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Editor’s Choice Articles

Editor’s Choice articles are based on recommendations by the scientific editors of MDPI journals from around the world. Editors select a small number of articles recently published in the journal that they believe will be particularly interesting to readers, or important in the respective research area. The aim is to provide a snapshot of some of the most exciting work published in the various research areas of the journal.

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30 pages, 5873 KiB  
Review
Recent Advances in Thermoplastic Microfluidic Bonding
by Kiran Giri and Chia-Wen Tsao
Micromachines 2022, 13(3), 486; https://doi.org/10.3390/mi13030486 - 20 Mar 2022
Cited by 23 | Viewed by 8227
Abstract
Microfluidics is a multidisciplinary technology with applications in various fields, such as biomedical, energy, chemicals and environment. Thermoplastic is one of the most prominent materials for polymer microfluidics. Properties such as good mechanical rigidity, organic solvent resistivity, acid/base resistivity, and low water absorbance [...] Read more.
Microfluidics is a multidisciplinary technology with applications in various fields, such as biomedical, energy, chemicals and environment. Thermoplastic is one of the most prominent materials for polymer microfluidics. Properties such as good mechanical rigidity, organic solvent resistivity, acid/base resistivity, and low water absorbance make thermoplastics suitable for various microfluidic applications. However, bonding of thermoplastics has always been challenging because of a wide range of bonding methods and requirements. This review paper summarizes the current bonding processes being practiced for the fabrication of thermoplastic microfluidic devices, and provides a comparison between the different bonding strategies to assist researchers in finding appropriate bonding methods for microfluidic device assembly. Full article
(This article belongs to the Special Issue Feature Papers of Micromachines in Biology and Biomedicine 2022)
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9 pages, 1698 KiB  
Communication
Characterization of Active Electrode Yield for Intracortical Arrays: Awake versus Anesthesia
by Brandon Sturgill, Rahul Radhakrishna, Teresa Thuc Doan Thai, Sourav S. Patnaik, Jeffrey R. Capadona and Joseph J. Pancrazio
Micromachines 2022, 13(3), 480; https://doi.org/10.3390/mi13030480 - 20 Mar 2022
Cited by 6 | Viewed by 2597
Abstract
Intracortical microelectrode arrays are used for recording neural signals at single-unit resolution and are promising tools for studying brain function and developing neuroprosthetics. Research is being done to increase the chronic performance and reliability of these probes, which tend to decrease or fail [...] Read more.
Intracortical microelectrode arrays are used for recording neural signals at single-unit resolution and are promising tools for studying brain function and developing neuroprosthetics. Research is being done to increase the chronic performance and reliability of these probes, which tend to decrease or fail within several months of implantation. Although recording paradigms vary, studies focused on assessing the reliability and performance of these devices often perform recordings under anesthesia. However, anesthetics—such as isoflurane—are known to alter neural activity and electrophysiologic function. Therefore, we compared the neural recording performance under anesthesia (2% isoflurane) followed by awake conditions for probes implanted in the motor cortex of both male and female Sprague-Dawley rats. While the single-unit spike rate was significantly higher by almost 600% under awake compared to anesthetized conditions, we found no difference in the active electrode yield between the two conditions two weeks after surgery. Additionally, the signal-to-noise ratio was greater under anesthesia due to the noise levels being nearly 50% greater in awake recordings, even though there was a 14% increase in the peak-to-peak voltage of distinguished single units when awake. We observe that these findings are similar for chronic time points as well. Our observations indicate that either anesthetized or awake recordings are acceptable for studies assessing the chronic reliability and performance of intracortical microelectrode arrays. Full article
(This article belongs to the Special Issue Micromachines for Neurological Research)
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6 pages, 1100 KiB  
Article
3D Printed PCB Microfluidics
by Stefan Gassmann, Sathurja Jegatheeswaran, Till Schleifer, Hesam Arbabi and Helmut Schütte
Micromachines 2022, 13(3), 470; https://doi.org/10.3390/mi13030470 - 19 Mar 2022
Cited by 4 | Viewed by 3263
Abstract
The combination of printed circuit boards (PCB) and microfluidics has many advantages. The combination of electrodes, sensors and electronics is needed for almost all microfluidic systems. Using PCBs as a substrate, this integration is intrinsic. Additive manufacturing has become a widely used technique [...] Read more.
The combination of printed circuit boards (PCB) and microfluidics has many advantages. The combination of electrodes, sensors and electronics is needed for almost all microfluidic systems. Using PCBs as a substrate, this integration is intrinsic. Additive manufacturing has become a widely used technique in industry, research and by hobbyists. One very promising rapid prototype technique is vat polymerization with an LCD as mask, also known as masked stereolithography (mSLA). These printers are available with resolutions down to 35 µm, and they are affordable. In this paper, a technology is described which creates microfluidics on a PCB substrate using an mSLA printer. All steps of the production process can be carried out with commercially available printers and resins: this includes the structuring of the copper layer of the PCB and the buildup of the channel layer on top of the PCB. Copper trace dimensions down to 100 µm and channel dimensions of 800 µm are feasible. The described technology is a low-cost solution for combining PCBs and microfluidics. Full article
(This article belongs to the Special Issue Lab-on-PCB Devices)
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9 pages, 21368 KiB  
Article
Miniaturized Sulfite-Based Gold Bath for Controlled Electroplating of Zone Plate Nanostructures
by Hanna Ohlin, Thomas Frisk, Mattias Åstrand and Ulrich Vogt
Micromachines 2022, 13(3), 452; https://doi.org/10.3390/mi13030452 - 17 Mar 2022
Cited by 5 | Viewed by 2932
Abstract
X-ray zone plates made from gold are common optical components used in X-ray imaging experiments. These nanostructures are normally fabricated using a combination of electron-beam lithography and gold electroplating with cyanide gold baths. In this study, we present a gold electroplating process in [...] Read more.
X-ray zone plates made from gold are common optical components used in X-ray imaging experiments. These nanostructures are normally fabricated using a combination of electron-beam lithography and gold electroplating with cyanide gold baths. In this study, we present a gold electroplating process in a miniaturized gold-suplphite bath. The miniaturization is enabled by on-chip reference plating areas with well defined sizes, offering a reliable way to control the height of the structures by carefully choosing the plating time at a given current density in accordance with a calibration curve. Fabricated gold zone plates were successfully used in X-ray imaging experiments with synchrotron radiation. Although gold electroplating of nanostructures is a well-established method, details about the actual process are often missing in the literature. Therefore, we think that our detailed descriptions and explanations will be helpful for other researchers that would like to fabricate similar structures. Full article
(This article belongs to the Special Issue Micro-Manufacturing and Applications, Volume III: Advanced Hybrid Processes in Micro-Manufacturing)
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33 pages, 22884 KiB  
Review
Printed Circuit Boards: The Layers’ Functions for Electronic and Biomedical Engineering
by Francisco Perdigones and José Manuel Quero
Micromachines 2022, 13(3), 460; https://doi.org/10.3390/mi13030460 - 17 Mar 2022
Cited by 7 | Viewed by 11512
Abstract
This paper describes the fabrication opportunities that Printed Circuit Boards (PCBs) offer for electronic and biomedical engineering. Historically, PCB substrates have been used to support the components of the electronic devices, linking them using copper lines, and providing input and output pads to [...] Read more.
This paper describes the fabrication opportunities that Printed Circuit Boards (PCBs) offer for electronic and biomedical engineering. Historically, PCB substrates have been used to support the components of the electronic devices, linking them using copper lines, and providing input and output pads to connect the rest of the system. In addition, this kind of substrate is an emerging material for biomedical engineering thanks to its many interesting characteristics, such as its commercial availability at a low cost with very good tolerance and versatility, due to its multilayer characteristics; that is, the possibility of using several metals and substrate layers. The alternative uses of copper, gold, Flame Retardant 4 (FR4) and silver layers, together with the use of vias, solder masks and a rigid and flexible substrate, are noted. Among other uses, these characteristics have been using to develop many sensors, biosensors and actuators, and PCB-based lab-on chips; for example, deoxyribonucleic acid (DNA) amplification devices for Polymerase Chain Reaction (PCR). In addition, several applications of these devices are going to be noted in this paper, and two tables summarizing the layers’ functions are included in the discussion: the first one for metallic layers, and the second one for the vias, solder mask, flexible and rigid substrate functions. Full article
(This article belongs to the Special Issue Lab-on-PCB Devices)
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11 pages, 2814 KiB  
Article
Observations on Detonation Growth of Lead Azide at Microscale
by Yunfei Mu, Wei Zhang, Ruiqi Shen and Yinghua Ye
Micromachines 2022, 13(3), 451; https://doi.org/10.3390/mi13030451 - 16 Mar 2022
Cited by 4 | Viewed by 2264
Abstract
Lead azide (LA) is a commonly used primary explosive, the detonation growth of which is difficult to study because it is so sensitive and usually has a small charge size in applications. We used photon Doppler velocimetry (PDV) and calibrated polyvinylidene fluoride (PVDF) [...] Read more.
Lead azide (LA) is a commonly used primary explosive, the detonation growth of which is difficult to study because it is so sensitive and usually has a small charge size in applications. We used photon Doppler velocimetry (PDV) and calibrated polyvinylidene fluoride (PVDF) gauges to reveal the detonation growth in LA, which was pressed in the confinements with controlled heights. The particle-velocity profiles, output pressure, unsteady detonation velocity, reaction time, and reaction-zone width were obtained and analyzed. Three phases of detonation propagation of LA microcharges are discussed. The volume reactions occur at the beginning of detonation in LA microcharges without forming complete shock profiles. Then the shock front is fast with a slow chemistry reaction zone, which is compressed continuously between the height of 0.8 mm and 2.5 mm. Finally, the steady detonation is built at a height of 2.5 mm. The stable detonation velocity and CJ pressure are 4726 ± 8 m/s and 17.12 ± 0.22 GPa. Additionally, the stable reaction zone time and width are 44 ± 7 ns and 148 ± 11 μm. The detailed detonation process has not previously been quantified in such a small geometry. Full article
(This article belongs to the Special Issue Microsystems for Space and Defense Applications)
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27 pages, 16459 KiB  
Review
Review of Electrothermal Micromirrors
by Yue Tang, Jianhua Li, Lixin Xu, Jeong-Bong Lee and Huikai Xie
Micromachines 2022, 13(3), 429; https://doi.org/10.3390/mi13030429 - 10 Mar 2022
Cited by 14 | Viewed by 3658
Abstract
Electrothermal micromirrors have become an important type of micromirrors due to their large angular scanning range and large linear motion. Typically, electrothermal micromirrors do not have a torsional bar, so they can easily generate linear motion. In this paper, electrothermal micromirrors based on [...] Read more.
