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.

Order results
Result details
Results per page
Select all
Export citation of selected articles as:
14 pages, 6585 KiB  
Article
Enhancing Manufacturability of SU-8 Piezoelectric Composite Films for Microsystem Applications
by Irma Rocio Vazquez, Zeynel Guler and Nathan Jackson
Micromachines 2024, 15(3), 397; https://doi.org/10.3390/mi15030397 - 14 Mar 2024
Viewed by 771
Abstract
Piezoelectric thin films are extensively used as sensing or actuating layers in various micro-electromechanical systems (MEMS) applications. However, most piezoelectrics are stiff ceramics, and current polymer piezoelectrics are not compatible with microfabrication due to their low Curie Temperature. Recent polymer-composite piezoelectrics have gained [...] Read more.
Piezoelectric thin films are extensively used as sensing or actuating layers in various micro-electromechanical systems (MEMS) applications. However, most piezoelectrics are stiff ceramics, and current polymer piezoelectrics are not compatible with microfabrication due to their low Curie Temperature. Recent polymer-composite piezoelectrics have gained interest but can be difficult to pattern. Photodefinable piezoelectric films could resolve these challenges by reducing the manufacturability steps by eliminating the etching process. But they typically have poor resolution and thickness properties. This study explores methods of enhancing the manufacturability of piezoelectric composite films by optimizing the process parameters and synthesis of SU-8 piezo-composite materials. Piezoelectric ceramic powders (barium titanate (BTO) and lead zirconate titanate (PZT)) were integrated into SU-8, a negative epoxy-based photoresist, to produce high-resolution composites in a non-cleanroom environment. I-line (365 nm) light was used to enhance resolution compared to broadband lithography. Two variations of SU-8 were prepared by thinning down SU-8 3050 and SU-8 3005. Different weight percentages of the piezoelectric powders were investigated: 5, 10, 15 and 20 wt.% along with varied photolithography processing parameters. The composites’ transmittance properties were characterized using UV-Vis spectroscopy and the films’ crystallinity was determined using X-ray diffraction (XRD). The 0–3 SU-8/piezo composites demonstrated resolutions < 2 μm while maintaining bulk piezoelectric coefficients d33 > 5 pm V−1. The films were developed with thicknesses >10 μm. Stacked layers were achieved and demonstrated significantly higher d33 properties. Full article
(This article belongs to the Special Issue Smart Functional Micro/Nano Structured Surfaces)
Show Figures

Figure 1

18 pages, 5866 KiB  
Review
Recent Progress in Droplet Structure Machining for Advanced Optics
by Jin-Kun Guo, W.D.N. Sandaruwan, Jinwei Li, Jinzhong Ling, Ying Yuan, Xin Liu, Qiang Li and Xiaorui Wang
Micromachines 2024, 15(3), 337; https://doi.org/10.3390/mi15030337 - 28 Feb 2024
Viewed by 780
Abstract
The development of optical and photonic applications using soft-matter droplets holds great scientific and application importance. The machining of droplet structures is expected to drive breakthroughs in advancing frontier applications. This review highlights recent advancements in micro–nanofabrication techniques for soft-matter droplets, encompassing microfluidics, [...] Read more.
The development of optical and photonic applications using soft-matter droplets holds great scientific and application importance. The machining of droplet structures is expected to drive breakthroughs in advancing frontier applications. This review highlights recent advancements in micro–nanofabrication techniques for soft-matter droplets, encompassing microfluidics, laser injection, and microfluidic 3D printing. The principles, advantages, and weaknesses of these technologies are thoroughly discussed. The review introduces the utilization of a phase separation strategy in microfluidics to assemble complex emulsion droplets and control droplet geometries by adjusting interfacial tension. Additionally, laser injection can take full advantage of the self-assembly properties of soft matter to control the spontaneous organization of internal substructures within droplets, thus providing the possibility of high-precision customized assembly of droplets. Microfluidic 3D printing demonstrates a 3D printing-based method for machining droplet structures. Its programmable nature holds promise for developing device-level applications utilizing droplet arrays. Finally, the review presents novel applications of soft-matter droplets in optics and photonics. The integration of processing concepts from microfluidics, laser micro–nano-machining, and 3D printing into droplet processing, combined with the self-assembly properties of soft materials, may offer novel opportunities for processing and application development. Full article
(This article belongs to the Special Issue Research Progress of Ultra-Precision Micro-nano Machining)
Show Figures

