Micromachines

15 pages, 3296 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Integration of Inkjet Printed Graphene as a Hole Transport Layer in Organic Solar Cells

by Julia Kastner, Flavia Tomarchio, Nicolas Decorde, Matthias Kehrer, Günter Hesser and Anita Fuchsbauer

Micromachines 2023, 14(10), 1858; https://doi.org/10.3390/mi14101858 - 28 Sep 2023

Cited by 2 | Viewed by 2047

Abstract

This work demonstrates the green production of a graphene ink for inkjet printing and its use as a hole transport layer (HTL) in an organic solar cell. Graphene as an HTL improves the selective hole extraction at the anode and prevents charge recombination [...] Read more.

This work demonstrates the green production of a graphene ink for inkjet printing and its use as a hole transport layer (HTL) in an organic solar cell. Graphene as an HTL improves the selective hole extraction at the anode and prevents charge recombination at the electronic interface and metal diffusion into the photoactive layer. Graphite was exfoliated in water, concentrated by iterative centrifugation, and characterized by Raman. The concentrated graphene ink was incorporated into inverted organic solar cells by inkjet printing on the active polymer in an ambient atmosphere. Argon plasma was used to enhance wetting of the polymer with the graphene ink during printing. The argon plasma treatment of the active polymer P3HT:PCBM was investigated by XPS, AFM and contact angle measurements. Efficiency and lifetime studies undertaken show that the device with graphene as HTL is fully functional and has good potential for an inkjet printable and flexible alternative to PEDOT:PSS. Full article

(This article belongs to the Special Issue Graphene-Based Metamaterial Solar Energy Devices)

► Show Figures

Figure 1

11 pages, 2798 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

A BTO/PVDF/PDMS Piezoelectric Tangential and Normal Force Sensor Inspired by a Wind Chime

by Chunyan Zhang, Xiaotian Zhang, Qiang Zhang, Shengbo Sang, Jianlong Ji, Runfang Hao and Yan Liu

Micromachines 2023, 14(10), 1848; https://doi.org/10.3390/mi14101848 - 27 Sep 2023

Cited by 3 | Viewed by 2187

Abstract

There is a growing demand for flexible pressure sensors in environmental monitoring and human–robot interaction robotics. A flexible and susceptible sensor can discriminate multidirectional pressure, thus effectively detecting signals of small environmental changes and providing solutions for personalized medicine. This paper proposes a [...] Read more.

There is a growing demand for flexible pressure sensors in environmental monitoring and human–robot interaction robotics. A flexible and susceptible sensor can discriminate multidirectional pressure, thus effectively detecting signals of small environmental changes and providing solutions for personalized medicine. This paper proposes a multidimensional force detection sensor inspired by a wind chime structure with a three-dimensional force structure to detect and analyze normal and shear forces in real time. The force-sensing structure of the sensor consists of an upper and lower membrane on a polydimethylsiloxane substrate and four surrounding cylinders. A piezoelectric hemisphere is made of BTO/PVDF/PDMS composite material. The sensor columns in the wind chime structure surround the piezoelectric layer in the middle. When pressure is applied externally, the sensor columns are connected to the piezoelectric layer with a light touch. The piezoelectric hemisphere generates a voltage signal. Due to the particular structure of the sensor, it can accurately capture multidimensional forces and identify the direction of the external force by analyzing the position of the sensor and the output voltage amplitude. The development of such sensors shows excellent potential for self-powered wearable sensors, human–computer interaction, electronic skin, and soft robotics applications. Full article

(This article belongs to the Special Issue Flexible and Wearable Sensors, 2nd Edition)

► Show Figures

Figure 1

18 pages, 3490 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Scalable Processing of Cyclic Olefin Copolymer (COC) Microfluidic Biochips

by Rodolfo G. Rodrigues, Pedro G. M. Condelipes, Rafaela R. Rosa, Virginia Chu and João Pedro Conde

Micromachines 2023, 14(10), 1837; https://doi.org/10.3390/mi14101837 - 27 Sep 2023

Cited by 5 | Viewed by 3366

Abstract

Microfluidics evolved with the appearance of polydimethylsiloxane (PDMS), an elastomer with a short processing time and the possibility for replication on a micrometric scale. Despite the many advantages of PDMS, there are well-known drawbacks, such as the hydrophobic surface, the absorption of small [...] Read more.

Microfluidics evolved with the appearance of polydimethylsiloxane (PDMS), an elastomer with a short processing time and the possibility for replication on a micrometric scale. Despite the many advantages of PDMS, there are well-known drawbacks, such as the hydrophobic surface, the absorption of small molecules, the low stiffness, relatively high cost, and the difficulty of scaling up the fabrication process for industrial production, creating a need for alternative materials. One option is the use of stiffer thermoplastics, such as the cyclic olefin copolymer (COC), which can be mass produced, have lower cost and possess excellent properties. In this work, a method to fabricate COC microfluidic structures was developed. The work was divided into process optimization and evaluation of material properties for application in microfluidics. In the processing step, moulding, sealing, and liquid handling aspects were developed and optimized. The resulting COC devices were evaluated from the point of view of molecular diffusion, burst pressure, temperature resistance, and susceptibility to surface treatments and these results were compared to PDMS devices. Lastly, a target DNA hybridization assay was performed showing the potential of the COC-based microfluidic device to be used in biosensing and Lab-on-a-Chip applications. Full article

(This article belongs to the Special Issue Novel Functional Materials and Techniques for 3D-Microfabrication)

► Show Figures

Figure 1

26 pages, 5246 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Microfluidic Mixing: A Physics-Oriented Review

by Sri Manikandan Saravanakumar and Paul-Vahe Cicek

Micromachines 2023, 14(10), 1827; https://doi.org/10.3390/mi14101827 - 25 Sep 2023

Cited by 23 | Viewed by 6539

Abstract

This comprehensive review paper focuses on the intricate physics of microfluidics and their application in micromixing techniques. Various methods for enhancing mixing in microchannels are explored, with a keen emphasis on the underlying fluid dynamics principles. Geometrical micromixers employ complex channel designs to [...] Read more.

This comprehensive review paper focuses on the intricate physics of microfluidics and their application in micromixing techniques. Various methods for enhancing mixing in microchannels are explored, with a keen emphasis on the underlying fluid dynamics principles. Geometrical micromixers employ complex channel designs to induce fluid–fluid interface distortions, yielding efficient mixing while retaining manufacturing simplicity. These methods synergize effectively with external techniques, showcasing promising potential. Electrohydrodynamics harnesses electrokinetic phenomena like electroosmosis, electrophoresis, and electrothermal effects. These methods offer dynamic control over mixing parameters via applied voltage, frequency, and electrode positioning, although power consumption and heating can be drawbacks. Acoustofluidics leverages acoustic waves to drive microstreaming, offering localized yet far-reaching effects. Magnetohydrodynamics, though limited in applicability to certain fluids, showcases potential by utilizing magnetic fields to propel mixing. Selecting an approach hinges on trade-offs among complexity, efficiency, and compatibility with fluid properties. Understanding the physics of fluid behavior and rationalizing these techniques aids in tailoring the most suitable micromixing solution. In a rapidly advancing field, this paper provides a consolidated understanding of these techniques, facilitating the informed choice of approach for specific microfluidic mixing needs. Full article

(This article belongs to the Special Issue Feature Papers from Micromachines Reviewers 2023)

► Show Figures

Figure 1

17 pages, 2046 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Rapid Production of Nanoscale Liposomes Using a 3D-Printed Reactor-In-A-Centrifuge: Formulation, Characterisation, and Super-Resolution Imaging

by Yongqing He, Davide De Grandi, Stanley Chandradoss, Gareth LuTheryn, Gianluca Cidonio, Ricardo Nunes Bastos, Valerio Pereno and Dario Carugo

Micromachines 2023, 14(9), 1763; https://doi.org/10.3390/mi14091763 - 12 Sep 2023

Cited by 7 | Viewed by 3284

Abstract

Nanoscale liposomes have been extensively researched and employed clinically for the delivery of biologically active compounds, including chemotherapy drugs and vaccines, offering improved pharmacokinetic behaviour and therapeutic outcomes. Traditional laboratory-scale production methods often suffer from limited control over liposome properties (e.g., size and [...] Read more.

Nanoscale liposomes have been extensively researched and employed clinically for the delivery of biologically active compounds, including chemotherapy drugs and vaccines, offering improved pharmacokinetic behaviour and therapeutic outcomes. Traditional laboratory-scale production methods often suffer from limited control over liposome properties (e.g., size and lamellarity) and rely on laborious multistep procedures, which may limit pre-clinical research developments and innovation in this area. The widespread adoption of alternative, more controllable microfluidic-based methods is often hindered by complexities and costs associated with device manufacturing and operation, as well as the short device lifetime and the relatively low liposome production rates in some cases. In this study, we demonstrated the production of liposomes comprising therapeutically relevant lipid formulations, using a cost-effective 3D-printed reactor-in-a-centrifuge (RIAC) device. By adjusting formulation- and production-related parameters, including the concentration of polyethylene glycol (PEG), temperature, centrifugation time and speed, and lipid concentration, the mean size of the produced liposomes could be tuned in the range of 140 to 200 nm. By combining selected experimental parameters, the method was capable of producing liposomes with a therapeutically relevant mean size of ~174 nm with narrow size distribution (polydispersity index, PDI ~0.1) at a production rate of >8 mg/min. The flow-through method proposed in this study has potential to become an effective and versatile laboratory-scale approach to simplify the synthesis of therapeutic liposomal formulations. Full article

(This article belongs to the Special Issue Feature Papers of Micromachines in Biology and Biomedicine 2022)

► Show Figures

Figure 1

25 pages, 5364 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Point-of-Care Devices for Viral Detection: COVID-19 Pandemic and Beyond

by Sumit K. Yadav, Damini Verma, Ujala Yadav, Ashish Kalkal, Nivedita Priyadarshini, Ashutosh Kumar and Kuldeep Mahato

Micromachines 2023, 14(9), 1744; https://doi.org/10.3390/mi14091744 - 7 Sep 2023

Cited by 17 | Viewed by 2819

Abstract

The pandemic of COVID-19 and its widespread transmission have made us realize the importance of early, quick diagnostic tests for facilitating effective cure and management. The primary obstacles encountered were accurately distinguishing COVID-19 from other illnesses including the flu, common cold, etc. While [...] Read more.

The pandemic of COVID-19 and its widespread transmission have made us realize the importance of early, quick diagnostic tests for facilitating effective cure and management. The primary obstacles encountered were accurately distinguishing COVID-19 from other illnesses including the flu, common cold, etc. While the polymerase chain reaction technique is a robust technique for the determination of SARS-CoV-2 in patients of COVID-19, there arises a high demand for affordable, quick, user-friendly, and precise point-of-care (POC) diagnostic in therapeutic settings. The necessity for available tests with rapid outcomes spurred the advancement of POC tests that are characterized by speed, automation, and high precision and accuracy. Paper-based POC devices have gained increasing interest in recent years because of rapid, low-cost detection without requiring external instruments. At present, microfluidic paper-based analysis devices have garnered public attention and accelerated the development of such POCT for efficient multistep assays. In the current review, our focus will be on the fabrication of detection modules for SARS-CoV-2. Here, we have included a discussion on various strategies for the detection of viral moieties. The compilation of these strategies would offer comprehensive insight into the detection of the causative agent preparedness for future pandemics. We also provide a descriptive outline for paper-based diagnostic platforms, involving the determination mechanisms, as well as a commercial kit for COVID-19 as well as their outlook. Full article

(This article belongs to the Special Issue Microfluidics and Biosensors for Point-of-Care Applications)

► Show Figures

Figure 1

22 pages, 6112 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Carbon-Based Electrochemical (Bio)sensors for the Detection of Carbendazim: A Review

by Constanza J. Venegas, Soledad Bollo and Paulina Sierra-Rosales

Micromachines 2023, 14(9), 1752; https://doi.org/10.3390/mi14091752 - 7 Sep 2023

Cited by 7 | Viewed by 2533

Abstract

Carbendazim, a fungicide widely used in agriculture, has been classified as a hazardous chemical by the World Health Organization due to its environmental persistence. It is prohibited in several countries; therefore, detecting it in food and environmental samples is highly necessary. A reliable, [...] Read more.

