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Micromachines, Volume 12, Issue 8 (August 2021) – 153 articles

Cover Story (view full-size image): The upregulated expression of tyrosine kinase AXL has been reported in several hematologic and solid human tumors, including gastric, breast, colorectal, prostate and ovarian cancers. Thus, AXL can potentially serve as a diagnostic and prognostic biomarker for various cancers. This paper reports the first ever loop-mediated isothermal amplification (LAMP) in a core-shell bead assay for the detection of AXL gene overexpression. We demonstrated simple instrumentation toward a point-of-care device to perform LAMP. This paper also reports the first ever use of core-shell beads as a microreactor to perform LAMP, as an attempt to promote environmentally friendly laboratory practices. View this paper.
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Article
Different Modes of Low-Frequency Focused Ultrasound-Mediated Attenuation of Epilepsy Based on the Topological Theory
Micromachines 2021, 12(8), 1001; https://doi.org/10.3390/mi12081001 - 23 Aug 2021
Cited by 3
Abstract
Epilepsy is common brain dysfunction, where abnormal synchronized activities can be observed across multiple brain regions. Low-frequency focused pulsed ultrasound has been proven to modulate the epileptic brain network. In this study, we used two modes of low-intensity focused ultrasound (pulsed-wave and continuous-wave) [...] Read more.
Epilepsy is common brain dysfunction, where abnormal synchronized activities can be observed across multiple brain regions. Low-frequency focused pulsed ultrasound has been proven to modulate the epileptic brain network. In this study, we used two modes of low-intensity focused ultrasound (pulsed-wave and continuous-wave) to sonicate the brains of KA-induced epileptic rats, analyzed the EEG functional brain connections to explore their respective effect on the epileptic brain network, and discuss the mechanism of ultrasound neuromodulation. By comparing the brain network characteristics before and after sonication, we found that two modes of ultrasound both significantly affected the functional brain network, especially in the low-frequency band below 12 Hz. After two modes of sonication, the power spectral density of the EEG signals and the connection strength of the brain network were significantly reduced, but there was no significant difference between the two modes. Our results indicated that the ultrasound neuromodulation could effectively regulate the epileptic brain connections. The ultrasound-mediated attenuation of epilepsy was independent of modes of ultrasound. Full article
(This article belongs to the Special Issue Fundamentals and Applications of Micro-nanorobotics)
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Article
Evaluation of Crystalline Volume Fraction of Laser-Annealed Polysilicon Thin Films Using Raman Spectroscopy and Spectroscopic Ellipsometry
Micromachines 2021, 12(8), 999; https://doi.org/10.3390/mi12080999 - 22 Aug 2021
Cited by 2
Abstract
We investigated the crystallinities of poly silicon (poly Si) annealed via green laser annealing (GLA) with a 532-nm pulsed laser and blue laser annealing (BLA) with 450-nm continuous-wave lasers. Three-dimensional heat transfer simulations were performed to obtain the temperature distributions in an amorphous [...] Read more.
We investigated the crystallinities of poly silicon (poly Si) annealed via green laser annealing (GLA) with a 532-nm pulsed laser and blue laser annealing (BLA) with 450-nm continuous-wave lasers. Three-dimensional heat transfer simulations were performed to obtain the temperature distributions in an amorphous silicon (a-Si) thin film, and GLA and BLA experiments were conducted based on the thermal simulation results. The crystallinity of annealed poly Si samples was analyzed using Raman spectroscopy and spectroscopic ellipsometry. To evaluate the degree of crystallization for the annealed samples quantitatively, the measured spectra of laser-annealed poly Si were fitted to those of crystalline Si and a-Si, and the crystal volume fraction (fc) of the annealed poly Si sample was determined. Both the Raman spectroscopy and ellipsometry showed consistent results on fc. The fc values were found to reach >85% for optimum laser power of GLA and BLA, showing good crystallinity of the laser-annealed poly Si thin films comparable to thermal furnace annealing. Full article
(This article belongs to the Special Issue Nano Korea 2021)
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Article
Research on Decomposition of Offset in MEMS Capacitive Accelerometer
Micromachines 2021, 12(8), 1000; https://doi.org/10.3390/mi12081000 - 22 Aug 2021
Cited by 2
Abstract
In a MEMS capacitive accelerometer, there is an offset due to mechanical and electrical factors, and the offset would deteriorate the performance of the accelerometer. Reducing the offset from mechanism would benefit the improvement in performance. Yet, the compositions of the offset are [...] Read more.
In a MEMS capacitive accelerometer, there is an offset due to mechanical and electrical factors, and the offset would deteriorate the performance of the accelerometer. Reducing the offset from mechanism would benefit the improvement in performance. Yet, the compositions of the offset are complex and mix together, so it is difficult to decompose the offset to provide guidance for the reduction. In this work, a decomposition method of offset in a MEMS capacitive accelerometer was proposed. The compositions of the offset were first analyzed quantitatively, and methods of measuring key parameters were developed. Based on our proposed decomposition method, the experiment of offset decomposition with a closed-loop MEMS capacitive accelerometer was carried out. The results showed that the offset successfully decomposed, and the major source was from the fabricated gap mismatch in the MEMS sensor. This work provides a new way for analyzing the offset in a MEMS capacitive accelerometer, and it is helpful for purposefully taking steps to reduce the offset and improve accelerometer performance. Full article
(This article belongs to the Special Issue Inertial MEMS Devices)
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Article
Air-Gap Interrogation of Surface Plasmon Resonance in Otto Configuration
Micromachines 2021, 12(8), 998; https://doi.org/10.3390/mi12080998 - 21 Aug 2021
Cited by 1
Abstract
In this study, a micromachined chip in Otto configuration with multiple air-gaps (1.86 μm, 2.42 μm, 3.01 μm, 3.43 μm) was fabricated, and the resonance characteristics for each air-gap was measured with a 980 nm laser source. To verify the variability of the [...] Read more.
In this study, a micromachined chip in Otto configuration with multiple air-gaps (1.86 μm, 2.42 μm, 3.01 μm, 3.43 μm) was fabricated, and the resonance characteristics for each air-gap was measured with a 980 nm laser source. To verify the variability of the reflectance characteristics of the Otto configuration and its applicability to multiple gas detection, the air-gap between the prism and metal film was adjusted by using a commercial piezoactuator. We experimentally verified that the SPR characteristics of the Otto chip configuration have a dependence on the air-gap distance and wavelength of the incident light. When a light source having a wavelength of 977 nm is used, the minimum reflectance becomes 0.22 when the displacement of the piezoactuator is about 9.3 μm. Full article
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Communication
Surface Roughness Tuning at Sub-Nanometer Level by Considering the Normal Stress Field in Magnetorheological Finishing
Micromachines 2021, 12(8), 997; https://doi.org/10.3390/mi12080997 - 21 Aug 2021
Cited by 2
Abstract
Although magnetorheological finishing (MRF) is being widely utilized to achieve ultra-smooth optical surfaces, the mechanisms for obtaining such extremely low roughness after the MRF process are not fully understood, especially the impact of finishing stresses. Herein we carefully investigated the relationship between the [...] Read more.