Figure 1

17 pages, 9913 KiB  
Article
Hollow Microcavity Electrode for Enhancing Light Extraction
by Seonghyeon Park, Byeongwoo Kang, Seungwon Lee, Jian Cheng Bi, Jaewon Park, Young Hyun Hwang, Jun-Young Park, Ha Hwang, Young Wook Park and Byeong-Kwon Ju
Micromachines 2024, 15(3), 328; https://doi.org/10.3390/mi15030328 - 27 Feb 2024
Viewed by 1037
Abstract
Luminous efficiency is a pivotal factor for assessing the performance of optoelectronic devices, wherein light loss caused by diverse factors is harvested and converted into the radiative mode. In this study, we demonstrate a nanoscale vacuum photonic crystal layer (nVPCL) for light extraction [...] Read more.
Luminous efficiency is a pivotal factor for assessing the performance of optoelectronic devices, wherein light loss caused by diverse factors is harvested and converted into the radiative mode. In this study, we demonstrate a nanoscale vacuum photonic crystal layer (nVPCL) for light extraction enhancement. A corrugated semi-transparent electrode incorporating a periodic hollow-structure array was designed through a simulation that utilizes finite-difference time-domain computational analysis. The corrugated profile, stemming from the periodic hollow structure, was fabricated using laser interference lithography, which allows the precise engineering of various geometrical parameters by controlling the process conditions. The semi-transparent electrode consisted of a 15 nm thick Ag film, which acted as the exit mirror and induced microcavity resonance. When applied to a conventional green organic light-emitting diode (OLED) structure, the optimized nVPCL-integrated device demonstrated a 21.5% enhancement in external quantum efficiency compared to the reference device. Further, the full width at half maximum exhibited a 27.5% reduction compared to that of the reference device, demonstrating improved color purity. This study presents a novel approach by applying a hybrid thin film electrode design to optoelectronic devices to enhance optical efficiency and color purity. Full article
Show Figures

Figure 1

15 pages, 4207 KiB  
Review
Beam Steering Technology of Optical Phased Array Based on Silicon Photonic Integrated Chip
by Jinyu Wang, Ruogu Song, Xinyu Li, Wencheng Yue, Yan Cai, Shuxiao Wang and Mingbin Yu
Micromachines 2024, 15(3), 322; https://doi.org/10.3390/mi15030322 - 26 Feb 2024
Viewed by 1031
Abstract
Light detection and ranging (LiDAR) is widely used in scenarios such as autonomous driving, imaging, remote sensing surveying, and space communication due to its advantages of high ranging accuracy and large scanning angle. Optical phased array (OPA) has been studied as an important [...] Read more.
Light detection and ranging (LiDAR) is widely used in scenarios such as autonomous driving, imaging, remote sensing surveying, and space communication due to its advantages of high ranging accuracy and large scanning angle. Optical phased array (OPA) has been studied as an important solution for achieving all-solid-state scanning. In this work, the recent research progress in improving the beam steering performance of the OPA based on silicon photonic integrated chips was reviewed. An optimization scheme for aperiodic OPA is proposed. Full article
(This article belongs to the Special Issue Silicon Photonic Devices and Integration)
Show Figures

Figure 1

19 pages, 7888 KiB  
Review
Research on the Reliability of Threshold Voltage Based on GaN High-Electron-Mobility Transistors
by Pengfei Dai, Shaowei Wang and Hongliang Lu
Micromachines 2024, 15(3), 321; https://doi.org/10.3390/mi15030321 - 25 Feb 2024
Viewed by 878
Abstract
With the development of high-voltage and high-frequency switching circuits, GaN high-electron-mobility transistor (HEMT) devices with high bandwidth, high electron mobility, and high breakdown voltage have become an important research topic in this field. It has been found that GaN HEMT devices have a [...] Read more.
With the development of high-voltage and high-frequency switching circuits, GaN high-electron-mobility transistor (HEMT) devices with high bandwidth, high electron mobility, and high breakdown voltage have become an important research topic in this field. It has been found that GaN HEMT devices have a drift in threshold voltage under the conditions of temperature and gate stress changes. Under high-temperature conditions, the difference in gate contact also causes the threshold voltage to shift. The variation in the threshold voltage affects the stability of the device as well as the overall circuit performance. Therefore, in this paper, a review of previous work is presented. Temperature variation, gate stress variation, and gate contact variation are investigated to analyze the physical mechanisms that generate the threshold voltage (VTH) drift phenomenon in GaN HEMT devices. Finally, improvement methods suitable for GaN HEMT devices under high-temperature and high-voltage conditions are summarized. Full article
Show Figures