Electrothermal micromirrors have become an important type of micromirrors due to their large angular scanning range and large linear motion. Typically, electrothermal micromirrors do not have a torsional bar, so they can easily generate linear motion. In this paper, electrothermal micromirrors based on different thermal actuators are reviewed, and also the mechanisms of those actuators are analyzed, including U-shape, chevron, thermo-pneumatic, thermo-capillary and thermal bimorph-based actuation. Special attention is given to bimorph based-electrothermal micromirrors due to their versatility in tip-tilt-piston motion. The exemplified applications of each type of electrothermal micromirrors are also presented. Moreover, electrothermal micromirrors integrated with electromagnetic or electrostatic actuators are introduced. Full article
(This article belongs to the Special Issue Optical MEMS, Volume III)
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11 pages, 3350 KiB  
Article
Electrochemical Glue for Binding Chitosan–Alginate Hydrogel Fibers for Cell Culture
by Yoshinobu Utagawa, Kosuke Ino, Tatsuki Kumagai, Kaoru Hiramoto, Masahiro Takinoue, Yuji Nashimoto and Hitoshi Shiku
Micromachines 2022, 13(3), 420; https://doi.org/10.3390/mi13030420 - 8 Mar 2022
Cited by 6 | Viewed by 3533
Abstract
Three-dimensional organs and tissues can be constructed using hydrogels as support matrices for cells. For the assembly of these gels, chemical and physical reactions that induce gluing should be induced locally in target areas without causing cell damage. Herein, we present a novel [...] Read more.
Three-dimensional organs and tissues can be constructed using hydrogels as support matrices for cells. For the assembly of these gels, chemical and physical reactions that induce gluing should be induced locally in target areas without causing cell damage. Herein, we present a novel electrochemical strategy for gluing hydrogel fibers. In this strategy, a microelectrode electrochemically generated HClO or Ca2+, and these chemicals were used to crosslink chitosan–alginate fibers fabricated using interfacial polyelectrolyte complexation. Further, human umbilical vein endothelial cells were incorporated into the fibers, and two such fibers were glued together to construct “+”-shaped hydrogels. After gluing, the hydrogels were embedded in Matrigel and cultured for several days. The cells spread and proliferated along the fibers, indicating that the electrochemical glue was not toxic toward the cells. This is the first report on the use of electrochemical glue for the assembly of hydrogel pieces containing cells. Based on our results, the electrochemical gluing method has promising applications in tissue engineering and the development of organs on a chip. Full article
(This article belongs to the Special Issue Frontiers in Micromachines in Japan)
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25 pages, 120720 KiB  
Review
Recent Progress in Silicon-Based Slow-Light Electro-Optic Modulators
by Changhao Han, Ming Jin, Yuansheng Tao, Bitao Shen and Xingjun Wang
Micromachines 2022, 13(3), 400; https://doi.org/10.3390/mi13030400 - 28 Feb 2022
Cited by 10 | Viewed by 5114
Abstract
As an important optoelectronic integration platform, silicon photonics has achieved significant progress in recent years, demonstrating the advantages on low power consumption, low cost, and complementary metal–oxide–semiconductor (CMOS) compatibility. Among the different silicon photonics devices, the silicon electro-optic modulator is a key active [...] Read more.
As an important optoelectronic integration platform, silicon photonics has achieved significant progress in recent years, demonstrating the advantages on low power consumption, low cost, and complementary metal–oxide–semiconductor (CMOS) compatibility. Among the different silicon photonics devices, the silicon electro-optic modulator is a key active component to implement the conversion of electric signal to optical signal. However, conventional silicon Mach–Zehnder modulators and silicon micro-ring modulators both have their own limitations, which will limit their use in future systems. For example, the conventional silicon Mach–Zehnder modulators are hindered by large footprint, while the silicon micro-ring modulators have narrow optical bandwidth and high temperature sensitivity. Therefore, developing a new structure for silicon modulators to improve the performance is a crucial research direction in silicon photonics. Meanwhile, slow-light effect is an important physical phenomenon that can reduce the group velocity of light. Applying slow-light effect on silicon modulators through photonics crystal and waveguide grating structures is an attractive research point, especially in the aspect of reducing the device footprint. In this paper, we review the recent progress of silicon-based slow-light electro-optic modulators towards future communication requirements. Beginning from the principle of slow-light effect, we summarize the research of silicon photonic crystal modulators and silicon waveguide grating modulators in detail. Simultaneously, the experimental results of representative silicon slow-light modulators are compared and analyzed. Finally, we discuss the existing challenges and development directions of silicon-based slow-light electro-optic modulators for the practical applications. Full article
(This article belongs to the Special Issue Photonic Chips for Optical Communications)
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13 pages, 3719 KiB  
Technical Note
Design and Massaging Force Analysis of Wearable Flexible Single Point Massager Imitating Traditional Chinese Medicine
by Zhou Zhou, Yixuan Wang, Chenjun Zhang, Ao Meng, Bingshan Hu and Hongliu Yu
Micromachines 2022, 13(3), 370; https://doi.org/10.3390/mi13030370 - 26 Feb 2022
Cited by 2 | Viewed by 3041
Abstract
In the theory of traditional Chinese medicine, acupoints refer to special points and areas on the meridian line of the human body. Traditional Chinese medicine believes that the application of unique techniques such as pressing, kneading, rubbing, pushing, and patting to acupoints or [...] Read more.
In the theory of traditional Chinese medicine, acupoints refer to special points and areas on the meridian line of the human body. Traditional Chinese medicine believes that the application of unique techniques such as pressing, kneading, rubbing, pushing, and patting to acupoints or massage with the help of specific tools has the effects of promoting blood circulation, dredging meridians, and eliminating fatigue. At present, most automatic massage devices are for large-area massage of the trunk, and few are specifically for acupoint massage of the limbs. First, this paper analyzes the characteristics of traditional Chinese medical acupoint massage and then obtains the design index of an automatic acupoint massage device. After that, based on the principle of a series elastic actuating mechanism, a flexible uni-acupoint massage device and control system, imitating the acupoint massage technique of traditional Chinese medicine, were designed. In order to analyze the massage force of the massage device, the man–machine contact dynamic model of the massage device was established, and the force of the massage device was simulated and analyzed. Finally, an experimental platform was built to verify the massage force and massage process of the massage device. The experimental results show that the massage device designed in this paper meets the indexes of traditional Chinese medical massage, in terms of the massage process and massage force, and verify the rationality of the design. Full article
(This article belongs to the Special Issue Wearable Robotics)
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12 pages, 2237 KiB  
Article
Electrospun Nanofiber Covered Polystyrene Micro-Nano Hybrid Structures for Triboelectric Nanogenerator and Supercapacitor
by Jihyeon Park, Seungju Jo, Youngsu Kim, Shakir Zaman and Daewon Kim
Micromachines 2022, 13(3), 380; https://doi.org/10.3390/mi13030380 - 26 Feb 2022
Cited by 14 | Viewed by 3738
Abstract
Recently, tremendous research on small energy supply devices is gaining popularity with the immerging Internet of Things (IoT) technologies. Especially, energy conversion and storage devices can provide opportunities for small electronics. In this research, a micro-nano structured design of electrodes is newly developed [...] Read more.
Recently, tremendous research on small energy supply devices is gaining popularity with the immerging Internet of Things (IoT) technologies. Especially, energy conversion and storage devices can provide opportunities for small electronics. In this research, a micro-nano structured design of electrodes is newly developed for high performing hybrid energy systems with the improved effective surface area. Further, it could be simply fabricated through two-steps synthesis of electrospinning and glass transition of a novel polystyrene (PS) substrate. Herein, the electro-spun nanofiber of polyacrylonitrile (PAN) and Nylon 66 (Nylon) are applied to the dielectric layer of a triboelectric generator (TENG), while the PAN and polyaniline (PANI) composites is utilized as an electroactive material of supercapacitor (SC). As a result, the self-charging power system is successfully integrated with the wrinkled PAN/PS (W-PAN/PS@PANI)-SC and W-TENG by using a rectifier. According to the fabricated hybrid energy systems, the electrical energy produced by W-TENG can be successfully stored into as-fabricated W-PAN/PS@PANI-SC and can also turn on a commercial green LED with the stored energy. Therefore, the micro-nano structured electrode designed for hybrid energy systems can contribute to improve the energy conversion and storage performance of various electronic devices. Full article
(This article belongs to the Special Issue Triboelectric Nanogenerators for Self-Powered Sensors and Artificial Intelligence)
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21 pages, 3557 KiB  
Review
Progress on Optical Fiber Biochemical Sensors Based on Graphene
by Yani Zhang, Lei Zhou, Dun Qiao, Mengyin Liu, Hongyan Yang, Cheng Meng, Ting Miao, Jia Xue and Yiming Yao
Micromachines 2022, 13(3), 348; https://doi.org/10.3390/mi13030348 - 23 Feb 2022
Cited by 17 | Viewed by 4071
Abstract
Graphene, a novel form of the hexagonal honeycomb two-dimensional carbon-based structural material with a zero-band gap and ultra-high specific surface area, has unique optoelectronic capabilities, promising a suitable basis for its application in the field of optical fiber sensing. Graphene optical fiber sensing [...] Read more.
Graphene, a novel form of the hexagonal honeycomb two-dimensional carbon-based structural material with a zero-band gap and ultra-high specific surface area, has unique optoelectronic capabilities, promising a suitable basis for its application in the field of optical fiber sensing. Graphene optical fiber sensing has also been a hotspot in cross-research in biology, materials, medicine, and micro-nano devices in recent years, owing to prospective benefits, such as high sensitivity, small size, and strong anti-electromagnetic interference capability and so on. Here, the progress of optical fiber biochemical sensors based on graphene is reviewed. The fabrication of graphene materials and the sensing mechanism of the graphene-based optical fiber sensor are described. The typical research works of graphene-based optical fiber biochemical sensor, such as long-period fiber grating, Bragg fiber grating, no-core fiber and photonic crystal fiber are introduced, respectively. Finally, prospects for graphene-based optical fiber biochemical sensing technology will also be covered, which will provide an important reference for the development of graphene-based optical fiber biochemical sensors. Full article
(This article belongs to the Special Issue Women’s Special Issue Series: Micromachines)
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13 pages, 4418 KiB  
Article
Hybrid Dissection for Neutron Tube Shell via Continuous-Wave Laser and Ultra-Short Pulse Laser
by Minqiang Kang, Yongfa Qiang, Canlin Zhu, Xiangjun Xiang, Dandan Zhou, Zhitao Peng, Xudong Xie and Qihua Zhu
Micromachines 2022, 13(3), 352; https://doi.org/10.3390/mi13030352 - 23 Feb 2022
Cited by 3 | Viewed by 1536
Abstract
The sealed neutron tube shell dissection process utilizing the traditional lathe turning method suffers from low efficiency and high cost due to the frequency of replacement of the diamond knife. In this study, a hybrid dissection method is introduced by combining the continuous-wave [...] Read more.
