Micromachines

15 pages, 1716 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

A Composite Microfiber for Biodegradable Stretchable Electronics

by Adeela Hanif, Gargi Ghosh, Montri Meeseepong, Hamna Haq Chouhdry, Atanu Bag, M. V. Chinnamani, Surjeet Kumar, Muhammad Junaid Sultan, Anupama Yadav and Nae-Eung Lee

Micromachines 2021, 12(9), 1036; https://doi.org/10.3390/mi12091036 - 28 Aug 2021

Cited by 8 | Viewed by 4940

Abstract

Biodegradable stretchable electronics have demonstrated great potential for future applications in stretchable electronics and can be resorbed, dissolved, and disintegrated in the environment. Most biodegradable electronic devices have used flexible biodegradable materials, which have limited conformality in wearable and implantable devices. Here, we [...] Read more.

Biodegradable stretchable electronics have demonstrated great potential for future applications in stretchable electronics and can be resorbed, dissolved, and disintegrated in the environment. Most biodegradable electronic devices have used flexible biodegradable materials, which have limited conformality in wearable and implantable devices. Here, we report a biodegradable, biocompatible, and stretchable composite microfiber of poly(glycerol sebacate) (PGS) and polyvinyl alcohol (PVA) for transient stretchable device applications. Compositing high-strength PVA with stretchable and biodegradable PGS with poor processability, formability, and mechanical strength overcomes the limits of pure PGS. As an application, the stretchable microfiber-based strain sensor developed by the incorporation of Au nanoparticles (AuNPs) into a composite microfiber showed stable current response under cyclic and dynamic stretching at 30% strain. The sensor also showed the ability to monitor the strain produced by tapping, bending, and stretching of the finger, knee, and esophagus. The biodegradable and stretchable composite materials of PGS with additive PVA have great potential for use in transient and environmentally friendly stretchable electronics with reduced environmental footprint. Full article

(This article belongs to the Special Issue Materials, Structures and Manufacturing towards Soft Electronics)

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12 pages, 27988 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Rapid Lipid Content Screening in Neochloris oleoabundans Utilizing Carbon-Based Dielectrophoresis

by Cynthia M. Galicia-Medina, Matías Vázquez-Piñón, Gibran S. Alemán-Nava, Roberto C. Gallo-Villanueva, Sergio O. Martínez-Chapa, Marc J. Madou, Sergio Camacho-León, Jonathan S. García-Pérez, Diego A. Esquivel-Hernández, Roberto Parra-Saldívar and Víctor H. Pérez-González

Micromachines 2021, 12(9), 1023; https://doi.org/10.3390/mi12091023 - 27 Aug 2021

Cited by 3 | Viewed by 3859

Abstract

In this study, we carried out a heterogeneous cytoplasmic lipid content screening of Neochloris oleoabundans microalgae by dielectrophoresis (DEP), using castellated glassy carbon microelectrodes in a PDMS microchannel. For this purpose, microalgae were cultured in nitrogen-replete (N+) and nitrogen-deplete (N−) suspensions to promote [...] Read more.

In this study, we carried out a heterogeneous cytoplasmic lipid content screening of Neochloris oleoabundans microalgae by dielectrophoresis (DEP), using castellated glassy carbon microelectrodes in a PDMS microchannel. For this purpose, microalgae were cultured in nitrogen-replete (N+) and nitrogen-deplete (N−) suspensions to promote low and high cytoplasmic lipid production in cells, respectively. Experiments were carried out over a wide frequency window (100 kHz–30 MHz) at a fixed amplitude of 7 V_PP. The results showed a statistically significant difference between the dielectrophoretic behavior of N+ and N− cells at low frequencies (100–800 kHz), whereas a weak response was observed for mid- and high frequencies (1–30 MHz). Additionally, a finite element analysis using a 3D model was conducted to determine the dielectrophoretic trapping zones across the electrode gaps. These results suggest that low-cost glassy carbon is a reliable material for microalgae classification—between low and high cytoplasmic lipid content—through DEP, providing a fast and straightforward mechanism. Full article

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

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10 pages, 1760 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Fabrication of Needle-Like Silicon Nanowires by Using a Nanoparticles-Assisted Bosch Process for Both High Hydrophobicity and Anti-Reflection

by Zengxing Zhang, Guohua Liu and Kaiying Wang

Micromachines 2021, 12(9), 1009; https://doi.org/10.3390/mi12091009 - 25 Aug 2021

Cited by 4 | Viewed by 3072

Abstract

In this work, a modified Bosch etching process is developed to create silicon nanowires. Au nanoparticles (NPs) formed by magnetron sputtering film deposition and thermal annealing were employed as the hard mask to achieve controllable density and high aspect ratios. Such silicon nanowire [...] Read more.

In this work, a modified Bosch etching process is developed to create silicon nanowires. Au nanoparticles (NPs) formed by magnetron sputtering film deposition and thermal annealing were employed as the hard mask to achieve controllable density and high aspect ratios. Such silicon nanowire exhibits the excellent anti-reflection ability of a reflectance value of below 2% within a broad light wave range between 220 and 1100 nm. In addition, Au NPs-induced surface plasmons significantly enhance the near-unity anti-reflection characteristics, achieving a reflectance below 3% within the wavelength range of 220 to 2600 nm. Furthermore, the nanowire array exhibits super-hydrophobic behavior with a contact angle over ~165.6° without enforcing any hydrophobic chemical treatment. Such behavior yields in water droplets bouncing off the surface many times. These properties render this silicon nanowire attractive for applications such as photothermal, photocatalysis, supercapacitor, and microfluidics. Full article

(This article belongs to the Special Issue Emerging Micro Manufacturing Technologies and Applications)

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28 pages, 12057 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Progress in Non-Traditional Processing for Fabricating Superhydrophobic Surfaces

by Dili Shen, Wuyi Ming, Xinggui Ren, Zhuobin Xie and Xuewen Liu

Micromachines 2021, 12(9), 1003; https://doi.org/10.3390/mi12091003 - 24 Aug 2021

Cited by 16 | Viewed by 4197

Abstract

When the water droplets are on some superhydrophobic surfaces, the surface only needs to be inclined at a very small angle to make the water droplets roll off. Hence, building a superhydrophobic surface on the material substrate, especially the metal substrate, can effectively [...] Read more.