Figure 1

15 pages, 8238 KiB  
Article
An Efficient 3D-Printed Gravity Mixer for Lab-on-a-CD Applications
by Yunxia Wang, Yong Zhang, Zheng Qiao and Wanjun Wang
Micromachines 2024, 15(3), 291; https://doi.org/10.3390/mi15030291 - 20 Feb 2024
Viewed by 715
Abstract
We introduced a new, highly efficient, and uncomplicated mixing device for centrifugal microfluidic platforms, called the gravity mixer. The gravity mixer featured a slope channel that can precisely and sequentially control micro-volume liquids using centrifugal, capillary, and gravitational forces to achieve the desired [...] Read more.
We introduced a new, highly efficient, and uncomplicated mixing device for centrifugal microfluidic platforms, called the gravity mixer. The gravity mixer featured a slope channel that can precisely and sequentially control micro-volume liquids using centrifugal, capillary, and gravitational forces to achieve the desired mixing effect. By adjusting the angular velocity, micro-volumes of liquids in the slope channel of the gravity mixer could be precisely controlled across a wide range. We evaluated the change in mixing efficiency by varying the slope geometry, including the slope angle and the number of mixing cycles. Our study of gravity mixers with different slope angles revealed that the 80° angle gravity mixer achieved the best mixing efficiency, with a standard deviation of 2.39. Additionally, the mixing process in the gravity mixer is highly repeatable, achieving the desired mixing efficiency after only three cycles of operation. Our gravity mixer design and implementation can facilitate the development of more complex 3D-printed lab-on-chip devices. Full article
Show Figures

Figure 1

17 pages, 3795 KiB  
Article
Consideration of Power Transmission Characteristics in a Micro-Gear Train
by Yasuhiko Arai
Micromachines 2024, 15(2), 284; https://doi.org/10.3390/mi15020284 - 17 Feb 2024
Viewed by 708
Abstract
Characteristics related to power transmission in the micro-domain, based on dry rolling contact of the gears, were investigated using a 3D-printed gear train with a pitch circle diameter of 84 µm in order to experimentally compare the power transmission efficiency in the macro- [...] Read more.
Characteristics related to power transmission in the micro-domain, based on dry rolling contact of the gears, were investigated using a 3D-printed gear train with a pitch circle diameter of 84 µm in order to experimentally compare the power transmission efficiency in the macro- and micro-domains. For a basic gear train with two intermeshing gears, it was shown that the gear train in the micro-domain was capable of transmitting power to the same extent as in the macro-domain. However, in gear trains with complex power transmission paths, assuming a planetary gear train with multiple meshing gears, it has been shown that the power transmission characteristics of micro-domain gears differ from those in the macro-domain. The use of gear trains in the micro-region necessitates consideration of the loss of transmitted torque due to contact between tooth surfaces, which is unique to the micro-region and different from its use in the macro-region. Full article
(This article belongs to the Section E:Engineering and Technology)
Show Figures

Figure 1

15 pages, 2385 KiB  
Article
In Vivo Characterization of Intracortical Probes with Focused Ion Beam-Etched Nanopatterned Topographies
by Jonathan L. Duncan, Jaime J. Wang, Gabriele Glusauskas, Gwendolyn R. Weagraff, Yue Gao, George F. Hoeferlin, Allen H. Hunter, Allison Hess-Dunning, Evon S. Ereifej and Jeffrey R. Capadona
Micromachines 2024, 15(2), 286; https://doi.org/10.3390/mi15020286 - 17 Feb 2024
Viewed by 741
Abstract
(1) Background: Intracortical microelectrodes (IMEs) are an important part of interfacing with the central nervous system (CNS) and recording neural signals. However, recording electrodes have shown a characteristic steady decline in recording performance owing to chronic neuroinflammation. The topography of implanted devices has [...] Read more.
(1) Background: Intracortical microelectrodes (IMEs) are an important part of interfacing with the central nervous system (CNS) and recording neural signals. However, recording electrodes have shown a characteristic steady decline in recording performance owing to chronic neuroinflammation. The topography of implanted devices has been explored to mimic the nanoscale three-dimensional architecture of the extracellular matrix. Our previous work used histology to study the implant sites of non-recording probes and showed that a nanoscale topography at the probe surface mitigated the neuroinflammatory response compared to probes with smooth surfaces. Here, we hypothesized that the improvement in the neuroinflammatory response for probes with nanoscale surface topography would extend to improved recording performance. (2) Methods: A novel design modification was implemented on planar silicon-based neural probes by etching nanopatterned grooves (with a 500 nm pitch) into the probe shank. To assess the hypothesis, two groups of rats were implanted with either nanopatterned (n = 6) or smooth control (n = 6) probes, and their recording performance was evaluated over 4 weeks. Postmortem gene expression analysis was performed to compare the neuroinflammatory response from the two groups. (3) Results: Nanopatterned probes demonstrated an increased impedance and noise floor compared to controls. However, the recording performances of the nanopatterned and smooth probes were similar, with active electrode yields for control probes and nanopatterned probes being approximately 50% and 45%, respectively, by 4 weeks post-implantation. Gene expression analysis showed one gene, Sirt1, differentially expressed out of 152 in the panel. (4) Conclusions: this study provides a foundation for investigating novel nanoscale topographies on neural probes. Full article
(This article belongs to the Special Issue Bioinspired Materials and Microdevices: Fabrications and Applications)
Show Figures