Although magnetorheological finishing (MRF) is being widely utilized to achieve ultra-smooth optical surfaces, the mechanisms for obtaining such extremely low roughness after the MRF process are not fully understood, especially the impact of finishing stresses. Herein we carefully investigated the relationship between the stresses and surface roughness. Normal stress shows stronger impacts on the surface roughness of fused silica (FS) when compared with the shear stress. In addition, normal stress in the polishing zone was found to be sensitive to the immersion depth of the magnetorheological (MR) fluid. Based on the above, a fine tuning of surface roughness (RMS: 0.22 nm) was obtained. This work fills gaps in understanding about the stresses that influence surface roughness during MRF. Full article
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Article
High-Efficiency, Wide Working Bandwidth Antenna Based on SOI Platform for Optical Phased Array
Micromachines 2021, 12(8), 996; https://doi.org/10.3390/mi12080996 - 21 Aug 2021
Cited by 3
Abstract
A novel structure of a subwavelength surface optical antenna for optical phased array is proposed in this paper. An asymmetric vertical grating structure is applied to achieve high emission efficiency (73% at 1550 nm). Optical antennas with large fabrication tolerances can also maintain [...] Read more.
A novel structure of a subwavelength surface optical antenna for optical phased array is proposed in this paper. An asymmetric vertical grating structure is applied to achieve high emission efficiency (73% at 1550 nm). Optical antennas with large fabrication tolerances can also maintain a wide working bandwidth of 1 dB between 1350 and 1850 nm. The far-field scanning characteristics of 16-channel optical phased array are investigated in this study by employing the proposed antenna. The results show that the background suppression without considering side lobes caused by the antenna arrangement is −24.5 dB when the phase difference is 0 and when the scan range is as large as ±14.8° × 73.6°. Full article
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Article
A Curve-Shaped Beam Bistable Piezoelectric Energy Harvester with Variable Potential Well: Modeling and Numerical Simulation
Micromachines 2021, 12(8), 995; https://doi.org/10.3390/mi12080995 - 21 Aug 2021
Abstract
To improve the energy harvesting performance of an energy harvester, a novel bistable piezoelectric energy harvester with variable potential well (BPEH-V) is proposed by introducing a spring to the external magnet from a curve-shaped beam bistable harvester (CBH-C). First, finite element simulation was [...] Read more.
To improve the energy harvesting performance of an energy harvester, a novel bistable piezoelectric energy harvester with variable potential well (BPEH-V) is proposed by introducing a spring to the external magnet from a curve-shaped beam bistable harvester (CBH-C). First, finite element simulation was performed in COMSOL software to validate that the curved beam configuration was superior to the straight beam in power generation performance, which benefits energy harvesting. Moreover, the nonlinear magnetic model was obtained by using the magnetic dipoles method, and the nonlinear restoring force model of the curve-shaped beam was acquired based on fitting the experimental data. The corresponding coupled governing equations were derived by using generalized Hamilton’s principle, the dynamic responses were obtained by solving the coupling equations with the ode45 method. Finally, the numerical simulations showed that the proposed harvester can make interwell oscillations easier due to the spring being efficiently introduced to pull down the potential barrier compared with the conventional bistable harvester. Spring stiffness has a great impact on characteristics of the system, and a suitable stiffness contributes to realize large-amplitude interwell oscillations over a wide range of excitation, especially in the low excitation condition. Full article
(This article belongs to the Special Issue Smart Devices and Systems for Vibration Sensing and Energy Harvesting)
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Article
Numerical Analysis of Viscous Dissipation in Microchannel Sensor Based on Phononic Crystal
Micromachines 2021, 12(8), 994; https://doi.org/10.3390/mi12080994 - 21 Aug 2021
Cited by 4
Abstract
Phononic crystals with phononic band gaps varying in different parameters represent a promising structure for sensing. Equipping microchannel sensors with phononic crystals has also become a great area of interest in research. For building a microchannels system compatible with conventional micro-electro-mechanical system (MEMS) [...] Read more.
Phononic crystals with phononic band gaps varying in different parameters represent a promising structure for sensing. Equipping microchannel sensors with phononic crystals has also become a great area of interest in research. For building a microchannels system compatible with conventional micro-electro-mechanical system (MEMS) technology, SU-8 is an optimal choice, because it has been used in both fields for a long time. However, its mechanical properties are greatly affected by temperature, as this affects the phononic bands of the phononic crystal. With this in mind, the viscous dissipation in microchannels of flowing liquid is required for application. To solve the problem of viscous dissipation, this article proposes a simulation model that considers the heat transfer between fluid and microchannel and analyzes the frequency domain properties of phononic crystals. The results show that when the channel length reaches 1 mm, the frequency shift caused by viscous dissipation will significantly affect detecting accuracy. Furthermore, the temperature gradient also introduces some weak passbands into the band gap. This article proves that viscous dissipation does influence the band gap of phononic crystal chemical sensors and highlights the necessity of temperature compensation in calibration. This work may promote the application of microchannel chemical sensors in the future. Full article
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Article
Rapid Fabrication by Digital Light Processing 3D Printing of a SlipChip with Movable Ports for Local Delivery to Ex Vivo Organ Cultures
Micromachines 2021, 12(8), 993; https://doi.org/10.3390/mi12080993 - 20 Aug 2021
Cited by 1
Abstract
SlipChips are two-part microfluidic devices that can be reconfigured to change fluidic pathways for a wide range of functions, including tissue stimulation. Currently, fabrication of these devices at the prototype stage requires a skilled microfluidic technician, e.g., for wet etching or alignment steps. [...] Read more.