When the water droplets are on some superhydrophobic surfaces, the surface only needs to be inclined at a very small angle to make the water droplets roll off. Hence, building a superhydrophobic surface on the material substrate, especially the metal substrate, can effectively alleviate the problems of its inability to resist corrosion and easy icing during use, and it can also give it special functions such as self-cleaning, lubrication, and drag reduction. Therefore, this study reviews and summarizes the development trends in the fabrication of superhydrophobic surface materials by non-traditional processing techniques. First, the principle of the superhydrophobic surfaces fabricated by laser beam machining (LBM) is introduced, and the machining performances of the LBM process, such as femtosecond laser, picosecond laser, and nanosecond laser, for fabricating the surfaces are compared and summarized. Second, the principle and the machining performances of the electrical discharge machining (EDM), for fabricating the superhydrophobic surfaces, are reviewed and compared, respectively. Third, the machining performances to fabricate the superhydrophobic surfaces by the electrochemical machining (ECM), including electrochemical oxidation process and electrochemical reduction process, are reviewed and grouped by materials fabricated. Lastly, other non-traditional machining processes for fabricating superhydrophobic surfaces, such as ultrasonic machining (USM), water jet machining (WJM), and plasma spraying machining (PSM), are compared and summarized. Moreover, the advantage and disadvantage of the above mentioned non-traditional machining processes are discussed. Thereafter, the prospect of non-traditional machining for fabricating the desired superhydrophobic surfaces is proposed. Full article

(This article belongs to the Special Issue Micromachining Method for Surface Morphology)

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10 pages, 3000 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Fabrication of 3D Micro-Blades for the Cutting of Biological Structures in a Microfluidic Guillotine

by Saisneha Koppaka, Kevin S. Zhang, Myra Kurosu Jalil, Lucas R. Blauch and Sindy K. Y. Tang

Micromachines 2021, 12(9), 1005; https://doi.org/10.3390/mi12091005 - 24 Aug 2021

Cited by 10 | Viewed by 4779

Abstract

Micro-blade design is an important factor in the cutting of single cells and other biological structures. This paper describes the fabrication process of three-dimensional (3D) micro-blades for the cutting of single cells in a microfluidic “guillotine” intended for fundamental wound repair and regeneration [...] Read more.

Micro-blade design is an important factor in the cutting of single cells and other biological structures. This paper describes the fabrication process of three-dimensional (3D) micro-blades for the cutting of single cells in a microfluidic “guillotine” intended for fundamental wound repair and regeneration studies. Our microfluidic guillotine consists of a fixed 3D micro-blade centered in a microchannel to bisect cells flowing through. We show that the Nanoscribe two-photon polymerization direct laser writing system is capable of fabricating complex 3D micro-blade geometries. However, structures made of the Nanoscribe IP-S resin have low adhesion to silicon, and they tend to peel off from the substrate after at most two times of replica molding in poly(dimethylsiloxane) (PDMS). Our work demonstrates that the use of a secondary mold replicates Nanoscribe-printed features faithfully for at least 10 iterations. Finally, we show that complex micro-blade features can generate different degrees of cell wounding and cell survival rates compared with simple blades possessing a vertical cutting edge fabricated with conventional 2.5D photolithography. Our work lays the foundation for future applications in single cell analyses, wound repair and regeneration studies, as well as investigations of the physics of cutting and the interaction between the micro-blade and biological structures. Full article

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

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12 pages, 5499 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Miniature Ultralight Deformable Squama Mechanics and Skin Based on Piezoelectric Actuation

by Xiang Lu, Xiang Xi, Kun Lu, Chengxiang Wang, Xiang Chen, Yulie Wu, Xuezhong Wu and Dingbang Xiao

Micromachines 2021, 12(8), 969; https://doi.org/10.3390/mi12080969 - 16 Aug 2021

Cited by 3 | Viewed by 2288

Abstract

A miniature deformable squama mechanics based on piezoelectric actuation inspired by the deformable squama is proposed in this paper. The overall size of the mechanics is 16 mm × 6 mm × 6 mm, the weight is only 140 mg, the deflection angle [...] Read more.

A miniature deformable squama mechanics based on piezoelectric actuation inspired by the deformable squama is proposed in this paper. The overall size of the mechanics is 16 mm × 6 mm × 6 mm, the weight is only 140 mg, the deflection angle range of the mechanical deformation is −15°~45°, and the mechanical deformation is controllable. The small-batch array processing of the miniature deformable squama mechanics, based on the stereoscopic process, laid the technological foundation for applying the deformed squama array arrangement. We also designed and manufactured a small actuation control boost circuit and a mobile phone piezoelectric control assistant application that makes it convenient to perform short-range non-contact control of the deformation of the squama. The proposed system arranges the deformed squamae into groups to form the skin and controlls the size and direction of the signals input to each group of the squama array, thereby making the skin able to produce different shapes to create deformable skin. Full article

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15 pages, 6249 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

A Prototype Sensor System Using Fabricated Piezoelectric Braided Cord for Work-Environment Measurement during Work from Home

by Yoshiro Tajitsu, Jun Takarada, Kohei Takatani, Riku Nakanishi, Hiroki Yanagimoto, Seita Shiomi, Isamu Nakagawa, Ikuo Kawahara, Takuo Nakiri, Saki Shimda, Yoji Shimura, Takuto Nonomura, Kazunori Kojima, Atsuhisa Ikeguch, Kazuhiro Okayama, Tomohiro Sakai, Yuichi Morioka, Mitsuru Takahashi, Kazuki Sugiyama, Rei Nisho and Koji Takeshita Show full author list Hide full author list

Micromachines 2021, 12(8), 966; https://doi.org/10.3390/mi12080966 - 15 Aug 2021

Cited by 8 | Viewed by 3114

Abstract

We proposed a new prototype sensor system to understand the workload of employees during telework. The goal of sensing using such a system is to index the degree of stress experienced by employees during work and recognize how to improve their work environment. [...] Read more.

We proposed a new prototype sensor system to understand the workload of employees during telework. The goal of sensing using such a system is to index the degree of stress experienced by employees during work and recognize how to improve their work environment. Currently, to realize this, image processing technology with a Web camera is generally used for vital sign sensing. However, it creates a sense of discomfort at work because of a strong sense of surveillance. To truly evaluate a working environment, it is necessary that an employee be unaware of the sensor system and for the system to be as unobtrusive as possible. To overcome these practical barriers, we have developed a new removable piezoelectric sensor incorporated in a piezoelectric poly-L-lactic acid (PLLA) braided cord. This cord is soft and flexible, and it does not cause any discomfort when attached to the cushion cover sheet. Thus, it was possible to measure the workload of an employee working from home without the employee being aware of the presence of a sensor. Additionally, we developed a system for storing data in a cloud system. We succeeded in acquiring continuous long-term data on the vital signs of employees during telework using this system. The analysis of the data revealed a strong correlation between behavior and stress. Full article

(This article belongs to the Special Issue Wearable Piezoelectric Devices)

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23 pages, 23135 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Road to Acquisition: Preparing a MEMS Microphone Array for Measurement of Fuselage Surface Pressure Fluctuations

by Thomas Ahlefeldt, Stefan Haxter, Carsten Spehr, Daniel Ernst and Tobias Kleindienst

Micromachines 2021, 12(8), 961; https://doi.org/10.3390/mi12080961 - 14 Aug 2021

Cited by 18 | Viewed by 3663

Abstract

Preparing and pre-testing experimental setups for flight tests is a lengthy but necessary task. One part of this preparation is comparing newly available measurement technology with proven setups. In our case, we wanted to compare acoustic Micro-Electro-Mechanical Systems (MEMS) to large and proven [...] Read more.