The sealed neutron tube shell dissection process utilizing the traditional lathe turning method suffers from low efficiency and high cost due to the frequency of replacement of the diamond knife. In this study, a hybrid dissection method is introduced by combining the continuous-wave (CW) laser for efficient tangential groove production with an ultra-short pulse laser for delamination scanning removal. In this method, a high-power CW laser is firstly employed to make a tapered groove on the shell’s surface, and then a femtosecond pulse laser is used to micromachine the groove in order to obtain a cutting kerf. The thermal field was theoretically investigated in a finite element model. The simulation results show that the width of the area of temperature exceeding 100 °C is 1.9 mm and 0.4 mm with rotating speeds of 20 rad/s and 60 rad/s, respectively. In addition, a 2 mm deep slot in the 25 mm diameter tube was successfully produced in 1 min by a kilowatt fiber laser, and a 500-femtosecond pulse laser was employed to cut a plate with a material removal rate of 0.2 mm3/min. By using the hybrid method, the cutting efficiency was improved about 49 times compared to the femtosecond laser cutting. According to the simulation and experimental results, this method provides a high-efficiency and non-thermal cutting technique for reclaimed metallic neutron tube shells with millimeter-level thick walls, which has the advantages of non-contact, minimal thermal diffusion, and no effect of molten slag. It is indicated that the hybrid dissection method not only offers a new solution for thick neutron tube shell cutting but also extends the application of laser cutting techniques. Full article
(This article belongs to the Special Issue Laser Additive Manufacturing: Design, Materials, Processes and Applications)
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21 pages, 7337 KiB  
Review
Silicon Carbide Technology for Advanced Human Healthcare Applications
by Stephen E. Saddow
Micromachines 2022, 13(3), 346; https://doi.org/10.3390/mi13030346 - 22 Feb 2022
Cited by 27 | Viewed by 4178
Abstract
Silicon carbide (SiC) is a highly robust semiconductor material that has the potential to revolutionize implantable medical devices for human healthcare, such as biosensors and neuro-implants, to enable advanced biomedical therapeutic applications for humans. SiC is both bio and hemocompatible, and is already [...] Read more.
Silicon carbide (SiC) is a highly robust semiconductor material that has the potential to revolutionize implantable medical devices for human healthcare, such as biosensors and neuro-implants, to enable advanced biomedical therapeutic applications for humans. SiC is both bio and hemocompatible, and is already commercially used for long-term human in vivo applications ranging from heart stent coatings and dental implants to short-term diagnostic applications involving neural implants and sensors. One challenge facing the medical community today is the lack of biocompatible materials which are inherently smart or, in other words, capable of electronic functionality. Such devices are currently implemented using silicon technology, which either has to be hermetically sealed so it does not directly interact with biological tissue or has a short lifetime due to instabilities in vivo. Long-term, permanently implanted devices such as glucose sensors, neural interfaces, smart bone and organ implants, etc., require a more robust material that does not degrade over time and is not recognized and rejected as a foreign object by the inflammatory response. SiC has displayed these exceptional material properties, which opens up a whole new host of applications and allows for the development of many advanced biomedical devices never before possible for long-term use in vivo. This paper is a review of the state-of-the art and discusses cutting-edge device applications where SiC medical devices are poised to translate to the commercial marketplace. Full article
(This article belongs to the Special Issue Feature Papers of Micromachines in Engineering and Technology 2021)
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20 pages, 17345 KiB  
Article
Design and Fabrication of a Magnetic Actuator for Torque and Force Control Estimated by the ANN/SA Algorithm
by Pooriya Kazemzadeh Heris and Mir Behrad Khamesee
Micromachines 2022, 13(2), 327; https://doi.org/10.3390/mi13020327 - 19 Feb 2022
Cited by 11 | Viewed by 2637
Abstract
Magnetic manipulation has the potential to recast the medical field both from an operational and drug delivery point of view as it can provide wireless controlled navigation over surgical devices and drug containers inside a human body. The presented system in this research [...] Read more.
Magnetic manipulation has the potential to recast the medical field both from an operational and drug delivery point of view as it can provide wireless controlled navigation over surgical devices and drug containers inside a human body. The presented system in this research implements a unique eight-coil configuration, where each coil is designed based on the characterization of the working space, generated force on a milliscale robot, and Fabry factor. A cylindrical iron-core coil with inner and outer diameters and length of 20.5, 66, and 124 mm is the optimized coil. Traditionally, FEM results are adopted from simulation and implemented into the motion logic; however, simulated values are associated with errors; 17% in this study. Instead of regularizing FEM results, for the first time, artificial intelligence has been used to approximate the actual values for manipulation purposes. Regression models for Artificial Neural Network (ANN) and a hybrid method called Artificial Neural Network with Simulated Annealing (ANN/SA) have been created. ANN/SA has shown outstanding performance with an average R2, and a root mean square error of 0.9871 and 0.0153, respectively. Implementation of the regression model into the manipulation logic has provided a motion with 13 μm of accuracy. Full article
(This article belongs to the Special Issue Flexible Micromanipulators and Micromanipulation)
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15 pages, 8744 KiB  
Article
Densification, Tailored Microstructure, and Mechanical Properties of Selective Laser Melted Ti–6Al–4V Alloy via Annealing Heat Treatment
by Di Wang, Han Wang, Xiaojun Chen, Yang Liu, Dong Lu, Xinyu Liu and Changjun Han
Micromachines 2022, 13(2), 331; https://doi.org/10.3390/mi13020331 - 19 Feb 2022
Cited by 13 | Viewed by 2666
Abstract
This work investigated the influence of process parameters on the densification, microstructure, and mechanical properties of a Ti–6Al–4V alloy printed by selective laser melting (SLM), followed by annealing heat treatment. In particular, the evolution mechanisms of the microstructure and mechanical properties of the [...] Read more.
This work investigated the influence of process parameters on the densification, microstructure, and mechanical properties of a Ti–6Al–4V alloy printed by selective laser melting (SLM), followed by annealing heat treatment. In particular, the evolution mechanisms of the microstructure and mechanical properties of the printed alloy with respect to the annealing temperature near the β phase transition temperature were investigated. The process parameter optimization of SLM can lead to the densification of the printed Ti–6Al–4V alloy with a relative density of 99.51%, accompanied by an ultimate tensile strength of 1204 MPa and elongation of 7.8%. The results show that the microstructure can be tailored by altering the scanning speed and annealing temperature. The SLM-printed Ti–6Al–4V alloy contains epitaxial growth β columnar grains and internal acicular martensitic α′ grains, and the width of the β columnar grain decreases with an increase in the scanning speed. Comparatively, the printed alloy after annealing in the range of 750–1050 °C obtains the microstructure consisting of α + β dual phases. In particular, network and Widmanstätten structures are formed at the annealing temperatures of 850 °C and 1050 °C, respectively. The maximum elongation of 14% can be achieved at the annealing temperature of 950 °C, which was 79% higher than that of as-printed samples. Meanwhile, an ultimate tensile strength larger than 1000 MPa can be maintained, which still meets the application requirements of the forged Ti–6Al–4V alloy. Full article
(This article belongs to the Special Issue Laser Additive Manufacturing: Design, Materials, Processes and Applications)
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13 pages, 10521 KiB  
Article
MEMS-Casting Fabricated Chip-Style 3D Metal Solenoidal Transformers towards Integrated Power Supply
by Nianying Wang, Changnan Chen, Pu Chen, Jiebin Gu, Pichao Pan, Ruofeng Han, Min Liu and Xinxin Li
Micromachines 2022, 13(2), 325; https://doi.org/10.3390/mi13020325 - 18 Feb 2022
Cited by 1 | Viewed by 2595
Abstract
A silicon-chip-based 3D metal solenoidal transformer is proposed and developed to achieve AC-DC conversion for integrated power supply applications. With wafer-level micro electromechanical systems (MEMS) fabrication technique to form the metal casting mold and the following micro-casting technique to rapidly (within 6 min) [...] Read more.
A silicon-chip-based 3D metal solenoidal transformer is proposed and developed to achieve AC-DC conversion for integrated power supply applications. With wafer-level micro electromechanical systems (MEMS) fabrication technique to form the metal casting mold and the following micro-casting technique to rapidly (within 6 min) fill molten ZnAl alloy into the pre-micromachined silicon mold, 45-turns primary solenoid and 7-turns secondary solenoid are fabricated in silicon wafers, where the two intertwining solenoids are located at inner deck and outer deck, respectively. Permalloy soft magnetic core is inserted into a pre-etched channel in the silicon chip, which is surrounded by the solenoids. The size of the chip-style transformer is as small as 8.5 mm × 6.6 mm × 2.5 mm. The internal resistance of the primary solenoid is 1.82 Ω and that of the secondary solenoid is 0.16 Ω. The working frequency of the transformer is 60 kHz. Combined with the testing circuit of the switch mode power supply, the DC voltage of 13.02 V is obtained when the input is 110 V at 50 Hz/60 Hz. Furthermore, the on-chip 3D solenoidal transformer is used for lighting four LEDs, which shows great potential for AC-DC power supply. The wafer-level fabricated chip-style solenoidal AC-DC transformer for integrated power supply is advantageous in uniform fabrication, small size and volume applications. Full article
(This article belongs to the Section A：Physics)
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31 pages, 6121 KiB  
Review
Therapeutic Applications of Programmable DNA Nanostructures
by Seaim Lwin Aye and Yusuke Sato
Micromachines 2022, 13(2), 315; https://doi.org/10.3390/mi13020315 - 17 Feb 2022
Cited by 5 | Viewed by 4164
Abstract
Deoxyribonucleic acid (DNA) nanotechnology, a frontier in biomedical engineering, is an emerging field that has enabled the engineering of molecular-scale DNA materials with applications in biomedicine such as bioimaging, biodetection, and drug delivery over the past decades. The programmability of DNA nanostructures allows [...] Read more.
Deoxyribonucleic acid (DNA) nanotechnology, a frontier in biomedical engineering, is an emerging field that has enabled the engineering of molecular-scale DNA materials with applications in biomedicine such as bioimaging, biodetection, and drug delivery over the past decades. The programmability of DNA nanostructures allows the precise engineering of DNA nanocarriers with controllable shapes, sizes, surface chemistries, and functions to deliver therapeutic and functional payloads to target cells with higher efficiency and enhanced specificity. Programmability and control over design also allow the creation of dynamic devices, such as DNA nanorobots, that can react to external stimuli and execute programmed tasks. This review focuses on the current findings and progress in the field, mainly on the employment of DNA nanostructures such as DNA origami nanorobots, DNA nanotubes, DNA tetrahedra, DNA boxes, and DNA nanoflowers in the biomedical field for therapeutic purposes. We will also discuss the fate of DNA nanostructures in living cells, the major obstacles to overcome, that is, the stability of DNA nanostructures in biomedical applications, and the opportunities for DNA nanostructure-based drug delivery in the future. Full article
(This article belongs to the Special Issue Biomolecule Manipulation in Micro/Nanoscale: Separation, Preconcentration, and Detection)
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18 pages, 3652 KiB  
Review
Nano/Micromotors in Active Matter
by Chenglin Lv, Yuguang Yang and Bo Li
Micromachines 2022, 13(2), 307; https://doi.org/10.3390/mi13020307 - 17 Feb 2022
Cited by 5 | Viewed by 2564
Abstract
Nano/micromotors (NMMs) are tiny objects capable of converting energy into mechanical motion. Recently, a wealth of active matter including synthetic colloids, cytoskeletons, bacteria, and cells have been used to construct NMMs. The self-sustained motion of active matter drives NMMs out of equilibrium, giving [...] Read more.
