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Micromachines
Volume 15
Issue 12
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Micromachines, Volume 15, Issue 12 (December 2024) – 128 articles

Cover Story (view full-size image): Magnetoelectric (ME) bulk and surface acoustic wave (BAW and SAW) devices drive innovation in wireless communication, bio-magnetic sensing, and quantum technology. An ultra-compact, low-power magnetoacoustic SAW isolator exploits coupling between quantum quasiparticles—magnons and phonons—in magnetic stacks to enable one-way RF power flow and efficient quantum information transduction. Paired with this isolator, a dual-band ME BAW antenna and sensor node utilizes its thickness and width modes to simultaneously detect ultra-weak bio-magnetic signals and realize bidirectional wireless communication, energy transfer, and data exchange with IoT. These devices revolutionize radar, IoT, full-duplex radio, and bio-sensing, advancing quantum and bio-magnetic technologies with ultra-compact, low-cost, and energy-efficient solutions. View this paper
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15 pages, 6148 KiB  
Article
Microfluidic Monodispersed Microbubble Generation for Production of Cavitation Nuclei
by Renjie Ning, Blake Acree, Mengren Wu and Yuan Gao
Micromachines 2024, 15(12), 1531; https://doi.org/10.3390/mi15121531 - 23 Dec 2024
Viewed by 591
Abstract
Microbubbles, acting as cavitation nuclei, undergo cycles of expansion, contraction, and collapse. This collapse generates shockwaves, alters local shear forces, and increases local temperature. Cavitation causes severe changes in pressure and temperature, resulting in surface erosion. Shockwaves strip material from surfaces, forming pits [...] Read more.
Microbubbles, acting as cavitation nuclei, undergo cycles of expansion, contraction, and collapse. This collapse generates shockwaves, alters local shear forces, and increases local temperature. Cavitation causes severe changes in pressure and temperature, resulting in surface erosion. Shockwaves strip material from surfaces, forming pits and cracks. Prolonged cavitation reduces the mechanical strength and fatigue life of materials, potentially leading to failure. Controlling bubble size and generating monodispersed bubbles is crucial for accurately modeling cavitation phenomena. In this work, we generate monodispersed microbubbles with controllable size using a novel and low-cost microfluidic method. We created an innovative T-junction structure that controls the two-phase flow for tiny, monodispersed bubble generation. Monodisperse microbubbles with diameters below one-fifth of the channel width (W = 100 µm) are produced due to the controlled pressure gradient. This microstructure, fabricated by a CNC milling technique, produces 20 μm bubbles without requiring high-resolution equipment and cleanroom environments. Bubble size is controlled with gas and liquid pressure ratio and microgeometry. This microbubble generation method provides a controllable and reproducible way for cavitation research. Full article
(This article belongs to the Special Issue Recent Advances in Microfluidic Lab-on-a-Chip Platform in North America and Europe)
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29 pages, 20951 KiB  
Article
Design and SAR Analysis of an AMC-Integrated Wearable Cavity-Backed SIW Antenna
by Yathavi Thangavelu, Balakumaran Thangaraju and Rajagopal Maheswar
Micromachines 2024, 15(12), 1530; https://doi.org/10.3390/mi15121530 - 23 Dec 2024
Viewed by 635
Abstract
Wearable communication technologies necessitate antenna designs that harmonize ergonomic compatibility, reliable performance, and minimal interaction with human tissues. However, high specific absorption rate (SAR) levels, limited radiation efficiency, and challenges in integration with flexible materials have significantly constrained widespread deployment. To address these [...] Read more.
Wearable communication technologies necessitate antenna designs that harmonize ergonomic compatibility, reliable performance, and minimal interaction with human tissues. However, high specific absorption rate (SAR) levels, limited radiation efficiency, and challenges in integration with flexible materials have significantly constrained widespread deployment. To address these limitations, this manuscript introduces a novel wearable cavity-backed substrate-integrated waveguide (SIW) antenna augmented with artificial magnetic conductor (AMC) structures. The proposed architecture is meticulously engineered using diverse textile substrates, including cotton, jeans, and jute, to synergistically integrate SIW and AMC technologies, mitigating body-induced performance degradation while ensuring safety and high radiation efficiency. The proposed design demonstrates significant performance enhancements, achieving SAR reductions to 0.672 W/kg on the spine and 0.341 W/kg on the forelimb for the cotton substrate. Furthermore, the AMC-backed implementation attains ultra-low reflection coefficients, as low as −26.56 dB, alongside a gain improvement of up to 1.37 dB, culminating in a total gain of 7.09 dBi. The impedance bandwidth exceeds the ISM band specifications, spanning 150 MHz (2.3–2.45 GHz). The design maintains remarkable resilience and operational stability under varying conditions, including dynamic bending and proximity to human body models. By substantially suppressing back radiation, enhancing directional gain, and preserving impedance matching, the AMC integration optimally adapts the antenna to body-centric communication scenarios. This study uniquely investigates the dielectric and mechanical properties of textile substrates within the AMC-SIW configuration, emphasizing their practicality for wearable applications. This research sets a precedent for wearable antenna innovation, achieving an unprecedented balance of flexibility, safety, and electromagnetic performance while establishing a foundation for next-generation wearable systems. Full article
(This article belongs to the Topic Innovation, Communication and Engineering)
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6 pages, 721 KiB  
Editorial
The Promise and Challenges of Bioprinting in Tissue Engineering
by Ryan Martin and Daeha Joung
Micromachines 2024, 15(12), 1529; https://doi.org/10.3390/mi15121529 - 23 Dec 2024
Viewed by 801
Abstract
Organ transplantation, biomimetic organ models, and the restoration of damaged or eviscerated tissues have been key goals in surgical and medical research since their inception [...] Full article
(This article belongs to the Section B2: Biofabrication and Tissue Engineering)
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3 pages, 156 KiB  
Editorial
Editorial for the Topic: MEMS in Italy
by Alberto Corigliano
Micromachines 2024, 15(12), 1528; https://doi.org/10.3390/mi15121528 - 23 Dec 2024
Viewed by 499
Abstract
Microsystems or microelectromechanical systems (MEMSs) over the last thirty years have seen impressive development in terms of potentialities and diffusion [...] Full article
18 pages, 10302 KiB  
Article
Investigation on Aluminum Alloy Reflector Mirror Processing Technology Combining Ultrasonic Rolling and Single-Point Diamond Turning
by Yuanhao Ma, Zhanjie Li, Gang Jin, Xiangyu Zhang, Longsi Li, Huaixin Lin, Guangyu Wang and Zhenyu Long
Micromachines 2024, 15(12), 1527; https://doi.org/10.3390/mi15121527 - 22 Dec 2024
Viewed by 636
Abstract
In the process of aluminum alloy reflector mirror processing, the structural defects of aluminum alloys present bottlenecks restricting the development of aluminum alloy reflector mirror processing technologies. Therefore, this study proposes an aluminum alloy reflector mirror processing method involving ultrasonic rolling and single-point [...] Read more.
