low-conductivity buffer (1.2 ± 0.04 mS/cm) to reduce current leakage and increase device sensitivity. Confirmed by live/dead staining and electron microscopy, a single optimum excitation frequency of 2 MHz was identified at which live and dead cells were discriminated based on the disruption in the cell membrane associated with cell death. At this frequency, live cells were found to exhibit changes in the impedance phase with no appreciable change in magnitude, while dead cells displayed the opposite behavior. Correlated with video microscopy, a computational algorithm was created that could identify cell detection events and determine cell viability status by application of a mathematical correlation method. Full article
(This article belongs to the Special Issue Advances in Microfluidic Flow Cytometry)
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17 pages, 1810 KiB  
Article
Static and Dynamic Analysis of a Bistable Frequency Up-Converter Piezoelectric Energy Harvester
by Mohammad Atmeh, Alwathiqbellah Ibrahim and Abdallah Ramini
Micromachines 2023, 14(2), 261; https://doi.org/10.3390/mi14020261 - 19 Jan 2023
Cited by 17 | Viewed by 2792
Abstract
Using energy harvesting to convert ambient vibrations efficiently to electrical energy has become a worthy concept in recent years. Nevertheless, the low frequencies of the ambient vibrations cannot be effectively converted to power using traditional harvesters. Therefore, a frequency up-conversion harvester is presented [...] Read more.
Using energy harvesting to convert ambient vibrations efficiently to electrical energy has become a worthy concept in recent years. Nevertheless, the low frequencies of the ambient vibrations cannot be effectively converted to power using traditional harvesters. Therefore, a frequency up-conversion harvester is presented to convert the low-frequency vibrations to high-frequency vibrations utilizing magnetic coupling. The presented harvester consists of a low-frequency beam (LFB) and a high-frequency beam (HFB) with identical tip magnets facing each other at the same polarity. The HFB, fully covered by a piezoelectric strip, is utilized for voltage generation. The dynamic behavior of the system and the corresponding generated voltage signal has been investigated by modeling the system as a two-degrees-of-freedom (2DOF) lumped-parameter model. A threshold distance of 15 mm that divides the system into a monostable regime with a weak magnetic coupling and a bistable regime with a strong magnetic coupling was revealed in the static analysis of the system. Hardening and softening behaviors were reported at the low frequency range for the mono and bistable regimes, respectively. In addition, a combined nonlinear hardening and softening behavior was captured for low frequencies at the threshold distance. Furthermore, a 100% increment was achieved in the generated voltage at the threshold compared to the monostable regime, and the maximum generated voltage was found to be in the bistable regime. The simulated results were validated experimentally. Moreover, the effect of the external resistance was investigated, and a 2 MΩ resistance was found to be optimal for maximizing the generated power. It was found that frequency up-converting based on magnetic nonlinearity can effectively scavenge energy from low-frequency external vibrations. Full article
(This article belongs to the Special Issue Piezoelectric MEMS/NEMS—Materials, Devices, and Applications)
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10 pages, 1826 KiB  
Article
Fabrication of Multi-Material Pneumatic Actuators and Microactuators Using Stereolithography
by Qingchuan Song, Yunong Chen, Peilong Hou, Pang Zhu, Dorothea Helmer, Frederik Kotz-Helmer and Bastian E. Rapp
Micromachines 2023, 14(2), 244; https://doi.org/10.3390/mi14020244 - 18 Jan 2023
Cited by 9 | Viewed by 3407
Abstract
Pneumatic actuators are of great interest for device miniaturization, microactuators, soft robots, biomedical engineering, and complex control systems. Recently, multi-material actuators have become of high interest to researchers due to their comprehensive range of suitable applications. Three-dimensional (3D) printing of multi-material pneumatic actuators [...] Read more.
Pneumatic actuators are of great interest for device miniaturization, microactuators, soft robots, biomedical engineering, and complex control systems. Recently, multi-material actuators have become of high interest to researchers due to their comprehensive range of suitable applications. Three-dimensional (3D) printing of multi-material pneumatic actuators would be the ideal way to fabricate customized actuators, but so far, this is mostly limited to deposition-based methodologies, such as fused deposition modeling (FDM) or Polyjetting. Vat-based stereolithography is one of the most relevant high-resolution 3D printing methods but is only rarely utilized in the multi-material 3D printing of materials. This study demonstrated multi-material stereolithography using combinations of materials with different Young’s moduli, i.e., 0.5 MPa and 1.1 GPa, for manufacturing pneumatic actuators and microactuators with a resolution as small as 200 μm. These multi-material actuators have advantages over single-material actuators in terms of their deformation controllability and ease of assembly. Full article
(This article belongs to the Special Issue Feature Papers of Micromachines in "Materials and Processing" 2022)
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13 pages, 9742 KiB  
Article
On-Chip Free-Flow Measurement Revealed Possible Depletion of Macrophages by Indigestible PM2.5 within a Few Hours by the Fastest Intervals of Serial Phagocytosis
by Dan Horonushi, Yuya Furumoto, Yoshiki Nakata, Toshiki Azuma, Amane Yoshida and Kenji Yasuda
Micromachines 2023, 14(1), 206; https://doi.org/10.3390/mi14010206 - 13 Jan 2023
Viewed by 1966
Abstract
To understand the influence of indigestible particles like particulate matter 2.5 (PM2.5) on macrophages, we examined the time course of the series phagocytosis of indigestible 2 μm polystyrene spheres (PS). Five kinds of antigens were used as samples for phagocytosis; Zymosan, non-coated 2 [...] Read more.
To understand the influence of indigestible particles like particulate matter 2.5 (PM2.5) on macrophages, we examined the time course of the series phagocytosis of indigestible 2 μm polystyrene spheres (PS). Five kinds of antigens were used as samples for phagocytosis; Zymosan, non-coated 2 μm PS, bovine serum albumin (BSA)-coated PS (BSA-PS), IgG-coated PS (IgG-PS), and IgG-BSA-coated PS (IgG/BSA-PS). To keep the surrounding concentration of antigens against single macrophages constant, antigens flowed at a continuous rate of 0.55 μm/s within a culture dish as a free-flow measurement assay (on-chip free-flow method). The interval of series phagocytosis for IgG/BSA-PS was the shortest among five samples; it was six times faster than Zymosan in terms of engulfment frequency, and up to 50 particles were engulfed within two hours, maintaining constant intervals until reaching the maximum number. The rate of increase in the total number of phagocytozed IgG/BSA-PS over time was constant, at 1.5 particles/min, in series phagocytosis with a 33-cell population, indicating that the phagocytosis rate constant remained constant independent of the number of phagocytoses. Reaction model fitting of the results showed that IgG/BSA-PS had the highest efficiency in terms of the phagocytosis rate constant, 2.3 × 10−2 particles/min, whereas those of IgG-PS, BSA-PS, PS, and Zymosan were 1.4 × 10−2, 1.1 × 10−2, 4.2 × 10−3, and 3.6 × 10−3 particles/min, respectively. One-by-one feeding of IgG/BSA-PS with optical tweezers was examined to confirm the phagocytosis intervals, and we found that the intervals remained constant until several times before the maximum number of antigens for engulfment, also indicating no change in the phagocytosis rate constant regardless of the history of former phagocytosis and phagocytosis number. Simultaneous phagocytosis of two IgG-BSA-decorated microneedle engulfments also showed that the initiation and progress of two simultaneous engulfments on the two different places on a cell were independent and had the same elongation velocity. Therefore, each phagocytosis of indigestible antigens does not affect both in series or in simultaneous subsequent phagocytosis until reaching the maximum capacity of the phagocytosis number. The results suggest (1) no change in the phagocytosis rate constant regardless of the history of phagocytosis numbers and attachment timing and positions, and (2) IgG-BSA decoration of indigestible microparticles in blood accelerates their engulfment faster, resulting in a severe shortage of macrophages within the shortest time. Full article
(This article belongs to the Special Issue Microfluidic Device Fabrication and Cell Manipulation)
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30 pages, 4479 KiB  
Review
Optical Sensing Technologies to Elucidate the Interplay between Plant and Microbes
by Asia Neelam and Shawana Tabassum
Micromachines 2023, 14(1), 195; https://doi.org/10.3390/mi14010195 - 12 Jan 2023
Cited by 6 | Viewed by 2745
Abstract
Plant-microbe interactions are critical for ecosystem functioning and driving rhizosphere processes. To fully understand the communication pathways between plants and rhizosphere microbes, it is crucial to measure the numerous processes that occur in the plant and the rhizosphere. The present review first provides [...] Read more.
Plant-microbe interactions are critical for ecosystem functioning and driving rhizosphere processes. To fully understand the communication pathways between plants and rhizosphere microbes, it is crucial to measure the numerous processes that occur in the plant and the rhizosphere. The present review first provides an overview of how plants interact with their surrounding microbial communities, and in turn, are affected by them. Next, different optical biosensing technologies that elucidate the plant-microbe interactions and provide pathogenic detection are summarized. Currently, most of the biosensors used for detecting plant parameters or microbial communities in soil are centered around genetically encoded optical and electrochemical biosensors that are often not suitable for field applications. Such sensors require substantial effort and cost to develop and have their limitations. With a particular focus on the detection of root exudates and phytohormones under biotic and abiotic stress conditions, novel low-cost and in-situ biosensors must become available to plant scientists. Full article
(This article belongs to the Section A：Physics)
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14 pages, 6036 KiB  
Article
High Frequency MEMS Capacitive Mirror for Space Applications
by Alvise Bagolini, Anze Sitar, Luca Porcelli, Maurizio Boscardin, Simone Dell’Agnello and Giovanni Delle Monache
Micromachines 2023, 14(1), 158; https://doi.org/10.3390/mi14010158 - 8 Jan 2023
Cited by 5 | Viewed by 3081
Abstract
Free space optics laser communication using modulating retroreflectors (MR) is a challenging application for an active mirror, due to the high frequencies (>100 kHz) required to enable sufficient data transfer. Micro Electromechanical (MEMS) mirrors are a promising option for high-frequency applications, given the [...] Read more.