Figure 1

18 pages, 8465 KiB  
Article
Geometry-Dependent Elastic Flow Dynamics in Micropillar Arrays
by Oskar E. Ström, Jason P. Beech and Jonas O. Tegenfeldt
Micromachines 2024, 15(2), 268; https://doi.org/10.3390/mi15020268 - 13 Feb 2024
Viewed by 651
Abstract
Regular device-scale DNA waves for high DNA concentrations and flow velocities have been shown to emerge in quadratic micropillar arrays with potentially strong relevance for a wide range of microfluidic applications. Hexagonal arrays constitute another geometry that is especially relevant for the microfluidic [...] Read more.
Regular device-scale DNA waves for high DNA concentrations and flow velocities have been shown to emerge in quadratic micropillar arrays with potentially strong relevance for a wide range of microfluidic applications. Hexagonal arrays constitute another geometry that is especially relevant for the microfluidic pulsed-field separation of DNA. Here, we report on the differences at the micro and macroscopic scales between the resulting wave patterns for these two regular array geometries and one disordered array geometry. In contrast to the large-scale regular waves visible in the quadratic array, in the hexagonal arrays, waves occur in a device-scale disordered zig-zag pattern with fluctuations on a much smaller scale. We connect the large-scale pattern to the microscopic flow and observe flow synchronization that switches between two directions for both the quadratic and hexagonal arrays. We show the importance of order using the disordered array, where steady-state stationary and highly fluctuating flow states persist in seemingly random locations across the array. We compare the flow dynamics of the arrays to that in a device with sparsely distributed pillars. Here, we observe similar vortex shedding, which is clearly observable in the quadratic and disordered arrays. However, the shedding of these vortices couples only in the flow direction and not laterally as in the dense, ordered arrays. We believe that our findings will contribute to the understanding of elastic flow dynamics in pillar arrays, helping us elucidate the fundamental principles of non-Newtonian fluid flow in complex environments as well as supporting applications in engineering involving e.g., transport, sorting, and mixing of complex fluids. Full article
Show Figures

Figure 1

24 pages, 6875 KiB  
Article
Pysanky to Microfluidics: An Innovative Wax-Based Approach to Low Cost, Rapid Prototyping of Microfluidic Devices
by Philip J. Schneider, Liam B. Christie, Nicholas M. Eadie, Tyler J. Siskar, Viktor Sukhotskiy, Domin Koh, Anyang Wang and Kwang W. Oh
Micromachines 2024, 15(2), 240; https://doi.org/10.3390/mi15020240 - 05 Feb 2024
Viewed by 1035
Abstract
A wax-based contact printing method to create microfluidic devices is demonstrated. This printing technology demonstrates a new pathway to rapid, cost-effective device prototyping, eliminating the use of expensive micromachining equipment and chemicals. Derived from the traditional Ukrainian Easter egg painting technique called “pysanky” [...] Read more.
A wax-based contact printing method to create microfluidic devices is demonstrated. This printing technology demonstrates a new pathway to rapid, cost-effective device prototyping, eliminating the use of expensive micromachining equipment and chemicals. Derived from the traditional Ukrainian Easter egg painting technique called “pysanky” a series of microfluidic devices were created. Pysanky is the use of a heated wax stylus, known as a “kistka”, to create micro-sized, intricate designs on the surface of an egg. The proposed technique involves the modification of an x-y-z actuation translation system with a wax extruder tip in junction with Polydimethysiloxane (PDMS) device fabrication techniques. Initial system optimization was performed considering design parameters such as extruder tip size, contact angle, write speed, substrate temperature, and wax temperature. Channels created ranged from 160 to 900 μm wide and 10 to 150 μm high based upon system operating parameters set by the user. To prove the capabilities of this technology, a series of microfluidic mixers were created via the wax technique as well as through traditional photolithography: a spiral mixer, a rainbow mixer, and a linear serial dilutor. A thermo-fluidic computational fluid dynamic (CFD) model was generated as a means of enabling rational tuning, critical to the optimization of systems in both normal and extreme conditions. A comparison between the computational and experimental models yielded a wax height of 57.98 μm and 57.30 μm, respectively, and cross-sectional areas of 11,568 μm2 and 12,951 μm2, respectively, resulting in an error of 1.18% between the heights and 10.76% between the cross-sectional areas. The device’s performance was then compared using both qualitative and quantitative measures, considering factors such as device performance, channel uniformity, repeatability, and resolution. Full article
Show Figures

