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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13 pages, 3698 KiB  
Article
Proof-of-Concept Vacuum Microelectronic NOR Gate Fabricated Using Microelectromechanical Systems and Carbon Nanotube Field Emitters
by Tasso von Windheim, Kristin H. Gilchrist, Charles B. Parker, Stephen Hall, James B. Carlson, David Stokes, Nicholas G. Baldasaro, Charles T. Hess, Leif Scheick, Bernard Rax, Brian Stoner, Jeffrey T. Glass and Jason J. Amsden
Micromachines 2023, 14(5), 973; https://doi.org/10.3390/mi14050973 - 29 Apr 2023
Cited by 2 | Viewed by 2121
Abstract
This paper demonstrates a fully integrated vacuum microelectronic NOR logic gate fabricated using microfabricated polysilicon panels oriented perpendicular to the device substrate with integrated carbon nanotube (CNT) field emission cathodes. The vacuum microelectronic NOR logic gate consists of two parallel vacuum tetrodes fabricated [...] Read more.
This paper demonstrates a fully integrated vacuum microelectronic NOR logic gate fabricated using microfabricated polysilicon panels oriented perpendicular to the device substrate with integrated carbon nanotube (CNT) field emission cathodes. The vacuum microelectronic NOR logic gate consists of two parallel vacuum tetrodes fabricated using the polysilicon Multi-User MEMS Processes (polyMUMPs). Each tetrode of the vacuum microelectronic NOR gate demonstrated transistor-like performance but with a low transconductance of 7.6 × 10−9 S as current saturation was not achieved due to a coupling effect between the anode voltage and cathode current. With both tetrodes working in parallel, the NOR logic capabilities were demonstrated. However, the device exhibited asymmetric performance due to differences in the CNT emitter performance in each tetrode. Because vacuum microelectronic devices are attractive for use in high radiation environments, to test the radiation survivability of this device platform, we demonstrated the function of a simplified diode device structure during exposure to gamma radiation at a rate of 45.6 rad(Si)/second. These devices represent a proof-of-concept for a platform that can be used to build intricate vacuum microelectronic logic devices for use in high-radiation environments. Full article
(This article belongs to the Special Issue On-Chip Electron Emission and Related Devices)
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11 pages, 2013 KiB  
Article
Designing Versatile Superhydrophilic Structures via an Alginate-Based Hydrophilic Plasticene
by Wenbo Shi, Haoyu Bai, Yaru Tian, Xinsheng Wang, Zhe Li, Xuanbo Zhu, Ye Tian and Moyuan Cao
Micromachines 2023, 14(5), 962; https://doi.org/10.3390/mi14050962 - 28 Apr 2023
Cited by 2 | Viewed by 2095
Abstract
The rational design of superhydrophilic materials with a controllable structure is a critical component in various applications, including solar steam generation, liquid spontaneous transport, etc. The arbitrary manipulation of the 2D, 3D, and hierarchical structures of superhydrophilic substrates is highly desirable for smart [...] Read more.
The rational design of superhydrophilic materials with a controllable structure is a critical component in various applications, including solar steam generation, liquid spontaneous transport, etc. The arbitrary manipulation of the 2D, 3D, and hierarchical structures of superhydrophilic substrates is highly desirable for smart liquid manipulation in both research and application fields. To design versatile superhydrophilic interfaces with various structures, here we introduce a hydrophilic plasticene that possesses high flexibility, deformability, water absorption, and crosslinking capabilities. Through a pattern-pressing process with a specific template, 2D prior fast spreading of liquids at speeds up to 600 mm/s was achieved on the superhydrophilic surface with designed channels. Additionally, 3D superhydrophilic structures can be facilely designed by combining the hydrophilic plasticene with a 3D-printed template. The assembly of 3D superhydrophilic microstructure arrays were explored, providing a promising route to facilitate the continuous and spontaneous liquid transport. The further modification of superhydrophilic 3D structures with pyrrole can promote the applications of solar steam generation. The optimal evaporation rate of an as-prepared superhydrophilic evaporator reached ~1.60 kg·m−2·h−1 with a conversion efficiency of approximately 92.96%. Overall, we envision that the hydrophilic plasticene should satisfy a wide range of requirements for superhydrophilic structures and update our understanding of superhydrophilic materials in both fabrication and application. Full article
(This article belongs to the Special Issue Fluid Manipulation: From Fundamentals to Applications)
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19 pages, 5149 KiB  
Review
Surface Acoustic Wave Humidity Sensor: A Review
by Maria Muzamil Memon, Qiong Liu, Ali Manthar, Tao Wang and Wanli Zhang
Micromachines 2023, 14(5), 945; https://doi.org/10.3390/mi14050945 - 27 Apr 2023
Cited by 23 | Viewed by 4293
Abstract
The Growing demands for humidity detection in commercial and industrial applications led to the rapid development of humidity sensors based on different techniques. Surface acoustic wave (SAW) technology is one of these methods that has been found to provide a powerful platform for [...] Read more.
The Growing demands for humidity detection in commercial and industrial applications led to the rapid development of humidity sensors based on different techniques. Surface acoustic wave (SAW) technology is one of these methods that has been found to provide a powerful platform for humidity sensing owing to its intrinsic features, including small size, high sensitivity, and simple operational mechanism. Similar to other techniques, the principle of humidity sensing in SAW devices is also realized by an overlaid sensitive film, which serves as the core element whose interaction with water molecules is responsible for overall performance. Therefore, most researchers are focused on exploring different sensing materials to achieve optimum performance characteristics. This article reviews sensing materials used to develop SAW humidity sensors and their responses based on theoretical aspects and experimental outcomes. Herein the influence of overlaid sensing film on the performance parameters of the SAW device, such as quality factor, signal amplitude, insertion loss, etc., is also highlighted. Lastly, a recommendation to minimize the significant change in device characteristics is presented, which we believe will be a good step for the future development of SAW humidity sensors. Full article
(This article belongs to the Special Issue Acoustic Transducers and Their Applications)
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16 pages, 9459 KiB  
Article
The Development of a 3D Printer-Inspired, Microgravity-Compatible Sample Preparation Device for Future Use Inside the International Space Station
by Kamfai Chan, Arunkumar Arumugam, Cole Markham, Ryan Jenson, Hao-Wei Wu and Season Wong
Micromachines 2023, 14(5), 937; https://doi.org/10.3390/mi14050937 - 26 Apr 2023
Cited by 3 | Viewed by 3268
Abstract
Biological testing on the International Space Station (ISS) is necessary in order to monitor the microbial burden and identify risks to crew health. With support from a NASA Phase I Small Business Innovative Research contract, we have developed a compact prototype of a [...] Read more.
Biological testing on the International Space Station (ISS) is necessary in order to monitor the microbial burden and identify risks to crew health. With support from a NASA Phase I Small Business Innovative Research contract, we have developed a compact prototype of a microgravity-compatible, automated versatile sample preparation platform (VSPP). The VSPP was built by modifying entry-level 3D printers that cost USD 200–USD 800. In addition, 3D printing was also used to prototype microgravity-compatible reagent wells and cartridges. The VSPP’s primary function would enable NASA to rapidly identify microorganisms that could affect crew safety. It has the potential to process samples from various sample matrices (swab, potable water, blood, urine, etc.), thus yielding high-quality nucleic acids for downstream molecular detection and identification in a closed-cartridge system. When fully developed and validated in microgravity environments, this highly automated system will allow labor-intensive and time-consuming processes to be carried out via a turnkey, closed system using prefilled cartridges and magnetic particle-based chemistries. This manuscript demonstrates that the VSPP can extract high-quality nucleic acids from urine (Zika viral RNA) and whole blood (human RNase P gene) in a ground-level laboratory setting using nucleic acid-binding magnetic particles. The viral RNA detection data showed that the VSPP can process contrived urine samples at clinically relevant levels (as low as 50 PFU/extraction). The extraction of human DNA from eight replicate samples showed that the DNA extraction yield is highly consistent (there was a standard deviation of 0.4 threshold cycle when the extracted and purified DNA was tested via real-time polymerase chain reaction). Additionally, the VSPP underwent 2.1 s drop tower microgravity tests to determine if its components are compatible for use in microgravity. Our findings will aid future research in adapting extraction well geometry for 1 g and low g working environments operated by the VSPP. Future microgravity testing of the VSPP in the parabolic flights and in the ISS is planned. Full article
(This article belongs to the Special Issue 3D-Printed Microdevices: From Design to Applications)
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15 pages, 15204 KiB  
Article
A Fast Soft Continuum Catheter Robot Manufacturing Strategy Based on Heterogeneous Modular Magnetic Units
by Tieshan Zhang, Gen Li, Xiong Yang, Hao Ren, Dong Guo, Hong Wang, Ki Chan, Zhou Ye, Tianshuo Zhao, Chengfei Zhang, Wanfeng Shang and Yajing Shen
Micromachines 2023, 14(5), 911; https://doi.org/10.3390/mi14050911 - 23 Apr 2023
Cited by 1 | Viewed by 3193
Abstract
Developing small-scale continuum catheter robots with inherent soft bodies and high adaptability to different environments holds great promise for biomedical engineering applications. However, current reports indicate that these robots meet challenges when it comes to quick and flexible fabrication with simpler processing components. [...] Read more.