In the process of aluminum alloy reflector mirror processing, the structural defects of aluminum alloys present bottlenecks restricting the development of aluminum alloy reflector mirror processing technologies. Therefore, this study proposes an aluminum alloy reflector mirror processing method involving ultrasonic rolling and single-point diamond turning. The core idea of this method is to use ultrasonic rolling to pretreat the surface of the workpiece to refine the grains and increase the hardness, then perform single-point diamond turning to improve the optical reflection performance. In this study, an ultrasonic rolling cutting experiment was carried out, and the influence of the material preparation method on the microstructure and hardness of the workpiece was analyzed. An ultrasonic rolling single-point diamond turning experiment was carried out, and the influence of the material preparation method on the reflection performance of single-point diamond turning was studied. Results showed that compared with single-point diamond turning after ordinary milling, the ultrasonic rolling single-point diamond turning method has certain advantages in improving the surface reflection performance, with an increase of 5.116%. The method proposed in this study can provide new ideas for the high-quality processing of aluminum alloy reflector mirrors. Full article
(This article belongs to the Special Issue Precision Optical Manufacturing and Processing)
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12 pages, 4881 KiB  
Article
Surface Enhancement of Titanium Ti-3Al-2.5V Through Laser Remelting Process—A Material Analysis
by Esmaeil Ghadiri Zahrani, Babak Soltani and Bahman Azarhoushang
Micromachines 2024, 15(12), 1526; https://doi.org/10.3390/mi15121526 - 22 Dec 2024
Viewed by 483
Abstract
This study evaluates the effects of laser parameters on the surface remelting of the Ti-3Al-2.5V alloy. A ms-laser equipped with a coaxial gas-pressure head integrated into a Swiss-type turning machine is used for the laser remelting process of cylindrical parts. The influence of [...] Read more.
This study evaluates the effects of laser parameters on the surface remelting of the Ti-3Al-2.5V alloy. A ms-laser equipped with a coaxial gas-pressure head integrated into a Swiss-type turning machine is used for the laser remelting process of cylindrical parts. The influence of different pulse frequencies, as well as varying intensities, is investigated. The results reveal that surface micro-cracks can be eliminated through laser remelting. Increasing the input laser intensity also increases the size of the melting pool. A similar effect is observed with higher pulse frequencies. The metallurgical microstructure and the size of the heat-affected zone of the remelted surface at different input laser energy levels are also examined. The results indicate that input laser energy influences phase transformation in the metallurgical microstructure, which correspondingly results in variations in micro-hardness within the heat-affected zone. The variations in laser fluence lead to a surface hardness improvement of approximately 15%. Full article
(This article belongs to the Special Issue Laser Micro/Nano Fabrication, Second Edition)
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9 pages, 2296 KiB  
Article
Improvement of the Thermal Performance of the GaN-on-Si Microwave High-Electron-Mobility Transistors by Introducing a GaN-on-Insulator Structure
by Lu Hao, Zhihong Liu, Hanghai Du, Shenglei Zhao, Han Wang, Jincheng Zhang and Yue Hao
Micromachines 2024, 15(12), 1525; https://doi.org/10.3390/mi15121525 - 21 Dec 2024
Viewed by 920
Abstract
GaN-on-Si high-electron-mobility transistors have emerged as the next generation of high-powered and cost-effective microwave devices; however, the limited thermal conductivity of the Si substrate prevents the realization of their potential. In this paper, a GaN-on-insulator (GNOI) structure is proposed to enhance the heat [...] Read more.
GaN-on-Si high-electron-mobility transistors have emerged as the next generation of high-powered and cost-effective microwave devices; however, the limited thermal conductivity of the Si substrate prevents the realization of their potential. In this paper, a GaN-on-insulator (GNOI) structure is proposed to enhance the heat dissipation ability of a GaN-on-Si HEMT. Electrothermal simulation was carried out to analyze the thermal performance of the GNOI-on-Si HEMTs with different insulator dielectrics, including SiO2, SiC, AlN, and diamond. The thermal resistance of the HEMTs was found to be able to be obviously reduced and the DC performance of the device can be obviously improved by removing the low-thermal-conductivity III-nitride transition layer and forming a GNOI-on-Si structure with SiC, AlN, or diamond as the bonding insulator dielectrics. Full article
(This article belongs to the Section D1: Semiconductor Devices)
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21 pages, 3013 KiB  
Review
Lab-on-a-Chip Devices for Nucleic Acid Analysis in Food Safety
by Inae Lee and Hae-Yeong Kim
Micromachines 2024, 15(12), 1524; https://doi.org/10.3390/mi15121524 - 21 Dec 2024
Viewed by 925
Abstract
Lab-on-a-chip (LOC) devices have been developed for nucleic acid analysis by integrating complex laboratory functions onto a miniaturized chip, enabling rapid, cost-effective, and highly sensitive on-site testing. This review examines the application of LOC technology in food safety, specifically in the context of [...] Read more.