Carbendazim, a fungicide widely used in agriculture, has been classified as a hazardous chemical by the World Health Organization due to its environmental persistence. It is prohibited in several countries; therefore, detecting it in food and environmental samples is highly necessary. A reliable, rapid, and low-cost method uses electrochemical sensors and biosensors, especially those modified with carbon-based materials with good analytical performance. In this review, we summarize the use of carbon-based electrochemical (bio)sensors for detecting carbendazim in environmental and food matrixes, with a particular interest in the role of carbon materials. Focus on publications between 2018 and 2023 that have been describing the use of carbon nanotubes, carbon nitride, graphene, and its derivatives, and carbon-based materials as modifiers, emphasizing the analytical performance obtained, such as linear range, detection limit, selectivity, and the matrix where the detection was applied. Full article

(This article belongs to the Special Issue Carbon-Based Electrodes for Electrochemical Analysis and Detection)

► Show Figures

Figure 1

13 pages, 1422 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

High-Frequency Dielectrophoresis Reveals That Distinct Bio-Electric Signatures of Colorectal Cancer Cells Depend on Ploidy and Nuclear Volume

by Josie L. Duncan, Mathew Bloomfield, Nathan Swami, Daniela Cimini and Rafael V. Davalos

Micromachines 2023, 14(9), 1723; https://doi.org/10.3390/mi14091723 - 1 Sep 2023

Cited by 1 | Viewed by 2015

Abstract

Aneuploidy, or an incorrect chromosome number, is ubiquitous among cancers. Whole-genome duplication, resulting in tetraploidy, often occurs during the evolution of aneuploid tumors. Cancers that evolve through a tetraploid intermediate tend to be highly aneuploid and are associated with poor patient prognosis. The [...] Read more.

Aneuploidy, or an incorrect chromosome number, is ubiquitous among cancers. Whole-genome duplication, resulting in tetraploidy, often occurs during the evolution of aneuploid tumors. Cancers that evolve through a tetraploid intermediate tend to be highly aneuploid and are associated with poor patient prognosis. The identification and enrichment of tetraploid cells from mixed populations is necessary to understand the role these cells play in cancer progression. Dielectrophoresis (DEP), a label-free electrokinetic technique, can distinguish cells based on their intracellular properties when stimulated above 10 MHz, but DEP has not been shown to distinguish tetraploid and/or aneuploid cancer cells from mixed tumor cell populations. Here, we used high-frequency DEP to distinguish cell subpopulations that differ in ploidy and nuclear size under flow conditions. We used impedance analysis to quantify the level of voltage decay at high frequencies and its impact on the DEP force acting on the cell. High-frequency DEP distinguished diploid cells from tetraploid clones due to their size and intracellular composition at frequencies above 40 MHz. Our findings demonstrate that high-frequency DEP can be a useful tool for identifying and distinguishing subpopulations with nuclear differences to determine their roles in disease progression. Full article

(This article belongs to the Special Issue Micromachines for Dielectrophoresis, 3rd Edition)

► Show Figures

Figure 1

20 pages, 7459 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Virtual Coriolis-Force-Based Mode-Matching Micromachine-Optimized Tuning Fork Gyroscope without a Quadrature-Nulling Loop

by Yixuan Wu, Weizheng Yuan, Yanjun Xue, Honglong Chang and Qiang Shen

Micromachines 2023, 14(9), 1704; https://doi.org/10.3390/mi14091704 - 31 Aug 2023

Cited by 2 | Viewed by 1775

Abstract

A VCF-based mode-matching micromachine-optimized tuning fork gyroscope is proposed to not only maximize the scale factor of the device, but also avoid use of an additional quadrature-nulling loop to prevent structure complexity, pick-up electrode occupation, and coupling with a mode-matching loop. In detail, [...] Read more.

A VCF-based mode-matching micromachine-optimized tuning fork gyroscope is proposed to not only maximize the scale factor of the device, but also avoid use of an additional quadrature-nulling loop to prevent structure complexity, pick-up electrode occupation, and coupling with a mode-matching loop. In detail, a mode-matching, closed-loop system without a quadrature-nulling loop is established, and the corresponding convergence and matching error are quantitatively analyzed. The optimal straight beam of the gyro structure is then modeled to significantly reduce the quadrature coupling. The test results show that the frequency split is narrowed from 20 Hz to 0.014 Hz. The scale factor is improved 20.6 times and the bias instability (BI) is suppressed 3.28 times. The observed matching accuracy demonstrates that a mode matching system without a quadrature suppression loop is feasible and that the proposed device represents a competitive design for a mode-matching gyroscope. Full article

(This article belongs to the Special Issue MEMS Inertial Device)

► Show Figures

Figure 1

10 pages, 9758 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Nano Groove and Prism-Structured Triboelectric Nanogenerators

by Resul Saritas, Majed Al-Ghamdi, Taylan Memik Das, Omar Rasheed, Samed Kocer, Ahmet Gulsaran, Asif Abdullah Khan, Md Masud Rana, Mahmoud Khater, Muhammed Kayaharman, Dayan Ban, Mustafa Yavuz and Eihab Abdel-Rahman

Micromachines 2023, 14(9), 1707; https://doi.org/10.3390/mi14091707 - 31 Aug 2023

Cited by 2 | Viewed by 2662

Abstract

Enhancing the output power of triboelectric nanogenerators (TENGs) requires the creation of micro or nano-features on polymeric triboelectric surfaces to increase the TENGs’ effective contact area and, therefore, output power. We deploy a novel bench-top fabrication method called dynamic Scanning Probe Lithography (d-SPL) [...] Read more.

Enhancing the output power of triboelectric nanogenerators (TENGs) requires the creation of micro or nano-features on polymeric triboelectric surfaces to increase the TENGs’ effective contact area and, therefore, output power. We deploy a novel bench-top fabrication method called dynamic Scanning Probe Lithography (d-SPL) to fabricate massive arrays of uniform 1 cm long and 2.5 µm wide nano-features comprising a 600 nm deep groove (NG) and a 600 nm high triangular prism (NTP). The method creates both features simultaneously in the polymeric surface, thereby doubling the structured surface area. Six thousand pairs of NGs and NTPs were patterned on a

6 \times 5

cm

^{2}

PMMA substrate. It was then used as a mold to structure the surface of a 200 µm thick Polydimethylsiloxane (PDMS) layer. We show that the output power of the nano-structured TENG is significantly more than that of a TENG using flat PDMS films, at 12.2 mW compared to 2.2 mW, under the same operating conditions (a base acceleration amplitude of 0.8 g). Full article

(This article belongs to the Topic Advanced Energy Harvesting Technology)

► Show Figures

Figure 1

26 pages, 3442 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Novel Artificial Intelligence-Based Approaches for Ab Initio Structure Determination and Atomic Model Building for Cryo-Electron Microscopy

by Megan C. DiIorio and Arkadiusz W. Kulczyk

Micromachines 2023, 14(9), 1674; https://doi.org/10.3390/mi14091674 - 27 Aug 2023

Cited by 8 | Viewed by 3684

Abstract

Single particle cryo-electron microscopy (cryo-EM) has emerged as the prevailing method for near-atomic structure determination, shedding light on the important molecular mechanisms of biological macromolecules. However, the inherent dynamics and structural variability of biological complexes coupled with the large number of experimental images [...] Read more.

Single particle cryo-electron microscopy (cryo-EM) has emerged as the prevailing method for near-atomic structure determination, shedding light on the important molecular mechanisms of biological macromolecules. However, the inherent dynamics and structural variability of biological complexes coupled with the large number of experimental images generated by a cryo-EM experiment make data processing nontrivial. In particular, ab initio reconstruction and atomic model building remain major bottlenecks that demand substantial computational resources and manual intervention. Approaches utilizing recent innovations in artificial intelligence (AI) technology, particularly deep learning, have the potential to overcome the limitations that cannot be adequately addressed by traditional image processing approaches. Here, we review newly proposed AI-based methods for ab initio volume generation, heterogeneous 3D reconstruction, and atomic model building. We highlight the advancements made by the implementation of AI methods, as well as discuss remaining limitations and areas for future development. Full article

(This article belongs to the Special Issue Electron Microscopy and Single Molecule Studies of Biomolecular Structure and Dynamics)

► Show Figures

Figure 1

19 pages, 11308 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

A High-Precision Quartz Resonant Ultra-High Pressure Sensor with Integrated Pressure Conversion Structure

by Quanwei Zhang, Cun Li, Huafeng Li, Yan Liu, Jue Wang, Xiaolong Wang, Yuan Wang, Fabin Cheng, Haijun Han and Peng Zhang

Micromachines 2023, 14(9), 1657; https://doi.org/10.3390/mi14091657 - 25 Aug 2023

Cited by 7 | Viewed by 2808

Abstract

A quartz resonant pressure sensor is proposed for high-precision measurement of ultra-high pressure. The resonant unit realizes a push–pull differential layout, which restrains the common-mode interference factor, and the resonator is only subject to axial force. The pressure conversion unit is made in [...] Read more.

A quartz resonant pressure sensor is proposed for high-precision measurement of ultra-high pressure. The resonant unit realizes a push–pull differential layout, which restrains the common-mode interference factor, and the resonator is only subject to axial force. The pressure conversion unit is made in an integrated manner, avoiding output drift problems caused by residual stress and small gaps during assembly, welding, and other processes in sensor preparation. Theoretical and simulation analysis was conducted on the overall design scheme of the sensor in this paper, verifying the feasibility. Sensor prototypes were created and performance experiments were conducted. The experimental results show that the sensitivity of the ultra-high pressure sensor is 46.32 Hz/MPa at room temperature within the pressure range of 120 MPa, and the comprehensive accuracy is 0.0266%. The comprehensive accuracy of the sensor is better than 0.0288% FS in the full temperature range environment. This proves that the sensor scheme is suitable for high-precision and high-stability detection of ultra-high pressure, providing new solutions in special pressure measurement fields such as deep-sea and oil exploration. Full article

► Show Figures

Figure 1

25 pages, 11049 KiB

Open AccessEditor’s ChoiceReview

Four-Dimensional Micro/Nanorobots via Laser Photochemical Synthesis towards the Molecular Scale

by Yufeng Tao, Liansheng Lin, Xudong Ren, Xuejiao Wang, Xia Cao, Heng Gu, Yunxia Ye, Yunpeng Ren and Zhiming Zhang

Micromachines 2023, 14(9), 1656; https://doi.org/10.3390/mi14091656 - 24 Aug 2023

Cited by 6 | Viewed by 3007

Abstract

Miniaturized four-dimensional (4D) micro/nanorobots denote a forerunning technique associated with interdisciplinary applications, such as in embeddable labs-on-chip, metamaterials, tissue engineering, cell manipulation, and tiny robotics. With emerging smart interactive materials, static micro/nanoscale architectures have upgraded to the fourth dimension, evincing time-dependent shape/property mutation. [...] Read more.