Nano/micromotors (NMMs) are tiny objects capable of converting energy into mechanical motion. Recently, a wealth of active matter including synthetic colloids, cytoskeletons, bacteria, and cells have been used to construct NMMs. The self-sustained motion of active matter drives NMMs out of equilibrium, giving rise to rich dynamics and patterns. Alongside the spontaneous dynamics, external stimuli such as geometric confinements, light, magnetic field, and chemical potential are also harnessed to control the movements of NMMs, yielding new application paradigms of active matter. Here, we review the recent advances, both experimental and theoretical, in exploring biological NMMs. The unique dynamical features of collective NMMs are focused on, along with some possible applications of these intriguing systems. Full article
(This article belongs to the Special Issue Dream Nanomachines: Recent Advances in Nano/Micromotors)
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21 pages, 4863 KiB  
Review
Microscopic Swarms: From Active Matter Physics to Biomedical and Environmental Applications
by Yulei Fu, Hengao Yu, Xinli Zhang, Paolo Malgaretti, Vimal Kishore and Wendong Wang
Micromachines 2022, 13(2), 295; https://doi.org/10.3390/mi13020295 - 13 Feb 2022
Cited by 16 | Viewed by 4499
Abstract
Microscopic swarms consisting of, e.g., active colloidal particles or microorganisms, display emergent behaviors not seen in equilibrium systems. They represent an emerging field of research that generates both fundamental scientific interest and practical technological value. This review seeks to unite the perspective of [...] Read more.
Microscopic swarms consisting of, e.g., active colloidal particles or microorganisms, display emergent behaviors not seen in equilibrium systems. They represent an emerging field of research that generates both fundamental scientific interest and practical technological value. This review seeks to unite the perspective of fundamental active matter physics and the perspective of practical applications of microscopic swarms. We first summarize experimental and theoretical results related to a few key aspects unique to active matter systems: the existence of long-range order, the prediction and observation of giant number fluctuations and motility-induced phase separation, and the exploration of the relations between information and order in the self-organizing patterns. Then we discuss microscopic swarms, particularly microrobotic swarms, from the perspective of applications. We introduce common methods to control and manipulate microrobotic swarms and summarize their potential applications in fields such as targeted delivery, in vivo imaging, biofilm removal, and wastewater treatment. We aim at bridging the gap between the community of active matter physics and the community of micromachines or microrobotics, and in doing so, we seek to inspire fruitful collaborations between the two communities. Full article
(This article belongs to the Special Issue Medical Micro/Nanorobots)
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12 pages, 4487 KiB  
Article
Wireless Control Combining Myoelectric Signal and Human Body Communication for Wearable Robots
by Taisuke Iguchi, Ikuma Kondo and Jianqing Wang
Micromachines 2022, 13(2), 290; https://doi.org/10.3390/mi13020290 - 12 Feb 2022
Cited by 2 | Viewed by 1849
Abstract
In this study, a communication module based on human body communication was developed to wirelessly control a wearable robot hand based on myoelectric signals. The communication module adopts 10–60 MHz band and an impulse radio multi-pulse position modulation method to achieve low transmission [...] Read more.
In this study, a communication module based on human body communication was developed to wirelessly control a wearable robot hand based on myoelectric signals. The communication module adopts 10–60 MHz band and an impulse radio multi-pulse position modulation method to achieve low transmission loss and high data rate. A technique to reduce the module size was developed by sharing the myoelectric signal detection electrode and transmitting electrode, and three receiving electrode structures were investigated to improve signal transmission performance. As a result, the developed communication module provides a packet detection rate of 100% and a bit error rate of less than 10−6 up to at least 110 cm along the arm, and a wearable robot hand was demonstrated to be properly controlled based on a human subject’s myoelectric signals. Full article
(This article belongs to the Special Issue Wearable Robotics)
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23 pages, 7183 KiB  
Review
Terahertz Reconfigurable Intelligent Surfaces (RISs) for 6G Communication Links
by Fengyuan Yang, Prakash Pitchappa and Nan Wang
Micromachines 2022, 13(2), 285; https://doi.org/10.3390/mi13020285 - 10 Feb 2022
Cited by 44 | Viewed by 9009
Abstract
The forthcoming sixth generation (6G) communication network is envisioned to provide ultra-fast data transmission and ubiquitous wireless connectivity. The terahertz (THz) spectrum, with higher frequency and wider bandwidth, offers great potential for 6G wireless technologies. However, the THz links suffers from high loss [...] Read more.
The forthcoming sixth generation (6G) communication network is envisioned to provide ultra-fast data transmission and ubiquitous wireless connectivity. The terahertz (THz) spectrum, with higher frequency and wider bandwidth, offers great potential for 6G wireless technologies. However, the THz links suffers from high loss and line-of-sight connectivity. To overcome these challenges, a cost-effective method to dynamically optimize the transmission path using reconfigurable intelligent surfaces (RISs) is widely proposed. RIS is constructed by embedding active elements into passive metasurfaces, which is an artificially designed periodic structure. However, the active elements (e.g., PIN diodes) used for 5G RIS are impractical for 6G RIS due to the cutoff frequency limitation and higher loss at THz frequencies. As such, various tuning elements have been explored to fill this THz gap between radio waves and infrared light. The focus of this review is on THz RISs with the potential to assist 6G communication functionalities including pixel-level amplitude modulation and dynamic beam manipulation. By reviewing a wide range of tuning mechanisms, including electronic approaches (complementary metal-oxide-semiconductor (CMOS) transistors, Schottky diodes, high electron mobility transistors (HEMTs), and graphene), optical approaches (photoactive semiconductor materials), phase-change materials (vanadium dioxide, chalcogenides, and liquid crystals), as well as microelectromechanical systems (MEMS), this review summarizes recent developments in THz RISs in support of 6G communication links and discusses future research directions in this field. Full article
(This article belongs to the Special Issue Broadband Terahertz Devices and Communication Technologies)
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13 pages, 1720 KiB  
Article
3D Bioprinting of an In Vitro Model of a Biomimetic Urinary Bladder with a Contract-Release System
by Suhun Chae, Jaewook Kim, Hee-Gyeong Yi and Dong-Woo Cho
Micromachines 2022, 13(2), 277; https://doi.org/10.3390/mi13020277 - 9 Feb 2022
Cited by 11 | Viewed by 3645
Abstract
The development of curative therapy for bladder dysfunction is usually hampered owing to the lack of reliable ex vivo human models that can mimic the complexity of the human bladder. To overcome this issue, 3D in vitro model systems offering unique opportunities to [...] Read more.
The development of curative therapy for bladder dysfunction is usually hampered owing to the lack of reliable ex vivo human models that can mimic the complexity of the human bladder. To overcome this issue, 3D in vitro model systems offering unique opportunities to engineer realistic human tissues/organs have been developed. However, existing in vitro models still cannot entirely reflect the key structural and physiological characteristics of the native human bladder. In this study, we propose an in vitro model of the urinary bladder that can create 3D biomimetic tissue structures and dynamic microenvironments to replicate the smooth muscle functions of an actual human urinary bladder. In other words, the proposed biomimetic model system, developed using a 3D bioprinting approach, can recreate the physiological motion of the urinary bladder by incorporating decellularized extracellular matrix from the bladder tissue and introducing cyclic mechanical stimuli. The results showed that the developed bladder tissue models exhibited high cell viability and proliferation rate and promoted myogenic differentiation potential given dynamic mechanical cues. We envision the developed in vitro bladder mimicry model can serve as a research platform for fundamental studies on human disease modeling and pharmaceutical testing. Full article
(This article belongs to the Special Issue Advanced Biofabrication Technologies)
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7 pages, 2342 KiB  
Article
Flexible CdSe/ZnS Quantum-Dot Light-Emitting Diodes with Higher Efficiency than Rigid Devices
by Mijin Kim, Dongjin Kim, Ohun Kwon and Honyeon Lee
Micromachines 2022, 13(2), 269; https://doi.org/10.3390/mi13020269 - 7 Feb 2022
Cited by 17 | Viewed by 3216
Abstract
Fabrication of high-performance, flexible quantum-dot light-emitting diodes (QLEDs) requires the reliable manufacture of a flexible transparent electrode to replace the conventional brittle indium tin oxide (ITO) transparent electrode, along with flexible substrate planarization. We deposited a transparent oxide/metal/oxide (OMO) electrode on a polymer [...] Read more.
Fabrication of high-performance, flexible quantum-dot light-emitting diodes (QLEDs) requires the reliable manufacture of a flexible transparent electrode to replace the conventional brittle indium tin oxide (ITO) transparent electrode, along with flexible substrate planarization. We deposited a transparent oxide/metal/oxide (OMO) electrode on a polymer planarization layer and co-optimized both layers. The visible transmittance of the OMO electrode on a polyethylene terephthalate substrate increased markedly. Good electron supply and injection into an electron-transporting layer were achieved using WOX/Ag/ WOX and MoOx/Ag/MoOX OMO electrodes. High-performance flexible QLEDs were fabricated from these electrodes; a QLED with a MoOX/Ag/ MoOX cathode and an SU-8 planarization layer had a current efficiency of 30.3 cd/A and luminance more than 7 × 104 cd/m2. The current efficiency was significantly higher than that of a rigid QLED with an ITO cathode and was higher than current efficiency values obtained from previously reported QLEDs that utilized the same quantum-dot and electron-transporting layer materials as our study. Full article
(This article belongs to the Special Issue Quantum Dot Frontiers)
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16 pages, 4042 KiB  
Article
A Monolithic 3D Printed Axisymmetric Co-Flow Single and Compound Emulsion Generator
by Amirreza Ghaznavi, Yang Lin, Mark Douvidzon, Adam Szmelter, Alannah Rodrigues, Malik Blackman, David Eddington, Tal Carmon, Lev Deych, Lan Yang and Jie Xu
Micromachines 2022, 13(2), 188; https://doi.org/10.3390/mi13020188 - 26 Jan 2022
Cited by 5 | Viewed by 3882
Abstract
We report a microfluidic droplet generator which can produce single and compound droplets using a 3D axisymmetric co-flow structure. The design considered for the fabrication of the device integrated a user-friendly and cost-effective 3D printing process. To verify the performance of the device, [...] Read more.
We report a microfluidic droplet generator which can produce single and compound droplets using a 3D axisymmetric co-flow structure. The design considered for the fabrication of the device integrated a user-friendly and cost-effective 3D printing process. To verify the performance of the device, single and compound emulsions of deionized water and mineral oil were generated and their features such as size, generation frequency, and emulsion structures were successfully characterized. In addition, the generation of bio emulsions such as alginate and collagen aqueous droplets in mineral oil was demonstrated in this study. Overall, the monolithic 3D printed axisymmetric droplet generator could offer any user an accessible and easy-to-utilize device for the generation of single and compound emulsions. Full article
(This article belongs to the Special Issue Microfluidics for Environmental Monitoring)
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10 pages, 2231 KiB  
Article
Anti-Counterfeiting Tags Using Flexible Substrate with Gradient Micropatterning of Silver Nanowires
by Hyeli Kim, Goomin Kwon, Cheolheon Park, Jungmok You and Wook Park
Micromachines 2022, 13(2), 168; https://doi.org/10.3390/mi13020168 - 22 Jan 2022
Cited by 4 | Viewed by 3366
Abstract
Anti-counterfeiting technologies for small products are being developed. We present an anti-counterfeiting tag, a grayscale pattern of silver nanowires (AgNWs) on a flexible substrate. The anti-counterfeiting tag that is observable with a thermal imaging camera was fabricated using the characteristics of silver nanowires [...] Read more.
