Micromachines

9 pages, 2559 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Viscosity-Controllable Graphene Oxide Colloids Using Electrophoretically Deposited Graphene Oxide Sheets

by Jinseok Choi, Seong-Gyu Park, Yeo-Jin Choi, Seung-Mun Baek, Han-Jung Kim, Yoonkap Kim, Ki-Sik Im and Sung-Jin An

Micromachines 2022, 13(12), 2157; https://doi.org/10.3390/mi13122157 - 7 Dec 2022

Cited by 1 | Viewed by 1864

Abstract

Graphene oxide (GO) is one of the interesting ink materials owing to its fascinating properties, such as high dissolubility in water and high controllable electric properties. For versatile printing application, the viscosity of GO colloids should be controlled in order to meet the [...] Read more.

Graphene oxide (GO) is one of the interesting ink materials owing to its fascinating properties, such as high dissolubility in water and high controllable electric properties. For versatile printing application, the viscosity of GO colloids should be controlled in order to meet the specific process requirements. Here, we report on the relatively rapid fabrication of viscosity-increased GO (VIGO) colloids mixed with electrophoretically deposited GO sheets (EPD-GO). As the GO colloid concentration, applied voltage, and deposition time increase, the viscosity of the GO colloids becomes high. The reason for the improved viscosity of GO colloids is because EPD-GO has parallel stacked GO sheets. The GO and VIGO colloids are compared and characterized using various chemical and structural analyzers. Consequently, our simple and fast method for the fabrication of GO colloids with enhanced viscosity can be used for producing inks for flexible and printed electronics. Full article

(This article belongs to the Special Issue Smart Carbon Nanostructures and Applications)

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21 pages, 8451 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Recent Progress in Blue Thermally Activated Delayed Fluorescence Emitters and Their Applications in OLEDs: Beyond Pure Organic Molecules with Twist D-π-A Structures

by Yiting Gao, Siping Wu, Guogang Shan and Gang Cheng

Micromachines 2022, 13(12), 2150; https://doi.org/10.3390/mi13122150 - 5 Dec 2022

Cited by 11 | Viewed by 6706

Abstract

Thermally activated delayed fluorescence (TADF) materials, which can harvest all excitons and emit light without the use of noble metals, are an appealing class of functional materials emerging as next-generation organic electroluminescent materials. Triplet excitons can be upconverted to the singlet state with [...] Read more.

Thermally activated delayed fluorescence (TADF) materials, which can harvest all excitons and emit light without the use of noble metals, are an appealing class of functional materials emerging as next-generation organic electroluminescent materials. Triplet excitons can be upconverted to the singlet state with the aid of ambient thermal energy under the reverse inter-system crossing owing to the small singlet–triplet splitting energy (ΔE_ST). This results from a specific molecular design consisting of minimal overlap between the highest occupied molecular orbital and the lowest unoccupied molecular orbital, due to the spatial separation of the electron-donating and electron-releasing part. When a well-designed device structure is applied, high-performance blue-emitting TADF organic light-emitting diodes can be realized with an appropriate molecular design. Unlike the previous literature that has reviewed general blue-emitting TADF materials, in this paper, we focus on materials other than pure organic molecules with twist D-π-A structures, including multi-resonance TADF, through-space charge transfer TADF, and metal-TADF materials. Cutting-edge molecules with extremely small and even negative ΔE_ST values are also introduced as candidates for next-generation TADF materials. In addition, OLED structures used to exploit the merits of the abovementioned TADF emitters are also described in this review. Full article

(This article belongs to the Special Issue Organic Light Emitting Diodes (OLEDs))

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23 pages, 4528 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Micro-Sized pH Sensors Based on Scanning Electrochemical Probe Microscopy

by Muhanad Al-Jeda, Emmanuel Mena-Morcillo and Aicheng Chen

Micromachines 2022, 13(12), 2143; https://doi.org/10.3390/mi13122143 - 4 Dec 2022

Cited by 10 | Viewed by 3464

Abstract

Monitoring pH changes at the micro/nano scale is essential to gain a fundamental understanding of surface processes. Detection of local pH changes at the electrode/electrolyte interface can be achieved through the use of micro-/nano-sized pH sensors. When combined with scanning electrochemical microscopy (SECM), [...] Read more.

Monitoring pH changes at the micro/nano scale is essential to gain a fundamental understanding of surface processes. Detection of local pH changes at the electrode/electrolyte interface can be achieved through the use of micro-/nano-sized pH sensors. When combined with scanning electrochemical microscopy (SECM), these sensors can provide measurements with high spatial resolution. This article reviews the state-of-the-art design and fabrication of micro-/nano-sized pH sensors, as well as their applications based on SECM. Considerations for selecting sensing probes for use in biological studies, corrosion science, in energy applications, and for environmental research are examined. Different types of pH sensitive probes are summarized and compared. Finally, future trends and emerging applications of micro-/nano-sized pH sensors are discussed. Full article

(This article belongs to the Special Issue MEMS Sensors: Fabrication and Application)

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14 pages, 3144 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Battery-Free Tattooing Mechanism-Based Functional Active Capsule Endoscopy

by Manh-Cuong Hoang, Jong-Oh Park and Jayoung Kim

Micromachines 2022, 13(12), 2111; https://doi.org/10.3390/mi13122111 - 29 Nov 2022

Cited by 4 | Viewed by 1853

Abstract

This paper presents a novel tattooing capsule endoscope (TCE) for delivering a certain amount of ink to the submucosal layer of digestive tract organs. A dual-function permanent magnet is used for locomotion and injection activation. The developed capsule endoscope can move actively in [...] Read more.

This paper presents a novel tattooing capsule endoscope (TCE) for delivering a certain amount of ink to the submucosal layer of digestive tract organs. A dual-function permanent magnet is used for locomotion and injection activation. The developed capsule endoscope can move actively in 5 DOF due to the interaction between the permanent magnet and a controllable external magnetic field produced by an electromagnet actuation system. In addition, the permanent magnet is involved in a specially designed mechanism to activate a process that creates a squeezing motion to eject the liquid from the storage room to the target. The dimension of the prototype is 12.5 mm in diameter and 34.6 mm in length. The proposed TCE is tested ex vivo using a fresh porcine small-intestine segment. We were able to direct the TCE to the target and deliver the tattoo agent into the tissue. The proposed mechanism can be used for drug delivery or lesion tattooing, as well as to accelerate the realization of the functional capsule endoscope in practice. Full article

(This article belongs to the Special Issue Integrated Robotics for Micromanipulation, Diagnosis and Microsurgery)

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11 pages, 2113 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

A Novel Memristive Neural Network Circuit and Its Application in Character Recognition

by Xinrui Zhang, Xiaoyuan Wang, Zhenyu Ge, Zhilong Li, Mingyang Wu and Shekharsuman Borah

Micromachines 2022, 13(12), 2074; https://doi.org/10.3390/mi13122074 - 25 Nov 2022

Cited by 11 | Viewed by 3730

Abstract

The memristor-based neural network configuration is a promising approach to realizing artificial neural networks (ANNs) at the hardware level. The memristors can effectively simulate the strength of synaptic connections between neurons in neural networks due to their diverse significant characteristics such as nonvolatility, [...] Read more.

The memristor-based neural network configuration is a promising approach to realizing artificial neural networks (ANNs) at the hardware level. The memristors can effectively simulate the strength of synaptic connections between neurons in neural networks due to their diverse significant characteristics such as nonvolatility, nanoscale dimensions, and variable conductance. This work presents a new synaptic circuit based on memristors and Complementary Metal Oxide Semiconductor(CMOS), which can realize the adjustment of positive, negative, and zero synaptic weights using only one control signal. The relationship between synaptic weights and the duration of control signals is also explained in detail. Accordingly, Widrow–Hoff algorithm-based memristive neural network (MNN) circuits are proposed to solve the recognition of three types of character pictures. The functionality of the proposed configurations is verified using SPICE simulation. Full article

(This article belongs to the Special Issue Novel Computing Architectures and Digital Circuit Designs Using Memristors and Memristive Systems)

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18 pages, 3237 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Ultrafast Pulse Generation from Quantum Cascade Lasers

by Feihu Wang, Xiaoqiong Qi, Zhichao Chen, Manijeh Razeghi and Sukhdeep Dhillon

Micromachines 2022, 13(12), 2063; https://doi.org/10.3390/mi13122063 - 24 Nov 2022

Cited by 6 | Viewed by 3625

Abstract

Quantum cascade lasers (QCLs) have broken the spectral barriers of semiconductor lasers and enabled a range of applications in the mid-infrared (MIR) and terahertz (THz) regimes. However, until recently, generating ultrashort and intense pulses from QCLs has been difficult. This would be useful [...] Read more.

Quantum cascade lasers (QCLs) have broken the spectral barriers of semiconductor lasers and enabled a range of applications in the mid-infrared (MIR) and terahertz (THz) regimes. However, until recently, generating ultrashort and intense pulses from QCLs has been difficult. This would be useful to study ultrafast processes in MIR and THz using the targeted wavelength-by-design properties of QCLs. Since the first demonstration in 2009, mode-locking of QCLs has undergone considerable development in the past decade, which includes revealing the underlying mechanism of pulse formation, the development of an ultrafast THz detection technique, and the invention of novel pulse compression technology, etc. Here, we review the history and recent progress of ultrafast pulse generation from QCLs in both the THz and MIR regimes. Full article

(This article belongs to the Special Issue Quantum Cascade Laser: Physics, Technology and Applications)

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21 pages, 1683 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Temperature-to-Digital Converters’ Evolution, Trends and Techniques across the Last Two Decades: A Review

by Antonio Aprile, Edoardo Bonizzoni and Piero Malcovati

Micromachines 2022, 13(11), 2025; https://doi.org/10.3390/mi13112025 - 19 Nov 2022

Cited by 7 | Viewed by 3215

Abstract

This paper presents an extensive review of the main highlights in the Temperature-to-Digital Converters (TDCs) field, which has gained importance and research interest throughout the last two decades. The key techniques and approaches that have led to the evolution of this kind of [...] Read more.

