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Editor’s Choice Articles

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

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13 pages, 3729 KiB  
Article
Integration of Riboflavin-Modified Carbon Fiber Mesh Electrode Systems in a 3D-Printed Catheter Hub
by Charnete Casimero, Robert B. Smith and James Davis
Micromachines 2024, 15(1), 79; https://doi.org/10.3390/mi15010079 - 30 Dec 2023
Viewed by 1873
Abstract
Background: Catheter line infection is a common complication within clinical environments, and there is a pressing need for technological options to aid in reducing the possibility of sepsis. The early identification of contamination could be pivotal in reducing cases and improving outcomes. Method: [...] Read more.
Background: Catheter line infection is a common complication within clinical environments, and there is a pressing need for technological options to aid in reducing the possibility of sepsis. The early identification of contamination could be pivotal in reducing cases and improving outcomes. Method: A sensing rationale based on a riboflavin-modified electrode system integrated within a modified 3D-printed catheter needle-free connector is proposed, which can monitor changes in pH brought about by bacterial contamination. Results: Riboflavin, vitamin B2, is a biocompatible chemical that possesses a redox-active flavin core that is pH dependent. The oxidation peak potential of the adsorbed riboflavin responds linearly to changes in pH with a near-Nernstian behavior of 63 mV/pH unit and is capable of accurately monitoring the pH of an authentic IV infusate. Conclusions: The proof of principle is demonstrated with an electrode-printed hub design offering a valuable foundation from which to explore bacterial interactions within the catheter lumen with the potential of providing an early warning of contamination. Full article
(This article belongs to the Special Issue Feature Papers of Micromachines in Chemistry 2023)
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18 pages, 9153 KiB  
Article
Application of Braided Piezoelectric Poly-l-Lactic Acid Cord Sensor to Sleep Bruxism Detection System with Less Physical or Mental Stress
by Yoshiro Tajitsu, Saki Shimda, Takuto Nonomura, Hiroki Yanagimoto, Shun Nakamura, Ryoma Ueshima, Miyu Kawanobe, Takuo Nakiri, Jun Takarada, Osamu Takeuchi, Rei Nisho, Koji Takeshita, Mitsuru Takahashi and Kazuki Sugiyama
Micromachines 2024, 15(1), 86; https://doi.org/10.3390/mi15010086 - 30 Dec 2023
Cited by 2 | Viewed by 2775
Abstract
For many years, we have been developing flexible sensors made of braided piezoelectric poly-l-lactic acid (PLLA) fibers that can be tied and untied for practical applications in society. To ensure good quality of sleep, the occurrence of bruxism has been attracting attention in [...] Read more.
For many years, we have been developing flexible sensors made of braided piezoelectric poly-l-lactic acid (PLLA) fibers that can be tied and untied for practical applications in society. To ensure good quality of sleep, the occurrence of bruxism has been attracting attention in recent years. Currently, there is a need for a system that can easily and accurately measure the frequency of bruxism at home. Therefore, taking advantage of the braided piezoelectric PLLA cord sensor’s unique characteristic of being sewable, we aimed to provide a system that can measure the frequency of bruxism using the braided piezoelectric PLLA cord sensor simply sewn onto a bed sheet on which the subject lies down. After many tests using trial and error, the sheet sensor was completed with zigzag stitching. Twenty subjects slept overnight in a hospital room on sheets integrated with a braided piezoelectric PLLA cord. Polysomnography (PSG) was simultaneously performed on these subjects. The results showed that their bruxism could be detected with an accuracy of more than 95% compared with PSG measurements, which can only be performed in a hospital by a physician and are more burdensome for the subjects, with the subjects simply lying on the bed sheet with a braided piezoelectric PLLA cord sensor sewn into it. Full article
(This article belongs to the Special Issue Exploring IoT Sensors and Their Applications: Advancements, Challenges, and Opportunities in Smart Environments)
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38 pages, 14476 KiB  
Article
Design and Investigation of Superatoms for Redox Applications: First-Principles Studies
by Celina Sikorska
Micromachines 2024, 15(1), 78; https://doi.org/10.3390/mi15010078 - 29 Dec 2023
Cited by 1 | Viewed by 2214
Abstract
A superatom is a cluster of atoms that acts like a single atom. Two main groups of superatoms are superalkalis and superhalogens, which mimic the chemistry of alkali and halogen atoms, respectively. The ionization energies of superalkalis are smaller than those of alkalis [...] Read more.
A superatom is a cluster of atoms that acts like a single atom. Two main groups of superatoms are superalkalis and superhalogens, which mimic the chemistry of alkali and halogen atoms, respectively. The ionization energies of superalkalis are smaller than those of alkalis (<3.89 eV for cesium atom), and the electron affinities of superhalogens are larger than that of halogens (>3.61 eV for chlorine atom). Exploring new superalkali/superhalogen aims to provide reliable data and predictions of the use of such compounds as redox agents in the reduction/oxidation of counterpart systems, as well as the role they can play more generally in materials science. The low ionization energies of superalkalis make them candidates for catalysts for CO2 conversion into renewable fuels and value-added chemicals. The large electron affinity of superhalogens makes them strong oxidizing agents for bonding and removing toxic molecules from the environment. By using the superatoms as building blocks of cluster-assembled materials, we can achieve the functional features of atom-based materials (like conductivity or catalytic potential) while having more flexibility to achieve higher performance. This feature paper covers the issues of designing such compounds and demonstrates how modifications of the superatoms (superhalogens and superalkalis) allow for the tuning of the electronic structure and might be used to create unique functional materials. The designed superatoms can form stable perovskites for solar cells, electrolytes for Li-ion batteries of electric vehicles, superatomic solids, and semiconducting materials. The designed superatoms and their redox potential evaluation could help experimentalists create new materials for use in fields such as energy storage and climate change. Full article
(This article belongs to the Special Issue Electrochemistry Applications in Energy and Environment: Battery, Sensors and Other Technologies)
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11 pages, 4884 KiB  
Article
Healthcare Wearable Sensors Adhesion to Human Fingernails and Toenails
by Katsuyuki Sakuma, Leanna Pancoast, Yiping Yao and John Knickerbocker
Micromachines 2024, 15(1), 69; https://doi.org/10.3390/mi15010069 - 29 Dec 2023
Cited by 2 | Viewed by 1576
Abstract
A novel adhesion method of a sensor to a fingernail is described. Wearable sensors can provide health insights to humans for a wide variety of benefits, such as continuous wellness monitoring and disease monitoring throughout a patient’s daily life. While there are many [...] Read more.
A novel adhesion method of a sensor to a fingernail is described. Wearable sensors can provide health insights to humans for a wide variety of benefits, such as continuous wellness monitoring and disease monitoring throughout a patient’s daily life. While there are many locations to place these wearable sensors on the body, we will focus on the fingertip, one significant way that people interact with the world. Like artificial fingernails used for aesthetics, wearable healthcare sensors can be attached to the fingernail for short or long time periods with minimal irritation and disruption to daily life. In this study the structure and methods of healthcare sensors’ attachment and removal have been explored to support (1) the sensor functional requirements, (2) biological and environmentally compatible solutions and (3) ease of attachment and removal for short- and long-term user applications. Initial fingernail sensors were attached using a thin adhesive layer of commonly available cosmetic nail glue. While this approach allowed for easy application and strong adhesion to the nail, the removal could expose the fingernail and finger to a commercially available cosmetic nail removal (acetone-based chemical) for extended times measured in minutes. Therefore, a novel structure and method were developed for rapid healthcare sensor attachment and removal in seconds, which supported both the sensor functional objectives and the biologically and environmentally safe use objectives. Full article
(This article belongs to the Special Issue Biomedical Devices and Technologies in Intelligent Diagnosis: Theoretical Principles to Basic Applications)
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26 pages, 6016 KiB  
Review
Structural and Material-Based Approaches for the Fabrication of Stretchable Light-Emitting Diodes
by Hamin Park and Dong Chan Kim
Micromachines 2024, 15(1), 66; https://doi.org/10.3390/mi15010066 - 28 Dec 2023
Cited by 3 | Viewed by 2940
Abstract
Stretchable displays, capable of freely transforming their shapes, have received significant attention as alternatives to conventional rigid displays, and they are anticipated to provide new opportunities in various human-friendly electronics applications. As a core component of stretchable displays, high-performance stretchable light-emitting diodes (LEDs) [...] Read more.
Stretchable displays, capable of freely transforming their shapes, have received significant attention as alternatives to conventional rigid displays, and they are anticipated to provide new opportunities in various human-friendly electronics applications. As a core component of stretchable displays, high-performance stretchable light-emitting diodes (LEDs) have recently emerged. The approaches to fabricate stretchable LEDs are broadly categorized into two groups, namely “structural” and “material-based” approaches, based on the mechanisms to tolerate strain. While structural approaches rely on specially designed geometries to dissipate applied strain, material-based approaches mainly focus on replacing conventional rigid components of LEDs to soft and stretchable materials. Here, we review the latest studies on the fabrication of stretchable LEDs, which is accomplished through these distinctive strategies. First, we introduce representative device designs for efficient strain distribution, encompassing island-bridge structures, wavy buckling, and kirigami-/origami-based structures. For the material-based approaches, we discuss the latest studies for intrinsically stretchable (is-) electronic/optoelectronic materials, including the formation of conductive nanocomposite and polymeric blending with various additives. The review also provides examples of is-LEDs, focusing on their luminous performance and stretchability. We conclude this review with a brief outlook on future technologies. Full article
(This article belongs to the Special Issue Wearable Organic Electronics and Applications)
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14 pages, 9014 KiB  
Article
Micro-Ring Resonator-Based Tunable Vortex Beam Emitter
by Liaisan I. Bakirova, Grigory S. Voronkov, Vladimir S. Lyubopytov, Muhammad A. Butt, Svetlana N. Khonina, Ivan V. Stepanov, Elizaveta P. Grakhova and Ruslan V. Kutluyarov
Micromachines 2024, 15(1), 34; https://doi.org/10.3390/mi15010034 - 23 Dec 2023
Cited by 7 | Viewed by 2315
Abstract
Light beams bearing orbital angular momentum (OAM) are used in various scientific and engineering applications, such as microscopy, laser material processing, and optical tweezers. Precise topological charge control is crucial for efficiently using vortex beams in different fields, such as information encoding in [...] Read more.
Light beams bearing orbital angular momentum (OAM) are used in various scientific and engineering applications, such as microscopy, laser material processing, and optical tweezers. Precise topological charge control is crucial for efficiently using vortex beams in different fields, such as information encoding in optical communications and sensor systems. This work presents a novel method for optimizing an emitting micro-ring resonator (MRR) for emitting vortex beams with variable orders of OAM. The MRR consists of a ring waveguide with periodic structures side-coupled to a bus waveguide. The resonator is tunable due to the phase change material Sb2Se3 deposited on the ring. This material can change from amorphous to crystalline while changing its refractive index. In the amorphous phase, it is 3.285 + 0i, while in the transition to the crystalline phase, it reaches 4.050 + 0i at emission wavelength 1550 nm. We used this property to control the vortex beam topological charge. In our study, we optimized the distance between the bus waveguide and the ring waveguide, the bending angle, and the width of the bus waveguide. The optimality criterion was chosen to maximize the flux density of the radiated energy emitted by the resonator. The numerical simulation results proved our method. The proposed approach can be used to optimize optical beam emitters carrying OAM for various applications. Full article
(This article belongs to the Special Issue Photonic and Optoelectronic Devices and Systems, Second Edition)
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11 pages, 3263 KiB  
Article
Image-Based Feedback of Multi-Component Microdroplets for Ultra-Monodispersed Library Preparation
by Christy Cantwell, John S. McGrath, Clive A. Smith and Graeme Whyte
Micromachines 2024, 15(1), 27; https://doi.org/10.3390/mi15010027 - 22 Dec 2023
Viewed by 1782
Abstract
Using devices with microfluidic channels can allow for precise control over liquids flowing through them. Merging flows of immiscible liquids can create emulsions with highly monodispersed microdroplets within a carrier liquid, which are ideal for miniaturised reaction vessels which can be generated with [...] Read more.