Free space optics laser communication using modulating retroreflectors (MR) is a challenging application for an active mirror, due to the high frequencies (>100 kHz) required to enable sufficient data transfer. Micro Electromechanical (MEMS) mirrors are a promising option for high-frequency applications, given the very small moving mass typical of such devices. Capacitive MEMS mirrors are presented here for free space communications, based on a novel fabrication sequence that introduces a single-layer thin film aluminum mirror structure with an underlying silicon oxide sacrificial layer. The use of aluminum instead of gold as a mirror layer diminishes the heating generated by the absorption of the sun’s radiation once the mirrors exit the earth’s atmosphere. Thanks to the novel fabrication sequence, the presented mirror devices have a full range actuation voltage of less than 40 V, and a high operational frequency with an eigenfrequency above 2 MHz. The devices were manufactured and characterized, and their main parameters were obtained from experimental data combined with finite element analysis, thus enabling future design optimization of the reported MEMS technology. By optical characterization of the far field diffraction pattern, good mirror performance was demonstrated. Full article
(This article belongs to the Special Issue MEMS in Italy)
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19 pages, 15987 KiB  
Article
Application of Piezoelectric PLLA Braided Cord as Wearable Sensor to Realize Monitoring System for Indoor Dogs with Less Physical or Mental Stress
by Yoshiro Tajitsu, Jun Takarada, Tokiya Hikichi, Ryoji Sugii, Kohei Takatani, Hiroki Yanagimoto, Riku Nakanishi, Seita Shiomi, Daiki Kitamoto, Takuo Nakiri, Osamu Takeuchi, Miki Deguchi, Takanori Muto, Kazuaki Kuroki, Wataru Amano, Ayaka Misumi, Mitsuru Takahashi, Kazuki Sugiyama, Akira Tanabe, Shiro Kamohara, Rei Nisho and Koji Takeshitaadd Show full author list remove Hide full author list
Micromachines 2023, 14(1), 143; https://doi.org/10.3390/mi14010143 - 5 Jan 2023
Cited by 7 | Viewed by 2372
Abstract
We attempted to realize a prototype system that monitors the living condition of indoor dogs without physical or mental burden by using a piezoelectric poly-l-lactic acid (PLLA) braided cord as a wearable sensor. First, to achieve flexibility and durability of the [...] Read more.
We attempted to realize a prototype system that monitors the living condition of indoor dogs without physical or mental burden by using a piezoelectric poly-l-lactic acid (PLLA) braided cord as a wearable sensor. First, to achieve flexibility and durability of the piezoelectric PLLA braided cord used as a sensor for indoor dogs, the process of manufacturing the piezoelectric PLLA fiber for the piezoelectric braided cord was studied in detail and improved to achieve the required performance. Piezoelectric PLLA braided cords were fabricated from the developed PLLA fibers, and the finite element method was used to realize an e-textile that can effectively function as a monitoring sensor. As a result, we realized an e-textile that feels similar to a high-grade textile and senses the complex movements of indoor dogs without the use of a complex computer system. Finally, a prototype system was constructed and applied to an actual indoor dog to demonstrate the usefulness of the e-textile as a sensor for indoor dog monitoring. Full article
(This article belongs to the Special Issue Recent Advances of Wearable and Flexible Sensor Devices and Their Future Prospects)
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13 pages, 3407 KiB  
Article
Membrane Surface Modification via In Situ Grafting of GO/Pt Nanoparticles for Nitrate Removal with Anti-Biofouling Properties
by Mohammad Khajouei, Mahsa Najafi, Seyed Ahmad Jafari and Mohammad Latifi
Micromachines 2023, 14(1), 128; https://doi.org/10.3390/mi14010128 - 3 Jan 2023
Cited by 8 | Viewed by 2157
Abstract
Nanofiltration processes for the removal of emerging contaminants such as nitrate are a focus of attention of research works as an efficient technique for providing drinking water for people. Polysulfone (PSF) nanofiltration membranes containing graphene oxide (GO)/Pt (0, 0.25, 0.5, 0.75, 1 wt%) [...] Read more.
Nanofiltration processes for the removal of emerging contaminants such as nitrate are a focus of attention of research works as an efficient technique for providing drinking water for people. Polysulfone (PSF) nanofiltration membranes containing graphene oxide (GO)/Pt (0, 0.25, 0.5, 0.75, 1 wt%) nanoparticles were generated with the phase inversion pathway. The as-synthesized samples were characterized by FTIR, SEM, AFM, and contact angle tests to study the effect of GO/Pt on hydrophilicity and antibacterial characteristics. The results conveyed that insertion of GO/Pt dramatically improved the biofouling resistance of the membranes. Permeation experiments indicated that PSF membrane embracing 0.75 wt% GO/Pt nanoparticles had the highest nitrate flux and rejection ability. The membrane’s configuration was simulated using OPEN-MX simulating software indicating membranes maintaining 0.75 wt% of GO/Pt nanoparticles revealed the highest stability, which is well in accordance with experimental outcomes. Full article
(This article belongs to the Special Issue Nanomaterial-Based Membranes and Applications)
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17 pages, 6084 KiB  
Review
Smart Nematic Liquid Crystal Polymers for Micromachining Advances
by Sébastien Dominici, Keynaz Kamranikia, Karine Mougin and Arnaud Spangenberg
Micromachines 2023, 14(1), 124; https://doi.org/10.3390/mi14010124 - 1 Jan 2023
Cited by 2 | Viewed by 2407
Abstract
The miniaturization of tools is an important step in human evolution to create faster devices as well as precise micromachines. Studies around this topic have allowed the creation of small-scale objects capable of a wide range of deformation to achieve complex tasks. Molecular [...] Read more.
The miniaturization of tools is an important step in human evolution to create faster devices as well as precise micromachines. Studies around this topic have allowed the creation of small-scale objects capable of a wide range of deformation to achieve complex tasks. Molecular arrangements have been investigated through liquid crystal polymer (LCP) to program such a movement. Smart polymers and hereby liquid crystal matrices are materials of interest for their easy structuration properties and their response to external stimuli. However, up until very recently, their employment at the microscale was mainly limited to 2D structuration. Among the numerous issues, one concerns the ability to 3D structure the material while controlling the molecular orientation during the polymerization process. This review aims to report recent efforts focused on the microstructuration of LCP, in particular those dealing with 3D microfabrication via two-photon polymerization (TPP). Indeed, the latter has revolutionized the production of 3D complex micro-objects and is nowadays recognized as the gold standard for 3D micro-printing. After a short introduction highlighting the interest in micromachines, some basic principles of liquid crystals are recalled from the molecular aspect to their implementation. Finally, the possibilities offered by TPP as well as the way to monitor the motion into the fabricated microrobots are highlighted. Full article
(This article belongs to the Special Issue Recent Advances in Microrobotics)
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24 pages, 3136 KiB  
Review
Exploring the Structural Variability of Dynamic Biological Complexes by Single-Particle Cryo-Electron Microscopy
by Megan C. DiIorio and Arkadiusz W. Kulczyk
Micromachines 2023, 14(1), 118; https://doi.org/10.3390/mi14010118 - 31 Dec 2022
Cited by 7 | Viewed by 2967
Abstract
Biological macromolecules and assemblies precisely rearrange their atomic 3D structures to execute cellular functions. Understanding the mechanisms by which these molecular machines operate requires insight into the ensemble of structural states they occupy during the functional cycle. Single-particle cryo-electron microscopy (cryo-EM) has become [...] Read more.
Biological macromolecules and assemblies precisely rearrange their atomic 3D structures to execute cellular functions. Understanding the mechanisms by which these molecular machines operate requires insight into the ensemble of structural states they occupy during the functional cycle. Single-particle cryo-electron microscopy (cryo-EM) has become the preferred method to provide near-atomic resolution, structural information about dynamic biological macromolecules elusive to other structure determination methods. Recent advances in cryo-EM methodology have allowed structural biologists not only to probe the structural intermediates of biochemical reactions, but also to resolve different compositional and conformational states present within the same dataset. This article reviews newly developed sample preparation and single-particle analysis (SPA) techniques for high-resolution structure determination of intrinsically dynamic and heterogeneous samples, shedding light upon the intricate mechanisms employed by molecular machines and helping to guide drug discovery efforts. Full article
(This article belongs to the Section B：Biology and Biomedicine)
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10 pages, 14092 KiB  
Article
Thin Film Piezoelectric Nanogenerator Based on (100)-Oriented Nanocrystalline AlN Grown by Pulsed Laser Deposition at Room Temperature
by Wei Li, Yunqi Cao and Nelson Sepúlveda
Micromachines 2023, 14(1), 99; https://doi.org/10.3390/mi14010099 - 30 Dec 2022
Cited by 4 | Viewed by 2104
Abstract
In wearable or implantable biomedical devices that typically rely on battery power for diagnostics or operation, the development of flexible piezoelectric nanogenerators (NGs) that enable mechanical-to-electrical energy harvesting is finding promising applications. Here, we present the construction of a flexible piezoelectric nanogenerator using [...] Read more.
In wearable or implantable biomedical devices that typically rely on battery power for diagnostics or operation, the development of flexible piezoelectric nanogenerators (NGs) that enable mechanical-to-electrical energy harvesting is finding promising applications. Here, we present the construction of a flexible piezoelectric nanogenerator using a thin film of room temperature deposited nanocrystalline aluminium nitride (AlN). On a thin layer of aluminium (Al), the AlN thin film was grown using pulsed laser deposition (PLD). The room temperature grown AlN film was composed of crystalline columnar grains oriented in the (100)-direction, as revealed in images from transmission electron microscopy (TEM) and X-ray diffraction (XRD). Fundamental characterization of the AlN thin film by piezoresponse force microscopy (PFM) indicated that its electro-mechanical energy conversion metrics were comparable to those of c-axis oriented AlN and zinc oxide (ZnO) thin films. Additionally, the AlN-based flexible piezoelectric NG was encapsulated in polyimide to further strengthen its mechanical robustness and protect it from some corrosive chemicals. Full article
(This article belongs to the Special Issue Piezoelectric MEMS/NEMS—Materials, Devices, and Applications)
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10 pages, 1913 KiB  
Article
Monitoring Xenon Capture in a Metal Organic Framework Using Laser-Induced Breakdown Spectroscopy
by Hunter B. Andrews, Praveen K. Thallapally and Alexander J. Robinson
Micromachines 2023, 14(1), 82; https://doi.org/10.3390/mi14010082 - 29 Dec 2022
Cited by 6 | Viewed by 2000
Abstract
Molten salt reactor operation will necessitate circulation of a cover gas to remove certain evolved fission products and maintain an inert atmosphere. The cover gas leaving the reactor core is expected to contain both noble and non-noble gases, aerosols, volatile species, tritium, and [...] Read more.