SlipChips are two-part microfluidic devices that can be reconfigured to change fluidic pathways for a wide range of functions, including tissue stimulation. Currently, fabrication of these devices at the prototype stage requires a skilled microfluidic technician, e.g., for wet etching or alignment steps. In most cases, SlipChip functionality requires an optically clear, smooth, and flat surface that is fluorophilic and hydrophobic. Here, we tested digital light processing (DLP) 3D printing, which is rapid, reproducible, and easily shared, as a solution for fabrication of SlipChips at the prototype stage. As a case study, we sought to fabricate a SlipChip intended for local delivery to live tissue slices through a movable microfluidic port. The device was comprised of two multi-layer components: an enclosed channel with a delivery port and a culture chamber for tissue slices with a permeable support. Once the design was optimized, we demonstrated its function by locally delivering a chemical probe to slices of hydrogel and to living tissue with up to 120 µm spatial resolution. By establishing the design principles for 3D printing of SlipChip devices, this work will enhance the ability to rapidly prototype such devices at mid-scale levels of production. Full article
(This article belongs to the Special Issue Microfluidic Artificial Organs)
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Article
Pump-Free Microfluidic Hemofiltration Device
Micromachines 2021, 12(8), 992; https://doi.org/10.3390/mi12080992 - 20 Aug 2021
Abstract
Hemofiltration removes water and small molecules from the blood via nanoporous filtering membranes. This paper discusses a pump-free hemofiltration device driven by the pressure difference between the artery and the vein. In the design of the filtering device, oncotic pressure needs to be [...] Read more.
Hemofiltration removes water and small molecules from the blood via nanoporous filtering membranes. This paper discusses a pump-free hemofiltration device driven by the pressure difference between the artery and the vein. In the design of the filtering device, oncotic pressure needs to be taken into consideration. Transmembrane pressure (TMP) determines the amount and direction of hemofiltration, which is calculated by subtracting the oncotic pressure from the blood pressure. Blood pressure decreases as the channels progress from the inlet to the outlet, while oncotic pressure increases slightly since no protein is removed from the blood to the filtrate in hemofiltration. When TMP is negative, the filtrate returns to the blood, i.e., backfiltration takes place. A small region of the device with negative TMP would thus result in a small amount of or even zero filtrates. First, we investigated this phenomenon using in vitro experiments. We then designed a hemofiltration system taking backfiltration into consideration. We divided the device into two parts. In the first part, the device has channels for the blood and filtrate with a nanoporous membrane. In the second part, the device does not have channels for filtration. This design ensures TMP is always positive in the first part and prevents backfiltration. The concept was verified using in vitro experiments and ex vivo experiments in beagle dogs. Given the simplicity of the device without pumps or electrical components, the proposed pump-free hemofiltration device may prove useful for either implantable or wearable hemofiltration. Full article
(This article belongs to the Special Issue Microfluidic Artificial Organs)
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Review
Recent Advances in Reactive Ion Etching and Applications of High-Aspect-Ratio Microfabrication
Micromachines 2021, 12(8), 991; https://doi.org/10.3390/mi12080991 - 20 Aug 2021
Cited by 18
Abstract
This paper reviews the recent advances in reaction-ion etching (RIE) for application in high-aspect-ratio microfabrication. High-aspect-ratio etching of materials used in micro- and nanofabrication has become a very important enabling technology particularly for bulk micromachining applications, but increasingly also for mainstream integrated circuit [...] Read more.
This paper reviews the recent advances in reaction-ion etching (RIE) for application in high-aspect-ratio microfabrication. High-aspect-ratio etching of materials used in micro- and nanofabrication has become a very important enabling technology particularly for bulk micromachining applications, but increasingly also for mainstream integrated circuit technology such as three-dimensional multi-functional systems integration. The characteristics of traditional RIE allow for high levels of anisotropy compared to competing technologies, which is important in microsystems device fabrication for a number of reasons, primarily because it allows the resultant device dimensions to be more accurately and precisely controlled. This directly leads to a reduction in development costs as well as improved production yields. Nevertheless, traditional RIE was limited to moderate etch depths (e.g., a few microns). More recent developments in newer RIE methods and equipment have enabled considerably deeper etches and higher aspect ratios compared to traditional RIE methods and have revolutionized bulk micromachining technologies. The most widely known of these technologies is called the inductively-coupled plasma (ICP) deep reactive ion etching (DRIE) and this has become a mainstay for development and production of silicon-based micro- and nano-machined devices. This paper will review deep high-aspect-ratio reactive ion etching technologies for silicon, fused silica (quartz), glass, silicon carbide, compound semiconductors and piezoelectric materials. Full article
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Review
The Development of Design and Manufacture Techniques for Bioresorbable Coronary Artery Stents
Micromachines 2021, 12(8), 990; https://doi.org/10.3390/mi12080990 - 20 Aug 2021
Cited by 3
Abstract
Coronary artery disease (CAD) is the leading killer of humans worldwide. Bioresorbable polymeric stents have attracted a great deal of interest because they can treat CAD without producing long-term complications. Bioresorbable polymeric stents (BMSs) have undergone a sustainable revolution in terms of material [...] Read more.
Coronary artery disease (CAD) is the leading killer of humans worldwide. Bioresorbable polymeric stents have attracted a great deal of interest because they can treat CAD without producing long-term complications. Bioresorbable polymeric stents (BMSs) have undergone a sustainable revolution in terms of material processing, mechanical performance, biodegradability and manufacture techniques. Biodegradable polymers and copolymers have been widely studied as potential material candidates for bioresorbable stents. It is a great challenge to find a reasonable balance between the mechanical properties and degradation behavior of bioresorbable polymeric stents. Surface modification and drug-coating methods are generally used to improve biocompatibility and drug loading performance, which are decisive factors for the safety and efficacy of bioresorbable stents. Traditional stent manufacture techniques include etching, micro-electro discharge machining, electroforming, die-casting and laser cutting. The rapid development of 3D printing has brought continuous innovation and the wide application of biodegradable materials, which provides a novel technique for the additive manufacture of bioresorbable stents. This review aims to describe the problems regarding and the achievements of biodegradable stents from their birth to the present and discuss potential difficulties and challenges in the future. Full article
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Article
Dynamic Performance of Partially Orifice Porous Aerostatic Thrust Bearing
Micromachines 2021, 12(8), 989; https://doi.org/10.3390/mi12080989 - 20 Aug 2021
Abstract
The aerostatic thrust bearing’s performance under vibration brings certain changes in stiffness and stability, especially in the range of 100 to 10,000 Hz, and it is accompanied by significant increase in fluctuations due to the changes in frequency, and the size of the [...] Read more.