This paper presents an extensive review of the main highlights in the Temperature-to-Digital Converters (TDCs) field, which has gained importance and research interest throughout the last two decades. The key techniques and approaches that have led to the evolution of this kind of systems are presented and compared; their peculiarities are identified in order to highlight the pros and cons of the different design methods, and the main trade-offs are extracted from this analysis. Finally, the trends that have emerged from the performance evaluation of the large amount of published works in this field are identified with the purpose of providing a directional view of the past, present and future features of these devices. Full article

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

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14 pages, 6781 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Micro Light Flow Controller on a Programmable Waveguide Engine

by Tao Chen, Zhangqi Dang, Zeyu Deng, Zhenming Ding and Ziyang Zhang

Micromachines 2022, 13(11), 1990; https://doi.org/10.3390/mi13111990 - 16 Nov 2022

Cited by 8 | Viewed by 3262

Abstract

A light flow controller that can regulate the three-port optical power in both lossless and lossy modus is realized on a programmable multimode waveguide engine. The microheaters on the waveguide chip mimic the tunable “pixels” that can continuously adjust the local refractive index. [...] Read more.

A light flow controller that can regulate the three-port optical power in both lossless and lossy modus is realized on a programmable multimode waveguide engine. The microheaters on the waveguide chip mimic the tunable “pixels” that can continuously adjust the local refractive index. Compared to the conventional method where the tuning takes place only on single-mode waveguides, the proposed structure is more compact and requires less electrodes. The local index changes in a multimode waveguide can alter the mode numbers, field distribution, and propagation constants of each individual mode, all of which can alter the multimode interference pattern significantly. However, these changes are mostly complex and not governed by analytical equations as in the single-mode case. Though numerical simulations can be performed to predict the device response, the thermal and electromagnetic computing involved is mostly time-consuming. Here, a multi-level search program is developed based on experiments only. It can reach a target output in real time by adjusting the microheaters collectively and iteratively. It can also jump over local optima and further improve the cost function on a global level. With only a simple waveguide structure and four microheaters, light can be routed freely into any of the three output ports with arbitrary power ratios, with and without extra attenuation. This work may trigger new ideas in developing compact and efficient photonic integrated devices for applications in optical communication and computing. Full article

(This article belongs to the Special Issue Micro/Nano-Structure Based Optoelectronics and Photonics Devices)

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10 pages, 2085 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Rapid Bacterial Motility Monitoring Using Inexpensive 3D-Printed OpenFlexure Microscopy Allows Microfluidic Antibiotic Susceptibility Testing

by Tai The Diep, Sarah Helen Needs, Samuel Bizley and Alexander D. Edwards

Micromachines 2022, 13(11), 1974; https://doi.org/10.3390/mi13111974 - 14 Nov 2022

Cited by 6 | Viewed by 3646

Abstract

Antibiotic susceptibility testing is vital to tackle the emergence and spread of antimicrobial resistance. Inexpensive digital CMOS cameras can be converted into portable digital microscopes using 3D printed x-y-z stages. Microscopic examination of bacterial motility can rapidly detect the response of microbes to [...] Read more.

Antibiotic susceptibility testing is vital to tackle the emergence and spread of antimicrobial resistance. Inexpensive digital CMOS cameras can be converted into portable digital microscopes using 3D printed x-y-z stages. Microscopic examination of bacterial motility can rapidly detect the response of microbes to antibiotics to determine susceptibility. Here, we present a new simple microdevice-miniature microscope cell measurement system for multiplexed antibiotic susceptibility testing. The microdevice is made using melt-extruded plastic film strips containing ten parallel 0.2 mm diameter microcapillaries. Two different antibiotics, ceftazidime and gentamicin, were prepared in Mueller-Hinton agar (0.4%) to produce an antibiotic-loaded microdevice for simple sample addition. This combination was selected to closely match current standard methods for both antibiotic susceptibility testing and motility testing. Use of low agar concentration permits observation of motile bacteria responding to antibiotic exposure as they enter capillaries. This device fits onto the OpenFlexure 3D-printed digital microscope using a Raspberry Pi computer and v2 camera, avoiding need for expensive laboratory microscopes. This inexpensive and portable digital microscope platform had sufficient magnification to detect motile bacteria, yet wide enough field of view to monitor bacteria behavior as they entered antibiotic-loaded microcapillaries. The image quality was sufficient to detect how bacterial motility was inhibited by different concentrations of antibiotic. We conclude that a 3D-printed Raspberry Pi-based microscope combined with disposable microfluidic test strips permit rapid, easy-to-use bacterial motility detection, with potential for aiding detection of antibiotic resistance. Full article

(This article belongs to the Special Issue Advances in Microfluidic Flow Cytometry)

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13 pages, 1861 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Improving Swimming Performance of Photolithography-Based Microswimmers Using Curvature Structures

by Liyuan Tan, Zihan Wang, Zhi Chen, Xiangcheng Shi and U Kei Cheang

Micromachines 2022, 13(11), 1965; https://doi.org/10.3390/mi13111965 - 12 Nov 2022

Cited by 4 | Viewed by 2441

Abstract

The emergence of robotic microswimmers and their huge potential in biomedical applications such as drug delivery, non-invasive surgery, and bio-sensing facilitates studies to improve their effectiveness. Recently, achiral microswimmers that have neither flexible nor helical structures have garnered attention because of their simple [...] Read more.

The emergence of robotic microswimmers and their huge potential in biomedical applications such as drug delivery, non-invasive surgery, and bio-sensing facilitates studies to improve their effectiveness. Recently, achiral microswimmers that have neither flexible nor helical structures have garnered attention because of their simple structures and fabrication process while preserving adequate swimming velocity and controllability. In this paper, the crescent shape was utilized to create photolithography-fabricated crescent-shaped achiral microswimmers. The microswimmers were actuated using rotating magnetic fields at low Reynolds numbers. Compared with the previously reported achiral microswimmers, the crescent-shaped microswimmers showed significant improvement in forward swimming speed. The effects of different curvatures, arm angles, and procession angles on the velocities of microswimmers were investigated. Moreover, the optimal swimming motion was defined by adjusting the field strength of the magnetic field. Finally, the effect of the thickness of the microswimmers on their swimming velocity was investigated. Full article

(This article belongs to the Special Issue Magnetic Microrobots for Biomedical Applications)

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14 pages, 7178 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Interface Dynamics and the Influence of Gravity on Droplet Generation in a Y-microchannel

by Alexandra Bran, Nicoleta Octavia Tanase and Corneliu Balan

Micromachines 2022, 13(11), 1941; https://doi.org/10.3390/mi13111941 - 10 Nov 2022

Cited by 1 | Viewed by 1980

Abstract

The present experimental investigation is focused on the influence of gravity upon water-droplet formation in a Y-microchannel filled with oil. The flows are in the Stokes regime, with very small capillary numbers and Ohnesorge numbers less than one. The study was performed in [...] Read more.

The present experimental investigation is focused on the influence of gravity upon water-droplet formation in a Y-microchannel filled with oil. The flows are in the Stokes regime, with very small capillary numbers and Ohnesorge numbers less than one. The study was performed in a square-cross-section channel, with a = 1.0 mm as the characteristic dimension and a flow rate ratio

κ

in a range between 0.55 and 1.8. The interface dynamics in the vicinity of breakup and the transitory plug flow regime after the detachment of the droplet were analysed. The dependence of droplet length L was correlated with the channel position against the gravity and

κ

parameters. The results of the work prove that, for

κ = 1

, the droplet length L is independent of channel orientation. Full article

(This article belongs to the Special Issue Microfluidics for Health Monitoring)

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12 pages, 1713 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Picoliter Droplet Generation and Dense Bead-in-Droplet Encapsulation via Microfluidic Devices Fabricated via 3D Printed Molds

by Tochukwu D. Anyaduba, Jonas A. Otoo and Travis S. Schlappi

Micromachines 2022, 13(11), 1946; https://doi.org/10.3390/mi13111946 - 10 Nov 2022

Cited by 10 | Viewed by 5165

Abstract

Picoliter-scale droplets have many applications in chemistry and biology, such as biomolecule synthesis, drug discovery, nucleic acid quantification, and single cell analysis. However, due to the complicated processes used to fabricate microfluidic channels, most picoliter (pL) droplet generation methods are limited to research [...] Read more.

Picoliter-scale droplets have many applications in chemistry and biology, such as biomolecule synthesis, drug discovery, nucleic acid quantification, and single cell analysis. However, due to the complicated processes used to fabricate microfluidic channels, most picoliter (pL) droplet generation methods are limited to research in laboratories with cleanroom facilities and complex instrumentation. The purpose of this work is to investigate a method that uses 3D printing to fabricate microfluidic devices that can generate droplets with sizes <100 pL and encapsulate single dense beads mechanistically. Our device generated monodisperse droplets as small as ~48 pL and we demonstrated the usefulness of this droplet generation technique in biomolecule analysis by detecting Lactobacillus acidophillus 16s rRNA via digital loop-mediated isothermal amplification (dLAMP). We also designed a mixer that can be integrated into a syringe to overcome dense bead sedimentation and found that the bead-in-droplet (BiD) emulsions created from our device had <2% of the droplets populated with more than 1 bead. This study will enable researchers to create devices that generate pL-scale droplets and encapsulate dense beads with inexpensive and simple instrumentation (3D printer and syringe pump). The rapid prototyping and integration ability of this module with other components or processes can accelerate the development of point-of-care microfluidic devices that use droplet-bead emulsions to analyze biological or chemical samples with high throughput and precision. Full article

(This article belongs to the Special Issue Droplet-Based Microfluidics: Design, Fabrication and Applications)

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12 pages, 4057 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Fabrication and Evaluation of Tubule-on-a-Chip with RPTEC/HUVEC Co-Culture Using Injection-Molded Polycarbonate Chips

by Ju-Bi Lee, Hyoungseob Kim, Sol Kim and Gun Yong Sung

Micromachines 2022, 13(11), 1932; https://doi.org/10.3390/mi13111932 - 9 Nov 2022

Cited by 13 | Viewed by 3283

Abstract

To simulate the ADME process such as absorption, distribution, metabolism, and excretion in the human body after drug administration and to confirm the applicability of the mass production process, a microfluidic chip injection molded with polycarbonate (injection-molded chip (I-M chip)) was fabricated. Polycarbonate [...] Read more.