Developing small-scale continuum catheter robots with inherent soft bodies and high adaptability to different environments holds great promise for biomedical engineering applications. However, current reports indicate that these robots meet challenges when it comes to quick and flexible fabrication with simpler processing components. Herein, we report a millimeter-scale magnetic-polymer-based modular continuum catheter robot (MMCCR) that is capable of performing multifarious bending through a fast and general modular fabrication strategy. By preprogramming the magnetization directions of two types of simple magnetic units, the assembled MMCCR with three discrete magnetic sections could be transformed from a single curvature pose with a large tender angle to a multicurvature S shape in the applied magnetic field. Through static and dynamic deformation analyses for MMCCRs, high adaptability to varied confined spaces can be predicted. By employing a bronchial tree phantom, the proposed MMCCRs demonstrated their capability to adaptively access different channels, even those with challenging geometries that require large bending angles and unique S-shaped contours. The proposed MMCCRs and the fabrication strategy shine new light on the design and development of magnetic continuum robots with versatile deformation styles, which would further enrich broad potential applications in biomedical engineering. Full article
(This article belongs to the Special Issue Magnetic Microrobots for Biomedical Applications)
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15 pages, 10278 KiB  
Article
Hyperelastic Modeling and Validation of Hybrid-Actuated Soft Robot with Pressure-Stiffening
by Majid Roshanfar, Salar Taki, Amir Sayadi, Renzo Cecere, Javad Dargahi and Amir Hooshiar
Micromachines 2023, 14(5), 900; https://doi.org/10.3390/mi14050900 - 22 Apr 2023
Cited by 15 | Viewed by 3356
Abstract
Soft robots have gained popularity, especially in intraluminal applications, because their soft bodies make them safer for surgical interventions than flexures with rigid backbones. This study investigates a pressure-regulating stiffness tendon-driven soft robot and provides a continuum mechanics model for it towards using [...] Read more.
Soft robots have gained popularity, especially in intraluminal applications, because their soft bodies make them safer for surgical interventions than flexures with rigid backbones. This study investigates a pressure-regulating stiffness tendon-driven soft robot and provides a continuum mechanics model for it towards using that in adaptive stiffness applications. To this end, first, a central single-chamber pneumatic and tri-tendon-driven soft robot was designed and fabricated. Afterward, the classic Cosserat’s rod model was adopted and augmented with the hyperelastic material model. The model was then formulated as a boundary-value problem and was solved using the shooting method. To identify the pressure-stiffening effect, a parameter-identification problem was formulated to identify the relationship between the flexural rigidity of the soft robot and internal pressure. The flexural rigidity of the robot at various pressures was optimized to match theoretical deformation and experiments. The theoretical findings of arbitrary pressures were then compared with the experiment for validation. The internal chamber pressure was in the range of 0 to 40 kPa and the tendon tensions were in the range of 0 to 3 N. The theoretical and experimental findings were in fair agreement for tip displacement with a maximum error of 6.40% of the flexure’s length. Full article
(This article belongs to the Special Issue Soft Actuators: Design, Fabrication and Applications)
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11 pages, 7409 KiB  
Article
Creating Stretchable Electronics from Dual Layer Flex-PCB for Soft Robotic Cardiac Mapping Catheters
by Abdellatif Ait Lahcen, Alexandre Caprio, Weihow Hsue, Cory Tschabrunn, Christopher Liu, Bobak Mosadegh and Simon Dunham
Micromachines 2023, 14(4), 884; https://doi.org/10.3390/mi14040884 - 20 Apr 2023
Cited by 4 | Viewed by 3223
Abstract
The authors present in this study the development of a novel method for creating stretchable electronics from dual-layer flex printed circuit boards (flex-PCBs) as a platform for soft robotic sensor arrays (SRSAs) for cardiac voltage mapping applications. There is a crucial need for [...] Read more.
The authors present in this study the development of a novel method for creating stretchable electronics from dual-layer flex printed circuit boards (flex-PCBs) as a platform for soft robotic sensor arrays (SRSAs) for cardiac voltage mapping applications. There is a crucial need for devices that utilize multiple sensors and provide high performance signal acquisition for cardiac mapping. Previously, our group demonstrated how single-layer flex-PCB can be postprocessed to create a stretchable electronic sensing array. In this work, a detailed fabrication process for creating a dual-layer multielectrode flex-PCB SRSA is presented, along with relevant parameters to achieve optimal postprocessing with a laser cutter. The dual-layer flex-PCB SRSA’s ability to acquire electrical signals is demonstrated both in vitro as well as in vivo on a Leporine cardiac surface. These SRSAs could be extended into full-chamber cardiac mapping catheter applications. Our results show a significant contribution towards the scalable use of dual-layer flex-PCB for stretchable electronics. Full article
(This article belongs to the Special Issue Feature Papers of Micromachines in 'Engineering and Technology' 2023)
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25 pages, 4865 KiB  
Review
Recent Trends in Structures and Interfaces of MEMS Transducers for Audio Applications: A Review
by Alessandro Gemelli, Marco Tambussi, Samuele Fusetto, Antonio Aprile, Elisabetta Moisello, Edoardo Bonizzoni and Piero Malcovati
Micromachines 2023, 14(4), 847; https://doi.org/10.3390/mi14040847 - 14 Apr 2023
Cited by 24 | Viewed by 8563
Abstract
In recent years, Micro-Electro-Mechanical Systems (MEMS) technology has had an impressive impact in the field of acoustic transducers, allowing the development of smart, low-cost, and compact audio systems that are employed in a wide variety of highly topical applications (consumer devices, medical equipment, [...] Read more.
In recent years, Micro-Electro-Mechanical Systems (MEMS) technology has had an impressive impact in the field of acoustic transducers, allowing the development of smart, low-cost, and compact audio systems that are employed in a wide variety of highly topical applications (consumer devices, medical equipment, automotive systems, and many more). This review, besides analyzing the main integrated sound transduction principles typically exploited, surveys the current State-of-the-Art scenario, presenting the recent performance advances and trends of MEMS microphones and speakers. In addition, the interface Integrated Circuits (ICs) needed to properly read the sensed signals or, on the other hand, to drive the actuation structures are addressed with the aim of offering a complete overview of the currently adopted solutions. Full article
(This article belongs to the Special Issue NEMS/MEMS Devices and Applications)
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19 pages, 2528 KiB  
Article
Importance of Spatial Arrangement of Cardiomyocyte Network for Precise and Stable On-Chip Predictive Cardiotoxicity Measurement
by Kazufumi Sakamoto, Suguru Matsumoto, Nanami Abe, Mitsuru Sentoku and Kenji Yasuda
Micromachines 2023, 14(4), 854; https://doi.org/10.3390/mi14040854 - 14 Apr 2023
Cited by 3 | Viewed by 2452
Abstract
One of the advantages of human stem cell-derived cell-based preclinical screening is the reduction of the false negative/positive misjudgment of lead compounds for predicting their effectiveness and risks during the early stage of development. However, as the community effect of cells was neglected [...] Read more.
One of the advantages of human stem cell-derived cell-based preclinical screening is the reduction of the false negative/positive misjudgment of lead compounds for predicting their effectiveness and risks during the early stage of development. However, as the community effect of cells was neglected in the conventional single cell-based in vitro screening, the potential difference in results caused by the cell number and their spatial arrangement differences has not yet been sufficiently evaluated. Here, we have investigated the effect of the community size and spatial arrangement difference for cardiomyocyte network response against the proarrhythmic compounds from the viewpoint of in vitro cardiotoxicity. Using three different typical types of cell networks of cardiomyocytes, small cluster, large square sheet, and large closed-loop sheet were formed in shaped agarose microchambers fabricated on a multielectrode array chip simultaneously, and their responses were compared against the proarrhythmic compound, E-4031. The interspike intervals (ISIs) in large square sheets and closed-loop sheets were durable and maintained stable against E-4031 even at a high dose of 100 nM. In contrast, those in the small cluster, which fluctuated even without E-4031, acquired stable beating reflecting the antiarrhythmic efficacy of E-4031 from a 10 nM medium dose administration. The repolarization index, field potential duration (FPD), was prolonged in closed-loop sheets with 10 nM E-4031, even though small clusters and large sheets remained normal at this concentration. Moreover, FPDs of large sheets were the most durable against E-4031 among the three geometries of cardiomyocyte networks. The results showed the apparent spatial arrangement dependence on the stability of their interspike intervals, and FPD prolongation, indicating the importance of the geometry control of cell networks for representing the appropriate response of cardiomyocytes against the adequate amount of compounds for in vitro ion channel measurement. Full article
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11 pages, 3577 KiB  
Article
Pulse-on-Demand Operation for Precise High-Speed UV Laser Microstructuring
by Jernej Jan Kočica, Jaka Mur, Julien Didierjean, Arnaud Guillossou, Julien Saby, Jaka Petelin, Girolamo Mincuzzi and Rok Petkovšek
Micromachines 2023, 14(4), 843; https://doi.org/10.3390/mi14040843 - 13 Apr 2023
Cited by 7 | Viewed by 3328
Abstract
Laser microstructuring has been studied extensively in the last decades due to its versatile, contactless processing and outstanding precision and structure quality on a wide range of materials. A limitation of the approach has been identified in the utilization of high average laser [...] Read more.