Preparing and pre-testing experimental setups for flight tests is a lengthy but necessary task. One part of this preparation is comparing newly available measurement technology with proven setups. In our case, we wanted to compare acoustic Micro-Electro-Mechanical Systems (MEMS) to large and proven surface-mounted condenser microphones. The task started with the comparison of spectra in low-speed wind tunnel environments. After successful completion, the challenge was increased to similar comparisons in a transonic wind tunnel. The final goal of performing in-flight measurements on the outside fuselage of a twin-engine turboprop aircraft was eventually achieved using a slim array of 45 MEMS microphones with additional large microphones installed on the same carrier to drawn on for comparison. Finally, the array arrangement of MEMS microphones allowed for a complex study of fuselage surface pressure fluctuations in the wavenumber domain. The study indicates that MEMS microphones are an inexpensive alternative to conventional microphones with increased potential for spatially high-resolved measurements even at challenging experimental conditions during flight tests. Full article

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

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12 pages, 2985 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Simulation Guided Hand-Driven Portable Triboelectric Nanogenerator: Design, Optimisation, and Evaluation

by Yunzhong Wang, Anh Tran Tam Pham, Damian Tohl and Youhong Tang

Micromachines 2021, 12(8), 955; https://doi.org/10.3390/mi12080955 - 12 Aug 2021

Cited by 6 | Viewed by 3282

Abstract

Inspired by the fundamental mechanics of an ancient whirligig (or buzzer toy; 3300 BC), a hand-driven rotational triboelectric nanogenerator (HDR-TENG) was designed and optimised, guided by our recently reported mathematical modelling. This modelling indicates that the power generated by HDR-TENG is a function [...] Read more.

Inspired by the fundamental mechanics of an ancient whirligig (or buzzer toy; 3300 BC), a hand-driven rotational triboelectric nanogenerator (HDR-TENG) was designed and optimised, guided by our recently reported mathematical modelling. This modelling indicates that the power generated by HDR-TENG is a function of the number of segments, rotational speed, and tribo-surface spacing with different weighting sensitivities. Based on the simulation results, additive manufacturing technology was combined with commercially available components to cost-effectively fabricate the HDR-TENG. The fabricated HDR-TENG can provide stable and adjustable rotational speed up to 15,000 rpm with a linear hand stretching. The output voltage of HDR-TENG maintains a constant value within 50,000 cycles of testing when using Nylon 66 and PTFE as the triboelectric material. It can charge a 47 μF capacitor to 2.2 V in one minute. This study provides a cost-effective portable HDR-TENG device with adjustable high rotational speed, high power output, and long durable life, creating opportunities to provide a power supply for point-of-care devices in remote or resource-poor settings and applications in science and engineering education. Full article

(This article belongs to the Special Issue Triboelectric Energy Harvesters)

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28 pages, 7218 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Heterogeneous Wafer Bonding Technology and Thin-Film Transfer Technology-Enabling Platform for the Next Generation Applications beyond 5G

by Zhihao Ren, Jikai Xu, Xianhao Le and Chengkuo Lee

Micromachines 2021, 12(8), 946; https://doi.org/10.3390/mi12080946 - 11 Aug 2021

Cited by 56 | Viewed by 11938

Abstract

Wafer bonding technology is one of the most effective methods for high-quality thin-film transfer onto different substrates combined with ion implantation processes, laser irradiation, and the removal of the sacrificial layers. In this review, we systematically summarize and introduce applications of the thin [...] Read more.

Wafer bonding technology is one of the most effective methods for high-quality thin-film transfer onto different substrates combined with ion implantation processes, laser irradiation, and the removal of the sacrificial layers. In this review, we systematically summarize and introduce applications of the thin films obtained by wafer bonding technology in the fields of electronics, optical devices, on-chip integrated mid-infrared sensors, and wearable sensors. The fabrication of silicon-on-insulator (SOI) wafers based on the Smart Cut^TM process, heterogeneous integrations of wide-bandgap semiconductors, infrared materials, and electro-optical crystals via wafer bonding technology for thin-film transfer are orderly presented. Furthermore, device design and fabrication progress based on the platforms mentioned above is highlighted in this work. They demonstrate that the transferred films can satisfy high-performance power electronics, molecular sensors, and high-speed modulators for the next generation applications beyond 5G. Moreover, flexible composite structures prepared by the wafer bonding and de-bonding methods towards wearable electronics are reported. Finally, the outlooks and conclusions about the further development of heterogeneous structures that need to be achieved by the wafer bonding technology are discussed. Full article

(This article belongs to the Special Issue Micro-Nano Science and Engineering)

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11 pages, 2713 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

A Soft Pressure Sensor Array Based on a Conducting Nanomembrane

by Daekwang Jung, Kyumin Kang, Hyunjin Jung, Duhwan Seong, Soojung An, Jiyong Yoon, Wooseok Kim, Mikyung Shin, Hyoung Won Baac, Sangmin Won, Changhwan Shin and Donghee Son

Micromachines 2021, 12(8), 933; https://doi.org/10.3390/mi12080933 - 6 Aug 2021

Cited by 4 | Viewed by 4491

Abstract

Although skin-like pressure sensors exhibit high sensitivity with a high performance over a wide area, they have limitations owing to the critical issue of being linear only in a narrow strain range. Various strategies have been proposed to improve the performance of soft [...] Read more.

Although skin-like pressure sensors exhibit high sensitivity with a high performance over a wide area, they have limitations owing to the critical issue of being linear only in a narrow strain range. Various strategies have been proposed to improve the performance of soft pressure sensors, but such a nonlinearity issue still exists and the sensors are only effective within a very narrow strain range. Herein, we fabricated a highly sensitive multi-channel pressure sensor array by using a simple thermal evaporation process of conducting nanomembranes onto a stretchable substrate. A rigid-island structure capable of dissipating accumulated strain energy induced by external mechanical stimuli was adopted for the sensor. The performance of the sensor was precisely controlled by optimizing the thickness of the stretchable substrate and the number of serpentines of an Au membrane. The fabricated sensor exhibited a sensitivity of 0.675 kPa⁻¹ in the broad pressure range of 2.3–50 kPa with linearity (~0.990), and good stability (>300 Cycles). Finally, we successfully demonstrated a mapping of pressure distribution. Full article

(This article belongs to the Special Issue Deformable Bioelectronics Based on Functional Micro/nanomaterials, Volume II)

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10 pages, 2195 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Fabrication of Microstructured Surface Topologies for the Promotion of Marine Bacteria Biofilm

by Ariadni Droumpali, Jörg Hübner, Lone Gram and Rafael Taboryski

Micromachines 2021, 12(8), 926; https://doi.org/10.3390/mi12080926 - 3 Aug 2021

Cited by 1 | Viewed by 3161

Abstract

Several marine bacteria of the Roseobacter group can inhibit other microorganisms and are especially antagonistic when growing in biofilms. This aptitude to naturally compete with other bacteria can reduce the need for antibiotics in large-scale aquaculture units, provided that their culture can be [...] Read more.