Lab-on-a-chip (LOC) devices have been developed for nucleic acid analysis by integrating complex laboratory functions onto a miniaturized chip, enabling rapid, cost-effective, and highly sensitive on-site testing. This review examines the application of LOC technology in food safety, specifically in the context of nucleic acid-based analyses for detecting pathogens and contaminants. We focus on microfluidic-based LOC devices that optimize nucleic acid extraction and purification on the chip or amplification and detection processes based on isothermal amplification and polymerase chain reaction. We also explore advancements in integrated LOC devices that combine nucleic acid extraction, amplification, and detection processes within a single chip to minimize sample preparation time and enhance testing accuracy. The review concludes with insights into future trends, particularly the development of portable LOC technologies for rapid and efficient nucleic acid testing in food safety. Full article
(This article belongs to the Special Issue Advances in Microfluidic Chips for Chemical and Biomedical Applications)
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2 pages, 142 KiB  
Editorial
Microstructured Sensors: The Nexus of Innovation and Functionality
by Mingliang Li
Micromachines 2024, 15(12), 1523; https://doi.org/10.3390/mi15121523 - 21 Dec 2024
Viewed by 2261
Abstract
In an era of rapid technological evolution, the demand for functional sensors that can keep up with the pace is more pressing than ever [...] Full article
(This article belongs to the Special Issue Microstructured Sensors: From Design to Application)
3 pages, 173 KiB  
Editorial
Editorial on Optical Tweezers for the 15th Anniversary of Micromachines
by Mark Cronin-Golomb
Micromachines 2024, 15(12), 1522; https://doi.org/10.3390/mi15121522 - 21 Dec 2024
Viewed by 533
Abstract
The electric fields of tightly focused laser beams can be strong enough to apply appreciable force to microscopic objects, including biological entities such as cells, bacteria, and even viruses and biomolecules [...] Full article
18 pages, 2406 KiB  
Article
A Novel Microfluidic Platform for Personalized Anticancer Drug Screening Through Image Analysis
by Maria Veronica Lipreri, Marilina Tamara Totaro, Julia Alicia Boos, Maria Sofia Basile, Nicola Baldini and Sofia Avnet
Micromachines 2024, 15(12), 1521; https://doi.org/10.3390/mi15121521 - 21 Dec 2024
Viewed by 547
Abstract
The advancement of personalized treatments in oncology has garnered increasing attention, particularly for rare and aggressive cancer with low survival rates like the bone tumors osteosarcoma and chondrosarcoma. This study introduces a novel PDMS–agarose microfluidic device tailored for generating patient-derived tumor spheroids and [...] Read more.
The advancement of personalized treatments in oncology has garnered increasing attention, particularly for rare and aggressive cancer with low survival rates like the bone tumors osteosarcoma and chondrosarcoma. This study introduces a novel PDMS–agarose microfluidic device tailored for generating patient-derived tumor spheroids and serving as a reliable tool for personalized drug screening. Using this platform in tandem with a custom imaging index, we evaluated the impact of the anticancer agent doxorubicin on spheroids from both tumor types. The device produces 20 spheroids, each around 300 µm in diameter, within a 24 h timeframe, facilitating assessments of characteristics and reproducibility. Following spheroid generation, we measured patient-derived spheroid diameters in bright-field images, calcein AM-positive areas/volume, and the binary fraction area, a metric analyzing fluorescence intensity. By employing a specially developed equation that combines viability signal extension and intensity, we observed a substantial decrease in spheroid viability of around 75% for both sarcomas at the highest dosage (10 µM). Osteosarcoma spheroids exhibited greater sensitivity to doxorubicin than chondrosarcoma spheroids within 48 h. This approach provides a reliable in vitro model for aggressive sarcomas, representing a personalized approach for drug screening that could lead to more effective cancer treatments tailored to individual patients, despite some implementation challenges. Full article
(This article belongs to the Section B：Biology and Biomedicine)
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17 pages, 5039 KiB  
Article
Optimization of Parameters and Comparison of Detection Signals for Planar Coil Particle Detection Sensors with Different Core Materials
by Changzhi Gu, Chao Liu, Bo Liu, Wenbo Zhang, Chenzhao Bai, Chenyong Wang, Yuqing Sun and Hongpeng Zhang
Micromachines 2024, 15(12), 1520; https://doi.org/10.3390/mi15121520 - 20 Dec 2024
Viewed by 536
Abstract
The cleanliness of lubricating oil plays a key role in determining the operational health of mechanical systems, serving as a critical metric that delineates the extent of equipment wear. In this study, we present a magnetic-core-type planar coil particle detection sensor. The detection [...] Read more.
The cleanliness of lubricating oil plays a key role in determining the operational health of mechanical systems, serving as a critical metric that delineates the extent of equipment wear. In this study, we present a magnetic-core-type planar coil particle detection sensor. The detection accuracy and detection limit are improved by optimizing the magnetic field inside the sensor. The optimization of the magnetic field is achieved through the finite element simulation analysis of the coil and the magnetic core. First, the finite element simulation software COMSOL 6.0 is used to model the sensor in three dimensions (3D). Then, we study the distribution of the magnetic field under different coil radii, core conductivity levels, and other parameters. We obtain the sensor structure after optimizing the magnetic field. The sensor is made using experimental methods, and the iron particles and copper particles are detected. The results show that the lower limit of detection of iron particles can reach 46 μm, and the lower limit of detection of copper particles can reach 110 μm. Full article
(This article belongs to the Special Issue Micro/Nanostructures in Sensors and Actuators, 2nd Edition)
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17 pages, 9960 KiB  
Article
Simulation and Assessment of Thermal-Stress Analysis of Welding Materials in IGBT
by Yang Yang, Jibing Chen, Bowen Liu and Yiping Wu
Micromachines 2024, 15(12), 1519; https://doi.org/10.3390/mi15121519 - 20 Dec 2024
Viewed by 496
Abstract
Insulated gate bipolar transistors (IGBTs), as an important power semiconductor device, are susceptible to thermal stress, thermal fatigue, and mechanical stresses under high-voltage, high-current, and high-power conditions. Elevated heat dissipation within the module leads to fluctuating rises in temperature that accelerate its own [...] Read more.