To simulate the ADME process such as absorption, distribution, metabolism, and excretion in the human body after drug administration and to confirm the applicability of the mass production process, a microfluidic chip injection molded with polycarbonate (injection-molded chip (I-M chip)) was fabricated. Polycarbonate materials were selected to minimize drug absorption. As a first step to evaluate the I-M chip, RPTEC (Human Renal Proximal Tubule Epithelial Cells) and HUVEC (Human Umbilical Vein Endothelial Cells) were co-cultured, and live and dead staining, TEER (trans-epithelial electrical resistance), glucose reabsorption, and permeability were compared using different membrane pore sizes of 0.4 μm and 3 μm. Drug excretion was confirmed through a pharmacokinetic test with metformin and cimetidine, and the gene expression of drug transporters was confirmed. As a result, it was confirmed that the cell viability was higher in the 3 μm pore size than in the 0.4 μm, the cell culture performed better, and the drug secretion was enhanced when the pore size was large. The injection-molded polycarbonate microfluidic chip is anticipated to be commercially viable for drug screening devices, particularly ADME tests. Full article

(This article belongs to the Special Issue Advances and Challenges in Biofabrication and Organ-on-a-Chip Platforms)

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6 pages, 2008 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Thermo-Optic Phase Shifter with Interleaved Suspended Design for Power Efficiency and Speed Adjustment

by Feng Gao, Wu Xie, James You Sian Tan, Chew Ping Leong, Chao Li, Xianshu Luo and Guo-Qiang Lo

Micromachines 2022, 13(11), 1925; https://doi.org/10.3390/mi13111925 - 8 Nov 2022

Cited by 4 | Viewed by 2356

Abstract

Conventional thermo-optic devices—which can be broadly categorized to that with and without a thermal isolation trench—typically come with a tradeoff between thermal tuning efficiency and tuning speed. Here, we propose a method that allows us to directly define the tradeoff using a specially [...] Read more.

Conventional thermo-optic devices—which can be broadly categorized to that with and without a thermal isolation trench—typically come with a tradeoff between thermal tuning efficiency and tuning speed. Here, we propose a method that allows us to directly define the tradeoff using a specially designed thermo-optic phase shifter with an interleaved isolation trench. With the design, the tuning efficiency and speed can be precisely tailored simply by controlling the duty ratio (suspended length over total heater length) of the suspended design. Phase shifters are one of the main components in photonic-integrated circuits, and having phase shifters with a flexible design approach may enable the wide adoption of photonic applications such as an optical neural network and LiDAR. Full article

(This article belongs to the Special Issue Silicon Photonic Devices and Integration)

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30 pages, 4456 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Recent Advances in Lossy Mode Resonance-Based Fiber Optic Sensors: A Review

by Vikas, Satyendra Kumar Mishra, Akhilesh Kumar Mishra, Paola Saccomandi and Rajneesh Kumar Verma

Micromachines 2022, 13(11), 1921; https://doi.org/10.3390/mi13111921 - 7 Nov 2022

Cited by 18 | Viewed by 4692

Abstract

Fiber optic sensors (FOSs) based on the lossy mode resonance (LMR) technique have gained substantial attention from the scientific community. The LMR technique displays several important features over the conventional surface plasmon resonance (SPR) phenomenon, for planning extremely sensitive FOSs. Unlike SPR, which [...] Read more.

Fiber optic sensors (FOSs) based on the lossy mode resonance (LMR) technique have gained substantial attention from the scientific community. The LMR technique displays several important features over the conventional surface plasmon resonance (SPR) phenomenon, for planning extremely sensitive FOSs. Unlike SPR, which mainly utilizes the thin film of metals, a wide range of materials such as conducting metal oxides and polymers support LMR. The past several years have witnessed a remarkable development in the field of LMR-based fiber optic sensors; through this review, we have tried to summarize the overall development of LMR-based fiber optic sensors. This review article not only provides the fundamental understanding and detailed explanation of LMR generation but also sheds light on the setup/configuration required to excite the lossy modes. Several geometries explored in the literature so far have also been addressed. In addition, this review includes a survey of the different materials capable of supporting lossy modes and explores new possible LMR supporting materials and their potential applications in sensing. Full article

(This article belongs to the Section A：Physics)

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14 pages, 3395 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Dynamic Behaviours of Monodisperse Double Emulsion Formation in a Tri-Axial Capillary Device

by Yuchen Dai, Haotian Cha, Nhat-Khuong Nguyen, Lingxi Ouyang, Fariba Galogahi, Ajeet Singh Yadav, Hongjie An, Jun Zhang, Chin Hong Ooi and Nam-Trung Nguyen

Micromachines 2022, 13(11), 1877; https://doi.org/10.3390/mi13111877 - 31 Oct 2022

Cited by 7 | Viewed by 2337

Abstract

We investigated experimentally, analytically, and numerically the formation process of double emulsion formations under a dripping regime in a tri-axial co-flow capillary device. The results show that mismatches of core and shell droplets under a given flow condition can be captured both experimentally [...] Read more.

We investigated experimentally, analytically, and numerically the formation process of double emulsion formations under a dripping regime in a tri-axial co-flow capillary device. The results show that mismatches of core and shell droplets under a given flow condition can be captured both experimentally and numerically. We propose a semi-analytical model using the match ratio between the pinch-off length of the shell droplet and the product of the core growth rate and its pinch-off time. The mismatch issue can be avoided if the match ratio is lower than unity. We considered a model with the wall effect to predict the size of the matched double emulsion. The model shows slight deviations with experimental data if the Reynolds number of the continuous phase is lower than 0.06 but asymptotically approaches good agreement if the Reynolds number increases from 0.06 to 0.14. The numerical simulation generally agrees with the experiments under various flow conditions. Full article

(This article belongs to the Special Issue Droplet-Based Microfluidics: Design, Fabrication and Applications)

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11 pages, 3146 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

High-Quality Fiber Bragg Gratings Inscribed by Femtosecond Laser Point-by-Point Technology

by Runxiao Chen, Jun He, Xizhen Xu, Jiafeng Wu, Ying Wang and Yiping Wang

Micromachines 2022, 13(11), 1808; https://doi.org/10.3390/mi13111808 - 23 Oct 2022

Cited by 15 | Viewed by 4448

Abstract

We experimentally studied the inscription of fiber Bragg gratings by using femtosecond (fs) laser point-by-point (PbP) technology. The effects of the focusing geometry, grating order, laser energy and grating length on the spectral characteristics of the PbP FBG were investigated. After [...] Read more.

We experimentally studied the inscription of fiber Bragg gratings by using femtosecond (fs) laser point-by-point (PbP) technology. The effects of the focusing geometry, grating order, laser energy and grating length on the spectral characteristics of the PbP FBG were investigated. After optimizing these parameters, a high-quality first-order PbP FBG with a reflectivity > 99.9% (i.e., Bragg resonance attenuation of 37.7 dB) and insertion loss (IL) of 0.03 dB was successfully created. Moreover, taking advantage of the excellent flexibility of the fs laser PbP technology, high-quality FBGs with various Bragg wavelengths ranging from 856 to 1902.6 nm were inscribed. Furthermore, wavelength-division-multiplexed (WDM) FBG arrays consisting of 10 FBGs were rapidly constructed. Additionally, a Fabry-Perot cavity was realized by using two high-quality FBGs, and its birefringence could be reduced from 3.04 × 10⁻⁵ to 1.77 × 10⁻⁶ by using a slit beam shaping-assisted femtosecond laser PbP technology. Therefore, such high-quality FBGs are promising to improve the performance of optical fiber sensors, lasers and communication devices. Full article

(This article belongs to the Special Issue Advanced Laser Fabrication for Optical Sensors)

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7 pages, 2605 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Heterogeneous CMOS Integration of InGaAs-OI nMOSFETs and Ge pMOSFETs Based on Dual-Gate Oxide Technique

by Xiaoyu Tang, Tao Hua, Yujie Liu and Zhezhe Han

Micromachines 2022, 13(11), 1806; https://doi.org/10.3390/mi13111806 - 23 Oct 2022

Cited by 1 | Viewed by 1661

Abstract

A compatible fabrication technology for integrating InGaAs nMOSFETs and Ge pMOSFETs is developed based on the development of the two-step gate oxide fabrication strategy. The direct wafer bonding method was utilized to obtain the InGaAs-Insulator-Ge structure, providing the heterogeneous channels for CMOS integration. [...] Read more.

A compatible fabrication technology for integrating InGaAs nMOSFETs and Ge pMOSFETs is developed based on the development of the two-step gate oxide fabrication strategy. The direct wafer bonding method was utilized to obtain the InGaAs-Insulator-Ge structure, providing the heterogeneous channels for CMOS integration. Superior transistor characteristics were achieved by optimizing the InGaAs gate oxide with a self-cleaning process in atomic layer deposition, and modifying the Ge gate oxide by the ozone post oxidation (OPO) technique, in the sequential two-step gate oxide fabrication process. With the combination of the gate-first fabrication process, superior on- and off-state characteristics, i.e., on current up to 8.3 µA/μm and leakage as low as 10⁻⁶ µA/μm, have been demonstrated in the integrated MOSFETs, together with the preferable symmetric output characteristics that promises excellent CMOS performances. Full article

(This article belongs to the Section D1: Semiconductor Devices)

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12 pages, 5301 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Origami Inspired Laser Scanner

by Yu-Shin Wu and Shao-Kang Hung

Micromachines 2022, 13(10), 1796; https://doi.org/10.3390/mi13101796 - 21 Oct 2022

Viewed by 2576

Abstract

Diverse origami techniques and various selections of paper open new possibilities to create micromachines. By folding paper, this article proposes an original approach to build laser scanners, which manipulate optical beams precisely and realize valuable applications, including laser marking, cutting, engraving, and displaying. [...] Read more.

Diverse origami techniques and various selections of paper open new possibilities to create micromachines. By folding paper, this article proposes an original approach to build laser scanners, which manipulate optical beams precisely and realize valuable applications, including laser marking, cutting, engraving, and displaying. A prototype has been designed, implemented, actuated, and controlled. The experimental results demonstrate that the angular stroke, repeatability, full scale settling time, and resonant frequency are 20°, 0.849 m°, 330 ms, 68 Hz, respectively. Its durability, more than 35 million cycles, shows the potential to carry out serious tasks. Full article

(This article belongs to the Special Issue Origami Devices: Design and Application)

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17 pages, 1526 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Developments in FRET- and BRET-Based Biosensors

by Yuexin Wu and Tianyu Jiang

Micromachines 2022, 13(10), 1789; https://doi.org/10.3390/mi13101789 - 20 Oct 2022

Cited by 27 | Viewed by 9374

Abstract

Resonance energy transfer technologies have achieved great success in the field of analysis. Particularly, fluorescence resonance energy transfer (FRET) and bioluminescence resonance energy transfer (BRET) provide strategies to design tools for sensing molecules and monitoring biological processes, which promote the development of biosensors. [...] Read more.