Molten salt reactor operation will necessitate circulation of a cover gas to remove certain evolved fission products and maintain an inert atmosphere. The cover gas leaving the reactor core is expected to contain both noble and non-noble gases, aerosols, volatile species, tritium, and radionuclides and their daughters. To remove these radioactive gases, it is necessary to develop a robust off-gas system, along with novel sensors to monitor the gas stream and the treatment system performance. In this study, a metal organic framework (MOF) was engineered for the capture of Xe, a major contributor to the off-gas source term. The engineered MOF column was tested with a laser-induced breakdown spectroscopy (LIBS) sensor for noble gas monitoring. The LIBS sensor was used to monitor breakthrough tests with various Xe, Kr, and Ar mixtures to determine the Xe selectivity of the MOF column. This study offers an initial demonstration of the feasibility of monitoring off-gas treatment systems using a LIBS sensor to aid in the development of new capture systems for molten salt reactors. Full article
(This article belongs to the Special Issue Recent Advances in Chemical Gas Sensors)
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10 pages, 4414 KiB  
Article
Crack-Based Sensor by Using the UV Curable Polyurethane-Acrylate Coated Film with V-Groove Arrays
by Jongsung Park, Dong-Su Kim, Youngsam Yoon, Arunkumar Shanmugasundaram and Dong-Weon Lee
Micromachines 2023, 14(1), 62; https://doi.org/10.3390/mi14010062 - 26 Dec 2022
Cited by 5 | Viewed by 2183
Abstract
Over the years, several bare metal and crack-based strain sensors have been proposed for various fields of science and technology. However, due to their low gauge factor, metal-based strain sensors have limited practical applications. The crack-based strain sensor, on the other hand, demonstrated [...] Read more.
Over the years, several bare metal and crack-based strain sensors have been proposed for various fields of science and technology. However, due to their low gauge factor, metal-based strain sensors have limited practical applications. The crack-based strain sensor, on the other hand, demonstrated excellent sensitivity and a high gauge factor. However, the crack-based strain sensor exhibited non-linear behavior at low strains, severely limiting its real-time applications. Generally, the crack-based strain sensors are fabricated by generating cracks by bending a polymer film on which a metal layer has been deposited with a constant curvature. However, the random formation of cracks produces nonlinear behavior in the crack sensors. To overcome the limitations of the current state of the art, we propose a V-groove-based metal strain sensor for human motion monitoring and Morse code generation. The V-groove crack-based strain sensor is fabricated on polyurethane acrylate (PUA) using the modified photolithography technique. During the procedure, a V-groove pattern formed on the surface of the sensor, and a uniform crack formed over the entire surface by concentrating stress along the groove. To improve the sensitivity and selectivity of the sensor, we generated the cracks in a controlled direction. The proposed strain sensor exhibited high sensitivity and excellent fidelity compared to the other reported metal strain sensors. The gauge factor of the proposed V-groove-induced crack sensor is 10-fold higher than the gauge factor of the reported metal strain sensors. In addition, the fabricated V-groove-based strain sensor exhibited rapid response and recovery times. The practical feasibility of the proposed V-groove-induced crack-based strain sensor is demonstrated through human motion monitoring and the generation of Morse code. The proposed V-groove crack sensor can detect multiple motions in a variety of human activities and is anticipated to be utilized in several applications due to its high durability and reproducibility. Full article
(This article belongs to the Section E：Engineering and Technology)
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16 pages, 5674 KiB  
Article
Magnetically Driven Manipulation of Nonmagnetic Liquid Marbles: Billiards with Liquid Marbles
by Parnian Azizian, Mahbod Mohammadrashidi, Ali Abbas Azimi, Mohamad Ali Bijarchi, Mohammad Behshad Shafii and Rohollah Nasiri
Micromachines 2023, 14(1), 49; https://doi.org/10.3390/mi14010049 - 25 Dec 2022
Cited by 10 | Viewed by 3619
Abstract
Liquid marbles are droplets encapsulated by a layer of hydrophobic nanoparticles and have been extensively employed in digital microfluidics and lab-on-a-chip systems in recent years. In this study, magnetic liquid marbles were used to manipulate nonmagnetic liquid marbles. To achieve this purpose, a [...] Read more.
Liquid marbles are droplets encapsulated by a layer of hydrophobic nanoparticles and have been extensively employed in digital microfluidics and lab-on-a-chip systems in recent years. In this study, magnetic liquid marbles were used to manipulate nonmagnetic liquid marbles. To achieve this purpose, a ferrofluid liquid marble (FLM) was employed and attracted toward an electromagnet, resulting in an impulse to a water liquid marble (WLM) on its way to the electromagnet. It was observed that the manipulation of the WLM by the FLM was similar to the collision of billiard balls except that the liquid marbles exhibited an inelastic collision. Taking the FLM as the projectile ball and the WLM as the other target balls, one can adjust the displacement and direction of the WLM precisely, similar to an expert billiard player. Firstly, the WLM displacement can be adjusted by altering the liquid marble volumes, the initial distances from the electromagnet, and the coil current. Secondly, the WLM direction can be adjusted by changing the position of the WLM relative to the connecting line between the FLM center and the electromagnet. Results show that when the FLM or WLM volume increases by five times, the WLM shooting distance approximately increases by 200% and decreases by 75%, respectively. Full article
(This article belongs to the Special Issue Micro- and Nano-Systems for Manipulation, Actuation and Sensing)
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33 pages, 7187 KiB  
Review
Fundamentals and Applications of ZnO-Nanowire-Based Piezotronics and Piezo-Phototronics
by Yitong Wang, Wanli Xie, Wenbo Peng, Fangpei Li and Yongning He
Micromachines 2023, 14(1), 47; https://doi.org/10.3390/mi14010047 - 25 Dec 2022
Cited by 8 | Viewed by 3773
Abstract
The piezotronic effect is a coupling effect of semiconductor and piezoelectric properties. The piezoelectric potential is used to adjust the p-n junction barrier width and Schottky barrier height to control carrier transportation. At present, it has been applied in the fields of sensors, [...] Read more.
The piezotronic effect is a coupling effect of semiconductor and piezoelectric properties. The piezoelectric potential is used to adjust the p-n junction barrier width and Schottky barrier height to control carrier transportation. At present, it has been applied in the fields of sensors, human–machine interaction, and active flexible electronic devices. The piezo-phototronic effect is a three-field coupling effect of semiconductor, photoexcitation, and piezoelectric properties. The piezoelectric potential generated by the applied strain in the piezoelectric semiconductor controls the generation, transport, separation, and recombination of carriers at the metal–semiconductor contact or p-n junction interface, thereby improving optoelectronic devices performance, such as photodetectors, solar cells, and light-emitting diodes (LED). Since then, the piezotronics and piezo-phototronic effects have attracted vast research interest due to their ability to remarkably enhance the performance of electronic and optoelectronic devices. Meanwhile, ZnO has become an ideal material for studying the piezotronic and piezo-phototronic effects due to its simple preparation process and better biocompatibility. In this review, first, the preparation methods and structural characteristics of ZnO nanowires (NWs) with different doping types were summarized. Then, the theoretical basis of the piezotronic effect and its application in the fields of sensors, biochemistry, energy harvesting, and logic operations (based on piezoelectric transistors) were reviewed. Next, the piezo-phototronic effect in the performance of photodetectors, solar cells, and LEDs was also summarized and analyzed. In addition, modulation of the piezotronic and piezo-phototronic effects was compared and summarized for different materials, structural designs, performance characteristics, and working mechanisms’ analysis. This comprehensive review provides fundamental theoretical and applied guidance for future research directions in piezotronics and piezo-phototronics for optoelectronic devices and energy harvesting. Full article
(This article belongs to the Special Issue Advanced Technologies in Piezo-Phototronics)
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15 pages, 7678 KiB  
Article
Low-Cost Light-Based GelMA 3D Bioprinting via Retrofitting: Manufacturability Test and Cell Culture Assessment
by Juan Enrique Pérez-Cortez, Víctor Hugo Sánchez-Rodríguez, Salvador Gallegos-Martínez, Cristina Chuck-Hernández, Ciro A. Rodriguez, Mario Moises Álvarez, Grissel Trujillo-de Santiago, Elisa Vázquez-Lepe and J. Israel Martínez-López
Micromachines 2023, 14(1), 55; https://doi.org/10.3390/mi14010055 - 25 Dec 2022
Cited by 10 | Viewed by 3737
Abstract
Light-based bioprinter manufacturing technology is still prohibitively expensive for organizations that rely on accessing three-dimensional biological constructs for research and tissue engineering endeavors. Currently, most of the bioprinting systems are based on commercial-grade-based systems or modified DIY (do it yourself) extrusion apparatuses. However, [...] Read more.
Light-based bioprinter manufacturing technology is still prohibitively expensive for organizations that rely on accessing three-dimensional biological constructs for research and tissue engineering endeavors. Currently, most of the bioprinting systems are based on commercial-grade-based systems or modified DIY (do it yourself) extrusion apparatuses. However, to date, few examples of the adoption of low-cost equipment have been found for light-based bioprinters. The requirement of large volumes of bioinks, their associated cost, and the lack of information regarding the parameter selection have undermined the adoption of this technology. This paper showcases the retrofitting and assessing of a low-cost Light-Based 3D printing system for tissue engineering. To evaluate the potential of a proposed design, a manufacturability test for different features, machine parameters, and Gelatin Methacryloyl (GelMA) concentrations for 7.5% and 10% was performed. Furthermore, a case study of a previously seeded hydrogel with C2C12 cells was successfully implemented as a proof of concept. On the manufacturability test, deviational errors were found between 0.7% to 13.3% for layer exposure times of 15 and 20 s. Live/Dead and Actin-Dapi fluorescence assays after 5 days of culture showed promising results in the cell viability, elongation, and alignment of 3D bioprinted structures. The retrofitting of low-cost equipment has the potential to enable researchers to create high-resolution structures and three-dimensional in vitro models. Full article
(This article belongs to the Special Issue 3D Bioprinting and Biofabrication for the Future of Tissue Engineering)
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7 pages, 4766 KiB  
Article
An Acoustic Flat Lens for Broadband Focusing via Cross-Shape Structure
by Shenlian Gao, Qinglei Zeng, Mengyang Gong, Jun Lan and Xiaozhou Liu
Micromachines 2023, 14(1), 12; https://doi.org/10.3390/mi14010012 - 21 Dec 2022
Cited by 2 | Viewed by 1772
Abstract
The manipulation of refracted wavefronts is eye-catching for owning attractive applications. In this article, an airborne acoustic flat lens for broadband focusing via cross-shape structure was proposed and demonstrated, introducing the broadband manipulation of wavefronts. The designed metasurface employs gradient refractive index cells [...] Read more.
