Micromachines

15 pages, 5024 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Detecting Redox Potentials Using Porous Boron Nitride/ATP-DNA Aptamer/Methylene Blue Biosensor to Monitor Microbial Activities

by Kai Guo, Zirui Song, Gaoxing Wang and Chengchun Tang

Micromachines 2022, 13(1), 83; https://doi.org/10.3390/mi13010083 - 4 Jan 2022

Cited by 6 | Viewed by 2518

Abstract

Microbial activity has gained attention because of its impact on the environment and the quality of people’s lives. Most of today’s methods, which include genome sequencing and electrochemistry, are costly and difficult to manage. Our group proposed a method using the redox potential [...] Read more.

Microbial activity has gained attention because of its impact on the environment and the quality of people’s lives. Most of today’s methods, which include genome sequencing and electrochemistry, are costly and difficult to manage. Our group proposed a method using the redox potential change to detect microbial activity, which is rooted in the concept that metabolic activity can change the redox potential of a microbial community. The redox potential change was captured by a biosensor consisting of porous boron nitride, ATP-DNA aptamer, and methylene blue as the fluorophore. This assembly can switch on or off when there is a redox potential change, and this change leads to a fluorescence change that can be examined using a multipurpose microplate reader. The results show that this biosensor can detect microbial community changes when its composition is changed or toxic metals are ingested. Full article

(This article belongs to the Section B1: Biosensors)

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21 pages, 4984 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Overview of 3D-Printed Silica Glass

by Han Zhang, Long Huang, Mingyue Tan, Shaoqing Zhao, Hua Liu, Zifeng Lu, Jinhuan Li and Zhongzhu Liang

Micromachines 2022, 13(1), 81; https://doi.org/10.3390/mi13010081 - 3 Jan 2022

Cited by 38 | Viewed by 9552

Abstract

Not satisfied with the current stage of the extensive research on 3D printing technology for polymers and metals, researchers are searching for more innovative 3D printing technologies for glass fabrication in what has become the latest trend of interest. The traditional glass manufacturing [...] Read more.

Not satisfied with the current stage of the extensive research on 3D printing technology for polymers and metals, researchers are searching for more innovative 3D printing technologies for glass fabrication in what has become the latest trend of interest. The traditional glass manufacturing process requires complex high-temperature melting and casting processes, which presents a great challenge to the fabrication of arbitrarily complex glass devices. The emergence of 3D printing technology provides a good solution. This paper reviews the recent advances in glass 3D printing, describes the history and development of related technologies, and lists popular applications of 3D printing for glass preparation. This review compares the advantages and disadvantages of various processing methods, summarizes the problems encountered in the process of technology application, and proposes the corresponding solutions to select the most appropriate preparation method in practical applications. The application of additive manufacturing in glass fabrication is in its infancy but has great potential. Based on this view, the methods for glass preparation with 3D printing technology are expected to achieve both high-speed and high-precision fabrication. Full article

(This article belongs to the Special Issue Microscale and Rheology in 3D Printing Processes)

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20 pages, 876 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Systems for Muscle Cell Differentiation: From Bioengineering to Future Food

by Kah-Yin Lee, Hui-Xin Loh and Andrew C. A. Wan

Micromachines 2022, 13(1), 71; https://doi.org/10.3390/mi13010071 - 31 Dec 2021

Cited by 20 | Viewed by 8621

Abstract

In light of pressing issues, such as sustainability and climate change, future protein sources will increasingly turn from livestock to cell-based production and manufacturing activities. In the case of cell-based or cultured meat a relevant aspect would be the differentiation of muscle cells [...] Read more.

In light of pressing issues, such as sustainability and climate change, future protein sources will increasingly turn from livestock to cell-based production and manufacturing activities. In the case of cell-based or cultured meat a relevant aspect would be the differentiation of muscle cells into mature muscle tissue, as well as how the microsystems that have been developed to date can be developed for larger-scale cultures. To delve into this aspect we review previous research that has been carried out on skeletal muscle tissue engineering and how various biological and physicochemical factors, mechanical and electrical stimuli, affect muscle cell differentiation on an experimental scale. Material aspects such as the different biomaterials used and 3D vs. 2D configurations in the context of muscle cell differentiation will also be discussed. Finally, the ability to translate these systems to more scalable bioreactor configurations and eventually bring them to a commercial scale will be touched upon. Full article

(This article belongs to the Special Issue Sensors, Devices and Systems for Future Food Production and Packaging)

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40 pages, 9254 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Engineering Biological Tissues from the Bottom-Up: Recent Advances and Future Prospects

by Xiaowen Wang, Zhen Wang, Wenya Zhai, Fengyun Wang, Zhixing Ge, Haibo Yu and Wenguang Yang

Micromachines 2022, 13(1), 75; https://doi.org/10.3390/mi13010075 - 31 Dec 2021

Cited by 12 | Viewed by 4921

Abstract

Tissue engineering provides a powerful solution for current organ shortages, and researchers have cultured blood vessels, heart tissues, and bone tissues in vitro. However, traditional top-down tissue engineering has suffered two challenges: vascularization and reconfigurability of functional units. With the continuous development of [...] Read more.

Tissue engineering provides a powerful solution for current organ shortages, and researchers have cultured blood vessels, heart tissues, and bone tissues in vitro. However, traditional top-down tissue engineering has suffered two challenges: vascularization and reconfigurability of functional units. With the continuous development of micro-nano technology and biomaterial technology, bottom-up tissue engineering as a promising approach for organ and tissue modular reconstruction has gradually developed. In this article, relevant advances in living blocks fabrication and assembly techniques for creation of higher-order bioarchitectures are described. After a critical overview of this technology, a discussion of practical challenges is provided, and future development prospects are proposed. Full article

(This article belongs to the Special Issue Feature Papers of Micromachines in "Materials and Processing" 2022)

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11 pages, 2177 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Deep-Learning Based Estimation of Dielectrophoretic Force

by Sunday Ajala, Harikrishnan Muraleedharan Jalajamony and Renny Edwin Fernandez

Micromachines 2022, 13(1), 41; https://doi.org/10.3390/mi13010041 - 28 Dec 2021

Cited by 3 | Viewed by 2910

Abstract

The ability to accurately quantify dielectrophoretic (DEP) force is critical in the development of high-efficiency microfluidic systems. This is the first reported work that combines a textile electrode-based DEP sensing system with deep learning in order to estimate the DEP forces invoked on [...] Read more.

The ability to accurately quantify dielectrophoretic (DEP) force is critical in the development of high-efficiency microfluidic systems. This is the first reported work that combines a textile electrode-based DEP sensing system with deep learning in order to estimate the DEP forces invoked on microparticles. We demonstrate how our deep learning model can process micrographs of pearl chains of polystyrene (PS) microbeads to estimate the DEP forces experienced. Numerous images obtained from our experiments at varying input voltages were preprocessed and used to train three deep convolutional neural networks, namely AlexNet, MobileNetV2, and VGG19. The performances of all the models was tested for their validation accuracies. Models were also tested with adversarial images to evaluate performance in terms of classification accuracy and resilience as a result of noise, image blur, and contrast changes. The results indicated that our method is robust under unfavorable real-world settings, demonstrating that it can be used for the direct estimation of dielectrophoretic force in point-of-care settings. Full article

(This article belongs to the Special Issue Microfluidic System for Biochemical Application)

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32 pages, 8787 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Current Development in Interdigital Transducer (IDT) Surface Acoustic Wave Devices for Live Cell In Vitro Studies: A Review

by Mazlee Bin Mazalan, Anas Mohd Noor, Yufridin Wahab, Shuhaida Yahud and Wan Safwani Wan Kamarul Zaman

Micromachines 2022, 13(1), 30; https://doi.org/10.3390/mi13010030 - 27 Dec 2021

Cited by 35 | Viewed by 10273

Abstract

Acoustics have a wide range of uses, from noise-cancelling to ultrasonic imaging. There has been a surge in interest in developing acoustic-based approaches for biological and biomedical applications in the last decade. This review focused on the application of surface acoustic waves (SAW) [...] Read more.

Acoustics have a wide range of uses, from noise-cancelling to ultrasonic imaging. There has been a surge in interest in developing acoustic-based approaches for biological and biomedical applications in the last decade. This review focused on the application of surface acoustic waves (SAW) based on interdigital transducers (IDT) for live-cell investigations, such as cell manipulation, cell separation, cell seeding, cell migration, cell characteristics, and cell behaviours. The approach is also known as acoustofluidic, because the SAW device is coupled with a microfluidic system that contains live cells. This article provides an overview of several forms of IDT of SAW devices on recently used cells. Conclusively, a brief viewpoint and overview of the future application of SAW techniques in live-cell investigations were presented. Full article

(This article belongs to the Special Issue Acoustic Resonators and Filters)

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12 pages, 2285 KiB

Open AccessEditor’s ChoiceArticle

Four-Dimensional Stimuli-Responsive Hydrogels Micro-Structured via Femtosecond Laser Additive Manufacturing

by Yufeng Tao, Chengchangfeng Lu, Chunsan Deng, Jing Long, Yunpeng Ren, Zijie Dai, Zhaopeng Tong, Xuejiao Wang, Shuai Meng, Wenguang Zhang, Yinuo Xu and Linlin Zhou

Micromachines 2022, 13(1), 32; https://doi.org/10.3390/mi13010032 - 27 Dec 2021

Cited by 14 | Viewed by 3983

Abstract

Rapid fabricating and harnessing stimuli-responsive behaviors of microscale bio-compatible hydrogels are of great interest to the emerging micro-mechanics, drug delivery, artificial scaffolds, nano-robotics, and lab chips. Herein, we demonstrate a novel femtosecond laser additive manufacturing process with smart materials for soft interactive hydrogel [...] Read more.

Rapid fabricating and harnessing stimuli-responsive behaviors of microscale bio-compatible hydrogels are of great interest to the emerging micro-mechanics, drug delivery, artificial scaffolds, nano-robotics, and lab chips. Herein, we demonstrate a novel femtosecond laser additive manufacturing process with smart materials for soft interactive hydrogel micro-machines. Bio-compatible hyaluronic acid methacryloyl was polymerized with hydrophilic diacrylate into an absorbent hydrogel matrix under a tight topological control through a 532 nm green femtosecond laser beam. The proposed hetero-scanning strategy modifies the hierarchical polymeric degrees inside the hydrogel matrix, leading to a controllable surface tension mismatch. Strikingly, these programmable stimuli-responsive matrices mechanized hydrogels into robotic applications at the micro/nanoscale (<300 × 300 × 100 μm³). Reverse high-freedom shape mutations of diversified microstructures were created from simple initial shapes and identified without evident fatigue. We further confirmed the biocompatibility, cell adhesion, and tunable mechanics of the as-prepared hydrogels. Benefiting from the high-efficiency two-photon polymerization (TPP), nanometer feature size (<200 nm), and flexible digitalized modeling technique, many more micro/nanoscale hydrogel robots or machines have become obtainable in respect of future interdisciplinary applications. Full article

(This article belongs to the Special Issue Laser Additive Manufacturing: Design, Materials, Processes and Applications)

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23 pages, 43500 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

A Novel MEMS Capacitive Microphone with Semiconstrained Diaphragm Supported with Center and Peripheral Backplate Protrusions

by Shubham Shubham, Yoonho Seo, Vahid Naderyan, Xin Song, Anthony J. Frank, Jeremy Thomas Morley Greenham Johnson, Mark da Silva and Michael Pedersen

Micromachines 2022, 13(1), 22; https://doi.org/10.3390/mi13010022 - 25 Dec 2021

Cited by 32 | Viewed by 13081

Abstract

Audio applications such as mobile phones, hearing aids, true wireless stereo earphones, and Internet of Things devices demand small size, high performance, and reduced cost. Microelectromechanical system (MEMS) capacitive microphones fulfill these requirements with improved reliability and specifications related to sensitivity, signal-to-noise ratio [...] Read more.