Resonance energy transfer technologies have achieved great success in the field of analysis. Particularly, fluorescence resonance energy transfer (FRET) and bioluminescence resonance energy transfer (BRET) provide strategies to design tools for sensing molecules and monitoring biological processes, which promote the development of biosensors. Here, we provide an overview of recent progress on FRET- and BRET-based biosensors and their roles in biomedicine, environmental applications, and synthetic biology. This review highlights FRET- and BRET-based biosensors and gives examples of their applications with their design strategies. The limitations of their applications and the future directions of their development are also discussed. Full article

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

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10 pages, 21721 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Millimeter-Wave Permittivity Variations of an HR Silicon Substrate from the Photoconductive Effect

by Charlotte Tripon-Canseliet and Jean Chazelas

Micromachines 2022, 13(10), 1782; https://doi.org/10.3390/mi13101782 - 19 Oct 2022

Cited by 1 | Viewed by 1821

Abstract

The photoinduced microwave complex permittivity of a highly resistive single-crystal silicon wafer was extracted from a bistatic free-space characterization test bench operating in the 26.5–40 GHz frequency band under CW optical illumination at wavelengths of 806 and 971 nm. Significant variations in the [...] Read more.

The photoinduced microwave complex permittivity of a highly resistive single-crystal silicon wafer was extracted from a bistatic free-space characterization test bench operating in the 26.5–40 GHz frequency band under CW optical illumination at wavelengths of 806 and 971 nm. Significant variations in the real and imaginary parts of the substrate’s permittivity induced by direct photoconductivity are reported, with an optical power density dependence, in agreement with the theoretical predictions. These experimental results open the route to ultrafast system reconfiguration of microwave devices in integrated technology by an external EMI-protected and contactless control with unprecedented performance. Full article

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13 pages, 5642 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

A Sensitive and Portable Double-Layer Microfluidic Biochip for Harmful Algae Detection

by Ping Li, Le Qiang, Yingkuan Han, Yujin Chu, Jiaoyan Qiu, Fangteng Song, Min Wang, Qihang He, Yunhong Zhang, Mingyuan Sun, Caiwen Li, Shuqun Song, Yun Liu, Lin Han and Yu Zhang

Micromachines 2022, 13(10), 1759; https://doi.org/10.3390/mi13101759 - 18 Oct 2022

Cited by 7 | Viewed by 2883

Abstract

Harmful algal blooms (HABs) are common disastrous ecological anomalies in coastal waters. An effective algae monitoring approach is important for natural disaster warning and environmental governance. However, conducting rapid and sensitive detection of multiple algae is still challenging. Here, we designed an ultrasensitive, [...] Read more.

Harmful algal blooms (HABs) are common disastrous ecological anomalies in coastal waters. An effective algae monitoring approach is important for natural disaster warning and environmental governance. However, conducting rapid and sensitive detection of multiple algae is still challenging. Here, we designed an ultrasensitive, rapid and portable double-layer microfluidic biochip for the simultaneous quantitative detection of six species of algae. Specific DNA probes based on the 18S ribosomal DNA (18S rDNA) gene fragments of HABs were designed and labeled with the fluorescent molecule cyanine-3 (Cy3). The biochip had multiple graphene oxide (GO) nanosheets-based reaction units, in which GO nanosheets were applied to transfer target DNA to the fluorescence signal through a photoluminescence detection system. The entire detection process of multiple algae was completed within 45 min with the linear range of fluorescence recovery of 0.1 fM–100 nM, and the detection limit reached 108 aM. The proposed approach has a simple detection process and high detection performance and is feasible to conduct accurate detection with matched portable detection equipment. It will have promising applications in marine natural disaster monitoring and environmental care. Full article

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12 pages, 61097 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Metasurfaces as Energy Valves for Sustainable Energy Management

by Yoshiaki Nishijima, Syunya Kimura, Yu Takeshima and Saulius Juodkazis

Micromachines 2022, 13(10), 1769; https://doi.org/10.3390/mi13101769 - 18 Oct 2022

Cited by 6 | Viewed by 2586

Abstract

Control of light absorption and transmission by metal–insulator–metal (MIM) metasurfaces are promising for applications in optical windows. This study shows the realization of photo-thermal energy conversion for radiative cooling by MIM metasurfaces with thin metal substrate and Indium–Tin–Oxide (ITO). High transparency of ITO [...] Read more.

Control of light absorption and transmission by metal–insulator–metal (MIM) metasurfaces are promising for applications in optical windows. This study shows the realization of photo-thermal energy conversion for radiative cooling by MIM metasurfaces with thin metal substrate and Indium–Tin–Oxide (ITO). High transparency of ITO at visible wavelengths and high absorption at mid-infrared wavelengths were realized for future applications of efficient cooling or heating applicable for living and working spaces. The MIM (ITO/CaF₂/ITO) metasurface was patterned with low-resolution photo-lithography as a demonstration of further simplification and possible scalability of the patterning for practical window applications. Full article

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12 pages, 2388 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

A Vertical Single Transistor Neuron with Core–Shell Dual-Gate for Excitatory–Inhibitory Function and Tunable Firing Threshold Voltage

by Taegoon Lee, Seung-Bae Jeon and Daewon Kim

Micromachines 2022, 13(10), 1740; https://doi.org/10.3390/mi13101740 - 14 Oct 2022

Cited by 2 | Viewed by 3116

Abstract

A novel inhibitable and firing threshold voltage tunable vertical nanowire (NW) single transistor neuron device with core–shell dual-gate (CSDG) was realized and verified by TCAD simulation. The CSDG NW neuron is enclosed by an independently accessed shell gate and core gate to serve [...] Read more.

A novel inhibitable and firing threshold voltage tunable vertical nanowire (NW) single transistor neuron device with core–shell dual-gate (CSDG) was realized and verified by TCAD simulation. The CSDG NW neuron is enclosed by an independently accessed shell gate and core gate to serve an excitatory–inhibitory transition and a firing threshold voltage adjustment, respectively. By utilizing the shell gate, the firing of specific neuron can be inhibited for winner-takes-all learning. It was confirmed that the independently accessed core gate can be used for adjustment of the firing threshold voltage to compensate random conductance variation before the learning and to fix inference error caused by unwanted synapse conductance change after the learning. This threshold voltage tuning can also be utilized for homeostatic function during the learning process. Furthermore, a myelination function which controls the transmission rate was obtained based on the inherent asymmetry between the source and drain in vertical NW structure. Finally, using the CSDG NW neuron device, a letter recognition test was conducted by SPICE simulation for a system-level validation. This multi-functional neuron device can contribute to construct a high-density monolithic SNN hardware combining with the previously developed vertical synapse MOSFET devices. Full article

(This article belongs to the Special Issue Self-Powered Devices and Systems)

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31 pages, 4256 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Micromachined Thermal Time-of-Flight Flow Sensors and Their Applications

by Liji Huang

Micromachines 2022, 13(10), 1729; https://doi.org/10.3390/mi13101729 - 13 Oct 2022

Cited by 7 | Viewed by 4185

Abstract

Micromachined thermal flow sensors on the market are primarily manufactured with the calorimetric sensing principle. The success has been in limited industries such as automotive, medical, and gas process control. Applications in some emerging and abrupt applications are hindered due to technical challenges. [...] Read more.

Micromachined thermal flow sensors on the market are primarily manufactured with the calorimetric sensing principle. The success has been in limited industries such as automotive, medical, and gas process control. Applications in some emerging and abrupt applications are hindered due to technical challenges. This paper reviews the current progress with micromachined devices based on the less popular thermal time-of-flight sensing technology: its theory, design of the micromachining process, control schemes, and applications. Thermal time-of-flight sensing could effectively solve some key technical hurdles that the calorimetric sensing approach has. It also offers fluidic property-independent data acquisition, multiparameter measurement, and the possibility for self-calibration. This technology may have a significant perspective on future development. Full article

(This article belongs to the Special Issue Novel Devices and Advances in MEMS Fabrication Processes)

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18 pages, 3687 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Electromechanical Properties of 3D-Printed Stretchable Carbon Fiber Composites

by Teemu Salo, Donato Di Vito, Aki Halme and Jukka Vanhala

Micromachines 2022, 13(10), 1732; https://doi.org/10.3390/mi13101732 - 13 Oct 2022

Cited by 18 | Viewed by 3672

Abstract

The addition of fillers has been implemented in fused filament fabrication (FFF), and robust carbon fillers have been found to improve the mechanical, electrical, and thermal properties of 3D-printed matrices. However, in stretchable matrices, the use of fillers imposes significant challenges related to [...] Read more.

The addition of fillers has been implemented in fused filament fabrication (FFF), and robust carbon fillers have been found to improve the mechanical, electrical, and thermal properties of 3D-printed matrices. However, in stretchable matrices, the use of fillers imposes significant challenges related to quality and durability. In this work, we show that long carbon staple fibers in the form of permeable carbon fiber cloth (CFC) can be placed into a stretchable thermoplastic polyurethane (TPU) matrix to improve the system. Four CFC sample series (nominally 53–159-µm-thick CFC layers) were prepared with a permeable and compliant thin CFC layer and a highly conductive and stiff thick CFC layer. The sample series was tested with single pull-up tests and cyclic tensile tests with 10,000 cycles and was further studied with digital image correlation (DIC) analyses. The results showed that embedded CFC layers in a TPU matrix can be used for stretchable 3D-printed electronics structures. Samples with a thin 53 µm CFC layer retained electrical properties at 50% cyclic tensile deformations, whereas the samples with a thick >150-µm CFC layer exhibited the lowest resistance (5 Ω/10 mm). Between those structures, the 106-µm-thick CFC layer exhibited balanced electromechanical properties, with resistance changes of 0.5% in the cyclic tests after the orientation of the samples. Furthermore, the suitability of the structure as a sensor was estimated. Full article

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

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14 pages, 8513 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Scalable, Dual-Band Metasurface Array for Electromagnetic Energy Harvesting and Wireless Power Transfer

by Yiqing Wei, Junping Duan, Huihui Jing, Huimin Yang, Hao Deng, Chengwei Song, Jiayun Wang, Zeng Qu and Binzhen Zhang

Micromachines 2022, 13(10), 1712; https://doi.org/10.3390/mi13101712 - 11 Oct 2022

Cited by 15 | Viewed by 3352

Abstract

A dual-band metasurface array is presented in this paper for electromagnetic (EM) energy harvesting in the Wi-Fi band and Ku band. The array consists of metasurface unit cells, rectifiers, and load resistors. The metasurface units within each column are interconnected to establish two [...] Read more.