Using devices with microfluidic channels can allow for precise control over liquids flowing through them. Merging flows of immiscible liquids can create emulsions with highly monodispersed microdroplets within a carrier liquid, which are ideal for miniaturised reaction vessels which can be generated with a high throughput of tens of thousands of droplets per second. Control of the size and composition of these droplets is generally performed by controlling the pumping system pushing the liquids into the device; however, this is an indirect manipulation and inadequate if absolute precision is required in the size or composition of the droplets. In this work, we extend the previous development of image-based closed-loop feedback control over microdroplet generation to allow for the control of not only the size of droplets but also the composition by merging two aqueous flows. The feedback allows direct control over the desired parameters of volume and ratio of the two components over a wide range of ratios and outperforms current techniques in terms of monodispersity in volume and composition. This technique is ideal for situations where precise control over droplets is critical, or where a library of droplets of different concentrations but the same volume is required. Full article
(This article belongs to the Special Issue Droplet Microfluidics: Fundamentals and Its Advanced Applications)
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12 pages, 2645 KiB  
Article
An Automated Centrifugal Microfluidic Platform for Efficient Multistep Blood Sample Preparation and Clean-Up towards Small Ion-Molecule Analysis
by Yuting Hou, Rohit Mishra, Yufeng Zhao, Jens Ducrée and Jed D. Harrison
Micromachines 2023, 14(12), 2257; https://doi.org/10.3390/mi14122257 - 18 Dec 2023
Cited by 1 | Viewed by 2193
Abstract
Sample preparation for mass spectroscopy typically involves several liquid and solid phase clean-ups, extractions, and other unit operations, which are labour-intensive and error-prone. We demonstrate a centrifugal microfluidic platform that automates the whole blood sample’s preparation and clean-up by combining traditional liquid-phase and [...] Read more.
Sample preparation for mass spectroscopy typically involves several liquid and solid phase clean-ups, extractions, and other unit operations, which are labour-intensive and error-prone. We demonstrate a centrifugal microfluidic platform that automates the whole blood sample’s preparation and clean-up by combining traditional liquid-phase and multiple solid-phase extractions for applications in mass spectroscopy (MS)-based small molecule detection. Liquid phase extraction was performed using methanol to precipitate proteins in plasma separated from a blood sample under centrifugal force. The preloaded solid phase composed of C18 beads then removed lipids with a combination of silica particles, which further cleaned up any remaining proteins. We further integrated the application of this sample prep disc with matrix-assisted laser desorption/ionization (MALDI) MS by using glancing angle deposition films, which further cleaned up the processed sample by segregating the electrolyte background from the sample salts. Additionally, hydrophilic interaction liquid chromatography (HILIC) MS was employed for detecting targeted free amino acids. Therefore, several representative ionic metabolites, including several amino acids and organic acids from blood samples, were analysed by both MALDI-MS and HILIC-MS to demonstrate the performance of this sample preparation disc. The fully automated blood sample preparation procedure only took 35 mins, with a throughput of three parallel units. Full article
(This article belongs to the Section B：Biology and Biomedicine)
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13 pages, 3967 KiB  
Article
Chameleon-Inspired Colorimetric Sensors for Real-Time Detections with Humidity
by Yu-Hsuan Cheng, Ching-Te Kuo and Bo-Yao Lian
Micromachines 2023, 14(12), 2254; https://doi.org/10.3390/mi14122254 - 18 Dec 2023
Viewed by 1994
Abstract
In recent decades, vapor sensors have gained substantial attention for their crucial roles in environmental monitoring and pharmaceutical applications. Herein, we introduce a chameleon-inspired colorimetric (CIC) sensor, detailing its design, fabrication, and versatile applications. The sensor seamlessly combines a PEDOT:PSS vapor sensor with [...] Read more.
In recent decades, vapor sensors have gained substantial attention for their crucial roles in environmental monitoring and pharmaceutical applications. Herein, we introduce a chameleon-inspired colorimetric (CIC) sensor, detailing its design, fabrication, and versatile applications. The sensor seamlessly combines a PEDOT:PSS vapor sensor with a colorimetric display, using thermochromic liquid crystal (TLC). We further explore the electrical characteristics of the CIC sensor when doped with ethylene glycol (EG) and polyvinyl alcohol (PVA). Comparative analyses of resistance change rates for different weight ratios of EG and PVA provide insights into fine-tuning the sensor’s responsiveness to varying humidity levels. The CIC sensor’s proficiency in measuring ambient humidity is investigated under a voltage input as small as 2.6 V, capturing resistance change rates and colorimetric shifts at relative humidity (RH) levels ranging from 20% to 90%. Notably, the sensor exhibits distinct resistance sensitivities of 9.7 mΩ (0.02% ∆R/R0)/%RH, 0.5 Ω (0.86% ∆R/R0)/%RH, and 5.7 Ω (9.68% ∆R/R0)/%RH at RH 20% to 30%, RH 30% to 80%, and RH 80% to 90%, respectively. Additionally, a linear temperature change is observed with a sensitivity of −0.04 °C/%RH. The sensor also demonstrates a colorimetric temperature sensitivity of −82,036 K/%RH at RH 20% to 30% and −514 K/%RH at RH 30% to 90%, per captured image. Furthermore, real-time measurements of ethanol vapor with varying concentrations showcase the sensor’s applicability in gas sensing applications. Overall, we present a comprehensive exploration of the CIC sensor, emphasizing its design flexibility, electrical characteristics, and diverse sensing capabilities. The sensor’s potential applications extend to real-time environmental monitoring, highlighting its promising role in various gas sensing fields. Full article
(This article belongs to the Special Issue Bioinspired Materials and Microdevices: Fabrications and Applications)
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15 pages, 5254 KiB  
Article
Dynamic Compressive Properties and Failure Mechanism of the Laser Powder Bed Fusion of Submicro-LaB6 Reinforced Ti-Based Composites
by Xianghui Li and Yang Liu
Micromachines 2023, 14(12), 2237; https://doi.org/10.3390/mi14122237 - 13 Dec 2023
Cited by 2 | Viewed by 1440
Abstract
In this study, lanthanum hexaboride (LaB6) particle-reinforced titanium matrix composites (PRTMCs, TC4/LaB6) were successfully manufactured using the laser powder bed fusion (LPBF) process. Thereafter, the effect of the mass fraction of LaB6 on the microstructure and the dynamic [...] Read more.
In this study, lanthanum hexaboride (LaB6) particle-reinforced titanium matrix composites (PRTMCs, TC4/LaB6) were successfully manufactured using the laser powder bed fusion (LPBF) process. Thereafter, the effect of the mass fraction of LaB6 on the microstructure and the dynamic compressive properties was investigated. The results show that the addition of LaB6 leads to significant grain refinement. Moreover, the general trend of grain size reveals a concave bend as the fraction increases from 0.2% to 1.0%. Furthermore, the texture intensity of prior β grains and α grains was found to be weakened in the composites. It was also observed that the TC4/LaB6 have higher quasi-static and dynamic compressive strengths but lower fracture strain when compared with the as-built TC4. The sample with 0.5 wt.% LaB6 was found to have the best strength–toughness synergy among the three groups of composites due to having the smallest grain size. Furthermore, the fracture mode of TC4/LaB6 was found to change from the fracture under the combined action of brittle and ductility to the cleavage fracture. This study was able to provide a theoretical basis for an in-depth understanding of the compressive properties of additive manufacturing of PRTMCs under high-speed loading conditions. Full article
(This article belongs to the Special Issue Laser Additive Manufacturing: Design, Materials, Processes and Applications, 2nd Edition)
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41 pages, 8330 KiB  
Review
Review on Bubble Dynamics in Proton Exchange Membrane Water Electrolysis: Towards Optimal Green Hydrogen Yield
by Bongliba T. Sangtam and Hanwook Park
Micromachines 2023, 14(12), 2234; https://doi.org/10.3390/mi14122234 - 12 Dec 2023
Cited by 12 | Viewed by 7593
Abstract
Water electrolysis using a proton exchange membrane (PEM) holds substantial promise to produce green hydrogen with zero carbon discharge. Although various techniques are available to produce hydrogen gas, the water electrolysis process tends to be more cost-effective with greater advantages for energy storage [...] Read more.
Water electrolysis using a proton exchange membrane (PEM) holds substantial promise to produce green hydrogen with zero carbon discharge. Although various techniques are available to produce hydrogen gas, the water electrolysis process tends to be more cost-effective with greater advantages for energy storage devices. However, one of the challenges associated with PEM water electrolysis is the accumulation of gas bubbles, which can impair cell performance and result in lower hydrogen output. Achieving an in-depth knowledge of bubble dynamics during electrolysis is essential for optimal cell performance. This review paper discusses bubble behaviors, measuring techniques, and other aspects of bubble dynamics in PEM water electrolysis. It also examines bubble behavior under different operating conditions, as well as the system geometry. The current review paper will further improve the understanding of bubble dynamics in PEM water electrolysis, facilitating more competent, inexpensive, and feasible green hydrogen production. Full article
(This article belongs to the Special Issue Micro Thermal Devices and Their Applications)
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12 pages, 4442 KiB  
Article
Polarization Z-Scan Studies Revealing Plasmon Coupling Enhancement Due to Dimer Formation of Gold Nanoparticles in Nematic Liquid Crystals
by Shengwei Wang, Edward J. Lipchus, Mohamed Amine Gharbi and Chandra S. Yelleswarapu
Micromachines 2023, 14(12), 2206; https://doi.org/10.3390/mi14122206 - 5 Dec 2023
Viewed by 1674
Abstract
We investigate the plasmon coupling of gold nanoparticle (AuNP) dimers dispersed in a nematic liquid crystal matrix using the polarization z-scan technique. Our experimental setup includes the precise control of incident light polarization through polarization angles of 0°, 45°, and 90°. Two distinct [...] Read more.
We investigate the plasmon coupling of gold nanoparticle (AuNP) dimers dispersed in a nematic liquid crystal matrix using the polarization z-scan technique. Our experimental setup includes the precise control of incident light polarization through polarization angles of 0°, 45°, and 90°. Two distinct cell orientations are examined: parallel and twisted nematic cells. In parallel-oriented cells, where liquid crystal molecules and AuNPs align with the rubbing direction, we observe a remarkable 2–3-fold increase in the nonlinear absorption coefficient when the polarization of the incident light is parallel to the rubbing direction. Additionally, a linear decrease in the third-order nonlinear absorption coefficient is noted as the polarization angle varies from 0° to 90°. In the case of twisted nematic cells, the NPs do not have any preferred orientation, and the enhancement remains consistent across all polarization angles. These findings conclusively establish that the observed enhancement in the nonlinear absorption coefficient is a direct consequence of plasmon coupling, shedding light on the intricate interplay between plasmonic nanostructures and liquid crystal matrices. Full article
(This article belongs to the Special Issue Optics & Photonics—Micro and Nano Structures, Materials and Devices (AOP2024))
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19 pages, 6413 KiB  
Article
Design and Fabrication of a 3D-Printed Microfluidic Immunoarray for Ultrasensitive Multiplexed Protein Detection
by Keshani Hiniduma, Ketki S. Bhalerao, Peyahandi I. Thilini De Silva, Tianqi Chen and James F. Rusling
Micromachines 2023, 14(12), 2187; https://doi.org/10.3390/mi14122187 - 30 Nov 2023
Cited by 7 | Viewed by 2649
Abstract
Microfluidic technology has revolutionized device fabrication by merging principles of fluid dynamics with technologies from chemistry, physics, biology, material science, and microelectronics. Microfluidic systems manipulate small volumes of fluids to perform automated tasks with applications ranging from chemical syntheses to biomedical diagnostics. The [...] Read more.