Laser microstructuring has been studied extensively in the last decades due to its versatile, contactless processing and outstanding precision and structure quality on a wide range of materials. A limitation of the approach has been identified in the utilization of high average laser powers, with scanner movement fundamentally limited by laws of inertia. In this work, we apply a nanosecond UV laser working in an intrinsic pulse-on-demand mode, ensuring maximal utilization of the fastest commercially available galvanometric scanners at scanning speeds from 0 to 20 m/s. The effects of high-frequency pulse-on-demand operation were analyzed in terms of processing speeds, ablation efficiency, resulting surface quality, repeatability, and precision of the approach. Additionally, laser pulse duration was varied in single-digit nanosecond pulse durations and applied to high throughput microstructuring. We studied the effects of scanning speed on pulse-on-demand operation, single- and multipass laser percussion drilling performance, surface structuring of sensitive materials, and ablation efficiency for pulse durations in the range of 1–4 ns. We confirmed the pulse-on-demand operation suitability for microstructuring for a range of frequencies from below 1 kHz to 1.0 MHz with 5 ns timing precision and identified the scanners as the limiting factor even at full utilization. The ablation efficiency was improved with longer pulse durations, but structure quality degraded. Full article
(This article belongs to the Special Issue Laser Micro/Nano Fabrication)
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13 pages, 2565 KiB  
Article
Flexible, Heat-Durable, and Highly Sensitive Piezoelectrets from Cyclic Olefin Copolymer with Microhoneycomb Structure
by Hui Wang, Xiaolin Wang and Changchun Zeng
Micromachines 2023, 14(4), 829; https://doi.org/10.3390/mi14040829 - 8 Apr 2023
Cited by 2 | Viewed by 2075
Abstract
This paper discusses the fabrication and characterization of cyclic olefin copolymer (COC)-based pseudo-piezoelectric materials (piezoelectrets) with exceptionally high piezoelectric activity, and their potential use in sensing applications. Piezoelectrets that utilize a novel microhoneycomb structure to achieve high piezoelectric sensitivity are carefully engineered and [...] Read more.
This paper discusses the fabrication and characterization of cyclic olefin copolymer (COC)-based pseudo-piezoelectric materials (piezoelectrets) with exceptionally high piezoelectric activity, and their potential use in sensing applications. Piezoelectrets that utilize a novel microhoneycomb structure to achieve high piezoelectric sensitivity are carefully engineered and fabricated at a low temperature using a supercritical CO2-assisted assembly. The quasistatic piezoelectric coefficient d33 of the material can reach up to 12,900 pCN−1 when charged at 8000 V. The materials also exhibit excellent thermal stability. The charge build-up in the materials and the actuation behavior of the materials are also investigated. Finally, applications of these materials in pressure sensing and mapping and in wearable sensing are demonstrated. Full article
(This article belongs to the Special Issue Advanced Electrostatic Sensors and Actuators)
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19 pages, 2417 KiB  
Article
Novel Size-Variable Dedicated Rodent Oxygenator for ECLS Animal Models—Introduction of the “RatOx” Oxygenator and Preliminary In Vitro Results
by Lasse J. Strudthoff, Jannis Focke, Felix Hesselmann, Andreas Kaesler, Ana Martins Costa, Peter C. Schlanstein, Thomas Schmitz-Rode, Ulrich Steinseifer, Niklas B. Steuer, Bettina Wiegmann, Jutta Arens and Sebastian V. Jansen
Micromachines 2023, 14(4), 800; https://doi.org/10.3390/mi14040800 - 31 Mar 2023
Cited by 6 | Viewed by 3011
Abstract
The overall survival rate of extracorporeal life support (ECLS) remains at 60%. Research and development has been slow, in part due to the lack of sophisticated experimental models. This publication introduces a dedicated rodent oxygenator (“RatOx”) and presents preliminary in vitro classification tests. [...] Read more.
The overall survival rate of extracorporeal life support (ECLS) remains at 60%. Research and development has been slow, in part due to the lack of sophisticated experimental models. This publication introduces a dedicated rodent oxygenator (“RatOx”) and presents preliminary in vitro classification tests. The RatOx has an adaptable fiber module size for various rodent models. Gas transfer performances over the fiber module for different blood flows and fiber module sizes were tested according to DIN EN ISO 7199. At the maximum possible amount of effective fiber surface area and a blood flow of 100 mL/min, the oxygenator performance was tested to a maximum of 6.27 mL O2/min and 8.2 mL CO2/min, respectively. The priming volume for the largest fiber module is 5.4 mL, while the smallest possible configuration with a single fiber mat layer has a priming volume of 1.1 mL. The novel RatOx ECLS system has been evaluated in vitro and has demonstrated a high degree of compliance with all pre-defined functional criteria for rodent-sized animal models. We intend for the RatOx to become a standard testing platform for scientific studies on ECLS therapy and technology. Full article
(This article belongs to the Special Issue Biohybrid Lung Assist Devices)
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12 pages, 5954 KiB  
Article
Improving the Thickness Uniformity of Micro Gear by Multi-Step, Self-Aligned Lithography and Electroforming
by Huan Wang, Jing Xie, Tao Fan, Dapeng Sun and Chaobo Li
Micromachines 2023, 14(4), 775; https://doi.org/10.3390/mi14040775 - 30 Mar 2023
Cited by 8 | Viewed by 1900
Abstract
The thickness nonuniformity of an electroformed layer is a bottleneck problem for electroformed micro metal devices. In this paper, a new fabrication method is proposed to improve the thickness uniformity of micro gear, which is the key element of various microdevices. The effect [...] Read more.
The thickness nonuniformity of an electroformed layer is a bottleneck problem for electroformed micro metal devices. In this paper, a new fabrication method is proposed to improve the thickness uniformity of micro gear, which is the key element of various microdevices. The effect of the thickness of the photoresist on the uniformity was studied by simulation analysis, which showed that as the thickness of the photoresist increased, the thickness nonuniformity of the electroformed gear should decrease due to the reduced edge effect of the current density. Differently from the traditional method performed by one-step front lithography and electroforming, multi-step, self-aligned lithography and electroforming are used to fabricate micro gear structures in proposed method, which intermittently keeps the thickness of photoresist from decreasing during processes of alternate lithography and electroforming. The experimental results show that the thickness uniformity of micro gear fabricated by the proposed method was improved by 45.7% compared with that fabricated by the traditional method. Meanwhile, the roughness of the middle region of the gear structure was reduced by 17.4%. Full article
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13 pages, 4949 KiB  
Article
A Design Approach to Reducing Stress and Distortion Caused by Adhesive Assembly in Micromachined Deformable Mirrors
by Wenkuan Man and Thomas G. Bifano
Micromachines 2023, 14(4), 740; https://doi.org/10.3390/mi14040740 - 27 Mar 2023
Cited by 2 | Viewed by 2398
Abstract
A common problem in deformable mirror assembly is that the adhesion of actuators to an optical mirror face sheet introduces unwanted topography due to large local stresses generated at the adhesive joint. A new approach to minimizing that effect is described, with inspiration [...] Read more.
A common problem in deformable mirror assembly is that the adhesion of actuators to an optical mirror face sheet introduces unwanted topography due to large local stresses generated at the adhesive joint. A new approach to minimizing that effect is described, with inspiration taken from St. Venant’s principle, a fundamental precept in solid mechanics. It is demonstrated that moving the adhesive joint to the end of a slender post extending from the face sheet largely eliminates deformation due to adhesive stresses. A practical implementation of this design innovation is described, using silicon-on-insulator wafers and deep reactive ion etching. Simulation and experiments validate the effectiveness of the approach, reducing stress-induced topography on a test structure by a factor of 50. A prototype electromagnetic DM using this design approach is described, and its actuation is demonstrated. This new design can benefit a wide range of DMs that rely on actuator arrays that are adhesively bonded to a mirror face sheet. Full article
(This article belongs to the Special Issue MEMS Packaging Technologies and 3D Integration, 2nd Edition)
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14 pages, 6754 KiB  
Article
Evaluation of Polydimethylsiloxane (PDMS) as a Substrate for the Realization of Flexible/Wearable Antennas and Sensors
by Praveen Kumar Sharma and Jae-Young Chung
Micromachines 2023, 14(4), 735; https://doi.org/10.3390/mi14040735 - 26 Mar 2023
Cited by 28 | Viewed by 5141
Abstract
To demonstrate that the silicone-based polymer polydimethylsiloxane (PDMS) is suitable as a substrate for flexible/wearable antennae and sensors, an investigation of its various properties was carried out. The substrate was first developed in compliance with the requirements, and then its anisotropy was investigated [...] Read more.
To demonstrate that the silicone-based polymer polydimethylsiloxane (PDMS) is suitable as a substrate for flexible/wearable antennae and sensors, an investigation of its various properties was carried out. The substrate was first developed in compliance with the requirements, and then its anisotropy was investigated using an experimental bi-resonator approach. This material exhibited modest but discernible anisotropy, with values of ~6.2/25 % for the dielectric constant and loss tangent, respectively. Its anisotropic behavior was confirmed by a parallel dielectric constant (εpar) ~2.717 and an evaluated perpendicular dielectric constant (εperp) ~2.570—εpar > εperp by 5.7%. Temperature affected PDMS’s dielectric properties. Lastly, the simultaneous impact of bending and anisotropy of the flexible substrate PDMS on the resonance properties of planar structures was also addressed, and these had diametrically opposed effects. PDMS appears to be a good contender as a substrate for flexible/wearable antennae and sensors based on all experimental evaluations conducted for this research. Full article
(This article belongs to the Special Issue Miniaturized Wearable Antennas)
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14 pages, 2473 KiB  
Article
Electrochemical Redox Cycling Behavior of Gold Nanoring Electrodes Microfabricated on a Silicon Micropillar
by Haocheng Yin, Chao Tan, Shabnam Siddiqui and Prabhu U. Arumugam
Micromachines 2023, 14(4), 726; https://doi.org/10.3390/mi14040726 - 24 Mar 2023
Viewed by 2320
Abstract
We report the microfabrication and characterization of concentric gold nanoring electrodes (Au NREs), which were fabricated by patterning two gold nanoelectrodes on the same silicon (Si) micropillar tip. Au NREs of 165 ± 10 nm in width were micropatterned on a 6.5 ± [...] Read more.