A dual-band metasurface array is presented in this paper for electromagnetic (EM) energy harvesting in the Wi-Fi band and Ku band. The array consists of metasurface unit cells, rectifiers, and load resistors. The metasurface units within each column are interconnected to establish two channels of energy delivery, enabling the transmission and aggregation of incident power. At the terminals of two channels, a single series diode rectifier and a voltage doubler rectifier are integrated into them to rectify the energy in the Wi-Fi band and the Ku band, respectively. A 7 × 7 prototype of the metasurface array is fabricated and tested. The measured results in the anechoic chamber show that the RF-to-dc efficiencies of the prototype at 2.4 GHz and 12.6 GHz reach 64% and 55% accordingly, when the available incident power at the surface is 3 dBm and 14 dBm, respectively. Full article

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

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26 pages, 4364 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Microfluidic Gas Sensors: Detection Principle and Applications

by Sreerag Kaaliveetil, Juliana Yang, Saud Alssaidy, Zhenglong Li, Yu-Hsuan Cheng, Niranjan Haridas Menon, Charmi Chande and Sagnik Basuray

Micromachines 2022, 13(10), 1716; https://doi.org/10.3390/mi13101716 - 11 Oct 2022

Cited by 22 | Viewed by 6685

Abstract

With the rapid growth of emerging point-of-use (POU)/point-of-care (POC) detection technologies, miniaturized sensors for the real-time detection of gases and airborne pathogens have become essential to fight pollution, emerging contaminants, and pandemics. However, the low-cost development of miniaturized gas sensors without compromising selectivity, [...] Read more.

With the rapid growth of emerging point-of-use (POU)/point-of-care (POC) detection technologies, miniaturized sensors for the real-time detection of gases and airborne pathogens have become essential to fight pollution, emerging contaminants, and pandemics. However, the low-cost development of miniaturized gas sensors without compromising selectivity, sensitivity, and response time remains challenging. Microfluidics is a promising technology that has been exploited for decades to overcome such limitations, making it an excellent candidate for POU/POC. However, microfluidic-based gas sensors remain a nascent field. In this review, the evolution of microfluidic gas sensors from basic electronic techniques to more advanced optical techniques such as surface-enhanced Raman spectroscopy to detect analytes is documented in detail. This paper focuses on the various detection methodologies used in microfluidic-based devices for detecting gases and airborne pathogens. Non-continuous microfluidic devices such as bubble/droplet-based microfluidics technology that have been employed to detect gases and airborne pathogens are also discussed. The selectivity, sensitivity, advantages/disadvantages vis-a-vis response time, and fabrication costs for all the microfluidic sensors are tabulated. The microfluidic sensors are grouped based on the target moiety, such as air pollutants such as carbon monoxide and nitrogen oxides, and airborne pathogens such as E. coli and SARS-CoV-2. The possible application scenarios for the various microfluidic devices are critically examined. Full article

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

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14 pages, 2409 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

The Effect of Non-Uniform Magnetic Field on the Efficiency of Mixing in Droplet-Based Microfluidics: A Numerical Investigation

by Masoud Rezaeian, Moein Nouri, Mojtaba Hassani-Gangaraj, Amir Shamloo and Rohollah Nasiri

Micromachines 2022, 13(10), 1661; https://doi.org/10.3390/mi13101661 - 2 Oct 2022

Cited by 12 | Viewed by 2723

Abstract

Achieving high efficiency and throughput in droplet-based mixing over a small characteristic length, such as microfluidic channels, is one of the crucial parameters in Lab-on-a-Chip (LOC) applications. One solution to achieve efficient mixing is to use active mixers in which an external power [...] Read more.

Achieving high efficiency and throughput in droplet-based mixing over a small characteristic length, such as microfluidic channels, is one of the crucial parameters in Lab-on-a-Chip (LOC) applications. One solution to achieve efficient mixing is to use active mixers in which an external power source is utilized to mix two fluids. One of these active methods is magnetic micromixers using ferrofluid. In this technique, magnetic nanoparticles are used to make one phase responsive to magnetic force, and then by applying a magnetic field, two fluid phases, one of which is magneto-responsive, will sufficiently mix. In this study, we investigated the effect of the magnetic field’s characteristics on the efficiency of the mixing process inside droplets. When different concentrations of ferrofluids are affected by a constant magnetic field, there is no significant change in mixing efficiency. As the magnetic field intensifies, the magnetic force makes the circulation flow inside the droplet asymmetric, leading to chaotic advection, which creates a flow that increases the mixing efficiency. The results show that the use of magnetic fields is an effective method to enhance the mixing efficiency within droplets, and the efficiency of mixing increases from 65.4 to 86.1% by increasing the magnetic field intensity from 0 to 90 mT. Besides that, the effect of ferrofluid’s concentration on the mixing efficiency is studied. It is shown that when the concentration of the ferrofluid changes from 0 to 0.6 mol/m³, the mixing efficiency increases considerably. It is also shown that by changing the intensity of the magnetic field, the mixing efficiency increases by about 11%. Full article

(This article belongs to the Special Issue Digital Microfluidics for Liquid Handling and Biochemical Analysis)

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19 pages, 7111 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

RETRACTED: Transient Response Characteristics Analysis of High-Power Piezoelectric Transducers

by Zhaopeng Dong, Liang Xu and Tianyue Yang

Micromachines 2022, 13(10), 1638; https://doi.org/10.3390/mi13101638 - 29 Sep 2022

Cited by 4 | Viewed by 2248

Abstract

To improve suitability in applications with high dynamic performance requirements, the transient response characteristics of high-power piezoelectric transducers should be studied quantitatively. This paper proposes the vector reduction method to solve the complex transient equations and obtains a transient matching scheme clarifying the [...] Read more.

To improve suitability in applications with high dynamic performance requirements, the transient response characteristics of high-power piezoelectric transducers should be studied quantitatively. This paper proposes the vector reduction method to solve the complex transient equations and obtains a transient matching scheme clarifying the mechanism of electrical matching resistance on electromechanical damping. A matching scheme with a combination of full-bridge inverter, transformer and series LC circuit is designed and validated, which can provide suitable electrical damping without causing energy losses. Consequently, the experiment verifies the transient properties of the proposed scheme. For a typical piezoelectric cutting transducer with 100.8 ms response time, our scheme is verified to have high dynamic performance within frequency response time of 5.5 ms and vibration response time of 15.0 ms. Full article

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21 pages, 6650 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Recent Progress of Terahertz Spatial Light Modulators: Materials, Principles and Applications

by Shengnan Guan, Jierong Cheng and Shengjiang Chang

Micromachines 2022, 13(10), 1637; https://doi.org/10.3390/mi13101637 - 29 Sep 2022

Cited by 24 | Viewed by 4892

Abstract

Terahertz (THz) technology offers unparalleled opportunities in a wide variety of applications, ranging from imaging and spectroscopy to communications and quality control, where lack of efficient modulation devices poses a major bottleneck. Spatial modulation allows for dynamically encoding various spatial information into the [...] Read more.

Terahertz (THz) technology offers unparalleled opportunities in a wide variety of applications, ranging from imaging and spectroscopy to communications and quality control, where lack of efficient modulation devices poses a major bottleneck. Spatial modulation allows for dynamically encoding various spatial information into the THz wavefront by electrical or optical control. It plays a key role in single-pixel imaging, beam scanning and wavefront shaping. Although mature techniques from the microwave and optical band are not readily applicable when scaled to the THz band, the rise of metasurfaces and the advance of new materials do inspire new possibilities. In this review, we summarize the recent progress of THz spatial light modulators from the perspective of functional materials and analyze their modulation principles, specifications, applications and possible challenges. We envision new advances of this technique in the near future to promote THz applications in different fields. Full article

(This article belongs to the Special Issue Passive and Active THz Components)

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54 pages, 2876 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Sustained Drug Release from Smart Nanoparticles in Cancer Therapy: A Comprehensive Review

by Xue Bai, Zara L. Smith, Yuheng Wang, Sam Butterworth and Annalisa Tirella

Micromachines 2022, 13(10), 1623; https://doi.org/10.3390/mi13101623 - 28 Sep 2022

Cited by 57 | Viewed by 7369

Abstract

Although nanomedicine has been highly investigated for cancer treatment over the past decades, only a few nanomedicines are currently approved and in the market; making this field poorly represented in clinical applications. Key research gaps that require optimization to successfully translate the use [...] Read more.

Although nanomedicine has been highly investigated for cancer treatment over the past decades, only a few nanomedicines are currently approved and in the market; making this field poorly represented in clinical applications. Key research gaps that require optimization to successfully translate the use of nanomedicines have been identified, but not addressed; among these, the lack of control of the release pattern of therapeutics is the most important. To solve these issues with currently used nanomedicines (e.g., burst release, systemic release), different strategies for the design and manufacturing of nanomedicines allowing for better control over the therapeutic release, are currently being investigated. The inclusion of stimuli-responsive properties and prolonged drug release have been identified as effective approaches to include in nanomedicine, and are discussed in this paper. Recently, smart sustained release nanoparticles have been successfully designed to safely and efficiently deliver therapeutics with different kinetic profiles, making them promising for many drug delivery applications and in specific for cancer treatment. In this review, the state-of-the-art of smart sustained release nanoparticles is discussed, focusing on the design strategies and performances of polymeric nanotechnologies. A complete list of nanomedicines currently tested in clinical trials and approved nanomedicines for cancer treatment is presented, critically discussing advantages and limitations with respect to the newly developed nanotechnologies and manufacturing methods. By the presented discussion and the highlight of nanomedicine design criteria and current limitations, this review paper could be of high interest to identify key features for the design of release-controlled nanomedicine for cancer treatment. Full article

(This article belongs to the Special Issue Advanced Functional Materials and 3D Printing for Tissue Engineering and Drug Delivery Applications)

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13 pages, 3461 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

A Miniaturized Piezoelectric MEMS Accelerometer with Polygon Topological Cantilever Structure

by Chaoxiang Yang, Bohao Hu, Liangyu Lu, Zekai Wang, Wenjuan Liu and Chengliang Sun

Micromachines 2022, 13(10), 1608; https://doi.org/10.3390/mi13101608 - 27 Sep 2022

Cited by 12 | Viewed by 3209

Abstract

This work proposes a miniaturized piezoelectric MEMS accelerometer based on polygonal topology with an area of only 868 × 833 μm². The device consists of six trapezoidal cantilever beams with shorter fixed sides. Meanwhile, a device with larger fixed sides is [...] Read more.