Figure 1

15 pages, 2736 KiB  
Article
A High-Voltage-Isolated MEMS Quad–Solenoid Transformer with Specific Insulation Barriers for Miniaturized Galvanically Isolated Power Applications
by Changnan Chen, Pichao Pan, Jiebin Gu and Xinxin Li
Micromachines 2024, 15(2), 228; https://doi.org/10.3390/mi15020228 - 31 Jan 2024
Viewed by 740
Abstract
The paper reports on high voltage (HV)-isolated MEMS quad–solenoid transformers for compact isolated gate drivers and bias power supplies. The component is wafer-level fabricated via a novel MEMS micro-casting technique, where the tightly coupled quad–solenoid chip consists of monolithically integrated 3D inductive coils [...] Read more.
The paper reports on high voltage (HV)-isolated MEMS quad–solenoid transformers for compact isolated gate drivers and bias power supplies. The component is wafer-level fabricated via a novel MEMS micro-casting technique, where the tightly coupled quad–solenoid chip consists of monolithically integrated 3D inductive coils and an inserted ferrite magnetic core for high-efficiency isolated power transmission through electromagnetic coupling. The proposed HV-isolated transformer demonstrates a high inductance value of 743.2 nH, along with a small DC resistance of only 0.39 Ω in a compact footprint of 6 mm2, making it achieve a very high inductance integration density (123.9 nH/mm2) and the ratio of L/R (1906 nH/Ω). More importantly, with embedded ultra-thick serpentine-shaped (S-shaped) SiO2 isolation barriers that completely separate the primary and secondary windings, an over 2 kV breakdown voltage is obtained. In addition, the HV-isolated transformer chips exhibit a superior power transfer efficiency of over 80% and ultra-high dual-phase saturation current of 1.4 A, thereby covering most practical cases in isolated, integrated bias power supplies such as high-efficiency high-voltage-isolated gate driver solutions. Full article
(This article belongs to the Section E:Engineering and Technology)
Show Figures

Figure 1

11 pages, 3877 KiB  
Communication
Microfabricated Nitinol Stent Retrievers with a Micro-Patterned Surface
by Shogo Kato, Yuzuki Ban, Takashi Ota and Norihisa Miki
Micromachines 2024, 15(2), 213; https://doi.org/10.3390/mi15020213 - 31 Jan 2024
Viewed by 757
Abstract
Stent retrievers are medical devices that are designed to physically remove blood clots from within the blood vessels of the brain. This paper focuses on microfabricated nitinol (nickel–titanium alloy) stent retrievers, which feature micro-patterns on their surface to enhance the effectiveness of mechanical [...] Read more.
Stent retrievers are medical devices that are designed to physically remove blood clots from within the blood vessels of the brain. This paper focuses on microfabricated nitinol (nickel–titanium alloy) stent retrievers, which feature micro-patterns on their surface to enhance the effectiveness of mechanical thrombectomy. A thick film of nitinol, which was 20 µm in thickness, was sputtered onto a substrate with a micro-patterned surface, using electroplated copper as the sacrificial layer. The nitinol film was released from the substrate and then thermally treated while folded into a cylindrical shape. In vitro experiments with pig blood clots demonstrated that the micro-patterns on the surface improved the efficacy of blood clot retrieval. Full article
Show Figures

Figure 1

20 pages, 5211 KiB  
Article
Wind Tunnel Characterization of a Graphene-Enhanced PEDOT:PSS Sensing Element for Aircraft Ice Detection Systems
by Dario Farina, Marco Mazio, Hatim Machrafi, Patrick Queeckers and Carlo Saverio Iorio
Micromachines 2024, 15(2), 198; https://doi.org/10.3390/mi15020198 - 28 Jan 2024
Cited by 1 | Viewed by 1661
Abstract
This study details the development and validation of a graphene-based ice detection system, designed to enhance flight safety by monitoring ice accumulation on aircraft surfaces. The system employs a semiconductive polymer (PEDOT:PSS) with graphene electrodes, interpreting resistance changes to detect water impact and [...] Read more.
This study details the development and validation of a graphene-based ice detection system, designed to enhance flight safety by monitoring ice accumulation on aircraft surfaces. The system employs a semiconductive polymer (PEDOT:PSS) with graphene electrodes, interpreting resistance changes to detect water impact and ice formation in real time. The sensor’s performance was rigorously tested in a wind tunnel under various temperature and airflow conditions, focusing on resistance signal dependency on air temperature and phase change. The results demonstrate the sensor’s ability to distinguish water droplet impacts from ice formation, with a notable correlation between resistance signal amplitude and water droplet impacts leading to ice accretion. Further analysis shows a significant relationship between air temperature and the resistance signal amplitude, particularly at lower temperatures beneficial to ice formation. This underlines the sensor’s precision in varied atmospheric conditions. The system’s compact design and accurate detection highlight its potential for improving aircraft ice monitoring, offering a path toward a robust and reliable ice detection system. Full article
(This article belongs to the Special Issue Functional Polymers for Optic/Electronic Applications)
Show Figures