Audio applications such as mobile phones, hearing aids, true wireless stereo earphones, and Internet of Things devices demand small size, high performance, and reduced cost. Microelectromechanical system (MEMS) capacitive microphones fulfill these requirements with improved reliability and specifications related to sensitivity, signal-to-noise ratio (SNR), distortion, and dynamic range when compared to their electret condenser microphone counterparts. We present the design and modeling of a semiconstrained polysilicon diaphragm with flexible springs that are simply supported under bias voltage with a center and eight peripheral protrusions extending from the backplate. The flexible springs attached to the diaphragm reduce the residual film stress effect more effectively compared to constrained diaphragms. The center and peripheral protrusions from the backplate further increase the effective area, linearity, and sensitivity of the diaphragm when the diaphragm engages with these protrusions under an applied bias voltage. Finite element modeling approaches have been implemented to estimate deflection, compliance, and resonance. We report an 85% increase in the effective area of the diaphragm in this configuration with respect to a constrained diaphragm and a 48% increase with respect to a simply supported diaphragm without the center protrusion. Under the applied bias, the effective area further increases by an additional 15% as compared to the unbiased diaphragm effective area. A lumped element model has been also developed to predict the mechanical and electrical behavior of the microphone. With an applied bias, the microphone has a sensitivity of −38 dB (ref. 1 V/Pa at 1 kHz) and an SNR of 67 dBA measured in a 3.25 mm × 1.9 mm × 0.9 mm package including an analog ASIC. Full article

(This article belongs to the Special Issue Micromachined Acoustic Transducers for Audio-Frequency Range)

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25 pages, 2183 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Synergy Factorized Bilinear Network with a Dual Suppression Strategy for Brain Tumor Classification in MRI

by Guanghua Xiao, Huibin Wang, Jie Shen, Zhe Chen, Zhen Zhang and Xiaomin Ge

Micromachines 2022, 13(1), 15; https://doi.org/10.3390/mi13010015 - 23 Dec 2021

Cited by 13 | Viewed by 2957

Abstract

Automatic brain tumor classification is a practicable means of accelerating clinical diagnosis. Recently, deep convolutional neural network (CNN) training with MRI datasets has succeeded in computer-aided diagnostic (CAD) systems. To further improve the classification performance of CNNs, there is still a difficult path [...] Read more.

Automatic brain tumor classification is a practicable means of accelerating clinical diagnosis. Recently, deep convolutional neural network (CNN) training with MRI datasets has succeeded in computer-aided diagnostic (CAD) systems. To further improve the classification performance of CNNs, there is still a difficult path forward with regards to subtle discriminative details among brain tumors. We note that the existing methods heavily rely on data-driven convolutional models while overlooking what makes a class different from the others. Our study proposes to guide the network to find exact differences among similar tumor classes. We first present a “dual suppression encoding” block tailored to brain tumor MRIs, which diverges two paths from our network to refine global orderless information and local spatial representations. The aim is to use more valuable clues for correct classes by reducing the impact of negative global features and extending the attention of salient local parts. Then we introduce a “factorized bilinear encoding” layer for feature fusion. The aim is to generate compact and discriminative representations. Finally, the synergy between these two components forms a pipeline that learns in an end-to-end way. Extensive experiments exhibited superior classification performance in qualitative and quantitative evaluation on three datasets. Full article

(This article belongs to the Special Issue Advanced Machine Learning Techniques for Sensing and Imaging Applications)

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14 pages, 3660 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Passivated Porous Silicon Membranes and Their Application to Optical Biosensing

by Clara Whyte Ferreira, Roselien Vercauteren and Laurent A. Francis

Micromachines 2022, 13(1), 10; https://doi.org/10.3390/mi13010010 - 22 Dec 2021

Cited by 10 | Viewed by 3766

Abstract

A robust fabrication method for stable mesoporous silicon membranes using standard microfabrication techniques is presented. The porous silicon membranes were passivated through the atomic layer deposition of different metal oxides, namely aluminium oxide Al₂O₃, hafnium oxide HfO₂ and [...] Read more.

A robust fabrication method for stable mesoporous silicon membranes using standard microfabrication techniques is presented. The porous silicon membranes were passivated through the atomic layer deposition of different metal oxides, namely aluminium oxide Al₂O₃, hafnium oxide HfO₂ and titanium oxide TiO₂. The fabricated membranes were characterized in terms of morphology, optical properties and chemical properties. Stability tests and optical probing noise level determination were also performed. Preliminary results using an Al₂O₃ passivated membranes for a biosensing application are also presented for selective optical detection of Bacillus cereus bacterial lysate. The biosensor was able to detect the bacterial lysate, with an initial bacteria concentration of 10⁶ colony forming units per mL (CFU/mL), in less than 10 min. Full article

(This article belongs to the Special Issue Selected Papers from ICMA2021)

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23 pages, 976 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Drug-Induced Nephrotoxicity Assessment in 3D Cellular Models

by Pengfei Yu, Zhongping Duan, Shuang Liu, Ivan Pachon, Jianxing Ma, George P. Hemstreet and Yuanyuan Zhang

Micromachines 2022, 13(1), 3; https://doi.org/10.3390/mi13010003 - 21 Dec 2021

Cited by 22 | Viewed by 6231

Abstract

The kidneys are often involved in adverse effects and toxicity caused by exposure to foreign compounds, chemicals, and drugs. Early predictions of these influences are essential to facilitate new, safe drugs to enter the market. However, in current drug treatments, drug-induced nephrotoxicity accounts [...] Read more.

The kidneys are often involved in adverse effects and toxicity caused by exposure to foreign compounds, chemicals, and drugs. Early predictions of these influences are essential to facilitate new, safe drugs to enter the market. However, in current drug treatments, drug-induced nephrotoxicity accounts for 1/4 of reported serious adverse reactions, and 1/3 of them are attributable to antibiotics. Drug-induced nephrotoxicity is driven by multiple mechanisms, including altered glomerular hemodynamics, renal tubular cytotoxicity, inflammation, crystal nephropathy, and thrombotic microangiopathy. Although the functional proteins expressed by renal tubules that mediate drug sensitivity are well known, current in vitro 2D cell models do not faithfully replicate the morphology and intact renal tubule function, and therefore, they do not replicate in vivo nephrotoxicity. The kidney is delicate and complex, consisting of a filter unit and a tubular part, which together contain more than 20 different cell types. The tubular epithelium is highly polarized, and maintaining cellular polarity is essential for the optimal function and response to environmental signals. Cell polarity depends on the communication between cells, including paracrine and autocrine signals, as well as biomechanical and chemotaxis processes. These processes affect kidney cell proliferation, migration, and differentiation. For drug disposal research, the microenvironment is essential for predicting toxic reactions. This article reviews the mechanism of drug-induced kidney injury, the types of nephrotoxicity models (in vivo and in vitro models), and the research progress related to drug-induced nephrotoxicity in three-dimensional (3D) cellular culture models. Full article

(This article belongs to the Special Issue 3D In Vitro Tissue and Organ Models)

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15 pages, 2538 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Static and Dynamic Optical Analysis of Micro Wrinkle Formation on a Liquid Surface

by Antariksh Saxena, Costas Tsakonas, David Chappell, Chi Shing Cheung, Andrew Michael John Edwards, Haida Liang, Ian Charles Sage and Carl Vernon Brown

Micromachines 2021, 12(12), 1583; https://doi.org/10.3390/mi12121583 - 19 Dec 2021

Cited by 3 | Viewed by 2749

Abstract

A spatially periodic voltage was used to create a dielectrophoresis induced periodic micro wrinkle deformation on the surface of a liquid film. Optical Coherence Tomography provided the equilibrium wrinkle profile at submicron accuracy. The dynamic wrinkle amplitude was derived from optical diffraction analysis [...] Read more.

A spatially periodic voltage was used to create a dielectrophoresis induced periodic micro wrinkle deformation on the surface of a liquid film. Optical Coherence Tomography provided the equilibrium wrinkle profile at submicron accuracy. The dynamic wrinkle amplitude was derived from optical diffraction analysis during sub-millisecond wrinkle formation and decay, after abruptly increasing or reducing the voltage, respectively. The decay time constant closely followed the film thickness dependence expected for surface tension driven viscous levelling. Modelling of the system using numerical solution of the Stokes flow equations with electrostatic forcing predicted that wrinkle formation was faster than decay, in accord with observations. Full article

(This article belongs to the Special Issue Advances in Electrowetting Devices)

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15 pages, 3541 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

A Cerebral Organoid Connectivity Apparatus to Model Neuronal Tract Circuitry

by Denise A. Robles, Andrew J. Boreland, Zhiping P. Pang and Jeffrey D. Zahn

Micromachines 2021, 12(12), 1574; https://doi.org/10.3390/mi12121574 - 17 Dec 2021

Cited by 8 | Viewed by 4055

Abstract

Mental disorders have high prevalence, but the efficacy of existing therapeutics is limited, in part, because the pathogenic mechanisms remain enigmatic. Current models of neural circuitry include animal models and post-mortem brain tissue, which have allowed enormous progress in understanding the pathophysiology of [...] Read more.

Mental disorders have high prevalence, but the efficacy of existing therapeutics is limited, in part, because the pathogenic mechanisms remain enigmatic. Current models of neural circuitry include animal models and post-mortem brain tissue, which have allowed enormous progress in understanding the pathophysiology of mental disorders. However, these models limit the ability to assess the functional alterations in short-range and long-range network connectivity between brain regions that are implicated in many mental disorders, e.g., schizophrenia and autism spectrum disorders. This work addresses these limitations by developing an in vitro model of the human brain that models the in vivo cerebral tract environment. In this study, microfabrication and stem cell differentiation techniques were combined to develop an in vitro cerebral tract model that anchors human induced pluripotent stem cell-derived cerebral organoids (COs) and provides a scaffold to promote the formation of a functional connecting neuronal tract. Two designs of a Cerebral Organoid Connectivity Apparatus (COCA) were fabricated using SU-8 photoresist. The first design contains a series of spikes which anchor the CO to the COCA (spiked design), whereas the second design contains flat supporting structures with open holes in a grid pattern to anchor the organoids (grid design); both designs allow effective media exchange. Morphological and functional analyses reveal the expression of key neuronal markers as well as functional activity and signal propagation along cerebral tracts connecting CO pairs. The reported in vitro models enable the investigation of critical neural circuitry involved in neurodevelopmental processes and has the potential to help devise personalized and targeted therapeutic strategies. Full article

(This article belongs to the Special Issue Microfluidic Platforms for the Nervous System)

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11 pages, 925 KiB

Open AccessFeature PaperEditor’s ChoiceConference Report

Advances in the Field of Micro- and Nanotechnologies Applied to Extracellular Vesicle Research: Take-Home Message from ISEV2021

by Silvia Picciolini, Francesca Rodà, Marzia Bedoni and Alice Gualerzi

Micromachines 2021, 12(12), 1563; https://doi.org/10.3390/mi12121563 - 16 Dec 2021

Cited by 4 | Viewed by 2690

Abstract

Extracellular Vesicles (EVs) are naturally secreted nanoparticles with a plethora of functions in the human body and remarkable potential as diagnostic and therapeutic tools. Starting from their discovery, EV nanoscale dimensions have hampered and slowed new discoveries in the field, sometimes generating confusion [...] Read more.