Several marine bacteria of the Roseobacter group can inhibit other microorganisms and are especially antagonistic when growing in biofilms. This aptitude to naturally compete with other bacteria can reduce the need for antibiotics in large-scale aquaculture units, provided that their culture can be promoted and controlled. Micropatterned surfaces may facilitate and promote the biofilm formation of species from the Roseobacter group, due to the increased contact between the cells and the surface material. Our research goal is to fabricate biofilm-optimal micropatterned surfaces and investigate the relevant length scales for surface topographies that can promote the growth and biofilm formation of the Roseobacter group of bacteria. In a preliminary study, silicon surfaces comprising arrays of pillars and pits with different periodicities, diameters, and depths were produced by UV lithography and deep reactive ion etching (DRIE) on polished silicon wafers. The resulting surface microscale topologies were characterized via optical profilometry and scanning electron microscopy (SEM). Screening of the bacterial biofilm on the patterned surfaces was performed using green fluorescent staining (SYBR green I) and confocal laser scanning microscopy (CLSM). Our results indicate that there is a correlation between the surface morphology and the spatial organization of the bacterial biofilm. Full article

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

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15 pages, 1887 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Fiber-Based Thermoelectric Materials and Devices for Wearable Electronics

by Pengxiang Zhang, Biao Deng, Wenting Sun, Zijian Zheng and Weishu Liu

Micromachines 2021, 12(8), 869; https://doi.org/10.3390/mi12080869 - 24 Jul 2021

Cited by 23 | Viewed by 5598

Abstract

Fiber-based thermoelectric materials and devices have the characteristics of light-weight, stability, and flexibility, which can be used in wearable electronics, attracting the wide attention of researchers. In this work, we present a review of state-of-the-art fiber-based thermoelectric material fabrication, device assembling, and its [...] Read more.

Fiber-based thermoelectric materials and devices have the characteristics of light-weight, stability, and flexibility, which can be used in wearable electronics, attracting the wide attention of researchers. In this work, we present a review of state-of-the-art fiber-based thermoelectric material fabrication, device assembling, and its potential applications in temperature sensing, thermoelectric generation, and temperature management. In this mini review, we also shine some light on the potential application in the next generation of wearable electronics, and discuss the challenges and opportunities. Full article

(This article belongs to the Special Issue Advanced Energy Conversion and Storage Microdevices)

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27 pages, 6347 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Droplet Microfluidics for Food and Nutrition Applications

by Karin Schroen, Claire Berton-Carabin, Denis Renard, Mélanie Marquis, Adeline Boire, Rémy Cochereau, Chloé Amine and Sébastien Marze

Micromachines 2021, 12(8), 863; https://doi.org/10.3390/mi12080863 - 23 Jul 2021

Cited by 47 | Viewed by 9769

Abstract

Droplet microfluidics revolutionizes the way experiments and analyses are conducted in many fields of science, based on decades of basic research. Applied sciences are also impacted, opening new perspectives on how we look at complex matter. In particular, food and nutritional sciences still [...] Read more.

Droplet microfluidics revolutionizes the way experiments and analyses are conducted in many fields of science, based on decades of basic research. Applied sciences are also impacted, opening new perspectives on how we look at complex matter. In particular, food and nutritional sciences still have many research questions unsolved, and conventional laboratory methods are not always suitable to answer them. In this review, we present how microfluidics have been used in these fields to produce and investigate various droplet-based systems, namely simple and double emulsions, microgels, microparticles, and microcapsules with food-grade compositions. We show that droplet microfluidic devices enable unprecedented control over their production and properties, and can be integrated in lab-on-chip platforms for in situ and time-resolved analyses. This approach is illustrated for on-chip measurements of droplet interfacial properties, droplet–droplet coalescence, phase behavior of biopolymer mixtures, and reaction kinetics related to food digestion and nutrient absorption. As a perspective, we present promising developments in the adjacent fields of biochemistry and microbiology, as well as advanced microfluidics–analytical instrument coupling, all of which could be applied to solve research questions at the interface of food and nutritional sciences. Full article

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

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15 pages, 8532 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Fabrication of a 3D Nanomagnetic Circuit with Multi-Layered Materials for Applications in Spintronics

by Fanfan Meng, Claire Donnelly, Luka Skoric, Aurelio Hierro-Rodriguez, Jung-wei Liao and Amalio Fernández-Pacheco

Micromachines 2021, 12(8), 859; https://doi.org/10.3390/mi12080859 - 22 Jul 2021

Cited by 12 | Viewed by 4212

Abstract

Three-dimensional (3D) spintronic devices are attracting significant research interest due to their potential for both fundamental studies and computing applications. However, their implementations face great challenges regarding not only the fabrication of 3D nanomagnets with high quality materials, but also their integration into [...] Read more.

Three-dimensional (3D) spintronic devices are attracting significant research interest due to their potential for both fundamental studies and computing applications. However, their implementations face great challenges regarding not only the fabrication of 3D nanomagnets with high quality materials, but also their integration into 2D microelectronic circuits. In this study, we developed a new fabrication process to facilitate the efficient integration of both non-planar 3D geometries and high-quality multi-layered magnetic materials to prototype 3D spintronic devices, as a first step to investigate new physical effects in such systems. Specifically, we exploited 3D nanoprinting, physical vapour deposition and lithographic techniques to realise a 3D nanomagnetic circuit based on a nanobridge geometry, coated with high quality Ta/CoFeB/Ta layers. The successful establishment of this 3D circuit was verified through magnetotransport measurements in combination with micromagnetic simulations and finite element modelling. This fabrication process provides new capabilities for the realisation of a greater variety of 3D nanomagnetic circuits, which will facilitate the understanding and exploitation of 3D spintronic systems. 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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10 pages, 4383 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Low-Cost Laser Micromachining Super Hydrophilic–Super Hydrophobic Microgrooves for Robotic Capillary Micromanipulation of Microfibers

by Bo Chang, Yuhang Feng, Jialong Jin and Quan Zhou

Micromachines 2021, 12(8), 854; https://doi.org/10.3390/mi12080854 - 21 Jul 2021

Cited by 6 | Viewed by 2940

Abstract

Capillary self-alignment technique can achieve highly accurate and fast alignment of micro components. Capillary self-alignment technique relies on the confinement of liquid droplets at receptor sites where hydrophobic–hydrophilic patterns are widely used. This paper reports a low-cost microsecond pulse laser micromachining method for [...] Read more.

Capillary self-alignment technique can achieve highly accurate and fast alignment of micro components. Capillary self-alignment technique relies on the confinement of liquid droplets at receptor sites where hydrophobic–hydrophilic patterns are widely used. This paper reports a low-cost microsecond pulse laser micromachining method for fabrication of super hydrophilic–super hydrophobic grooves as receptor sites for capillary self-alignment of microfibers. We investigated the influence of major manufacturing parameters on groove sizes and wetting properties. The effects of the width (20 µm–100 µm) and depth (8 µm–36 µm) of the groove on the volume of water droplet contained inside the groove were also investigated. We show that by altering scanning speed, using a de-focused laser beam, we can modify the wetting properties of the microgrooves from 10° to 120° in terms of the contact angle. We demonstrated that different types of microfibers including natural and artificial microfibers can self-align to the size matching super hydrophilic–super hydrophobic microgrooves. The results show that super hydrophilic–super hydrophobic microgrooves have great potential in microfiber micromanipulation applications such as natural microfiber categorization, fiber-based microsensor construction, and fiber-enforced material development. Full article

(This article belongs to the Special Issue Robotic Micromanipulation, Volume II)

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28 pages, 7562 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Artificial Compound Eye Systems and Their Application: A Review

by Huu Lam Phan, Jungho Yi, Joonsung Bae, Hyoungho Ko, Sangmin Lee, Dongil Cho, Jong-Mo Seo and Kyo-in Koo

Micromachines 2021, 12(7), 847; https://doi.org/10.3390/mi12070847 - 20 Jul 2021

Cited by 36 | Viewed by 8146

Abstract

The natural compound eye system has many outstanding properties, such as a more compact size, wider-angle view, better capacity to detect moving objects, and higher sensitivity to light intensity, compared to that of a single-aperture vision system. Thanks to the development of micro- [...] Read more.