This work proposes a miniaturized piezoelectric MEMS accelerometer based on polygonal topology with an area of only 868 × 833 μm². The device consists of six trapezoidal cantilever beams with shorter fixed sides. Meanwhile, a device with larger fixed sides is also designed for comparison. The theoretical and finite element models are established to analyze the effect of the beam′s effective stiffness on the output voltage and natural frequency. As the stiffness of the device decreases, the natural frequency of the device decreases while the output signal increases. The proposed polygonal topology with shorter fixed sides has higher voltage sensitivity than the larger fixed one based on finite element simulations. The piezoelectric accelerometers are fabricated using Cavity-SOI substrates with a core piezoelectric film of aluminum nitride (AlN) of about 928 nm. The fabricated piezoelectric MEMS accelerometers have good linearity (0.99996) at accelerations less than 2 g. The measured natural frequency of the accelerometer with shorter fixed sides is 98 kHz, and the sensitivity, resolution, and minimum detectable signal at 400 Hz are 1.553 mV/g, 1 mg, and 2 mg, respectively. Compared with the traditional trapezoidal cantilever with the same diaphragm area, its output voltage sensitivity is increased by 22.48%. Full article

(This article belongs to the Special Issue MEMS Accelerometers: Design, Applications and Characterization)

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36 pages, 4899 KiB

Open AccessFeature PaperEditor’s ChoiceReview

A Critical Review on the Junction Temperature Measurement of Light Emitting Diodes

by Ceren Cengiz, Mohammad Azarifar and Mehmet Arik

Micromachines 2022, 13(10), 1615; https://doi.org/10.3390/mi13101615 - 27 Sep 2022

Cited by 20 | Viewed by 5351

Abstract

In the new age of illumination, light emitting diodes (LEDs) have been proven to be the most efficient alternative to conventional light sources. Yet, in comparison to other lighting systems, LEDs operate at low temperatures while junction temperature (T_j) is [...] Read more.

In the new age of illumination, light emitting diodes (LEDs) have been proven to be the most efficient alternative to conventional light sources. Yet, in comparison to other lighting systems, LEDs operate at low temperatures while junction temperature (T_j) is is among the main factors dictating their lifespan, reliability, and performance. This indicates that accurate measurement of LED temperature is of great importance to better understand the thermal effects over a system and improve performance. Over the years, various T_j measurement techniques have been developed, and existing methods have been improved in many ways with technological and scientific advancements. Correspondingly, in order to address the governing phenomena, benefits, drawbacks, possibilities, and applications, a wide range of measurement techniques and systems are covered. This paper comprises a large number of published studies on junction temperature measurement approaches for LEDs, and a summary of the experimental parameters employed in the literature are given as a reference. In addition, some of the corrections noted in non-ideal thermal calibration processes are discussed and presented. Finally, a comparison between methods will provide the readers a better insight into the topic and direction for future research. Full article

(This article belongs to the Special Issue Advanced Technologies in Electronic Packaging)

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19 pages, 7670 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

A Disposable Electromagnetic Bi-Directional Micropump Utilizing a Rotating Multi-Pole Ring Magnetic Coupling

by Chao Qi, Naohiro Sugita and Tadahiko Shinshi

Micromachines 2022, 13(10), 1565; https://doi.org/10.3390/mi13101565 - 21 Sep 2022

Cited by 5 | Viewed by 2405

Abstract

Electromagnetic bi-directional micropumps (EMBM) are indispensable for the development of portable devices which enable fluid transportation in forward and reverse directions. However, the high disposal cost of rare-earth magnets attached to the fluidic part and the low pump density due to multiple motors [...] Read more.

Electromagnetic bi-directional micropumps (EMBM) are indispensable for the development of portable devices which enable fluid transportation in forward and reverse directions. However, the high disposal cost of rare-earth magnets attached to the fluidic part and the low pump density due to multiple motors limit their practical application in disposable multi-channel microfluidic applications such as droplet-based oscillatory-flow (DBOF) rapid PCR amplification. Therefore, this paper presented a low-cost, disposable, high-pump-density EMBM. To reduce the disposal cost, we separated the magnets from the disposable fluidic part and used cylindrical holes to store and guide the magnet, which resulted in the ability to reuse all the magnets. To increase the pump density, we used the combination of one motor and one multi-pole ring magnet to drive several channels simultaneously. A proof-of-concept prototype with a pump density of 0.28 cm⁻² was fabricated and experimentally evaluated. The fabricated micropump exhibited a maximum flow rate of 0.86 mL/min and a maximum backpressure of 0.5 kPa at a resonant frequency around 50 Hz. The developed multi-channel micropump with reusable magnets is highly beneficial to the development of low-cost and high-throughput rapid PCR amplification microchips and therefore can have a significant impact on timely infectious disease recognition and intervention. Full article

(This article belongs to the Special Issue Microfluidics: Emerging Tool in Point-of-Care Testing)

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8 pages, 3530 KiB

Open AccessFeature PaperEditor’s ChoiceCommunication

The Reflectance Characteristics of an Inverse Moth-Eye Structure in a Silicon Substrate Depending on SF₆/O₂ Plasma Etching Conditions

by Jong-Chang Woo and Doo-Seung Um

Micromachines 2022, 13(10), 1556; https://doi.org/10.3390/mi13101556 - 20 Sep 2022

Cited by 2 | Viewed by 2210

Abstract

The global RE100 campaign is attracting attention worldwide due to climate change caused by global warming, increasingly highlighting the efficiency of renewable energy. Texturing of photovoltaic devices increases the devices’ efficiency by reducing light reflectance at their surfaces. This study introduces the change [...] Read more.

The global RE100 campaign is attracting attention worldwide due to climate change caused by global warming, increasingly highlighting the efficiency of renewable energy. Texturing of photovoltaic devices increases the devices’ efficiency by reducing light reflectance at their surfaces. This study introduces the change in light reflectance following the process conditions of plasma etching as a texturing process to increase the efficiency of photovoltaic cells. Isotropic etching was induced through plasma using SF₆ gas, and the etch profile was modulated by adding O₂ gas to reduce light reflectance. A high etch rate produces high surface roughness, which results in low surface reflectance properties. The inverse moth-eye structure was implemented using a square PR pattern arranged diagonally and showed the minimum reflectance in visible light at a tip spacing of 1 μm. This study can be applied to the development of higher-efficiency optical devices. Full article

(This article belongs to the Special Issue Micro/Nano-Functional Structures: Design, Manufacturing, Characterization and Applications)

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22 pages, 6973 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Smart Manufacturing Processes of Low-Tortuous Structures for High-Rate Electrochemical Energy Storage Devices

by Chun-Yang Kang and Yu-Sheng Su

Micromachines 2022, 13(9), 1534; https://doi.org/10.3390/mi13091534 - 16 Sep 2022

Cited by 7 | Viewed by 3671

Abstract

To maximize the performance of energy storage systems more effectively, modern batteries/supercapacitors not only require high energy density but also need to be fully recharged within a short time or capable of high-power discharge for electric vehicles and power applications. Thus, how to [...] Read more.

To maximize the performance of energy storage systems more effectively, modern batteries/supercapacitors not only require high energy density but also need to be fully recharged within a short time or capable of high-power discharge for electric vehicles and power applications. Thus, how to improve the rate capability of batteries or supercapacitors is a very important direction of research and engineering. Making low-tortuous structures is an efficient means to boost power density without replacing materials or sacrificing energy density. In recent years, numerous manufacturing methods have been developed to prepare low-tortuous configurations for fast ion transportation, leading to impressive high-rate electrochemical performance. This review paper summarizes several smart manufacturing processes for making well-aligned 3D microstructures for batteries and supercapacitors. These techniques can also be adopted in other advanced fields that require sophisticated structural control to achieve superior properties. Full article

(This article belongs to the Special Issue Micro and Smart Devices and Systems, 2nd Edition)

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6 pages, 3076 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Low Buffer Trapping Effects above 1200 V in Normally off GaN-on-Silicon Field Effect Transistors

by Idriss Abid, Youssef Hamdaoui, Jash Mehta, Joff Derluyn and Farid Medjdoub

Micromachines 2022, 13(9), 1519; https://doi.org/10.3390/mi13091519 - 14 Sep 2022

Cited by 2 | Viewed by 2365

Abstract

We report on the fabrication and electrical characterization of AlGaN/GaN normally off transistors on silicon designed for high-voltage operation. The normally off configuration was achieved with a p-gallium nitride (p-GaN) cap layer below the gate, enabling a positive threshold voltage higher than +1 [...] Read more.