Extracellular Vesicles (EVs) are naturally secreted nanoparticles with a plethora of functions in the human body and remarkable potential as diagnostic and therapeutic tools. Starting from their discovery, EV nanoscale dimensions have hampered and slowed new discoveries in the field, sometimes generating confusion and controversies among experts. Microtechnological and especially nanotechnological advances have sped up biomedical research dealing with EVs, but efforts are needed to further clarify doubts and knowledge gaps. In the present review, we summarize some of the most interesting data presented in the Annual Meeting of the International Society for Extracellular Vesicles (ISEV), ISEV2021, to stimulate discussion and to share knowledge with experts from all fields of research. Indeed, EV research requires a multidisciplinary knowledge exchange and effort. EVs have demonstrated their importance and significant biological role; still, further technological achievements are crucial to avoid artifacts and misleading conclusions in order to enable outstanding discoveries. Full article

(This article belongs to the Special Issue Micro- and Nano-Technologies for the Application of Nanocarriers as Theranostics)

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19 pages, 6336 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Waveguide Manufacturing Technologies for Next-Generation Millimeter-Wave Antennas

by Lucas Polo-López, Pablo Sanchez-Olivares, Eduardo García-Marín, Jorge A. Ruiz-Cruz, Juan Córcoles, José L. Masa-Campos, José R. Montejo-Garai and Jesús M. Rebollar

Micromachines 2021, 12(12), 1565; https://doi.org/10.3390/mi12121565 - 16 Dec 2021

Cited by 5 | Viewed by 4203

Abstract

Some recent waveguide-based antennas are presented in this paper, designed for the next generation of communication systems operating at the millimeter-wave band. The presented prototypes have been conceived to be manufactured using different state-of-the-art techniques, involving subtractive and additive approaches. All the designs [...] Read more.

Some recent waveguide-based antennas are presented in this paper, designed for the next generation of communication systems operating at the millimeter-wave band. The presented prototypes have been conceived to be manufactured using different state-of-the-art techniques, involving subtractive and additive approaches. All the designs have used the latest developments in the field of manufacturing to guarantee the required accuracy for operation at millimeter-wave frequencies, where tolerances are extremely tight. Different designs will be presented, including a monopulse antenna combining a comparator network, a mode converter, and a spline profile horn; a tunable phase shifter that is integrated into an array to implement reconfigurability of the main lobe direction; and a conformal array antenna. These prototypes were manufactured by diverse approaches taking into account the waveguide configuration, combining parts with high-precision milling, electrical discharge machining, direct metal laser sintering, or stereolithography with spray metallization, showing very competitive performances at the millimeter-wave band till 40 GHz. Full article

(This article belongs to the Special Issue Micro Manufacturing for 5G Communications)

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12 pages, 19448 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

SiGe/Si Multi-Quantum-Well Micro-Bolometer Array Design and Fabrication with Heterogeneous Integration

by Zhong Fang, Yong He, Zhequan Chen, Yunlei Shi, Junjie Jiao and Xuchao Pan

Micromachines 2021, 12(12), 1553; https://doi.org/10.3390/mi12121553 - 13 Dec 2021

Cited by 2 | Viewed by 2976

Abstract

The micro-bolometer is important in the field of infrared imaging, although improvements in its performance have been limited by traditional materials. SiGe/Si multi-quantum-well materials (SiGe/Si MQWs) are novelty thermal-sensitive materials with a significantly high TCR and a comparably low 1/f noise. The application [...] Read more.

The micro-bolometer is important in the field of infrared imaging, although improvements in its performance have been limited by traditional materials. SiGe/Si multi-quantum-well materials (SiGe/Si MQWs) are novelty thermal-sensitive materials with a significantly high TCR and a comparably low 1/f noise. The application of such high-performance monocrystalline films in a micro-bolometer has been limited by film integration technology. This paper reports a SiGe/Si MQWs micro-bolometer fabrication with heterogeneous integration. The integration with the SiGe/Si MQWs handle wafer and dummy read-out circuit wafer was achieved based on adhesive wafer bonding. The SiGe/Si MQWs infrared-absorption structure and thermal bridge were calculated and designed. The SiGe/Si MQWs wafer and a 320 × 240 micro-bolometer array of 40 µm pitch L-type pixels were fabricated. The test results for the average absorption efficiency were more than 90% at the wavelength of 8–14 µm. The test pixel was measured to have a thermal capacity of 1.043 × 10⁻⁹ J/K, a thermal conductivity of 1.645 × 10⁻⁷ W/K, and a thermal time constant of 7.25 ms. Furthermore, the total TCR value of the text pixel was measured as 2.91%/K with a bias voltage of 0.3 V. The SiGe/Si MQWs micro-bolometer can be widely applied in commercial fields, especially in early medical diagnosis and biological detection. Full article

(This article belongs to the Special Issue Micro- and Nano-Systems for Manipulation, Actuation and Sensing)

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30 pages, 3790 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Fabricating Silicon Resonators for Analysing Biological Samples

by Momoko Kumemura, Deniz Pekin, Vivek Anand Menon, Isabelle Van Seuningen, Dominique Collard and Mehmet Cagatay Tarhan

Micromachines 2021, 12(12), 1546; https://doi.org/10.3390/mi12121546 - 12 Dec 2021

Cited by 4 | Viewed by 3173

Abstract

The adaptability of microscale devices allows microtechnologies to be used for a wide range of applications. Biology and medicine are among those fields that, in recent decades, have applied microtechnologies to achieve new and improved functionality. However, despite their ability to achieve assay [...] Read more.

The adaptability of microscale devices allows microtechnologies to be used for a wide range of applications. Biology and medicine are among those fields that, in recent decades, have applied microtechnologies to achieve new and improved functionality. However, despite their ability to achieve assay sensitivities that rival or exceed conventional standards, silicon-based microelectromechanical systems remain underutilised for biological and biomedical applications. Although microelectromechanical resonators and actuators do not always exhibit optimal performance in liquid due to electrical double layer formation and high damping, these issues have been solved with some innovative fabrication processes or alternative experimental approaches. This paper focuses on several examples of silicon-based resonating devices with a brief look at their fundamental sensing elements and key fabrication steps, as well as current and potential biological/biomedical applications. Full article

(This article belongs to the Special Issue Micro/Nano Fabrication for Life Sciences)

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30 pages, 15488 KiB

Open AccessFeature PaperEditor’s ChoiceReview

A Review of Sharp-Switching Band-Modulation Devices

by Sorin Cristoloveanu, Joris Lacord, Sébastien Martinie, Carlos Navarro, Francisco Gamiz, Jing Wan, Hassan El Dirani, Kyunghwa Lee and Alexander Zaslavsky

Micromachines 2021, 12(12), 1540; https://doi.org/10.3390/mi12121540 - 11 Dec 2021

Cited by 4 | Viewed by 3346

Abstract

This paper reviews the recently-developed class of band-modulation devices, born from the recent progress in fully-depleted silicon-on-insulator (FD-SOI) and other ultrathin-body technologies, which have enabled the concept of gate-controlled electrostatic doping. In a lateral PIN diode, two additional gates can construct a reconfigurable [...] Read more.

This paper reviews the recently-developed class of band-modulation devices, born from the recent progress in fully-depleted silicon-on-insulator (FD-SOI) and other ultrathin-body technologies, which have enabled the concept of gate-controlled electrostatic doping. In a lateral PIN diode, two additional gates can construct a reconfigurable PNPN structure with unrivalled sharp-switching capability. We describe the implementation, operation, and various applications of these band-modulation devices. Physical and compact models are presented to explain the output and transfer characteristics in both steady-state and transient modes. Not only can band-modulation devices be used for quasi-vertical current switching, but they also show promise for compact capacitorless memories, electrostatic discharge (ESD) protection, sensing, and reconfigurable circuits, while retaining full compatibility with modern silicon processing and standard room-temperature low-voltage operation. Full article

(This article belongs to the Special Issue Steep Switching Field Effect Transistor)

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24 pages, 30512 KiB

Open AccessFeature PaperEditor’s ChoiceReview

State of the Art of Non-Invasive Electrode Materials for Brain–Computer Interface

by Haowen Yuan, Yao Li, Junjun Yang, Hongjie Li, Qinya Yang, Cuiping Guo, Shenmin Zhu and Xiaokang Shu

Micromachines 2021, 12(12), 1521; https://doi.org/10.3390/mi12121521 - 8 Dec 2021

Cited by 27 | Viewed by 8429

Abstract

The brain–computer interface (BCI) has emerged in recent years and has attracted great attention. As an indispensable part of the BCI signal acquisition system, brain electrodes have a great influence on the quality of the signal, which determines the final effect. Due to [...] Read more.

The brain–computer interface (BCI) has emerged in recent years and has attracted great attention. As an indispensable part of the BCI signal acquisition system, brain electrodes have a great influence on the quality of the signal, which determines the final effect. Due to the special usage scenario of brain electrodes, some specific properties are required for them. In this study, we review the development of three major types of EEG electrodes from the perspective of material selection and structural design, including dry electrodes, wet electrodes, and semi-dry electrodes. Additionally, we provide a reference for the current chaotic performance evaluation of EEG electrodes in some aspects such as electrochemical performance, stability, and so on. Moreover, the challenges and future expectations for EEG electrodes are analyzed. Full article

(This article belongs to the Section B1: Biosensors)

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14 pages, 15660 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Design and Optimization of a Novel SAW Gyroscope Structure Based on Amplitude Modulation with 1-D Phononic Crystals

by Fei Ge, Liye Zhao and Yang Zhang

Micromachines 2021, 12(12), 1485; https://doi.org/10.3390/mi12121485 - 30 Nov 2021

Cited by 4 | Viewed by 2355

Abstract

Surface acoustic wave gyroscopes (SAWGs), as a kind of all-solid-state micro-electro-mechanical system (MEMS) gyroscopes, can work normally under extremely high-impact environmental conditions. Among the current SAWGs, amplitude-modulated gyroscopes (AMGs) are all based on the same gyro effect, which was proved weak, and their [...] Read more.