Microfluidic technology has revolutionized device fabrication by merging principles of fluid dynamics with technologies from chemistry, physics, biology, material science, and microelectronics. Microfluidic systems manipulate small volumes of fluids to perform automated tasks with applications ranging from chemical syntheses to biomedical diagnostics. The advent of low-cost 3D printers has revolutionized the development of microfluidic systems. For measuring molecules, 3D printing offers cost-effective, time, and ease-of-designing benefits. In this paper, we present a comprehensive tutorial for design, optimization, and validation for creating a 3D-printed microfluidic immunoarray for ultrasensitive detection of multiple protein biomarkers. The target is the development of a point of care array to determine five protein biomarkers for aggressive cancers. The design phase involves defining dimensions of microchannels, reagent chambers, detection wells, and optimizing parameters and detection methods. In this study, the physical design of the array underwent multiple iterations to optimize key features, such as developing open detection wells for uniform signal distribution and a flap for covering wells during the assay. Then, full signal optimization for sensitivity and limit of detection (LOD) was performed, and calibration plots were generated to assess linear dynamic ranges and LODs. Varying characteristics among biomarkers highlighted the need for tailored assay conditions. Spike-recovery studies confirmed the assay’s accuracy. Overall, this paper showcases the methodology, rigor, and innovation involved in designing a 3D-printed microfluidic immunoarray. Optimized parameters, calibration equations, and sensitivity and accuracy data contribute valuable metrics for future applications in biomarker analyses. Full article
(This article belongs to the Special Issue Feature Papers of Micromachines in Biology and Biomedicine 2023)
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22 pages, 7435 KiB  
Review
Fabrication and Applications of Magnetic Polymer Composites for Soft Robotics
by Sayan Ganguly and Shlomo Margel
Micromachines 2023, 14(12), 2173; https://doi.org/10.3390/mi14122173 - 29 Nov 2023
Cited by 10 | Viewed by 3452
Abstract
The emergence of magnetic polymer composites has had a transformative impact on the field of soft robotics. This overview will examine the various methods by which innovative materials can be synthesized and utilized. The advancement of soft robotic systems has been significantly enhanced [...] Read more.
The emergence of magnetic polymer composites has had a transformative impact on the field of soft robotics. This overview will examine the various methods by which innovative materials can be synthesized and utilized. The advancement of soft robotic systems has been significantly enhanced by the utilization of magnetic polymer composites, which amalgamate the pliability of polymers with the reactivity of magnetic materials. This study extensively examines the production methodologies involved in dispersing magnetic particles within polymer matrices and controlling their spatial distribution. The objective is to gain insights into the strategies required to attain the desired mechanical and magnetic properties. Additionally, this study delves into the potential applications of these composites in the field of soft robotics, encompassing various devices such as soft actuators, grippers, and wearable gadgets. The study emphasizes the transformative capabilities of magnetic polymer composites, which offer a novel framework for the advancement of biocompatible, versatile soft robotic systems that utilize magnetic actuation. Full article
(This article belongs to the Special Issue Advances in Nano and Hydrogel Platforms for Biomedical Applications)
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13 pages, 6406 KiB  
Article
Acoustic Bubble and Magnetic Actuation-Based Microrobot for Enhanced Multiphase Drug Delivery Efficiency
by Jihyeok Park, Youngkwang Kim, Jinwon Jeong, Deasung Jang, Daegeun Kim and Sangkug Chung
Micromachines 2023, 14(12), 2169; https://doi.org/10.3390/mi14122169 - 29 Nov 2023
Cited by 1 | Viewed by 2551
Abstract
This paper proposes an acoustic bubble and magnetic actuation-based microrobot for enhancing multiphase drug delivery efficiency. The proposed device can encapsulate multiphase drugs, including liquids, using the two bubbles embedded within the microtube. Additionally, using the magnetic actuation of the loaded magnetic liquid [...] Read more.
This paper proposes an acoustic bubble and magnetic actuation-based microrobot for enhancing multiphase drug delivery efficiency. The proposed device can encapsulate multiphase drugs, including liquids, using the two bubbles embedded within the microtube. Additionally, using the magnetic actuation of the loaded magnetic liquid metal, it can deliver drugs to target cells. This study visualized the flow patterns generated by the oscillating bubble within the tube to validate the drug release principle. In addition, to investigate the effect of the oscillation properties of the inner bubble on drug release, the oscillation amplitude of the inner bubble was measured under various experimental variables using a high-speed camera. Subsequently, we designed a microrobot capable of encapsulating bubbles, drugs, and magnetic liquid metal and fabricated it using microfabrication technology based on ultra-precision 3D printing. As a proof of concept, we demonstrated the transport and drug release of the microrobot encapsulating the drug in a Y-shaped channel simulating a blood vessel. The proposed device is anticipated to enhance the efficiency of drug therapy by minimizing drug side effects, reducing drug administration frequency, and improving the stability of the drug within the body. This paper is expected to be applicable not only to targeted drug delivery but also to various biomedical fields, such as minimally invasive surgery and cell manipulation, by effectively delivering multiphase drugs using the simple structure of a microrobot. Full article
(This article belongs to the Special Issue Acoustical Tweezers: From Fundamental Research to Applications)
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13 pages, 19497 KiB  
Article
Charge Characteristics of Dielectric Particle Swarm Involving Comprehensive Electrostatic Information
by Yue Feng, Xingfeng Shen, Ruiguo Wang, Zilong Zhou, Zhaoxu Yang, Yanhui Han and Ying Xiong
Micromachines 2023, 14(12), 2151; https://doi.org/10.3390/mi14122151 - 24 Nov 2023
Cited by 1 | Viewed by 1413
Abstract
The triboelectrification effect caused by dynamic contact between particles is an issue for explosions caused by electrostatic discharging (ESD) in the triboelectric nanogenerators (TENGs) for powering the flexible and wearable sensors. The electrostatic strength of dielectric particles (surface charge density, surface potential, electric [...] Read more.
The triboelectrification effect caused by dynamic contact between particles is an issue for explosions caused by electrostatic discharging (ESD) in the triboelectric nanogenerators (TENGs) for powering the flexible and wearable sensors. The electrostatic strength of dielectric particles (surface charge density, surface potential, electric field, etc.) is essential to evaluate the level of ESD risk. Those differential electrostatic characteristics concerned with unhomogenized swarmed particles cannot be offered via in-current employed-joint COMSOL 6.1 simulation, in which the discrete charged dielectric particles are mistakenly regarded as continuous ones. In this paper, the hybrid discrete element method (EDEM tool) associated with programming in COMSOL Multiphysics 6.1 with MATLAB R2023a was employed to obtain the electrostatic information of the triboelectric dielectric particle swarm. We revealed that the high-accuracy strengths of electric potential and electric field inside particle warm are crucial to evaluating ESD risk. The calculated electrostatic characteristics differ from the grid method and continuous method in the surface potential and electric field. This EDEM-based simulation method is significant for microcosmic understanding and the assessment of the ESD risk in TENGs. Full article
(This article belongs to the Special Issue Flexible and Wearable Sensors, 2nd Edition)
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13 pages, 3741 KiB  
Article
Untreated vs. Treated Carbon Felt Anodes: Impacts on Power Generation in Microbial Fuel Cells
by Abdelghani Ghanam, Sebastien Cecillon, Andrei Sabac, Hasna Mohammadi, Aziz Amine, François Buret and Naoufel Haddour
Micromachines 2023, 14(12), 2142; https://doi.org/10.3390/mi14122142 - 23 Nov 2023
Cited by 4 | Viewed by 2932
Abstract
This research sought to enhance the efficiency and biocompatibility of anodes in bioelectrochemical systems (BESs) such as microbial fuel cells (MFCs), with an aim toward large-scale, real-world applications. The study focused on the effects of acid-heat treatment and chemical modification of three-dimensional porous [...] Read more.
This research sought to enhance the efficiency and biocompatibility of anodes in bioelectrochemical systems (BESs) such as microbial fuel cells (MFCs), with an aim toward large-scale, real-world applications. The study focused on the effects of acid-heat treatment and chemical modification of three-dimensional porous pristine carbon felt (CF) on power generation. Different treatments were applied to the pristine CF, including coating with carbon nanofibers (CNFs) dispersed using dodecylbenzene sulfonate (SDBS) surfactant and biopolymer chitosan (CS). These processes were expected to improve the hydrophilicity, reduce the internal resistance, and increase the electrochemically active surface area of CF anodes. A high-resolution scanning electron microscopy (HR-SEM) analysis confirmed successful CNF coating. An electrochemical analysis showed improved conductivity and charge transfer toward [Fe(CN)6]3−/4− redox probe with treated anodes. When used in an air cathode single-chamber MFC system, the untreated CF facilitated quicker electroactive biofilm growth and reached a maximum power output density of 3.4 W m−2, with an open-circuit potential of 550 mV. Despite a reduction in charge transfer resistance (Rct) with the treated CF anodes, the power densities remained unchanged. These results suggest that untreated CF anodes could be most promising for enhancing power output in BESs, offering a cost-effective solution for large-scale MFC applications. Full article
(This article belongs to the Special Issue Nanostructures for Application in Electronics and Renewable Energy Sources)
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23 pages, 26808 KiB  
Review
Leveraging Ferroelectret Nanogenerators for Acoustic Applications
by Ziling Song, Xianfa Cai, Yiqin Wang, Wenyu Yang and Wei Li
Micromachines 2023, 14(12), 2145; https://doi.org/10.3390/mi14122145 - 23 Nov 2023
Cited by 3 | Viewed by 2394
Abstract
Ferroelectret nanogenerator (FENG), renowned for its remarkable electromechanical conversion efficiency and low Young’s modulus, has gained significant attention in various acoustic applications. The increasing interest is attributed to the crucial role acoustic devices play in our daily lives. This paper provides a comprehensive [...] Read more.
Ferroelectret nanogenerator (FENG), renowned for its remarkable electromechanical conversion efficiency and low Young’s modulus, has gained significant attention in various acoustic applications. The increasing interest is attributed to the crucial role acoustic devices play in our daily lives. This paper provides a comprehensive review of the advancements made in using FENG for acoustic applications. It elaborates on the operational mechanism of FENG in acoustics, with a special focus on comparing the influence of different fabrication materials and techniques on its properties. This review categorizes acoustic applications of FENG into three primary areas: acoustic sensing, acoustic actuation, and acoustic energy harvesting. The detailed descriptions of FENG’s implementations in these areas are provided, and potential directions and challenges for further development are outlined. By demonstrating the wide range of potential applications for FENG, it is shown that FENG can be adapted to meet different individual needs. Full article
(This article belongs to the Special Issue Piezoelectric MEMS/NEMS—Materials, Devices, and Applications, Second Edition)
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10 pages, 3656 KiB  
Article
Controllable Carrier Doping in Two-Dimensional Materials Using Electron-Beam Irradiation and Scalable Oxide Dielectrics
by Lu Wang, Zejing Guo, Qing Lan, Wenqing Song, Zhipeng Zhong, Kunlin Yang, Tuoyu Zhao, Hai Huang, Cheng Zhang and Wu Shi
Micromachines 2023, 14(11), 2125; https://doi.org/10.3390/mi14112125 - 19 Nov 2023
Cited by 2 | Viewed by 2690
Abstract
Two-dimensional (2D) materials, characterized by their atomically thin nature and exceptional properties, hold significant promise for future nano-electronic applications. The precise control of carrier density in these 2D materials is essential for enhancing performance and enabling complex device functionalities. In this study, we [...] Read more.