Miniaturized four-dimensional (4D) micro/nanorobots denote a forerunning technique associated with interdisciplinary applications, such as in embeddable labs-on-chip, metamaterials, tissue engineering, cell manipulation, and tiny robotics. With emerging smart interactive materials, static micro/nanoscale architectures have upgraded to the fourth dimension, evincing time-dependent shape/property mutation. Molecular-level 4D robotics promises complex sensing, self-adaption, transformation, and responsiveness to stimuli for highly valued functionalities. To precisely control 4D behaviors, current-laser-induced photochemical additive manufacturing, such as digital light projection, stereolithography, and two-photon polymerization, is pursuing high-freeform shape-reconfigurable capacities and high-resolution spatiotemporal programming strategies, which challenge multi-field sciences while offering new opportunities. Herein, this review summarizes the recent development of micro/nano 4D laser photochemical manufacturing, incorporating active materials and shape-programming strategies to provide an envisioning of these miniaturized 4D micro/nanorobots. A comparison with other chemical/physical fabricated micro/nanorobots further explains the advantages and potential usage of laser-synthesized micro/nanorobots. Full article

(This article belongs to the Special Issue Laser Additive Manufacturing: Design, Materials, Processes and Applications, 2nd Edition)

► Show Figures

Figure 1

35 pages, 3159 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Flexible and Stretchable Pressure Sensors: From Basic Principles to State-of-the-Art Applications

by Thara Seesaard and Chatchawal Wongchoosuk

Micromachines 2023, 14(8), 1638; https://doi.org/10.3390/mi14081638 - 20 Aug 2023

Cited by 30 | Viewed by 12741

Abstract

Flexible and stretchable electronics have emerged as highly promising technologies for the next generation of electronic devices. These advancements offer numerous advantages, such as flexibility, biocompatibility, bio-integrated circuits, and light weight, enabling new possibilities in diverse applications, including e-textiles, smart lenses, healthcare technologies, [...] Read more.

Flexible and stretchable electronics have emerged as highly promising technologies for the next generation of electronic devices. These advancements offer numerous advantages, such as flexibility, biocompatibility, bio-integrated circuits, and light weight, enabling new possibilities in diverse applications, including e-textiles, smart lenses, healthcare technologies, smart manufacturing, consumer electronics, and smart wearable devices. In recent years, significant attention has been devoted to flexible and stretchable pressure sensors due to their potential integration with medical and healthcare devices for monitoring human activity and biological signals, such as heartbeat, respiratory rate, blood pressure, blood oxygen saturation, and muscle activity. This review comprehensively covers all aspects of recent developments in flexible and stretchable pressure sensors. It encompasses fundamental principles, force/pressure-sensitive materials, fabrication techniques for low-cost and high-performance pressure sensors, investigations of sensing mechanisms (piezoresistivity, capacitance, piezoelectricity), and state-of-the-art applications. Full article

(This article belongs to the Special Issue Feature Reviews in Micromachines 2023)

► Show Figures

Figure 1

15 pages, 2915 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Simultaneous Hydrostatic and Compressive Loading System for Mimicking the Mechanical Environment of Living Cartilage Tissue

by Minki Chang, Yosuke Takahashi, Kyosuke Miyahira, Yuma Omuro, Kevin Montagne, Ryusei Yamada, Junki Gondo, Yu Kambe, Masashi Yasuno, Noriyasu Masumoto, Takashi Ushida and Katsuko S. Furukawa

Micromachines 2023, 14(8), 1632; https://doi.org/10.3390/mi14081632 - 18 Aug 2023

Viewed by 1737

Abstract

In vivo, articular cartilage tissue is surrounded by a cartilage membrane, and hydrostatic pressure (HP) and compressive strain increase simultaneously with the compressive stress. However, it has been impossible to investigate the effects of simultaneous loading in vitro. In this study, a bioreactor [...] Read more.

In vivo, articular cartilage tissue is surrounded by a cartilage membrane, and hydrostatic pressure (HP) and compressive strain increase simultaneously with the compressive stress. However, it has been impossible to investigate the effects of simultaneous loading in vitro. In this study, a bioreactor capable of applying compressive stress under HP was developed to reproduce ex vivo the same physical loading environment found in cartilage. First, a HP stimulation unit was constructed to apply a cyclic HP pressure-resistant chamber by controlling a pump and valve. A compression-loading mechanism that can apply compressive stress using an electromagnetic force was implemented in the chamber. The synchronization between the compression and HP units was evaluated, and the stimulation parameters were quantitatively evaluated. Physiological HP and compressive strain were applied to the chondrocytes encapsulated in alginate and gelatin gels after applying high HP at 25 MPa, which induced damage to the chondrocytes. It was found that compressive stimulation increased the expression of genes related to osteoarthritis. Furthermore, the simultaneous application of compressive strain and HP, which is similar to the physiological environment in cartilage, had an inhibitory effect on the expression of genes related to osteoarthritis. HP alone also suppressed the expression of osteoarthritis-related genes. Therefore, the simultaneous hydrostatic and compressive stress-loading device developed to simulate the mechanical environment in vivo may be an important tool for elucidating the mechanisms of disease onset and homeostasis in cartilage. Full article

(This article belongs to the Topic Materials, Structure Designs and Device Fabrications for Highly Efficient/Long Lifetime Organic Light-Emitting Diodes)

► Show Figures

Figure 1

18 pages, 15136 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Biocompatible High-Resolution 3D-Printed Microfluidic Devices: Integrated Cell Chemotaxis Demonstration

by Mawla Boaks, Connor Roper, Matthew Viglione, Kent Hooper, Adam T. Woolley, Kenneth A. Christensen and Gregory P. Nordin

Micromachines 2023, 14(8), 1589; https://doi.org/10.3390/mi14081589 - 12 Aug 2023

Cited by 13 | Viewed by 3229

Abstract

We demonstrate a method to effectively 3D print microfluidic devices with high-resolution features using a biocompatible resin based on avobenzone as the UV absorber. Our method relies on spectrally shaping the 3D printer source spectrum so that it is fully overlapped by avobenzone’s [...] Read more.

We demonstrate a method to effectively 3D print microfluidic devices with high-resolution features using a biocompatible resin based on avobenzone as the UV absorber. Our method relies on spectrally shaping the 3D printer source spectrum so that it is fully overlapped by avobenzone’s absorption spectrum. Complete overlap is essential to effectively limit the optical penetration depth, which is required to achieve high out-of-plane resolution. We demonstrate the high resolution in practice by 3D printing 15

μ

m square pillars in a microfluidic chamber, where the pillars are separated by 7.7

μ

m and are printed with 5

μ

m layers. Furthermore, we show reliable membrane valves and pumps using the biocompatible resin. Valves are tested to 1,000,000 actuations with no observable degradation in performance. Finally, we create a concentration gradient generation (CG) component and utilize it in two device designs for cell chemotaxis studies. The first design relies on an external dual syringe pump to generate source and sink flows to supply the CG channel, while the second is a complete integrated device incorporating on-chip pumps, valves, and reservoirs. Both device types are seeded with adherent cells that are subjected to a chemoattractant CG, and both show clear evidence of chemotactic cellular migration. Moreover, the integrated device demonstrates cellular migration comparable to the external syringe pump device. This demonstration illustrates the effectiveness of our integrated chemotactic assay approach and high-resolution biocompatible resin 3D printing fabrication process. In addition, our 3D printing process has been tuned for rapid fabrication, as printing times for the two device designs are, respectively, 8 and 15 min. Full article

(This article belongs to the Special Issue 3D Printing of MEMS Technology, 3rd Edition)

► Show Figures

Figure 1

42 pages, 10600 KiB

Open AccessFeature PaperEditor’s ChoiceReview

A Comprehensive Review of Surface Acoustic Wave-Enabled Acoustic Droplet Ejection Technology and Its Applications

by Jia Ning, Yulin Lei, Hong Hu and Chenhui Gai

Micromachines 2023, 14(8), 1543; https://doi.org/10.3390/mi14081543 - 31 Jul 2023

Cited by 14 | Viewed by 4917

Abstract

This review focuses on the development of surface acoustic wave-enabled acoustic drop ejection (SAW-ADE) technology, which utilizes surface acoustic waves to eject droplets from liquids without touching the sample. The technology offers advantages such as high throughput, high precision, non-contact, and integration with [...] Read more.

This review focuses on the development of surface acoustic wave-enabled acoustic drop ejection (SAW-ADE) technology, which utilizes surface acoustic waves to eject droplets from liquids without touching the sample. The technology offers advantages such as high throughput, high precision, non-contact, and integration with automated systems while saving samples and reagents. The article first provides an overview of the SAW-ADE technology, including its basic theory, simulation verification, and comparison with other types of acoustic drop ejection technology. The influencing factors of SAW-ADE technology are classified into four categories: fluid properties, device configuration, presence of channels or chambers, and driving signals. The influencing factors discussed in detail from various aspects, such as the volume, viscosity, and surface tension of the liquid; the type of substrate material, interdigital transducers, and the driving waveform; sessile droplets and fluid in channels/chambers; and the power, frequency, and modulation of the input signal. The ejection performance of droplets is influenced by various factors, and their optimization can be achieved by taking into account all of the above factors and designing appropriate configurations. Additionally, the article briefly introduces the application scenarios of SAW-ADE technology in bioprinters and chemical analyses and provides prospects for future development. The article contributes to the field of microfluidics and lab-on-a-chip technology and may help researchers to design and optimize SAW-ADE systems for specific applications. Full article

► Show Figures

Figure 1

10 pages, 2367 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Double-Glued Multi-Focal Bionic Compound Eye Camera

by Xin Feng, Xiao Lv, Junyu Dong, Yongshun Liu, Fengfeng Shu and Yihui Wu

Micromachines 2023, 14(8), 1548; https://doi.org/10.3390/mi14081548 - 31 Jul 2023

Cited by 2 | Viewed by 1816

Abstract

Compound eye cameras are a vital component of bionics. Compound eye lenses are currently used in light field cameras, monitoring imaging, medical endoscopes, and other fields. However, the resolution of the compound eye lens is still low at the moment, which has an [...] Read more.

Compound eye cameras are a vital component of bionics. Compound eye lenses are currently used in light field cameras, monitoring imaging, medical endoscopes, and other fields. However, the resolution of the compound eye lens is still low at the moment, which has an impact on the application scene. Photolithography and negative pressure molding were used to create a double-glued multi-focal bionic compound eye camera in this study. The compound eye camera has 83 microlenses, with ommatidium diameters ranging from 400 μm to 660 μm, and a 92.3 degree field-of-view angle. The double-gluing structure significantly improves the optical performance of the compound eye lens, and the spatial resolution of the ommatidium is 57.00 lp mm⁻¹. Additionally, the measurement of speed is investigated. This double-glue compound eye camera has numerous potential applications in the military, machine vision, and other fields. Full article

► Show Figures

Figure 1

10 pages, 9365 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Non-Buffer Epi-AlGaN/GaN on SiC for High-Performance Depletion-Mode MIS-HEMTs Fabrication

by Penghao Zhang, Luyu Wang, Kaiyue Zhu, Qiang Wang, Maolin Pan, Ziqiang Huang, Yannan Yang, Xinling Xie, Hai Huang, Xin Hu, Saisheng Xu, Min Xu, Chen Wang, Chunlei Wu and David Wei Zhang

Micromachines 2023, 14(8), 1523; https://doi.org/10.3390/mi14081523 - 29 Jul 2023

Cited by 1 | Viewed by 1929

Abstract

A systematic study of epi-AlGaN/GaN on a SiC substrate was conducted through a comprehensive analysis of material properties and device performance. In this novel epitaxial design, an AlGaN/GaN channel layer was grown directly on the AlN nucleation layer, without the conventional doped thick [...] Read more.