Figure 1

22 pages, 44037 KiB  
Review
Acoustic Actuators for the Manipulation of Micro/Nanorobots: State-of-the-Art and Future Outlooks
by Hiep Xuan Cao, Van Du Nguyen, Jong-Oh Park, Eunpyo Choi and Byungjeon Kang
Micromachines 2024, 15(2), 186; https://doi.org/10.3390/mi15020186 - 26 Jan 2024
Viewed by 1013
Abstract
Compared to other actuating methods, acoustic actuators offer the distinctive capability of the contactless manipulation of small objects, such as microscale and nanoscale robots. Furthermore, they have the ability to penetrate the skin, allowing for the trapping and manipulation of micro/nanorobots that carry [...] Read more.
Compared to other actuating methods, acoustic actuators offer the distinctive capability of the contactless manipulation of small objects, such as microscale and nanoscale robots. Furthermore, they have the ability to penetrate the skin, allowing for the trapping and manipulation of micro/nanorobots that carry therapeutic agents in diverse media. In this review, we summarize the current progress in using acoustic actuators for the manipulation of micro/nanorobots used in various biomedical applications. First, we introduce the actuating method of using acoustic waves to manipulate objects, including the principle of operation and different types of acoustic actuators that are usually employed. Then, applications involving manipulating different types of devices are reviewed, including bubble-based microrobots, bubble-free robots, biohybrid microrobots, and nanorobots. Finally, we discuss the challenges and future perspectives for the development of the field. Full article
(This article belongs to the Special Issue Acoustical Tweezers: From Fundamental Research to Applications)
Show Figures

Figure 1

19 pages, 3771 KiB  
Review
Nanomaterials Based Micro/Nanoelectromechanical System (MEMS and NEMS) Devices
by Ziba Torkashvand, Farzaneh Shayeganfar and Ali Ramazani
Micromachines 2024, 15(2), 175; https://doi.org/10.3390/mi15020175 - 24 Jan 2024
Viewed by 1214
Abstract
The micro- and nanoelectromechanical system (MEMS and NEMS) devices based on two-dimensional (2D) materials reveal novel functionalities and higher sensitivity compared to their silicon-base counterparts. Unique properties of 2D materials boost the demand for 2D material-based nanoelectromechanical devices and sensing. During the last [...] Read more.
The micro- and nanoelectromechanical system (MEMS and NEMS) devices based on two-dimensional (2D) materials reveal novel functionalities and higher sensitivity compared to their silicon-base counterparts. Unique properties of 2D materials boost the demand for 2D material-based nanoelectromechanical devices and sensing. During the last decades, using suspended 2D membranes integrated with MEMS and NEMS emerged high-performance sensitivities in mass and gas sensors, accelerometers, pressure sensors, and microphones. Actively sensing minute changes in the surrounding environment is provided by means of MEMS/NEMS sensors, such as sensing in passive modes of small changes in momentum, temperature, and strain. In this review, we discuss the materials preparation methods, electronic, optical, and mechanical properties of 2D materials used in NEMS and MEMS devices, fabrication routes besides device operation principles. Full article
Show Figures

Figure 1

19 pages, 4477 KiB  
Article
Laser-Induced Intracellular Delivery: Exploiting Gold-Coated Spiky Polymeric Nanoparticles and Gold Nanorods under Near-Infrared Pulses for Single-Cell Nano-Photon-Poration
by Ashish Kumar, Bishal Kumar Nahak, Pallavi Gupta, Tuhin Subhra Santra and Fan-Gang Tseng
Micromachines 2024, 15(2), 168; https://doi.org/10.3390/mi15020168 - 23 Jan 2024
Cited by 1 | Viewed by 1028
Abstract
This study explores the potential of laser-induced nano-photon-poration as a non-invasive technique for the intracellular delivery of micro/macromolecules at the single-cell level. This research proposes the utilization of gold-coated spiky polymeric nanoparticles (Au-PNPs) and gold nanorods (GNRs) to achieve efficient intracellular micro/macromolecule delivery [...] Read more.
This study explores the potential of laser-induced nano-photon-poration as a non-invasive technique for the intracellular delivery of micro/macromolecules at the single-cell level. This research proposes the utilization of gold-coated spiky polymeric nanoparticles (Au-PNPs) and gold nanorods (GNRs) to achieve efficient intracellular micro/macromolecule delivery at the single-cell level. By shifting the operating wavelength towards the near-infrared (NIR) range, the intracellular delivery efficiency and viability of Au-PNP-mediated photon-poration are compared to those using GNR-mediated intracellular delivery. Employing Au-PNPs as mediators in conjunction with nanosecond-pulsed lasers, a highly efficient intracellular delivery, while preserving high cell viability, is demonstrated. Laser pulses directed at Au-PNPs generate over a hundred hot spots per particle through plasmon resonance, facilitating the formation of photothermal vapor nanobubbles (PVNBs). These PVNBs create transient pores, enabling the gentle transfer of cargo from the extracellular to the intracellular milieu, without inducing deleterious effects in the cells. The optimization of wavelengths in the NIR region, coupled with low laser fluence (27 mJ/cm2) and nanoparticle concentrations (34 µg/mL), achieves outstanding delivery efficiencies (96%) and maintains high cell viability (up to 99%) across the various cell types, including cancer and neuronal cells. Importantly, sustained high cell viability (90–95%) is observed even 48 h post laser exposure. This innovative development holds considerable promise for diverse applications, encompassing drug delivery, gene therapy, and regenerative medicine. This study underscores the efficiency and versatility of the proposed technique, positioning it as a valuable tool for advancing intracellular delivery strategies in biomedical applications. Full article
(This article belongs to the Special Issue Biosensors for Biomedical and Environmental Applications, Volume 2)
Show Figures