The natural compound eye system has many outstanding properties, such as a more compact size, wider-angle view, better capacity to detect moving objects, and higher sensitivity to light intensity, compared to that of a single-aperture vision system. Thanks to the development of micro- and nano-fabrication techniques, many artificial compound eye imaging systems have been studied and fabricated to inherit fascinating optical features of the natural compound eye. This paper provides a review of artificial compound eye imaging systems. This review begins by introducing the principle of the natural compound eye, and then, the analysis of two types of artificial compound eye systems. We equally present the applications of the artificial compound eye imaging systems. Finally, we suggest our outlooks about the artificial compound eye imaging system. Full article

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23 pages, 3558 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

An In Vivo Microfluidic Study of Bacterial Load Dynamics and Absorption in the C. elegans Intestine

by Vittorio Viri, Maël Arveiler, Thomas Lehnert and Martin A. M. Gijs

Micromachines 2021, 12(7), 832; https://doi.org/10.3390/mi12070832 - 17 Jul 2021

Cited by 9 | Viewed by 5110

Abstract

Caenorhabditiselegans (C. elegans) has gained importance as a model for studying host-microbiota interactions and bacterial infections related to human pathogens. Assessing the fate of ingested bacteria in the worm’s intestine is therefore of great interest, in particular with respect to [...] Read more.

Caenorhabditiselegans (C. elegans) has gained importance as a model for studying host-microbiota interactions and bacterial infections related to human pathogens. Assessing the fate of ingested bacteria in the worm’s intestine is therefore of great interest, in particular with respect to normal bacterial digestion or intestinal colonization by pathogens. Here, we report an in vivo study of bacteria in the gut of C. elegans. We take advantage of a polydimethylsiloxane (PDMS) microfluidic device enabling passive immobilization of adult worms under physiological conditions. Non-pathogenic Escherichia coli (E. coli) bacteria expressing either pH-sensitive or pH-insensitive fluorescence reporters as well as fluorescently marked indigestible microbeads were used for the different assays. Dynamic fluorescence patterns of the bacterial load in the worm gut were conveniently monitored by time-lapse imaging. Cyclic motion of the bacterial load due to peristaltic activity of the gut was observed and biochemical digestion of E. coli was characterized by high-resolution fluorescence imaging of the worm’s intestine. We could discriminate between individual intact bacteria and diffuse signals related to disrupted bacteria that can be digested. From the decay of the diffuse fluorescent signal, we determined a digestion time constant of 14 ± 4 s. In order to evaluate the possibility to perform infection assays with our platform, immobilized C. elegans worms were fed pathogenic Mycobacterium marinum (M. marinum) bacteria. We analyzed bacterial fate and accumulation in the gut of N2 worms and mitochondrial stress response in a hsp-6::gfp mutant. Full article

(This article belongs to the Special Issue Organisms-on-Chips)

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20 pages, 13167 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Microfluidic Airborne Metal Particle Sensor Using Oil Microcirculation for Real-Time and Continuous Monitoring of Metal Particle Emission

by Jong-Seo Yoon, Jiwon Park, Hye-Rin Ahn, Seong-Jae Yoo and Yong-Jun Kim

Micromachines 2021, 12(7), 825; https://doi.org/10.3390/mi12070825 - 14 Jul 2021

Cited by 4 | Viewed by 3528

Abstract

Airborne metal particles (MPs; particle size > 10 μm) in workplaces result in a loss in production yield if not detected in time. The demand for compact and cost-efficient MP sensors to monitor airborne MP generation is increasing. However, contemporary instruments and laboratory-grade [...] Read more.

Airborne metal particles (MPs; particle size > 10 μm) in workplaces result in a loss in production yield if not detected in time. The demand for compact and cost-efficient MP sensors to monitor airborne MP generation is increasing. However, contemporary instruments and laboratory-grade sensors exhibit certain limitations in real-time and on-site monitoring of airborne MPs. This paper presents a microfluidic MP detection chip to address these limitations. By combining the proposed system with microcirculation-based particle-to-liquid collection and a capacitive sensing method, the continuous detection of airborne MPs can be achieved. A few microfabrication processes were realized, resulting in a compact system, which can be easily replaced after contamination with a low-priced microfluidic chip. In our experiments, the frequency-dependent capacitive changes were characterized using MP (aluminum) samples (sizes ranging from 10 μm to 40 μm). Performance evaluation of the proposed system under test-bed conditions indicated that it is capable of real-time and continuous monitoring of airborne MPs (minimum size 10 μm) under an optimal frequency, with superior sensitivity and responsivity. Therefore, the proposed system can be used as an on-site MP sensor for unexpected airborne MP generation in precise manufacturing facilities where metal sources are used. Full article

(This article belongs to the Special Issue MEMS/NEMS Sensors and Actuators)

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36 pages, 9659 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Membrane Fouling Phenomena in Microfluidic Systems: From Technical Challenges to Scientific Opportunities

by Andrea Iginio Cirillo, Giovanna Tomaiuolo and Stefano Guido

Micromachines 2021, 12(7), 820; https://doi.org/10.3390/mi12070820 - 13 Jul 2021

Cited by 39 | Viewed by 5750

Abstract

The almost ubiquitous, though undesired, deposition and accumulation of suspended/dissolved matter on solid surfaces, known as fouling, represents a crucial issue strongly affecting the efficiency and sustainability of micro-scale reactors. Fouling becomes even more detrimental for all the applications that require the use [...] Read more.

The almost ubiquitous, though undesired, deposition and accumulation of suspended/dissolved matter on solid surfaces, known as fouling, represents a crucial issue strongly affecting the efficiency and sustainability of micro-scale reactors. Fouling becomes even more detrimental for all the applications that require the use of membrane separation units. As a matter of fact, membrane technology is a key route towards process intensification, having the potential to replace conventional separation procedures, with significant energy savings and reduced environmental impact, in a broad range of applications, from water purification to food and pharmaceutical industries. Despite all the research efforts so far, fouling still represents an unsolved problem. The complex interplay of physical and chemical mechanisms governing its evolution is indeed yet to be fully unraveled and the role played by foulants’ properties or operating conditions is an area of active research where microfluidics can play a fundamental role. The aim of this review is to explore fouling through microfluidic systems, assessing the fundamental interactions involved and how microfluidics enables the comprehension of the mechanisms characterizing the process. The main mathematical models describing the fouling stages will also be reviewed and their limitations discussed. Finally, the principal dynamic investigation techniques in which microfluidics represents a key tool will be discussed, analyzing their employment to study fouling. Full article

(This article belongs to the Special Issue Micro-Reaction Engineering)

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15 pages, 1649 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Post-Operative Monitoring of Intestinal Tissue Oxygenation Using an Implantable Microfabricated Oxygen Sensor

by Jamie R. K. Marland, Mark E. Gray, David J. Argyle, Ian Underwood, Alan F. Murray and Mark A. Potter

Micromachines 2021, 12(7), 810; https://doi.org/10.3390/mi12070810 - 10 Jul 2021

Cited by 6 | Viewed by 4577

Abstract

Anastomotic leakage (AL) is a common and dangerous post-operative complication following intestinal resection, causing substantial morbidity and mortality. Ischaemia in the tissue surrounding the anastomosis is a major risk-factor for AL development. Continuous tissue oxygenation monitoring during the post-operative recovery period would provide [...] Read more.