Two-dimensional (2D) materials, characterized by their atomically thin nature and exceptional properties, hold significant promise for future nano-electronic applications. The precise control of carrier density in these 2D materials is essential for enhancing performance and enabling complex device functionalities. In this study, we present an electron-beam (e-beam) doping approach to achieve controllable carrier doping effects in graphene and MoS2 field-effect transistors (FETs) by leveraging charge-trapping oxide dielectrics. By adding an atomic layer deposition (ALD)-grown Al2O3 dielectric layer on top of the SiO2/Si substrate, we demonstrate that controllable and reversible carrier doping effects can be effectively induced in graphene and MoS2 FETs through e-beam doping. This new device configuration establishes an oxide interface that enhances charge-trapping capabilities, enabling the effective induction of electron and hole doping beyond the SiO2 breakdown limit using high-energy e-beam irradiation. Importantly, these high doping effects exhibit non-volatility and robust stability in both vacuum and air environments for graphene FET devices. This methodology enhances carrier modulation capabilities in 2D materials and holds great potential for advancing the development of scalable 2D nano-devices. Full article
(This article belongs to the Special Issue 2D Materials: Devices and Functionalities)
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16 pages, 2599 KiB  
Article
Printing MEMS: Application of Inkjet Techniques to the Manufacturing of Inertial Accelerometers
by Roberto Bernasconi, Gabriele Pietro Invernizzi, Elisa Gallo Stampino, Riccardo Gotti, Davide Gatti and Luca Magagnin
Micromachines 2023, 14(11), 2082; https://doi.org/10.3390/mi14112082 - 10 Nov 2023
Cited by 6 | Viewed by 1998
Abstract
In the last few years, the manufacturing of microelectromechanical systems (MEMS) by means of innovative tridimensional and bidimensional printing technologies has significantly catalyzed the attention of researchers. Inkjet material deposition, in particular, can become a key enabling technology for the production of polymer-based [...] Read more.
In the last few years, the manufacturing of microelectromechanical systems (MEMS) by means of innovative tridimensional and bidimensional printing technologies has significantly catalyzed the attention of researchers. Inkjet material deposition, in particular, can become a key enabling technology for the production of polymer-based inertial sensors characterized by low cost, high manufacturing scalability and superior sensitivity. In this paper, a fully inkjet-printed polymeric accelerometer is proposed, and its manufacturing steps are described. The manufacturing challenges connected with the inkjet deposition of SU-8 as a structural material are identified and addressed, resulting in the production of a functional spring-mass sensor. A step-crosslinking process allows optimization of the final shape of the device and limits defects typical of inkjet printing. The resulting device is characterized from a morphological point of view, and its functionality is assessed in performing optical readout. The acceleration range of the optimized device is 0–0.7 g, its resolution is 2 × 10−3 g and its sensitivity is 6745 nm/g. In general, the work demonstrates the feasibility of polymeric accelerometer production via inkjet printing, and these characteristic parameters demonstrate their potential applicability in a broad range of uses requiring highly accurate acceleration measurements over small displacements. Full article
(This article belongs to the Special Issue MEMS in Italy 2023)
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19 pages, 7528 KiB  
Review
Patterning Techniques in Coplanar Micro/Nano Capacitive Sensors
by Seokwon Joo, Jung Yeon Han, Soonmin Seo and Ju-Hyung Kim
Micromachines 2023, 14(11), 2034; https://doi.org/10.3390/mi14112034 - 31 Oct 2023
Cited by 1 | Viewed by 2632
Abstract
Rapid technological advancements have led to increased demands for sensors. Hence, high performance suitable for next-generation technology is required. As sensing technology has numerous applications, various materials and patterning methods are used for sensor fabrication. This affects the characteristics and performance of sensors, [...] Read more.
Rapid technological advancements have led to increased demands for sensors. Hence, high performance suitable for next-generation technology is required. As sensing technology has numerous applications, various materials and patterning methods are used for sensor fabrication. This affects the characteristics and performance of sensors, and research centered specifically on these patterns is necessary for high integration and high performance of these devices. In this paper, we review the patterning techniques used in recently reported sensors, specifically the most widely used capacitive sensors, and their impact on sensor performance. Moreover, we introduce a method for increasing sensor performance through three-dimensional (3D) structures. Full article
(This article belongs to the Special Issue Micro/Nanostructures in Sensors and Actuators)
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11 pages, 2942 KiB  
Article
The Efficient Energy Collection of an Autoregulatory Driving Arm Harvester in a Breeze Environment
by Chao Zhang, Xinlong Yang, Boren Zhang, Kangqi Fan, Zhiming Liu and Zejia Liu
Micromachines 2023, 14(11), 2032; https://doi.org/10.3390/mi14112032 - 31 Oct 2023
Cited by 2 | Viewed by 1380
Abstract
Breezes are a common source of renewable energy in the natural world. However, effectively harnessing breeze energy is challenging with conventional wind generators. These generators have a relatively high start-up wind speed requirement due to their large and steady rotational inertia. This study [...] Read more.
Breezes are a common source of renewable energy in the natural world. However, effectively harnessing breeze energy is challenging with conventional wind generators. These generators have a relatively high start-up wind speed requirement due to their large and steady rotational inertia. This study puts forth the idea of an autoregulatory driving arm (ADA), utilizing a stretchable arm for every wind cup and an elastic thread to provide adjustable rotational inertia and a low start-up speed. The self-adjustable rotational inertia of the harvester is achieved through coordinated interaction between the centrifugal and elastic forces. As the wind speed varies, the arm length of the wind cup automatically adjusts, thereby altering the rotational inertia of the harvester. This self-adjustment mechanism allows the harvester to optimize its performance and adapt to different wind conditions. By implementing the suggested ADA harvester, a low start-up speed of 1 m/s is achieved due to the small rotational inertia in its idle state. With the escalation of wind speed, the amplified centrifugal force leads to the elongation of the driving arms. When compared to a comparable harvester with a constant driving arm (CDA), the ADA harvester can generate more power thanks to this stretching effect. Additionally, the ADA harvester can operate for a longer time than the CDA harvester even after the wind has stopped. This extended operation time enables the ADA harvester to serve as a renewable power source for sensors and other devices in natural breeze environments. By efficiently utilizing and storing energy, the ADA harvester ensures a continuous and reliable power supply in such settings. Full article
(This article belongs to the Special Issue Energy Conversion and Storage: From Materials to Devices)
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13 pages, 2108 KiB  
Article
An Analytical Thermal Buckling Model for Semiconductor Chips on a Substrate
by Guangping Gong, Dian Xu, Sijun Xiong, Fangyu Yi, Chengbo Wang and Rui Li
Micromachines 2023, 14(11), 2025; https://doi.org/10.3390/mi14112025 - 30 Oct 2023
Cited by 1 | Viewed by 1695
Abstract
Semiconductor chips on a substrate have a wide range of applications in electronic devices. However, environmental temperature changes may cause mechanical buckling of the chips, resulting in an urgent demand to develop analytical models to study this issue with high efficiency and accuracy [...] Read more.
Semiconductor chips on a substrate have a wide range of applications in electronic devices. However, environmental temperature changes may cause mechanical buckling of the chips, resulting in an urgent demand to develop analytical models to study this issue with high efficiency and accuracy such that safety designs can be sought. In this paper, the thermal buckling of chips on a substrate is considered as that of plates on a Winkler elastic foundation and is studied by the symplectic superposition method (SSM) within the symplectic space-based Hamiltonian system. The solution procedure starts by converting the original problem into two subproblems, which are solved by using the separation of variables and the symplectic eigenvector expansion. Through the equivalence between the original problem and the superposition of subproblems, the final analytical thermal buckling solutions are obtained. The SSM does not require any assumptions of solution forms, which is a distinctive advantage compared with traditional analytical methods. Comprehensive numerical results by the SSM for both buckling temperatures and mode shapes are presented and are well validated through comparison with those using the finite element method. With the solutions obtained, the effects of the moduli of elastic foundations and geometric parameters on critical buckling temperatures and buckling mode shapes are investigated. Full article
(This article belongs to the Special Issue Structural Analyses and Designs for Flexible/Stretchable Electronics, Volume II)
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13 pages, 3025 KiB  
Article
Thomson–Einstein’s Tea Leaf Paradox Revisited: Aggregation in Rings
by Kirill Kolesnik, Daniel Quang Le Pham, Jessica Fong and David John Collins
Micromachines 2023, 14(11), 2024; https://doi.org/10.3390/mi14112024 - 30 Oct 2023
Cited by 1 | Viewed by 2426
Abstract
A distinct particle focusing spot occurs in the center of a rotating fluid, presenting an apparent paradox given the presence of particle inertia. It is recognized, however, that the presence of a secondary flow with a radial component drives this particle aggregation. In [...] Read more.
A distinct particle focusing spot occurs in the center of a rotating fluid, presenting an apparent paradox given the presence of particle inertia. It is recognized, however, that the presence of a secondary flow with a radial component drives this particle aggregation. In this study, we expand on the examination of this “Thomson–Einstein’s tea leaf paradox” phenomenon, where we use a combined experimental and computational approach to investigate particle aggregation dynamics. We show that not only the rotational velocity, but also the vessel shape, have a significant influence on a particle’s equilibrium position. We accordingly demonstrate the formation of a single focusing spot in a vessel center, as has been conclusively demonstrated elsewhere, but also the repeatable formation of stable ring-shaped particle arrangements. Full article
(This article belongs to the Special Issue Micro-Tweezers, Integrated Sensors and Micro-Manipulations Techniques)
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13 pages, 3845 KiB  
Article
Surface Roughness Prediction in Ultra-Precision Milling: An Extreme Learning Machine Method with Data Fusion
by Suiyan Shang, Chunjin Wang, Xiaoliang Liang, Chi Fai Cheung and Pai Zheng
Micromachines 2023, 14(11), 2016; https://doi.org/10.3390/mi14112016 - 29 Oct 2023
Cited by 5 | Viewed by 2548
Abstract
This paper pioneers the use of the extreme learning machine (ELM) approach for surface roughness prediction in ultra-precision milling, leveraging the excellent fitting ability with small datasets and the fast learning speed of the extreme learning machine method. By providing abundant machining information, [...] Read more.
This paper pioneers the use of the extreme learning machine (ELM) approach for surface roughness prediction in ultra-precision milling, leveraging the excellent fitting ability with small datasets and the fast learning speed of the extreme learning machine method. By providing abundant machining information, the machining parameters and force signal data are fused on the feature level to further improve ELM prediction accuracy. An ultra-precision milling experiment was designed and conducted to verify our proposed data-fusion-based ELM method. The results show that the ELM with data fusion outperforms other state-of-art methods in surface roughness prediction. It achieves an impressively low mean absolute percentage error of 1.6% while requiring a mere 18 s for model training. Full article
(This article belongs to the Special Issue Intelligent Precision Machining)
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13 pages, 7166 KiB  
Article
Electric-Force Conversion Performance of Si-Based LiNbO3 Devices Based on Four Cantilever Beams
by Huiyi Zhang, Xiaojun Qiao, Huifen Wei, Xiaohuang Li, Xiaohui Wu, Nanxin Yu, Hao Lu, Tao Guo, Xiujian Chou and Wenping Geng
Micromachines 2023, 14(11), 1988; https://doi.org/10.3390/mi14111988 - 27 Oct 2023
Cited by 1 | Viewed by 1861
Abstract
In micron or nano smart sensing systems, piezoelectric cantilever beams are distributed as major components in microsensors, actuators, and energy harvesters. This paper investigates the performance of four cantilever beam devices with “electric-force” conversion based on the inverse piezoelectric effect of lithium niobate [...] Read more.