Insulated gate bipolar transistors (IGBTs), as an important power semiconductor device, are susceptible to thermal stress, thermal fatigue, and mechanical stresses under high-voltage, high-current, and high-power conditions. Elevated heat dissipation within the module leads to fluctuating rises in temperature that accelerate its own degradation and failure, ultimately causing damage to the module as a whole and posing a threat to operator safety. Through ANSYS Workbench simulation analysis, it is possible to accurately predict the temperature distribution, equivalent stress, and equivalent strain of solder materials under actual working conditions, thus revealing the changing laws of the heat–mechanical interaction in solder materials. Simulation analysis results show that, under steady-state operating conditions, the highest point of the IGBT module’s overall junction temperature occurs in the center of the chip. Nanogold exhibited the best performance in terms of temperature and equivalent stress-strain among the five solders studied in this paper; defects near the edges caused greater harm to the module compared to those closer to the solder layer’s center. In terms of stress, defects located near the edge corners produced larger strains. Crazing damage in joints allows for a faster transfer of heat sources away from the center; in terms of stress, crazing has fewer detrimental effects on the integrity of the module as compared to through cracks. Simulation analysis can model the interaction of heat and equipment under realistic work conditions, comparing and evaluating different types of solder materials to select the most suitable solder material for product design and material selection. This aids in enhancing design precision and reliability. Full article
(This article belongs to the Topic Enhanced Heat Transfer and Advanced Energy Conversion Technology, 2nd Edition)
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9 pages, 2086 KiB  
Article
White Light-Emitting Flexible Displays with Quantum-Dot Film and Greenish-Blue Organic Light-Emitting Diodes
by Young Woo Kim, Seojin Kim, Chaeyeong Lee, Joo Hyun Jeong, Yun Hyeok Jeong, Yuhwa Bak, Seo Hyeon Kim, Sung Jin Park, Ko Eun Ham, Doeun Lee, Junpyo Song, Youngjin Song, Seung-Chan Jung, Oh Kwan Kwon, Jae-Hee Han, Sang Jik Kwon, Eou-Sik Cho and Yongmin Jeon
Micromachines 2024, 15(12), 1518; https://doi.org/10.3390/mi15121518 - 20 Dec 2024
Viewed by 695
Abstract
White organic light-emitting diodes (OLEDs) represent a significant technology in the display industry for the achievement of full color. However, sophisticated technologies are required for white light emission. In this paper, we developed a simple white light-emitting display device using a quantum-dot (QD) [...] Read more.
White organic light-emitting diodes (OLEDs) represent a significant technology in the display industry for the achievement of full color. However, sophisticated technologies are required for white light emission. In this paper, we developed a simple white light-emitting display device using a quantum-dot (QD) film and a greenish-blue OLED. The resulting QD-OLED produced a high-purity white color with a color temperature of 6000 K (CIEx,y = 0.32, 0.34) and achieved a maximum brightness of 14,638 cd/m2 at 7 V. This paper reports the fabrication of a white light-emitting QD-OLED with a straightforward structure and technology suitable for flexible displays. Full article
(This article belongs to the Special Issue Organic Electronic-Based Devices for Biomedical Applications)
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12 pages, 3196 KiB  
Article
Hollow Fiber Microreactor Combined with Digital Twin to Optimize the Antimicrobial Evaluation Process
by Kazuhiro Noda, Toshihiro Kasama, Marie Shinohara, Masakaze Hamada, Yukiko T. Matsunaga, Madoka Takai, Yoshikazu Ishii and Ryo Miyake
Micromachines 2024, 15(12), 1517; https://doi.org/10.3390/mi15121517 - 20 Dec 2024
Viewed by 510
Abstract
In order to reproduce pharmacokinetics (PK) profiles seen in vivo, the Hollow Fiber Infection Model (HFIM) is a useful in vitro module in the evaluation of antimicrobial resistance. In order to reduce the consumption of culture medium and drugs, we developed a hollow [...] Read more.
In order to reproduce pharmacokinetics (PK) profiles seen in vivo, the Hollow Fiber Infection Model (HFIM) is a useful in vitro module in the evaluation of antimicrobial resistance. In order to reduce the consumption of culture medium and drugs, we developed a hollow fiber microreactor applicable to the HFIM by integrating the HFIM function. Next, we constructed a novel control method by using the “digital twin” of the microreactor to achieve precise concentration control. By integrating functions of the HFIM, the extra-capillary space volume was reduced to less than 1/10 of conventional HFIM. The control method with the digital twin can keep drug concentration in the extra-capillary space within an error of 10% under simulated drug destruction. The control method with the digital twin can also stabilize the drug concentration both in the intra-capillary space and the extra-capillary space within 15 min. Full article
(This article belongs to the Section C：Chemistry)
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12 pages, 3116 KiB  
Article
Origin of the Temperature Dependence of Gate-Induced Drain Leakage-Assisted Erase in Three-Dimensional nand Flash Memories
by David G. Refaldi, Gerardo Malavena, Luca Chiavarone, Alessandro S. Spinelli and Christian Monzio Compagnoni
Micromachines 2024, 15(12), 1516; https://doi.org/10.3390/mi15121516 - 20 Dec 2024
Viewed by 585
Abstract
Through detailed experimental and modeling activities, this paper investigates the origin of the temperature dependence of the Erase operation in 3D nand flash arrays. First of all, experimental data collected down to the cryogenic regime on both charge-trap and floating-gate arrays are provided [...] Read more.
Through detailed experimental and modeling activities, this paper investigates the origin of the temperature dependence of the Erase operation in 3D nand flash arrays. First of all, experimental data collected down to the cryogenic regime on both charge-trap and floating-gate arrays are provided to demonstrate that the reduction in temperature makes cells harder to Erase irrespective of the nature of their storage layer. This evidence is then attributed to the weakening, with the decrease in temperature, of the gate-induced drain leakage (GIDL) current exploited to set the electrostatic potential of the body of the nand strings during Erase. Modeling results for the GIDL-assisted Erase operation, finally, allow not only to support this conclusion but also to directly correlate the change with temperature of the electrostatic potential of the string body with the change with temperature of the erased threshold-voltage of the memory cells. Full article
(This article belongs to the Section E：Engineering and Technology)
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13 pages, 3683 KiB  
Article
Automatic Single-Cell Harvesting for Fetal Nucleated Red Blood Cell Isolation on a Self-Assemble Cell Array (SACA) Chip
by Hsin-Yu Yang, Che-Hsien Lin, Yi-Wen Hu, Chih-Hsuan Chien, Mu-Chi Huang, Chun-Hao Lai, Jen-Kuei Wu and Fan-Gang Tseng
Micromachines 2024, 15(12), 1515; https://doi.org/10.3390/mi15121515 - 20 Dec 2024
Viewed by 715
Abstract
(1) Background: Fetal chromosomal examination is a critical component of modern prenatal testing. Traditionally, maternal serum biomarkers such as free β-human chorionic gonadotropin (Free β-HCG) and pregnancy-associated plasma protein A (PAPPA) have been employed for screening, achieving a detection rate of approximately 90% [...] Read more.