We report the microfabrication and characterization of concentric gold nanoring electrodes (Au NREs), which were fabricated by patterning two gold nanoelectrodes on the same silicon (Si) micropillar tip. Au NREs of 165 ± 10 nm in width were micropatterned on a 6.5 ± 0.2 µm diameter 80 ± 0.5 µm height Si micropillar with an intervening ~ 100 nm thick hafnium oxide insulating layer between the two nanoelectrodes. Excellent cylindricality of the micropillar with vertical sidewalls as well as a completely intact layer of a concentric Au NRE including the entire micropillar perimeter has been achieved as observed via scanning electron microscopy and energy dispersive spectroscopy data. The electrochemical behavior of the Au NREs was characterized by steady-state cyclic voltammetry and electrochemical impedance spectroscopy. The applicability of Au NREs to electrochemical sensing was demonstrated by redox cycling with the ferro/ferricyanide redox couple. The redox cycling amplified the currents by 1.63-fold with a collection efficiency of > 90% on a single collection cycle. The proposed micro-nanofabrication approach with further optimization studies shows great promise for the creation and expansion of concentric 3D NRE arrays with controllable width and nanometer spacing for electroanalytical research and applications such as single-cell analysis and advanced biological and neurochemical sensing. Full article
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9 pages, 3778 KiB  
Article
Design of Wearable Finger Sensors for Rehabilitation Applications
by Beyza Bozali, Sepideh Ghodrat and Kaspar M. B. Jansen
Micromachines 2023, 14(4), 710; https://doi.org/10.3390/mi14040710 - 23 Mar 2023
Cited by 6 | Viewed by 2674
Abstract
As an emerging technology, smart textiles have attracted attention for rehabilitation purposes or to monitor heart rate, blood pressure, breathing rate, body posture, as well as limb movements. Traditional rigid sensors do not always provide the desired level of comfort, flexibility, and adaptability. [...] Read more.
As an emerging technology, smart textiles have attracted attention for rehabilitation purposes or to monitor heart rate, blood pressure, breathing rate, body posture, as well as limb movements. Traditional rigid sensors do not always provide the desired level of comfort, flexibility, and adaptability. To improve this, recent research focuses on the development of textile-based sensors. In this study, knitted strain sensors that are linear up to 40% strain with a sensitivity of 1.19 and a low hysteresis characteristic were integrated into different versions of wearable finger sensors for rehabilitation purposes. The results showed that the different finger sensor versions have accurate responses to different angles of the index finger at relaxation, 45° and 90°. Additionally, the effect of spacer layer thickness between the finger and sensor was investigated. Full article
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12 pages, 4085 KiB  
Article
Heterogeneous Multi-Material Flexible Piezoresistive Sensor with High Sensitivity and Wide Measurement Range
by Tingting Yu, Yebo Tao, Yali Wu, Dongguang Zhang, Jiayi Yang and Gang Ge
Micromachines 2023, 14(4), 716; https://doi.org/10.3390/mi14040716 - 23 Mar 2023
Cited by 9 | Viewed by 2301
Abstract
Flexible piezoresistive sensors (FPSs) have the advantages of compact structure, convenient signal acquisition and fast dynamic response; they are widely used in motion detection, wearable electronic devices and electronic skins. FPSs accomplish the measurement of stresses through piezoresistive material (PM). However, FPSs based [...] Read more.
Flexible piezoresistive sensors (FPSs) have the advantages of compact structure, convenient signal acquisition and fast dynamic response; they are widely used in motion detection, wearable electronic devices and electronic skins. FPSs accomplish the measurement of stresses through piezoresistive material (PM). However, FPSs based on a single PM cannot achieve high sensitivity and wide measurement range simultaneously. To solve this problem, a heterogeneous multi-material flexible piezoresistive sensor (HMFPS) with high sensitivity and a wide measurement range is proposed. The HMFPS consists of a graphene foam (GF), a PDMS layer and an interdigital electrode. Among them, the GF serves as a sensing layer, providing high sensitivity, and the PDMS serves as a supporting layer, providing a large measurement range. The influence and principle of the heterogeneous multi-material (HM) on the piezoresistivity were investigated by comparing the three HMFPS with different sizes. The HM proved to be an effective way to produce flexible sensors with high sensitivity and a wide measurement range. The HMFPS-10 has a sensitivity of 0.695 kPa−1, a measurement range of 0–14,122 kPa, fast response/recovery (83 ms and 166 ms) and excellent stability (2000 cycles). In addition, the potential application of the HMFPS-10 in human motion monitoring was demonstrated. Full article
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29 pages, 12157 KiB  
Review
Recent State and Challenges in Spectroelectrochemistry with Its Applications in Microfluidics
by Zhenglong Li, Charmi Chande, Yu-Hsuan Cheng and Sagnik Basuray
Micromachines 2023, 14(3), 667; https://doi.org/10.3390/mi14030667 - 17 Mar 2023
Cited by 2 | Viewed by 3438
Abstract
This review paper presents the recent developments in spectroelectrochemical (SEC) technologies. The coupling of spectroscopy and electrochemistry enables SEC to do a detailed and comprehensive study of the electron transfer kinetics and vibrational spectroscopic fingerprint of analytes during electrochemical reactions. Though SEC is [...] Read more.
This review paper presents the recent developments in spectroelectrochemical (SEC) technologies. The coupling of spectroscopy and electrochemistry enables SEC to do a detailed and comprehensive study of the electron transfer kinetics and vibrational spectroscopic fingerprint of analytes during electrochemical reactions. Though SEC is a promising technique, the usage of SEC techniques is still limited. Therefore, enough publicity for SEC is required, considering the promising potential in the analysis fields. Unlike previously published review papers primarily focused on the relatively frequently used SEC techniques (ultraviolet-visible SEC and surface-enhanced Raman spectroscopy SEC), the two not-frequently used but promising techniques (nuclear magnetic resonance SEC and dark-field microscopy SEC) have also been studied in detail. This review paper not only focuses on the applications of each SEC method but also details their primary working mechanism. In short, this paper summarizes each SEC technique’s working principles, current applications, challenges encountered, and future development directions. In addition, each SEC technique’s applicative research directions are detailed and compared in this review work. Furthermore, integrating SEC techniques into microfluidics is becoming a trend in minimized analysis devices. Therefore, the usage of SEC techniques in microfluidics is discussed. Full article
(This article belongs to the Special Issue Micro- and Nano-Systems for Manipulation, Actuation and Sensing)
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36 pages, 6688 KiB  
Review
Photonic Crystal Enhanced Fluorescence: A Review on Design Strategies and Applications
by Yanyu Xiong, Skye Shepherd, Joseph Tibbs, Amanda Bacon, Weinan Liu, Lucas D. Akin, Takhmina Ayupova, Seemesh Bhaskar and Brian T. Cunningham
Micromachines 2023, 14(3), 668; https://doi.org/10.3390/mi14030668 - 17 Mar 2023
Cited by 72 | Viewed by 11083
Abstract
Nanoscale fluorescence emitters are efficient for measuring biomolecular interactions, but their utility for applications requiring single-unit observations is constrained by the need for large numerical aperture objectives, fluorescence intermittency, and poor photon collection efficiency resulting from omnidirectional emission. Photonic crystal (PC) structures hold [...] Read more.
Nanoscale fluorescence emitters are efficient for measuring biomolecular interactions, but their utility for applications requiring single-unit observations is constrained by the need for large numerical aperture objectives, fluorescence intermittency, and poor photon collection efficiency resulting from omnidirectional emission. Photonic crystal (PC) structures hold promise to address the aforementioned challenges in fluorescence enhancement. In this review, we provide a broad overview of PCs by explaining their structures, design strategies, fabrication techniques, and sensing principles. Furthermore, we discuss recent applications of PC-enhanced fluorescence-based biosensors incorporated with emerging technologies, including nucleic acids sensing, protein detection, and steroid monitoring. Finally, we discuss current challenges associated with PC-enhanced fluorescence and provide an outlook for fluorescence enhancement with photonic-plasmonics coupling and their promise for point-of-care biosensing as well monitoring analytes of biological and environmental relevance. The review presents the transdisciplinary applications of PCs in the broad arena of fluorescence spectroscopy with broad applications in photo-plasmonics, life science research, materials chemistry, cancer diagnostics, and internet of things. Full article
(This article belongs to the Special Issue Photon-Driven Technologies: Exploring the Latest Advancements)
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17 pages, 5904 KiB  
Review
Electric and Magnetic Field-Driven Dynamic Structuring for Smart Functional Devices
by Koohee Han
Micromachines 2023, 14(3), 661; https://doi.org/10.3390/mi14030661 - 16 Mar 2023
Cited by 12 | Viewed by 3943
Abstract
The field of soft matter is rapidly growing and pushing the limits of conventional materials science and engineering. Soft matter refers to materials that are easily deformed by thermal fluctuations and external forces, allowing for better adaptation and interaction with the environment. This [...] Read more.