Anti-counterfeiting technologies for small products are being developed. We present an anti-counterfeiting tag, a grayscale pattern of silver nanowires (AgNWs) on a flexible substrate. The anti-counterfeiting tag that is observable with a thermal imaging camera was fabricated using the characteristics of silver nanowires with high visible light transmittance and high infrared emissivity. AgNWs were patterned at microscale via a maskless lithography method using UV dicing tape with UV patterns. By attaching and detaching an AgNW coated glass slide and UV dicing tape irradiated with multiple levels of UV, we obtained AgNW patterns with four or more grayscales. Peel tests confirmed that the adhesive strength of the UV dicing tape varied according to the amount of UV irradiation, and electrical resistance and IR image intensity measurements confirmed that the pattern obtained using this tape has multi-level AgNW concentrations. When applied for anti-counterfeiting, the gradient-concentration AgNW micropattern could contain more information than a single-concentration micropattern. In addition, the gradient AgNW micropattern could be transferred to a flexible polymer substrate using a simple method and then attached to various surfaces for use as an anti-counterfeiting tag. Full article
(This article belongs to the Special Issue Microparticle Fabrication and Its Biomedical Application)
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14 pages, 4521 KiB  
Article
3D Culture Platform for Enabling Large-Scale Imaging and Control of Cell Distribution into Complex Shapes by Combining 3D Printing with a Cube Device
by Atsushi Takano, Isabel Koh and Masaya Hagiwara
Micromachines 2022, 13(2), 156; https://doi.org/10.3390/mi13020156 - 21 Jan 2022
Cited by 4 | Viewed by 3810
Abstract
While organoid differentiation protocols have been widely developed, local control of initial cell seeding position and imaging of large-scale organoid samples with high resolution remain challenging. 3D bioprinting is an effective method to achieve control of cell positioning, but existing methods mainly rely [...] Read more.
While organoid differentiation protocols have been widely developed, local control of initial cell seeding position and imaging of large-scale organoid samples with high resolution remain challenging. 3D bioprinting is an effective method to achieve control of cell positioning, but existing methods mainly rely on the use of synthetic hydrogels that could compromise the native morphogenesis of organoids. To address this problem, we developed a 3D culture platform that combines 3D printing with a cube device to enable an unrestricted range of designs to be formed in biological hydrogels. We demonstrated the formation of channels in collagen hydrogel in the cube device via a molding process using a 3D-printed water-soluble mold. The mold is first placed in uncured hydrogel solution, then easily removed by immersion in water after the gel around it has cured, thus creating a mold-shaped gap in the hydrogel. At the same time, the difficulty in obtaining high-resolution imaging on a large scale can also be solved as the cube device allows us to scan the tissue sample from multiple directions, so that the imaging quality can be enhanced without having to rely on higher-end microscopes. Using this developed technology, we demonstrated (1) mimicking vascular structure by seeding HUVEC on the inner walls of helix-shaped channels in collagen gels, and (2) multi-directional imaging of the vascular structure in the cube device. Thus, this paper describes a concerted method that simultaneously allows for the precise control of cell positioning in hydrogels for organoid morphogenesis, and the imaging of large-sized organoid samples. It is expected that the platform developed here can lead to advancements in organoid technology to generate organoids with more sophisticated structures. Full article
(This article belongs to the Special Issue Frontiers in Micromachines in Japan)
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20 pages, 11405 KiB  
Article
Dynamic Modeling and Experimental Validation of a Water Hydraulic Soft Manipulator Based on an Improved Newton—Euler Iterative Method
by Yinglong Chen, Qiang Sun, Qiang Guo and Yongjun Gong
Micromachines 2022, 13(1), 130; https://doi.org/10.3390/mi13010130 - 14 Jan 2022
Cited by 11 | Viewed by 4473
Abstract
Compared with rigid robots, soft robots have better adaptability to the environment because of their pliability. However, due to the lower structural stiffness of the soft manipulator, the posture of the manipulator is usually decided by the weight and the external load under [...] Read more.
Compared with rigid robots, soft robots have better adaptability to the environment because of their pliability. However, due to the lower structural stiffness of the soft manipulator, the posture of the manipulator is usually decided by the weight and the external load under operating conditions. Therefore, it is necessary to conduct dynamics modeling and movement analysis of the soft manipulator. In this paper, a fabric reinforced soft manipulator driven by a water hydraulic system is firstly proposed, and the dynamics of both the soft manipulator and hydraulic system are considered. Specifically, a dynamic model of the soft manipulator is established based on an improved Newton–Euler iterative method, which comprehensively considers the influence of inertial force, elastic force, damping force, as well as combined bending and torsion moments. The dynamics of the water hydraulic system consider the effects of cylinder inertia, friction, and water response. Finally, the accuracy of the proposed dynamic model is verified by comparing the simulation results with the experimental data about the steady and dynamic characteristics of the soft manipulator under various conditions. The results show that the maximum sectional error is about 0.0245 m and that the maximum cumulative error is 0.042 m, which validate the effectiveness of the proposed model. Full article
(This article belongs to the Special Issue Soft Robotics: Design, Fabrication, Modeling, Control and Applications)
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13 pages, 2916 KiB  
Article
Optical Dielectrophoretic (DEP) Manipulation of Oil-Immersed Aqueous Droplets on a Plasmonic-Enhanced Photoconductive Surface
by Si Kuan Thio and Sung-Yong Park
Micromachines 2022, 13(1), 112; https://doi.org/10.3390/mi13010112 - 11 Jan 2022
Cited by 4 | Viewed by 2896
Abstract
We present a plasmonic-enhanced dielectrophoretic (DEP) phenomenon to improve optical DEP performance of a floating electrode optoelectronic tweezers (FEOET) device, where aqueous droplets can be effectively manipulated on a light-patterned photoconductive surface immersed in an oil medium. To offer device simplicity and cost-effectiveness, [...] Read more.
We present a plasmonic-enhanced dielectrophoretic (DEP) phenomenon to improve optical DEP performance of a floating electrode optoelectronic tweezers (FEOET) device, where aqueous droplets can be effectively manipulated on a light-patterned photoconductive surface immersed in an oil medium. To offer device simplicity and cost-effectiveness, recent studies have utilized a polymer-based photoconductive material such as titanium oxide phthalocyanine (TiOPc). However, the TiOPc has much poorer photoconductivity than that of semiconductors like amorphous silicon (a-Si), significantly limiting optical DEP applications. The study herein focuses on the FEOET device for which optical DEP performance can be greatly enhanced by utilizing plasmonic nanoparticles as light scattering elements to improve light absorption of the low-quality TiOPc. Numerical simulation studies of both plasmonic light scattering and electric field enhancement were conducted to verify wide-angle scattering light rays and an approximately twofold increase in electric field gradient with the presence of nanoparticles. Similarly, a spectrophotometric study conducted on the absorption spectrum of the TiOPc has shown light absorption improvement (nearly twofold) of the TiOPc layer. Additionally, droplet dynamics study experimentally demonstrated a light-actuated droplet speed of 1.90 mm/s, a more than 11-fold improvement due to plasmonic light scattering. This plasmonic-enhanced FEOET technology can considerably improve optical DEP capability even with poor-quality photoconductive materials, thus providing low-cost, easy-fabrication solutions for various droplet-based microfluidic applications. Full article
(This article belongs to the Special Issue Advances in Electrowetting Devices)
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12 pages, 2949 KiB  
Article
In-Situ Integration of 3D C-MEMS Microelectrodes with Bipolar Exfoliated Graphene for Label-Free Electrochemical Cancer Biomarkers Aptasensor
by Shahrzad Forouzanfar, Nezih Pala and Chunlei Wang
Micromachines 2022, 13(1), 104; https://doi.org/10.3390/mi13010104 - 9 Jan 2022
Cited by 5 | Viewed by 3387
Abstract
The electrochemical label-free aptamer-based biosensors (also known as aptasensors) are highly suitable for point-of-care applications. The well-established C-MEMS (carbon microelectromechanical systems) platforms have distinguishing features which are highly suitable for biosensing applications such as low background noise, high capacitance, high stability when exposed [...] Read more.
The electrochemical label-free aptamer-based biosensors (also known as aptasensors) are highly suitable for point-of-care applications. The well-established C-MEMS (carbon microelectromechanical systems) platforms have distinguishing features which are highly suitable for biosensing applications such as low background noise, high capacitance, high stability when exposed to different physical/chemical treatments, biocompatibility, and good electrical conductivity. This study investigates the integration of bipolar exfoliated (BPE) reduced graphene oxide (rGO) with 3D C-MEMS microelectrodes for developing PDGF-BB (platelet-derived growth factor-BB) label-free aptasensors. A simple setup has been used for exfoliation, reduction, and deposition of rGO on the 3D C-MEMS microelectrodes based on the principle of bipolar electrochemistry of graphite in deionized water. The electrochemical bipolar exfoliation of rGO resolves the drawbacks of commonly applied methods for synthesis and deposition of rGO, such as requiring complicated and costly processes, excessive use of harsh chemicals, and complex subsequent deposition procedures. The PDGF-BB affinity aptamers were covalently immobilized by binding amino-tag terminated aptamers and rGO surfaces. The turn-off sensing strategy was implemented by measuring the areal capacitance from CV plots. The aptasensor showed a wide linear range of 1 pM–10 nM, high sensitivity of 3.09 mF cm−2 Logc−1 (unit of c, pM), and a low detection limit of 0.75 pM. This study demonstrated the successful and novel in-situ deposition of BPE-rGO on 3D C-MEMS microelectrodes. Considering the BPE technique’s simplicity and efficiency, along with the high potential of C-MEMS technology, this novel procedure is highly promising for developing high-performance graphene-based viable lab-on-chip and point-of-care cancer diagnosis technologies. Full article
(This article belongs to the Special Issue C-MEMS: Microstructure, Shapes, and Applications in Carbon)
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21 pages, 36330 KiB  
Article
Intelligent Design Optimization System for Additively Manufactured Flow Channels Based on Fluid–Structure Interaction
by Haonan Ji, Bin Zou, Yongsheng Ma, Carlos F. Lange, Jikai Liu and Lei Li
Micromachines 2022, 13(1), 100; https://doi.org/10.3390/mi13010100 - 8 Jan 2022
Cited by 2 | Viewed by 2133
Abstract
Based on expert system theory and fluid–structure interaction (FSI), this paper suggests an intelligent design optimization system to derive the optimal shape of both the fluid and solid domain of flow channels. A parametric modeling scheme of flow channels is developed by design [...] Read more.