Surface acoustic wave gyroscopes (SAWGs), as a kind of all-solid-state micro-electro-mechanical system (MEMS) gyroscopes, can work normally under extremely high-impact environmental conditions. Among the current SAWGs, amplitude-modulated gyroscopes (AMGs) are all based on the same gyro effect, which was proved weak, and their sensitivity and intensity of the output are both lower than frequency-modulated gyroscopes (FMGs). However, because FMGs need to process a series of frequency signals, their signal processing and circuits are far less straightforward and simple than AMGs. In order to own both high-sensitivity and simple signal processing, a novel surface acoustic traveling wave gyroscope based on amplitude modulation is proposed, using one-dimensional phononic crystals (PCs) in this paper. In view of its specific structure, the proposed gyroscope consists of a surface acoustic wave oscillator and a surface acoustic wave delay line within a one-dimensional phononic crystal with a high-Q defect mode. In this paper, the working principle is analyzed theoretically through the partial wave method (PWM), and the gyroscopes with different numbers of PCs are also designed and studied by using the finite element method (FEM) and multiphysics simulation. The research results demonstrate that under a 1 V oscillator voltage output, the higher sensitivity of −23.1 mV·(rad/s)⁻¹ in the linear range from −8 rad/s to 8 rad/s is reached when the gyro with three PC walls, and the wider linear range from −15 rad/s to 17.5 rad/s with the sensitivity of −6.7 mV·(rad/s)⁻¹ with only one PC wall. Compared with the existing AMGs using metal dots to enhance the gyro effect, the sensitivity of the proposed gyro is increased by 15 to 112 times, and the linear range is increased by 4.6 to 186 times, even without the enhancement of the metal dots. Full article

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25 pages, 1001 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Low Intensity Pulsed Ultrasound for Bone Tissue Engineering

by Colleen McCarthy and Gulden Camci-Unal

Micromachines 2021, 12(12), 1488; https://doi.org/10.3390/mi12121488 - 30 Nov 2021

Cited by 34 | Viewed by 6602

Abstract

As explained by Wolff’s law and the mechanostat hypothesis, mechanical stimulation can be used to promote bone formation. Low intensity pulsed ultrasound (LIPUS) is a source of mechanical stimulation that can activate the integrin/phosphatidylinositol 3-OH kinase/Akt pathway and upregulate osteogenic proteins through the [...] Read more.

As explained by Wolff’s law and the mechanostat hypothesis, mechanical stimulation can be used to promote bone formation. Low intensity pulsed ultrasound (LIPUS) is a source of mechanical stimulation that can activate the integrin/phosphatidylinositol 3-OH kinase/Akt pathway and upregulate osteogenic proteins through the production of cyclooxygenase-2 (COX-2) and prostaglandin E₂ (PGE₂). This paper analyzes the results of in vitro and in vivo studies that have evaluated the effects of LIPUS on cell behavior within three-dimensional (3D) titanium, ceramic, and hydrogel scaffolds. We focus specifically on cell morphology and attachment, cell proliferation and viability, osteogenic differentiation, mineralization, bone volume, and osseointegration. As shown by upregulated levels of alkaline phosphatase and osteocalcin, increased mineral deposition, improved cell ingrowth, greater scaffold pore occupancy by bone tissue, and superior vascularization, LIPUS generally has a positive effect and promotes bone formation within engineered scaffolds. Additionally, LIPUS can have synergistic effects by producing the piezoelectric effect and enhancing the benefits of 3D hydrogel encapsulation, growth factor delivery, and scaffold modification. Additional research should be conducted to optimize the ultrasound parameters and evaluate the effects of LIPUS with other types of scaffold materials and cell types. Full article

(This article belongs to the Special Issue Women’s Special Issue Series: Micromachines)

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19 pages, 2746 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Recent Insights and Multifactorial Applications of Carbon Nanotubes

by Muthu Thiruvengadam, Govindasamy Rajakumar, Venkata Swetha, Mohammad Azam Ansari, Saad Alghamdi, Mazen Almehmadi, Mustafa Halawi, Lakshmanan Kungumadevi, Vaishnavi Raja, Sulthana Sabura Sarbudeen, Saranya Madhavan, Maksim Rebezov, Mohammad Ali Shariati, Alexandr Sviderskiy and Konstantin Bogonosov

Micromachines 2021, 12(12), 1502; https://doi.org/10.3390/mi12121502 - 30 Nov 2021

Cited by 21 | Viewed by 4433

Abstract

Nanotechnology has undergone significant development in recent years, particularly in the fabrication of sensors with a wide range of applications. The backbone of nanotechnology is nanostructures, which are determined on a nanoscale. Nanoparticles are abundant throughout the universe and are thought to be [...] Read more.

Nanotechnology has undergone significant development in recent years, particularly in the fabrication of sensors with a wide range of applications. The backbone of nanotechnology is nanostructures, which are determined on a nanoscale. Nanoparticles are abundant throughout the universe and are thought to be essential building components in the process of planet creation. Nanotechnology is generally concerned with structures that are between 1 and 100 nm in at least one dimension and involves the production of materials or electronics that are that small. Carbon nanotubes (CNTs) are carbon-based nanomaterials that have the structure of tubes. Carbon nanotubes are often referred to as the kings of nanomaterials. The diameter of carbon is determined in nanometers. They are formed from graphite sheets and are available in a variety of colors. Carbon nanotubes have a number of characteristics, including high flexibility, good thermal conductivity, low density, and chemical stability. Carbon nanotubes have played an important part in nanotechnology, semiconductors, optical and other branches of materials engineering owing to their remarkable features. Several of the applications addressed in this review have already been developed and used to benefit people worldwide. CNTs have been discussed in several domains, including industry, construction, adsorption, sensors, silicon chips, water purifiers, and biomedical uses, to show many treatments such as injecting CNTs into kidney cancers in rats, drug delivery, and directing a near-infrared laser at the cancers. With the orderly development of research in this field, additional therapeutic modalities will be identified, mainly for dispersion and densification techniques and targeted drug delivery systems for managing and curing posterior cortical atrophy. This review discusses the characteristics of carbon nanotubes as well as therapeutic applications such as medical diagnostics and drug delivery. Full article

(This article belongs to the Special Issue Advances in Biomedical Nanotechnology)

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9 pages, 6366 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Topological Nanophotonic Wavelength Router Based on Topology Optimization

by Hongyi Yuan, Zhouhui Liu, Maoliang Wei, Hongtao Lin, Xiaoyong Hu and Cuicui Lu

Micromachines 2021, 12(12), 1506; https://doi.org/10.3390/mi12121506 - 30 Nov 2021

Cited by 13 | Viewed by 4546

Abstract

The topological nanophotonic wavelength router, which can steer light with different wavelength signals into different topological channels, plays a key role in optical information processing. However, no effective method has been found to realize such a topological nanophotonic device. Here, an on-chip topological [...] Read more.

The topological nanophotonic wavelength router, which can steer light with different wavelength signals into different topological channels, plays a key role in optical information processing. However, no effective method has been found to realize such a topological nanophotonic device. Here, an on-chip topological nanophotonic wavelength router working in an optical telecom band is designed based on a topology optimization algorithm and experimentally demonstrated. Valley photonic crystal is used to provide a topological state in the optical telecom band. The measured topological wavelength router has narrow signal peaks and is easy for integration. This work offers an efficient scheme for the realization of topological devices and lays a foundation for the future application of topological photonics. Full article

(This article belongs to the Special Issue Photonic Chips for Optical Communications)

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29 pages, 11434 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Non-Invasive Manipulation of Two-Phase Liquid–Liquid Slug Flow Parameters Using Magnetofluidics

by Anoj Winston Gladius, Simon Höving, Mehdy Mendelawi, Harikrishna Sreekumar Sheeba and David W. Agar

Micromachines 2021, 12(12), 1449; https://doi.org/10.3390/mi12121449 - 26 Nov 2021

Cited by 1 | Viewed by 2500

Abstract

Liquid–liquid slug flow in a microcapillary, with its improved heat and mass transfer properties and narrow residence time, plays a vital role in process intensification. Knowledge of the flow properties in microchannels along variables’ controllability (e.g., phase ratio, slug length along with classical [...] Read more.

Liquid–liquid slug flow in a microcapillary, with its improved heat and mass transfer properties and narrow residence time, plays a vital role in process intensification. Knowledge of the flow properties in microchannels along variables’ controllability (e.g., phase ratio, slug length along with classical variables, such as pressure, temperature, and flow velocity) during operation is crucial. This work aids in this by using magnetofluidics to manipulate these parameters. A ferrofluid with reproducible properties is produced and, together with another phase, stable slug flow is generated. Micro-gear pumps and syringe pumps, with their traditional mechanical components, result in parts degrading over time due to fatigue caused by pressure differentials and corrosive chemicals. The microflow is also disturbed by the invasive nature of these pumps. A considerably energy-efficient, non-invasive alternative, with reduced mechanical interfacing is suggested in this work. It uses magnetic gradients to manipulate two-phase flow, one of which is a magnetically active phase. Conveying concepts using permanent magnets in the immediate vicinity of the flow are investigated. To operate this pump continuously and to be able to regulate the phase ratio, an electromagnetic non-invasive valve is developed. Phase separation is also carried out with an existing decanter design, modified using electromagnetism to work without a selective membrane, usually necessary for phase separation at this scale. This pump is then compared with similar pumps developed in the past. Full article

(This article belongs to the Section E：Engineering and Technology)

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37 pages, 11417 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Electroreforming of Biomass for Value-Added Products

by Zi Iun Lai, Li Quan Lee and Hong Li

Micromachines 2021, 12(11), 1405; https://doi.org/10.3390/mi12111405 - 16 Nov 2021

Cited by 15 | Viewed by 5113

Abstract

Humanity’s overreliance on fossil fuels for chemical and energy production has resulted in uncontrollable carbon emissions that have warranted widespread concern regarding global warming. To address this issue, there is a growing body of research on renewable resources such as biomass, of which [...] Read more.

Humanity’s overreliance on fossil fuels for chemical and energy production has resulted in uncontrollable carbon emissions that have warranted widespread concern regarding global warming. To address this issue, there is a growing body of research on renewable resources such as biomass, of which cellulose is the most abundant type. In particular, the electrochemical reforming of biomass is especially promising, as it allows greater control over valorization processes and requires milder conditions. Driven by renewable electricity, electroreforming of biomass can be green and sustainable. Moreover, green hydrogen generation can be coupled to anodic biomass electroforming, which has attracted ever-increasing attention. The following review is a summary of recent developments related to electroreforming cellulose and its derivatives (glucose, hydroxymethylfurfural, levulinic acid). The electroreforming of biomass can be achieved on the anode of an electrochemical cell through electrooxidation, as well as on the cathode through electroreduction. Recent advances in the anodic electroreforming of cellulose and cellulose-derived glucose and 5-hydrooxylmethoylfurural (5-HMF) are first summarized. Then, the key achievements in the cathodic electroreforming of cellulose and cellulose-derived 5-HMF and levulinic acid are discussed. Afterward, the emerging research focusing on coupling hydrogen evolution with anodic biomass reforming for the cogeneration of green hydrogen fuel and value-added chemicals is reviewed. The final chapter of this paper provides our perspective on the challenges and future research directions of biomass electroreforming. Full article

(This article belongs to the Special Issue Recent Advances in Nanotechnology and Nanomaterials)

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20 pages, 5052 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Parametric Study of Jet/Droplet Formation Process during LIFT Printing of Living Cell-Laden Bioink

by Christina Kryou, Ioannis Theodorakos, Panagiotis Karakaidos, Apostolos Klinakis, Antonios Hatziapostolou and Ioanna Zergioti

Micromachines 2021, 12(11), 1408; https://doi.org/10.3390/mi12111408 - 16 Nov 2021

Cited by 6 | Viewed by 2748

Abstract

Bioprinting offers great potential for the fabrication of three-dimensional living tissues by the precise layer-by-layer printing of biological materials, including living cells and cell-laden hydrogels. The laser-induced forward transfer (LIFT) of cell-laden bioinks is one of the most promising laser-printing technologies enabling biofabrication. [...] Read more.