The aerostatic thrust bearing’s performance under vibration brings certain changes in stiffness and stability, especially in the range of 100 to 10,000 Hz, and it is accompanied by significant increase in fluctuations due to the changes in frequency, and the size of the gas film damping. In this research work, an analysis is carried out to evaluate the impact of throttling characteristics of small size orifice on stiffness and stability optimization of aerostatic thrust bearings. There are two types of thrust bearing orifices such as: partial porous multiple orifice and porous thrust bearings and their effects on variations in damping and dynamic stiffness are evaluated. A simulation based analysis is carried out with the help of the perturbation analysis model of an aerostatic thrust bearing simulation by using FLUENT software (CFD). Therefore, two models of aerostatic thrust bearings—one with the porous and other with partial porous orifice are developed—are simulated to evaluate the effects of perturbation frequencies on the damping and dynamic stiffness. The results reveal a decrease in the amplitude of dynamics capacity with an increase in its frequency, as well as a decrease in the damping of partial porous aerostatic thrust bearings with an increase in the number of orifices. It also reveals an increase in the radius of an orifice with an increment of damping of bearing at the same perturbation frequency and, with an increase in orifice height, a corresponding decrease in the damping characteristics of bearings and in the dynamic stiffness and coefficient of damping of bearing film in the frequency range less than 100 Hz. Full article
(This article belongs to the Special Issue Advances in Ultra-Precision Machining Technology and Applications)
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Review
Evolution of the Electromagnetic Manipulation: From Tunable to Programmable and Intelligent Metasurfaces
Micromachines 2021, 12(8), 988; https://doi.org/10.3390/mi12080988 - 20 Aug 2021
Cited by 6
Abstract
Looking back on the development of metamaterials in the past 20 years, metamaterials have gradually developed from three-dimensional complex electromagnetic structures to a two-dimensional metasurface with a low profile, during which a series of subversive achievements have been produced. The form of electromagnetic [...] Read more.
Looking back on the development of metamaterials in the past 20 years, metamaterials have gradually developed from three-dimensional complex electromagnetic structures to a two-dimensional metasurface with a low profile, during which a series of subversive achievements have been produced. The form of electromagnetic manipulation of the metasurface has evolved from passive to active tunable, programmable, and other dynamic and real-time controllable forms. In particular, the proposal of coding and programmable metasurfaces endows metasurfaces with new vitality. By describing metamaterials through binary code, the digital world and the physical world are connected, and the research of metasurfaces also steps into a new era of digitalization. However, the function switch of traditional programmable metamaterials cannot be achieved without human instruction and control. In order to achieve richer and more flexible function regulation and even higher level metasurface design, the intelligence of metamaterials is an important direction in its future development. In this paper, we review the development of tunable, programmable, and intelligent metasurfaces over the past 5 years, focusing on basic concepts, working principles, design methods, manufacturing, and experimental validation. Firstly, several manipulation modes of tunable metasurfaces are discussed; in particular, the metasurfaces based on temperature control, mechanical control, and electrical control are described in detail. It is demonstrated that the amplitude and phase responses can be flexibly manipulated by the tunable metasurfaces. Then, the concept, working principle, and design method of digital coding metasurfaces are briefly introduced. At the same time, we introduce the active programmable metasurfaces from the following aspects, such as structure, coding method, and three-dimensional far-field results, to show the excellent electromagnetic manipulation ability of programmable metasurfaces. Finally, the basic concepts and research status of intelligent metasurfaces are discussed in detail. Different from the previous programmable metamaterials, which must be controlled by human intervention, the new intelligent metamaterials control system will realize autonomous perception, autonomous decision-making, and even adaptive functional manipulation to a certain extent. Full article
(This article belongs to the Special Issue Advanced Photonics and Metamaterials)
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Article
The Specific Gravity-Free Method for the Isolation of Circulating Tumor KRAS Mutant DNA and Exosome in Colorectal Cancer
Micromachines 2021, 12(8), 987; https://doi.org/10.3390/mi12080987 - 20 Aug 2021
Cited by 1
Abstract
Background: Circulating tumor DNA (ctDNA) and exosome have been widely researched in the field of medical technology and diagnosis platforms. The purpose of our study was to improve the capturing properties of ctDNA and exosome, which involved combining two beads using approaches that [...] Read more.
Background: Circulating tumor DNA (ctDNA) and exosome have been widely researched in the field of medical technology and diagnosis platforms. The purpose of our study was to improve the capturing properties of ctDNA and exosome, which involved combining two beads using approaches that may provide a new method for cancer diagnoses. Methods: We present a dual isolation system including a polydopamine (PDA)–silica-coated alginate bead for circulating tumor DNA (ctDNA) capture and an anti-CD63 immobilized bead for exosome capture. We examined the ctDNA mutation in pre-operative plasma samples obtained from 91 colorectal cancer (CRC) patients using a droplet digital PCR (ddPCR). Results: The area under the curve (AUROC) of ctKRAS G12D mutation in the buffy coat was 0.718 (95% CI: 0.598−0.838; p = 0.001). Patients with CRC that had unmethylation of MLH1 and MSH2 showed significantly higher buffy coat ctKRAS G12D mutations, ascites ctKRAS G12D mutations, miR-31-5, and mixed scores than the patients with a methylation of MLH1 and MSH2. Conclusion: Our proposed alginate bead using the specific gravity-free method suggests that the screening of mutated ctKRAS DNA and miR-31-5 by liquid biopsy aids in identifying the patients, predicting a primary tumor, and monitoring in the early detection of a tumor. Full article
(This article belongs to the Special Issue Micro/Nanotechnologies for Liquid Biopsy)
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Article
Path Planning for 3-D In-Hand Manipulation of Micro-Objects Using Rotation Decomposition
Micromachines 2021, 12(8), 986; https://doi.org/10.3390/mi12080986 - 19 Aug 2021
Cited by 1
Abstract
Robotic manipulation and assembly of micro and nanocomponents in confined spaces is still a challenge. Indeed, the current proposed solutions that are highly inspired by classical industrial robotics are not currently able to combine precision, compactness, dexterity, and high blocking forces. In a [...] Read more.
Robotic manipulation and assembly of micro and nanocomponents in confined spaces is still a challenge. Indeed, the current proposed solutions that are highly inspired by classical industrial robotics are not currently able to combine precision, compactness, dexterity, and high blocking forces. In a previous work, we proposed 2-D in-hand robotic dexterous manipulation methods of arbitrary shaped objects that considered adhesion forces that exist at the micro and nanoscales. Direct extension of the proposed method to 3-D would involve an exponential increase in complexity. In this paper, we propose an approach that allows to plan for 3-D dexterous in-hand manipulation with a moderate increase in complexity. The main idea is to decompose any 3-D motion into a 3-D translation and three rotations about specific axes related to the object. The obtained simulation results show that 3-D in-hand dexterous micro-manipulation of arbitrary objects in presence of adhesion forces can be planned in just few seconds. Full article
(This article belongs to the Special Issue Robotic Micromanipulation, Volume II)
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Article
Optimal Combination of Mixing Units Using the Design of Experiments Method
Micromachines 2021, 12(8), 985; https://doi.org/10.3390/mi12080985 - 19 Aug 2021
Cited by 4
Abstract
A passive micromixer was designed by combining two mixing units: the cross-channel split and recombined (CC-SAR) and a mixing cell with baffles (MC-B). The passive micromixer was comprised of eight mixing slots that corresponded to four combination units; two mixing slots were grouped [...] Read more.