We report on the fabrication and electrical characterization of AlGaN/GaN normally off transistors on silicon designed for high-voltage operation. The normally off configuration was achieved with a p-gallium nitride (p-GaN) cap layer below the gate, enabling a positive threshold voltage higher than +1 V. The buffer structure was based on AlN/GaN superlattices (SLs), delivering a vertical breakdown voltage close to 1.5 kV with a low leakage current all the way to 1200 V. With the grounded substrate, the hard breakdown voltage transistors at V_GS = 0 V is 1.45 kV, corresponding to an outstanding average vertical breakdown field higher than 2.4 MV/cm. High-voltage characterizations revealed a state-of-the-art combination of breakdown voltage at V_GS = 0 V together with low buffer electron trapping effects up to 1.4 kV, as assessed by means of substrate ramp measurements. Full article

(This article belongs to the Special Issue III–V Compound Semiconductors and Devices)

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16 pages, 3787 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Rapid and Continuous Cryopreservation of Stem Cells with a 3D Micromixer

by Lin Ding, Sajad Razavi Bazaz, Jesus Shrestha, Hoseyn A. Amiri, Sima Mas-hafi, Balarka Banerjee, Graham Vesey, Morteza Miansari and Majid Ebrahimi Warkiani

Micromachines 2022, 13(9), 1516; https://doi.org/10.3390/mi13091516 - 13 Sep 2022

Cited by 6 | Viewed by 3025

Abstract

Cryopreservation is the final step of stem cell production before the cryostorage of the product. Conventional methods of adding cryoprotecting agents (CPA) into the cells can be manual or automated with robotic arms. However, challenging issues with these methods at industrial-scale production are [...] Read more.

Cryopreservation is the final step of stem cell production before the cryostorage of the product. Conventional methods of adding cryoprotecting agents (CPA) into the cells can be manual or automated with robotic arms. However, challenging issues with these methods at industrial-scale production are the insufficient mixing of cells and CPA, leading to damage of cells, discontinuous feeding, the batch-to-batch difference in products, and, occasionally, cross-contamination. Therefore, the current study proposes an alternative way to overcome the abovementioned challenges; a highly efficient micromixer for low-cost, continuous, labour-free, and automated mixing of stem cells with CPA solutions. Our results show that our micromixer provides a more homogenous mixing of cells and CPA compared to the manual mixing method, while the cell properties, including surface markers, differentiation potential, proliferation, morphology, and therapeutic potential, are well preserved. Full article

(This article belongs to the Special Issue Advanced Functional Materials and 3D Printing for Tissue Engineering and Drug Delivery Applications)

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25 pages, 5618 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Ultrasound-Responsive Nanocarriers for Breast Cancer Chemotherapy

by Gelan Ayana, Jaemyung Ryu and Se-woon Choe

Micromachines 2022, 13(9), 1508; https://doi.org/10.3390/mi13091508 - 11 Sep 2022

Cited by 20 | Viewed by 6443

Abstract

Breast cancer is the most common type of cancer and it is treated with surgical intervention, radiotherapy, chemotherapy, or a combination of these regimens. Despite chemotherapy’s ample use, it has limitations such as bioavailability, adverse side effects, high-dose requirements, low therapeutic indices, multiple [...] Read more.

Breast cancer is the most common type of cancer and it is treated with surgical intervention, radiotherapy, chemotherapy, or a combination of these regimens. Despite chemotherapy’s ample use, it has limitations such as bioavailability, adverse side effects, high-dose requirements, low therapeutic indices, multiple drug resistance development, and non-specific targeting. Drug delivery vehicles or carriers, of which nanocarriers are prominent, have been introduced to overcome chemotherapy limitations. Nanocarriers have been preferentially used in breast cancer chemotherapy because of their role in protecting therapeutic agents from degradation, enabling efficient drug concentration in target cells or tissues, overcoming drug resistance, and their relatively small size. However, nanocarriers are affected by physiological barriers, bioavailability of transported drugs, and other factors. To resolve these issues, the use of external stimuli has been introduced, such as ultrasound, infrared light, thermal stimulation, microwaves, and X-rays. Recently, ultrasound-responsive nanocarriers have become popular because they are cost-effective, non-invasive, specific, tissue-penetrating, and deliver high drug concentrations to their target. In this paper, we review recent developments in ultrasound-guided nanocarriers for breast cancer chemotherapy, discuss the relevant challenges, and provide insights into future directions. Full article

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

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9 pages, 2834 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Thermal Performance Improvement of AlGaN/GaN HEMTs Using Nanocrystalline Diamond Capping Layers

by Huaixin Guo, Yizhuang Li, Xinxin Yu, Jianjun Zhou and Yuechan Kong

Micromachines 2022, 13(9), 1486; https://doi.org/10.3390/mi13091486 - 7 Sep 2022

Cited by 13 | Viewed by 2399

Abstract

Nanocrystalline diamond capping layers have been demonstrated to improve thermal management for AlGaN/GaN HEMTs. To improve the RF devices, the application of the technology, the technological approaches and device characteristics of AlGaN/GaN HEMTs with gate length less than 0.5 μm using nanocrystalline diamond [...] Read more.

Nanocrystalline diamond capping layers have been demonstrated to improve thermal management for AlGaN/GaN HEMTs. To improve the RF devices, the application of the technology, the technological approaches and device characteristics of AlGaN/GaN HEMTs with gate length less than 0.5 μm using nanocrystalline diamond capping layers have been studied systematically. The approach of diamond-before-gate has been adopted to resolve the growth of nanocrystalline diamond capping layers and compatibility with the Schottky gate of GaN HEMTs, and the processes of diamond multi-step etching technique and AlGaN barrier protection are presented to improve the technological challenge of gate metal. The GaN HEMTs with nanocrystalline diamond passivated structure have been successfully prepared; the heat dissipation capability and electrical characteristics have been evaluated. The results show the that thermal resistance of GaN HEMTs with nanocrystalline diamond passivated structure is lower than conventional SiN-GaN HEMTs by 21.4%, and the mechanism of heat transfer for NDC-GaN HEMTs is revealed by simulation method in theory. Meanwhile, the GaN HEMTs with nanocrystalline diamond passivated structure has excellent output, small signal gain and cut-off frequency characteristics, especially the current–voltage, which has a 27.9% improvement than conventional SiN-GaN HEMTs. The nanocrystalline diamond capping layers for GaN HEMTs has significant performance advantages over the conventional SiN passivated structure. Full article

(This article belongs to the Special Issue Novel Diamond Electronic Devices)

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16 pages, 54271 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Soft Molds with Micro-Machined Internal Skeletons Improve Robustness of Flapping-Wing Robots

by Hang Gao, James Lynch and Nick Gravish

Micromachines 2022, 13(9), 1489; https://doi.org/10.3390/mi13091489 - 7 Sep 2022

Cited by 1 | Viewed by 2734

Abstract

Mobile millimeter and centimeter scale robots often use smart composite manufacturing (SCM) for the construction of body components and mechanisms. The fabrication of SCM mechanisms requires laser machining and laminating flexible, adhesive, and structural materials into small-scale hinges, transmissions, and, ultimately, wings or [...] Read more.

Mobile millimeter and centimeter scale robots often use smart composite manufacturing (SCM) for the construction of body components and mechanisms. The fabrication of SCM mechanisms requires laser machining and laminating flexible, adhesive, and structural materials into small-scale hinges, transmissions, and, ultimately, wings or legs. However, a fundamental limitation of SCM components is the plastic deformation and failure of flexures. In this work, we demonstrate that encasing SCM components in a soft silicone mold dramatically improves the durability of SCM flexure hinges and provides robustness to SCM components. We demonstrate this advance in the design of a flapping-wing robot that uses an underactuated compliant transmission fabricated with an inner SCM skeleton and exterior silicone mold. The transmission design is optimized to achieve desired wingstroke requirements and to allow for independent motion of each wing. We validate these design choices in bench-top tests, measuring transmission compliance, kinematics, and fatigue. We integrate the transmission with laminate wings and two types of actuation, demonstrating elastic energy exchange and limited lift-off capabilities. Lastly, we tested collision mitigation through flapping-wing experiments that obstructed the motion of a wing. These experiments demonstrate that an underactuated compliant transmission can provide resilience and robustness to flapping-wing robots. Full article

(This article belongs to the Special Issue Microrobotics: A Commemorative Issue in Honor of Professor Robert J. Wood)

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15 pages, 6706 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

All-MEMS Lidar Using Hybrid Optical Architecture with Digital Micromirror Devices and a 2D-MEMS Mirror

by Eunmo Kang, Heejoo Choi, Brandon Hellman, Joshua Rodriguez, Braden Smith, Xianyue Deng, Parker Liu, Ted Liang-Tai Lee, Eric Evans, Yifan Hong, Jiafan Guan, Chuan Luo and Yuzuru Takashima

Micromachines 2022, 13(9), 1444; https://doi.org/10.3390/mi13091444 - 1 Sep 2022

Cited by 8 | Viewed by 6494

Abstract

In a lidar system, replacing moving components with solid-state devices is highly anticipated to make a reliable and compact lidar system, provided that a substantially large beam area with a large angular extent as well as high angular resolution is assured for the [...] Read more.

In a lidar system, replacing moving components with solid-state devices is highly anticipated to make a reliable and compact lidar system, provided that a substantially large beam area with a large angular extent as well as high angular resolution is assured for the lidar transmitter and receiver. A new quasi-solid-state lidar optical architecture employs a transmitter with a two-dimensional MEMS mirror for fine beam steering at a fraction of the degree of the angular resolution and is combined with a digital micromirror device for wide FOV scanning over 37 degree while sustaining a large aperture area of 140 mm squared. In the receiver, a second digital micromirror device is synchronized to the transmitter DMD, which enables a large FOV receiver. An angular resolution of

0.57 ° (H)

by

0.23 ° (V)

was achieved with 0.588 fps for scanning 1344 points within the field of view. Full article

(This article belongs to the Special Issue Beam Steering via Arrayed Micromachines)

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15 pages, 2366 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Supercritical Fluids and Nanoparticles in Cancer Therapy

by Iolanda De Marco

Micromachines 2022, 13(9), 1449; https://doi.org/10.3390/mi13091449 - 1 Sep 2022

Cited by 9 | Viewed by 2054

Abstract

Nanoparticles are widely used in the pharmaceutical industry due to their high surface-to-volume ratio. Among the many techniques used to obtain nanoparticles, those based on supercritical fluids ensure reduced dimensions, narrow particle size distributions, and a very low or zero solvent residue in [...] Read more.