The manipulation of refracted wavefronts is eye-catching for owning attractive applications. In this article, an airborne acoustic flat lens for broadband focusing via cross-shape structure was proposed and demonstrated, introducing the broadband manipulation of wavefronts. The designed metasurface employs gradient refractive index cells to redirect the sound wave. Based on our theory, the effective refractive indexes of our unit cells can be easily calculated. The shackle of narrowband metasurfaces is conquered, and applications in medical ultrasound imaging are just around the corner. Full article
(This article belongs to the Section A：Physics)
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10 pages, 3561 KiB  
Article
Sapphire Selective Laser Etching Dependence on Radiation Wavelength and Etchant
by Agnė Butkutė, Romualdas Sirutkaitis, Darius Gailevičius, Domas Paipulas and Valdas Sirutkaitis
Micromachines 2023, 14(1), 7; https://doi.org/10.3390/mi14010007 - 20 Dec 2022
Cited by 8 | Viewed by 3612
Abstract
Transparent and high-hardness materials have become the object of wide interest due to their optical and mechanical properties; most notably, concerning technical glasses and crystals. A notable example is sapphire—one of the most rigid materials having impressive mechanical stability, high melting point and [...] Read more.
Transparent and high-hardness materials have become the object of wide interest due to their optical and mechanical properties; most notably, concerning technical glasses and crystals. A notable example is sapphire—one of the most rigid materials having impressive mechanical stability, high melting point and a wide transparency window reaching into the UV range, together with impressive laser-induced damage thresholds. Nonetheless, using this material for 3D micro-fabrication is not straightforward due to its brittle nature. On the microscale, selective laser etching (SLE) technology is an appropriate approach for such media. Therefore, we present our research on C-cut crystalline sapphire microprocessing by using femtosecond radiation-induced SLE. Here, we demonstrate a comparison between different wavelength radiation (1030 nm, 515 nm, 343 nm) usage for material modification and various etchants (hydrofluoric acid, sodium hydroxide, potassium hydroxide and sulphuric and phosphoric acid mixture) comparison. Due to the inability to etch crystalline sapphire, regular SLE etchants, such as hydrofluoric acid or potassium hydroxide, have limited adoption in sapphire selective laser etching. Meanwhile, a 78% sulphuric and 22% phosphoric acid mixture at 270 °C temperature is a good alternative for this process. We present the changes in the material after the separate processing steps. After comparing different processing protocols, the perspective is demonstrated for sapphire structure formation. Full article
(This article belongs to the Special Issue Ultrafast Laser Processing of Difficult-to-Machine Materials and Micro/Nano Structures)
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11 pages, 3886 KiB  
Article
A Nitrocellulose Paper-Based Multi-Well Plate for Point-of-Care ELISA
by Zhen Qin, Zongjie Huang, Peng Pan, Yueyue Pan, Runze Zuo, Yu Sun and Xinyu Liu
Micromachines 2022, 13(12), 2232; https://doi.org/10.3390/mi13122232 - 16 Dec 2022
Cited by 10 | Viewed by 3987
Abstract
Low-cost diagnostic tools for point-of-care immunoassays, such as the paper-based enzyme-linked immunoassay (ELISA), have become increasingly important, especially so in the recent COVID-19 pandemic. ELISA is the gold-standard antibody/antigen sensing method. This paper reports an easy-to-fabricate nitrocellulose (NC) paper plate, coupled with a [...] Read more.
Low-cost diagnostic tools for point-of-care immunoassays, such as the paper-based enzyme-linked immunoassay (ELISA), have become increasingly important, especially so in the recent COVID-19 pandemic. ELISA is the gold-standard antibody/antigen sensing method. This paper reports an easy-to-fabricate nitrocellulose (NC) paper plate, coupled with a desktop scanner for ELISA, which provides a higher protein immobilization efficiency than the conventional cellulose paper-based ELISA platforms. The experiments were performed using spiked samples for the direct ELISA of rabbit IgG with a limit of detection (LOD) of 1.016 μg/mL, in a measurement range of 10 ng/mL to 1 mg/mL, and for the sandwich ELISA of sperm protein (SP-10) with an LOD of 88.8 ng/mL, in a measurement range of 1 ng/mL to 100 μg/mL. The described fabrication method, based on laser-cutting, is a highly flexible one-step laser micromachining process, which enables the rapid production of low-cost NC paper-based multi-well plates with different sizes for the ELISA measurements. Full article
(This article belongs to the Topic Advances in Microfluidics and Lab on a Chip Technology)
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13 pages, 2497 KiB  
Article
Vibration-Assisted Synthesis of Nanoporous Anodic Aluminum Oxide (AAO) Membranes
by Urte Cigane, Arvydas Palevicius and Giedrius Janusas
Micromachines 2022, 13(12), 2236; https://doi.org/10.3390/mi13122236 - 16 Dec 2022
Cited by 2 | Viewed by 1577
Abstract
In recent years, many research achievements in the field of anodic aluminum oxide (AAO) membranes can be observed. Nevertheless, it is still an interesting research topic due to its high versatility and applications in various fields, such as template-assisted methods, filtration, sensors, etc. [...] Read more.
In recent years, many research achievements in the field of anodic aluminum oxide (AAO) membranes can be observed. Nevertheless, it is still an interesting research topic due to its high versatility and applications in various fields, such as template-assisted methods, filtration, sensors, etc. Nowadays, miniaturization is an integral part of different technologies; therefore, research on micro- and nanosized elements is relevant in areas such as LEDs and OLEDs, solar cells, etc. To achieve an efficient mixing process of fluid flow in straight nanopores, acoustofluidic physics has attracted great interest in recent decades. Unfortunately, the renewal of the electrolyte concentration at the bottom of a pore is limited. Thus, excitation is used to improve fluid mixing along nanosized diameters. The effect of excitation by high-frequency vibrations on pore geometry is also investigated. In this study, theoretical simulations were performed. Using theoretical calculations, the acoustic pressure, acoustic velocity, and velocity magnitude were obtained at frequencies of 2, 20, and 40 kHz. Moreover, nanoporous AAO membranes were synthesized, and the influence of high-frequency vibrations on the geometry of the pores was determined. Using a high-frequency excitation of 20 kHz, the thickness of the AAO membrane increased by 17.8%. In addition, the thickness increased by 31.1% at 40 kHz and 33.3% at the resonant frequency of 40 kHz. Using high-frequency vibrations during the anodization process, the electrolyte inside the pores is mixed, and as a result, a higher oxide growth rate and a deeper structure can be achieved. On the other hand, to obtain pores of the same depth, the reaction can be performed in a shorter time. Full article
(This article belongs to the Special Issue Advance in Energy Conversion and Storage: Material, Design and Application)
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8 pages, 1456 KiB  
Communication
Fabrication and Properties of InGaZnO Thin-Film Transistors Based on a Sol–Gel Method with Different Electrode Patterns
by Xingzhen Yan, Bo Li, Kaian Song, Yiqiang Zhang, Yanjie Wang, Fan Yang, Chao Wang, Yaodan Chi and Xiaotian Yang
Micromachines 2022, 13(12), 2207; https://doi.org/10.3390/mi13122207 - 13 Dec 2022
Cited by 6 | Viewed by 1884
Abstract
The preparation of thin-film transistors (TFTs) with InGaZnO (IGZO) channels using sol–gel technology has the advantages of simplicity in terms of process and weak substrate selectivity. We prepared a series of TFT devices with a top contact and bottom gate structure, in which [...] Read more.
The preparation of thin-film transistors (TFTs) with InGaZnO (IGZO) channels using sol–gel technology has the advantages of simplicity in terms of process and weak substrate selectivity. We prepared a series of TFT devices with a top contact and bottom gate structure, in which the top contact was divided into rectangular and circular structures of drain/source electrodes. The field-effect performance of TFT devices with circular pattern drain/source electrodes was better than that with a traditional rectangular structure on both substrates. The uniform distribution of the potential in the circular electrode structure was more conducive to the regulation of carriers under the same channel length at different applied voltages. In addition, with the development of transparent substrate devices, we also constructed a hafnium oxide (HfO2) insulation layer and an IGZO active layer on an indium tin oxide conductive substrate, and explored the effect of circular drain/source electrodes on field-effect properties of the semitransparent TFT device. The IGZO deposited on the HfO2 dielectric layer by spin-coating can effectively reduce the surface roughness of the HfO2 layer and optimize the scattering of carriers at the interface in TFT devices. Full article
(This article belongs to the Special Issue Recent Advances in Thin Film Transistors)
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13 pages, 10691 KiB  
Article
Flexible Heater Fabrication Using Amino Acid-Based Ink and Laser-Direct Writing
by Sangmo Koo
Micromachines 2022, 13(12), 2209; https://doi.org/10.3390/mi13122209 - 13 Dec 2022
Viewed by 1806
Abstract
Nature’s systems have evolved over a long period to operate efficiently, and this provides hints for metal nanoparticle synthesis, including the enhancement, efficient generation, and transport of electrons toward metal ions for nanoparticle synthesis. The organic material-based ink composed of the natural materials [...] Read more.