Anastomotic leakage (AL) is a common and dangerous post-operative complication following intestinal resection, causing substantial morbidity and mortality. Ischaemia in the tissue surrounding the anastomosis is a major risk-factor for AL development. Continuous tissue oxygenation monitoring during the post-operative recovery period would provide early and accurate early identification of AL risk. We describe the construction and testing of a miniature implantable electrochemical oxygen sensor that addresses this need. It consisted of an array of platinum microelectrodes, microfabricated on a silicon substrate, with a poly(2-hydroxyethyl methacrylate) hydrogel membrane to protect the sensor surface. The sensor was encapsulated in a biocompatible package with a wired connection to external instrumentation. It gave a sensitive and highly linear response to variations in oxygen partial pressure in vitro, although over time its sensitivity was partially decreased by protein biofouling. Using a pre-clinical in vivo pig model, acute intestinal ischaemia was robustly and accurately detected by the sensor. Graded changes in tissue oxygenation were also measurable, with relative differences detected more accurately than absolute differences. Finally, we demonstrated its suitability for continuous monitoring of tissue oxygenation at a colorectal anastomosis over a period of at least 45 h. This study provides evidence to support the development and use of implantable electrochemical oxygen sensors for post-operative monitoring of anastomosis oxygenation. Full article

(This article belongs to the Special Issue Reliability and Biostability of Microfabricated Implantable Medical Devices: Towards Standardized Manufacturing and Lab-Bench/Preclinical Testing)

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12 pages, 2577 KiB

Open AccessFeature PaperEditor’s ChoiceCommunication

Magnetic-Propelled Janus Yeast Cell Robots Functionalized with Metal-Organic Frameworks for Mycotoxin Decontamination

by Dongdong Lu, Songsong Tang, Yangyang Li, Zhaoqing Cong, Xueji Zhang and Song Wu

Micromachines 2021, 12(7), 797; https://doi.org/10.3390/mi12070797 - 5 Jul 2021

Cited by 11 | Viewed by 3788

Abstract

Cell robots that transform natural cells into active platforms hold great potential to enrich the biomedical prospects of artificial microrobots. Here, we present Janus yeast cell microrobots (JYC-robots) prepared by asymmetrically coating Fe₃O₄ nanoparticles (NPs) and subsequent in situ growth [...] Read more.

Cell robots that transform natural cells into active platforms hold great potential to enrich the biomedical prospects of artificial microrobots. Here, we present Janus yeast cell microrobots (JYC-robots) prepared by asymmetrically coating Fe₃O₄ nanoparticles (NPs) and subsequent in situ growth of zeolitic imidazolate framework-67 (ZIF-67) on the surface of yeast cells. The magnetic actuation relies on the Fe₃O₄ NPs wrapping. As the compositions of cell robots, the cell wall with abundant polysaccharide coupling with porous and oxidative ZIF-67 can concurrently remove mycotoxin (e.g., zearalenone (ZEN)). The magnetic propulsion accelerates the decontamination efficiency of JYC-robots against ZEN. Although yeast cells with fully coating of Fe₃O₄ NPs and ZIF-67 (FC-yeasts) show faster movement than JYC-robots, higher toxin-removal efficacy is observed for JYC-robots compared with that of FC-yeasts, reflecting the vital factor of the yeast cell wall in removing mycotoxin. Such design with Janus modification of magnetic NPs (MNPs) and entire coating of ZIF-67 generates active cell robot platform capable of fuel-free propulsion and enhanced detoxification, offering a new formation to develop cell-based robotics system for environmental remediation. Full article

(This article belongs to the Special Issue Fundamentals and Applications of Micro-Nanorobotics)

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19 pages, 5184 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Biocompatibility of SU-8 and Its Biomedical Device Applications

by Ziyu Chen and Jeong-Bong Lee

Micromachines 2021, 12(7), 794; https://doi.org/10.3390/mi12070794 - 4 Jul 2021

Cited by 49 | Viewed by 6066

Abstract

SU-8 is an epoxy-based, negative-tone photoresist that has been extensively utilized to fabricate myriads of devices including biomedical devices in the recent years. This paper first reviews the biocompatibility of SU-8 for in vitro and in vivo applications. Surface modification techniques as well [...] Read more.

SU-8 is an epoxy-based, negative-tone photoresist that has been extensively utilized to fabricate myriads of devices including biomedical devices in the recent years. This paper first reviews the biocompatibility of SU-8 for in vitro and in vivo applications. Surface modification techniques as well as various biomedical applications based on SU-8 are also discussed. Although SU-8 might not be completely biocompatible, existing surface modification techniques, such as O₂ plasma treatment or grafting of biocompatible polymers, might be sufficient to minimize biofouling caused by SU-8. As a result, a great deal of effort has been directed to the development of SU-8-based functional devices for biomedical applications. This review includes biomedical applications such as platforms for cell culture and cell encapsulation, immunosensing, neural probes, and implantable pressure sensors. Proper treatments of SU-8 and slight modification of surfaces have enabled the SU-8 as one of the unique choices of materials in the fabrication of biomedical devices. Due to the versatility of SU-8 and comparative advantages in terms of improved Young’s modulus and yield strength, we believe that SU-8-based biomedical devices would gain wider proliferation among the biomedical community in the future. Full article

(This article belongs to the Special Issue 20 Years of SU8 as MEMS Material)

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13 pages, 2890 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Fabrication of Ultranarrow Nanochannels with Ultrasmall Nanocomponents in Glass Substrates

by Hiroki Kamai and Yan Xu

Micromachines 2021, 12(7), 775; https://doi.org/10.3390/mi12070775 - 30 Jun 2021

Cited by 14 | Viewed by 4401

Abstract

Nanofluidics is supposed to take advantage of a variety of new physical phenomena and unusual effects at nanoscales typically below 100 nm. However, the current chip-based nanofluidic applications are mostly based on the use of nanochannels with linewidths above 100 nm, due to [...] Read more.

Nanofluidics is supposed to take advantage of a variety of new physical phenomena and unusual effects at nanoscales typically below 100 nm. However, the current chip-based nanofluidic applications are mostly based on the use of nanochannels with linewidths above 100 nm, due to the restricted ability of the efficient fabrication of nanochannels with narrow linewidths in glass substrates. In this study, we established the fabrication of nanofluidic structures in glass substrates with narrow linewidths of several tens of nanometers by optimizing a nanofabrication process composed of electron-beam lithography and plasma dry etching. Using the optimized process, we achieved the efficient fabrication of fine glass nanochannels with sub-40 nm linewidths, uniform lateral features, and smooth morphologies, in an accurate and precise way. Furthermore, the use of the process allowed the integration of similar or dissimilar material-based ultrasmall nanocomponents in the ultranarrow nanochannels, including arrays of pockets with volumes as less as 42 zeptoliters (zL, 10⁻²¹ L) and well-defined gold nanogaps as narrow as 19 nm. We believe that the established nanofabrication process will be very useful for expanding fundamental research and in further improving the applications of nanofluidic devices. Full article

(This article belongs to the Special Issue Advances in Nanofluidics, Volume II)

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16 pages, 12537 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Recent Development and Perspectives of Optimization Design Methods for Piezoelectric Ultrasonic Transducers

by Dongdong Chen, Linwei Wang, Xingjun Luo, Chunlong Fei, Di Li, Guangbao Shan and Yintang Yang

Micromachines 2021, 12(7), 779; https://doi.org/10.3390/mi12070779 - 30 Jun 2021

Cited by 27 | Viewed by 6966

Abstract

A piezoelectric ultrasonic transducer (PUT) is widely used in nondestructive testing, medical imaging, and particle manipulation, etc., and the performance of the PUT determines its functional performance and effectiveness in these applications. The optimization design method of a PUT is very important for [...] Read more.