Bioprinting offers great potential for the fabrication of three-dimensional living tissues by the precise layer-by-layer printing of biological materials, including living cells and cell-laden hydrogels. The laser-induced forward transfer (LIFT) of cell-laden bioinks is one of the most promising laser-printing technologies enabling biofabrication. However, for it to be a viable bioprinting technology, bioink printability must be carefully examined. In this study, we used a time-resolved imaging system to study the cell-laden bioink droplet formation process in terms of the droplet size, velocity, and traveling distance. For this purpose, the bioinks were prepared using breast cancer cells with different cell concentrations to evaluate the effect of the cell concentration on the droplet formation process and the survival of the cells after printing. These bioinks were compared with cell-free bioinks under the same printing conditions to understand the effect of the particle physical properties on the droplet formation procedure. The morphology of the printed droplets indicated that it is possible to print uniform droplets for a wide range of cell concentrations. Overall, it is concluded that the laser fluence and the distance of the donor–receiver substrates play an important role in the printing impingement type; consequently, a careful adjustment of these parameters can lead to high-quality printing. Full article

(This article belongs to the Special Issue Advanced Laser Bio-Printing)

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13 pages, 2838 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Polycarbonate Masters for Soft Lithography

by Filippo Amadeo, Prithviraj Mukherjee, Hua Gao, Jian Zhou and Ian Papautsky

Micromachines 2021, 12(11), 1392; https://doi.org/10.3390/mi12111392 - 13 Nov 2021

Cited by 7 | Viewed by 4163

Abstract

Fabrication of microfluidic devices by soft lithography is by far the most popular approach due to its simplicity and low cost. The approach relies on casting of elastomers, such as polydimethylsiloxane (PDMS), on masters fabricated from photoresists on silicon substrates. These masters, however, [...] Read more.

Fabrication of microfluidic devices by soft lithography is by far the most popular approach due to its simplicity and low cost. The approach relies on casting of elastomers, such as polydimethylsiloxane (PDMS), on masters fabricated from photoresists on silicon substrates. These masters, however, can be expensive, complicated to fabricate, and fragile. Here we describe an optimized replica molding approach to preserve the original masters by heat molding of polycarbonate (PC) sheets on PDMS molds. The process is faster and simpler than previously reported methods and does not result in a loss of resolution or aspect ratio for the features. The generated PC masters were used to successfully replicate a wide range of microfluidic devices, including rectangular channels with aspect ratios from 0.025 to 7.3, large area spiral channels, and micropost arrays with 5 µm spacing. Moreover, fabrication of rounded features, such as semi-spherical microwells, was possible and easy. Quantitative analysis of the replicated features showed variability of <2%. The approach is low cost, does not require cleanroom setting or hazardous chemicals, and is rapid and simple. The fabricated masters are rigid and survive numerous replication cycles. Moreover, damaged or missing masters can be easily replaced by reproduction from previously cast PDMS replicas. All of these advantages make the PC masters highly desirable for long-term preservation of soft lithography masters for microfluidic devices. Full article

(This article belongs to the Special Issue Feature Papers of Micromachines in Materials and Processing 2021)

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20 pages, 7135 KiB

Open AccessEditor’s ChoiceArticle

A Layer-Dependent Analytical Model for Printability Assessment of Additive Manufacturing Copper/Steel Multi-Material Components by Directed Energy Deposition

by Wenqi Zhang, Baopeng Zhang, Haifeng Xiao, Huanqing Yang, Yun Wang and Haihong Zhu

Micromachines 2021, 12(11), 1394; https://doi.org/10.3390/mi12111394 - 13 Nov 2021

Cited by 11 | Viewed by 2625

Abstract

Copper/steel bimetal, one of the most popular and typical multi-material components (MMC), processes excellent comprehensive properties with the high strength of steel and the high thermal conductivity of copper alloy. Additive manufacturing (AM) technology is characterized by layer-wise fabrication, and thus is especially [...] Read more.

Copper/steel bimetal, one of the most popular and typical multi-material components (MMC), processes excellent comprehensive properties with the high strength of steel and the high thermal conductivity of copper alloy. Additive manufacturing (AM) technology is characterized by layer-wise fabrication, and thus is especially suitable for fabricating MMC. However, considering both the great difference in thermophysical properties between copper and steel and the layer-based fabrication character of the AM process, the optimal processing parameters will vary throughout the deposition process. In this paper, we propose an analytical calculation model to predict the layer-dependent processing parameters when fabricating the 07Cr15Ni5 steel on the CuCr substrate at the fixed layer thickness (0.3 mm) and hatching space (0.3 mm). Specifically, the changes in effective thermal conductivity and specific heat capacity with the layer number, as well as the absorption rate and catchment efficiency with the processing parameters are considered. The parameter maps predicted by the model have good agreement with the experimental results. The proposed analytical model provides new guidance to determine the processing windows for novel multi-material components, especially for the multi-materials whose physical properties are significantly different. Full article

(This article belongs to the Special Issue Laser Additive Manufacturing: Design, Materials, Processes and Applications)

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10 pages, 5052 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

A Novel Fabricating Method of Micro Lens-on-Lens Arrays with Two Focal Lengths

by Xin Liu, Min Li, Jiang Bian, Junfeng Du, Bincheng Li and Bin Fan

Micromachines 2021, 12(11), 1372; https://doi.org/10.3390/mi12111372 - 8 Nov 2021

Cited by 6 | Viewed by 3197

Abstract

Micro lens-on-lens array (MLLA) is a novel 3D structure with unique optical properties that cannot be fabricated accurately and quickly by existing processing methods. In this paper, a new fabricating method of MLLAs with two focal lengths is proposed. By introducing the soft [...] Read more.

Micro lens-on-lens array (MLLA) is a novel 3D structure with unique optical properties that cannot be fabricated accurately and quickly by existing processing methods. In this paper, a new fabricating method of MLLAs with two focal lengths is proposed. By introducing the soft lithography technology, nano-imprint technology and mask alignment exposure technology, MLLAs with high precisions can be obtained. A MLLA is successfully fabricated with two focal lengths of 58 μm and 344 μm, and an experiment is carried out. The results show that the MLLA has excellent two-level focusing and imaging abilities. Furthermore, the fabricated profiles of the MLLA agree well with the designed profiles, and the morphology deviation of the MLLA is better than 2%, satisfying the application requirements. The results verify the feasibility and validity of the novel fabricating method. By adjusting mask patterns and processing parameters, MLLAs with both changeable sizes and focal lengths can be obtained. Full article

(This article belongs to the Special Issue Design and Manufacture of Micro-Optical Lens)

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12 pages, 53958 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

A Miniature Optical Force Dual-Axis Accelerometer Based on Laser Diodes and Small Particles Cavities

by Junji Pu, Kai Zeng, Yulie Wu and Dingbang Xiao

Micromachines 2021, 12(11), 1375; https://doi.org/10.3390/mi12111375 - 8 Nov 2021

Cited by 7 | Viewed by 2762

Abstract

In recent years, the optical accelerometer based on the optical trapping force effect has gradually attracted the attention of researchers for its high sensitivity and high measurement accuracy. However, due to its large size and the complexity of optical path adjustment, the optical [...] Read more.

In recent years, the optical accelerometer based on the optical trapping force effect has gradually attracted the attention of researchers for its high sensitivity and high measurement accuracy. However, due to its large size and the complexity of optical path adjustment, the optical force accelerometers reported are only suitable for the laboratory environment up to now. In this paper, a miniature optical force dual-axis accelerometer based on the miniature optical system and a particles cavity which is prepared by Micro-Electro-Mechanical Systems (MEMS) technology is proposed. The overall system of the miniature optical levitation including the miniature optical system and MEMS particles cavity is a cylindrical structure with a diameter of about 10 mm and a height of 33 mm (Φ 10 mm × 33 mm). Moreover, the size of this accelerometer is 200 mm × 100 mm × 100 mm. Due to the selected light source being a laser diode light source with elliptical distribution, it is sensitive to the external acceleration in both the long axis and the short axis. This accelerometer achieves a measurement range of ±0.17 g–±0.26 g and measurement resolution of 0.49 mg and 1.88 mg. The result shows that the short-term zero-bias stability of the two orthogonal axes of the optical force accelerometer is 4.4 mg and 9.2 mg, respectively. The main conclusion that can be drawn is that this optical force accelerometer could provide an effective solution for measuring acceleration with an optical force effect for compact engineering devices. Full article

(This article belongs to the Section E：Engineering and Technology)

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27 pages, 8154 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Research Progress of Microtransfer Printing Technology for Flexible Electronic Integrated Manufacturing

by Li Zhang, Chong Zhang, Zheng Tan, Jingrong Tang, Chi Yao and Bo Hao

Micromachines 2021, 12(11), 1358; https://doi.org/10.3390/mi12111358 - 3 Nov 2021

Cited by 17 | Viewed by 3943

Abstract

In recent years, with the rapid development of the flexible electronics industry, there is an urgent need for a large-area, multilayer, and high-production integrated manufacturing technology for scalable and flexible electronic products. To solve this technical demand, researchers have proposed and developed microtransfer [...] Read more.

In recent years, with the rapid development of the flexible electronics industry, there is an urgent need for a large-area, multilayer, and high-production integrated manufacturing technology for scalable and flexible electronic products. To solve this technical demand, researchers have proposed and developed microtransfer printing technology, which picks up and prints inks in various material forms from the donor substrate to the target substrate, successfully realizing the integrated manufacturing of flexible electronic products. This review retrospects the representative research progress of microtransfer printing technology for the production of flexible electronic products and emphasizes the summary of seal materials, the basic principles of various transfer technology and fracture mechanics models, and the influence of different factors on the transfer effect. In the end, the unique functions, technical features, and related printing examples of each technology are concluded and compared, and the prospects of further research work on microtransfer printing technology is finally presented. Full article

(This article belongs to the Special Issue Micro/Nano Manipulation Technologies for Flexible Electronics)

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13 pages, 3121 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Suspended Silicon Waveguide with Sub-Wavelength Grating Cladding for Optical MEMS in Mid-Infrared

by Qifeng Qiao, Haoyang Sun, Xinmiao Liu, Bowei Dong, Ji Xia, Chengkuo Lee and Guangya Zhou

Micromachines 2021, 12(11), 1311; https://doi.org/10.3390/mi12111311 - 26 Oct 2021

Cited by 20 | Viewed by 4330

Abstract

Mid-infrared (MIR) photonics are generating considerable interest because of the potential applications in spectroscopic sensing, thermal imaging, and remote sensing. Silicon photonics is believed to be a promising solution to realize MIR photonic integrated circuits (PICs). The past decade has seen a huge [...] Read more.