Based on expert system theory and fluid–structure interaction (FSI), this paper suggests an intelligent design optimization system to derive the optimal shape of both the fluid and solid domain of flow channels. A parametric modeling scheme of flow channels is developed by design for additive manufacturing (DfAM). By changing design parameters, a series of flow channel models can be obtained. According to the design characteristics, the system can intelligently allocate suitable computational models to compute the flow field of a specific model. The pressure-based normal stress is abstracted from the results and transmitted to the solid region by the fluid–structure (FS) interface to analyze the strength of the structure. The design space is obtained by investigating the simulation results with the metamodeling method, which is further applied for pursuing design objectives under constraints. Finally, the improved design is derived by gradient-based optimization. This system can improve the accuracy of the FSI simulation and the efficiency of the optimization process. The design optimization of a flow channel in a simplified hydraulic manifold is applied as the case study to validate the feasibility of the proposed system. Full article
(This article belongs to the Special Issue Intelligent Additive/Subtractive Manufacturing)
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11 pages, 2311 KiB  
Article
Molecular Recognition by Silicon Nanowire Field-Effect Transistor and Single-Molecule Force Spectroscopy
by Francisco M. Espinosa, Manuel R. Uhlig and Ricardo Garcia
Micromachines 2022, 13(1), 97; https://doi.org/10.3390/mi13010097 - 8 Jan 2022
Cited by 3 | Viewed by 2469
Abstract
Silicon nanowire (SiNW) field-effect transistors (FETs) have been developed as very sensitive and label-free biomolecular sensors. The detection principle operating in a SiNW biosensor is indirect. The biomolecules are detected by measuring the changes in the current through the transistor. Those changes are [...] Read more.
Silicon nanowire (SiNW) field-effect transistors (FETs) have been developed as very sensitive and label-free biomolecular sensors. The detection principle operating in a SiNW biosensor is indirect. The biomolecules are detected by measuring the changes in the current through the transistor. Those changes are produced by the electrical field created by the biomolecule. Here, we have combined nanolithography, chemical functionalization, electrical measurements and molecular recognition methods to correlate the current measured by the SiNW transistor with the presence of specific molecular recognition events on the surface of the SiNW. Oxidation scanning probe lithography (o-SPL) was applied to fabricate sub-12 nm SiNW field-effect transistors. The devices were applied to detect very small concentrations of proteins (500 pM). Atomic force microscopy (AFM) single-molecule force spectroscopy (SMFS) experiments allowed the identification of the protein adsorption sites on the surface of the nanowire. We detected specific interactions between the biotin-functionalized AFM tip and individual avidin molecules adsorbed to the SiNW. The measurements confirmed that electrical current changes measured by the device were associated with the deposition of avidin molecules. Full article
(This article belongs to the Special Issue Nanolithography: A Theme Issue in Honor of Professor José María De Teresa on the Occasion of His 50th Birthday)
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15 pages, 5024 KiB  
Article
Detecting Redox Potentials Using Porous Boron Nitride/ATP-DNA Aptamer/Methylene Blue Biosensor to Monitor Microbial Activities
by Kai Guo, Zirui Song, Gaoxing Wang and Chengchun Tang
Micromachines 2022, 13(1), 83; https://doi.org/10.3390/mi13010083 - 4 Jan 2022
Cited by 5 | Viewed by 1594
Abstract
Microbial activity has gained attention because of its impact on the environment and the quality of people’s lives. Most of today’s methods, which include genome sequencing and electrochemistry, are costly and difficult to manage. Our group proposed a method using the redox potential [...] Read more.
Microbial activity has gained attention because of its impact on the environment and the quality of people’s lives. Most of today’s methods, which include genome sequencing and electrochemistry, are costly and difficult to manage. Our group proposed a method using the redox potential change to detect microbial activity, which is rooted in the concept that metabolic activity can change the redox potential of a microbial community. The redox potential change was captured by a biosensor consisting of porous boron nitride, ATP-DNA aptamer, and methylene blue as the fluorophore. This assembly can switch on or off when there is a redox potential change, and this change leads to a fluorescence change that can be examined using a multipurpose microplate reader. The results show that this biosensor can detect microbial community changes when its composition is changed or toxic metals are ingested. Full article
(This article belongs to the Section B1: Biosensors)
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21 pages, 4984 KiB  
Review
Overview of 3D-Printed Silica Glass
by Han Zhang, Long Huang, Mingyue Tan, Shaoqing Zhao, Hua Liu, Zifeng Lu, Jinhuan Li and Zhongzhu Liang
Micromachines 2022, 13(1), 81; https://doi.org/10.3390/mi13010081 - 3 Jan 2022
Cited by 25 | Viewed by 7346
Abstract
Not satisfied with the current stage of the extensive research on 3D printing technology for polymers and metals, researchers are searching for more innovative 3D printing technologies for glass fabrication in what has become the latest trend of interest. The traditional glass manufacturing [...] Read more.
Not satisfied with the current stage of the extensive research on 3D printing technology for polymers and metals, researchers are searching for more innovative 3D printing technologies for glass fabrication in what has become the latest trend of interest. The traditional glass manufacturing process requires complex high-temperature melting and casting processes, which presents a great challenge to the fabrication of arbitrarily complex glass devices. The emergence of 3D printing technology provides a good solution. This paper reviews the recent advances in glass 3D printing, describes the history and development of related technologies, and lists popular applications of 3D printing for glass preparation. This review compares the advantages and disadvantages of various processing methods, summarizes the problems encountered in the process of technology application, and proposes the corresponding solutions to select the most appropriate preparation method in practical applications. The application of additive manufacturing in glass fabrication is in its infancy but has great potential. Based on this view, the methods for glass preparation with 3D printing technology are expected to achieve both high-speed and high-precision fabrication. Full article
(This article belongs to the Special Issue Microscale and Rheology in 3D Printing Processes)
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40 pages, 9254 KiB  
Review
Engineering Biological Tissues from the Bottom-Up: Recent Advances and Future Prospects
by Xiaowen Wang, Zhen Wang, Wenya Zhai, Fengyun Wang, Zhixing Ge, Haibo Yu and Wenguang Yang
Micromachines 2022, 13(1), 75; https://doi.org/10.3390/mi13010075 - 31 Dec 2021
Cited by 8 | Viewed by 3772
Abstract
Tissue engineering provides a powerful solution for current organ shortages, and researchers have cultured blood vessels, heart tissues, and bone tissues in vitro. However, traditional top-down tissue engineering has suffered two challenges: vascularization and reconfigurability of functional units. With the continuous development of [...] Read more.
Tissue engineering provides a powerful solution for current organ shortages, and researchers have cultured blood vessels, heart tissues, and bone tissues in vitro. However, traditional top-down tissue engineering has suffered two challenges: vascularization and reconfigurability of functional units. With the continuous development of micro-nano technology and biomaterial technology, bottom-up tissue engineering as a promising approach for organ and tissue modular reconstruction has gradually developed. In this article, relevant advances in living blocks fabrication and assembly techniques for creation of higher-order bioarchitectures are described. After a critical overview of this technology, a discussion of practical challenges is provided, and future development prospects are proposed. Full article
(This article belongs to the Special Issue Feature Papers of Micromachines in "Materials and Processing" 2022)
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20 pages, 876 KiB  
Review
Systems for Muscle Cell Differentiation: From Bioengineering to Future Food
by Kah-Yin Lee, Hui-Xin Loh and Andrew C. A. Wan
Micromachines 2022, 13(1), 71; https://doi.org/10.3390/mi13010071 - 31 Dec 2021
Cited by 15 | Viewed by 6730
Abstract
In light of pressing issues, such as sustainability and climate change, future protein sources will increasingly turn from livestock to cell-based production and manufacturing activities. In the case of cell-based or cultured meat a relevant aspect would be the differentiation of muscle cells [...] Read more.
In light of pressing issues, such as sustainability and climate change, future protein sources will increasingly turn from livestock to cell-based production and manufacturing activities. In the case of cell-based or cultured meat a relevant aspect would be the differentiation of muscle cells into mature muscle tissue, as well as how the microsystems that have been developed to date can be developed for larger-scale cultures. To delve into this aspect we review previous research that has been carried out on skeletal muscle tissue engineering and how various biological and physicochemical factors, mechanical and electrical stimuli, affect muscle cell differentiation on an experimental scale. Material aspects such as the different biomaterials used and 3D vs. 2D configurations in the context of muscle cell differentiation will also be discussed. Finally, the ability to translate these systems to more scalable bioreactor configurations and eventually bring them to a commercial scale will be touched upon. Full article
(This article belongs to the Special Issue Sensors, Devices and Systems for Future Food Production and Packaging)
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11 pages, 2177 KiB  
Article
Deep-Learning Based Estimation of Dielectrophoretic Force
by Sunday Ajala, Harikrishnan Muraleedharan Jalajamony and Renny Edwin Fernandez
Micromachines 2022, 13(1), 41; https://doi.org/10.3390/mi13010041 - 28 Dec 2021
Cited by 3 | Viewed by 2196
Abstract
The ability to accurately quantify dielectrophoretic (DEP) force is critical in the development of high-efficiency microfluidic systems. This is the first reported work that combines a textile electrode-based DEP sensing system with deep learning in order to estimate the DEP forces invoked on [...] Read more.
The ability to accurately quantify dielectrophoretic (DEP) force is critical in the development of high-efficiency microfluidic systems. This is the first reported work that combines a textile electrode-based DEP sensing system with deep learning in order to estimate the DEP forces invoked on microparticles. We demonstrate how our deep learning model can process micrographs of pearl chains of polystyrene (PS) microbeads to estimate the DEP forces experienced. Numerous images obtained from our experiments at varying input voltages were preprocessed and used to train three deep convolutional neural networks, namely AlexNet, MobileNetV2, and VGG19. The performances of all the models was tested for their validation accuracies. Models were also tested with adversarial images to evaluate performance in terms of classification accuracy and resilience as a result of noise, image blur, and contrast changes. The results indicated that our method is robust under unfavorable real-world settings, demonstrating that it can be used for the direct estimation of dielectrophoretic force in point-of-care settings. Full article
(This article belongs to the Special Issue Microfluidic System for Biochemical Application)
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12 pages, 2285 KiB  
Article
Four-Dimensional Stimuli-Responsive Hydrogels Micro-Structured via Femtosecond Laser Additive Manufacturing
by Yufeng Tao, Chengchangfeng Lu, Chunsan Deng, Jing Long, Yunpeng Ren, Zijie Dai, Zhaopeng Tong, Xuejiao Wang, Shuai Meng, Wenguang Zhang, Yinuo Xu and Linlin Zhou
Micromachines 2022, 13(1), 32; https://doi.org/10.3390/mi13010032 - 27 Dec 2021
Cited by 12 | Viewed by 3255
Abstract
Rapid fabricating and harnessing stimuli-responsive behaviors of microscale bio-compatible hydrogels are of great interest to the emerging micro-mechanics, drug delivery, artificial scaffolds, nano-robotics, and lab chips. Herein, we demonstrate a novel femtosecond laser additive manufacturing process with smart materials for soft interactive hydrogel [...] Read more.