In micron or nano smart sensing systems, piezoelectric cantilever beams are distributed as major components in microsensors, actuators, and energy harvesters. This paper investigates the performance of four cantilever beam devices with “electric-force” conversion based on the inverse piezoelectric effect of lithium niobate (LiNbO3, LN) single-crystal materials. A new compact piezoelectric smart device model is proposed, designed as a single mass block connected by four beams, where devices exhibit smaller lateral errors (0.39–0.41%). The relationship between the displacement characteristics of cantilever beams and driving voltage was researched by applying excitation signals. The results show that the device has the maximum displacement at a first-order intrinsic frequency (fosc = 11.338 kHz), while the displacement shows a good linear relationship (R2 = 0.998) with driving voltage. The square wave signals of the same amplitude have greater “electrical-force” conversion efficiency. The output displacement can reach 12 nm, which is much higher than the output displacement with sinusoidal excitation. In addition, the relative displacement deviation of devices can be maintained within ±1% under multiple cycles of electrical signal loading. The small size, high reliability, and ultra-stability of Si–LN ferroelectric single-crystal cantilever beam devices with lower vibration amplitudes are promising for nanopositioning techniques in microscopy, diagnostics, and high-precision manufacturing applications. Full article
(This article belongs to the Topic Piezoelectric Materials and Applications)
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38 pages, 3783 KiB  
Review
Analytical Gas Sensing in the Terahertz Spectral Range
by Andreja Abina, Uroš Puc, Mojca Jazbinšek and Aleksander Zidanšek
Micromachines 2023, 14(11), 1987; https://doi.org/10.3390/mi14111987 - 27 Oct 2023
Cited by 9 | Viewed by 3664
Abstract
Exploiting the terahertz (THz) part of the electromagnetic spectrum is attracting attention in various scientific and applied disciplines worldwide. THz technology has also revealed its potential as an effective tool for gas analysis in astronomy, biomedicine and chemical analysis. Recently, it has also [...] Read more.
Exploiting the terahertz (THz) part of the electromagnetic spectrum is attracting attention in various scientific and applied disciplines worldwide. THz technology has also revealed its potential as an effective tool for gas analysis in astronomy, biomedicine and chemical analysis. Recently, it has also become important in environmental applications for monitoring hazardous and toxic gases in the atmosphere. This paper gives an overview of THz gas detection analytical methods for environmental and biomedical applications, starting with a brief introduction to THz technology and an explanation of the interaction of THz radiation with gaseous species and the atmosphere. The review focuses on several gaseous species and groups of air pollutants that have been or can be analysed by THz spectrometry. The review concludes that different but complementary THz detection methods allow unique detection, identification and quantification of gaseous and particulate air pollutants with high selectivity, specificity and sensitivity. THz detection methods also allow further technological improvements and open new application possibilities. Full article
(This article belongs to the Special Issue Photon-Driven Technologies: Exploring the Latest Advancements)
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11 pages, 4102 KiB  
Article
Construction of MoS2-ReS2 Hybrid on Ti3C2Tx MXene for Enhanced Microwave Absorption
by Xiaoxuan Xu, Youqiang Xing and Lei Liu
Micromachines 2023, 14(11), 1996; https://doi.org/10.3390/mi14111996 - 27 Oct 2023
Cited by 4 | Viewed by 1536
Abstract
Utilizing interface engineering to construct abundant heterogeneous interfaces is an important means to improve the absorbing performance of microwave absorbers. Here, we have prepared the MXene/MoS2-ReS2 (MMR) composite with rich heterogeneous interfaces composed of two-dimensional Ti3C2Tx [...] Read more.
Utilizing interface engineering to construct abundant heterogeneous interfaces is an important means to improve the absorbing performance of microwave absorbers. Here, we have prepared the MXene/MoS2-ReS2 (MMR) composite with rich heterogeneous interfaces composed of two-dimensional Ti3C2Tx MXene and two-dimensional transition metal disulfides through a facile hydrothermal process. The surface of MXene is completely covered by nanosheets of MoS2 and ReS2, forming a hybrid structure. MRR exhibits excellent absorption performance, with its strongest reflection loss reaching −51.15 dB at 2.0 mm when the filling ratio is only 10 wt%. Meanwhile, the effective absorption bandwidth covers the range of 5.5–18 GHz. Compared to MXene/MoS2 composites, MRR with a MoS2-ReS2 heterogeneous interface exhibits stronger polarization loss ability and superior absorption efficiency at the same thickness. This study provides a reference for the design of transition metal disulfides-based absorbing materials. Full article
(This article belongs to the Special Issue Semiconductors and Nanostructures for Electronics and Photonics)
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16 pages, 7440 KiB  
Article
Tackling Multi-Physics Nano-Scale Phenomena in Capillary Force Lithography with Small Data by Hybrid Intelligence
by Ashish Chapagain and In Ho Cho
Micromachines 2023, 14(11), 1984; https://doi.org/10.3390/mi14111984 - 26 Oct 2023
Cited by 2 | Viewed by 1448
Abstract
The scientific community has been looking for novel approaches to develop nanostructures inspired by nature. However, due to the complicated processes involved, controlling the height of these nanostructures is challenging. Nanoscale capillary force lithography (CFL) is one way to use a photopolymer and [...] Read more.
The scientific community has been looking for novel approaches to develop nanostructures inspired by nature. However, due to the complicated processes involved, controlling the height of these nanostructures is challenging. Nanoscale capillary force lithography (CFL) is one way to use a photopolymer and alter its properties by exposing it to ultraviolet radiation. Nonetheless, the working mechanism of CFL is not fully understood due to a lack of enough information and first principles. One of these obscure behaviors is the sudden jump phenomenon—the sudden change in the height of the photopolymer depending on the UV exposure time and height of nano-grating (based on experimental data). This paper uses known physical principles alongside artificial intelligence to uncover the unknown physical principles responsible for the sudden jump phenomenon. The results showed promising results in identifying air diffusivity, dynamic viscosity, surface tension, and electric potential as the previously unknown physical principles that collectively explain the sudden jump phenomenon. Full article
(This article belongs to the Special Issue Micromachines Research and Development in North America)
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10 pages, 1721 KiB  
Article
High-Performance Vertical Light-Emitting Transistors Based on ZnO Transistor/Quantum-Dot Light-Emitting Diode Integration and Electron Injection Layer Modification
by Jui-Fen Chang and Jia-Min Yu
Micromachines 2023, 14(10), 1933; https://doi.org/10.3390/mi14101933 - 15 Oct 2023
Cited by 2 | Viewed by 2280
Abstract
Vertical light-emitting transistors (VLETs) consisting of vertically stacked unipolar transistors and organic light-emitting diodes (OLEDs) have been proposed as a prospective building block for display technologies. In addition to OLEDs, quantum-dot (QD) LEDs (QLEDs) with high brightness and high color purity have also [...] Read more.
Vertical light-emitting transistors (VLETs) consisting of vertically stacked unipolar transistors and organic light-emitting diodes (OLEDs) have been proposed as a prospective building block for display technologies. In addition to OLEDs, quantum-dot (QD) LEDs (QLEDs) with high brightness and high color purity have also become attractive light-emitting devices for display applications. However, few studies have attempted to integrate QLEDs into VLETs, as this not only involves technical issues such as compatible solution process of QDs and fine patterning of electrodes in multilayer stacked geometries but also requires a high driving current that is demanding on transistor design. Here we show that these integration issues of QLEDs can be addressed by using inorganic transistors with robust processability and high mobility, such as the studied ZnO transistor, which facilitates simple fabrication of QD VLETs (QVLETs) with efficient emission in the patterned channel area, suitable for high-resolution display applications. We perform a detailed optimization of QVLET by modifying ZnO:polyethylenimine nanocomposite as the electron injection layer (EIL) between the integrated ZnO transistor/QLED, and achieve the highest external quantum efficiency of ~3% and uniform emission in the patterned transistor channel. Furthermore, combined with a systematic study of corresponding QLEDs, electron-only diodes, and electroluminescence images, we provide a deeper understanding of the effect of EIL modification on current balance and distribution, and thus on QVLET performance. Full article
(This article belongs to the Special Issue Thin-Film Transistors: Materials, Fabrications and Applications)
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33 pages, 4097 KiB  
Review
Advancements in Wearable and Implantable Intraocular Pressure Biosensors for Ophthalmology: A Comprehensive Review
by Kevin Y. Wu, Mina Mina, Marjorie Carbonneau, Michael Marchand and Simon D. Tran
Micromachines 2023, 14(10), 1915; https://doi.org/10.3390/mi14101915 - 9 Oct 2023
Cited by 15 | Viewed by 4618
Abstract
Glaucoma, marked by its intricate association with intraocular pressure (IOP), stands as a predominant cause of non-reversible vision loss. In this review, the physiological relevance of IOP is detailed, alongside its potential pathological consequences. The review further delves into innovative engineering solutions for [...] Read more.
Glaucoma, marked by its intricate association with intraocular pressure (IOP), stands as a predominant cause of non-reversible vision loss. In this review, the physiological relevance of IOP is detailed, alongside its potential pathological consequences. The review further delves into innovative engineering solutions for IOP monitoring, highlighting the latest advancements in wearable and implantable sensors and their potential in enhancing glaucoma management. These technological innovations are interwoven with clinical practice, underscoring their real-world applications, patient-centered strategies, and the prospects for future development in IOP control. By synthesizing theoretical concepts, technological innovations, and practical clinical insights, this review contributes a cohesive and comprehensive perspective on the IOP biosensor’s role in glaucoma, serving as a reference for ophthalmological researchers, clinicians, and professionals. Full article
(This article belongs to the Special Issue Feature Reviews in Micromachines 2023)
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17 pages, 2804 KiB  
Article
Orange Carotenoid Protein in Mesoporous Silica: A New System towards the Development of Colorimetric and Fluorescent Sensors for pH and Temperature
by Silvia Leccese, Andrea Calcinoni, Adjélé Wilson, Diana Kirilovsky, Donatella Carbonera, Thomas Onfroy, Claude Jolivalt and Alberto Mezzetti
Micromachines 2023, 14(10), 1871; https://doi.org/10.3390/mi14101871 - 29 Sep 2023
Cited by 3 | Viewed by 1520
Abstract
Orange carotenoid protein (OCP) is a photochromic carotenoprotein involved in the photoprotection of cyanobacteria. It is activated by blue-green light to a red form OCPR capable of dissipating the excess of energy of the cyanobacterial photosynthetic light-harvesting systems. Activation to OCPR [...] Read more.