Mid-infrared (MIR) photonics are generating considerable interest because of the potential applications in spectroscopic sensing, thermal imaging, and remote sensing. Silicon photonics is believed to be a promising solution to realize MIR photonic integrated circuits (PICs). The past decade has seen a huge growth in MIR PIC building blocks. However, there is still a need for the development of MIR reconfigurable photonics to enable powerful on-chip optical systems and new functionalities. In this paper, we present an MIR (3.7~4.1 μm wavelength range) MEMS reconfiguration approach using the suspended silicon waveguide platform on the silicon-on-insulator. With the sub-wavelength grating claddings, the photonic waveguide can be well integrated with the MEMS actuator, thus offering low-loss, energy-efficient, and effective reconfiguration. We present a simulation study on the waveguide design and depict the MEMS-integration approach. Moreover, we experimentally report the suspended waveguide with propagation loss (−2.9 dB/cm) and bending loss (−0.076 dB each). The suspended waveguide coupler is experimentally investigated. In addition, we validate the proposed optical MEMS approach using a reconfigurable ring resonator design. In conclusion, we experimentally demonstrate the proposed waveguide platform’s capability for MIR MEMS-reconfigurable photonics, which empowers the MIR on-chip optical systems for various applications. Full article

(This article belongs to the Special Issue Feature Papers of Micromachines in Materials and Processing 2021)

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13 pages, 2508 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

New Method for Preparing Small-Caliber Artificial Blood Vessel with Controllable Microstructure on the Inner Wall Based on Additive Material Composite Molding

by Junchao Hu, Zhian Jian, Chunxiang Lu, Na Liu, Tao Yue, Weixia Lan and Yuanyuan Liu

Micromachines 2021, 12(11), 1312; https://doi.org/10.3390/mi12111312 - 26 Oct 2021

Cited by 9 | Viewed by 3724

Abstract

The diameter of most blood vessels in cardiovascular and peripheral vascular system is less than 6 mm. Because the inner diameter of such vessels is small, a built-in stent often leads to thrombosis and other problems. It is an important goal to replace [...] Read more.

The diameter of most blood vessels in cardiovascular and peripheral vascular system is less than 6 mm. Because the inner diameter of such vessels is small, a built-in stent often leads to thrombosis and other problems. It is an important goal to replace it directly with artificial vessels. This paper creatively proposed a preparation method of a small-diameter artificial vascular graft which can form a controllable microstructure on the inner wall and realize a multi-material composite. On the one hand, the inner wall of blood vessels containing direct writing structure is constructed by electrostatic direct writing and micro-imprinting technology to regulate cell behavior and promote endothelialization; on the other hand, the outer wall of blood vessels was prepared by electrospinning PCL to ensure the stability of mechanical properties of composite grafts. By optimizing the key parameters of the graft, a small-diameter artificial blood vessel with controllable microstructure on the inner wall is finally prepared. The corresponding performance characterization experimental results show that it has advantages in structure, mechanical properties, and promoting endothelialization. Full article

(This article belongs to the Special Issue Micro/Nano Devices for Blood Analysis, Volume II)

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14 pages, 51434 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Improving the Performance of the ToGoFET Probe: Advances in Design, Fabrication, and Signal Processing

by Hoontaek Lee, Junsoo Kim, Kumjae Shin and Wonkyu Moon

Micromachines 2021, 12(11), 1303; https://doi.org/10.3390/mi12111303 - 23 Oct 2021

Viewed by 2210

Abstract

We report recent improvements of the tip-on-gate of field-effect-transistor (ToGoFET) probe used for capacitive measurement. Probe structure, fabrication, and signal processing were modified. The inbuilt metal-oxide-semiconductor field-effect-transistor (MOSFET) was redesigned to ensure reliable probe operation. Fabrication was based on the standard complementary metal-oxide-semiconductor [...] Read more.

We report recent improvements of the tip-on-gate of field-effect-transistor (ToGoFET) probe used for capacitive measurement. Probe structure, fabrication, and signal processing were modified. The inbuilt metal-oxide-semiconductor field-effect-transistor (MOSFET) was redesigned to ensure reliable probe operation. Fabrication was based on the standard complementary metal-oxide-semiconductor (CMOS) process, and trench formation and the channel definition were modified. Demodulation of the amplitude-modulated drain current was varied, enhancing the signal-to-noise ratio. The I-V characteristics of the inbuilt MOSFET reflect the design and fabrication modifications, and measurement of a buried electrode revealed improved ToGoFET imaging performance. The minimum measurable value was enhanced 20-fold. Full article

(This article belongs to the Special Issue Functional Probes for Scanning Probe Microscopy)

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24 pages, 25265 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Flexohand: A Hybrid Exoskeleton-Based Novel Hand Rehabilitation Device

by Tanvir Ahmed, Md Assad-Uz-Zaman, Md Rasedul Islam, Drew Gottheardt, Erin McGonigle, Brahim Brahmi and Mohammad Habibur Rahman

Micromachines 2021, 12(11), 1274; https://doi.org/10.3390/mi12111274 - 20 Oct 2021

Cited by 14 | Viewed by 5056

Abstract

Home-based hand rehabilitation has excellent potential as it may reduce patient dropouts due to travel, transportation, and insurance constraints. Being able to perform exercises precisely, accurately, and in a repetitive manner, robot-aided portable devices have gained much traction these days in hand rehabilitation. [...] Read more.

Home-based hand rehabilitation has excellent potential as it may reduce patient dropouts due to travel, transportation, and insurance constraints. Being able to perform exercises precisely, accurately, and in a repetitive manner, robot-aided portable devices have gained much traction these days in hand rehabilitation. However, existing devices fall short in allowing some key natural movements, which are crucial to achieving full potential motion in performing activities of daily living. Firstly, existing exoskeleton type devices often restrict or suffer from uncontrolled wrist and forearm movement during finger exercises due to their setup of actuation and transmission mechanism. Secondly, they restrict passive metacarpophalangeal (MCP) abduction–adduction during MCP flexion–extension motion. Lastly, though a few of them can provide isolated finger ROM, none of them can offer isolated joint motion as per therapeutic need. All these natural movements are crucial for effective robot-aided finger rehabilitation. To bridge these gaps, in this research, a novel lightweight robotic device, namely “Flexohand”, has been developed for hand rehabilitation. A novel compliant mechanism has been developed and included in Flexohand to compensate for the passive movement of MCP abduction–adduction. The isolated and composite digit joint flexion–extension has been achieved by integrating a combination of sliding locks for IP joints and a wire locking system for finger MCP joints. Besides, the intuitive design of Flexohand inherently allows wrist joint movement during hand digit exercises. Experiments of passive exercises involving isolated joint motion, composite joint motions of individual fingers, and isolated joint motion of multiple fingers have been conducted to validate the functionality of the developed device. The experimental results show that Flexohand addresses the limitations of existing robot-aided hand rehabilitation devices. Full article

(This article belongs to the Special Issue Wearable Robotics)

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25 pages, 5882 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Reliability of MEMS in Shock Environments: 2000–2020

by Tianfang Peng and Zheng You

Micromachines 2021, 12(11), 1275; https://doi.org/10.3390/mi12111275 - 20 Oct 2021

Cited by 23 | Viewed by 5702

Abstract

The reliability of MEMS in shock environments is a complex area which involves structural dynamics, fracture mechanics, and system reliability theory etc. With growth in the use of MEMS in automotive, IoT, aerospace and other harsh environments, there is a need for an [...] Read more.

The reliability of MEMS in shock environments is a complex area which involves structural dynamics, fracture mechanics, and system reliability theory etc. With growth in the use of MEMS in automotive, IoT, aerospace and other harsh environments, there is a need for an in-depth understanding of the reliability of MEMS in shock environments. Despite the contributions of many articles that have overviewed the reliability of MEMS panoramically, a review paper that specifically focuses on the reliability research of MEMS in shock environments is, to date, absent. This paper reviews studies which examine the reliability of MEMS in shock environments from 2000 to 2020 in six sub-areas, which are: (i) response model of microstructure, (ii) shock experimental progresses, (iii) shock resistant microstructures, (iv) reliability quantification models of microstructure, (v) electronics-system-level reliability, and (vi) the coupling phenomenon of shock with other factors. This paper fills the gap around overviews of MEMS reliability in shock environments. Through the framework of these six sub-areas, we propose some directions potentially worthy of attention for future research. Full article

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12 pages, 3447 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Microfluidic Bioreactor Made of Cyclo-Olefin Polymer for Observing On-Chip Platelet Production

by Hiroki Kumon, Shinya Sakuma, Sou Nakamura, Hisataka Maruyama, Koji Eto and Fumihito Arai

Micromachines 2021, 12(10), 1253; https://doi.org/10.3390/mi12101253 - 15 Oct 2021

Cited by 7 | Viewed by 3297

Abstract

We previously proposed a microfluidic bioreactor with glass–Si–glass layers to evaluate the effect of the fluid force on platelet (PLT) production and fabricated a three-dimensional (3D) microchannel by combining grayscale photolithography and deep reactive ion etching. However, a challenge remains in observing the [...] Read more.

We previously proposed a microfluidic bioreactor with glass–Si–glass layers to evaluate the effect of the fluid force on platelet (PLT) production and fabricated a three-dimensional (3D) microchannel by combining grayscale photolithography and deep reactive ion etching. However, a challenge remains in observing the detailed process of PLT production owing to the low visibility of the microfluidic bioreactor. In this paper, we present a transparent microfluidic bioreactor made of cyclo-olefin polymer (COP) with which to observe the process of platelet-like particle (PLP) production under a bright-field, which allows us to obtain image data at a high sampling rate. We succeeded in fabricating the COP microfluidic bioreactor with a 3D microchannel. We investigated the bonding strength of COP-COP layers and confirmed the effectiveness of the microfluidic bioreactor. Results of on-chip PLP production using immortalized megakaryocyte cell lines (imMKCLs) derived from human-induced pluripotent stem cells show that the average total number of produced PLPs per imMKCL was 17.6 PLPs/imMKCL, which is comparable to that of our previous glass–Si–glass microfluidic bioreactor (17.4 PLPs/imMKCL). We succeeded in observing PLP production under a bright-field using the presented microfluidic bioreactor and confirmed that PLP fragmented in a narrow area of proplatelet-like protrusions. Full article

(This article belongs to the Special Issue 3D Biomedical Microdevices)

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11 pages, 2266 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Transparent and Flexible Vibration Sensor Based on a Wheel-Shaped Hybrid Thin Membrane

by Siyoung Lee, Eun Kwang Lee, Eunho Lee and Geun Yeol Bae

Micromachines 2021, 12(10), 1246; https://doi.org/10.3390/mi12101246 - 14 Oct 2021

Cited by 3 | Viewed by 3297

Abstract

With the advent of human–machine interaction and the Internet of Things, wearable and flexible vibration sensors have been developed to detect human voices and surrounding vibrations transmitted to humans. However, previous wearable vibration sensors have limitations in the sensing performance, such as frequency [...] Read more.