The field of soft matter is rapidly growing and pushing the limits of conventional materials science and engineering. Soft matter refers to materials that are easily deformed by thermal fluctuations and external forces, allowing for better adaptation and interaction with the environment. This has opened up opportunities for applications such as stretchable electronics, soft robotics, and microfluidics. In particular, soft matter plays a crucial role in microfluidics, where viscous forces at the microscale pose a challenge to controlling dynamic material behavior and operating functional devices. Field-driven active colloidal systems are a promising model system for building smart functional devices, where dispersed colloidal particles can be activated and controlled by external fields such as magnetic and electric fields. This review focuses on building smart functional devices from field-driven collective patterns, specifically the dynamic structuring of hierarchically ordered structures. These structures self-organize from colloidal building blocks and exhibit reconfigurable collective patterns that can implement smart functions such as shape shifting and self-healing. The review clarifies the basic mechanisms of field-driven particle dynamic behaviors and how particle–particle interactions determine the collective patterns of dynamic structures. Finally, the review concludes by highlighting representative application areas and future directions. Full article
(This article belongs to the Special Issue Microfluidics for Soft Matter and Mechanobiology, Volume II)
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15 pages, 4433 KiB  
Article
Design and Print Terahertz Metamaterials Based on Electrohydrodynamic Jet
by Tong Yang, Xinyu Li, Bo Yu and Cheng Gong
Micromachines 2023, 14(3), 659; https://doi.org/10.3390/mi14030659 - 15 Mar 2023
Cited by 6 | Viewed by 3031
Abstract
Terahertz metamaterials are some of the core components of the new generation of high-frequency optoelectronic devices, which have excellent properties that natural materials do not have. The unit structures are generally much smaller than the wavelength, so preparation is mainly based on semiconductor [...] Read more.
Terahertz metamaterials are some of the core components of the new generation of high-frequency optoelectronic devices, which have excellent properties that natural materials do not have. The unit structures are generally much smaller than the wavelength, so preparation is mainly based on semiconductor processes, such as coating, photolithography and etching. Although the processing resolution is high, it is also limited by complex processing, long cycles, and high cost. In this paper, a design method for dual-band terahertz metamaterials and a simple, rapid, low-cost metamaterial preparation scheme based on step-motor-driven electrohydrodynamic jet technology are proposed. By transforming an open-source 3D printer, the metamaterial structures can be directly printed without complex semiconductor processes. To verify effectiveness, the sample was directly printed using nano conductive silver paste as consumable material. Then, a fiber-based multi-mode terahertz time-domain spectroscopy system was built for testing. The experimental results were in good agreement with the theoretical simulation. Full article
(This article belongs to the Special Issue Terahertz and Infrared Metamaterial Devices, 2nd Edition)
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7 pages, 1829 KiB  
Article
Electrically Inspired Flexible Electrochemical Film Power Supply for Long-Term Epidermal Sensors
by Hao Zheng, Xingguo Zhang, Chengcheng Li, Wangwang Zhu, Dachao Li and Zhihua Pu
Micromachines 2023, 14(3), 650; https://doi.org/10.3390/mi14030650 - 13 Mar 2023
Cited by 4 | Viewed by 2265
Abstract
This paper, for the first time, reports an electrically inspired flexible electrochemical film power supply for long-term epidermal sensors. This device can periodically provide electrical power for several hours after a short-time electrical activation. The electrical activation makes acetylcholine, which is infused into [...] Read more.
This paper, for the first time, reports an electrically inspired flexible electrochemical film power supply for long-term epidermal sensors. This device can periodically provide electrical power for several hours after a short-time electrical activation. The electrical activation makes acetylcholine, which is infused into the subcutaneous tissue by iontophoresis. The interstitial fluid (ISF) with glucose molecules is then permeated autonomously for several hours. At this period, the device can provide electrical power. The electrical power is generated from the catalyzing reaction between the glucose oxidase immobilized on the anode and the permeated glucose molecules. After the ISF permeation stops, we give a short-time electrical activation to provide electrical power for several hours again. The power supply is flexible, which makes it adaptively conform to skin. The episodic short-time electrical activation can be enabled by an integrated small film lithium-ion battery. This method extends the service life of a lithium-ion battery 10-fold and suggests the application of small lithium-ion batteries for long-term epidermal sensors. Full article
(This article belongs to the Special Issue Physics in Micro/Nano Devices: From Fundamental to Application)
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14 pages, 3004 KiB  
Article
High-Throughput Gel Microbeads as Incubators for Bacterial Competition Study
by Trang Anh Nguyen-Le, Xinne Zhao, Michael Bachmann, Philip Ruelens, J. Arjan G. M. de Visser and Larysa Baraban
Micromachines 2023, 14(3), 645; https://doi.org/10.3390/mi14030645 - 12 Mar 2023
Cited by 3 | Viewed by 2849
Abstract
Bacteria primarily live in structured environments, such as colonies and biofilms, attached to surfaces or growing within soft tissues. They are engaged in local competitive and cooperative interactions impacting our health and well-being, for example, by affecting population-level drug resistance. Our knowledge of [...] Read more.
Bacteria primarily live in structured environments, such as colonies and biofilms, attached to surfaces or growing within soft tissues. They are engaged in local competitive and cooperative interactions impacting our health and well-being, for example, by affecting population-level drug resistance. Our knowledge of bacterial competition and cooperation within soft matrices is incomplete, partly because we lack high-throughput tools to quantitatively study their interactions. Here, we introduce a method to generate a large amount of agarose microbeads that mimic the natural culture conditions experienced by bacteria to co-encapsulate two strains of fluorescence-labeled Escherichia coli. Focusing specifically on low bacterial inoculum (1–100 cells/capsule), we demonstrate a study on the formation of colonies of both strains within these 3D scaffolds and follow their growth kinetics and interaction using fluorescence microscopy in highly replicated experiments. We confirmed that the average final colony size is inversely proportional to the inoculum size in this semi-solid environment as a result of limited available resources. Furthermore, the colony shape and fluorescence intensity per colony are distinctly different in monoculture and co-culture. The experimental observations in mono- and co-culture are compared with predictions from a simple growth model. We suggest that our high throughput and small footprint microbead system is an excellent platform for future investigation of competitive and cooperative interactions in bacterial communities under diverse conditions, including antibiotics stress. Full article
(This article belongs to the Special Issue Biomaterials and Biodevices for Rapid Detection)
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12 pages, 8877 KiB  
Article
Microfluidic Coupling of Step Emulsification and Deterministic Lateral Displacement for Producing Satellite-Free Droplets and Particles
by Guangchong Ji, Yusuke Kanno and Takasi Nisisako
Micromachines 2023, 14(3), 622; https://doi.org/10.3390/mi14030622 - 8 Mar 2023
Cited by 8 | Viewed by 2793
Abstract
Step emulsification, which uses a geometry-dependent mechanism for generating uniformly sized droplets, has recently gained considerable attention because of its robustness against flow fluctuations. However, like shear-based droplet generation, step emulsification is susceptible to impurities caused by satellite droplets. Herein, we demonstrate the [...] Read more.
Step emulsification, which uses a geometry-dependent mechanism for generating uniformly sized droplets, has recently gained considerable attention because of its robustness against flow fluctuations. However, like shear-based droplet generation, step emulsification is susceptible to impurities caused by satellite droplets. Herein, we demonstrate the integration of deterministic lateral displacement (DLD) to separate the main and satellite droplets produced during step emulsification. Step-emulsification nozzles (16 μm deep) in the upstream region of the proposed device were arrayed on the sidewalls of the main channel (91 μm deep). In the downstream region, the DLD micropillars were arrayed periodically with a critical diameter (cut-off value for size-based separation) of 37 μm. When an acrylate monomer and aqueous polyvinyl alcohol solution were infused as the dispersed and continuous phases, respectively, the nozzles produced monodisperse main droplets in the dripping regime, with an average diameter of ~60 μm, coefficient of variation (CV) value below 3%, and satellite droplets of ~3 μm. Upon entering the DLD region near the sidewall, these main and satellite droplets were gradually separated through the pillars based on their sizes. Finally, off-chip photopolymerization yielded monodisperse polymeric microspheres with an average diameter of 55 μm and a CV value of 2.9% (n = 202). Full article
(This article belongs to the Section E:Engineering and Technology)
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15 pages, 2952 KiB  
Article
Innovative Fabrication of Hollow Microneedle Arrays Enabling Blood Sampling with a Self-Powered Microfluidic Patch
by Lorenz Van Hileghem, Shashwat Kushwaha, Agnese Piovesan, Pieter Verboven, Bart Nicolaï, Dominiek Reynaerts, Francesco Dal Dosso and Jeroen Lammertyn
Micromachines 2023, 14(3), 615; https://doi.org/10.3390/mi14030615 - 7 Mar 2023
Cited by 12 | Viewed by 5639
Abstract
Microneedles are gaining a lot of attention in the context of sampling cutaneous biofluids such as capillary blood. Their minimal invasiveness and user-friendliness make them a prominent substitute for venous puncture or finger-pricking. Although the latter is suitable for self-sampling, the impracticality of [...] Read more.