Nature’s systems have evolved over a long period to operate efficiently, and this provides hints for metal nanoparticle synthesis, including the enhancement, efficient generation, and transport of electrons toward metal ions for nanoparticle synthesis. The organic material-based ink composed of the natural materials used in this study requires low laser power for sintering compared to conventional nanoparticle ink sintering. This suggests applicability in various and sophisticated pattern fabrication applications without incurring substrate damage. An efficient electron transfer mechanism between amino acids (e.g., tryptophan) enables silver patterning on flexible polymer substrates (e.g., PET) by laser-direct writing. The reduction of silver ions to nanoparticles was induced and sintered by simultaneous photo/thermalchemical reactions on substrates. Furthermore, it was possible to fabricate a stable, transparent, and flexible heater that operates under mechanical deformation. Full article
(This article belongs to the Special Issue Micro-Manufacturing and Applications, Volume III: Advanced Hybrid Processes in Micro-Manufacturing)
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25 pages, 3606 KiB  
Review
Synergistic Electric and Thermal Effects of Electrochromic Devices
by Meng Yuan, Hanlin Yin, Yitong Liu, Xiaohua Wang, Long Yuan and Yu Duan
Micromachines 2022, 13(12), 2187; https://doi.org/10.3390/mi13122187 - 10 Dec 2022
Cited by 7 | Viewed by 2363
Abstract
Electrochromic devices are the preferred devices for smart windows because they work independently of uncontrollable environmental factors and rely more on the user’s personal feelings to adjust actively. However, in practical applications, the ambient temperature still has an impact on device performance, such [...] Read more.
Electrochromic devices are the preferred devices for smart windows because they work independently of uncontrollable environmental factors and rely more on the user’s personal feelings to adjust actively. However, in practical applications, the ambient temperature still has an impact on device performance, such as durability, reversibility and switching performance, etc. These technical issues have significantly slowed down the commercialization of electrochromic devices (ECDs). It is necessary to investigate the main reasons for the influence of temperature on the device and make reasonable optimization to enhance the effectiveness of the device and extend its lifetime. In recent years, with the joint efforts of various outstanding research teams, the performance of electrochromic devices has been rapidly improved, with a longer lifetime, richer colors, and better color contrast. This review highlights the important research on temperature–dependent electrochromic properties in recent years. Also, the reported structures, mechanisms, characteristics, and methods for improving electrochromic properties are discussed in detail. In addition, the challenges and corresponding strategies in this field are presented in this paper. This paper will inspire more researchers to enrich the temperature–dependent properties of ECDs and their related fields with innovative means and methods to overcome the technical obstacles faced. Full article
(This article belongs to the Special Issue Light Emitting Devices: From Fundamental Research to Applications)
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10 pages, 2962 KiB  
Article
Curvature-Adjustable Polymeric Nanolens Fabrication Using UV-Controlled Nanoimprint Lithography
by Qiang Li, Myung Gi Ji, Ashish Chapagain, In Ho Cho and Jaeyoun Kim
Micromachines 2022, 13(12), 2183; https://doi.org/10.3390/mi13122183 - 9 Dec 2022
Cited by 4 | Viewed by 1767
Abstract
Nanolenses are gaining importance in nanotechnology, but their challenging fabrication is thwarting their wider adoption. Of particular challenge is facile control of the lens’ curvature. In this work, we demonstrate a new nanoimprinting technique capable of realizing polymeric nanolenses in which the nanolens’ [...] Read more.
Nanolenses are gaining importance in nanotechnology, but their challenging fabrication is thwarting their wider adoption. Of particular challenge is facile control of the lens’ curvature. In this work, we demonstrate a new nanoimprinting technique capable of realizing polymeric nanolenses in which the nanolens’ curvature is optically controlled by the ultraviolet (UV) dose at the pre-curing step. Our results reveal a regime in which the nanolens’ height changes linearly with the UV dose. Computational modeling further uncovers that the polymer undergoes highly nonlinear dynamics during the UV-controlled nanoimprinting process. Both the technique and the process model will greatly advance nanoscale science and manufacturing technology. Full article
(This article belongs to the Section E：Engineering and Technology)
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26 pages, 8160 KiB  
Article
Film Thickness and Glycerol Concentration Mapping of Falling Films Based on Fluorescence and Near-Infrared Technique
by Isabel Medina, Stephan Scholl and Matthias Rädle
Micromachines 2022, 13(12), 2184; https://doi.org/10.3390/mi13122184 - 9 Dec 2022
Cited by 2 | Viewed by 2496
Abstract
Falling film evaporation processes involve high fluid velocities with continuous variations in local film thickness, fluid composition, and viscosity. This contribution presents a parallel and complementary film thickness and concentration mapping distribution in falling films using a non-invasive fluorescence and near-infrared imaging technique. [...] Read more.
Falling film evaporation processes involve high fluid velocities with continuous variations in local film thickness, fluid composition, and viscosity. This contribution presents a parallel and complementary film thickness and concentration mapping distribution in falling films using a non-invasive fluorescence and near-infrared imaging technique. The experiments were performed with a mixture of glycerol/water with a mass fraction from 0 to 0.65 gglycgtotal−1 and operating ranges similar to evaporation processes. The measurement system was designed by integrating two optical measurement methods for experimental image analysis. The film thickness was evaluated using a VIS camera and high-power LEDs at 470 nm. The local glycerol concentration gglycgtotal−1 was determined using a NIR camera and high-power LEDs at 1050, 1300, 1450 and 1550 nm. A multiwavelength analysis with all NIR wavelengths was implemented with a better correlation for falling films at low flow velocity. The results show an improvement in the analysis of falling films with high flow velocities up to almost 500 mm/s by using only the 1450 nm wavelength and the fluorescence measurement. Simultaneous imaging analysis of film thickness and concentration in falling films provides further insight into understanding mass and heat transport and thus supports the optimization of falling film evaporators. Full article
(This article belongs to the Special Issue Optics and Photonics in Micromachines)
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12 pages, 2663 KiB  
Article
Additive Nanosecond Laser-Induced Forward Transfer of High Antibacterial Metal Nanoparticle Dose onto Foodborne Bacterial Biofilms
by Alena Nastulyavichus, Liliana Khaertdinova, Eteri Tolordava, Yulia Yushina, Andrey Ionin, Anastasia Semenova and Sergey Kudryashov
Micromachines 2022, 13(12), 2170; https://doi.org/10.3390/mi13122170 - 8 Dec 2022
Cited by 4 | Viewed by 1288
Abstract
Additive laser-induced forward transfer (LIFT) of metal bactericidal nanoparticles from a polymer substrate directly onto food bacterial biofilms has demonstrated its unprecedented efficiency in combating pathogenic microorganisms. Here, a comprehensive study of laser fluence, metal (gold, silver and copper) film thickness, and the [...] Read more.
Additive laser-induced forward transfer (LIFT) of metal bactericidal nanoparticles from a polymer substrate directly onto food bacterial biofilms has demonstrated its unprecedented efficiency in combating pathogenic microorganisms. Here, a comprehensive study of laser fluence, metal (gold, silver and copper) film thickness, and the transfer distance effects on the antibacterial activity regarding biofilms of Gram-negative and Gram-positive food bacteria (Staphylococcus aureus, Pseudomonas aeruginosa, Escherichia coli, Listeria monocytogenes, Salmonella spp.) indicated the optimal operation regimes of the versatile modality. LIFT-induced nanoparticle penetration into a biofilm was studied by energy-dispersion X-ray spectroscopy, which demonstrated that nanoparticles remained predominantly on the surface of the biofilm. Full article
(This article belongs to the Special Issue Fundamentals and Applications of Light-Matter Interactions in Laser Metal Additive Manufacturing)
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16 pages, 5926 KiB  
Article
Continuous Particle Aggregation and Separation in Acoustofluidic Microchannels Driven by Standing Lamb Waves
by Jin-Chen Hsu and Chih-Yu Chang
Micromachines 2022, 13(12), 2175; https://doi.org/10.3390/mi13122175 - 8 Dec 2022
Cited by 1 | Viewed by 1777
Abstract
In this study, we realize acoustic aggregation and separation of microparticles in fluid channels driven by standing Lamb waves of a 300-μm-thick double-side polished lithium-niobate (LiNbO3) plate. We demonstrate that the counter-propagating lowest-order antisymmetric and symmetric Lamb modes can be excited [...] Read more.
In this study, we realize acoustic aggregation and separation of microparticles in fluid channels driven by standing Lamb waves of a 300-μm-thick double-side polished lithium-niobate (LiNbO3) plate. We demonstrate that the counter-propagating lowest-order antisymmetric and symmetric Lamb modes can be excited by double interdigitated transducers on the LiNbO3 plate to produce interfacial coupling with the fluid in channels. Consequently, the solid–fluid coupling generates radiative acoustic pressure and streaming fields to actuate controlled acoustophoretic motion of particles by means of acoustic radiation and Stokes drag forces. We conducted finite-element simulations based on the acoustic perturbation theory with full-wave modeling to tailor the acoustic and streaming fields in the channels driven by the standing Lamb waves. As a result, the acoustic process and the mechanism of particle aggregation and separation were elucidated. Experiments on acoustic manipulation of particles in channels validate the capability of aggregation and separation by the designed devices. It is observed that strong streaming dominates the particle aggregation while the acoustic radiation force differentially expels particles with different sizes from pressure antinodes to achieve continuous particle separation. This study paves the way for Lamb-wave acoustofluidics and may trigger more innovative acoustofluidic systems driven by Lamb waves and other manipulating approaches incorporated on a thin-plate platform. Full article
(This article belongs to the Special Issue Acoustofluidics: Applications, Phenomena and Fabrication Technique)
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9 pages, 2559 KiB  
Article
Viscosity-Controllable Graphene Oxide Colloids Using Electrophoretically Deposited Graphene Oxide Sheets
by Jinseok Choi, Seong-Gyu Park, Yeo-Jin Choi, Seung-Mun Baek, Han-Jung Kim, Yoonkap Kim, Ki-Sik Im and Sung-Jin An
Micromachines 2022, 13(12), 2157; https://doi.org/10.3390/mi13122157 - 7 Dec 2022
Cited by 1 | Viewed by 1598
Abstract
Graphene oxide (GO) is one of the interesting ink materials owing to its fascinating properties, such as high dissolubility in water and high controllable electric properties. For versatile printing application, the viscosity of GO colloids should be controlled in order to meet the [...] Read more.