A passive micromixer was designed by combining two mixing units: the cross-channel split and recombined (CC-SAR) and a mixing cell with baffles (MC-B). The passive micromixer was comprised of eight mixing slots that corresponded to four combination units; two mixing slots were grouped as one combination unit. The combination of the two mixing units was based on four combination schemes: (A) first mixing unit, (B) first combination unit, (C) first combination module, and (D) second combination module. The statistical significance of the four combination schemes was analyzed using analysis of variance (ANOVA) in terms of the degree of mixing (DOM) and mixing energy cost (MEC). The DOM and MEC were simulated numerically for three Reynolds numbers (Re = 0.5, 2, and 50), representing three mixing regimes. The combination scheme (B), using different mixing units in the first two mixing slots, was significant for Re = 2 and 50. The four combination schemes had little effect on the mixing performance of a passive micromixer operating in the mixing regime of molecular dominance. The combination scheme (B) was generalized to arbitrary mixing slots, and its significance was analyzed for Re = 2 and 50. The general combination scheme meant two different mixing units in two consecutive mixing slots. The numerical simulation results showed that the general combination scheme was statistically significant in the first three combination units for Re = 2, and significant in the first two combination units for Re = 50. The combined micromixer based on the general combination scheme throughout the entire micromixer showed the best mixing performance over a wide range of Reynolds numbers, compared to other micromixers that did not adopt completely the general combination scheme. The most significant enhancement due to the general combination scheme was observed in the transition mixing scheme and was negligible in the molecular dominance scheme. The combination order was less significant after three combination units. Full article
(This article belongs to the Special Issue Micromixing Machines: Fundamentals, Design and Fabrication)
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Article
Noncascading Quadratic Buck-Boost Converter for Photovoltaic Applications
Micromachines 2021, 12(8), 984; https://doi.org/10.3390/mi12080984 - 19 Aug 2021
Cited by 2
Abstract
The development of switching converters to perform with the power processing of photovoltaic (PV) applications has been a topic receiving growing interest in recent years. This work presents a nonisolated buck-boost converter with a quadratic voltage conversion gain based on the I–IIA noncascading [...] Read more.
The development of switching converters to perform with the power processing of photovoltaic (PV) applications has been a topic receiving growing interest in recent years. This work presents a nonisolated buck-boost converter with a quadratic voltage conversion gain based on the I–IIA noncascading structure. The converter has a reduced component count and it is formed by a pair of LC networks and two active switches, which are operated synchronously to achieve a wide conversion ratio and a quadratic dependence with the duty ratio. Additionally, the analysis using different sources and loads demonstrates the differences in the behavior of the converter, as well as the pertinence of including PV devices (current sources) into the analysis of new switching converter topologies for PV applications. In this work, the voltage conversion ratio, steady-state operating conditions and semiconductor stresses of the proposed converter are discussed in the context of PV applications. The operation of the converter in a PV scenario is verified by experimental results. Full article
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Article
Modelling Renal Filtration and Reabsorption Processes in a Human Glomerulus and Proximal Tubule Microphysiological System
Micromachines 2021, 12(8), 983; https://doi.org/10.3390/mi12080983 - 19 Aug 2021
Cited by 4
Abstract
Kidney microphysiological systems (MPS) serve as potentially valuable preclinical instruments in probing mechanisms of renal clearance and osmoregulation. Current kidney MPS models target regions of the nephron, such as the glomerulus and proximal tubule (PCT), but fail to incorporate multiple filtration and absorption [...] Read more.
Kidney microphysiological systems (MPS) serve as potentially valuable preclinical instruments in probing mechanisms of renal clearance and osmoregulation. Current kidney MPS models target regions of the nephron, such as the glomerulus and proximal tubule (PCT), but fail to incorporate multiple filtration and absorption interfaces. Here, we describe a novel, partially open glomerulus and PCT microdevice that integrates filtration and absorption in a single MPS. The system equalizes pressure on each side of the PCT that operates with one side “closed” by recirculating into the bloodstream, and the other “opened” by exiting as primary filtrate. This design precisely controls the internal fluid dynamics and prevents loss of all fluid to the open side. Through this feature, an in vitro human glomerulus and proximal tubule MPS was constructed to filter human serum albumin and reabsorb glucose for seven days of operation. For proof-of-concept experiments, three human-derived cell types—conditionally immortalized human podocytes (CIHP-1), human umbilical vein endothelial cells (HUVECs), and human proximal tubule cells (HK-2)—were adapted into a common serum-free medium prior to being seeded into the three-component MPS (T-junction splitter, glomerular housing unit, and parallel proximal tubule barrier model). This system was optimized geometrically (tubing length, tubing internal diameter, and inlet flow rate) using in silico computational modeling. The prototype tri-culture MPS successfully filtered blood serum protein and generated albumin filtration in a physiologically realistic manner, while the device cultured only with proximal tubule cells did not. This glomerulus and proximal convoluted tubule MPS is a potential prototype for the human kidney used in both human-relevant testing and examining pharmacokinetic interactions. Full article
(This article belongs to the Special Issue Cell Culture Platforms and Microphysiological Systems)
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Article
Levitation Characteristics Analysis of a Diamagnetically Stabilized Levitation Structure
Micromachines 2021, 12(8), 982; https://doi.org/10.3390/mi12080982 - 19 Aug 2021
Cited by 7
Abstract
A diamagnetically stabilized levitation structure is composed of a floating magnet, diamagnetic material, and a lifting magnet. The floating magnet is freely levitated between two diamagnetic plates without any external energy input. In this paper, the levitation characteristics of a floating magnet were [...] Read more.