Rapid fabricating and harnessing stimuli-responsive behaviors of microscale bio-compatible hydrogels are of great interest to the emerging micro-mechanics, drug delivery, artificial scaffolds, nano-robotics, and lab chips. Herein, we demonstrate a novel femtosecond laser additive manufacturing process with smart materials for soft interactive hydrogel micro-machines. Bio-compatible hyaluronic acid methacryloyl was polymerized with hydrophilic diacrylate into an absorbent hydrogel matrix under a tight topological control through a 532 nm green femtosecond laser beam. The proposed hetero-scanning strategy modifies the hierarchical polymeric degrees inside the hydrogel matrix, leading to a controllable surface tension mismatch. Strikingly, these programmable stimuli-responsive matrices mechanized hydrogels into robotic applications at the micro/nanoscale (<300 × 300 × 100 μm3). Reverse high-freedom shape mutations of diversified microstructures were created from simple initial shapes and identified without evident fatigue. We further confirmed the biocompatibility, cell adhesion, and tunable mechanics of the as-prepared hydrogels. Benefiting from the high-efficiency two-photon polymerization (TPP), nanometer feature size (<200 nm), and flexible digitalized modeling technique, many more micro/nanoscale hydrogel robots or machines have become obtainable in respect of future interdisciplinary applications. Full article
(This article belongs to the Special Issue Laser Additive Manufacturing: Design, Materials, Processes and Applications)
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32 pages, 8787 KiB  
Review
Current Development in Interdigital Transducer (IDT) Surface Acoustic Wave Devices for Live Cell In Vitro Studies: A Review
by Mazlee Bin Mazalan, Anas Mohd Noor, Yufridin Wahab, Shuhaida Yahud and Wan Safwani Wan Kamarul Zaman
Micromachines 2022, 13(1), 30; https://doi.org/10.3390/mi13010030 - 27 Dec 2021
Cited by 27 | Viewed by 7443
Abstract
Acoustics have a wide range of uses, from noise-cancelling to ultrasonic imaging. There has been a surge in interest in developing acoustic-based approaches for biological and biomedical applications in the last decade. This review focused on the application of surface acoustic waves (SAW) [...] Read more.
Acoustics have a wide range of uses, from noise-cancelling to ultrasonic imaging. There has been a surge in interest in developing acoustic-based approaches for biological and biomedical applications in the last decade. This review focused on the application of surface acoustic waves (SAW) based on interdigital transducers (IDT) for live-cell investigations, such as cell manipulation, cell separation, cell seeding, cell migration, cell characteristics, and cell behaviours. The approach is also known as acoustofluidic, because the SAW device is coupled with a microfluidic system that contains live cells. This article provides an overview of several forms of IDT of SAW devices on recently used cells. Conclusively, a brief viewpoint and overview of the future application of SAW techniques in live-cell investigations were presented. Full article
(This article belongs to the Special Issue Acoustic Resonators and Filters)
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23 pages, 43500 KiB  
Article
A Novel MEMS Capacitive Microphone with Semiconstrained Diaphragm Supported with Center and Peripheral Backplate Protrusions
by Shubham Shubham, Yoonho Seo, Vahid Naderyan, Xin Song, Anthony J. Frank, Jeremy Thomas Morley Greenham Johnson, Mark da Silva and Michael Pedersen
Micromachines 2022, 13(1), 22; https://doi.org/10.3390/mi13010022 - 25 Dec 2021
Cited by 18 | Viewed by 10731
Abstract
Audio applications such as mobile phones, hearing aids, true wireless stereo earphones, and Internet of Things devices demand small size, high performance, and reduced cost. Microelectromechanical system (MEMS) capacitive microphones fulfill these requirements with improved reliability and specifications related to sensitivity, signal-to-noise ratio [...] Read more.
Audio applications such as mobile phones, hearing aids, true wireless stereo earphones, and Internet of Things devices demand small size, high performance, and reduced cost. Microelectromechanical system (MEMS) capacitive microphones fulfill these requirements with improved reliability and specifications related to sensitivity, signal-to-noise ratio (SNR), distortion, and dynamic range when compared to their electret condenser microphone counterparts. We present the design and modeling of a semiconstrained polysilicon diaphragm with flexible springs that are simply supported under bias voltage with a center and eight peripheral protrusions extending from the backplate. The flexible springs attached to the diaphragm reduce the residual film stress effect more effectively compared to constrained diaphragms. The center and peripheral protrusions from the backplate further increase the effective area, linearity, and sensitivity of the diaphragm when the diaphragm engages with these protrusions under an applied bias voltage. Finite element modeling approaches have been implemented to estimate deflection, compliance, and resonance. We report an 85% increase in the effective area of the diaphragm in this configuration with respect to a constrained diaphragm and a 48% increase with respect to a simply supported diaphragm without the center protrusion. Under the applied bias, the effective area further increases by an additional 15% as compared to the unbiased diaphragm effective area. A lumped element model has been also developed to predict the mechanical and electrical behavior of the microphone. With an applied bias, the microphone has a sensitivity of −38 dB (ref. 1 V/Pa at 1 kHz) and an SNR of 67 dBA measured in a 3.25 mm × 1.9 mm × 0.9 mm package including an analog ASIC. Full article
(This article belongs to the Special Issue Micromachined Acoustic Transducers for Audio-Frequency Range)
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25 pages, 2183 KiB  
Article
Synergy Factorized Bilinear Network with a Dual Suppression Strategy for Brain Tumor Classification in MRI
by Guanghua Xiao, Huibin Wang, Jie Shen, Zhe Chen, Zhen Zhang and Xiaomin Ge
Micromachines 2022, 13(1), 15; https://doi.org/10.3390/mi13010015 - 23 Dec 2021
Cited by 8 | Viewed by 2343
Abstract
Automatic brain tumor classification is a practicable means of accelerating clinical diagnosis. Recently, deep convolutional neural network (CNN) training with MRI datasets has succeeded in computer-aided diagnostic (CAD) systems. To further improve the classification performance of CNNs, there is still a difficult path [...] Read more.
Automatic brain tumor classification is a practicable means of accelerating clinical diagnosis. Recently, deep convolutional neural network (CNN) training with MRI datasets has succeeded in computer-aided diagnostic (CAD) systems. To further improve the classification performance of CNNs, there is still a difficult path forward with regards to subtle discriminative details among brain tumors. We note that the existing methods heavily rely on data-driven convolutional models while overlooking what makes a class different from the others. Our study proposes to guide the network to find exact differences among similar tumor classes. We first present a “dual suppression encoding” block tailored to brain tumor MRIs, which diverges two paths from our network to refine global orderless information and local spatial representations. The aim is to use more valuable clues for correct classes by reducing the impact of negative global features and extending the attention of salient local parts. Then we introduce a “factorized bilinear encoding” layer for feature fusion. The aim is to generate compact and discriminative representations. Finally, the synergy between these two components forms a pipeline that learns in an end-to-end way. Extensive experiments exhibited superior classification performance in qualitative and quantitative evaluation on three datasets. Full article
(This article belongs to the Special Issue Advanced Machine Learning Techniques for Sensing and Imaging Applications)
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14 pages, 3660 KiB  
Article
Passivated Porous Silicon Membranes and Their Application to Optical Biosensing
by Clara Whyte Ferreira, Roselien Vercauteren and Laurent A. Francis
Micromachines 2022, 13(1), 10; https://doi.org/10.3390/mi13010010 - 22 Dec 2021
Cited by 7 | Viewed by 3102
Abstract
A robust fabrication method for stable mesoporous silicon membranes using standard microfabrication techniques is presented. The porous silicon membranes were passivated through the atomic layer deposition of different metal oxides, namely aluminium oxide Al2O3, hafnium oxide HfO2 and [...] Read more.
A robust fabrication method for stable mesoporous silicon membranes using standard microfabrication techniques is presented. The porous silicon membranes were passivated through the atomic layer deposition of different metal oxides, namely aluminium oxide Al2O3, hafnium oxide HfO2 and titanium oxide TiO2. The fabricated membranes were characterized in terms of morphology, optical properties and chemical properties. Stability tests and optical probing noise level determination were also performed. Preliminary results using an Al2O3 passivated membranes for a biosensing application are also presented for selective optical detection of Bacillus cereus bacterial lysate. The biosensor was able to detect the bacterial lysate, with an initial bacteria concentration of 106 colony forming units per mL (CFU/mL), in less than 10 min. Full article
(This article belongs to the Special Issue Selected Papers from ICMA2021)
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23 pages, 976 KiB  
Review
Drug-Induced Nephrotoxicity Assessment in 3D Cellular Models
by Pengfei Yu, Zhongping Duan, Shuang Liu, Ivan Pachon, Jianxing Ma, George P. Hemstreet and Yuanyuan Zhang
Micromachines 2022, 13(1), 3; https://doi.org/10.3390/mi13010003 - 21 Dec 2021
Cited by 17 | Viewed by 4793
Abstract
The kidneys are often involved in adverse effects and toxicity caused by exposure to foreign compounds, chemicals, and drugs. Early predictions of these influences are essential to facilitate new, safe drugs to enter the market. However, in current drug treatments, drug-induced nephrotoxicity accounts [...] Read more.
The kidneys are often involved in adverse effects and toxicity caused by exposure to foreign compounds, chemicals, and drugs. Early predictions of these influences are essential to facilitate new, safe drugs to enter the market. However, in current drug treatments, drug-induced nephrotoxicity accounts for 1/4 of reported serious adverse reactions, and 1/3 of them are attributable to antibiotics. Drug-induced nephrotoxicity is driven by multiple mechanisms, including altered glomerular hemodynamics, renal tubular cytotoxicity, inflammation, crystal nephropathy, and thrombotic microangiopathy. Although the functional proteins expressed by renal tubules that mediate drug sensitivity are well known, current in vitro 2D cell models do not faithfully replicate the morphology and intact renal tubule function, and therefore, they do not replicate in vivo nephrotoxicity. The kidney is delicate and complex, consisting of a filter unit and a tubular part, which together contain more than 20 different cell types. The tubular epithelium is highly polarized, and maintaining cellular polarity is essential for the optimal function and response to environmental signals. Cell polarity depends on the communication between cells, including paracrine and autocrine signals, as well as biomechanical and chemotaxis processes. These processes affect kidney cell proliferation, migration, and differentiation. For drug disposal research, the microenvironment is essential for predicting toxic reactions. This article reviews the mechanism of drug-induced kidney injury, the types of nephrotoxicity models (in vivo and in vitro models), and the research progress related to drug-induced nephrotoxicity in three-dimensional (3D) cellular culture models. Full article
(This article belongs to the Special Issue 3D In Vitro Tissue and Organ Models)
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15 pages, 2538 KiB  
Article
Static and Dynamic Optical Analysis of Micro Wrinkle Formation on a Liquid Surface
by Antariksh Saxena, Costas Tsakonas, David Chappell, Chi Shing Cheung, Andrew Michael John Edwards, Haida Liang, Ian Charles Sage and Carl Vernon Brown
Micromachines 2021, 12(12), 1583; https://doi.org/10.3390/mi12121583 - 19 Dec 2021
Cited by 1 | Viewed by 2299
Abstract
A spatially periodic voltage was used to create a dielectrophoresis induced periodic micro wrinkle deformation on the surface of a liquid film. Optical Coherence Tomography provided the equilibrium wrinkle profile at submicron accuracy. The dynamic wrinkle amplitude was derived from optical diffraction analysis [...] Read more.