(1) Background: Fetal chromosomal examination is a critical component of modern prenatal testing. Traditionally, maternal serum biomarkers such as free β-human chorionic gonadotropin (Free β-HCG) and pregnancy-associated plasma protein A (PAPPA) have been employed for screening, achieving a detection rate of approximately 90% for fetuses with Down syndrome, albeit with a false positive rate of 5%. While amniocentesis remains the gold standard for the prenatal diagnosis of chromosomal abnormalities, including Down syndrome and Edwards syndrome, its invasive nature carries a significant risk of complications, such as infection, preterm labor, or miscarriage, occurring at a rate of 7 per 1000 procedures. Beyond Down syndrome and Edwards syndrome, other chromosomal abnormalities, such as trisomy of chromosomes 9, 16, or Barr bodies, pose additional diagnostic challenges. Non-invasive prenatal testing (NIPT) has emerged as a powerful alternative for fetal genetic screening by leveraging maternal blood sampling. However, due to the extremely low abundance of fetal cells in maternal circulation, NIPT based on fetal cells faces substantial technical challenges. (2) Methods: Fetal nucleated red blood cells (FnRBCs) were first identified in maternal circulation in a landmark study published in The Lancet in 1959. Due to their fetal origin and presence in maternal peripheral blood, FnRBCs represent an ideal target for non-invasive prenatal testing (NIPT). In this study, we introduce a novel self-assembled cell array (SACA) chip system, a microfluidic-based platform designed to efficiently settle and align cells into a monolayer at the chip’s base within five minutes using lateral flow dynamics and gravity. This system is integrated with a fully automated, multi-channel fluorescence scanning module, enabling the real-time imaging and molecular profiling of fetal cells through fluorescence-tagged antibodies. By employing a combination of Hoechst+/CD71+/HbF+/CD45− markers, the platform achieves the precise enrichment and isolation of FnRBCs at the single-cell level from maternal peripheral blood. (3) Results: The SACA chip system effectively reduces the displacement of non-target cells by 31.2%, achieving a single-cell capture accuracy of 97.85%. This isolation and enrichment system for single cells is well suited for subsequent genetic analysis. Furthermore, the platform achieves a high purity of isolated cells, overcoming the concentration detection limit of short tandem repeat (STR) analysis, demonstrating its capability for reliable non-invasive prenatal testing. (4) Conclusions: This study demonstrates that the SACA chip, combined with an automated image positioning system, can efficiently isolate single fetal nucleated red blood cells (FnRBCs) from 50 million PBMCs in 2 mL of maternal blood, completing STR analysis within 120 min. With higher purification efficiency compared to existing NIPT methods, this platform shows great promise for prenatal diagnostics and potential applications in other clinical fields. Full article
(This article belongs to the Special Issue Application of Microfluidic Technology in Bioengineering)
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16 pages, 3094 KiB  
Article
Optimization of Glucose Dehydrogenase Immobilization Strategies in a 3D-Printed Millireactor
by Vilim Marijan Boroša, Kristian Koštan, Renata Vičević, Ivan Karlo Cingesar, Domagoj Vrsaljko, Bruno Zelić, Ana Jurinjak Tušek and Anita Šalić
Micromachines 2024, 15(12), 1514; https://doi.org/10.3390/mi15121514 - 20 Dec 2024
Viewed by 803
Abstract
Enzymatic reactions play an important role in numerous industrial processes, e.g., in food production, pharmaceuticals and the production of biofuels. However, a major challenge when using enzymes in industrial applications is maintaining their stability and activity, especially under harsh operating conditions. To solve [...] Read more.
Enzymatic reactions play an important role in numerous industrial processes, e.g., in food production, pharmaceuticals and the production of biofuels. However, a major challenge when using enzymes in industrial applications is maintaining their stability and activity, especially under harsh operating conditions. To solve this problem, enzyme immobilization techniques have been developed. Immobilization involves fixing the enzymes on solid supports, which increases their stability, enables their reusability and facilitates the easy separation of reaction mixtures. In addition, immobilized enzymes are ideal for continuous flow systems such as millireactors, where they allow better control of reaction conditions, improving efficiency and product consistency. Glucose dehydrogenase is an important enzyme in biotechnology, particularly in biosensors and the production of biofuels, as it catalyzes the oxidation of glucose to gluconolactone, reducing NAD+ to NADH. However, like many other enzymes, it tends to lose activity over time. The immobilization of glucose dehydrogenase in a millireactor provides a controlled environment that increases the stability and activity of the enzyme. The aim of this study was to investigate the effects of different immobilization strategies on the performance of glucose dehydrogenase in a 3D printed millireactor. The enzyme was immobilized in alginate gel in three immobilization strategies: as beads, on the bottom surface, and on both the top and bottom surfaces of the millireactor. The results showed that the application of the enzyme on both surfaces improved the glucose conversion two-fold compared to immobilization in beads and four-fold compared to immobilization only on the bottom surface. The dual-surface enzyme immobilization strategy showed the highest efficiency, achieving the highest conversion of 95.76 ± 1.01% (τ = 131 min) and NADH productivity of 0.166 ± 0.01 mmol/(L·min) (τ = 7.11 min) combined with operational stability over five days. Effective diffusion rates comparable to those of aqueous solutions confirmed the suitability of alginate gels for biocatalysis. These advancements highlight the potential of this modular and scalable platform for various biotechnological applications. Full article
(This article belongs to the Special Issue Feature Papers of Micromachines in Biology and Biomedicine 2024)
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14 pages, 8807 KiB  
Article
A High-Repeatability Three-Dimensional Force Tactile Sensing System for Robotic Dexterous Grasping and Object Recognition
by Yaoguang Shi, Xiaozhou Lü, Wenran Wang, Xiaohui Zhou and Wensong Zhu
Micromachines 2024, 15(12), 1513; https://doi.org/10.3390/mi15121513 - 20 Dec 2024
Viewed by 592
Abstract
Robotic devices with integrated tactile sensors can accurately perceive the contact force, pressure, sliding, and other tactile information, and they have been widely used in various fields, including human–robot interaction, dexterous manipulation, and object recognition. To address the challenges associated with the initial [...] Read more.