A diamagnetically stabilized levitation structure is composed of a floating magnet, diamagnetic material, and a lifting magnet. The floating magnet is freely levitated between two diamagnetic plates without any external energy input. In this paper, the levitation characteristics of a floating magnet were firstly studied through simulation. Three different levitation states were found by adjusting the gap between the two diamagnetic plates, namely symmetric monostable levitation, bistable levitation, and asymmetric monostable levitation. Then, according to experimental comparison, it was found that the stability of the symmetric monostable levitation system is better than that of the other two. Lastly, the maximum moving space that allows the symmetric monostable levitation state is investigated by Taguchi method. The key factors affecting the maximum gap were determined as the structure parameters of the floating magnet and the thickness of highly oriented pyrolytic graphite (HOPG) sheets. According to the optimal parameters, work performance was obtained by an experiment with an energy harvester based on the diamagnetic levitation structure. The effective value of voltage is 250.69 mV and the power is 86.8 μW. An LED light is successfully lit on when the output voltage is boosted with a Cockcroft–Walton cascade voltage doubler circuit. This work offers an effective method to choose appropriate parameters for a diamagnetically stabilized levitation structure. Full article
(This article belongs to the Special Issue Energy Harvesters and Self-powered Sensors for Smart Electronics)
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Article
Towards Biohybrid Lung: Induced Pluripotent Stem Cell Derived Endothelial Cells as Clinically Relevant Cell Source for Biologization
Micromachines 2021, 12(8), 981; https://doi.org/10.3390/mi12080981 - 19 Aug 2021
Cited by 4
Abstract
In order to provide an alternative treatment option to lung transplantation for patients with end-stage lung disease, we aim for the development of an implantable biohybrid lung (BHL), based on hollow fiber membrane (HFM) technology used in extracorporeal membrane oxygenators. Complete hemocompatibility of [...] Read more.
In order to provide an alternative treatment option to lung transplantation for patients with end-stage lung disease, we aim for the development of an implantable biohybrid lung (BHL), based on hollow fiber membrane (HFM) technology used in extracorporeal membrane oxygenators. Complete hemocompatibility of all blood contacting surfaces is crucial for long-lasting BHL durability and can be achieved by their endothelialization. Autologous endothelial cells (ECs) would be the ideal cell source, but their limited proliferation potential excludes them for this purpose. As induced pluripotent stem cell-derived ECs enable the generation of a large number of ECs, we assessed and compared their capacity to form a viable and confluent monolayer on HFM, while indicating physiologic EC-specific anti-thrombogenic and anti-inflammatory properties. ECs were generated from three different human iPSC lines, and seeded onto fibronectin-coated poly-4-methyl-1-pentene (PMP) HFM. Following phenotypical characterization, ECs were analyzed for their thrombogenic and inflammatory behavior with or without TNFα induction, using FACS and qRT-PCR. Complementary, leukocyte- and platelet adhesion assays were carried out. The capacity of the iPSC-ECs to reendothelialize cell-free monolayer areas was assessed in a scratch assay. ECs sourced from umbilical cord blood (hCBECs) were used as control. iPSC-derived ECs formed confluent monolayers on the HFM and showed the typical EC-phenotype by expression of VE-cadherin and collagen-IV. A low protein and gene expression level of E-selectin and tissue factor was detected for all iPSC-ECs and the hCBECs, while a strong upregulation of these markers was noted upon stimulation with TNFα. This was in line with the physiological and strong induction of leukocyte adhesion detected after treatment with TNFα, iPSC-EC and hCBEC monolayers were capable of reducing thrombocyte adhesion and repopulating scratched areas. iPSCs offer the possibility to provide patient-specific ECs in abundant numbers needed to cover all blood contacting surfaces of the BHL with a viable, non-thrombogenic and non-inflammatory monolayer. iPSC-EC clones can differ in terms of their reendothelialization rate, and pro-inflammatory response. However, a less profound inflammatory response may even be advantageous for BHL application. With the proven ability of the seeded iPSC-ECs to reduce thrombocyte adhesion, we expect that thrombotic events that could lead to BHL occlusion can be avoided, and thus, justifies further studies on enabling BHL long-term application. Full article
(This article belongs to the Special Issue Microfluidic Artificial Organs)
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Article
Pool Boiling Performance of Multilayer Micromeshes for Commercial High-Power Cooling
Micromachines 2021, 12(8), 980; https://doi.org/10.3390/mi12080980 - 18 Aug 2021
Cited by 2
Abstract
With the rapid development of electronics, thermal management has become one of the most crucial issues. Intense research has focused on surface modifications used to enhance heat transfer. In this study, multilayer copper micromeshes (MCMs) are developed for commercial compact electronic cooling. Boiling [...] Read more.
With the rapid development of electronics, thermal management has become one of the most crucial issues. Intense research has focused on surface modifications used to enhance heat transfer. In this study, multilayer copper micromeshes (MCMs) are developed for commercial compact electronic cooling. Boiling heat transfer performance, including critical heat flux (CHF), heat transfer coefficients (HTCs), and the onset of nucleate boiling (ONB), are investigated. The effect of micromesh layers on the boiling performance is studied, and the bubbling characteristics are analyzed. In the study, MCM-5 shows the highest critical heat flux (CHF) of 207.5 W/cm2 and an HTC of 16.5 W(cm2·K) because of its abundant micropores serving as nucleate sites, and outstanding capillary wicking capability. In addition, MCMs are compared with other surface structures in the literature and perform with high competitiveness and potential in commercial applications for high-power cooling. Full article
(This article belongs to the Special Issue Microsystem for Electronic Devices)
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Review
2D Electronics Based on Graphene Field Effect Transistors: Tutorial for Modelling and Simulation
Micromachines 2021, 12(8), 979; https://doi.org/10.3390/mi12080979 - 18 Aug 2021
Cited by 4
Abstract
This paper provides modeling and simulation insights into field-effect transistors based on graphene (GFET), focusing on the devices’ architecture with regards to the position of the gate (top-gated graphene transistors, back-gated graphene transistors, and top-/back-gated graphene transistors), substrate (silicon, silicon carbide, and quartz/glass), [...] Read more.