A piezoelectric ultrasonic transducer (PUT) is widely used in nondestructive testing, medical imaging, and particle manipulation, etc., and the performance of the PUT determines its functional performance and effectiveness in these applications. The optimization design method of a PUT is very important for the fabrication of a high-performance PUT. In this paper, traditional and efficient optimization design methods for a PUT are presented. The traditional optimization design methods are mainly based on an analytical model, an equivalent circuit model, or a finite element model and the design parameters are adjusted by a trial-and-error method, which relies on the experience of experts and has a relatively low efficiency. Recently, by combining intelligent optimization algorithms, efficient optimization design methods for a PUT have been developed based on a traditional model or a data-driven model, which can effectively improve the design efficiency of a PUT and reduce its development cycle and cost. The advantages and disadvantages of the presented methods are compared and discussed. Finally, the optimization design methods for PUT are concluded, and their future perspectives are discussed. Full article

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19 pages, 3579 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Machine Assisted Experimentation of Extrusion-Based Bioprinting Systems

by Shuyu Tian, Rory Stevens, Bridget T. McInnes and Nastassja A. Lewinski

Micromachines 2021, 12(7), 780; https://doi.org/10.3390/mi12070780 - 30 Jun 2021

Cited by 34 | Viewed by 5185

Abstract

Optimization of extrusion-based bioprinting (EBB) parameters have been systematically conducted through experimentation. However, the process is time- and resource-intensive and not easily translatable to other laboratories. This study approaches EBB parameter optimization through machine learning (ML) models trained using data collected from the [...] Read more.

Optimization of extrusion-based bioprinting (EBB) parameters have been systematically conducted through experimentation. However, the process is time- and resource-intensive and not easily translatable to other laboratories. This study approaches EBB parameter optimization through machine learning (ML) models trained using data collected from the published literature. We investigated regression-based and classification-based ML models and their abilities to predict printing outcomes of cell viability and filament diameter for cell-containing alginate and gelatin composite bioinks. In addition, we interrogated if regression-based models can predict suitable extrusion pressure given the desired cell viability when keeping other experimental parameters constant. We also compared models trained across data from general literature to models trained across data from one literature source that utilized alginate and gelatin bioinks. The results indicate that models trained on large amounts of data can impart physical trends on cell viability, filament diameter, and extrusion pressure seen in past literature. Regression models trained on the larger dataset also predict cell viability closer to experimental values for material concentration combinations not seen in training data of the single-paper-based regression models. While the best performing classification models for cell viability can achieve an average prediction accuracy of 70%, the cell viability predictions remained constant despite altering input parameter combinations. Our trained models on bioprinting literature data show the potential usage of applying ML models to bioprinting experimental design. Full article

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

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9 pages, 2300 KiB

Open AccessFeature PaperEditor’s ChoiceCommunication

Large-Area and Ultrathin MEMS Mirror Using Silicon Micro Rim

by Myeong-Su Ahn, Jaehun Jeon, Kyung-Won Jang and Ki-Hun Jeong

Micromachines 2021, 12(7), 754; https://doi.org/10.3390/mi12070754 - 26 Jun 2021

Cited by 8 | Viewed by 3661

Abstract

A large-area and ultrathin MEMS (microelectromechanical system) mirror can provide efficient light-coupling, a large scanning area, and high energy efficiency for actuation. However, the ultrathin mirror is significantly vulnerable to diverse film deformation due to residual thin film stresses, so that high flatness [...] Read more.

A large-area and ultrathin MEMS (microelectromechanical system) mirror can provide efficient light-coupling, a large scanning area, and high energy efficiency for actuation. However, the ultrathin mirror is significantly vulnerable to diverse film deformation due to residual thin film stresses, so that high flatness of the mirror is hardly achieved. Here, we report a MEMS mirror of large-area and ultrathin membrane with high flatness by using the silicon rim microstructure (SRM). The ultrathin MEMS mirror with SRM (SRM-mirror) consists of aluminum (Al) deposited silicon nitride membrane, bimorph actuator, and the SRM. The SRM is simply fabricated underneath the silicon nitride membrane, and thus effectively inhibits the tensile stress relaxation of the membrane. As a result, the membrane has high flatness of 10.6 m⁻¹ film curvature at minimum without any deformation. The electrothermal actuation of the SRM-mirror shows large tilting angles from 15° to −45° depending on the applied DC voltage of 0~4 V_DC, preserving high flatness of the tilting membrane. This stable and statically actuated SRM-mirror spurs diverse micro-optic applications such as optical sensing, beam alignment, or optical switching. Full article

(This article belongs to the Special Issue Advanced MEMS and Optical System Assembly and Integration)

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17 pages, 3541 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Functionalized Mesoporous Thin Films for Biotechnology

by Barbara Sartori, Heinz Amenitsch and Benedetta Marmiroli

Micromachines 2021, 12(7), 740; https://doi.org/10.3390/mi12070740 - 24 Jun 2021

Cited by 10 | Viewed by 3800

Abstract

Mesoporous materials bear great potential for biotechnological applications due to their biocompatibility and versatility. Their high surface area and pore interconnection allow the immobilization of molecules and their subsequent controlled delivery. Modifications of the mesoporous material with the addition of different chemical species, [...] Read more.

Mesoporous materials bear great potential for biotechnological applications due to their biocompatibility and versatility. Their high surface area and pore interconnection allow the immobilization of molecules and their subsequent controlled delivery. Modifications of the mesoporous material with the addition of different chemical species, make them particularly suitable for the production of bioactive coatings. Functionalized thin films of mesoporous silica and titania can be used as scaffolds with properties as diverse as promotion of cell growth, inhibition of biofilms formation, or development of sensors based on immobilized enzymes. The possibility to pattern them increase their appeal as they can be incorporated into devices and can be tailored both with respect to architecture and functionalization. In fact, selective surface manipulation is the ground for the fabrication of advanced micro devices that combine standard micro/nanofluids with functional materials. In this review, we will present the advantages of the functionalization of silica and titania mesoporous materials deposited in thin film. Different functional groups used to modify their properties will be summarized, as well as functionalization methods and some examples of applications of modified materials, thus giving an overview of the essential role of functionalization to improve the performance of such innovative materials. Full article

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

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19 pages, 1190 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Geometric Methods for Efficient Planar Swimming of Copepod Nauplii

by Corey Shanbrom, Jonas Balisacan, George Wilkens and Monique Chyba

Micromachines 2021, 12(6), 706; https://doi.org/10.3390/mi12060706 - 16 Jun 2021

Cited by 1 | Viewed by 2366

Abstract

Copepod nauplii are larval crustaceans with important ecological functions. Due to their small size, they experience an environment of low Reynolds number within their aquatic habitat. Here we provide a mathematical model of a swimming copepod nauplius with two legs moving in a [...] Read more.