A systematic study of epi-AlGaN/GaN on a SiC substrate was conducted through a comprehensive analysis of material properties and device performance. In this novel epitaxial design, an AlGaN/GaN channel layer was grown directly on the AlN nucleation layer, without the conventional doped thick buffer layer. Compared to the conventional epi-structures on the SiC and Si substrates, the non-buffer epi-AlGaN/GaN structure had a better crystalline quality and surface morphology, with reliable control of growth stress. Hall measurements showed that the novel structure exhibited comparable transport properties to the conventional epi-structure on the SiC substrate, regardless of the buffer layer. Furthermore, almost unchanged carrier distribution from room temperature to 150 °C indicated excellent two-dimensional electron gas (2DEG) confinement due to the pulling effect of the conduction band from the nucleation layer as a back-barrier. High-performance depletion-mode MIS-HEMTs were demonstrated with on-resistance of 5.84 Ω·mm and an output current of 1002 mA/mm. The dynamic characteristics showed a much smaller decrease in the saturation current (only ~7%), with a quiescent drain bias of 40 V, which was strong evidence of less electron trapping owing to the high-quality non-buffer AlGaN/GaN epitaxial growth. Full article

(This article belongs to the Special Issue Advanced Micro- and Nano-Manufacturing Technologies)

► Show Figures

Figure 1

13 pages, 9055 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Investigation on Wire Electrochemical Discharge Micro-Machining

by Weijing Kong, Ziyu Liu, Rudong Zhang and Yongbin Zeng

Micromachines 2023, 14(8), 1505; https://doi.org/10.3390/mi14081505 - 27 Jul 2023

Cited by 5 | Viewed by 2072

Abstract

With the development of MEMS, the machining demand and requirements for difficult-to-machine metal micro parts are getting higher. Microelectric discharge machining is an effective method to process difficult-to-machine metals. However, the recast layer caused by high temperatures in microelectric discharge machining affects the [...] Read more.

With the development of MEMS, the machining demand and requirements for difficult-to-machine metal micro parts are getting higher. Microelectric discharge machining is an effective method to process difficult-to-machine metals. However, the recast layer caused by high temperatures in microelectric discharge machining affects the properties of machined materials. Here, we propose the wire electrochemical discharge micro-machining (WECDMM) and develop a new electrolyte system, which removes the recast layer. In this study, the mechanism of WECDMM was elucidated. The electrolyte was optimized through a comparison experiment, and NaNO₃-glycol solution was determined as the best electrolyte. The influences of key process parameters including the conductivity of the electrolyte, pulse voltage, pulse-on time and wire feed rate were analyzed on the slit width, standard deviation, the radius of fillet at the entrance of the slit and roughness. Typical microstructures were machined, which verified the machining ability of WECDMM. Full article

(This article belongs to the Special Issue Micro- and Nanoscale Science, Technology and Engineering in Nanjing University of Aeronautics and Astronautics: Celebrating 70th Anniversary)

► Show Figures

Figure 1

16 pages, 13506 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Experimental Investigations upon Ultrasound Influence on Calefaction of AdBlue in Selective Catalytic Reduction Systems (SCR)

by Claudiu Marian Picus, Ioan Mihai and Cornel Suciu

Micromachines 2023, 14(8), 1488; https://doi.org/10.3390/mi14081488 - 25 Jul 2023

Cited by 1 | Viewed by 1399

Abstract

The present paper intends to provide an analysis of how the process of calefaction occurs in a selective catalytic reduction (SCR) system and the mechanisms by which the deposition of AdBlue crystals on a hot surface evolve. Experimentally, two aluminium samples heated to [...] Read more.

The present paper intends to provide an analysis of how the process of calefaction occurs in a selective catalytic reduction (SCR) system and the mechanisms by which the deposition of AdBlue crystals on a hot surface evolve. Experimentally, two aluminium samples heated to 200 °C were used, over which AdBlue droplets with different atomisation rates were dropped, maintaining the same dynamic flow parameters, in order to observe the influence of temperature effects on the degree of deposition of crystallised sediment on the surface. The authors proposed the use of calefaction in an ultrasonic environment to prevent deposition and to increase droplet fragmentation by a break-up process. To prove the performance of this method one sample was subjected to a normal flow regime while a second sample was exposed to ultrasound. Both samples were assembled on a magneto-strictive concentrator operating at a frequency of 20 kHz. The obtained results indicated that the sample exposed to ultrasound demonstrated lower urea crystallisation compared to the sample that was not exposed to this treatment. Thus, it can be seen that the proposed method of injecting AdBlue into an ultrasonic zone gives the desired results. Full article

(This article belongs to the Special Issue Heat Transfer and Fluid Flow in Microstructures)

► Show Figures

Figure 1

19 pages, 3113 KiB

Open AccessFeature PaperEditor’s ChoiceReview

MXene-Embedded Electrospun Polymeric Nanofibers for Biomedical Applications: Recent Advances

by Bishweshwar Pant, Mira Park and Allison A. Kim

Micromachines 2023, 14(7), 1477; https://doi.org/10.3390/mi14071477 - 23 Jul 2023

Cited by 14 | Viewed by 4116

Abstract

Recently MXenes has gained immense attention as a new and exciting class of two-dimensional material. Due to their unique layered microstructure, the presence of various functional groups at the surface, earth abundance, and attractive electrical, optical, and thermal properties, MXenes are considered promising [...] Read more.

Recently MXenes has gained immense attention as a new and exciting class of two-dimensional material. Due to their unique layered microstructure, the presence of various functional groups at the surface, earth abundance, and attractive electrical, optical, and thermal properties, MXenes are considered promising candidates for various applications such as energy, environmental, and biomedical. The ease of dispersibility and metallic conductivity of MXene render them promising candidates for use as fillers in polymer nanocomposites. MXene–polymer nanocomposites simultaneously benefit from the attractive properties of MXenes and the flexibility and facile processability of polymers. However, the potentiality of MXene to modify the electrospun nanofibers has been less studied. Understanding the interactions between polymeric nanofibers and MXenes is important to widen their role in biomedical applications. This review explores diverse methods of MXene synthesis, discusses our current knowledge of the various biological characteristics of MXene, and the synthesis of MXene incorporated polymeric nanofibers and their utilization in biomedical applications. The information discussed in this review serves to guide the future development and application of MXene–polymer nanofibers in biomedical fields. Full article

(This article belongs to the Special Issue Rise of MXenes: A New Family of Two-Dimensional (2D) Materials and Devices)

► Show Figures

Figure 1

12 pages, 3389 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Silicon Micromachined TSVs for Backside Interconnection of Ultra-Small Pressure Sensors

by Weiwen Feng, Peng Li, Haozhi Zhang, Ke Sun, Wei Li, Jiachou Wang, Heng Yang and Xinxin Li

Micromachines 2023, 14(7), 1448; https://doi.org/10.3390/mi14071448 - 19 Jul 2023

Cited by 5 | Viewed by 2790

Abstract

This paper presents an ultra-small absolute pressure sensor with a silicon-micromachined TSV backside interconnection for high-performance, high spatial resolution contact pressure sensing, including flexible-substrate applications. By exploiting silicon-micromachined TSVs that are compatibly fabricated with the pressure sensor, the sensing signals are emitted from [...] Read more.

This paper presents an ultra-small absolute pressure sensor with a silicon-micromachined TSV backside interconnection for high-performance, high spatial resolution contact pressure sensing, including flexible-substrate applications. By exploiting silicon-micromachined TSVs that are compatibly fabricated with the pressure sensor, the sensing signals are emitted from the chip backside, thereby eliminating the fragile leads on the front-side. Such a design achieves a flat and fully passivated top surface to protect the sensor from mechanical damage, for reliable direct-contact pressure sensing. A single-crystal silicon beam–island structure is designed to reduce the deflection of the pressure-sensing diaphragm and improve output linearity. Using our group-developed microholes interetch and sealing (MIS) micromachining technique, we fabricated ultra-small piezoresistive pressure sensors with the chip size as small as 0.4 mm × 0.6 mm, in which the polysilicon-micromachined TSVs transfer the signal interconnection from the front-side to the backside of the wafer, and the sensor chips can be densely packaged on the flexible substrate via the TSVs. The ultra-small pressure sensor has high sensitivity of 0.84 mV/kPa under 3.3 V of supply voltage and low nonlinearity of ±0.09% full scale (FS) in the measurement range of 120 kPa. The proposed pressure sensors with backside-interconnection TSVs hold promise for tactile sensing applications, including flexible sensing of wearable wristwatches. Full article

(This article belongs to the Section A：Physics)

► Show Figures

Figure 1

14 pages, 2985 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

High-Performance Low-Voltage Transparent Metal-Semiconductor-Metal Ultraviolet Photodetectors Based on Ultrathin Gold Asymmetric Interdigitated Electrodes

by Jianfeng Huang, Liu Yang and Sailing He

Micromachines 2023, 14(7), 1447; https://doi.org/10.3390/mi14071447 - 19 Jul 2023

Cited by 5 | Viewed by 2000

Abstract

A high-performance, low-voltage, transparent, metal-semiconductor-metal ultraviolet (UV) photodetector (PD) is proposed and experimentally demonstrated, based on gold (Au) asymmetric interdigitated (aIDT) electrodes with thicknesses well below 10 nm. A 7-nm-thick Au film, with a visible transmittance of 80.4% and a sheet resistance of [...] Read more.

A high-performance, low-voltage, transparent, metal-semiconductor-metal ultraviolet (UV) photodetector (PD) is proposed and experimentally demonstrated, based on gold (Au) asymmetric interdigitated (aIDT) electrodes with thicknesses well below 10 nm. A 7-nm-thick Au film, with a visible transmittance of 80.4% and a sheet resistance of 11.55 Ω/sq, is patterned into aIDT electrodes on a ZnO active layer, whose average visible transmittance is up to 74.3%. Meshing the pads further improves the overall transmittance of the device. Among all fabricated devices, the PD with the aIDT finger width ratio of 1:4 performs the best. Very low dark currents are achieved at 0, 0.5 and 1 V, allowing for high responsivities and specific detectivities to the UV light. It is also a fast device, especially under the biases of 0.5 and 1 V. The comprehensive performances are comparable and even superior to those of the reported devices. The asymmetric Schottky junctions induced by the aIDT electrodes under UV illumination are the main mechanism for the low-voltage operation of our transparent PD, which is promising to be applied widely. Full article

(This article belongs to the Special Issue Transparent Flexible Optoelectronic Devices)

► Show Figures

Figure 1

17 pages, 7014 KiB

Open AccessEditor’s ChoiceArticle

Superelastic NiTi Functional Components by High-Precision Laser Powder Bed Fusion Process: The Critical Roles of Energy Density and Minimal Feature Size

by Shuo Qu, Liqiang Wang, Junhao Ding, Jin Fu, Shiming Gao, Qingping Ma, Hui Liu, Mingwang Fu, Yang Lu and Xu Song

Micromachines 2023, 14(7), 1436; https://doi.org/10.3390/mi14071436 - 18 Jul 2023

Cited by 8 | Viewed by 2408

Abstract

Additive manufacturing (AM) was recently developed for building intricate devices in many fields. Especially for laser powder bed fusion (LPBF), its high-precision manufacturing capability and adjustable process parameters are involved in tailoring the performance of functional components. NiTi is well-known as smart material [...] Read more.

Additive manufacturing (AM) was recently developed for building intricate devices in many fields. Especially for laser powder bed fusion (LPBF), its high-precision manufacturing capability and adjustable process parameters are involved in tailoring the performance of functional components. NiTi is well-known as smart material utilized widely in biomedical fields thanks to its unique superelastic and shape-memory performance. However, the properties of NiTi are extremely sensitive to material microstructure, which is mainly determined by process parameters in LPBF. In this work, we choose a unique NiTi intricate component: a robotic cannula tip, in which material superelasticity is a crucial requirement as the optimal object. First, the process window was confirmed by printing thin walls and bulk structures. Then, for optimizing parameters precisely, a Gyroid-type sheet triply periodic minimal-surface (G-TPMS) structure was proposed as the standard test sample. Finally, we verified that when the wall thickness of the G-TPMS structure is smaller than 130 μm, the optimal energy density changes from 167 J/m³ to 140 J/m³ owing to the lower cooling rate of thinner walls. To sum up, this work puts forward a novel process optimization methodology and provides the processing guidelines for intricate NiTi components by LPBF. Full article

(This article belongs to the Special Issue Laser Additive Manufacturing: Design, Materials, Processes and Applications, 2nd Edition)

► Show Figures

Figure 1

12 pages, 13543 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

A Magnetic Millirobot Walks on Slippery Biological Surfaces for Targeted Cargo Delivery

by Moonkwang Jeong, Xiangzhou Tan, Felix Fischer and Tian Qiu

Micromachines 2023, 14(7), 1439; https://doi.org/10.3390/mi14071439 - 18 Jul 2023

Cited by 7 | Viewed by 2511

Abstract

Small-scale robots hold great potential for targeted cargo delivery in minimally invasive medicine. However, current robots often face challenges in locomoting efficiently on slippery biological tissue surfaces, especially when loaded with heavy cargo. Here, we report a magnetic millirobot that can walk on [...] Read more.