This paper provides modeling and simulation insights into field-effect transistors based on graphene (GFET), focusing on the devices’ architecture with regards to the position of the gate (top-gated graphene transistors, back-gated graphene transistors, and top-/back-gated graphene transistors), substrate (silicon, silicon carbide, and quartz/glass), and the graphene growth (CVD, CVD on SiC, and mechanical exfoliation). These aspects are explored and discussed in order to facilitate the selection of the appropriate topology for system-level design, based on the most common topologies. Since most of the GFET models reported in the literature are complex and hard to understand, a model of a GFET was implemented and made available in MATLAB, Verilog in Cadence, and VHDL-AMS in Simplorer—useful tools for circuit designers with different backgrounds. A tutorial is presented, enabling the researchers to easily implement the model to predict the performance of their devices. In short, this paper aims to provide the initial knowledge and tools for researchers willing to use GFETs in their designs at the system level, who are looking to implement an initial setup that allows the inclusion of the performance of GFETs. Full article
(This article belongs to the Special Issue Electronic Devices and Circuits Based on 2D Materials)
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Article
Single-Pass VDD Pacing Lead for Cardiac Resynchronization Therapy: A Reliable Alternative
Micromachines 2021, 12(8), 978; https://doi.org/10.3390/mi12080978 - 18 Aug 2021
Abstract
(1) Background: Cardiac resynchronization therapy (CRT) systems can be simplified by excluding the atrial lead and using a Ventricular-Dual-Dual (VDD) pacing lead. Possible disadvantages might include atrial undersensing and Ventricular-Ventricular-Inhibition (VVI) pacing. Because literature data concerning these systems are scarce, we analyzed their [...] Read more.
(1) Background: Cardiac resynchronization therapy (CRT) systems can be simplified by excluding the atrial lead and using a Ventricular-Dual-Dual (VDD) pacing lead. Possible disadvantages might include atrial undersensing and Ventricular-Ventricular-Inhibition (VVI) pacing. Because literature data concerning these systems are scarce, we analyzed their benefits and technical safety. (2) Methods: this retrospective study compared 50 patients implanted with VDD–CRT systems (group A), mainly because of unfavorable venous anatomy concerning the complication rate, with 103 subjects with Dual-Dual-Dual (DDD)–CRT systems (group B) implanted during 2000–2016 and 49 (group C) during 2016–2020. To analyze the functional parameters of the devices, we selected subgroups of 27 patients (subgroup A) and 47 (subgroup B) patients with VDD–CRT in 2000–2016, and 36 subjects (subgroup C) with DDD–CRT implanted were selected in 2017–2020. (3) Results: There was a trend of a lower complication rate with VDD–CRT systems, especially concerning infections during 2000–2016 (p = 0.0048), but similar results were obtained after rigorous selection of patients and employment of an upgraded design of devices/leads. With a proper device programing, CRT pacing had similar results, atrial undersensing being minimal (p = 0.65). For VDD-systems, VVI pacing was recorded only 1.7 ± 2.24% of the time. (4) Conclusions: In patients with a less favorable venous anatomy, VDD–CRT systems may represent a safe alternative regarding complications rates and functional parameters. Full article
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Article
High-Sensitivity Enzymatic Glucose Sensor Based on ZnO Urchin-like Nanostructure Modified with Fe3O4 Magnetic Particles
Micromachines 2021, 12(8), 977; https://doi.org/10.3390/mi12080977 - 18 Aug 2021
Cited by 2
Abstract
A novel and efficient enzymatic glucose sensor was fabricated based on Fe3O4 magnetic nanoparticles (Fe3O4MNPs)-modified urchin-like ZnO nanoflowers (ZnONFs). ZnONFs were hydrothermally synthesizing on a flexible PET substrate. Fe3O4MNPs were deposited on [...] Read more.
A novel and efficient enzymatic glucose sensor was fabricated based on Fe3O4 magnetic nanoparticles (Fe3O4MNPs)-modified urchin-like ZnO nanoflowers (ZnONFs). ZnONFs were hydrothermally synthesizing on a flexible PET substrate. Fe3O4MNPs were deposited on the surface of the ZnONFs by the drop-coating process. The results showed that the urchin-like ZnONFs provided strong support for enzyme adsorption. For Fe3O4MNPs, it significantly promoted the redox electron transfer from the active center of GOx to the ZnO nanoflowers beneath. More importantly, it promoted the hydrolysis of H2O2, the intermediate product of glucose catalytic reaction, and thus improved the electron yield. The sensitivity of the Nafion/GOx/Fe3O4MNPs/ZnONFs/Au/PET sensor was up to 4.52 μA·mM−1·cm−2, which was improved by 7.93 times more than the Nafion/GOx/ZnONFs/Au/PET sensors (0.57 μA·mM−1·cm−2). The detection limit and linear range were also improved. Additionally, the as-fabricated glucose sensors show strong anti-interference performance in the test environment containing organic compounds (such as urea, uric acid, and ascorbic acid) and inorganic salt (for instance, NaCl and KCl). The glucose sensor’s service life was evaluated, and it can still maintain about 80% detection performance when it was reused about 20 times. Compared with other existing sensors, the as-fabricated glucose sensor exhibits an ultrahigh sensitivity and wide detection range. In addition, the introduction of Fe3O4MNPs optimized the catalytic efficiency from the perspective of the reaction mechanism and provided potential ideas for improving the performance of other enzymatic biosensors. Full article
(This article belongs to the Special Issue MEMS/NEMS Sensors and Actuators)
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Article
Flexible Wireless Passive LC Pressure Sensor with Design Methodology and Cost-Effective Preparation
Micromachines 2021, 12(8), 976; https://doi.org/10.3390/mi12080976 - 18 Aug 2021
Cited by 2
Abstract
Continuous monitoring of physical motion, which can be successfully achieved via a wireless flexible wearable electronic device, is essential for people to ensure the appropriate level of exercise. Currently, most of the flexible LC pressure sensors have low sensitivity because of the high [...] Read more.
Continuous monitoring of physical motion, which can be successfully achieved via a wireless flexible wearable electronic device, is essential for people to ensure the appropriate level of exercise. Currently, most of the flexible LC pressure sensors have low sensitivity because of the high Young’s modulus of the dielectric properties (such as PDMS) and the inflexible polymer films (as the substrate of the sensors), which don’t have excellent stretchability to conform to arbitrarily curved and moving surfaces such as joints. In the LC sensing system, the metal rings, as the traditional readout device, are difficult to meet the needs of the portable readout device for the integrated and planar readout antenna. In order to improve the pressure sensitivity of the sensor, the Ecoflex microcolumn used as the dielectric of the capacitive pressure sensor was prepared by using a metal mold copying method. The Ecoflex elastomer substrates enhanced the levels of conformability, which offered improved capabilities to establish intimate contact with the curved and moving surfaces of the skin. The pressure was applied to the sensor by weights, and the resonance frequency curves of the sensor under different pressures were obtained by the readout device connected to the vector network analyzer. The experimental results show that resonant frequency decreases linearly with the increase of applied pressure in a range of 0–23,760 Pa with a high sensitivity of −2.2 MHz/KPa. We designed a coplanar waveguide-fed monopole antenna used to read the information of the LC sensor, which has the potential to be integrated with RF signal processing circuits as a portable readout device and a higher vertical readout distance (up to 4 cm) than the copper ring. The flexible LC pressure sensor can be attached to the skin conformally and is sensitive to limb bending and facial muscle movements. Therefore, it has the potential to be integrated as a body sensor network that can be used to monitor physical motion. Full article
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Article
Remote Temperature-Responsive Parafilm Dermal Patch for On-Demand Topical Drug Delivery
Micromachines 2021, 12(8), 975; https://doi.org/10.3390/mi12080975 - 18 Aug 2021
Cited by 1
Abstract
The development of externally controlled drug delivery systems that can rapidly trigger drug release is widely expected to change the landscape of future drug carriers. In this study, a drug delivery system was developed for on-demand therapeutic effects. The thermoresponsive paraffin film can [...] Read more.