Orange carotenoid protein (OCP) is a photochromic carotenoprotein involved in the photoprotection of cyanobacteria. It is activated by blue-green light to a red form OCPR capable of dissipating the excess of energy of the cyanobacterial photosynthetic light-harvesting systems. Activation to OCPR can also be achieved in the dark. In the present work, activation by pH changes of two different OCPs—containing echinenone or canthaxanthin as carotenoids—is investigated in different conditions. A particular emphasis is put on OCP encapsulated in SBA-15 mesoporous silica nanoparticles. It is known that in these hybrid systems, under appropriate conditions, OCP remains photoactive. Here, we show that when immobilised in SBA-15, the OCP visible spectrum is sensitive to pH changes, but such a colorimetric response is very different from the one observed for OCP in solution. In both cases (SBA-15 matrices and solutions), pH-induced colour changes are related either by orange-to-red OCP activation, or by carotenoid loss from the denatured protein. Of particular interest is the response of OCP in SBA-15 matrices, where a sudden change in the Vis absorption spectrum and in colour is observed for pH changing from 2 to 3 (in the case of canthaxanthin-binding OCP in SBA-15: λMAX shifts from 454 to 508 nm) and for pH changing from 3 to 4 (in the case of echinenone-binding OCP in SBA-15: λMAX shifts from 445 to 505 nm). The effect of temperature on OCP absorption spectrum and colour (in SBA-15 matrices) has also been investigated and found to be highly dependent on the properties of the used mesoporous silica matrix. Finally, we also show that simultaneous encapsulation in selected surface-functionalised SBA-15 nanoparticles of appropriate fluorophores makes it possible to develop OCP-based pH-sensitive fluorescent systems. This work therefore represents a proof of principle that OCP immobilised in mesoporous silica is a promising system in the development of colorimetric and fluorometric pH and temperature sensors. Full article
(This article belongs to the Section C：Chemistry)
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15 pages, 3296 KiB  
Article
Integration of Inkjet Printed Graphene as a Hole Transport Layer in Organic Solar Cells
by Julia Kastner, Flavia Tomarchio, Nicolas Decorde, Matthias Kehrer, Günter Hesser and Anita Fuchsbauer
Micromachines 2023, 14(10), 1858; https://doi.org/10.3390/mi14101858 - 28 Sep 2023
Cited by 2 | Viewed by 1907
Abstract
This work demonstrates the green production of a graphene ink for inkjet printing and its use as a hole transport layer (HTL) in an organic solar cell. Graphene as an HTL improves the selective hole extraction at the anode and prevents charge recombination [...] Read more.
This work demonstrates the green production of a graphene ink for inkjet printing and its use as a hole transport layer (HTL) in an organic solar cell. Graphene as an HTL improves the selective hole extraction at the anode and prevents charge recombination at the electronic interface and metal diffusion into the photoactive layer. Graphite was exfoliated in water, concentrated by iterative centrifugation, and characterized by Raman. The concentrated graphene ink was incorporated into inverted organic solar cells by inkjet printing on the active polymer in an ambient atmosphere. Argon plasma was used to enhance wetting of the polymer with the graphene ink during printing. The argon plasma treatment of the active polymer P3HT:PCBM was investigated by XPS, AFM and contact angle measurements. Efficiency and lifetime studies undertaken show that the device with graphene as HTL is fully functional and has good potential for an inkjet printable and flexible alternative to PEDOT:PSS. Full article
(This article belongs to the Special Issue Graphene-Based Metamaterial Solar Energy Devices)
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18 pages, 3490 KiB  
Article
Scalable Processing of Cyclic Olefin Copolymer (COC) Microfluidic Biochips
by Rodolfo G. Rodrigues, Pedro G. M. Condelipes, Rafaela R. Rosa, Virginia Chu and João Pedro Conde
Micromachines 2023, 14(10), 1837; https://doi.org/10.3390/mi14101837 - 27 Sep 2023
Cited by 4 | Viewed by 3061
Abstract
Microfluidics evolved with the appearance of polydimethylsiloxane (PDMS), an elastomer with a short processing time and the possibility for replication on a micrometric scale. Despite the many advantages of PDMS, there are well-known drawbacks, such as the hydrophobic surface, the absorption of small [...] Read more.
Microfluidics evolved with the appearance of polydimethylsiloxane (PDMS), an elastomer with a short processing time and the possibility for replication on a micrometric scale. Despite the many advantages of PDMS, there are well-known drawbacks, such as the hydrophobic surface, the absorption of small molecules, the low stiffness, relatively high cost, and the difficulty of scaling up the fabrication process for industrial production, creating a need for alternative materials. One option is the use of stiffer thermoplastics, such as the cyclic olefin copolymer (COC), which can be mass produced, have lower cost and possess excellent properties. In this work, a method to fabricate COC microfluidic structures was developed. The work was divided into process optimization and evaluation of material properties for application in microfluidics. In the processing step, moulding, sealing, and liquid handling aspects were developed and optimized. The resulting COC devices were evaluated from the point of view of molecular diffusion, burst pressure, temperature resistance, and susceptibility to surface treatments and these results were compared to PDMS devices. Lastly, a target DNA hybridization assay was performed showing the potential of the COC-based microfluidic device to be used in biosensing and Lab-on-a-Chip applications. Full article
(This article belongs to the Special Issue Novel Functional Materials and Techniques for 3D-Microfabrication)
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11 pages, 2798 KiB  
Article
A BTO/PVDF/PDMS Piezoelectric Tangential and Normal Force Sensor Inspired by a Wind Chime
by Chunyan Zhang, Xiaotian Zhang, Qiang Zhang, Shengbo Sang, Jianlong Ji, Runfang Hao and Yan Liu
Micromachines 2023, 14(10), 1848; https://doi.org/10.3390/mi14101848 - 27 Sep 2023
Cited by 3 | Viewed by 2024
Abstract
There is a growing demand for flexible pressure sensors in environmental monitoring and human–robot interaction robotics. A flexible and susceptible sensor can discriminate multidirectional pressure, thus effectively detecting signals of small environmental changes and providing solutions for personalized medicine. This paper proposes a [...] Read more.
There is a growing demand for flexible pressure sensors in environmental monitoring and human–robot interaction robotics. A flexible and susceptible sensor can discriminate multidirectional pressure, thus effectively detecting signals of small environmental changes and providing solutions for personalized medicine. This paper proposes a multidimensional force detection sensor inspired by a wind chime structure with a three-dimensional force structure to detect and analyze normal and shear forces in real time. The force-sensing structure of the sensor consists of an upper and lower membrane on a polydimethylsiloxane substrate and four surrounding cylinders. A piezoelectric hemisphere is made of BTO/PVDF/PDMS composite material. The sensor columns in the wind chime structure surround the piezoelectric layer in the middle. When pressure is applied externally, the sensor columns are connected to the piezoelectric layer with a light touch. The piezoelectric hemisphere generates a voltage signal. Due to the particular structure of the sensor, it can accurately capture multidimensional forces and identify the direction of the external force by analyzing the position of the sensor and the output voltage amplitude. The development of such sensors shows excellent potential for self-powered wearable sensors, human–computer interaction, electronic skin, and soft robotics applications. Full article
(This article belongs to the Special Issue Flexible and Wearable Sensors, 2nd Edition)
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26 pages, 5246 KiB  
Review
Microfluidic Mixing: A Physics-Oriented Review
by Sri Manikandan Saravanakumar and Paul-Vahe Cicek
Micromachines 2023, 14(10), 1827; https://doi.org/10.3390/mi14101827 - 25 Sep 2023
Cited by 20 | Viewed by 5647
Abstract
This comprehensive review paper focuses on the intricate physics of microfluidics and their application in micromixing techniques. Various methods for enhancing mixing in microchannels are explored, with a keen emphasis on the underlying fluid dynamics principles. Geometrical micromixers employ complex channel designs to [...] Read more.
This comprehensive review paper focuses on the intricate physics of microfluidics and their application in micromixing techniques. Various methods for enhancing mixing in microchannels are explored, with a keen emphasis on the underlying fluid dynamics principles. Geometrical micromixers employ complex channel designs to induce fluid–fluid interface distortions, yielding efficient mixing while retaining manufacturing simplicity. These methods synergize effectively with external techniques, showcasing promising potential. Electrohydrodynamics harnesses electrokinetic phenomena like electroosmosis, electrophoresis, and electrothermal effects. These methods offer dynamic control over mixing parameters via applied voltage, frequency, and electrode positioning, although power consumption and heating can be drawbacks. Acoustofluidics leverages acoustic waves to drive microstreaming, offering localized yet far-reaching effects. Magnetohydrodynamics, though limited in applicability to certain fluids, showcases potential by utilizing magnetic fields to propel mixing. Selecting an approach hinges on trade-offs among complexity, efficiency, and compatibility with fluid properties. Understanding the physics of fluid behavior and rationalizing these techniques aids in tailoring the most suitable micromixing solution. In a rapidly advancing field, this paper provides a consolidated understanding of these techniques, facilitating the informed choice of approach for specific microfluidic mixing needs. Full article
(This article belongs to the Special Issue Feature Papers from Micromachines Reviewers 2023)
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17 pages, 2046 KiB  
Article
Rapid Production of Nanoscale Liposomes Using a 3D-Printed Reactor-In-A-Centrifuge: Formulation, Characterisation, and Super-Resolution Imaging
by Yongqing He, Davide De Grandi, Stanley Chandradoss, Gareth LuTheryn, Gianluca Cidonio, Ricardo Nunes Bastos, Valerio Pereno and Dario Carugo
Micromachines 2023, 14(9), 1763; https://doi.org/10.3390/mi14091763 - 12 Sep 2023
Cited by 5 | Viewed by 3077
Abstract
Nanoscale liposomes have been extensively researched and employed clinically for the delivery of biologically active compounds, including chemotherapy drugs and vaccines, offering improved pharmacokinetic behaviour and therapeutic outcomes. Traditional laboratory-scale production methods often suffer from limited control over liposome properties (e.g., size and [...] Read more.
Nanoscale liposomes have been extensively researched and employed clinically for the delivery of biologically active compounds, including chemotherapy drugs and vaccines, offering improved pharmacokinetic behaviour and therapeutic outcomes. Traditional laboratory-scale production methods often suffer from limited control over liposome properties (e.g., size and lamellarity) and rely on laborious multistep procedures, which may limit pre-clinical research developments and innovation in this area. The widespread adoption of alternative, more controllable microfluidic-based methods is often hindered by complexities and costs associated with device manufacturing and operation, as well as the short device lifetime and the relatively low liposome production rates in some cases. In this study, we demonstrated the production of liposomes comprising therapeutically relevant lipid formulations, using a cost-effective 3D-printed reactor-in-a-centrifuge (RIAC) device. By adjusting formulation- and production-related parameters, including the concentration of polyethylene glycol (PEG), temperature, centrifugation time and speed, and lipid concentration, the mean size of the produced liposomes could be tuned in the range of 140 to 200 nm. By combining selected experimental parameters, the method was capable of producing liposomes with a therapeutically relevant mean size of ~174 nm with narrow size distribution (polydispersity index, PDI ~0.1) at a production rate of >8 mg/min. The flow-through method proposed in this study has potential to become an effective and versatile laboratory-scale approach to simplify the synthesis of therapeutic liposomal formulations. Full article
(This article belongs to the Special Issue Feature Papers of Micromachines in Biology and Biomedicine 2022)
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25 pages, 5364 KiB  
Review
Point-of-Care Devices for Viral Detection: COVID-19 Pandemic and Beyond
by Sumit K. Yadav, Damini Verma, Ujala Yadav, Ashish Kalkal, Nivedita Priyadarshini, Ashutosh Kumar and Kuldeep Mahato
Micromachines 2023, 14(9), 1744; https://doi.org/10.3390/mi14091744 - 7 Sep 2023
Cited by 16 | Viewed by 2662
Abstract
The pandemic of COVID-19 and its widespread transmission have made us realize the importance of early, quick diagnostic tests for facilitating effective cure and management. The primary obstacles encountered were accurately distinguishing COVID-19 from other illnesses including the flu, common cold, etc. While [...] Read more.