Graphene oxide (GO) is one of the interesting ink materials owing to its fascinating properties, such as high dissolubility in water and high controllable electric properties. For versatile printing application, the viscosity of GO colloids should be controlled in order to meet the specific process requirements. Here, we report on the relatively rapid fabrication of viscosity-increased GO (VIGO) colloids mixed with electrophoretically deposited GO sheets (EPD-GO). As the GO colloid concentration, applied voltage, and deposition time increase, the viscosity of the GO colloids becomes high. The reason for the improved viscosity of GO colloids is because EPD-GO has parallel stacked GO sheets. The GO and VIGO colloids are compared and characterized using various chemical and structural analyzers. Consequently, our simple and fast method for the fabrication of GO colloids with enhanced viscosity can be used for producing inks for flexible and printed electronics. Full article
(This article belongs to the Special Issue Smart Carbon Nanostructures and Applications)
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21 pages, 8451 KiB  
Review
Recent Progress in Blue Thermally Activated Delayed Fluorescence Emitters and Their Applications in OLEDs: Beyond Pure Organic Molecules with Twist D-π-A Structures
by Yiting Gao, Siping Wu, Guogang Shan and Gang Cheng
Micromachines 2022, 13(12), 2150; https://doi.org/10.3390/mi13122150 - 5 Dec 2022
Cited by 9 | Viewed by 5785
Abstract
Thermally activated delayed fluorescence (TADF) materials, which can harvest all excitons and emit light without the use of noble metals, are an appealing class of functional materials emerging as next-generation organic electroluminescent materials. Triplet excitons can be upconverted to the singlet state with [...] Read more.
Thermally activated delayed fluorescence (TADF) materials, which can harvest all excitons and emit light without the use of noble metals, are an appealing class of functional materials emerging as next-generation organic electroluminescent materials. Triplet excitons can be upconverted to the singlet state with the aid of ambient thermal energy under the reverse inter-system crossing owing to the small singlet–triplet splitting energy (ΔEST). This results from a specific molecular design consisting of minimal overlap between the highest occupied molecular orbital and the lowest unoccupied molecular orbital, due to the spatial separation of the electron-donating and electron-releasing part. When a well-designed device structure is applied, high-performance blue-emitting TADF organic light-emitting diodes can be realized with an appropriate molecular design. Unlike the previous literature that has reviewed general blue-emitting TADF materials, in this paper, we focus on materials other than pure organic molecules with twist D-π-A structures, including multi-resonance TADF, through-space charge transfer TADF, and metal-TADF materials. Cutting-edge molecules with extremely small and even negative ΔEST values are also introduced as candidates for next-generation TADF materials. In addition, OLED structures used to exploit the merits of the abovementioned TADF emitters are also described in this review. Full article
(This article belongs to the Special Issue Organic Light Emitting Diodes (OLEDs))
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23 pages, 4528 KiB  
Review
Micro-Sized pH Sensors Based on Scanning Electrochemical Probe Microscopy
by Muhanad Al-Jeda, Emmanuel Mena-Morcillo and Aicheng Chen
Micromachines 2022, 13(12), 2143; https://doi.org/10.3390/mi13122143 - 4 Dec 2022
Cited by 10 | Viewed by 2943
Abstract
Monitoring pH changes at the micro/nano scale is essential to gain a fundamental understanding of surface processes. Detection of local pH changes at the electrode/electrolyte interface can be achieved through the use of micro-/nano-sized pH sensors. When combined with scanning electrochemical microscopy (SECM), [...] Read more.
Monitoring pH changes at the micro/nano scale is essential to gain a fundamental understanding of surface processes. Detection of local pH changes at the electrode/electrolyte interface can be achieved through the use of micro-/nano-sized pH sensors. When combined with scanning electrochemical microscopy (SECM), these sensors can provide measurements with high spatial resolution. This article reviews the state-of-the-art design and fabrication of micro-/nano-sized pH sensors, as well as their applications based on SECM. Considerations for selecting sensing probes for use in biological studies, corrosion science, in energy applications, and for environmental research are examined. Different types of pH sensitive probes are summarized and compared. Finally, future trends and emerging applications of micro-/nano-sized pH sensors are discussed. Full article
(This article belongs to the Special Issue MEMS Sensors: Fabrication and Application)
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14 pages, 3144 KiB  
Article
Battery-Free Tattooing Mechanism-Based Functional Active Capsule Endoscopy
by Manh-Cuong Hoang, Jong-Oh Park and Jayoung Kim
Micromachines 2022, 13(12), 2111; https://doi.org/10.3390/mi13122111 - 29 Nov 2022
Cited by 3 | Viewed by 1626
Abstract
This paper presents a novel tattooing capsule endoscope (TCE) for delivering a certain amount of ink to the submucosal layer of digestive tract organs. A dual-function permanent magnet is used for locomotion and injection activation. The developed capsule endoscope can move actively in [...] Read more.
This paper presents a novel tattooing capsule endoscope (TCE) for delivering a certain amount of ink to the submucosal layer of digestive tract organs. A dual-function permanent magnet is used for locomotion and injection activation. The developed capsule endoscope can move actively in 5 DOF due to the interaction between the permanent magnet and a controllable external magnetic field produced by an electromagnet actuation system. In addition, the permanent magnet is involved in a specially designed mechanism to activate a process that creates a squeezing motion to eject the liquid from the storage room to the target. The dimension of the prototype is 12.5 mm in diameter and 34.6 mm in length. The proposed TCE is tested ex vivo using a fresh porcine small-intestine segment. We were able to direct the TCE to the target and deliver the tattoo agent into the tissue. The proposed mechanism can be used for drug delivery or lesion tattooing, as well as to accelerate the realization of the functional capsule endoscope in practice. Full article
(This article belongs to the Special Issue Integrated Robotics for Micromanipulation, Diagnosis and Microsurgery)
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11 pages, 2113 KiB  
Article
A Novel Memristive Neural Network Circuit and Its Application in Character Recognition
by Xinrui Zhang, Xiaoyuan Wang, Zhenyu Ge, Zhilong Li, Mingyang Wu and Shekharsuman Borah
Micromachines 2022, 13(12), 2074; https://doi.org/10.3390/mi13122074 - 25 Nov 2022
Cited by 9 | Viewed by 3283
Abstract
The memristor-based neural network configuration is a promising approach to realizing artificial neural networks (ANNs) at the hardware level. The memristors can effectively simulate the strength of synaptic connections between neurons in neural networks due to their diverse significant characteristics such as nonvolatility, [...] Read more.
The memristor-based neural network configuration is a promising approach to realizing artificial neural networks (ANNs) at the hardware level. The memristors can effectively simulate the strength of synaptic connections between neurons in neural networks due to their diverse significant characteristics such as nonvolatility, nanoscale dimensions, and variable conductance. This work presents a new synaptic circuit based on memristors and Complementary Metal Oxide Semiconductor(CMOS), which can realize the adjustment of positive, negative, and zero synaptic weights using only one control signal. The relationship between synaptic weights and the duration of control signals is also explained in detail. Accordingly, Widrow–Hoff algorithm-based memristive neural network (MNN) circuits are proposed to solve the recognition of three types of character pictures. The functionality of the proposed configurations is verified using SPICE simulation. Full article
(This article belongs to the Special Issue Novel Computing Architectures and Digital Circuit Designs Using Memristors and Memristive Systems)
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18 pages, 3237 KiB  
Review
Ultrafast Pulse Generation from Quantum Cascade Lasers
by Feihu Wang, Xiaoqiong Qi, Zhichao Chen, Manijeh Razeghi and Sukhdeep Dhillon
Micromachines 2022, 13(12), 2063; https://doi.org/10.3390/mi13122063 - 24 Nov 2022
Cited by 6 | Viewed by 3111
Abstract
Quantum cascade lasers (QCLs) have broken the spectral barriers of semiconductor lasers and enabled a range of applications in the mid-infrared (MIR) and terahertz (THz) regimes. However, until recently, generating ultrashort and intense pulses from QCLs has been difficult. This would be useful [...] Read more.
Quantum cascade lasers (QCLs) have broken the spectral barriers of semiconductor lasers and enabled a range of applications in the mid-infrared (MIR) and terahertz (THz) regimes. However, until recently, generating ultrashort and intense pulses from QCLs has been difficult. This would be useful to study ultrafast processes in MIR and THz using the targeted wavelength-by-design properties of QCLs. Since the first demonstration in 2009, mode-locking of QCLs has undergone considerable development in the past decade, which includes revealing the underlying mechanism of pulse formation, the development of an ultrafast THz detection technique, and the invention of novel pulse compression technology, etc. Here, we review the history and recent progress of ultrafast pulse generation from QCLs in both the THz and MIR regimes. Full article
(This article belongs to the Special Issue Quantum Cascade Laser: Physics, Technology and Applications)
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21 pages, 1683 KiB  
Review
Temperature-to-Digital Converters’ Evolution, Trends and Techniques across the Last Two Decades: A Review
by Antonio Aprile, Edoardo Bonizzoni and Piero Malcovati
Micromachines 2022, 13(11), 2025; https://doi.org/10.3390/mi13112025 - 19 Nov 2022
Cited by 6 | Viewed by 2711
Abstract
This paper presents an extensive review of the main highlights in the Temperature-to-Digital Converters (TDCs) field, which has gained importance and research interest throughout the last two decades. The key techniques and approaches that have led to the evolution of this kind of [...] Read more.
This paper presents an extensive review of the main highlights in the Temperature-to-Digital Converters (TDCs) field, which has gained importance and research interest throughout the last two decades. The key techniques and approaches that have led to the evolution of this kind of systems are presented and compared; their peculiarities are identified in order to highlight the pros and cons of the different design methods, and the main trade-offs are extracted from this analysis. Finally, the trends that have emerged from the performance evaluation of the large amount of published works in this field are identified with the purpose of providing a directional view of the past, present and future features of these devices. Full article
(This article belongs to the Special Issue Feature Papers of Micromachines in Engineering and Technology 2021)
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14 pages, 6781 KiB  
Article
Micro Light Flow Controller on a Programmable Waveguide Engine
by Tao Chen, Zhangqi Dang, Zeyu Deng, Zhenming Ding and Ziyang Zhang
Micromachines 2022, 13(11), 1990; https://doi.org/10.3390/mi13111990 - 16 Nov 2022
Cited by 6 | Viewed by 2997
Abstract
A light flow controller that can regulate the three-port optical power in both lossless and lossy modus is realized on a programmable multimode waveguide engine. The microheaters on the waveguide chip mimic the tunable “pixels” that can continuously adjust the local refractive index. [...] Read more.