Robotic devices with integrated tactile sensors can accurately perceive the contact force, pressure, sliding, and other tactile information, and they have been widely used in various fields, including human–robot interaction, dexterous manipulation, and object recognition. To address the challenges associated with the initial value drift, and to improve the durability and accuracy of the tactile detection for a robotic dexterous hand, in this study, a flexible tactile sensor is designed with high repeatability by introducing a supporting layer for pre-separation. The proposed tactile sensor has a detection range of 0–5 N with a resolution of 0.2 N, and the repeatability error is as relatively small as 1.5%. In addition, the response time of the proposed tactile sensor under loading and unloading conditions are 80 ms and 160 ms, respectively. Moreover, a three-dimensional force decoupling detection method is developed by distributing tactile sensor units on a non-coplanar robotic fingertip. Finally, using a backpropagation neural network, the classification and recognition processes of nine types of objects with different shapes and categories are realized, achieving an accuracy higher than 95%. The results show that the proposed three-dimensional force tactile sensing system could be beneficial for the delicate manipulation and recognition for robotic dexterous hands. Full article
(This article belongs to the Special Issue Wearable Electronics: Advances in Design, Materials, Fabrication, and Applications)
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12 pages, 6227 KiB  
Article
Study on the Influence of Au Content and Bonding Parameters on the Free Air Ball Morphology and Bonding Reliability of Ag-Au-Pd Alloy Wire
by Junling Fan, Fang He, Bing Chen, Junchao Zhang, Fan Yang, Jun Cao and Furong Wang
Micromachines 2024, 15(12), 1512; https://doi.org/10.3390/mi15121512 - 20 Dec 2024
Viewed by 423
Abstract
This article conducts wire bonding tests and cold/hot-cycle tests using φ 0.025 mm Ag-Au alloy wires and Ag-Au-Pd alloy wires with different specifications. The results show that, due to the addition of the alloying element Pd, under the same bonding parameters, the fracture [...] Read more.
This article conducts wire bonding tests and cold/hot-cycle tests using φ 0.025 mm Ag-Au alloy wires and Ag-Au-Pd alloy wires with different specifications. The results show that, due to the addition of the alloying element Pd, under the same bonding parameters, the fracture strength and ball-bonded point shear force of the Ag-Au-Pd alloy wires are significantly higher than those of the Ag-Au alloy wires. After the cold/hot-cycle tests, the failure probability of the Ag-Au-Pd alloy wires is approximately half that of the Ag-Au alloy wires. Among Ag-Au-Pd alloy wires, 92% break at the ideal positions, while 77% of the Ag-Au alloy wires break at the necks. As the Au content increases, the Free Air Ball (FAB) morphology of the Ag-Au-Pd alloy wires becomes more and more regular, gradually transitioning from a pointed ball to an ellipsoid and finally presenting a spherical shape. Full article
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11 pages, 16323 KiB  
Article
A D-Band Dual-Polarized High-Gain LTCC-Based Reflectarray Antenna Using SIW Magnetoelectric-Dipole Elements
by Zhuo-Wei Miao
Micromachines 2024, 15(12), 1511; https://doi.org/10.3390/mi15121511 - 20 Dec 2024
Viewed by 559
Abstract
This paper presents a D-band dual linear-polarized wideband high-gain reflectarray (RA) antenna using low-temperature co-fired-ceramic (LTCC) technology. The proposed element comprises a dual-polarized magnetoelectric (ME) dipole and a multilayer slot-coupling substrate-integrated waveguide (SIW) phase-delay structure, which are organized in accordance with the receiving/reradiating [...] Read more.
This paper presents a D-band dual linear-polarized wideband high-gain reflectarray (RA) antenna using low-temperature co-fired-ceramic (LTCC) technology. The proposed element comprises a dual-polarized magnetoelectric (ME) dipole and a multilayer slot-coupling substrate-integrated waveguide (SIW) phase-delay structure, which are organized in accordance with the receiving/reradiating (R/R) principle. The coverage of phase shifts for both orthogonal polarizations is set to be greater than 360 degrees by varying the length of the phase-delay structure. For verification, a D-band 1296-element RA prototype using the proposed unit cell is fabricated and measured in a THz chamber. The measured results show that the proposed RA achieves a peak gain of 32.25 and 33.03 dBi for the two orthogonal polarizations. The measured 3 dB gain bandwidths for the two orthogonal polarizations are 122–149 GHz (20%) and 123–149 GHz (19.3%), respectively. Full article
(This article belongs to the Section E：Engineering and Technology)
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22 pages, 8086 KiB  
Article
Research on Structural Optimization and Excitation Control Method Using a Two-Dimensional OWPT System for Capsule Robots Based on Non-Equivalent Coils
by Wenwei Li, Pingping Jiang, Zhiwu Wang and Guozheng Yan
Micromachines 2024, 15(12), 1510; https://doi.org/10.3390/mi15121510 - 19 Dec 2024
Viewed by 508
Abstract
The rapid development of wireless power transfer (WPT) technology has provided new avenues for supplying continuous and stable power to capsule robots. In this article, we propose a two-dimensional omnidirectional wireless power transfer (OWPT) system, which enables power to be transmitted effectively in [...] Read more.
The rapid development of wireless power transfer (WPT) technology has provided new avenues for supplying continuous and stable power to capsule robots. In this article, we propose a two-dimensional omnidirectional wireless power transfer (OWPT) system, which enables power to be transmitted effectively in multiple spatial directions. This system features a three-dimensional transmitting structure with a Helmholtz coil and saddle coil pairs, combined with a one-dimensional receiving structure. This design provides sufficient internal space, accommodating patients of various body types. Based on the magnetic field calculation and finite element analysis, the saddle coil structure is optimized to enhance magnetic field uniformity; to achieve a two-dimensional rotating magnetic field, a phase difference control method for the excitation signal is developed through the analysis of circuit topology and quantitative synthesis of non-equivalent magnetic field vectors. Finally, an experimental prototype is built, and the experimental results show that the one-dimensional transmitting coil achieves a minimum received voltage stability of 94.5% across different positions. When the three-dimensional transmitting coils operate together, a two-dimensional rotating magnetic field in the plane is achieved at the origin, providing a minimum received power of 550 mW with a voltage fluctuation rate of 7.68%. Full article
(This article belongs to the Section B：Biology and Biomedicine)
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16 pages, 3745 KiB  
Review
Biosensors for Seafood Safety Control—A Review
by Thi Ngoc Diep Trinh, Hanh An Nguyen, Nguyen Pham Anh Thi, Nguyen Nhat Nam, Nguyen Khoi Song Tran and Kieu The Loan Trinh
Micromachines 2024, 15(12), 1509; https://doi.org/10.3390/mi15121509 - 18 Dec 2024
Viewed by 770
Abstract
The increased demand for consuming seafood has made seafood production undergo a rapid period of growth. However, seafood has a high risk of contamination from harmful microorganisms and marine toxins which can cause health problems for humans consuming it. Concerning this issue, monitoring [...] Read more.