Figure 1

16 pages, 12989 KiB  
Article
Design of a Micro-Electro Mechanical System Quad Mass Gyroscope with Compliant Mechanical Amplification
by Jingchuan Zhou, Dacheng Xu, Xinxin Li and Fang Chen
Micromachines 2024, 15(1), 124; https://doi.org/10.3390/mi15010124 - 11 Jan 2024
Viewed by 954
Abstract
In this work, a novel mechanical amplification structure for a MEMS vibratory gyroscope is proposed with the aim of improving their sensitivity. The scheme is implemented using a system of micromachined V-shaped springs as a deflection amplifying mechanism. The effectiveness of the mechanism [...] Read more.
In this work, a novel mechanical amplification structure for a MEMS vibratory gyroscope is proposed with the aim of improving their sensitivity. The scheme is implemented using a system of micromachined V-shaped springs as a deflection amplifying mechanism. The effectiveness of the mechanism is first demonstrated for a capacitive fully decoupled quad mass gyroscope. A proof of concept vertical-axis mechanically amplified gyroscope with an amplification factor of 365% has been designed, simulated and fabricated, and results from its evaluation are presented in this paper. Experimental results show that the natural frequency of the gyroscope is 11.67 KHz, and the full scale measurement range is up to ±400°/s with a maximum nonlinearity of 54.69 ppm. The bias stability is 44.53°/h. The experiment results show that this quad mass gyroscope’s performance is a very potential new way of reaching the navigation grade in the future. Full article
(This article belongs to the Special Issue MEMS/NEMS Devices and Applications, 2nd Edition)
Show Figures

Figure 1

19 pages, 12908 KiB  
Article
A 3D-Printed Piezoelectric Microdevice for Human Energy Harvesting for Wearable Biosensors
by Ihor Sobianin, Sotiria D. Psoma and Antonios Tourlidakis
Micromachines 2024, 15(1), 118; https://doi.org/10.3390/mi15010118 - 10 Jan 2024
Viewed by 1168
Abstract
The human body is a source of multiple types of energy, such as mechanical, thermal and biochemical, which can be scavenged through appropriate technological means. Mechanical vibrations originating from contraction and expansion of the radial artery represent a reliable source of displacement to [...] Read more.
The human body is a source of multiple types of energy, such as mechanical, thermal and biochemical, which can be scavenged through appropriate technological means. Mechanical vibrations originating from contraction and expansion of the radial artery represent a reliable source of displacement to be picked up and exploited by a harvester. The continuous monitoring of physiological biomarkers is an essential part of the timely and accurate diagnosis of a disease with subsequent medical treatment, and wearable biosensors are increasingly utilized for biomedical data acquisition of important biomarkers. However, they rely on batteries and their replacement introduces a discontinuity in measured signals, which could be critical for the patients and also causes discomfort. In the present work, the research into a novel 3D-printed wearable energy harvesting platform for scavenging energy from arterial pulsations via a piezoelectric material is described. An elastic thermoplastic polyurethane (TPU) film, which forms an air chamber between the skin and the piezoelectric disc electrode, was introduced to provide better adsorption to the skin, prevent damage to the piezoelectric disc and electrically isolate components in the platform from the human body. Computational fluid dynamics in the framework of COMSOL Multiphysics 6.1 software was employed to perform a series of coupled time-varying simulations of the interaction among a number of associated physical phenomena. The mathematical model of the harvester was investigated computationally, and quantification of the output energy and power parameters was used for comparisons. A prototype wearable platform enclosure was designed and manufactured using fused filament fabrication (FFF). The influence of the piezoelectric disc material and its diameter on the electrical output were studied and various geometrical parameters of the enclosure and the TPU film were optimized based on theoretical and empirical data. Physiological data, such as interdependency between the harvester skin fit and voltage output, were obtained. Full article
Show Figures