Small-scale robots hold great potential for targeted cargo delivery in minimally invasive medicine. However, current robots often face challenges in locomoting efficiently on slippery biological tissue surfaces, especially when loaded with heavy cargo. Here, we report a magnetic millirobot that can walk on rough and slippery biological tissues by anchoring itself on the soft tissue surface alternatingly with two feet and reciprocally rotating the body to move forward. We experimentally studied the locomotion, validated it with numerical simulations, and optimized the actuation parameters to fit various terrains and loading conditions. Furthermore, we developed a permanent magnet set-up to enable wireless actuation within a human-scale volume that allows precise control of the millirobot to follow complex trajectories, climb vertical walls, and carry cargo up to four times its own weight. Upon reaching the target location, it performs a deployment sequence to release the liquid drug into tissues. The robust gait of our millirobot on rough biological terrains, combined with its heavy load capacity, makes it a versatile and effective miniaturized vehicle for targeted cargo delivery. Full article

(This article belongs to the Special Issue Recent Advances in Microrobotics)

► Show Figures

Figure 1

11 pages, 3940 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Red Blood Cell Partitioning Using a Microfluidic Channel with Ladder Structure

by Toru Hyakutake, Yuya Tsutsumi, Yohei Miyoshi, Manabu Yasui, Tomoki Mizuno and Mizuki Tateno

Micromachines 2023, 14(7), 1421; https://doi.org/10.3390/mi14071421 - 14 Jul 2023

Cited by 1 | Viewed by 1696

Abstract

This study investigated the partitioning characteristics of red blood cells (RBCs) within capillaries, with a specific focus on ladder structures observed near the end of the capillaries. In vitro experiments were conducted using microfluidic channels with a ladder structure model comprising six bifurcating [...] Read more.

This study investigated the partitioning characteristics of red blood cells (RBCs) within capillaries, with a specific focus on ladder structures observed near the end of the capillaries. In vitro experiments were conducted using microfluidic channels with a ladder structure model comprising six bifurcating channels that exhibited an anti-parallel flow configuration. The effects of various factors, such as the parent channel width, distance between branches, and hematocrit, on RBC partitioning in bifurcating channels were evaluated. A decrease in the parent channel width resulted in an increase in the heterogeneity in the hematocrit distribution and a bias in the fractional RBC flux. Additionally, variations in the distance between branches affected the RBC distribution, with smaller distances resulting in greater heterogeneity. The bias of the RBC distribution in the microchannel cross section had a major effect on the RBC partitioning characteristics. The influence of hematocrit variations on the RBC distribution was also investigated, with lower hematocrit values leading to a more pronounced bias in the RBC distribution. Overall, this study provides valuable insights into RBC distribution characteristics in capillary networks, contributing to our understanding of the physiological mechanisms of RBC phase separation in the microcirculatory system. These findings have implications for predicting oxygen heterogeneity in tissues and could aid in the study of diseases associated with impaired microcirculation. Full article

(This article belongs to the Special Issue Microfluidic Device Fabrication and Cell Manipulation)

► Show Figures

Figure 1

16 pages, 6623 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Two−Dimensional Planar Penta−NiPN with Ultrahigh Carrier Mobility and Its Potential Application in NO and NO₂ Gas Sensing

by Hao Wang, Gang Li, Jun-Hui Yuan, Jiafu Wang, Pan Zhang and Yahui Shan

Micromachines 2023, 14(7), 1407; https://doi.org/10.3390/mi14071407 - 12 Jul 2023

Cited by 5 | Viewed by 1778

Abstract

Two−dimensional (2D) materials with novel structures and electronic properties are promising candidates for the next generation of micro− and nano−electronic devices. Herein, inspired by the recent experimental synthesis of penta−NiN₂ (ACS Nano, 2021, 15, 13539–13546), we propose for the first [...] Read more.

Two−dimensional (2D) materials with novel structures and electronic properties are promising candidates for the next generation of micro− and nano−electronic devices. Herein, inspired by the recent experimental synthesis of penta−NiN₂ (ACS Nano, 2021, 15, 13539–13546), we propose for the first time a novel ternary penta−NiPN monolayer with high stability by partial element substitution. Our predicted penta−NiPN monolayer is a quasi−direct bandgap (1.237 eV) semiconductor with ultrahigh carrier mobilities (10³–10⁵ cm²V⁻¹s⁻¹). Furthermore, we systematically studied the adsorption properties of common gas molecules (CO, CO₂, CH₄, H₂, H₂O, H₂S, N₂, NO, NO₂, NH₃, and SO₂) on the penta−NiPN monolayer and its effects on electronic properties. According to the energetic, geometric, and electronic analyses, the penta−NiPN monolayer is predicted to be a promising candidate for NO and NO₂ molecules. The excellent electronic properties of and the unique selectivity of the penta−NiPN monolayer for NO and NO₂ adsorption suggest that it has high potential in advanced electronics and gas sensing applications. Full article

(This article belongs to the Special Issue Recent Progress of Lab-on-a-Chip Assays)

► Show Figures

Figure 1

16 pages, 6127 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Ultra-Wideband and Narrowband Switchable, Bi-Functional Metamaterial Absorber Based on Vanadium Dioxide

by Xiaoyan Wang, Yanfei Liu, Yilin Jia, Ningning Su and Qiannan Wu

Micromachines 2023, 14(7), 1381; https://doi.org/10.3390/mi14071381 - 6 Jul 2023

Cited by 10 | Viewed by 2232

Abstract

A switchable ultra-wideband THz absorber based on vanadium dioxide was proposed, which consists of a lowermost gold layer, a PMI dielectric layer, and an insulating and surface vanadium dioxide layer. Based on the phase transition properties of vanadium dioxide, switching performance between ultra-broadband [...] Read more.

A switchable ultra-wideband THz absorber based on vanadium dioxide was proposed, which consists of a lowermost gold layer, a PMI dielectric layer, and an insulating and surface vanadium dioxide layer. Based on the phase transition properties of vanadium dioxide, switching performance between ultra-broadband and narrowband can achieve a near-perfect absorption. The constructed model was simulated and analyzed using finite element analysis. Simulations show that the absorption frequency of vanadium dioxide above 90% is between 3.8 THz and 15.6 THz when the vanadium dioxide is in the metallic state. The broadband absorber has an absorption bandwidth of 11.8 THz, is insensitive to TE and TM polarization, and has universal incidence angle insensitivity. When vanadium dioxide is in the insulating state, the narrowband absorber has a Q value as high as 1111 at a frequency of 13.89 THz when the absorption is more excellent than 99%. The absorber proposed in this paper has favorable symmetry properties, excellent TE and TM wave insensitivity, overall incidence angle stability, and the advantages of its small size, ultra-widebands and narrowbands, and elevated Q values. The designed absorber has promising applications in multifunctional devices, electromagnetic cloaking, and optoelectronic switches. Full article

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

► Show Figures

Figure 1

14 pages, 3020 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Screen Printed Particle-Based Microfluidics: Optimization and Exemplary Application for Heavy Metals Analysis

by Indrek Saar and Hanno Evard

Micromachines 2023, 14(7), 1369; https://doi.org/10.3390/mi14071369 - 4 Jul 2023

Cited by 3 | Viewed by 1792

Abstract

In this work, a screen-printing method was developed to create porous particle-based materials as layers with specifically designed shape to produce microfluidics systems. Among several tested binding agents, xanthan gum was found to be an excellent choice for a printing mixture thickener as [...] Read more.

In this work, a screen-printing method was developed to create porous particle-based materials as layers with specifically designed shape to produce microfluidics systems. Among several tested binding agents, xanthan gum was found to be an excellent choice for a printing mixture thickener as well as a durable binder for the resulting material. In addition to demonstrating control over the shape of the printed microfluidics chips, control over material thickness, wetting characteristics and general method accuracy were also investigated. The applicability of the introduced method was further demonstrated with a development of an exemplary microfluidics chip for quantitative detection of Fe (III), Ni (II), Cu (II), Cd (II), and Pb (II) from a mixed sample at millimolar levels. The novel approaches demonstrated in this article offer new perspective into creating multiplexed on-site chemical analysis tests. Full article

(This article belongs to the Special Issue Porous-Materials-Based Devices)

► Show Figures

Figure 1

17 pages, 10242 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Improvement of the Airflow Energy Harvester Based on the New Diamagnetic Levitation Structure

by Long Zhang, Hang Shao, Jiaxiang Zhang, Deping Liu, Kean C. Aw and Yufeng Su

Micromachines 2023, 14(7), 1374; https://doi.org/10.3390/mi14071374 - 4 Jul 2023

Cited by 1 | Viewed by 1535

Abstract

This paper presents an improved solution for the airflow energy harvester based on the push–pull diamagnetic levitation structure. A four-notch rotor is adopted to eliminate the offset of the floating rotor and substantially increase the energy conversion rate. The new rotor is a [...] Read more.

This paper presents an improved solution for the airflow energy harvester based on the push–pull diamagnetic levitation structure. A four-notch rotor is adopted to eliminate the offset of the floating rotor and substantially increase the energy conversion rate. The new rotor is a centrally symmetrical-shaped magnet, which ensures that it is not subjected to cyclically varying unbalanced radial forces, thus avoiding the rotor’s offset. Considering the output voltage and power of several types of rotors, the four-notch rotor was found to be optimal. Furthermore, with the four-notch rotor, the overall average increase in axial magnetic spring stiffness is 9.666% and the average increase in maximum monostable levitation space is 1.67%, but the horizontal recovery force is reduced by 3.97%. The experimental results show that at an airflow rate of 3000 sccm, the peak voltage and rotation speed of the four-notch rotor are 2.709 V and 21,367 rpm, respectively, which are 40.80% and 5.99% higher compared to the three-notch rotor. The experimental results were consistent with the analytical simulation. Based on the improvement, the energy conversion factor of the airflow energy harvester increased to 0.127 mV/rpm, the output power increased to 138.47 mW and the energy conversion rate increased to 58.14%, while the trend of the levitation characteristics also matched the simulation results. In summary, the solution proposed in this paper significantly improves the performance of the airflow energy harvester. Full article

(This article belongs to the Special Issue Energy Harvesters and Self-Powered Sensors for Smart Electronics, 2nd Edition)

► Show Figures

Graphical abstract

14 pages, 5466 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Piezotronic and Piezo-Phototronic Effects-Enhanced Core–Shell Structure-Based Nanowire Field-Effect Transistors

by Xiang Liu, Fangpei Li, Wenbo Peng, Quanzhe Zhu, Yangshan Li, Guodong Zheng, Hongyang Tian and Yongning He

Micromachines 2023, 14(7), 1335; https://doi.org/10.3390/mi14071335 - 29 Jun 2023

Cited by 3 | Viewed by 1661

Abstract

Piezotronic and piezo-phototronic effects have been extensively applied to modulate the performance of advanced electronics and optoelectronics. In this study, to systematically investigate the piezotronic and piezo-phototronic effects in field-effect transistors (FETs), a core–shell structure-based Si/ZnO nanowire heterojunction FET (HJFET) model was established [...] Read more.