With the advent of human–machine interaction and the Internet of Things, wearable and flexible vibration sensors have been developed to detect human voices and surrounding vibrations transmitted to humans. However, previous wearable vibration sensors have limitations in the sensing performance, such as frequency response, linearity of sensitivity, and esthetics. In this study, a transparent and flexible vibration sensor was developed by incorporating organic/inorganic hybrid materials into ultrathin membranes. The sensor exhibited a linear and high sensitivity (20 mV/g) and a flat frequency response (80–3000 Hz), which are attributed to the wheel-shaped capacitive diaphragm structure fabricated by exploiting the high processability and low stiffness of the organic material SU-8 and the high conductivity of the inorganic material ITO. The sensor also has sufficient esthetics as a wearable device because of the high transparency of SU-8 and ITO. In addition, the temperature of the post-annealing process after ITO sputtering was optimized for the high transparency and conductivity. The fabricated sensor showed significant potential for use in transparent healthcare devices to monitor the vibrations transmitted from hand-held vibration tools and in a skin-attachable vocal sensor. Full article

(This article belongs to the Special Issue Hybrid Organic Electronics: Material, Structure and Application)

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10 pages, 1311 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

A Parallelized Nanofluidic Device for High-Throughput Optical DNA Mapping of Bacterial Plasmids

by Sriram KK, Yii-Lih Lin, Tsegaye Sewunet, Marie Wrande, Linus Sandegren, Christian G. Giske and Fredrik Westerlund

Micromachines 2021, 12(10), 1234; https://doi.org/10.3390/mi12101234 - 11 Oct 2021

Cited by 5 | Viewed by 3514

Abstract

Optical DNA mapping (ODM) has developed into an important technique for DNA analysis, where single DNA molecules are sequence-specifically labeled and stretched, for example, in nanofluidic channels. We have developed an ODM assay to analyze bacterial plasmids—circular extrachromosomal DNA that often carry genes [...] Read more.

Optical DNA mapping (ODM) has developed into an important technique for DNA analysis, where single DNA molecules are sequence-specifically labeled and stretched, for example, in nanofluidic channels. We have developed an ODM assay to analyze bacterial plasmids—circular extrachromosomal DNA that often carry genes that make bacteria resistant to antibiotics. As for most techniques, the next important step is to increase throughput and automation. In this work, we designed and fabricated a nanofluidic device that, together with a simple automation routine, allows parallel analysis of up to 10 samples at the same time. Using plasmids encoding extended-spectrum beta-lactamases (ESBL), isolated from Escherichia coli and Klebsiella pneumoniae, we demonstrate the multiplexing capabilities of the device when it comes to both many samples in parallel and different resistance genes. As a final example, we combined the device with a novel protocol for rapid cultivation and extraction of plasmids from fecal samples collected from patients. This combined protocol will make it possible to analyze many patient samples in one device already on the day the sample is collected, which is an important step forward for the ODM analysis of plasmids in clinical diagnostics. Full article

(This article belongs to the Special Issue Micro/Nano Fabrication for Life Sciences)

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20 pages, 2219 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Autonomously Propelled Colloids for Penetration and Payload Delivery in Complex Extracellular Matrices

by Shrishti Singh and Jeffrey L. Moran

Micromachines 2021, 12(10), 1216; https://doi.org/10.3390/mi12101216 - 6 Oct 2021

Cited by 3 | Viewed by 2977

Abstract

For effective treatment of diseases such as cancer or fibrosis, it is essential to deliver therapeutic agents such as drugs to the diseased tissue, but these diseased sites are surrounded by a dense network of fibers, cells, and proteins known as the extracellular [...] Read more.

For effective treatment of diseases such as cancer or fibrosis, it is essential to deliver therapeutic agents such as drugs to the diseased tissue, but these diseased sites are surrounded by a dense network of fibers, cells, and proteins known as the extracellular matrix (ECM). The ECM forms a barrier between the diseased cells and blood circulation, the main route of administration of most drug delivery nanoparticles. Hence, a stiff ECM impedes drug delivery by limiting the transport of drugs to the diseased tissue. The use of self-propelled particles (SPPs) that can move in a directional manner with the application of physical or chemical forces can help in increasing the drug delivery efficiency. Here, we provide a comprehensive look at the current ECM models in use to mimic the in vivo diseased states, the different types of SPPs that have been experimentally tested in these models, and suggest directions for future research toward clinical translation of SPPs in diverse biomedical settings. Full article

(This article belongs to the Special Issue X-fluidics at the Micro/Nanoscale)

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18 pages, 14588 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Performance Evaluation of a Magnetically Driven Microrobot for Targeted Drug Delivery

by Zhuocong Cai, Qiang Fu, Songyuan Zhang, Chunliu Fan, Xi Zhang, Jian Guo and Shuxiang Guo

Micromachines 2021, 12(10), 1210; https://doi.org/10.3390/mi12101210 - 3 Oct 2021

Cited by 21 | Viewed by 3880

Abstract

Given that the current microrobot cannot achieve fixed-point and quantitative drug application in the gastrointestinal (GI) tract, a targeted drug delivery microrobot is proposed, and its principle and characteristics are studied. Through the control of an external magnetic field, it can actively move [...] Read more.

Given that the current microrobot cannot achieve fixed-point and quantitative drug application in the gastrointestinal (GI) tract, a targeted drug delivery microrobot is proposed, and its principle and characteristics are studied. Through the control of an external magnetic field, it can actively move to the affected area to realize the targeted drug delivery function. The microrobot has a cam structure connected with a radially magnetized permanent magnet, which can realize two movement modes: movement and targeted drug delivery. Firstly, the magnetic actuated capsule microrobotic system (MACMS) is analyzed. Secondly, the dynamic model and quantitative drug delivery model of the targeted drug delivery microrobot driven by the spiral jet structure are established, and the motion characteristics of the targeted drug delivery microrobot are simulated and analyzed by the method of Computational Fluid Dynamics (CFD). Finally, the whole process of the targeted drug delivery task of the microrobot is simulated. The results show that the targeted drug delivery microrobot can realize basic movements such as forward, backward, fixed-point parking and drug delivery through external magnetic field control, which lays the foundation for gastrointestinal diagnosis and treatment. Full article

(This article belongs to the Special Issue Micromachines in Medical Devices, Prosthetics, Diagnostics, Therapeutics and Equipment)

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15 pages, 11855 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Solution for Mass Production of High-Throughput Digital Microfluidic Chip Based on a-Si TFT with In-Pixel Boost Circuit

by Feng Qin, Kaidi Zhang, Baiquan Lin, Ping Su, Zhenyu Jia, Kerui Xi, Jiandong Ye and Shulin Gu

Micromachines 2021, 12(10), 1199; https://doi.org/10.3390/mi12101199 - 30 Sep 2021

Cited by 16 | Viewed by 3876

Abstract

As one of the most popular research hotspot of lab-on-chip, digital microfluidic (DMF) technology based on the principle of electrowetting has unique advantages of high-precision, low cost and programmable control. However, due to the limitation of electrodes number, the throughput is hard to [...] Read more.

As one of the most popular research hotspot of lab-on-chip, digital microfluidic (DMF) technology based on the principle of electrowetting has unique advantages of high-precision, low cost and programmable control. However, due to the limitation of electrodes number, the throughput is hard to further upgrade. Therefore, active matrix electrowetting-on-dielectric (AM-EWOD) technology is a solution to acquire larger scale of driving electrodes. However, the process of manufacturing of AM-EWOD based on thin-film-transistor (TFT) is complex and expensive. Besides, the driving voltage of DMF chip is usually much higher than that of common display products.In this paper, a solution for mass production of AM-EWOD based on amorphous silicon (a-Si) is provided. Samples of 32 × 32 matrix AM-EWOD chips was designed and manufactured. A boost circuit was integrated into the pixel, which can raise the pixel voltage up by about 50%. Customized designed Printed Circuit Board (PCB) was used to supply the timing signals and driving voltage to make the motion of droplets programmable. The process of moving, mixing and generation of droplets was demonstrated.The minimum voltage in need was about 20 V and a velocity of up to 96 mm/s was achieved. Such an DMF device with large-scale matrix and low driving voltage will be very suitable for POCT applications. Full article

(This article belongs to the Special Issue Microfluidic Systems for Diagnostic Applications)

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13 pages, 5465 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Efficiency Enhancement of Electro-Adsorption Desalination Using Iron Oxide Nanoparticle-Incorporated Activated Carbon Nanocomposite

by Ahmed S. Yasin, Ahmed Yousef Mohamed, Donghyun Kim, Sungmin Yoon, Howon Ra and Kyubock Lee

Micromachines 2021, 12(10), 1148; https://doi.org/10.3390/mi12101148 - 24 Sep 2021

Cited by 7 | Viewed by 2617

Abstract

Capacitive deionization (CDI) technology is currently considered a potential candidate for brackish water desalination. In this study, we designed iron oxide nanoparticle-incorporated activated carbon (AC/Fe₂O₃) via a facile and cost-effective hydrothermal process. The as-synthesized material was characterized using several [...] Read more.

Capacitive deionization (CDI) technology is currently considered a potential candidate for brackish water desalination. In this study, we designed iron oxide nanoparticle-incorporated activated carbon (AC/Fe₂O₃) via a facile and cost-effective hydrothermal process. The as-synthesized material was characterized using several techniques and tested as electrodes in CDI applications. We found that the distinctive properties of the AC/Fe₂O₃ electrode, i.e., high wettability, high surface area, unique structural morphology, and high conductivity, resulted in promising CDI performance. The electrosorptive capacity of the AC/Fe₂O₃ nanocomposite reached 6.76 mg g⁻¹ in the CDI process, with a high specific capacitance of 1157.5 F g⁻¹ at 10 mV s⁻¹ in a 1 M NaCl electrolyte. This study confirms the potential use of AC/Fe₂O₃ nanocomposites as viable electrode materials in CDI and other electrochemical applications. Full article

(This article belongs to the Special Issue Engineering Micro/Nanostructured Electrodes for Electrochemical Systems)

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12 pages, 2331 KiB

Open AccessFeature PaperEditor’s ChoiceOpinion

Next-Generation Imaging Techniques: Functional and Miniaturized Optical Lenses Based on Metamaterials and Metasurfaces

by Dasol Lee, Minkyung Kim and Junsuk Rho

Micromachines 2021, 12(10), 1142; https://doi.org/10.3390/mi12101142 - 23 Sep 2021

Cited by 10 | Viewed by 3944

Abstract

A variety of applications using miniaturized optical lenses can be found among rapidly evolving technologies. From smartphones and cameras in our daily life to augmented and virtual reality glasses for the recent trends of the untact era, miniaturization of optical lenses permits the [...] Read more.

A variety of applications using miniaturized optical lenses can be found among rapidly evolving technologies. From smartphones and cameras in our daily life to augmented and virtual reality glasses for the recent trends of the untact era, miniaturization of optical lenses permits the development of many types of compact devices. Here, we highlight the importance of ultrasmall and ultrathin lens technologies based on metamaterials and metasurfaces. Focusing on hyperlenses and metalenses that can replace or be combined with the existing conventional lenses, we review the state-of-art of research trends and discuss their limitations. We also cover applications that use miniaturized imaging devices. The miniaturized imaging devices are expected to be an essential foundation for next-generation imaging techniques. Full article

(This article belongs to the Section A：Physics)

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20 pages, 2725 KiB

Open AccessFeature PaperEditor’s ChoiceReview

The Fusion of Microfluidics and Optics for On-Chip Detection and Characterization of Microalgae

by Xinqi Zheng, Xiudong Duan, Xin Tu, Shulan Jiang and Chaolong Song

Micromachines 2021, 12(10), 1137; https://doi.org/10.3390/mi12101137 - 22 Sep 2021

Cited by 16 | Viewed by 3892

Abstract

It has been demonstrated that microalgae play an important role in the food, agriculture and medicine industries. Additionally, the identification and counting of the microalgae are also a critical step in evaluating water quality, and some lipid-rich microalgae species even have the potential [...] Read more.