Figure 1

30 pages, 17885 KiB  
Review
Review on Abrasive Machining Technology of SiC Ceramic Composites
by Huiyun Zhang, Zhigang Zhao, Jiaojiao Li, Linzheng Ye and Yao Liu
Micromachines 2024, 15(1), 106; https://doi.org/10.3390/mi15010106 - 07 Jan 2024
Viewed by 1272
Abstract
Ceramic matrix composites have the advantages of low density, high specific strength, high specific die, high-temperature resistance, wear resistance, chemical corrosion resistance, etc., which are widely used in aerospace, energy, transportation, and other fields. CMCs have become an important choice for engine components [...] Read more.
Ceramic matrix composites have the advantages of low density, high specific strength, high specific die, high-temperature resistance, wear resistance, chemical corrosion resistance, etc., which are widely used in aerospace, energy, transportation, and other fields. CMCs have become an important choice for engine components and other high-temperature component manufacturing. However, ceramic matrix composite is a kind of multi-phase structure, anisotropy, high hardness material, due to the brittleness of the ceramic matrix, the weak bonding force between fiber and matrix, and the anisotropy of composite material. Burr, delamination, tearing, chips, and other surface damage tend to generate in the machining, resulting in surface quality and strength decline. This paper reviewed the latest abrasive machining technology for SiC ceramic composites. The characteristics and research directions of the main abrasive machining technology, including grinding, laser-assisted grinding, ultrasonic-assisted grinding, and abrasive waterjet machining, are introduced first. Then, the commonly used numerical simulation research for modeling and simulating the machining of ceramic matrix composites is briefly summarized. Finally, the processing difficulties and research hotspots of ceramic matrix composites are summarized. Full article
(This article belongs to the Special Issue Recent Advances in Micro/Nano-Fabrication)
Show Figures

Figure 1

33 pages, 12133 KiB  
Review
A Review on Machining SiCp/Al Composite Materials
by Zhigao Chen, Fei Ding, Zhichao Zhang, Qiuyan Liao, Zheng Qiao, Yuan Jin, Mingjun Chen and Bo Wang
Micromachines 2024, 15(1), 107; https://doi.org/10.3390/mi15010107 - 07 Jan 2024
Cited by 1 | Viewed by 1830
Abstract
SiCp/Al composite materials are widely used in various industries such as the aerospace and the electronics industries, primarily due to their excellent material properties. However, their machinability is significantly weakened due to their unique characteristics. Consequently, efficient and precise machining technology for SiCp/Al [...] Read more.
SiCp/Al composite materials are widely used in various industries such as the aerospace and the electronics industries, primarily due to their excellent material properties. However, their machinability is significantly weakened due to their unique characteristics. Consequently, efficient and precise machining technology for SiCp/Al composite materials has become a crucial research area. By conducting a comprehensive analysis of the relevant research literature from both domestic and international sources, this study examines the processing mechanism, as well as the turning, milling, drilling, grinding, special machining, and hybrid machining characteristics, of SiCp/Al composite materials. Moreover, it summarizes the latest research progress in composite material processing while identifying the existing problems and shortcomings in this area. The aim of this review is to enhance the machinability of SiCp/Al composite materials and promote high-quality and efficient processing methods. Full article
(This article belongs to the Section D:Materials and Processing)
Show Figures

Figure 1

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
Viewed by 1544
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
Show Figures

Figure 1

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 991
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)
Show Figures

Figure 1

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
Viewed by 1174
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
Show Figures

Figure 1

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
Viewed by 754
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
Show Figures

Figure 1

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
Viewed by 1235
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)
Show Figures

Figure 1

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 1 | Viewed by 990
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)
Show Figures

Figure 1

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 801
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)
Show Figures

Figure 1

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 (registering DOI) - 18 Dec 2023
Viewed by 849
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)
Show Figures

Figure 1

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 934
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)
Show Figures

Figure 1

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
Viewed by 3285
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)
Show Figures

Figure 1

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 - 05 Dec 2023
Viewed by 819
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
Show Figures

Figure 1

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
Viewed by 1195
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)
Show Figures

Figure 1

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 1 | Viewed by 1157
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)
Show Figures

Figure 1

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
Viewed by 1063
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)
Show Figures

Figure 1

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
Viewed by 765
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)
Show Figures

Figure 1

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
Viewed by 1424
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
Show Figures

Figure 1

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
Viewed by 1562
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
Show Figures

Figure 1

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 1 | Viewed by 1225
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)
Show Figures

Figure 1

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 1 | Viewed by 980
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)
Show Figures

Figure 1

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
Viewed by 1274
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)
Show Figures