Piezotronic and piezo-phototronic effects have been extensively applied to modulate the performance of advanced electronics and optoelectronics. In this study, to systematically investigate the piezotronic and piezo-phototronic effects in field-effect transistors (FETs), a core–shell structure-based Si/ZnO nanowire heterojunction FET (HJFET) model was established using the finite element method. We performed a sweep analysis of several parameters of the model. The results show that the channel current increases with the channel radial thickness and channel doping concentration, while it decreases with the channel length, gate doping concentration, and gate voltage. Under a tensile strain of 0.39‰, the saturation current change rate can reach 38%. Finally, another core–shell structure-based ZnO/Si nanowire HJFET model with the same parameters was established. The simulation results show that at a compressive strain of −0.39‰, the saturation current change rate is about 18%, which is smaller than that of the Si/ZnO case. Piezoelectric potential and photogenerated electromotive force jointly regulate the carrier distribution in the channel, change the width of the channel depletion layer and the channel conductivity, and thus regulate the channel current. The research results provide a certain degree of reference for the subsequent experimental design of Zn-based HJFETs and are applicable to other kinds of FETs. Full article

(This article belongs to the Special Issue Nanowires for Novel Technological Applications)

► Show Figures

Figure 1

19 pages, 11040 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Design and Modeling of a Miniature Hydraulic Motor for Powering a Cutting Tool for Minimally Invasive Procedures

by Manjeera Vinnakota, Kishan Bellur, Sandra L. Starnes and Mark J. Schulz

Micromachines 2023, 14(7), 1338; https://doi.org/10.3390/mi14071338 - 29 Jun 2023

Cited by 2 | Viewed by 2500

Abstract

Miniaturization of multifunctional instruments is key to evolving less invasive medical procedures. The current work outlines steps towards developing a miniature motor to power a cutting tool of a millimeter-scale robot/device (target outside diameter ~2 mm) for minimally invasive procedures. Multiple motor concepts [...] Read more.

Miniaturization of multifunctional instruments is key to evolving less invasive medical procedures. The current work outlines steps towards developing a miniature motor to power a cutting tool of a millimeter-scale robot/device (target outside diameter ~2 mm) for minimally invasive procedures. Multiple motor concepts were explored and ranked using a Pugh matrix. The single-rotor hydraulic design was deemed most viable for prototyping and scale-down to the target size. Prototypes were manufactured to be progressively smaller using additive manufacturing. The smallest prototype fabricated was 2:1 scale of the desired final size with a 2 mm outside diameter (OD) rotor and a device OD of 4 mm. The scaled prototypes with an 8 mm rotor were lab tested and achieved average speeds of 5000–6000 RPM at a flowrate of 15–18 mL/s and 45 PSI water pressure. Ansys CFX was used as a design tool to explore the parameter space and 3D transient simulations were implemented using the immersed solid method. The predicted rotor RPM from the modeling matched the experimental values within 3% error. The model was then used to develop performance curves for the miniature hydraulic motor. In summary, the single-rotor hydraulic design shows promise for miniaturization to the target 2 mm size. Full article

(This article belongs to the Special Issue Women’s Special Issue Series: Micromachines 2023)

► Show Figures

Figure 1

13 pages, 1073 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Ultra-Narrow Bandwidth Microwave Photonic Filter Implemented by Single Longitudinal Mode Parity Time Symmetry Brillouin Fiber Laser

by Jiaxin Hou, Yajun You, Yuan Liu, Kai Jiang, Xuefeng Han, Wenjun He, Wenping Geng, Yi Liu and Xiujian Chou

Micromachines 2023, 14(7), 1322; https://doi.org/10.3390/mi14071322 - 27 Jun 2023

Cited by 4 | Viewed by 2495

Abstract

In this paper, a novel microwave photonic filter (MPF) based on a single longitudinal mode Brillouin laser achieved by parity time (PT) symmetry mode selection is proposed, and its unparalleled ultra-narrow bandwidth as low as to sub-kHz together with simple and agile tuning [...] Read more.

In this paper, a novel microwave photonic filter (MPF) based on a single longitudinal mode Brillouin laser achieved by parity time (PT) symmetry mode selection is proposed, and its unparalleled ultra-narrow bandwidth as low as to sub-kHz together with simple and agile tuning performance is experimentally verified. The Brillouin fiber laser ring resonator is cascaded with a PT symmetric system to achieve this MPF. Wherein, the Brillouin laser resonator is excited by a 5 km single mode fiber to generate Brillouin gain, and the PT symmetric system is configured with Polarization Beam Splitter (PBS) and polarization controller (PC) to achieve PT symmetry. Thanks to the significant enhancement of the gain difference between the main mode and the edge mode when the polarization state PT symmetry system breaks, a single mode oscillating Brillouin laser is generated. Through the selective amplification of sideband modulated signals by ultra-narrow linewidth Brillouin single mode laser gain, the MPF with ultra-narrow single passband performance is obtained. By simply tuning the central wavelength of the stimulated Brillouin scattering (SBS) pumped laser to adjust the Brillouin oscillation frequency, the gain position of the Brillouin laser can be shifted, thereby achieving flexible tunability. The experimental results indicate that the MPF proposed in this paper achieves a single pass band narrow to 72 Hz and the side mode rejection ratio of more than 18 dB, with a center frequency tuning range of 0–20 GHz in the testing range of vector network analysis, which means that the MPF possesses ultra high spectral resolution and enormous potential application value in the domain of ultra fine microwave spectrum filtering such as radar imaging and electronic countermeasures. Full article

(This article belongs to the Special Issue Progress and Application of Ultra-Precision Laser Interferometry)

► Show Figures

Figure 1

11 pages, 3447 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Multi-Layered Bipolar Ionic Diode Working in Broad Range Ion Concentration

by Jaehyun Kim, Cong Wang and Jungyul Park

Micromachines 2023, 14(7), 1311; https://doi.org/10.3390/mi14071311 - 26 Jun 2023

Cited by 3 | Viewed by 2527

Abstract

Ion current rectification (ICR) is the ratio of ion current by forward bias to backward bias and is a critical indicator of diode performance. In previous studies, there have been many attempts to improve the performance of this ICR, but there is the [...] Read more.

Ion current rectification (ICR) is the ratio of ion current by forward bias to backward bias and is a critical indicator of diode performance. In previous studies, there have been many attempts to improve the performance of this ICR, but there is the intrinsic problem for geometric changes that induce ionic rectification due to fabrication problems. Additionally, the high ICR could be achieved in the narrow salt concentration range only. Here, we propose a multi-layered bipolar ionic diode based on an asymmetric nanochannel network membrane (NCNM), which is realized by soft lithography and self-assembly of homogenous-sized nanoparticles. Owing to the freely changeable geometry based on soft lithography, the ICR performance can be explored according to the variation of microchannel shape. The presented diode with multi-layered configuration shows strong ICR performance, and in a broad range of salt concentrations (0.1 mM~100 mM), steady ICR performance. It is interesting to note that when each anion-selective (AS) and cation-selective (CS) NCNM volume was similar to each optimized volume in a single-layered device, the maximum ICR was obtained. Multi-physics simulation, which reveals greater ionic concentration at the bipolar diode junction under forward bias and less depletion under backward in comparison to the single-layer scenario, supports this tendency as well. Additionally, under different frequencies and salt concentrations, a large-area hysteresis loop emerges, which indicates fascinating potential for electroosmotic pumps, memristors, biosensors, etc. Full article

(This article belongs to the Special Issue Micro/Nanostructures in Sensors and Actuators)

► Show Figures

Figure 1

17 pages, 7839 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Research on Intelligent Wheelchair Attitude-Based Adjustment Method Based on Action Intention Recognition

by Jianwei Cui, Zizheng Huang, Xiang Li, Linwei Cui, Yucheng Shang and Liyan Tong

Micromachines 2023, 14(6), 1265; https://doi.org/10.3390/mi14061265 - 17 Jun 2023

Cited by 7 | Viewed by 2752

Abstract

At present, research on intelligent wheelchairs mostly focuses on motion control, while research on attitude-based adjustment is relatively insufficient. The existing methods for adjusting wheelchair posture generally lack collaborative control and good human–machine collaboration. This article proposes an intelligent wheelchair posture-adjustment method based [...] Read more.

At present, research on intelligent wheelchairs mostly focuses on motion control, while research on attitude-based adjustment is relatively insufficient. The existing methods for adjusting wheelchair posture generally lack collaborative control and good human–machine collaboration. This article proposes an intelligent wheelchair posture-adjustment method based on action intention recognition by studying the relationship between the force changes on the contact surface between the human body and the wheelchair and the action intention. This method is applied to a multi-part adjustable electric wheelchair, which is equipped with multiple force sensors to collect pressure information from various parts of the passenger’s body. The upper level of the system converts the pressure data into the form of a pressure distribution map, extracts the shape features using the VIT deep learning model, identifies and classifies them, and ultimately identifies the action intentions of the passengers. Based on different action intentions, the electric actuator is controlled to adjust the wheelchair posture. After testing, this method can effectively collect the body pressure data of passengers, with an accuracy of over 95% for the three common intentions of lying down, sitting up, and standing up. The wheelchair can adjust its posture based on the recognition results. By adjusting the wheelchair posture through this method, users do not need to wear additional equipment and are less affected by the external environment. The target function can be achieved with simple learning, which has good human–machine collaboration and can solve the problem of some people having difficulty adjusting the wheelchair posture independently during wheelchair use. Full article

(This article belongs to the Special Issue Assistive Robots)

► Show Figures

Figure 1

16 pages, 2250 KiB

Open AccessFeature PaperEditor’s ChoiceReview

How Practical Are Fiber Supercapacitors for Wearable Energy Storage Applications?

by Parya Teymoory, Jingzhou Zhao and Caiwei Shen

Micromachines 2023, 14(6), 1249; https://doi.org/10.3390/mi14061249 - 14 Jun 2023

Cited by 9 | Viewed by 2791

Abstract

Future wearable electronics and smart textiles face a major challenge in the development of energy storage devices that are high-performing while still being flexible, lightweight, and safe. Fiber supercapacitors are one of the most promising energy storage technologies for such applications due to [...] Read more.

Future wearable electronics and smart textiles face a major challenge in the development of energy storage devices that are high-performing while still being flexible, lightweight, and safe. Fiber supercapacitors are one of the most promising energy storage technologies for such applications due to their excellent electrochemical characteristics and mechanical flexibility. Over the past decade, researchers have put in tremendous effort and made significant progress on fiber supercapacitors. It is now the time to assess the outcomes to ensure that this kind of energy storage device will be practical for future wearable electronics and smart textiles. While the materials, fabrication methods, and energy storage performance of fiber supercapacitors have been summarized and evaluated in many previous publications, this review paper focuses on two practical questions: Are the reported devices providing sufficient energy and power densities to wearable electronics? Are the reported devices flexible and durable enough to be integrated into smart textiles? To answer the first question, we not only review the electrochemical performance of the reported fiber supercapacitors but also compare them to the power needs of a variety of commercial electronics. To answer the second question, we review the general approaches to assess the flexibility of wearable textiles and suggest standard methods to evaluate the mechanical flexibility and stability of fiber supercapacitors for future studies. Lastly, this article summarizes the challenges for the practical application of fiber supercapacitors and proposes possible solutions. Full article

(This article belongs to the Special Issue Micro Supercapacitors for Energy Storage and Power Management)

► Show Figures

Figure 1

12 pages, 2127 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Integration of Microfluidic Chip and Probe with a Dual Pump System for Measurement of Single Cells Transient Response

by Xu Du, Shingo Kaneko, Hisataka Maruyama, Hirotaka Sugiura, Masaru Tsujii, Nobuyuki Uozumi and Fumihito Arai

Micromachines 2023, 14(6), 1210; https://doi.org/10.3390/mi14061210 - 7 Jun 2023

Cited by 4 | Viewed by 3107

Abstract

The integration of liquid exchange and microfluidic chips plays a critical role in the biomedical and biophysical fields as it enables the control of the extracellular environment and allows for the simultaneous stimulation and detection of single cells. In this study, we present [...] Read more.