Microneedles are gaining a lot of attention in the context of sampling cutaneous biofluids such as capillary blood. Their minimal invasiveness and user-friendliness make them a prominent substitute for venous puncture or finger-pricking. Although the latter is suitable for self-sampling, the impracticality of manual handling and the difficulty of obtaining enough qualitative sample is driving the search for better solutions. In this context, hollow microneedle arrays (HMNAs) are particularly interesting for completely integrating sample-to-answer solutions as they create a duct between the skin and the sampling device. However, the fabrication of sharp-tipped HMNAs with a high aspect ratio (AR) is challenging, especially since a length of ≥1500 μm is desired to reach the blood capillaries. In this paper, we first described a novel two-step fabrication protocol for HMNAs in stainless steel by percussion laser drilling and subsequent micro-milling. The HMNAs were then integrated into a self-powered microfluidic sampling patch, containing a capillary pump which was optimized to generate negative pressure differences up to 40.9 ± 1.8 kPa. The sampling patch was validated in vitro, showing the feasibility of sampling 40 μL of liquid. It is anticipated that our proof-of-concept is a starting point for more sophisticated all-in-one biofluid sampling and point-of-care testing systems. Full article
(This article belongs to the Special Issue Feature Papers of Micromachines in Biology and Biomedicine 2023)
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12 pages, 5697 KiB  
Article
Multi-Depth Computer-Generated Hologram Based on Stochastic Gradient Descent Algorithm with Weighted Complex Loss Function and Masked Diffraction
by Jiale Quan, Binbin Yan, Xinzhu Sang, Chongli Zhong, Hui Li, Xiujuan Qin, Rui Xiao, Zhi Sun, Yu Dong and Huming Zhang
Micromachines 2023, 14(3), 605; https://doi.org/10.3390/mi14030605 - 6 Mar 2023
Cited by 4 | Viewed by 2679
Abstract
In this paper, we propose a method to generate multi-depth phase-only holograms using stochastic gradient descent (SGD) algorithm with weighted complex loss function and masked multi-layer diffraction. The 3D scene can be represented by a combination of layers in different depths. In the [...] Read more.
In this paper, we propose a method to generate multi-depth phase-only holograms using stochastic gradient descent (SGD) algorithm with weighted complex loss function and masked multi-layer diffraction. The 3D scene can be represented by a combination of layers in different depths. In the wave propagation procedure of multiple layers in different depths, the complex amplitude of layers in different depths will gradually diffuse and produce occlusion at another layer. To solve this occlusion problem, a mask is used in the process of layers diffracting. Whether it is forward wave propagation or backward wave propagation of layers, the mask can reduce the occlusion problem between different layers. Otherwise, weighted complex loss function is implemented in the gradient descent optimization process, which analyzes the real part, the imaginary part, and the amplitude part of the focus region between the reconstructed images of the hologram and the target images. The weight parameter is used to adjust the ratio of the amplitude loss of the focus region in the whole loss function. The weight amplitude loss part in weighted complex loss function can decrease the interference of the focus region from the defocus region. The simulations and experiments have validated the effectiveness of the proposed method. Full article
(This article belongs to the Special Issue Three-Dimensional Display Technologies)
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12 pages, 4649 KiB  
Article
The Size-Dependent Photonic Characteristics of Colloidal-Quantum-Dot-Enhanced Micro-LEDs
by Kai-Ling Liang, Wei-Hung Kuo, Chien-Chung Lin and Yen-Hsiang Fang
Micromachines 2023, 14(3), 589; https://doi.org/10.3390/mi14030589 - 28 Feb 2023
Cited by 3 | Viewed by 2925
Abstract
Colloidal CdSe/ZnS quantum dots (QD) enhanced micro-LEDs with sizes varying from 10 to 100 μm were fabricated and measured. The direct photolithography of quantum-dot-contained photoresists can place this color conversion layer on the top of an InGaN-based micro-LED and have a high throughput [...] Read more.
Colloidal CdSe/ZnS quantum dots (QD) enhanced micro-LEDs with sizes varying from 10 to 100 μm were fabricated and measured. The direct photolithography of quantum-dot-contained photoresists can place this color conversion layer on the top of an InGaN-based micro-LED and have a high throughput and semiconductor-grade precision. Both the uncoated and coated devices were characterized, and we determined that much higher brightness of a QD-enhanced micro-LED under the same current level was observed when compared to its AlGaInP counterpart. The color stability across the device sizes and injection currents were also examined. QD LEDs show low redshift of emission wavelength, which was recorded within 1 nm in some devices, with increasing current density from 1 to 300 A/cm2. On the other hand, the light conversion efficiency (LCE) of QD-enhanced micro-LEDs was detected to decrease under the high current density or when the device is small. The angular intensities of QD-enhanced micro-LEDs were measured and compared with blue devices. With the help of the black matrix and omnidirectional light emission of colloidal QD, we observed that the angular intensities of the red and blue colors are close to Lambertian distribution, which can lead to a low color shift in all angles. From our study, the QD-enhanced micro-LEDs can effectively increase the brightness, the color stability, and the angular color match, and thus play a promising role in future micro-display technology. Full article
(This article belongs to the Special Issue Micro-Light Emitting Diode: From Chips to Applications)
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13 pages, 1801 KiB  
Article
Design and Fabrication of a Fully-Integrated, Miniaturised Fluidic System for the Analysis of Enzyme Kinetics
by Andreas Tsiamis, Anthony Buchoux, Stephen T. Mahon, Anthony J. Walton, Stewart Smith, David J. Clarke and Adam A. Stokes
Micromachines 2023, 14(3), 537; https://doi.org/10.3390/mi14030537 - 25 Feb 2023
Cited by 4 | Viewed by 2705
Abstract
The lab-on-a-chip concept, enabled by microfluidic technology, promises the integration of multiple discrete laboratory techniques into a miniaturised system. Research into microfluidics has generally focused on the development of individual elements of the total system (often with relatively limited functionality), without full consideration [...] Read more.
The lab-on-a-chip concept, enabled by microfluidic technology, promises the integration of multiple discrete laboratory techniques into a miniaturised system. Research into microfluidics has generally focused on the development of individual elements of the total system (often with relatively limited functionality), without full consideration for integration into a complete fully optimised and miniaturised system. Typically, the operation of many of the reported lab-on-a-chip devices is dependent on the support of a laboratory framework. In this paper, a demonstrator platform for routine laboratory analysis is designed and built, which fully integrates a number of technologies into a single device with multiple domains such as fluidics, electronics, pneumatics, hydraulics, and photonics. This facilitates the delivery of breakthroughs in research, by incorporating all physical requirements into a single device. To highlight this proposed approach, this demonstrator microsystem acts as a fully integrated biochemical assay reaction system. The resulting design determines enzyme kinetics in an automated process and combines reservoirs, three-dimensional fluidic channels, optical sensing, and electronics in a low-cost, low-power and portable package. Full article
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12 pages, 7025 KiB  
Article
Fabrication and Characterization of Acicular Micro-Textured Copper Sheet Device for Low-Temperature Heat Radiation
by Tatsuhiko Aizawa, Hiroki Nakata and Takeshi Nasu
Micromachines 2023, 14(3), 507; https://doi.org/10.3390/mi14030507 - 22 Feb 2023
Cited by 2 | Viewed by 1967
Abstract
An acicular microtextured sheet was developed as a heat radiation device from the high-temperature source to the cooling medium in the infrared (IR) spectrum. The copper surface was modified by acicular micro-texturing to place a semi-regular micro-/nano-cone structure onto it. FT-IR (Fourier transformation [...] Read more.
An acicular microtextured sheet was developed as a heat radiation device from the high-temperature source to the cooling medium in the infrared (IR) spectrum. The copper surface was modified by acicular micro-texturing to place a semi-regular micro-/nano-cone structure onto it. FT-IR (Fourier transformation IR) spectroscopy was utilized to measure the transmittance diagram in near-IR to far-IR wavelengths. The wavelength (λ) of 6.7 μm, where the highest absorbance valley was detected in the diagram, was equivalent to the doubled size of the micro-cone average height, with Have = 3.3 μm; λ ~ 2 × Have. The electromagnetic waves in the far-IR wavelength were emitted by acicular micro-textured metallic sheets. The heat radiation transfer experiment was performed to describe this low-temperature heat radiation behavior. No temperature rise was detected on the black-colored polycarbonate (BC-PC) plate away from the bare copper sheet without textures, located on the high-temperature source. The temperature increased by 4 K on the BC-PC plate using the acicular textured copper sheet device. The emitter temperature also decreased significantly by 50 K or 50% of the heat source temperature. Full article
(This article belongs to the Special Issue 5th World Congress on Micro and Nano Manufacturing (WCMNM2022))
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13 pages, 6775 KiB  
Article
TEER and Ion Selective Transwell-Integrated Sensors System for Caco-2 Cell Model
by Elisa Sciurti, Laura Blasi, Carmela Tania Prontera, Amilcare Barca, Lucia Giampetruzzi, Tiziano Verri, Pietro Aleardo Siciliano and Luca Francioso
Micromachines 2023, 14(3), 496; https://doi.org/10.3390/mi14030496 - 21 Feb 2023
Cited by 16 | Viewed by 5383
Abstract
Monitoring of ions in real-time directly in cell culture systems and in organ-on-a-chip platforms represents a significant investigation tool to understand ion regulation and distribution in the body and ions’ involvement in biological mechanisms and specific pathologies. Innovative flexible sensors coupling electrochemical stripping [...] Read more.