The increased demand for consuming seafood has made seafood production undergo a rapid period of growth. However, seafood has a high risk of contamination from harmful microorganisms and marine toxins which can cause health problems for humans consuming it. Concerning this issue, monitoring seafood safety has become a center of attention for researchers, and developing effective methods for detecting contamination in seafood has become a critical research field. In this context, biosensors have served as a promising approach to monitor seafood contamination. Compared to conventional methods, biosensors have some key benefits such as high sensitivity, selectivity, portability, and user-friendly operation. Along with significant advances in biosensors, processes of seafood monitoring can be simplified and performed outside the laboratory. In this review article, we describe the mechanisms of two main types of biosensors regarding electrochemical and optical biosensors. The current reports within the last five years on the application of these biosensors for seafood monitoring are also summarized. Full article
(This article belongs to the Special Issue Integrated Optical Sensors in Microfluidic Systems)
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21 pages, 5732 KiB  
Article
A Selective Electrochemical Sensor for Bisphenol A Detection Based on Cadmium (II) (bromophenyl)porphyrin and Gold Nanoparticles
by Fatma Rejab, Nour Elhouda Dardouri, Ahlem Rouis, Mosaab Echabaane, Habib Nasri, Boris Lakard, Hamdi Ben Halima and Nicole Jaffrezic-Renault
Micromachines 2024, 15(12), 1508; https://doi.org/10.3390/mi15121508 - 18 Dec 2024
Viewed by 694
Abstract
Bisphenol A (BPA) is a commonly synthetic chemical mainly used in producing plastic items. It is an endocrine-disrupting compound that causes irreversible health and environmental damage. Developing a simple method for BPA effective quantitative monitoring is emergently necessary. Herein, a novel electrochemical sensor [...] Read more.
Bisphenol A (BPA) is a commonly synthetic chemical mainly used in producing plastic items. It is an endocrine-disrupting compound that causes irreversible health and environmental damage. Developing a simple method for BPA effective quantitative monitoring is emergently necessary. Herein, a novel electrochemical sensor for BPA detection based on [(5,10,15,20-tetrakis(p-bromophenyl) porphyrinato] cadmium (II) [(CdTBrPP)] and gold nanoparticle (AuNPs)-modified screen-printed carbon electrode (SPCE) was elaborated. CdTBrPP was synthesized and then characterized with Ultraviolet–Visible Spectroscopy (UV/vis), Infrared Spectroscopy (IR), and Proton Nuclear Magnetic Resonance Spectroscopy (1H NMR) to confirm its successful synthesis. After drop-coating AuNPs and CdTBrPP on the SPCE, the sensor performance was evaluated using square wave voltammetry (SWV), a linear response in a concentration range from 10−11 M to 10−2 M, with a low detection limit (LOD) of 9.5 pM. The CdTBrPP/AuNPs/SPCE sensor demonstrates a high selectivity and reproducibility, making it a promising candidate for developing a low-cost water-monitoring system for detecting BPA. Additionally, the proposed sensor effectively detected BPA in both tap and mineral water samples. Full article
(This article belongs to the Section C：Chemistry)
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15 pages, 4141 KiB  
Article
The Role of Re-Entrant Microstructures in Modulating Droplet Evaporation Modes
by Hoang Huy Vu, Nam-Trung Nguyen and Navid Kashaninejad
Micromachines 2024, 15(12), 1507; https://doi.org/10.3390/mi15121507 - 18 Dec 2024
Viewed by 574
Abstract
The evaporation dynamics of sessile droplets on re-entrant microstructures are critical for applications in microfluidics, thermal management, and self-cleaning surfaces. Re-entrant structures, such as mushroom-like shapes with overhanging features, trap air beneath droplets to enhance non-wettability. The present study examines the evaporation of [...] Read more.
The evaporation dynamics of sessile droplets on re-entrant microstructures are critical for applications in microfluidics, thermal management, and self-cleaning surfaces. Re-entrant structures, such as mushroom-like shapes with overhanging features, trap air beneath droplets to enhance non-wettability. The present study examines the evaporation of a water droplet on silicon carbide (SiC) and silicon dioxide (SiO2) re-entrant structures, focusing on the effects of material composition and solid area fraction on volume reduction, contact angle, and evaporation modes. Using surface free energy (SFE) as an indicator of wettability, we find that the low SFE of SiC promotes quick depinning and contact line retraction, resulting in shorter CCL phases across different structures. For instance, the CCL phase accounts for 55–59% of the evaporation time on SiC surfaces, while on SiO2 it extends to 51–68%, reflecting a 7–23% increase in duration due to stronger pinning effects. Additionally, narrower pillar gaps, which increase the solid area fraction, further stabilize droplets by extending both CCL and constant contact angle (CCA) phases, while wider gaps enable faster depinning and evaporation. These findings illustrate how hydrophobicity (via SFE) and structural geometry (via solid area fraction) influence microscale interactions, offering insights for designing surfaces with optimized liquid management properties. Full article
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12 pages, 1940 KiB  
Article
Cost-Effective Bioimpedance Spectroscopy System for Monitoring Syncytialization In Vitro: Experimental and Numerical Validation of BeWo Cell Fusion
by Karim Saadé, Mohammed Areeb Hussain, Shannon A. Bainbridge, Raphael St-Gelais, Fabio Variola and Marianne Fenech
Micromachines 2024, 15(12), 1506; https://doi.org/10.3390/mi15121506 - 18 Dec 2024
Viewed by 938
Abstract
The placenta plays a critical role in nutrient and oxygen exchange during pregnancy, yet the effects of medicinal drugs on this selective barrier remain poorly understood. To overcome this, this study presents a cost-effective bioimpedance spectroscopy (BIS) system to assess tight junction integrity [...] Read more.