It has been demonstrated that microalgae play an important role in the food, agriculture and medicine industries. Additionally, the identification and counting of the microalgae are also a critical step in evaluating water quality, and some lipid-rich microalgae species even have the potential to be an alternative to fossil fuels. However, current technologies for the detection and analysis of microalgae are costly, labor-intensive, time-consuming and throughput limited. In the past few years, microfluidic chips integrating optical components have emerged as powerful tools that can be used for the analysis of microalgae with high specificity, sensitivity and throughput. In this paper, we review recent optofluidic lab-on-chip systems and techniques used for microalgal detection and characterization. We introduce three optofluidic technologies that are based on fluorescence, Raman spectroscopy and imaging-based flow cytometry, each of which can achieve the determination of cell viability, lipid content, metabolic heterogeneity and counting. We analyze and summarize the merits and drawbacks of these micro-systems and conclude the direction of the future development of the optofluidic platforms applied in microalgal research. Full article

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10 pages, 2227 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Micro-Prism Patterned Remote Phosphor Film for Enhanced Luminous Efficiency and Color Uniformity of Phosphor-Converted Light-Emitting Diodes

by Jiadong Yu, Shudong Yu, Ting Fu and Yong Tang

Micromachines 2021, 12(9), 1117; https://doi.org/10.3390/mi12091117 - 17 Sep 2021

Cited by 4 | Viewed by 3007

Abstract

In this work, we propose micro-prism patterned remote phosphor (RP) films to enhance both luminous efficiency and color uniformity (CU) of remote phosphor-converted light-emitting diodes (rpc-LEDs) simultaneously. On the incident surface of the RP film, one micro-prism film is used to extract backward [...] Read more.

In this work, we propose micro-prism patterned remote phosphor (RP) films to enhance both luminous efficiency and color uniformity (CU) of remote phosphor-converted light-emitting diodes (rpc-LEDs) simultaneously. On the incident surface of the RP film, one micro-prism film is used to extract backward light by double reflection. On the exit surface, the other micro-prism film is adopted to retain blue light inside the RP film, thus enhancing the phosphor excitation. Experimental results show that double prism-patterned RP (DP-RP) film configuration shows a luminous flux of 55.16 lm, which is 45.1% higher than that of RP film configuration at 300 mA. As regards the CU, the DP-RP film configuration reduces the angular CIE-x and CIE-y standard variations by 68% and 69.32%, respectively, compared with the pristine device. Moreover, the DP-RP film configuration shows excellent color stability under varying driving currents. Since micro-prism films can be easily fabricated by a roll-to-roll process, the micro-prism patterned RP film can be an alternative to a conventional RP layer to enable the practical application of rpc-LEDs. Full article

(This article belongs to the Special Issue Microsystem for Electronic Devices)

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10 pages, 3265 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

P-Doped Carbon Quantum Dots with Antibacterial Activity

by Shuiqin Chai, Lijia Zhou, Shuchen Pei, Zhiyuan Zhu and Bin Chen

Micromachines 2021, 12(9), 1116; https://doi.org/10.3390/mi12091116 - 16 Sep 2021

Cited by 61 | Viewed by 6108

Abstract

It is a major challenge to effectively inhibit microbial pathogens in the treatment of infectious diseases. Research on the application of nanomaterials as antibacterial agents has evidenced their great potential for the remedy of infectious disease. Among these nanomaterials, carbon quantum dots (CQDs) [...] Read more.

It is a major challenge to effectively inhibit microbial pathogens in the treatment of infectious diseases. Research on the application of nanomaterials as antibacterial agents has evidenced their great potential for the remedy of infectious disease. Among these nanomaterials, carbon quantum dots (CQDs) have attracted much attention owing to their unique optical properties and high biosafety. In this work, P-doped CQDs were prepared by simple hydrothermal treatment of m-aminophenol and phosphoric acid with fluorescence emission at 501 nm when excited at 429 nm. The P-doped CQDs showed effective antibacterial activity against Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus). The minimal inhibitory concentrations (MICs) of P-doped CQD were 1.23 mg/mL for E. coli and 1.44 mg/mL for S. aureus. Furthermore, the morphologies of E. coli cells were damaged and S. aureus became irregular when treated with the P-doped CQDs. The results of zeta potential analysis demonstrated that the P-doped CQDs inhibit antibacterial activity and destroy the structure of bacteria by electronic interaction. In combination, the results of this study indicate that the as-prepared P-doped CQDs can be a promising candidate for the treatment of bacterial infections. Full article

(This article belongs to the Special Issue Flexible Sensors and Actuators for Biomedicine)

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13 pages, 2243 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Physiological and Behavioral Effects of SiO₂ Nanoparticle Ingestion on Daphnia magna

by Youngsam Kim, Afshin Samadi, Eun Heui Gwag, Jayoung Park, Minjeong Kwak, Jihoon Park, Tae Geol Lee and Young Jun Kim

Micromachines 2021, 12(9), 1105; https://doi.org/10.3390/mi12091105 - 14 Sep 2021

Cited by 14 | Viewed by 3489

Abstract

The increasingly widespread use of engineered nanoparticles in medical, industrial, and food applications has raised concerns regarding their potential toxicity to humans and the environment. Silicon dioxide nanoparticles (SiO₂ NPs), which have relatively low direct toxicity, have been increasingly applied in both [...] Read more.

The increasingly widespread use of engineered nanoparticles in medical, industrial, and food applications has raised concerns regarding their potential toxicity to humans and the environment. Silicon dioxide nanoparticles (SiO₂ NPs), which have relatively low direct toxicity, have been increasingly applied in both consumer products and biomedical applications, leading to significantly higher exposure for humans and the environment. We carried out a toxicity assessment of SiO₂ NPs using the common water flea D. magna by focusing on physiological and behavioral indicators such as heart rate, swimming performance, and growth. Exposure to SiO₂ NPs did not produce acute or chronic toxicity at limited concentrations (<100 μg/mL), but did have statistically significant negative effects on heart rate, swimming distance, and body size. The use of fluorescein isothiocyanate in a silica matrix allowed the tracing and visualization of clear SiO₂ NP accumulation in D. magna, which was confirmed by ICP-MS. Although exposure to SiO₂ NPs seemed to affect cardiac and swimming performance, such end-point experiments may be insufficient to fully understand the toxicity of these nanoparticles. However, the physiological and behavioral changes shown here suggest potential adverse effects on the aquatic environment by substances previously considered nontoxic. Full article

(This article belongs to the Special Issue Nano Korea 2021)

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13 pages, 3230 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Distinct Roles of Tensile and Compressive Stresses in Graphitizing and Properties of Carbon Nanofibers

by Yujia Liu, Edmund Lau, Dario Mager, Marc J. Madou and Maziar Ghazinejad

Micromachines 2021, 12(9), 1096; https://doi.org/10.3390/mi12091096 - 11 Sep 2021

Cited by 4 | Viewed by 2674

Abstract

It is generally accepted that inducing molecular alignment in a polymer precursor via mechanical stresses influences its graphitization during pyrolysis. However, our understanding of how variations of the imposed mechanics can influence pyrolytic carbon microstructure and functionality is inadequate. Developing such insight is [...] Read more.

It is generally accepted that inducing molecular alignment in a polymer precursor via mechanical stresses influences its graphitization during pyrolysis. However, our understanding of how variations of the imposed mechanics can influence pyrolytic carbon microstructure and functionality is inadequate. Developing such insight is consequential for different aspects of carbon MEMS manufacturing and applicability, as pyrolytic carbons are the main building blocks of MEMS devices. Herein, we study the outcomes of contrasting routes of stress-induced graphitization by providing a comparative analysis of the effects of compressive stress versus standard tensile treatment of PAN-based carbon precursors. The results of different materials characterizations (including scanning electron microscopy, Raman and X-ray photoelectron spectroscopies, as well as high-resolution transmission electron microscopy) reveal that while subjecting precursor molecules to both types of mechanical stresses will induce graphitization in the resulting pyrolytic carbon, this effect is more pronounced in the case of compressive stress. We also evaluated the mechanical behavior of three carbon types, namely compression-induced (CIPC), tension-induced (TIPC), and untreated pyrolytic carbon (PC) by Dynamic Mechanical Analysis (DMA) of carbon samples in their as-synthesized mat format. Using DMA, the elastic modulus, ultimate tensile strength, and ductility of CIPC and TIPC films are determined and compared with untreated pyrolytic carbon. Both stress-induced carbons exhibit enhanced stiffness and strength properties over untreated carbons. The compression-induced films reveal remarkably larger mechanical enhancement with the elastic modulus 26 times higher and tensile strength 2.85 times higher for CIPC compared to untreated pyrolytic carbon. However, these improvements come at the expense of lowered ductility for compression-treated carbon, while tension-treated carbon does not show any loss of ductility. The results provided by this report point to the ways that the carbon MEMS industry can improve and revise the current standard strategies for manufacturing and implementing carbon-based micro-devices. Full article

(This article belongs to the Special Issue C-MEMS: Microstructure, Shapes, and Applications in Carbon)

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15 pages, 5091 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Additive Manufacturing of Textured FePrCuB Permanent Magnets

by Dagmar Goll, Felix Trauter, Ralf Loeffler, Thomas Gross and Gerhard Schneider

Micromachines 2021, 12(9), 1056; https://doi.org/10.3390/mi12091056 - 31 Aug 2021

Cited by 13 | Viewed by 3594

Abstract

Permanent magnets based on FePrCuB were realized on a laboratory scale through additive manufacturing (laser powder bed fusion, L-PBF) and book mold casting (reference). A well-adjusted two-stage heat treatment of the as-cast/as-printed FePrCuB alloys produces hard magnetic properties without the need for subsequent [...] Read more.

Permanent magnets based on FePrCuB were realized on a laboratory scale through additive manufacturing (laser powder bed fusion, L-PBF) and book mold casting (reference). A well-adjusted two-stage heat treatment of the as-cast/as-printed FePrCuB alloys produces hard magnetic properties without the need for subsequent powder metallurgical processing. This resulted in a coercivity of 0.67 T, remanence of 0.67 T and maximum energy density of 69.8 kJ/m³ for the printed parts. While the annealed book-mold-cast FePrCuB alloys are easy-plane permanent magnets (BMC magnet), the printed magnets are characterized by a distinct, predominantly directional microstructure that originated from the AM process and was further refined during heat treatment. Due to the higher degree of texturing, the L-PBF magnet has a 26% higher remanence compared to the identically annealed BMC magnet of the same composition. Full article

(This article belongs to the Special Issue Laser Additive Manufacturing of Metallic Materials)

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