The integration of liquid exchange and microfluidic chips plays a critical role in the biomedical and biophysical fields as it enables the control of the extracellular environment and allows for the simultaneous stimulation and detection of single cells. In this study, we present a novel approach for measuring the transient response of single cells using a system integrated with a microfluidic chip and a probe with a dual pump. The system was composed of a probe with a dual pump system, a microfluidic chip, optical tweezers, an external manipulator, an external piezo actuator, etc. Particularly, we incorporated the probe with the dual pump to allow for high-speed liquid change, and the localized flow control enabled a low disturbance contact force detection of single cells on the chip. Using this system, we measured the transient response of the cell swelling against the osmotic shock with a very fine time resolution. To demonstrate the concept, we first designed the double-barreled pipette, which was assembled with two piezo pumps to achieve a probe with the dual pump system, allowing for simultaneous liquid injection and suction. The microfluidic chip with on-chip probes was fabricated, and the integrated force sensor was calibrated. Second, we characterized the performance of the probe with the dual pump system, and the effect of the analysis position and area of the liquid exchange time was investigated. In addition, we optimized the applied injection voltage to achieve a complete concentration change, and the average liquid exchange time was achieved at approximately 3.33 ms. Finally, we demonstrated that the force sensor was only subjected to minor disturbances during the liquid exchange. This system was utilized to measure the deformation and the reactive force of Synechocystis sp. strain PCC 6803 in osmotic shock, with an average response time of approximately 16.33 ms. This system reveals the transient response of compressed single cells under millisecond osmotic shock which has the potential to characterize the accurate physiological function of ion channels. Full article

(This article belongs to the Special Issue Selected Papers from the 36th International Conference on Micro Electro Mechanical Systems (MEMS 2023))

► Show Figures

Figure 1

13 pages, 3078 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Comparison of Circular and Rectangular-Shaped Electrodes for Electrical Impedance Myography Measurements on Human Upper Arms

by Mohammad A. Ahad, Somen Baidya and Md. Nurul Tarek

Micromachines 2023, 14(6), 1179; https://doi.org/10.3390/mi14061179 - 31 May 2023

Cited by 4 | Viewed by 2282

Abstract

Electrical Impedance Myography (EIM) is a painless, noninvasive approach for assessing muscle conditions through the application of a high-frequency, low-intensity current to the muscle region of interest. However, besides muscle properties, EIM measurements vary significantly with changes in some other anatomical properties such [...] Read more.

Electrical Impedance Myography (EIM) is a painless, noninvasive approach for assessing muscle conditions through the application of a high-frequency, low-intensity current to the muscle region of interest. However, besides muscle properties, EIM measurements vary significantly with changes in some other anatomical properties such as subcutaneous skin-fat (SF) thickness and muscle girth, as well as non-anatomical factors, such as ambient temperature, electrode shape, inter-electrode distance, etc. This study has been conducted to compare the effects of different electrode shapes in EIM experiments, and to propose an acceptable configuration that is less dependent on factors other than the cellular properties of the muscle. Initially, a finite element model with two different kinds of electrode shapes, namely, rectangular (the conventional shape) and circular (the proposed shape) was designed for a subcutaneous fat thickness ranging from 5 mm to 25 mm. The study concludes, based on the FEM study, that replacing the conventional electrodes with our proposed electrodes can decrease the variation in EIM parameters due to changes in skin-fat thickness by 31.92%. EIM experiments on human subjects with these two kinds of electrode shapes validate our finite element simulation results, and show that circular electrodes can improve EIM effectiveness significantly, irrespective of muscle shape variation. Full article

(This article belongs to the Special Issue Prospects and Challenges of Biosensors towards Diagnostics of the Diseases and Health Monitoring)

► Show Figures

Figure 1

26 pages, 7501 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Revolutionizing Prosthetic Design with Auxetic Metamaterials and Structures: A Review of Mechanical Properties and Limitations

by Muhammad Faris Fardan, Bhre Wangsa Lenggana, U Ubaidillah, Seung-Bok Choi, Didik Djoko Susilo and Sohaib Zia Khan

Micromachines 2023, 14(6), 1165; https://doi.org/10.3390/mi14061165 - 31 May 2023

Cited by 11 | Viewed by 5597

Abstract

Prosthetics have come a long way since their inception, and recent advancements in materials science have enabled the development of prosthetic devices with improved functionality and comfort. One promising area of research is the use of auxetic metamaterials in prosthetics. Auxetic materials have [...] Read more.

Prosthetics have come a long way since their inception, and recent advancements in materials science have enabled the development of prosthetic devices with improved functionality and comfort. One promising area of research is the use of auxetic metamaterials in prosthetics. Auxetic materials have a negative Poisson’s ratio, which means that they expand laterally when stretched, unlike conventional materials, which contract laterally. This unique property allows for the creation of prosthetic devices that can better conform to the contours of the human body and provide a more natural feel. In this review article, we provide an overview of the current state of the art in the development of prosthetics using auxetic metamaterials. We discuss the mechanical properties of these materials, including their negative Poisson’s ratio and other properties that make them suitable for use in prosthetic devices. We also explore the limitations that currently exist in implementing these materials in prosthetic devices, including challenges in manufacturing and cost. Despite these challenges, the future prospects for the development of prosthetic devices using auxetic metamaterials are promising. Continued research and development in this field could lead to the creation of more comfortable, functional, and natural-feeling prosthetic devices. Overall, the use of auxetic metamaterials in prosthetics represents a promising area of research with the potential to improve the lives of millions of people around the world who rely on prosthetic devices. Full article

(This article belongs to the Special Issue Smart Material-Based Micromechatronics in Soft Robotics)

► Show Figures

Figure 1

14 pages, 5790 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Spiral Chiral Metamaterial Structure Shape for Optical Activity Improvements

by Kohei Maruyama, Miyako Mizuna, Takuya Kosuge, Yuki Takeda, Eiji Iwase and Tetsuo Kan

Micromachines 2023, 14(6), 1156; https://doi.org/10.3390/mi14061156 - 30 May 2023

Cited by 5 | Viewed by 2312

Abstract

We report on a spiral structure suitable for obtaining a large optical response. We constructed a structural mechanics model of the shape of the planar spiral structure when deformed and verified the effectiveness of the model. As a verification structure, we fabricated a [...] Read more.

We report on a spiral structure suitable for obtaining a large optical response. We constructed a structural mechanics model of the shape of the planar spiral structure when deformed and verified the effectiveness of the model. As a verification structure, we fabricated a large-scale spiral structure that operates in the GHz band by laser processing. Based on the GHz radio wave experiments, a more uniform deformation structure exhibited a higher cross-polarization component. This result suggests that uniform deformation structures can improve circular dichroism. Since large-scale devices enable speedy prototype verification, the obtained knowledge can be exported to miniaturized-scale devices, such as MEMS terahertz metamaterials. Full article

(This article belongs to the Special Issue Selected Papers from the 13th Symposium on Micro-Nano Science and Technology on Micromachines)

► Show Figures

Figure 1

9 pages, 13440 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Design of an Intelligent MEMS Safety and Arming Device with a Condition Feedback Function

by Kexin Wang, Tengjiang Hu, Yulong Zhao, Wei Ren and Yifei Wang

Micromachines 2023, 14(6), 1130; https://doi.org/10.3390/mi14061130 - 27 May 2023

Cited by 4 | Viewed by 2633

Abstract

A safety and arming device with a condition feedback function has been designed in this article to improve the intelligence and safety of ignition devices. The device achieves active control and recoverability by virtue of four groups of bistable mechanisms which consist of [...] Read more.

A safety and arming device with a condition feedback function has been designed in this article to improve the intelligence and safety of ignition devices. The device achieves active control and recoverability by virtue of four groups of bistable mechanisms which consist of two electrothermal actuators to drive a semi-circular barrier and a pawl. According to a specific operation sequence, the barrier is engaged by the pawl at the safety or the arming position. The four groups of bistable mechanisms are connected in parallel, and the device detects the contact resistance generated by the engagement of the barrier and pawl by the voltage division of an external resistor to determine the parallel number of the mechanism and give feedback on the device’s condition. The pawl as a safety lock can restrain the in-plane deformation of the barrier in the safety condition to improve the safety function of the device. An igniter (a NiCr bridge foil covered with different thicknesses of Al/CuO films) and boron/potassium nitrate (B/KNO₃, BPN) are assembled on both sides of the S&A device to verify the safety of the barrier. The test results show that the S&A device with a safety lock can realize the safety and arming functions when the thickness of the Al/CuO film is set to 80 μm and 100 μm. Full article

(This article belongs to the Special Issue MEMS/NEMS Sensors and Actuators, 2nd Edition)

► Show Figures

Figure 1

14 pages, 5162 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Stability Study of Multi-Level Grayscales Based on Driving Waveforms for Electrowetting Displays

by Wanzhen Xu, Zichuan Yi, Zhengxing Long, Hu Zhang, Jiaquan Jiang, Liming Liu, Feng Chi, Ding Tan and Huan Wang

Micromachines 2023, 14(6), 1123; https://doi.org/10.3390/mi14061123 - 26 May 2023

Cited by 4 | Viewed by 1612

Abstract

Electrowetting Display (EWD) is a new reflective display with an outstanding performance of color video playback. However, some problems still exist and affect its performance. For instance, oil backflow, oil splitting, and charge trapping phenomena may occur during the driving process of EWDs, [...] Read more.

Electrowetting Display (EWD) is a new reflective display with an outstanding performance of color video playback. However, some problems still exist and affect its performance. For instance, oil backflow, oil splitting, and charge trapping phenomena may occur during the driving process of EWDs, which would decrease its stability of multi-level grayscales. Therefore, an efficient driving waveform was proposed to solve these disadvantages. It consisted of a driving stage and a stabilizing stage. First, an exponential function waveform was used in the driving stage for driving the EWDs quickly. Then, an alternating current (AC) pulse signal waveform was used in the stabilizing stage to release the trapped positive charges of the insulating layer to improve display stability. A set of four level grayscale driving waveforms were designed by using the proposed method, and it was used in comparative experiments. The experiments showed that the proposed driving waveform could mitigate oil backflow and splitting effects. Compared to a traditional driving waveform, the luminance stability was increased by 8.9%, 5.9%, 10.9%, and 11.6% for the four level grayscales after 12 s, respectively. Full article

(This article belongs to the Special Issue Advances in Optoelectronic Devices, 2nd Edition)

► Show Figures

Graphical abstract

20 pages, 4113 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Laser-Formed Sensors with Electrically Conductive MWCNT Networks for Gesture Recognition Applications

by Natalia A. Nikitina, Dmitry I. Ryabkin, Victoria V. Suchkova, Artem V. Kuksin, Evgeny S. Pyankov, Levan P. Ichkitidze, Aleksey V. Maksimkin, Evgeny P. Kitsyuk, Ekaterina A. Gerasimenko, Dmitry V. Telyshev, Ivan Bobrinetskiy, Sergey V. Selishchev and Alexander Yu. Gerasimenko

Micromachines 2023, 14(6), 1106; https://doi.org/10.3390/mi14061106 - 24 May 2023

Cited by 8 | Viewed by 3166

Abstract

Currently, an urgent need in the field of wearable electronics is the development of flexible sensors that can be attached to the human body to monitor various physiological indicators and movements. In this work, we propose a method for forming an electrically conductive [...] Read more.