The development of externally controlled drug delivery systems that can rapidly trigger drug release is widely expected to change the landscape of future drug carriers. In this study, a drug delivery system was developed for on-demand therapeutic effects. The thermoresponsive paraffin film can be loaded on the basis of therapeutic need, including local anesthetic (lidocaine) or topical antibiotic (neomycin), controlled remotely by a portable mini-heater. The application of mild temperature (45 °C) to the drug-loaded paraffin film allowed a rapid stimulus response within a short time (5 min). This system exploits regular drug release and the rapid generation of mild heat to trigger a burst release of 80% within 6 h of any locally administered drug. The in vitro drug release studies and in vivo therapeutic activity were observed for local anesthesia and wound healing using a neomycin-loaded film. The studies demonstrated on-demand drug release with minimized inflammation and microbial infection. This temperature-responsive drug-loaded film can be triggered remotely to provide flexible control of dose magnitude and timing. Our preclinical studies on these remotely adjustable drug delivery systems can significantly improve patient compliance and medical practice. Full article
(This article belongs to the Special Issue Advances in Biomedical Nanotechnology)
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Article
Modeling Red Blood Cell Viscosity Contrast Using Inner Soft Particle Suspension
Micromachines 2021, 12(8), 974; https://doi.org/10.3390/mi12080974 - 18 Aug 2021
Cited by 2
Abstract
The inner viscosity of a biological red blood cell is about five times larger than the viscosity of the blood plasma. In this work, we use dissipative particles to enable the proper viscosity contrast in a mesh-based red blood cell model. Each soft [...] Read more.
The inner viscosity of a biological red blood cell is about five times larger than the viscosity of the blood plasma. In this work, we use dissipative particles to enable the proper viscosity contrast in a mesh-based red blood cell model. Each soft particle represents a coarse-grained virtual cluster of hemoglobin proteins contained in the cytosol of the red blood cell. The particle interactions are governed by conservative and dissipative forces. The conservative forces have purely repulsive character, whereas the dissipative forces depend on the relative velocity between the particles. We design two computational experiments that mimic the classical viscometers. With these experiments we study the effects of particle suspension parameters on the inner cell viscosity and provide parameter sets that result in the correct viscosity contrast. The results are validated with both static and dynamic biological experiment, showing an improvement in the accuracy of the original model without major increase in computational complexity. Full article
(This article belongs to the Special Issue Microfluidic Flow Cells: Modelling and Experiments)
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Article
Bandwidth Broadening of Piezoelectric Energy Harvesters Using Arrays of a Proposed Piezoelectric Cantilever Structure
Micromachines 2021, 12(8), 973; https://doi.org/10.3390/mi12080973 - 17 Aug 2021
Cited by 6
Abstract
One of the most important challenges in the design of the piezoelectric energy harvester is its narrow bandwidth. Most of the input vibration sources are exposed to frequency variation during their operation. The piezoelectric energy harvester’s narrow bandwidth makes it difficult for the [...] Read more.
One of the most important challenges in the design of the piezoelectric energy harvester is its narrow bandwidth. Most of the input vibration sources are exposed to frequency variation during their operation. The piezoelectric energy harvester’s narrow bandwidth makes it difficult for the harvester to track the variations of the input vibration source frequency. Thus, the harvester’s output power and overall performance is expected to decline from the designed value. This current study aims to solve the problem of the piezoelectric energy harvester’s narrow bandwidth. The main objective is to achieve bandwidth broadening which is carried out by segmenting the piezoelectric material of the energy harvester into n segments; where n could be more than one. Three arrays with two, four, and six beams are shaped with two piezoelectric segments. The effect of changing the length of the piezoelectric material segment on the resonant frequency, output power, and bandwidth, as well as the frequency response is investigated. The proposed piezoelectric energy harvesters were implemented utilizing a finite element method (FEM) simulation in a MATLAB environment. The results show that increasing the number of array beams increases the output power and bandwidth. For the three-beam arrays, at n equals 2, 6 mW output power and a 9 Hz bandwidth were obtained. Moreover, the bandwidth of such arrays covered around 5% deviation from its resonant frequency. All structures were designed to operate as a steel wheel safety sensor which could be used in train tracks. Full article
(This article belongs to the Section E:Engineering and Technology)
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Review
Intracortical Microelectrode Array Unit Yield under Chronic Conditions: A Comparative Evaluation
Micromachines 2021, 12(8), 972; https://doi.org/10.3390/mi12080972 - 17 Aug 2021
Cited by 5
Abstract
While microelectrode arrays (MEAs) offer the promise of elucidating functional neural circuitry and serve as the basis for a cortical neuroprosthesis, the challenge of designing and demonstrating chronically reliable technology remains. Numerous studies report “chronic” data but the actual time spans and performance [...] Read more.
While microelectrode arrays (MEAs) offer the promise of elucidating functional neural circuitry and serve as the basis for a cortical neuroprosthesis, the challenge of designing and demonstrating chronically reliable technology remains. Numerous studies report “chronic” data but the actual time spans and performance measures corresponding to the experimental work vary. In this study, we reviewed the experimental durations that constitute chronic studies across a range of MEA types and animal species to gain an understanding of the widespread variability in reported study duration. For rodents, which are the most commonly used animal model in chronic studies, we examined active electrode yield (AEY) for different array types as a means to contextualize the study duration variance, as well as investigate and interpret the performance of custom devices in comparison to conventional MEAs. We observed wide-spread variance within species for the chronic implantation period and an AEY that decayed linearly in rodent models that implanted commercially-available devices. These observations provide a benchmark for comparing the performance of new technologies and highlight the need for consistency in chronic MEA studies. Additionally, to fully derive performance under chronic conditions, the duration of abiotic failure modes, biological processes induced by indwelling probes, and intended application of the device are key determinants. Full article
(This article belongs to the Special Issue Microelectrode Arrays and Application to Medical Devices, Volume II)
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