The placenta plays a critical role in nutrient and oxygen exchange during pregnancy, yet the effects of medicinal drugs on this selective barrier remain poorly understood. To overcome this, this study presents a cost-effective bioimpedance spectroscopy (BIS) system to assess tight junction integrity and monolayer formation in BeWo b30 cells, a widely used model of the multinucleated maternal–fetal exchange surface of the placental barrier. Cells were cultured on collagen-coated porous membranes and treated with forskolin to induce controlled syncytialization. Electrical impedance was measured using an entry level impedance analyzer, while immunofluorescence staining was used to confirm monolayer formation and syncytialization. The measurements and staining confirmed the formation of a confluent monolayer on day 4. In fact, the electrical resistance tripled for treated samples indicating a more electrically restrictive barrier. This resistance remained constant for treated samples reflecting the intact barrier’s integrity over the next 3 days. The measurements show that, on day 4, the electrical capacitance of the cells decreased for the treated samples as opposed to the untreated samples. This reflects that the surface area of the BeWo b30 cells decreased when the samples were treated with forskolin. Finally, a COMSOL model was developed to explore the effects of electrode positioning, depth, and distance on TEER measurements, explaining discrepancies in the literature. In fact, there was a substantial 97% and 39.4% difference in the obtained TEER values. This study demonstrates the AD2 device’s feasibility for monitoring placental barrier integrity and emphasizes the need for standardized setups for comparable results. The system can hence be used to analyze drug effects and nutrient transfer across the placental barrier. Full article
(This article belongs to the Special Issue Biosensors for Diagnostic and Detection Applications, 2nd Edition)
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9 pages, 2483 KiB  
Article
PET-PZT Dielectric Polarization: Electricity Harvested from Photon Energy
by Alex Nikolov, Sohail Murad and Jongju Lee
Micromachines 2024, 15(12), 1505; https://doi.org/10.3390/mi15121505 - 18 Dec 2024
Viewed by 543
Abstract
The effect of residual stress or heat on ferroelectrics used to convert photons into electricity was investigated. The data analysis reveals that when the PET-PZT piezoelectric transducer is UV-irradiated with a 405 nm wavelength, it becomes a photon–heat–stress electric energy converter and capacitator. [...] Read more.
The effect of residual stress or heat on ferroelectrics used to convert photons into electricity was investigated. The data analysis reveals that when the PET-PZT piezoelectric transducer is UV-irradiated with a 405 nm wavelength, it becomes a photon–heat–stress electric energy converter and capacitator. Our objective was to evaluate the PET-PZT photon–heat–stress electric energy conversion performance and the role of the light’s wavelength and intensity. Converting waste energy from energy-intensive processes and systems is crucial to reducing the environmental impact and achieving net-zero emissions. To achieve these, innovative materials are needed to efficiently convert ambient energy into electricity through various physical mechanisms, such as the photovoltaic effect, thermoelectricity, piezoelectricity, triboelectricity, and radiofrequency wireless power transfer. Full article
(This article belongs to the Collection Piezoelectric Transducers: Materials, Devices and Applications)
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19 pages, 506 KiB  
Review
MOSFET-Based Voltage Reference Circuits in the Last Decade: A Review
by Elisabetta Moisello, Edoardo Bonizzoni and Piero Malcovati
Micromachines 2024, 15(12), 1504; https://doi.org/10.3390/mi15121504 - 17 Dec 2024
Viewed by 1877
Abstract
Voltage reference circuits are a basic building block in most integrated microsystems, covering a wide spectrum of applications. Hence, they constitute a subject of great interest for the entire microelectronics community. MOSFET-based solutions, in particular, have emerged as the implementation of choice for [...] Read more.
Voltage reference circuits are a basic building block in most integrated microsystems, covering a wide spectrum of applications. Hence, they constitute a subject of great interest for the entire microelectronics community. MOSFET-based solutions, in particular, have emerged as the implementation of choice for realizing voltage reference circuits, given the supply voltage scaling and the ever-lower power consumption specifications in various applications. For these reasons, this paper aims to review MOSFET-based voltage reference circuits, illustrating their principles of operation, as well as presenting a detailed overview of the state-of-the-art, in order to paint an accurate picture of the encountered challenges and proposed solutions found in the field in the last decade, thus providing a starting point for future research in the field. Full article
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3 pages, 183 KiB  
Editorial
Thin-Film Deposition: From Fundamental Research to Applications
by Laura Patricia Rivera Reséndiz and José Guadalupe Quiñones Galván
Micromachines 2024, 15(12), 1503; https://doi.org/10.3390/mi15121503 - 17 Dec 2024
Viewed by 668
Abstract
In recent decades, we have witnessed incredible advancements in technology [...] Full article
(This article belongs to the Special Issue Thin Film Deposition: From Fundamental Research to Applications)
11 pages, 2514 KiB  
Article
Study on the Carrier Transport Process in Deep Ultraviolet Light-Emitting Diodes with Al-Content-Varied AlGaN Composite Last Quantum Barrier
by Wei Liu, Yujia Liu, Junhua Gao, Zeyu Liu, Bohan Shi, Linyuan Zhang, Xinnan Zhao and Runzhi Wang
Micromachines 2024, 15(12), 1502; https://doi.org/10.3390/mi15121502 - 16 Dec 2024
Viewed by 634
Abstract
Serious electron leakage and poor hole injection efficiency are still challenges for deep ultraviolet AlGaN-based light-emitting diodes with a traditional structure in achieving high performance. Currently, the majority of research works concentrate on optimizing the structures of the electron blocking layer (EBL) and [...] Read more.
Serious electron leakage and poor hole injection efficiency are still challenges for deep ultraviolet AlGaN-based light-emitting diodes with a traditional structure in achieving high performance. Currently, the majority of research works concentrate on optimizing the structures of the electron blocking layer (EBL) and last quantum barrier (LQB) separately, rather than considering them as an integrated structure. Therefore, in this study, an Al-content-varied AlGaN composite last quantum barrier (CLQB) layer is proposed to replace the traditional EBL and LQB layers. It is found that when the Al content in the CLQB decreases from 70% to 60% along the growth direction, the sample’s luminescence efficiency is improved, which can be ascribed to the higher carrier concentration in the multiple quantum well active region caused by suppressed electron leakage and enhanced hole injection. Additionally, in the CLQB structure, the carrier loss at the EBL/LQB hetero-interface, which is inevitable in the traditional structure, can be avoided. However, if the Al content in the CLQB changes in an opposite way, i.e., increasing from 60% to 70%, the device optoelectronic performance deteriorates, since the electron leakage is enhanced and the hole injection is suppressed. Full article
(This article belongs to the Section D1: Semiconductor Devices)
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