A light flow controller that can regulate the three-port optical power in both lossless and lossy modus is realized on a programmable multimode waveguide engine. The microheaters on the waveguide chip mimic the tunable “pixels” that can continuously adjust the local refractive index. Compared to the conventional method where the tuning takes place only on single-mode waveguides, the proposed structure is more compact and requires less electrodes. The local index changes in a multimode waveguide can alter the mode numbers, field distribution, and propagation constants of each individual mode, all of which can alter the multimode interference pattern significantly. However, these changes are mostly complex and not governed by analytical equations as in the single-mode case. Though numerical simulations can be performed to predict the device response, the thermal and electromagnetic computing involved is mostly time-consuming. Here, a multi-level search program is developed based on experiments only. It can reach a target output in real time by adjusting the microheaters collectively and iteratively. It can also jump over local optima and further improve the cost function on a global level. With only a simple waveguide structure and four microheaters, light can be routed freely into any of the three output ports with arbitrary power ratios, with and without extra attenuation. This work may trigger new ideas in developing compact and efficient photonic integrated devices for applications in optical communication and computing. Full article
(This article belongs to the Special Issue Micro/Nano-Structure Based Optoelectronics and Photonics Devices)
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10 pages, 2085 KiB  
Article
Rapid Bacterial Motility Monitoring Using Inexpensive 3D-Printed OpenFlexure Microscopy Allows Microfluidic Antibiotic Susceptibility Testing
by Tai The Diep, Sarah Helen Needs, Samuel Bizley and Alexander D. Edwards
Micromachines 2022, 13(11), 1974; https://doi.org/10.3390/mi13111974 - 14 Nov 2022
Cited by 6 | Viewed by 2979
Abstract
Antibiotic susceptibility testing is vital to tackle the emergence and spread of antimicrobial resistance. Inexpensive digital CMOS cameras can be converted into portable digital microscopes using 3D printed x-y-z stages. Microscopic examination of bacterial motility can rapidly detect the response of microbes to [...] Read more.
Antibiotic susceptibility testing is vital to tackle the emergence and spread of antimicrobial resistance. Inexpensive digital CMOS cameras can be converted into portable digital microscopes using 3D printed x-y-z stages. Microscopic examination of bacterial motility can rapidly detect the response of microbes to antibiotics to determine susceptibility. Here, we present a new simple microdevice-miniature microscope cell measurement system for multiplexed antibiotic susceptibility testing. The microdevice is made using melt-extruded plastic film strips containing ten parallel 0.2 mm diameter microcapillaries. Two different antibiotics, ceftazidime and gentamicin, were prepared in Mueller-Hinton agar (0.4%) to produce an antibiotic-loaded microdevice for simple sample addition. This combination was selected to closely match current standard methods for both antibiotic susceptibility testing and motility testing. Use of low agar concentration permits observation of motile bacteria responding to antibiotic exposure as they enter capillaries. This device fits onto the OpenFlexure 3D-printed digital microscope using a Raspberry Pi computer and v2 camera, avoiding need for expensive laboratory microscopes. This inexpensive and portable digital microscope platform had sufficient magnification to detect motile bacteria, yet wide enough field of view to monitor bacteria behavior as they entered antibiotic-loaded microcapillaries. The image quality was sufficient to detect how bacterial motility was inhibited by different concentrations of antibiotic. We conclude that a 3D-printed Raspberry Pi-based microscope combined with disposable microfluidic test strips permit rapid, easy-to-use bacterial motility detection, with potential for aiding detection of antibiotic resistance. Full article
(This article belongs to the Special Issue Advances in Microfluidic Flow Cytometry)
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13 pages, 1861 KiB  
Article
Improving Swimming Performance of Photolithography-Based Microswimmers Using Curvature Structures
by Liyuan Tan, Zihan Wang, Zhi Chen, Xiangcheng Shi and U Kei Cheang
Micromachines 2022, 13(11), 1965; https://doi.org/10.3390/mi13111965 - 12 Nov 2022
Cited by 3 | Viewed by 2197
Abstract
The emergence of robotic microswimmers and their huge potential in biomedical applications such as drug delivery, non-invasive surgery, and bio-sensing facilitates studies to improve their effectiveness. Recently, achiral microswimmers that have neither flexible nor helical structures have garnered attention because of their simple [...] Read more.
The emergence of robotic microswimmers and their huge potential in biomedical applications such as drug delivery, non-invasive surgery, and bio-sensing facilitates studies to improve their effectiveness. Recently, achiral microswimmers that have neither flexible nor helical structures have garnered attention because of their simple structures and fabrication process while preserving adequate swimming velocity and controllability. In this paper, the crescent shape was utilized to create photolithography-fabricated crescent-shaped achiral microswimmers. The microswimmers were actuated using rotating magnetic fields at low Reynolds numbers. Compared with the previously reported achiral microswimmers, the crescent-shaped microswimmers showed significant improvement in forward swimming speed. The effects of different curvatures, arm angles, and procession angles on the velocities of microswimmers were investigated. Moreover, the optimal swimming motion was defined by adjusting the field strength of the magnetic field. Finally, the effect of the thickness of the microswimmers on their swimming velocity was investigated. Full article
(This article belongs to the Special Issue Magnetic Microrobots for Biomedical Applications)
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14 pages, 7178 KiB  
Article
Interface Dynamics and the Influence of Gravity on Droplet Generation in a Y-microchannel
by Alexandra Bran, Nicoleta Octavia Tanase and Corneliu Balan
Micromachines 2022, 13(11), 1941; https://doi.org/10.3390/mi13111941 - 10 Nov 2022
Viewed by 1705
Abstract
The present experimental investigation is focused on the influence of gravity upon water-droplet formation in a Y-microchannel filled with oil. The flows are in the Stokes regime, with very small capillary numbers and Ohnesorge numbers less than one. The study was performed in [...] Read more.
The present experimental investigation is focused on the influence of gravity upon water-droplet formation in a Y-microchannel filled with oil. The flows are in the Stokes regime, with very small capillary numbers and Ohnesorge numbers less than one. The study was performed in a square-cross-section channel, with a = 1.0 mm as the characteristic dimension and a flow rate ratio κ in a range between 0.55 and 1.8. The interface dynamics in the vicinity of breakup and the transitory plug flow regime after the detachment of the droplet were analysed. The dependence of droplet length L was correlated with the channel position against the gravity and κ parameters. The results of the work prove that, for κ=1, the droplet length L is independent of channel orientation. Full article
(This article belongs to the Special Issue Microfluidics for Health Monitoring)
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12 pages, 1713 KiB  
Article
Picoliter Droplet Generation and Dense Bead-in-Droplet Encapsulation via Microfluidic Devices Fabricated via 3D Printed Molds
by Tochukwu D. Anyaduba, Jonas A. Otoo and Travis S. Schlappi
Micromachines 2022, 13(11), 1946; https://doi.org/10.3390/mi13111946 - 10 Nov 2022
Cited by 8 | Viewed by 4465
Abstract
Picoliter-scale droplets have many applications in chemistry and biology, such as biomolecule synthesis, drug discovery, nucleic acid quantification, and single cell analysis. However, due to the complicated processes used to fabricate microfluidic channels, most picoliter (pL) droplet generation methods are limited to research [...] Read more.
Picoliter-scale droplets have many applications in chemistry and biology, such as biomolecule synthesis, drug discovery, nucleic acid quantification, and single cell analysis. However, due to the complicated processes used to fabricate microfluidic channels, most picoliter (pL) droplet generation methods are limited to research in laboratories with cleanroom facilities and complex instrumentation. The purpose of this work is to investigate a method that uses 3D printing to fabricate microfluidic devices that can generate droplets with sizes <100 pL and encapsulate single dense beads mechanistically. Our device generated monodisperse droplets as small as ~48 pL and we demonstrated the usefulness of this droplet generation technique in biomolecule analysis by detecting Lactobacillus acidophillus 16s rRNA via digital loop-mediated isothermal amplification (dLAMP). We also designed a mixer that can be integrated into a syringe to overcome dense bead sedimentation and found that the bead-in-droplet (BiD) emulsions created from our device had <2% of the droplets populated with more than 1 bead. This study will enable researchers to create devices that generate pL-scale droplets and encapsulate dense beads with inexpensive and simple instrumentation (3D printer and syringe pump). The rapid prototyping and integration ability of this module with other components or processes can accelerate the development of point-of-care microfluidic devices that use droplet-bead emulsions to analyze biological or chemical samples with high throughput and precision. Full article
(This article belongs to the Special Issue Droplet-Based Microfluidics: Design, Fabrication and Applications)
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12 pages, 4057 KiB  
Article
Fabrication and Evaluation of Tubule-on-a-Chip with RPTEC/HUVEC Co-Culture Using Injection-Molded Polycarbonate Chips
by Ju-Bi Lee, Hyoungseob Kim, Sol Kim and Gun Yong Sung
Micromachines 2022, 13(11), 1932; https://doi.org/10.3390/mi13111932 - 9 Nov 2022
Cited by 5 | Viewed by 2896
Abstract
To simulate the ADME process such as absorption, distribution, metabolism, and excretion in the human body after drug administration and to confirm the applicability of the mass production process, a microfluidic chip injection molded with polycarbonate (injection-molded chip (I-M chip)) was fabricated. Polycarbonate [...] Read more.
To simulate the ADME process such as absorption, distribution, metabolism, and excretion in the human body after drug administration and to confirm the applicability of the mass production process, a microfluidic chip injection molded with polycarbonate (injection-molded chip (I-M chip)) was fabricated. Polycarbonate materials were selected to minimize drug absorption. As a first step to evaluate the I-M chip, RPTEC (Human Renal Proximal Tubule Epithelial Cells) and HUVEC (Human Umbilical Vein Endothelial Cells) were co-cultured, and live and dead staining, TEER (trans-epithelial electrical resistance), glucose reabsorption, and permeability were compared using different membrane pore sizes of 0.4 μm and 3 μm. Drug excretion was confirmed through a pharmacokinetic test with metformin and cimetidine, and the gene expression of drug transporters was confirmed. As a result, it was confirmed that the cell viability was higher in the 3 μm pore size than in the 0.4 μm, the cell culture performed better, and the drug secretion was enhanced when the pore size was large. The injection-molded polycarbonate microfluidic chip is anticipated to be commercially viable for drug screening devices, particularly ADME tests. Full article
(This article belongs to the Special Issue Advances and Challenges in Biofabrication and Organ-on-a-Chip Platforms)
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6 pages, 2008 KiB  
Article
Thermo-Optic Phase Shifter with Interleaved Suspended Design for Power Efficiency and Speed Adjustment
by Feng Gao, Wu Xie, James You Sian Tan, Chew Ping Leong, Chao Li, Xianshu Luo and Guo-Qiang Lo
Micromachines 2022, 13(11), 1925; https://doi.org/10.3390/mi13111925 - 8 Nov 2022
Cited by 4 | Viewed by 1889
Abstract
Conventional thermo-optic devices—which can be broadly categorized to that with and without a thermal isolation trench—typically come with a tradeoff between thermal tuning efficiency and tuning speed. Here, we propose a method that allows us to directly define the tradeoff using a specially [...] Read more.