Currently, an urgent need in the field of wearable electronics is the development of flexible sensors that can be attached to the human body to monitor various physiological indicators and movements. In this work, we propose a method for forming an electrically conductive network of multi-walled carbon nanotubes (MWCNT) in a matrix of silicone elastomer to make stretchable sensors sensitive to mechanical strain. The electrical conductivity and sensitivity characteristics of the sensor were improved by using laser exposure, through the effect of forming strong carbon nanotube (CNT) networks. The initial electrical resistance of the sensors obtained using laser technology was ~3 kOhm (in the absence of deformation) at a low concentration of nanotubes of 3 wt% in composition. For comparison, in a similar manufacturing process, but without laser exposure, the active material had significantly higher values of electrical resistance, which was ~19 kOhm in this case. The laser-fabricated sensors have a high tensile sensitivity (gauge factor ~10), linearity of >0.97, a low hysteresis of 2.4%, tensile strength of 963 kPa, and a fast strain response of 1 ms. The low Young’s modulus values of ~47 kPa and the high electrical and sensitivity characteristics of the sensors made it possible to fabricate a smart gesture recognition sensor system based on them, with a recognition accuracy of ~94%. Data reading and visualization were performed using the developed electronic unit based on the ATXMEGA8E5-AU microcontroller and software. The obtained results open great prospects for the application of flexible CNT sensors in intelligent wearable devices (IWDs) for medical and industrial applications. Full article

(This article belongs to the Special Issue Flexible and Wearable Sensors)

► Show Figures

Figure 1

8 pages, 3540 KiB

Open AccessFeature PaperEditor’s ChoiceCommunication

Improving Performance of Al₂O₃/AlN/GaN MIS HEMTs via In Situ N₂ Plasma Annealing

by Mengyuan Sun, Luyu Wang, Penghao Zhang and Kun Chen

Micromachines 2023, 14(6), 1100; https://doi.org/10.3390/mi14061100 - 23 May 2023

Cited by 2 | Viewed by 2990

Abstract

A novel monocrystalline AlN interfacial layer formation method is proposed to improve the device performance of the fully recessed-gate Al₂O₃/AlN/GaN Metal-Insulator-Semiconductor High Electron Mobility Transistors (MIS-HEMTs), which is achieved by plasma-enhanced atomic layer deposition (PEALD) and in situ N [...] Read more.

A novel monocrystalline AlN interfacial layer formation method is proposed to improve the device performance of the fully recessed-gate Al₂O₃/AlN/GaN Metal-Insulator-Semiconductor High Electron Mobility Transistors (MIS-HEMTs), which is achieved by plasma-enhanced atomic layer deposition (PEALD) and in situ N₂ plasma annealing (NPA). Compared with the traditional RTA method, the NPA process not only avoids the device damage caused by high temperatures but also obtains a high-quality AlN monocrystalline film that avoids natural oxidation by in situ growth. As a contrast with the conventional PELAD amorphous AlN, C-V results indicated a significantly lower interface density of states (D_it) in a MIS C-V characterization, which could be attributed to the polarization effect induced by the AlN crystal from the X-ray Diffraction (XRD) and Transmission Electron Microscope (TEM) characterizations. The proposed method could reduce the subthreshold swing, and the Al₂O₃/AlN/GaN MIS-HEMTs were significantly enhanced with ~38% lower on-resistance at V_g = 10 V. What is more, in situ NPA provides a more stable threshold voltage (V_th) after a long gate stress time, and ΔV_th is inhibited by about 40 mV under V_g,stress = 10 V for 1000 s, showing great potential for improving Al₂O₃/AlN/GaN MIS-HEMT gate reliability. Full article

(This article belongs to the Special Issue Advanced Micro- and Nano-Manufacturing Technologies)

► Show Figures

Figure 1

14 pages, 3640 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

A Wireless, High-Quality, Soft and Portable Wrist-Worn System for sEMG Signal Detection

by Zekai Liang, Xuanqi Wang, Jun Guo, Yuanming Ye, Haoyang Zhang, Liang Xie, Kai Tao, Wen Zeng, Erwei Yin and Bowen Ji

Micromachines 2023, 14(5), 1085; https://doi.org/10.3390/mi14051085 - 21 May 2023

Cited by 6 | Viewed by 3130

Abstract

The study of wearable systems based on surface electromyography (sEMG) signals has attracted widespread attention and plays an important role in human–computer interaction, physiological state monitoring, and other fields. Traditional sEMG signal acquisition systems are primarily targeted at body parts that are not [...] Read more.

The study of wearable systems based on surface electromyography (sEMG) signals has attracted widespread attention and plays an important role in human–computer interaction, physiological state monitoring, and other fields. Traditional sEMG signal acquisition systems are primarily targeted at body parts that are not in line with daily wearing habits, such as the arms, legs, and face. In addition, some systems rely on wired connections, which impacts their flexibility and user-friendliness. This paper presents a novel wrist-worn system with four sEMG acquisition channels and a high common-mode rejection ratio (CMRR) greater than 120 dB. The circuit has an overall gain of 2492 V/V and a bandwidth of 15~500 Hz. It is fabricated using flexible circuit technologies and is encapsulated in a soft skin-friendly silicone gel. The system acquires sEMG signals at a sampling rate of over 2000 Hz with a 16-bit resolution and transmits data to a smart device via low-power Bluetooth. Muscle fatigue detection and four-class gesture recognition experiments (accuracy greater than 95%) were conducted to validate its practicality. The system has potential applications in natural and intuitive human–computer interaction and physiological state monitoring. Full article

(This article belongs to the Special Issue Wearable and Implantable Bio-MEMS Devices and Applications)

► Show Figures

Figure 1

13 pages, 8123 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Giant Magnetoimpedance Effect of Multilayered Thin Film Meanders Formed on Flexible Substrates

by Mengyu Liu, Zhenbao Wang, Ziqin Meng, Xuecheng Sun, Yong Huang, Yongbin Guo and Zhen Yang

Micromachines 2023, 14(5), 1002; https://doi.org/10.3390/mi14051002 - 6 May 2023

Cited by 3 | Viewed by 2900

Abstract

The giant magnetoimpedance effect of multilayered thin films under stress has great application prospects in magnetic sensing, but related studies are rarely reported. Therefore, the giant magnetoimpedance effects in multilayered thin film meanders under different stresses were thoroughly investigated. Firstly, multilayered FeNi/Cu/FeNi thin [...] Read more.

The giant magnetoimpedance effect of multilayered thin films under stress has great application prospects in magnetic sensing, but related studies are rarely reported. Therefore, the giant magnetoimpedance effects in multilayered thin film meanders under different stresses were thoroughly investigated. Firstly, multilayered FeNi/Cu/FeNi thin film meanders with the same thickness were manufactured on polyimide (PI) and polyester (PET) substrates by DC magnetron sputtering and MEMS technology. The characterization of meanders was analyzed by SEM, AFM, XRD, and VSM. The results show that multilayered thin film meanders on flexible substrates also have the advantages of good density, high crystallinity, and excellent soft magnetic properties. Then, we observed the giant magnetoimpedance effect under tensile and compressive stresses. The results show that the application of longitudinal compressive stress increases the transverse anisotropy and enhances the GMI effect of multilayered thin film meanders, while the application of longitudinal tensile stress yields the opposite result. The results provide novel solutions for the fabrication of more stable and flexible giant magnetoimpedance sensors, as well as for the development of stress sensors. Full article

(This article belongs to the Special Issue NEMS/MEMS Devices and Applications)

► Show Figures

Figure 1

19 pages, 6225 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Recent Advances on GaN-Based Micro-LEDs

by Youwei Zhang, Ruiqiang Xu, Qiushi Kang, Xiaoli Zhang and Zi-hui Zhang

Micromachines 2023, 14(5), 991; https://doi.org/10.3390/mi14050991 - 1 May 2023

Cited by 24 | Viewed by 9390

Abstract

GaN-based micro-size light-emitting diodes (µLEDs) have a variety of attractive and distinctive advantages for display, visible-light communication (VLC), and other novel applications. The smaller size of LEDs affords them the benefits of enhanced current expansion, fewer self-heating effects, and higher current density bearing [...] Read more.

GaN-based micro-size light-emitting diodes (µLEDs) have a variety of attractive and distinctive advantages for display, visible-light communication (VLC), and other novel applications. The smaller size of LEDs affords them the benefits of enhanced current expansion, fewer self-heating effects, and higher current density bearing capacity. Low external quantum efficiency (EQE) resulting from non-radiative recombination and quantum confined stark effect (QCSE) is a serious barrier for application of µLEDs. In this work, the reasons for the poor EQE of µLEDs are reviewed, as are the optimization techniques for improving the EQE of µLEDs. Full article

► Show Figures

Figure 1

14 pages, 3494 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Neurotoxicity of Silver Nanoparticles and Non-Linear Development of Adaptive Homeostasis with Age

by Anna A. Antsiferova, Marina Yu. Kopaeva, Vyacheslav N. Kochkin, Alexander A. Reshetnikov and Pavel K. Kashkarov

Micromachines 2023, 14(5), 984; https://doi.org/10.3390/mi14050984 - 30 Apr 2023

Cited by 10 | Viewed by 1839

Abstract

For the first time in the world, the behavioral functions of laboratory mammals exposed to silver nanoparticles were studied with regard to age. Silver nanoparticles coated with polyvinylpyrrolidone with a size of 8.7 nm were used in the present research as a potential [...] Read more.

For the first time in the world, the behavioral functions of laboratory mammals exposed to silver nanoparticles were studied with regard to age. Silver nanoparticles coated with polyvinylpyrrolidone with a size of 8.7 nm were used in the present research as a potential xenobiotic. Elder mice adapted to the xenobiotic better than the younger animals. Younger animals demonstrated more drastic anxiety than the elder ones. A hormetic effect of the xenobiotic in elder animals was observed. Thus, it is concluded that adaptive homeostasis non-linearly changes with age increase. Presumably, it may improve during the prime of life and start to decline just after a certain stage. This work demonstrates that age growth is not directly conjugated with the organism fading and pathology development. Oppositely, vitality and resistance to xenobiotics may even improve with age at least until the prime of life. Full article

(This article belongs to the Section B：Biology and Biomedicine)

► Show Figures

Figure 1

44 pages, 15284 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Polymeric and Paper-Based Lab-on-a-Chip Devices in Food Safety: A Review

by Athina-Marina Mitrogiannopoulou, Vasiliki Tselepi and Kosmas Ellinas

Micromachines 2023, 14(5), 986; https://doi.org/10.3390/mi14050986 - 30 Apr 2023

Cited by 25 | Viewed by 5655

Abstract

Food quality and safety are important to protect consumers from foodborne illnesses. Currently, laboratory scale analysis, which takes several days to complete, is the main way to ensure the absence of pathogenic microorganisms in a wide range of food products. However, new methods [...] Read more.

Food quality and safety are important to protect consumers from foodborne illnesses. Currently, laboratory scale analysis, which takes several days to complete, is the main way to ensure the absence of pathogenic microorganisms in a wide range of food products. However, new methods such as PCR, ELISA, or even accelerated plate culture tests have been proposed for the rapid detection of pathogens. Lab-on-chip (LOC) devices and microfluidics are miniaturized devices that can enable faster, easier, and at the point of interest analysis. Nowadays, methods such as PCR are often coupled with microfluidics, providing new LOC devices that can replace or complement the standard methods by offering highly sensitive, fast, and on-site analysis. This review’s objective is to present an overview of recent advances in LOCs used for the identification of the most prevalent foodborne and waterborne pathogens that put consumer health at risk. In particular, the paper is organized as follows: first, we discuss the main fabrication methods of microfluidics as well as the most popular materials used, and then we present recent literature examples for LOCs used for the detection of pathogenic bacteria found in water and other food samples. In the final section, we summarize our findings and also provide our point of view on the challenges and opportunities in the field. Full article

(This article belongs to the Special Issue Microfluidics for Food Science Applications)

► Show Figures

Figure 1

Journal Menu

Journal Browser

Editor’s Choice Articles

Further Information

Guidelines

MDPI Initiatives

Follow MDPI