The pandemic of COVID-19 and its widespread transmission have made us realize the importance of early, quick diagnostic tests for facilitating effective cure and management. The primary obstacles encountered were accurately distinguishing COVID-19 from other illnesses including the flu, common cold, etc. While the polymerase chain reaction technique is a robust technique for the determination of SARS-CoV-2 in patients of COVID-19, there arises a high demand for affordable, quick, user-friendly, and precise point-of-care (POC) diagnostic in therapeutic settings. The necessity for available tests with rapid outcomes spurred the advancement of POC tests that are characterized by speed, automation, and high precision and accuracy. Paper-based POC devices have gained increasing interest in recent years because of rapid, low-cost detection without requiring external instruments. At present, microfluidic paper-based analysis devices have garnered public attention and accelerated the development of such POCT for efficient multistep assays. In the current review, our focus will be on the fabrication of detection modules for SARS-CoV-2. Here, we have included a discussion on various strategies for the detection of viral moieties. The compilation of these strategies would offer comprehensive insight into the detection of the causative agent preparedness for future pandemics. We also provide a descriptive outline for paper-based diagnostic platforms, involving the determination mechanisms, as well as a commercial kit for COVID-19 as well as their outlook. Full article
(This article belongs to the Special Issue Microfluidics and Biosensors for Point-of-Care Applications)
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22 pages, 6112 KiB  
Review
Carbon-Based Electrochemical (Bio)sensors for the Detection of Carbendazim: A Review
by Constanza J. Venegas, Soledad Bollo and Paulina Sierra-Rosales
Micromachines 2023, 14(9), 1752; https://doi.org/10.3390/mi14091752 - 7 Sep 2023
Cited by 3 | Viewed by 2310
Abstract
Carbendazim, a fungicide widely used in agriculture, has been classified as a hazardous chemical by the World Health Organization due to its environmental persistence. It is prohibited in several countries; therefore, detecting it in food and environmental samples is highly necessary. A reliable, [...] Read more.
Carbendazim, a fungicide widely used in agriculture, has been classified as a hazardous chemical by the World Health Organization due to its environmental persistence. It is prohibited in several countries; therefore, detecting it in food and environmental samples is highly necessary. A reliable, rapid, and low-cost method uses electrochemical sensors and biosensors, especially those modified with carbon-based materials with good analytical performance. In this review, we summarize the use of carbon-based electrochemical (bio)sensors for detecting carbendazim in environmental and food matrixes, with a particular interest in the role of carbon materials. Focus on publications between 2018 and 2023 that have been describing the use of carbon nanotubes, carbon nitride, graphene, and its derivatives, and carbon-based materials as modifiers, emphasizing the analytical performance obtained, such as linear range, detection limit, selectivity, and the matrix where the detection was applied. Full article
(This article belongs to the Special Issue Carbon-Based Electrodes for Electrochemical Analysis and Detection)
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13 pages, 1422 KiB  
Article
High-Frequency Dielectrophoresis Reveals That Distinct Bio-Electric Signatures of Colorectal Cancer Cells Depend on Ploidy and Nuclear Volume
by Josie L. Duncan, Mathew Bloomfield, Nathan Swami, Daniela Cimini and Rafael V. Davalos
Micromachines 2023, 14(9), 1723; https://doi.org/10.3390/mi14091723 - 1 Sep 2023
Cited by 1 | Viewed by 1891
Abstract
Aneuploidy, or an incorrect chromosome number, is ubiquitous among cancers. Whole-genome duplication, resulting in tetraploidy, often occurs during the evolution of aneuploid tumors. Cancers that evolve through a tetraploid intermediate tend to be highly aneuploid and are associated with poor patient prognosis. The [...] Read more.
Aneuploidy, or an incorrect chromosome number, is ubiquitous among cancers. Whole-genome duplication, resulting in tetraploidy, often occurs during the evolution of aneuploid tumors. Cancers that evolve through a tetraploid intermediate tend to be highly aneuploid and are associated with poor patient prognosis. The identification and enrichment of tetraploid cells from mixed populations is necessary to understand the role these cells play in cancer progression. Dielectrophoresis (DEP), a label-free electrokinetic technique, can distinguish cells based on their intracellular properties when stimulated above 10 MHz, but DEP has not been shown to distinguish tetraploid and/or aneuploid cancer cells from mixed tumor cell populations. Here, we used high-frequency DEP to distinguish cell subpopulations that differ in ploidy and nuclear size under flow conditions. We used impedance analysis to quantify the level of voltage decay at high frequencies and its impact on the DEP force acting on the cell. High-frequency DEP distinguished diploid cells from tetraploid clones due to their size and intracellular composition at frequencies above 40 MHz. Our findings demonstrate that high-frequency DEP can be a useful tool for identifying and distinguishing subpopulations with nuclear differences to determine their roles in disease progression. Full article
(This article belongs to the Special Issue Micromachines for Dielectrophoresis, 3rd Edition)
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20 pages, 7459 KiB  
Article
Virtual Coriolis-Force-Based Mode-Matching Micromachine-Optimized Tuning Fork Gyroscope without a Quadrature-Nulling Loop
by Yixuan Wu, Weizheng Yuan, Yanjun Xue, Honglong Chang and Qiang Shen
Micromachines 2023, 14(9), 1704; https://doi.org/10.3390/mi14091704 - 31 Aug 2023
Cited by 1 | Viewed by 1667
Abstract
A VCF-based mode-matching micromachine-optimized tuning fork gyroscope is proposed to not only maximize the scale factor of the device, but also avoid use of an additional quadrature-nulling loop to prevent structure complexity, pick-up electrode occupation, and coupling with a mode-matching loop. In detail, [...] Read more.
A VCF-based mode-matching micromachine-optimized tuning fork gyroscope is proposed to not only maximize the scale factor of the device, but also avoid use of an additional quadrature-nulling loop to prevent structure complexity, pick-up electrode occupation, and coupling with a mode-matching loop. In detail, a mode-matching, closed-loop system without a quadrature-nulling loop is established, and the corresponding convergence and matching error are quantitatively analyzed. The optimal straight beam of the gyro structure is then modeled to significantly reduce the quadrature coupling. The test results show that the frequency split is narrowed from 20 Hz to 0.014 Hz. The scale factor is improved 20.6 times and the bias instability (BI) is suppressed 3.28 times. The observed matching accuracy demonstrates that a mode matching system without a quadrature suppression loop is feasible and that the proposed device represents a competitive design for a mode-matching gyroscope. Full article
(This article belongs to the Special Issue MEMS Inertial Device)
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10 pages, 9758 KiB  
Article
Nano Groove and Prism-Structured Triboelectric Nanogenerators
by Resul Saritas, Majed Al-Ghamdi, Taylan Memik Das, Omar Rasheed, Samed Kocer, Ahmet Gulsaran, Asif Abdullah Khan, Md Masud Rana, Mahmoud Khater, Muhammed Kayaharman, Dayan Ban, Mustafa Yavuz and Eihab Abdel-Rahman
Micromachines 2023, 14(9), 1707; https://doi.org/10.3390/mi14091707 - 31 Aug 2023
Cited by 2 | Viewed by 2518
Abstract
Enhancing the output power of triboelectric nanogenerators (TENGs) requires the creation of micro or nano-features on polymeric triboelectric surfaces to increase the TENGs’ effective contact area and, therefore, output power. We deploy a novel bench-top fabrication method called dynamic Scanning Probe Lithography (d-SPL) [...] Read more.
Enhancing the output power of triboelectric nanogenerators (TENGs) requires the creation of micro or nano-features on polymeric triboelectric surfaces to increase the TENGs’ effective contact area and, therefore, output power. We deploy a novel bench-top fabrication method called dynamic Scanning Probe Lithography (d-SPL) to fabricate massive arrays of uniform 1 cm long and 2.5 µm wide nano-features comprising a 600 nm deep groove (NG) and a 600 nm high triangular prism (NTP). The method creates both features simultaneously in the polymeric surface, thereby doubling the structured surface area. Six thousand pairs of NGs and NTPs were patterned on a 6×5 cm2 PMMA substrate. It was then used as a mold to structure the surface of a 200 µm thick Polydimethylsiloxane (PDMS) layer. We show that the output power of the nano-structured TENG is significantly more than that of a TENG using flat PDMS films, at 12.2 mW compared to 2.2 mW, under the same operating conditions (a base acceleration amplitude of 0.8 g). Full article
(This article belongs to the Topic Advanced Energy Harvesting Technology)
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26 pages, 3442 KiB  
Review
Novel Artificial Intelligence-Based Approaches for Ab Initio Structure Determination and Atomic Model Building for Cryo-Electron Microscopy
by Megan C. DiIorio and Arkadiusz W. Kulczyk
Micromachines 2023, 14(9), 1674; https://doi.org/10.3390/mi14091674 - 27 Aug 2023
Cited by 8 | Viewed by 3455
Abstract
Single particle cryo-electron microscopy (cryo-EM) has emerged as the prevailing method for near-atomic structure determination, shedding light on the important molecular mechanisms of biological macromolecules. However, the inherent dynamics and structural variability of biological complexes coupled with the large number of experimental images [...] Read more.
Single particle cryo-electron microscopy (cryo-EM) has emerged as the prevailing method for near-atomic structure determination, shedding light on the important molecular mechanisms of biological macromolecules. However, the inherent dynamics and structural variability of biological complexes coupled with the large number of experimental images generated by a cryo-EM experiment make data processing nontrivial. In particular, ab initio reconstruction and atomic model building remain major bottlenecks that demand substantial computational resources and manual intervention. Approaches utilizing recent innovations in artificial intelligence (AI) technology, particularly deep learning, have the potential to overcome the limitations that cannot be adequately addressed by traditional image processing approaches. Here, we review newly proposed AI-based methods for ab initio volume generation, heterogeneous 3D reconstruction, and atomic model building. We highlight the advancements made by the implementation of AI methods, as well as discuss remaining limitations and areas for future development. Full article
(This article belongs to the Special Issue Electron Microscopy and Single Molecule Studies of Biomolecular Structure and Dynamics)
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19 pages, 11308 KiB  
Article
A High-Precision Quartz Resonant Ultra-High Pressure Sensor with Integrated Pressure Conversion Structure
by Quanwei Zhang, Cun Li, Huafeng Li, Yan Liu, Jue Wang, Xiaolong Wang, Yuan Wang, Fabin Cheng, Haijun Han and Peng Zhang
Micromachines 2023, 14(9), 1657; https://doi.org/10.3390/mi14091657 - 25 Aug 2023
Cited by 6 | Viewed by 2581
Abstract
A quartz resonant pressure sensor is proposed for high-precision measurement of ultra-high pressure. The resonant unit realizes a push–pull differential layout, which restrains the common-mode interference factor, and the resonator is only subject to axial force. The pressure conversion unit is made in [...] Read more.