Conventional thermo-optic devices—which can be broadly categorized to that with and without a thermal isolation trench—typically come with a tradeoff between thermal tuning efficiency and tuning speed. Here, we propose a method that allows us to directly define the tradeoff using a specially designed thermo-optic phase shifter with an interleaved isolation trench. With the design, the tuning efficiency and speed can be precisely tailored simply by controlling the duty ratio (suspended length over total heater length) of the suspended design. Phase shifters are one of the main components in photonic-integrated circuits, and having phase shifters with a flexible design approach may enable the wide adoption of photonic applications such as an optical neural network and LiDAR. Full article
(This article belongs to the Special Issue Silicon Photonic Devices and Integration)
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30 pages, 4456 KiB  
Review
Recent Advances in Lossy Mode Resonance-Based Fiber Optic Sensors: A Review
by Vikas, Satyendra Kumar Mishra, Akhilesh Kumar Mishra, Paola Saccomandi and Rajneesh Kumar Verma
Micromachines 2022, 13(11), 1921; https://doi.org/10.3390/mi13111921 - 7 Nov 2022
Cited by 13 | Viewed by 3835
Abstract
Fiber optic sensors (FOSs) based on the lossy mode resonance (LMR) technique have gained substantial attention from the scientific community. The LMR technique displays several important features over the conventional surface plasmon resonance (SPR) phenomenon, for planning extremely sensitive FOSs. Unlike SPR, which [...] Read more.
Fiber optic sensors (FOSs) based on the lossy mode resonance (LMR) technique have gained substantial attention from the scientific community. The LMR technique displays several important features over the conventional surface plasmon resonance (SPR) phenomenon, for planning extremely sensitive FOSs. Unlike SPR, which mainly utilizes the thin film of metals, a wide range of materials such as conducting metal oxides and polymers support LMR. The past several years have witnessed a remarkable development in the field of LMR-based fiber optic sensors; through this review, we have tried to summarize the overall development of LMR-based fiber optic sensors. This review article not only provides the fundamental understanding and detailed explanation of LMR generation but also sheds light on the setup/configuration required to excite the lossy modes. Several geometries explored in the literature so far have also been addressed. In addition, this review includes a survey of the different materials capable of supporting lossy modes and explores new possible LMR supporting materials and their potential applications in sensing. Full article
(This article belongs to the Section A：Physics)
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14 pages, 3395 KiB  
Article
Dynamic Behaviours of Monodisperse Double Emulsion Formation in a Tri-Axial Capillary Device
by Yuchen Dai, Haotian Cha, Nhat-Khuong Nguyen, Lingxi Ouyang, Fariba Galogahi, Ajeet Singh Yadav, Hongjie An, Jun Zhang, Chin Hong Ooi and Nam-Trung Nguyen
Micromachines 2022, 13(11), 1877; https://doi.org/10.3390/mi13111877 - 31 Oct 2022
Cited by 5 | Viewed by 2017
Abstract
We investigated experimentally, analytically, and numerically the formation process of double emulsion formations under a dripping regime in a tri-axial co-flow capillary device. The results show that mismatches of core and shell droplets under a given flow condition can be captured both experimentally [...] Read more.
We investigated experimentally, analytically, and numerically the formation process of double emulsion formations under a dripping regime in a tri-axial co-flow capillary device. The results show that mismatches of core and shell droplets under a given flow condition can be captured both experimentally and numerically. We propose a semi-analytical model using the match ratio between the pinch-off length of the shell droplet and the product of the core growth rate and its pinch-off time. The mismatch issue can be avoided if the match ratio is lower than unity. We considered a model with the wall effect to predict the size of the matched double emulsion. The model shows slight deviations with experimental data if the Reynolds number of the continuous phase is lower than 0.06 but asymptotically approaches good agreement if the Reynolds number increases from 0.06 to 0.14. The numerical simulation generally agrees with the experiments under various flow conditions. Full article
(This article belongs to the Special Issue Droplet-Based Microfluidics: Design, Fabrication and Applications)
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7 pages, 2605 KiB  
Article
Heterogeneous CMOS Integration of InGaAs-OI nMOSFETs and Ge pMOSFETs Based on Dual-Gate Oxide Technique
by Xiaoyu Tang, Tao Hua, Yujie Liu and Zhezhe Han
Micromachines 2022, 13(11), 1806; https://doi.org/10.3390/mi13111806 - 23 Oct 2022
Viewed by 1380
Abstract
A compatible fabrication technology for integrating InGaAs nMOSFETs and Ge pMOSFETs is developed based on the development of the two-step gate oxide fabrication strategy. The direct wafer bonding method was utilized to obtain the InGaAs-Insulator-Ge structure, providing the heterogeneous channels for CMOS integration. [...] Read more.
A compatible fabrication technology for integrating InGaAs nMOSFETs and Ge pMOSFETs is developed based on the development of the two-step gate oxide fabrication strategy. The direct wafer bonding method was utilized to obtain the InGaAs-Insulator-Ge structure, providing the heterogeneous channels for CMOS integration. Superior transistor characteristics were achieved by optimizing the InGaAs gate oxide with a self-cleaning process in atomic layer deposition, and modifying the Ge gate oxide by the ozone post oxidation (OPO) technique, in the sequential two-step gate oxide fabrication process. With the combination of the gate-first fabrication process, superior on- and off-state characteristics, i.e., on current up to 8.3 µA/μm and leakage as low as 10−6 µA/μm, have been demonstrated in the integrated MOSFETs, together with the preferable symmetric output characteristics that promises excellent CMOS performances. Full article
(This article belongs to the Section D1: Semiconductor Devices)
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11 pages, 3146 KiB  
Article
High-Quality Fiber Bragg Gratings Inscribed by Femtosecond Laser Point-by-Point Technology
by Runxiao Chen, Jun He, Xizhen Xu, Jiafeng Wu, Ying Wang and Yiping Wang
Micromachines 2022, 13(11), 1808; https://doi.org/10.3390/mi13111808 - 23 Oct 2022
Cited by 9 | Viewed by 3722
Abstract
We experimentally studied the inscription of fiber Bragg gratings by using femtosecond (fs) laser point-by-point (PbP) technology. The effects of the focusing geometry, grating order, laser energy and grating length on the spectral characteristics of the PbP FBG were investigated. After [...] Read more.
We experimentally studied the inscription of fiber Bragg gratings by using femtosecond (fs) laser point-by-point (PbP) technology. The effects of the focusing geometry, grating order, laser energy and grating length on the spectral characteristics of the PbP FBG were investigated. After optimizing these parameters, a high-quality first-order PbP FBG with a reflectivity > 99.9% (i.e., Bragg resonance attenuation of 37.7 dB) and insertion loss (IL) of 0.03 dB was successfully created. Moreover, taking advantage of the excellent flexibility of the fs laser PbP technology, high-quality FBGs with various Bragg wavelengths ranging from 856 to 1902.6 nm were inscribed. Furthermore, wavelength-division-multiplexed (WDM) FBG arrays consisting of 10 FBGs were rapidly constructed. Additionally, a Fabry-Perot cavity was realized by using two high-quality FBGs, and its birefringence could be reduced from 3.04 × 10−5 to 1.77 × 10−6 by using a slit beam shaping-assisted femtosecond laser PbP technology. Therefore, such high-quality FBGs are promising to improve the performance of optical fiber sensors, lasers and communication devices. Full article
(This article belongs to the Special Issue Advanced Laser Fabrication for Optical Sensors)
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12 pages, 5301 KiB  
Article
Origami Inspired Laser Scanner
by Yu-Shin Wu and Shao-Kang Hung
Micromachines 2022, 13(10), 1796; https://doi.org/10.3390/mi13101796 - 21 Oct 2022
Viewed by 2155
Abstract
Diverse origami techniques and various selections of paper open new possibilities to create micromachines. By folding paper, this article proposes an original approach to build laser scanners, which manipulate optical beams precisely and realize valuable applications, including laser marking, cutting, engraving, and displaying. [...] Read more.
Diverse origami techniques and various selections of paper open new possibilities to create micromachines. By folding paper, this article proposes an original approach to build laser scanners, which manipulate optical beams precisely and realize valuable applications, including laser marking, cutting, engraving, and displaying. A prototype has been designed, implemented, actuated, and controlled. The experimental results demonstrate that the angular stroke, repeatability, full scale settling time, and resonant frequency are 20°, 0.849 m°, 330 ms, 68 Hz, respectively. Its durability, more than 35 million cycles, shows the potential to carry out serious tasks. Full article
(This article belongs to the Special Issue Origami Devices: Design and Application)
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17 pages, 1526 KiB  
Review
Developments in FRET- and BRET-Based Biosensors
by Yuexin Wu and Tianyu Jiang
Micromachines 2022, 13(10), 1789; https://doi.org/10.3390/mi13101789 - 20 Oct 2022
Cited by 19 | Viewed by 7382
Abstract
Resonance energy transfer technologies have achieved great success in the field of analysis. Particularly, fluorescence resonance energy transfer (FRET) and bioluminescence resonance energy transfer (BRET) provide strategies to design tools for sensing molecules and monitoring biological processes, which promote the development of biosensors. [...] Read more.
Resonance energy transfer technologies have achieved great success in the field of analysis. Particularly, fluorescence resonance energy transfer (FRET) and bioluminescence resonance energy transfer (BRET) provide strategies to design tools for sensing molecules and monitoring biological processes, which promote the development of biosensors. Here, we provide an overview of recent progress on FRET- and BRET-based biosensors and their roles in biomedicine, environmental applications, and synthetic biology. This review highlights FRET- and BRET-based biosensors and gives examples of their applications with their design strategies. The limitations of their applications and the future directions of their development are also discussed. Full article
(This article belongs to the Special Issue Prospects and Challenges of Biosensors towards Diagnostics of the Diseases and Health Monitoring)
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