Monitoring of ions in real-time directly in cell culture systems and in organ-on-a-chip platforms represents a significant investigation tool to understand ion regulation and distribution in the body and ions’ involvement in biological mechanisms and specific pathologies. Innovative flexible sensors coupling electrochemical stripping analysis (square wave anodic stripping voltammetry, SWASV) with an ion selective membrane (ISM) were developed and integrated in Transwell™ cell culture systems to investigate the transport of zinc and copper ions across a human intestinal Caco-2 cell monolayer. The fabricated ion-selective sensors demonstrated good sensitivity (1 × 10−11 M ion concentration) and low detection limits, consistent with pathophysiological cellular concentration ranges. A non-invasive electrochemical impedance spectroscopy (EIS) analysis, in situ, across a selected spectrum of frequencies (10–105 Hz), and an equivalent circuit fitting were employed to obtain useful electrical parameters for cellular barrier integrity monitoring. Transepithelial electrical resistance (TEER) data and immunofluorescent images were used to validate the intestinal epithelial integrity and the permeability enhancer effect of ethylene glycol-bis(2-aminoethylether)-N,N,N’,N’-tetraacetic acid (EGTA) treatment. The proposed devices represent a real prospective tool for monitoring cellular and molecular events and for studies on gut metabolism/permeability. They will enable a rapid integration of these sensors into gut-on-chip systems. Full article
(This article belongs to the Special Issue Electrochemical Sensors in Biological Applications, Volume II)
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28 pages, 3745 KiB  
Review
Core–Shell Particles: From Fabrication Methods to Diverse Manipulation Techniques
by Ajeet Singh Yadav, Du Tuan Tran, Adrian J. T. Teo, Yuchen Dai, Fariba Malekpour Galogahi, Chin Hong Ooi and Nam-Trung Nguyen
Micromachines 2023, 14(3), 497; https://doi.org/10.3390/mi14030497 - 21 Feb 2023
Cited by 15 | Viewed by 5673
Abstract
Core–shell particles are micro- or nanoparticles with solid, liquid, or gas cores encapsulated by protective solid shells. The unique composition of core and shell materials imparts smart properties on the particles. Core–shell particles are gaining increasing attention as tuneable and versatile carriers for [...] Read more.
Core–shell particles are micro- or nanoparticles with solid, liquid, or gas cores encapsulated by protective solid shells. The unique composition of core and shell materials imparts smart properties on the particles. Core–shell particles are gaining increasing attention as tuneable and versatile carriers for pharmaceutical and biomedical applications including targeted drug delivery, controlled drug release, and biosensing. This review provides an overview of fabrication methods for core–shell particles followed by a brief discussion of their application and a detailed analysis of their manipulation including assembly, sorting, and triggered release. We compile current methodologies employed for manipulation of core–shell particles and demonstrate how existing methods of assembly and sorting micro/nanospheres can be adopted or modified for core–shell particles. Various triggered release approaches for diagnostics and drug delivery are also discussed in detail. Full article
(This article belongs to the Special Issue Digital Microfluidics for Liquid Handling and Biochemical Analysis)
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16 pages, 8301 KiB  
Article
Nanoparticle Printing for Microfluidic Applications: Bipolar Electrochemistry and Localized Raman Sensing Spots
by Alessia Broccoli, Anke R. Vollertsen, Pauline Roels, Aaike van Vugt, Albert van den Berg and Mathieu Odijk
Micromachines 2023, 14(2), 453; https://doi.org/10.3390/mi14020453 - 15 Feb 2023
Cited by 4 | Viewed by 4002
Abstract
The local integration of metal nanoparticle films on 3D-structured polydimethylsiloxane (PDMS)-based microfluidic devices is of high importance for applications including electronics, electrochemistry, electrocatalysis, and localized Raman sensing. Conventional processes to locally deposit and pattern metal nanoparticles require multiple steps and shadow masks, or [...] Read more.
The local integration of metal nanoparticle films on 3D-structured polydimethylsiloxane (PDMS)-based microfluidic devices is of high importance for applications including electronics, electrochemistry, electrocatalysis, and localized Raman sensing. Conventional processes to locally deposit and pattern metal nanoparticles require multiple steps and shadow masks, or access to cleanroom facilities, and therefore, are relatively imprecise, or time and cost-ineffective. As an alternative, we present an aerosol-based direct-write method, in which patterns of nanoparticles generated via spark ablation are locally printed with sub-mm size and precision inside of microfluidic structures without the use of lithography or other masking methods. As proof of principle, films of Pt or Ag nanoparticles were printed in the chambers of a multiplexed microfluidic device and successfully used for two different applications: Screening electrochemical activity in a high-throughput fashion, and localized sensing of chemicals via surface-enhanced Raman spectroscopy (SERS). The versatility of the approach will enable the generation of functional microfluidic devices for applications that include sensing, high-throughput screening platforms, and microreactors using catalytically driven chemical conversions. Full article
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11 pages, 8081 KiB  
Article
Surface Nanotexturing of Boron-Doped Diamond Films by Ultrashort Laser Pulses
by Matteo Mastellone, Eleonora Bolli, Veronica Valentini, Stefano Orlando, Antonio Lettino, Riccardo Polini, Josephus Gerardus Buijnsters, Alessandro Bellucci and Daniele Maria Trucchi
Micromachines 2023, 14(2), 389; https://doi.org/10.3390/mi14020389 - 4 Feb 2023
Cited by 7 | Viewed by 2406
Abstract
Polycrystalline boron-doped diamond (BDD) films were surface nanotextured by femtosecond pulsed laser irradiation (100 fs duration, 800 nm wavelength, 1.44 J cm−2 single pulse fluence) to analyse the evolution of induced alterations on the surface morphology and structural properties. The aim was [...] Read more.
Polycrystalline boron-doped diamond (BDD) films were surface nanotextured by femtosecond pulsed laser irradiation (100 fs duration, 800 nm wavelength, 1.44 J cm−2 single pulse fluence) to analyse the evolution of induced alterations on the surface morphology and structural properties. The aim was to identify the occurrence of laser-induced periodic surface structures (LIPSS) as a function of the number of pulses released on the unit area. Micro-Raman spectroscopy pointed out an increase in the graphite surface content of the films following the laser irradiation due to the formation of ordered carbon sites with respect to the pristine sample. SEM and AFM surface morphology studies allowed the determination of two different types of surface patterning: narrow but highly irregular ripples without a definite spatial periodicity or long-range order for irradiations with relatively low accumulated fluences (<14.4 J cm−2) and coarse but highly regular LIPSS with a spatial periodicity of approximately 630 nm ± 30 nm for higher fluences up to 230.4 J cm−2. Full article
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29 pages, 1134 KiB  
Review
Exhaled Biomarkers for Point-of-Care Diagnosis: Recent Advances and New Challenges in Breathomics
by Helga Kiss, Zoltán Örlős, Áron Gellért, Zsolt Megyesfalvi, Angéla Mikáczó, Anna Sárközi, Attila Vaskó, Zsuzsanna Miklós and Ildikó Horváth
Micromachines 2023, 14(2), 391; https://doi.org/10.3390/mi14020391 - 4 Feb 2023
Cited by 18 | Viewed by 6267
Abstract
Cancers, chronic diseases and respiratory infections are major causes of mortality and present diagnostic and therapeutic challenges for health care. There is an unmet medical need for non-invasive, easy-to-use biomarkers for the early diagnosis, phenotyping, predicting and monitoring of the therapeutic responses of [...] Read more.
Cancers, chronic diseases and respiratory infections are major causes of mortality and present diagnostic and therapeutic challenges for health care. There is an unmet medical need for non-invasive, easy-to-use biomarkers for the early diagnosis, phenotyping, predicting and monitoring of the therapeutic responses of these disorders. Exhaled breath sampling is an attractive choice that has gained attention in recent years. Exhaled nitric oxide measurement used as a predictive biomarker of the response to anti-eosinophil therapy in severe asthma has paved the way for other exhaled breath biomarkers. Advances in laser and nanosensor technologies and spectrometry together with widespread use of algorithms and artificial intelligence have facilitated research on volatile organic compounds and artificial olfaction systems to develop new exhaled biomarkers. We aim to provide an overview of the recent advances in and challenges of exhaled biomarker measurements with an emphasis on the applicability of their measurement as a non-invasive, point-of-care diagnostic and monitoring tool. Full article
(This article belongs to the Special Issue Microfluidics and Biosensors for Point-of-Care Applications)
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12 pages, 2152 KiB  
Article
Production of Lipid Constructs by Design via Three-Dimensional Nanoprinting
by Yuqi Huang, Arpad Karsai, Pallavi D. Sambre, Wan-Chih Su, Roland Faller, Atul N. Parikh and Gang-yu Liu
Micromachines 2023, 14(2), 372; https://doi.org/10.3390/mi14020372 - 2 Feb 2023
Cited by 3 | Viewed by 2439
Abstract
Atomic force microscopy (AFM) in conjunction with microfluidic delivery was utilized to produce three-dimensional (3D) lipid structures following a custom design. While AFM is well-known for its spatial precision in imaging and 2D nanolithography, the development of AFM-based nanotechnology into 3D nanoprinting requires [...] Read more.