Nanoparticles are widely used in the pharmaceutical industry due to their high surface-to-volume ratio. Among the many techniques used to obtain nanoparticles, those based on supercritical fluids ensure reduced dimensions, narrow particle size distributions, and a very low or zero solvent residue in the powders. This review focuses on using supercritical carbon dioxide-based processes to obtain the nanoparticles of compounds used for the treatment or prevention of cancer. The scientific literature papers have been classified into two groups: nanoparticles consisting of a single active principle ingredient (API) and carrier/API nanopowders. Various supercritical carbon dioxide (scCO₂) based techniques for obtaining the nanoparticles were considered, along with the operating conditions and advantages and disadvantages of each process. Full article

(This article belongs to the Special Issue Nanoparticles in Biomedical Sciences)

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12 pages, 2554 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Evaluating and Visualizing the Contribution of ECG Characteristic Waveforms for PPG-Based Blood Pressure Estimation

by Gang Ma, Yuhang Chen, Wenliang Zhu, Lesong Zheng, Hui Tang, Yong Yu and Lirong Wang

Micromachines 2022, 13(9), 1438; https://doi.org/10.3390/mi13091438 - 31 Aug 2022

Cited by 4 | Viewed by 2946

Abstract

Non-invasive continuous blood pressure monitoring is of great significance for the preventing, diagnosing, and treating of cardiovascular diseases (CVDs). Studies have demonstrated that photoplethysmogram (PPG) and electrocardiogram (ECG) signals can effectively and continuously predict blood pressure (BP). However, most of the BP estimation [...] Read more.

Non-invasive continuous blood pressure monitoring is of great significance for the preventing, diagnosing, and treating of cardiovascular diseases (CVDs). Studies have demonstrated that photoplethysmogram (PPG) and electrocardiogram (ECG) signals can effectively and continuously predict blood pressure (BP). However, most of the BP estimation models focus on the waveform features of the PPG signal, while the peak value of R-wave in ECG is only used as a time reference, and few references investigated the ECG waveforms. This paper aims to evaluate the influence of three characteristic waveforms in ECG on the improvement of BP estimation. PPG is the primary signal, and five input combinations are formed by adding ECG, P wave, QRS complex, T wave, and none. We employ five common convolutional neural networks (CNN) to validate the consistency of the contribution. Meanwhile, with the visualization of Gradient-weighted class activation mapping (Grad-CAM), we generate the heat maps and further visualize the distribution of CNN’s attention to each waveform of PPG and ECG. The heat maps show that networks pay more attention to the QRS complex and T wave. In the comparison results, the QRS complex and T wave have more contribution to minimizing errors than P wave. By separately adding P wave, QRS complex, and T wave, the average MAE of these networks reaches 7.87 mmHg, 6.57 mmHg, and 6.21 mmHg for systolic blood pressure (SBP), and 4.27 mmHg, 3.65 mmHg, and 3.73 mmHg, respectively, for diastolic blood pressure (DBP). The results of the experiment show that QRS complex and T wave deserves more attention and feature extraction like PPG waveform features in the continuous BP estimation. Full article

(This article belongs to the Special Issue Bioelectronics & Wearable Devices: Sensing, Signal Processing and Powering)

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10 pages, 1676 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Nucleic Acid Detection with Ion Concentration Polarization Microfluidic Chip for Reduced Cycle Numbers of Polymerase Chain Reaction

by Chengzhuang Yu, Shijie Dai, Shanshan Li, Junwei Li, Hezhi Hu, Jiyu Meng, Chunyang Wei and Jie Jayne Wu

Micromachines 2022, 13(9), 1394; https://doi.org/10.3390/mi13091394 - 26 Aug 2022

Cited by 3 | Viewed by 2636

Abstract

Nucleic acid detection is widely used in disease diagnosis, food safety, environmental monitoring and many other research fields. The continuous development of rapid and sensitive new methods to detective nucleic acid is very important for practical application. In this study, we developed a [...] Read more.

Nucleic acid detection is widely used in disease diagnosis, food safety, environmental monitoring and many other research fields. The continuous development of rapid and sensitive new methods to detective nucleic acid is very important for practical application. In this study, we developed a rapid nucleic-acid detection method using polymerase chain reaction (PCR) combined with electrokinetic preconcentration based on ion concentration polarization (ICP). Using a Nafion film, the proposed ICP microfluidic chip is utilized to enrich the nucleic acid molecules amplified by PCR thermal cycles. To demonstrate the capability of the microfluidic device and the hybrid nucleic-acid detection method, we present an animal-derived component detection experiment for meat product identification applications. With the reduced cycle numbers of 24 cycles, the detection can be completed in about 35 min. The experimental results show that this work can provide a microfluidic device and straightforward method for rapid detection of nucleic acids with reduced cycle numbers. Full article

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

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14 pages, 2378 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Disease Modeling with Kidney Organoids

by Sophie Karp, Martin R Pollak and Balajikarthick Subramanian

Micromachines 2022, 13(9), 1384; https://doi.org/10.3390/mi13091384 - 25 Aug 2022

Cited by 7 | Viewed by 3614

Abstract

Kidney diseases often lack optimal treatments, causing millions of deaths each year. Thus, developing appropriate model systems to study human kidney disease is of utmost importance. Some of the most promising human kidney models are organoids or small organ-resembling tissue collectives, derived from [...] Read more.

Kidney diseases often lack optimal treatments, causing millions of deaths each year. Thus, developing appropriate model systems to study human kidney disease is of utmost importance. Some of the most promising human kidney models are organoids or small organ-resembling tissue collectives, derived from human-induced pluripotent stem cells (hiPSCs). However, they are more akin to a first-trimester fetal kidney than an adult kidney. Therefore, new strategies are needed to advance their maturity. They have great potential for disease modeling and eventually auxiliary therapy if they can reach the maturity of an adult kidney. In this review, we will discuss the current state of kidney organoids in terms of their similarity to the human kidney and use as a disease modeling system thus far. We will then discuss potential pathways to advance the maturity of kidney organoids to match an adult kidney for more accurate human disease modeling. Full article

(This article belongs to the Section B2: Biofabrication and Tissue Engineering)

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11 pages, 5536 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

On-Skin Flexible Pressure Sensor with High Sensitivity for Portable Pulse Monitoring

by Weihao Zheng, Hongcheng Xu, Meng Wang, Qikai Duan, Yangbo Yuan, Weidong Wang and Libo Gao

Micromachines 2022, 13(9), 1390; https://doi.org/10.3390/mi13091390 - 25 Aug 2022

Cited by 18 | Viewed by 3856

Abstract

Radial artery pulse pressure contains abundant cardiovascular physiological and pathological information, which plays an important role in clinical diagnosis of traditional Chinese medical science. However, many photoelectric sensors and pressure sensors will lose a large number of waveform features in monitoring pulse, which [...] Read more.

Radial artery pulse pressure contains abundant cardiovascular physiological and pathological information, which plays an important role in clinical diagnosis of traditional Chinese medical science. However, many photoelectric sensors and pressure sensors will lose a large number of waveform features in monitoring pulse, which will make it difficult for doctors to precisely evaluate the patients’ health. In this letter, we proposed an on-skin flexible pressure sensor for monitoring radial artery pulse. The sensor consists of the MXene (Ti₃C₂T_x)-coated nonwoven fabrics (n-WFs) sensitive layer and laser-engraved interdigital copper electrodes. Benefiting from substantially increased conductive paths between fibers and electrodes during normal compression, the sensor obtains high sensitivity (3.187 kPa⁻¹), fast response time (15 ms), low detection limit (11.1 Pa), and long-term durability (20,000 cycles). Furthermore, a flexible processing circuit was connected with the sensor mounted on wrist radial artery, achieving wirelessly precise monitoring of the pulse on smart phones in real time. Compared with the commercial flexible pressure sensor, our sensor successfully captures weak systolic peak precisely, showing its great clinical potential and commercial value. Full article

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

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13 pages, 15307 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Scalable Additive Construction of Arrayed Microstructures with Encoded Properties for Bioimaging

by Matthew DiSalvo, Belén Cortés-Llanos, Cody A. LaBelle, David M. Murdoch and Nancy L. Allbritton

Micromachines 2022, 13(9), 1392; https://doi.org/10.3390/mi13091392 - 25 Aug 2022

Cited by 1 | Viewed by 2016

Abstract

Microarrays are essential components of analytical instruments. The elements of microarrays may be imbued with additional functionalities and encodings using composite materials and structures, but traditional microfabrication methods present substantial barriers to fabrication, design, and scalability. In this work, a tool-free technique was [...] Read more.

Microarrays are essential components of analytical instruments. The elements of microarrays may be imbued with additional functionalities and encodings using composite materials and structures, but traditional microfabrication methods present substantial barriers to fabrication, design, and scalability. In this work, a tool-free technique was reported to additively batch-construct micromolded, composite, and arrayed microstructures. The method required only a compatible carrier fluid to deposit a material onto a substrate with some topography. Permutations of this basic fabrication approach were leveraged to gain control over the volumes and positions of deposited materials within the microstructures. As a proof of concept, cell micro-carrier arrays were constructed to demonstrate a range of designs, compositions, functionalities, and applications for composite microstructures. This approach is envisioned to enable the fabrication of complex composite biological and synthetic microelements for biosensing, cellular analysis, and biochemical screening. Full article

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10 pages, 3764 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Oscillation Dynamics of Multiple Water Droplets Levitated in an Acoustic Field

by Koji Hasegawa and Manami Murata

Micromachines 2022, 13(9), 1373; https://doi.org/10.3390/mi13091373 - 23 Aug 2022

Cited by 12 | Viewed by 3530

Abstract

This study aimed to improve and investigate the oscillation dynamics and levitation stability of acoustically levitated water droplets. Contactless sample manipulation technology in mid-air has attracted significant attention in the fields of biochemistry and pharmaceutical science. Although one promising method is acoustic levitation, [...] Read more.

This study aimed to improve and investigate the oscillation dynamics and levitation stability of acoustically levitated water droplets. Contactless sample manipulation technology in mid-air has attracted significant attention in the fields of biochemistry and pharmaceutical science. Although one promising method is acoustic levitation, most studies have focused on a single sample. Therefore, it is important to determine the stability of multiple samples during acoustic levitation. Here, we aim to understand the effect of multiple-sample levitation on levitation stability in acoustic fields. We visualized the oscillatory motion of multiple levitated droplets using a high-speed video camera. To characterize the dynamics of multiple levitating droplets, the oscillation frequency and restoring force coefficients of the levitated samples, which were obtained from the experimental data, were analyzed to quantify the droplet–droplet interaction. The oscillation model of the spring-mass system was compared with the experimental results, and we found that the number of levitating droplets and their position played an important role in the levitation stability of the droplets. Our insights could help us understand the oscillatory behavior of levitated droplets to achieve more stable levitation. Full article

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