A quartz resonant pressure sensor is proposed for high-precision measurement of ultra-high pressure. The resonant unit realizes a push–pull differential layout, which restrains the common-mode interference factor, and the resonator is only subject to axial force. The pressure conversion unit is made in an integrated manner, avoiding output drift problems caused by residual stress and small gaps during assembly, welding, and other processes in sensor preparation. Theoretical and simulation analysis was conducted on the overall design scheme of the sensor in this paper, verifying the feasibility. Sensor prototypes were created and performance experiments were conducted. The experimental results show that the sensitivity of the ultra-high pressure sensor is 46.32 Hz/MPa at room temperature within the pressure range of 120 MPa, and the comprehensive accuracy is 0.0266%. The comprehensive accuracy of the sensor is better than 0.0288% FS in the full temperature range environment. This proves that the sensor scheme is suitable for high-precision and high-stability detection of ultra-high pressure, providing new solutions in special pressure measurement fields such as deep-sea and oil exploration. Full article
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25 pages, 11049 KiB  
Review
Four-Dimensional Micro/Nanorobots via Laser Photochemical Synthesis towards the Molecular Scale
by Yufeng Tao, Liansheng Lin, Xudong Ren, Xuejiao Wang, Xia Cao, Heng Gu, Yunxia Ye, Yunpeng Ren and Zhiming Zhang
Micromachines 2023, 14(9), 1656; https://doi.org/10.3390/mi14091656 - 24 Aug 2023
Cited by 5 | Viewed by 2855
Abstract
Miniaturized four-dimensional (4D) micro/nanorobots denote a forerunning technique associated with interdisciplinary applications, such as in embeddable labs-on-chip, metamaterials, tissue engineering, cell manipulation, and tiny robotics. With emerging smart interactive materials, static micro/nanoscale architectures have upgraded to the fourth dimension, evincing time-dependent shape/property mutation. [...] Read more.
Miniaturized four-dimensional (4D) micro/nanorobots denote a forerunning technique associated with interdisciplinary applications, such as in embeddable labs-on-chip, metamaterials, tissue engineering, cell manipulation, and tiny robotics. With emerging smart interactive materials, static micro/nanoscale architectures have upgraded to the fourth dimension, evincing time-dependent shape/property mutation. Molecular-level 4D robotics promises complex sensing, self-adaption, transformation, and responsiveness to stimuli for highly valued functionalities. To precisely control 4D behaviors, current-laser-induced photochemical additive manufacturing, such as digital light projection, stereolithography, and two-photon polymerization, is pursuing high-freeform shape-reconfigurable capacities and high-resolution spatiotemporal programming strategies, which challenge multi-field sciences while offering new opportunities. Herein, this review summarizes the recent development of micro/nano 4D laser photochemical manufacturing, incorporating active materials and shape-programming strategies to provide an envisioning of these miniaturized 4D micro/nanorobots. A comparison with other chemical/physical fabricated micro/nanorobots further explains the advantages and potential usage of laser-synthesized micro/nanorobots. Full article
(This article belongs to the Special Issue Laser Additive Manufacturing: Design, Materials, Processes and Applications, 2nd Edition)
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35 pages, 3159 KiB  
Review
Flexible and Stretchable Pressure Sensors: From Basic Principles to State-of-the-Art Applications
by Thara Seesaard and Chatchawal Wongchoosuk
Micromachines 2023, 14(8), 1638; https://doi.org/10.3390/mi14081638 - 20 Aug 2023
Cited by 23 | Viewed by 11601
Abstract
Flexible and stretchable electronics have emerged as highly promising technologies for the next generation of electronic devices. These advancements offer numerous advantages, such as flexibility, biocompatibility, bio-integrated circuits, and light weight, enabling new possibilities in diverse applications, including e-textiles, smart lenses, healthcare technologies, [...] Read more.
Flexible and stretchable electronics have emerged as highly promising technologies for the next generation of electronic devices. These advancements offer numerous advantages, such as flexibility, biocompatibility, bio-integrated circuits, and light weight, enabling new possibilities in diverse applications, including e-textiles, smart lenses, healthcare technologies, smart manufacturing, consumer electronics, and smart wearable devices. In recent years, significant attention has been devoted to flexible and stretchable pressure sensors due to their potential integration with medical and healthcare devices for monitoring human activity and biological signals, such as heartbeat, respiratory rate, blood pressure, blood oxygen saturation, and muscle activity. This review comprehensively covers all aspects of recent developments in flexible and stretchable pressure sensors. It encompasses fundamental principles, force/pressure-sensitive materials, fabrication techniques for low-cost and high-performance pressure sensors, investigations of sensing mechanisms (piezoresistivity, capacitance, piezoelectricity), and state-of-the-art applications. Full article
(This article belongs to the Special Issue Feature Reviews in Micromachines 2023)
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15 pages, 2915 KiB  
Article
Simultaneous Hydrostatic and Compressive Loading System for Mimicking the Mechanical Environment of Living Cartilage Tissue
by Minki Chang, Yosuke Takahashi, Kyosuke Miyahira, Yuma Omuro, Kevin Montagne, Ryusei Yamada, Junki Gondo, Yu Kambe, Masashi Yasuno, Noriyasu Masumoto, Takashi Ushida and Katsuko S. Furukawa
Micromachines 2023, 14(8), 1632; https://doi.org/10.3390/mi14081632 - 18 Aug 2023
Viewed by 1636
Abstract
In vivo, articular cartilage tissue is surrounded by a cartilage membrane, and hydrostatic pressure (HP) and compressive strain increase simultaneously with the compressive stress. However, it has been impossible to investigate the effects of simultaneous loading in vitro. In this study, a bioreactor [...] Read more.
In vivo, articular cartilage tissue is surrounded by a cartilage membrane, and hydrostatic pressure (HP) and compressive strain increase simultaneously with the compressive stress. However, it has been impossible to investigate the effects of simultaneous loading in vitro. In this study, a bioreactor capable of applying compressive stress under HP was developed to reproduce ex vivo the same physical loading environment found in cartilage. First, a HP stimulation unit was constructed to apply a cyclic HP pressure-resistant chamber by controlling a pump and valve. A compression-loading mechanism that can apply compressive stress using an electromagnetic force was implemented in the chamber. The synchronization between the compression and HP units was evaluated, and the stimulation parameters were quantitatively evaluated. Physiological HP and compressive strain were applied to the chondrocytes encapsulated in alginate and gelatin gels after applying high HP at 25 MPa, which induced damage to the chondrocytes. It was found that compressive stimulation increased the expression of genes related to osteoarthritis. Furthermore, the simultaneous application of compressive strain and HP, which is similar to the physiological environment in cartilage, had an inhibitory effect on the expression of genes related to osteoarthritis. HP alone also suppressed the expression of osteoarthritis-related genes. Therefore, the simultaneous hydrostatic and compressive stress-loading device developed to simulate the mechanical environment in vivo may be an important tool for elucidating the mechanisms of disease onset and homeostasis in cartilage. Full article
(This article belongs to the Topic Materials, Structure Designs and Device Fabrications for Highly Efficient/Long Lifetime Organic Light-Emitting Diodes)
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18 pages, 15136 KiB  
Article
Biocompatible High-Resolution 3D-Printed Microfluidic Devices: Integrated Cell Chemotaxis Demonstration
by Mawla Boaks, Connor Roper, Matthew Viglione, Kent Hooper, Adam T. Woolley, Kenneth A. Christensen and Gregory P. Nordin
Micromachines 2023, 14(8), 1589; https://doi.org/10.3390/mi14081589 - 12 Aug 2023
Cited by 13 | Viewed by 2967
Abstract
We demonstrate a method to effectively 3D print microfluidic devices with high-resolution features using a biocompatible resin based on avobenzone as the UV absorber. Our method relies on spectrally shaping the 3D printer source spectrum so that it is fully overlapped by avobenzone’s [...] Read more.
We demonstrate a method to effectively 3D print microfluidic devices with high-resolution features using a biocompatible resin based on avobenzone as the UV absorber. Our method relies on spectrally shaping the 3D printer source spectrum so that it is fully overlapped by avobenzone’s absorption spectrum. Complete overlap is essential to effectively limit the optical penetration depth, which is required to achieve high out-of-plane resolution. We demonstrate the high resolution in practice by 3D printing 15 μm square pillars in a microfluidic chamber, where the pillars are separated by 7.7 μm and are printed with 5 μm layers. Furthermore, we show reliable membrane valves and pumps using the biocompatible resin. Valves are tested to 1,000,000 actuations with no observable degradation in performance. Finally, we create a concentration gradient generation (CG) component and utilize it in two device designs for cell chemotaxis studies. The first design relies on an external dual syringe pump to generate source and sink flows to supply the CG channel, while the second is a complete integrated device incorporating on-chip pumps, valves, and reservoirs. Both device types are seeded with adherent cells that are subjected to a chemoattractant CG, and both show clear evidence of chemotactic cellular migration. Moreover, the integrated device demonstrates cellular migration comparable to the external syringe pump device. This demonstration illustrates the effectiveness of our integrated chemotactic assay approach and high-resolution biocompatible resin 3D printing fabrication process. In addition, our 3D printing process has been tuned for rapid fabrication, as printing times for the two device designs are, respectively, 8 and 15 min. Full article
(This article belongs to the Special Issue 3D Printing of MEMS Technology, 3rd Edition)
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42 pages, 10600 KiB  
Review
A Comprehensive Review of Surface Acoustic Wave-Enabled Acoustic Droplet Ejection Technology and Its Applications
by Jia Ning, Yulin Lei, Hong Hu and Chenhui Gai
Micromachines 2023, 14(8), 1543; https://doi.org/10.3390/mi14081543 - 31 Jul 2023
Cited by 11 | Viewed by 4468
Abstract
This review focuses on the development of surface acoustic wave-enabled acoustic drop ejection (SAW-ADE) technology, which utilizes surface acoustic waves to eject droplets from liquids without touching the sample. The technology offers advantages such as high throughput, high precision, non-contact, and integration with [...] Read more.
This review focuses on the development of surface acoustic wave-enabled acoustic drop ejection (SAW-ADE) technology, which utilizes surface acoustic waves to eject droplets from liquids without touching the sample. The technology offers advantages such as high throughput, high precision, non-contact, and integration with automated systems while saving samples and reagents. The article first provides an overview of the SAW-ADE technology, including its basic theory, simulation verification, and comparison with other types of acoustic drop ejection technology. The influencing factors of SAW-ADE technology are classified into four categories: fluid properties, device configuration, presence of channels or chambers, and driving signals. The influencing factors discussed in detail from various aspects, such as the volume, viscosity, and surface tension of the liquid; the type of substrate material, interdigital transducers, and the driving waveform; sessile droplets and fluid in channels/chambers; and the power, frequency, and modulation of the input signal. The ejection performance of droplets is influenced by various factors, and their optimization can be achieved by taking into account all of the above factors and designing appropriate configurations. Additionally, the article briefly introduces the application scenarios of SAW-ADE technology in bioprinters and chemical analyses and provides prospects for future development. The article contributes to the field of microfluidics and lab-on-a-chip technology and may help researchers to design and optimize SAW-ADE systems for specific applications. Full article
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10 pages, 2367 KiB  
Article
Double-Glued Multi-Focal Bionic Compound Eye Camera
by Xin Feng, Xiao Lv, Junyu Dong, Yongshun Liu, Fengfeng Shu and Yihui Wu
Micromachines 2023, 14(8), 1548; https://doi.org/10.3390/mi14081548 - 31 Jul 2023
Cited by 2 | Viewed by 1722
Abstract
Compound eye cameras are a vital component of bionics. Compound eye lenses are currently used in light field cameras, monitoring imaging, medical endoscopes, and other fields. However, the resolution of the compound eye lens is still low at the moment, which has an [...] Read more.
Compound eye cameras are a vital component of bionics. Compound eye lenses are currently used in light field cameras, monitoring imaging, medical endoscopes, and other fields. However, the resolution of the compound eye lens is still low at the moment, which has an impact on the application scene. Photolithography and negative pressure molding were used to create a double-glued multi-focal bionic compound eye camera in this study. The compound eye camera has 83 microlenses, with ommatidium diameters ranging from 400 μm to 660 μm, and a 92.3 degree field-of-view angle. The double-gluing structure significantly improves the optical performance of the compound eye lens, and the spatial resolution of the ommatidium is 57.00 lp mm−1. Additionally, the measurement of speed is investigated. This double-glue compound eye camera has numerous potential applications in the military, machine vision, and other fields. Full article
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