Atomic force microscopy (AFM) in conjunction with microfluidic delivery was utilized to produce three-dimensional (3D) lipid structures following a custom design. While AFM is well-known for its spatial precision in imaging and 2D nanolithography, the development of AFM-based nanotechnology into 3D nanoprinting requires overcoming the technical challenges of controlling material delivery and interlayer registry. This work demonstrates the concept of 3D nanoprinting of amphiphilic molecules such as 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC). Various formulations of POPC solutions were tested to achieve point, line, and layer-by-layer material delivery. The produced structures include nanometer-thick disks, long linear spherical caps, stacking grids, and organizational chiral architectures. The POPC molecules formed stacking bilayers in these constructions, as revealed by high-resolution structural characterizations. The 3D printing reached nanometer spatial precision over a range of 0.5 mm. The outcomes reveal the promising potential of our designed technology and methodology in the production of 3D structures from nanometer to continuum, opening opportunities in biomaterial sciences and engineering, such as in the production of 3D nanodevices, chiral nanosensors, and scaffolds for tissue engineering and regeneration. Full article
(This article belongs to the Special Issue Women’s Special Issue Series: Micromachines)
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13 pages, 5558 KiB  
Article
A Cryostat Applicable to Long-Wavelength Light-Driven Scanning Probe Microscopy
by Kui Xiang, Caihong Xie, Qiyuan Feng, Ze Wang, Guangbin Dai, Jihao Wang, Jing Zhang, Wenjie Meng, Yubin Hou, Qingyou Lu and Yalin Lu
Micromachines 2023, 14(2), 378; https://doi.org/10.3390/mi14020378 - 2 Feb 2023
Cited by 1 | Viewed by 2459
Abstract
Recently, there has been growing interest in using lightwave-driven scanning probe microscopy (LD-SPM) to break through the Abbe diffraction limit of focusing, yielding insight into various energy couplings and conversion processes and revealing the internal information of matter. We describe a compact and [...] Read more.
Recently, there has been growing interest in using lightwave-driven scanning probe microscopy (LD-SPM) to break through the Abbe diffraction limit of focusing, yielding insight into various energy couplings and conversion processes and revealing the internal information of matter. We describe a compact and efficient optical cryostat designed for LD-SPM testing under magnetic fields. The exceptional multilayer radiation shielding insert (MRSI) forms an excellent temperature gradient when filled with heat conducting gas, which removes the requirement to install an optical window in the liquid helium cooling shell. This not only critically avoids the vibration and thermal drift caused by solid heat conduction but also minimizes light transmission loss. The application of gate valves and bellows allows a simpler and more effective replacement of the sample and working cell in the test cavity. ANSYS software is used for steady-state thermal analysis of the MRSI to obtain the temperature distribution and heat transfer rate, and the necessity of the flexible copper shielding strips is illustrated by the simulations. The topography and magnetic domain images of 45 nm-thick La0.67Ca0.33MnO3 thin films on NdGaO3(001) substrates under a magnetic field were obtained by a self-made lightwave-driven magnetic force microscope in this cryostat. The resolution and noise spectra during imaging reveal temperature stability and low vibration throughout the cryostat. The experience acquired during the development of this cryostat will help to establish cryostats of similar types for a variety of optic applications requiring the use of cryogenic temperatures. Full article
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10 pages, 9630 KiB  
Article
High−Accuracy Film−Integrated Optical Sensor for Real−Time Intraocular Pressure Monitoring
by Xiaobin Xu, Zixuan Liu, Liqiang Wang, Yifei Huang and He Yang
Micromachines 2023, 14(2), 353; https://doi.org/10.3390/mi14020353 - 31 Jan 2023
Cited by 5 | Viewed by 2458
Abstract
Intraocular pressure (IOP) is a key indicator to evaluate the risk and status of glaucoma, which is one of the main causes of irreversible blindness. However, the IOP value is susceptible to circadian changes and is difficult to be measured real−time. In this [...] Read more.
Intraocular pressure (IOP) is a key indicator to evaluate the risk and status of glaucoma, which is one of the main causes of irreversible blindness. However, the IOP value is susceptible to circadian changes and is difficult to be measured real−time. In this paper, we designed a thin−film integrated optical IOP sensor based on the interferometry principle, which could read out the IOP value by interference patterns and monitor the value changes real−time at the same time. The theoretical and experimental results indicated that our sensor exhibited a sensitivity of 0.19 μm/mmHg and an average accuracy of 0.84 mmHg over the pressure range of 0–45 mmHg, which is comparable with the other reported optical systems but with the advantage of easier fabrication process and low−cost. Our sensor device implies great potential in the application of human physiological index measurement and other chip−integrated medical sensing instruments. Full article
(This article belongs to the Special Issue Integrated Photonics and Optoelectronics)
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22 pages, 5898 KiB  
Article
Influence of the Ground Electrode on the Dynamics of Electrowetting
by Iftekhar Khan, Stefania Castelletto and Gary Rosengarten
Micromachines 2023, 14(2), 348; https://doi.org/10.3390/mi14020348 - 30 Jan 2023
Cited by 2 | Viewed by 2755
Abstract
The ability to manipulate a liquid meniscus using electrowetting has many applications. In any electrowetting design, at least two electrodes are required: one forms the field to change the contact angle and the other functions as a ground electrode. The contribution of the [...] Read more.
The ability to manipulate a liquid meniscus using electrowetting has many applications. In any electrowetting design, at least two electrodes are required: one forms the field to change the contact angle and the other functions as a ground electrode. The contribution of the ground electrode (GE) to the dynamics of electrowetting has not yet been thoroughly investigated. In this paper, we discovered that with a bare ground electrode, the contact angle of a sessile drop increases instead of decreases when a direct current (DC) voltage varying from zero to the threshold voltage is applied. This phenomenon is opposite to what occurs when the GE is coated with a dielectric, where the contact-angle change follows the Lippmann–Young equation above the threshold voltage of electrowetting. However, this behaviour is not observed with either a dielectric-coated electrode using direct current (DC) or a bare ground electrode using alternating current (AC) voltage electrowetting. This study explains this phenomenon with finite element simulation and theory. From previous research work, the ground electrode configuration is inconsistent. In some studies, the ground electrode is exposed to water; in other studies, the ground electrode is covered with dielectric. This study identified that an exposed ground electrode is not required in electrowetting. Moreover, this research work suggests that for applications where precise control of the contact angle is paramount, a dielectric-coated ground electrode should be used since it prevents the increase in the contact angle when increasing the applied potential from zero to the threshold voltage. This study also identified that contact angle hysteresis is lower with a Cytop-coated ground electrode and DC voltage than with a bare ground electrode using AC or DC voltages. Full article
(This article belongs to the Special Issue Advances in Electrowetting Devices)
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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 6 | Viewed by 3156
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 25 | Viewed by 6127
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 12 | Viewed by 3454
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 3 | Viewed by 3358
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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18 pages, 3299 KiB  
Article
Tree-Based Machine Learning Models with Optuna in Predicting Impedance Values for Circuit Analysis
by Jung-Pin Lai, Ying-Lei Lin, Ho-Chuan Lin, Chih-Yuan Shih, Yu-Po Wang and Ping-Feng Pai
Micromachines 2023, 14(2), 265; https://doi.org/10.3390/mi14020265 - 20 Jan 2023
Cited by 37 | Viewed by 5363
Abstract
The transmission characteristics of the printed circuit board (PCB) ensure signal integrity and support the entire circuit system, with impedance matching being critical in the design of high-speed PCB circuits. Because the factors affecting impedance are closely related to the PCB production process, [...] Read more.
The transmission characteristics of the printed circuit board (PCB) ensure signal integrity and support the entire circuit system, with impedance matching being critical in the design of high-speed PCB circuits. Because the factors affecting impedance are closely related to the PCB production process, circuit designers and manufacturers must work together to adjust the target impedance to maintain signal integrity. Five machine learning models, including decision tree (DT), random forest (RF), extreme gradient boosting (XGBoost), categorical boosting (CatBoost), and light gradient boosting machine (LightGBM), were used to forecast target impedance values. Furthermore, the Optuna algorithm is used to determine forecasting model hyperparameters. This study applied tree-based machine learning techniques with Optuna to predict impedance. The results revealed that five tree-based machine learning models with Optuna can generate satisfying forecasting accuracy in terms of three measurements, including mean absolute percentage error (MAPE), root mean square error (RMSE), and coefficient of determination (R2). Meanwhile, the LightGBM model with Optuna outperformed the other models. In addition, by using Optuna to tune the parameters of machine learning models, the accuracy of impedance matching can be increased. Thus, the results of this study suggest that the tree-based machine learning techniques with Optuna are a viable and promising alternative for predicting impedance values for circuit analysis. Full article
(This article belongs to the Special Issue Hardware-Friendly Machine Learning and Its Applications, 2nd Edition)
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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 21 | Viewed by 3229
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 15 | Viewed by 4088
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
Cited by 5 | Viewed by 2318
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 × 102 particles/min, whereas those of IgG-PS, BSA-PS, PS, and Zymosan were 1.4 × 102, 1.1 × 102, 4.2 × 103, and 3.6 × 103 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 9 | Viewed by 3450
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 7 | Viewed by 3753
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 11 | Viewed by 2966
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
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