A spatially periodic voltage was used to create a dielectrophoresis induced periodic micro wrinkle deformation on the surface of a liquid film. Optical Coherence Tomography provided the equilibrium wrinkle profile at submicron accuracy. The dynamic wrinkle amplitude was derived from optical diffraction analysis during sub-millisecond wrinkle formation and decay, after abruptly increasing or reducing the voltage, respectively. The decay time constant closely followed the film thickness dependence expected for surface tension driven viscous levelling. Modelling of the system using numerical solution of the Stokes flow equations with electrostatic forcing predicted that wrinkle formation was faster than decay, in accord with observations. Full article
(This article belongs to the Special Issue Advances in Electrowetting Devices)
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15 pages, 3541 KiB  
Article
A Cerebral Organoid Connectivity Apparatus to Model Neuronal Tract Circuitry
by Denise A. Robles, Andrew J. Boreland, Zhiping P. Pang and Jeffrey D. Zahn
Micromachines 2021, 12(12), 1574; https://doi.org/10.3390/mi12121574 - 17 Dec 2021
Cited by 4 | Viewed by 3344
Abstract
Mental disorders have high prevalence, but the efficacy of existing therapeutics is limited, in part, because the pathogenic mechanisms remain enigmatic. Current models of neural circuitry include animal models and post-mortem brain tissue, which have allowed enormous progress in understanding the pathophysiology of [...] Read more.
Mental disorders have high prevalence, but the efficacy of existing therapeutics is limited, in part, because the pathogenic mechanisms remain enigmatic. Current models of neural circuitry include animal models and post-mortem brain tissue, which have allowed enormous progress in understanding the pathophysiology of mental disorders. However, these models limit the ability to assess the functional alterations in short-range and long-range network connectivity between brain regions that are implicated in many mental disorders, e.g., schizophrenia and autism spectrum disorders. This work addresses these limitations by developing an in vitro model of the human brain that models the in vivo cerebral tract environment. In this study, microfabrication and stem cell differentiation techniques were combined to develop an in vitro cerebral tract model that anchors human induced pluripotent stem cell-derived cerebral organoids (COs) and provides a scaffold to promote the formation of a functional connecting neuronal tract. Two designs of a Cerebral Organoid Connectivity Apparatus (COCA) were fabricated using SU-8 photoresist. The first design contains a series of spikes which anchor the CO to the COCA (spiked design), whereas the second design contains flat supporting structures with open holes in a grid pattern to anchor the organoids (grid design); both designs allow effective media exchange. Morphological and functional analyses reveal the expression of key neuronal markers as well as functional activity and signal propagation along cerebral tracts connecting CO pairs. The reported in vitro models enable the investigation of critical neural circuitry involved in neurodevelopmental processes and has the potential to help devise personalized and targeted therapeutic strategies. Full article
(This article belongs to the Special Issue Microfluidic Platforms for the Nervous System)
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19 pages, 6336 KiB  
Article
Waveguide Manufacturing Technologies for Next-Generation Millimeter-Wave Antennas
by Lucas Polo-López, Pablo Sanchez-Olivares, Eduardo García-Marín, Jorge A. Ruiz-Cruz, Juan Córcoles, José L. Masa-Campos, José R. Montejo-Garai and Jesús M. Rebollar
Micromachines 2021, 12(12), 1565; https://doi.org/10.3390/mi12121565 - 16 Dec 2021
Cited by 4 | Viewed by 3240
Abstract
Some recent waveguide-based antennas are presented in this paper, designed for the next generation of communication systems operating at the millimeter-wave band. The presented prototypes have been conceived to be manufactured using different state-of-the-art techniques, involving subtractive and additive approaches. All the designs [...] Read more.
Some recent waveguide-based antennas are presented in this paper, designed for the next generation of communication systems operating at the millimeter-wave band. The presented prototypes have been conceived to be manufactured using different state-of-the-art techniques, involving subtractive and additive approaches. All the designs have used the latest developments in the field of manufacturing to guarantee the required accuracy for operation at millimeter-wave frequencies, where tolerances are extremely tight. Different designs will be presented, including a monopulse antenna combining a comparator network, a mode converter, and a spline profile horn; a tunable phase shifter that is integrated into an array to implement reconfigurability of the main lobe direction; and a conformal array antenna. These prototypes were manufactured by diverse approaches taking into account the waveguide configuration, combining parts with high-precision milling, electrical discharge machining, direct metal laser sintering, or stereolithography with spray metallization, showing very competitive performances at the millimeter-wave band till 40 GHz. Full article
(This article belongs to the Special Issue Micro Manufacturing for 5G Communications)
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11 pages, 925 KiB  
Conference Report
Advances in the Field of Micro- and Nanotechnologies Applied to Extracellular Vesicle Research: Take-Home Message from ISEV2021
by Silvia Picciolini, Francesca Rodà, Marzia Bedoni and Alice Gualerzi
Micromachines 2021, 12(12), 1563; https://doi.org/10.3390/mi12121563 - 16 Dec 2021
Cited by 3 | Viewed by 2227
Abstract
Extracellular Vesicles (EVs) are naturally secreted nanoparticles with a plethora of functions in the human body and remarkable potential as diagnostic and therapeutic tools. Starting from their discovery, EV nanoscale dimensions have hampered and slowed new discoveries in the field, sometimes generating confusion [...] Read more.
Extracellular Vesicles (EVs) are naturally secreted nanoparticles with a plethora of functions in the human body and remarkable potential as diagnostic and therapeutic tools. Starting from their discovery, EV nanoscale dimensions have hampered and slowed new discoveries in the field, sometimes generating confusion and controversies among experts. Microtechnological and especially nanotechnological advances have sped up biomedical research dealing with EVs, but efforts are needed to further clarify doubts and knowledge gaps. In the present review, we summarize some of the most interesting data presented in the Annual Meeting of the International Society for Extracellular Vesicles (ISEV), ISEV2021, to stimulate discussion and to share knowledge with experts from all fields of research. Indeed, EV research requires a multidisciplinary knowledge exchange and effort. EVs have demonstrated their importance and significant biological role; still, further technological achievements are crucial to avoid artifacts and misleading conclusions in order to enable outstanding discoveries. Full article
(This article belongs to the Special Issue Micro- and Nano-Technologies for the Application of Nanocarriers as Theranostics)
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12 pages, 19448 KiB  
Article
SiGe/Si Multi-Quantum-Well Micro-Bolometer Array Design and Fabrication with Heterogeneous Integration
by Zhong Fang, Yong He, Zhequan Chen, Yunlei Shi, Junjie Jiao and Xuchao Pan
Micromachines 2021, 12(12), 1553; https://doi.org/10.3390/mi12121553 - 13 Dec 2021
Cited by 1 | Viewed by 2398
Abstract
The micro-bolometer is important in the field of infrared imaging, although improvements in its performance have been limited by traditional materials. SiGe/Si multi-quantum-well materials (SiGe/Si MQWs) are novelty thermal-sensitive materials with a significantly high TCR and a comparably low 1/f noise. The application [...] Read more.
The micro-bolometer is important in the field of infrared imaging, although improvements in its performance have been limited by traditional materials. SiGe/Si multi-quantum-well materials (SiGe/Si MQWs) are novelty thermal-sensitive materials with a significantly high TCR and a comparably low 1/f noise. The application of such high-performance monocrystalline films in a micro-bolometer has been limited by film integration technology. This paper reports a SiGe/Si MQWs micro-bolometer fabrication with heterogeneous integration. The integration with the SiGe/Si MQWs handle wafer and dummy read-out circuit wafer was achieved based on adhesive wafer bonding. The SiGe/Si MQWs infrared-absorption structure and thermal bridge were calculated and designed. The SiGe/Si MQWs wafer and a 320 × 240 micro-bolometer array of 40 µm pitch L-type pixels were fabricated. The test results for the average absorption efficiency were more than 90% at the wavelength of 8–14 µm. The test pixel was measured to have a thermal capacity of 1.043 × 10−9 J/K, a thermal conductivity of 1.645 × 10−7 W/K, and a thermal time constant of 7.25 ms. Furthermore, the total TCR value of the text pixel was measured as 2.91%/K with a bias voltage of 0.3 V. The SiGe/Si MQWs micro-bolometer can be widely applied in commercial fields, especially in early medical diagnosis and biological detection. Full article
(This article belongs to the Special Issue Micro- and Nano-Systems for Manipulation, Actuation and Sensing)
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30 pages, 3790 KiB  
Review
Fabricating Silicon Resonators for Analysing Biological Samples
by Momoko Kumemura, Deniz Pekin, Vivek Anand Menon, Isabelle Van Seuningen, Dominique Collard and Mehmet Cagatay Tarhan
Micromachines 2021, 12(12), 1546; https://doi.org/10.3390/mi12121546 - 12 Dec 2021
Cited by 3 | Viewed by 2593
Abstract
The adaptability of microscale devices allows microtechnologies to be used for a wide range of applications. Biology and medicine are among those fields that, in recent decades, have applied microtechnologies to achieve new and improved functionality. However, despite their ability to achieve assay [...] Read more.
The adaptability of microscale devices allows microtechnologies to be used for a wide range of applications. Biology and medicine are among those fields that, in recent decades, have applied microtechnologies to achieve new and improved functionality. However, despite their ability to achieve assay sensitivities that rival or exceed conventional standards, silicon-based microelectromechanical systems remain underutilised for biological and biomedical applications. Although microelectromechanical resonators and actuators do not always exhibit optimal performance in liquid due to electrical double layer formation and high damping, these issues have been solved with some innovative fabrication processes or alternative experimental approaches. This paper focuses on several examples of silicon-based resonating devices with a brief look at their fundamental sensing elements and key fabrication steps, as well as current and potential biological/biomedical applications. Full article
(This article belongs to the Special Issue Micro/Nano Fabrication for Life Sciences)
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30 pages, 15488 KiB  
Review
A Review of Sharp-Switching Band-Modulation Devices
by Sorin Cristoloveanu, Joris Lacord, Sébastien Martinie, Carlos Navarro, Francisco Gamiz, Jing Wan, Hassan El Dirani, Kyunghwa Lee and Alexander Zaslavsky
Micromachines 2021, 12(12), 1540; https://doi.org/10.3390/mi12121540 - 11 Dec 2021
Cited by 3 | Viewed by 2731
Abstract
This paper reviews the recently-developed class of band-modulation devices, born from the recent progress in fully-depleted silicon-on-insulator (FD-SOI) and other ultrathin-body technologies, which have enabled the concept of gate-controlled electrostatic doping. In a lateral PIN diode, two additional gates can construct a reconfigurable [...] Read more.
This paper reviews the recently-developed class of band-modulation devices, born from the recent progress in fully-depleted silicon-on-insulator (FD-SOI) and other ultrathin-body technologies, which have enabled the concept of gate-controlled electrostatic doping. In a lateral PIN diode, two additional gates can construct a reconfigurable PNPN structure with unrivalled sharp-switching capability. We describe the implementation, operation, and various applications of these band-modulation devices. Physical and compact models are presented to explain the output and transfer characteristics in both steady-state and transient modes. Not only can band-modulation devices be used for quasi-vertical current switching, but they also show promise for compact capacitorless memories, electrostatic discharge (ESD) protection, sensing, and reconfigurable circuits, while retaining full compatibility with modern silicon processing and standard room-temperature low-voltage operation. Full article
(This article belongs to the Special Issue Steep Switching Field Effect Transistor)
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