Copepod nauplii are larval crustaceans with important ecological functions. Due to their small size, they experience an environment of low Reynolds number within their aquatic habitat. Here we provide a mathematical model of a swimming copepod nauplius with two legs moving in a plane. This model allows for both rotation and two-dimensional displacement by the periodic deformation of the swimmer’s body. The system is studied from the framework of optimal control theory, with a simple cost function designed to approximate the mechanical energy expended by the copepod. We find that this model is sufficiently realistic to recreate behavior similar to those of observed copepod nauplii, yet much of the mathematical analysis is tractable. In particular, we show that the system is controllable, but there exist singular configurations where the degree of non-holonomy is non-generic. We also partially characterize the abnormal extremals and provide explicit examples of families of abnormal curves. Finally, we numerically simulate normal extremals and observe some interesting and surprising phenomena. Full article

(This article belongs to the Special Issue Advances in Microswimmers)

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14 pages, 7061 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Numerical Evaluation on Residual Thermal Stress-Induced Delamination at PDMS–Metal Interface of Neural Prostheses

by Yuyang Mao, Ivan Pechenizkiy, Thomas Stieglitz and Theodor Doll

Micromachines 2021, 12(6), 669; https://doi.org/10.3390/mi12060669 - 8 Jun 2021

Cited by 5 | Viewed by 3649

Abstract

The most common failure mode of implantable neural implants has been delamination of layers in compound structures and encapsulations in a wet body environment. Current knowledge of failure mechanisms of adhesion and its standardized test procedures are lacking and must be established. This [...] Read more.

The most common failure mode of implantable neural implants has been delamination of layers in compound structures and encapsulations in a wet body environment. Current knowledge of failure mechanisms of adhesion and its standardized test procedures are lacking and must be established. This study demonstrated a combined experimental and numerical method to investigate the residual stresses from one of the most common encapsulation materials, silicone rubber (polydimethylsiloxane-PDMS) during the coating process at elevated temperatures. Measured shrinkage of test specimen correlates well to a modified shrinkage model using thermal-mechanical finite element method (FEM) simulation. All simulated interfacial stresses show stress concentration at the PDMS coating front depending on curing temperature and coating thickness, while Griffith’s condition estimated the delamination of the coating front. This study emphasizes the understanding of the interfacial delamination giving the possibility to predict failure mode of neural interface. Full article

(This article belongs to the Special Issue Implantable Neural Interfaces)

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12 pages, 2573 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

A Comparison between Finite Element Model (FEM) Simulation and an Integrated Artificial Neural Network (ANN)-Particle Swarm Optimization (PSO) Approach to Forecast Performances of Micro Electro Discharge Machining (Micro-EDM) Drilling

by Mariangela Quarto, Gianluca D’Urso, Claudio Giardini, Giancarlo Maccarini and Mattia Carminati

Micromachines 2021, 12(6), 667; https://doi.org/10.3390/mi12060667 - 7 Jun 2021

Cited by 32 | Viewed by 5404

Abstract

Artificial Neural Network (ANN), together with a Particle Swarm Optimization (PSO) and Finite Element Model (FEM), was used to forecast the process performances for the Micro Electrical Discharge Machining (micro-EDM) drilling process. The integrated ANN-PSO methodology has a double direction functionality, responding to [...] Read more.

Artificial Neural Network (ANN), together with a Particle Swarm Optimization (PSO) and Finite Element Model (FEM), was used to forecast the process performances for the Micro Electrical Discharge Machining (micro-EDM) drilling process. The integrated ANN-PSO methodology has a double direction functionality, responding to different industrial needs. It allows to optimize the process parameters as a function of the required performances and, at the same time, it allows to forecast the process performances fixing the process parameters. The functionality is strictly related to the input and/or output fixed in the model. The FEM model was based on the capacity of modeling the removal process through the mesh element deletion, simulating electrical discharges through a proper heat-flux. This paper compares these prevision models, relating the expected results with the experimental data. In general, the results show that the integrated ANN-PSO methodology is more accurate in the performance previsions. Furthermore, the ANN-PSO model is faster and easier to apply, but it requires a large amount of historical data for the ANN training. On the contrary, the FEM is more complex to set up, since many physical and thermal characteristics of the materials are necessary, and a great deal of time is required for a single simulation. Full article

(This article belongs to the Special Issue Advances in Micro and Nano Manufacturing: Process Modeling and Applications, Volume II)

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16 pages, 54577 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

In Vivo Assessment of Hypoxia Levels in Pancreatic Tumors Using a Dual-Modality Ultrasound/Photoacoustic Imaging System

by Yuhling Wang, De-Fu Jhang, Chia-Hua Tsai, Nai-Jung Chiang, Chia-Hui Tsao, Chiung-Cheng Chuang, Li-Tzong Chen, Wun-Shaing Wayne Chang and Lun-De Liao

Micromachines 2021, 12(6), 668; https://doi.org/10.3390/mi12060668 - 7 Jun 2021

Cited by 11 | Viewed by 4452

Abstract

Noninvasive anatomical and functional imaging has become an essential tool to evaluate tissue oxygen saturation dynamics in preclinical or clinical studies of hypoxia. Our dual-wavelength technique for photoacoustic (PA) imaging based on the differential absorbance spectrum of oxyhemoglobin (oxy-Hb) and deoxyhemoglobin (deoxy-Hb) can [...] Read more.

Noninvasive anatomical and functional imaging has become an essential tool to evaluate tissue oxygen saturation dynamics in preclinical or clinical studies of hypoxia. Our dual-wavelength technique for photoacoustic (PA) imaging based on the differential absorbance spectrum of oxyhemoglobin (oxy-Hb) and deoxyhemoglobin (deoxy-Hb) can quantify tissue oxygen saturation using the intrinsic contrast property. PA imaging of tissue oxygen saturation can be used to monitor tumor-related hypoxia, which is a particularly relevant functional parameter of the tumor microenvironment that has a strong influence on tumor aggressiveness. The simultaneous acquisition of anatomical and functional information using dual-modality ultrasound (US) and PA imaging technology enhances the preclinical applicability of the method. Here, the developed dual-modality US/PA system was used to measure relative tissue oxygenation using the dual-wavelength technique. Tissue oxygen saturation was quantified in a pancreatic tumor mouse model. The differences in tissue oxygenation were detected by comparing pancreatic samples from normal and tumor-bearing mice at various time points after implantation. The use of an in vivo pancreatic tumor model revealed changes in hypoxia at various stages of tumor growth. The US/PA imaging data positively correlated with the results of immunohistochemical staining for hypoxia. Thus, our dual-modality US/PA imaging system can be used to reliably assess and monitor hypoxia in pancreatic tumor mouse models. These findings enable the use of a combination of US and PA imaging to acquire anatomical and functional information on tumor growth and to evaluate treatment responses in longitudinal preclinical studies. Full article

(This article belongs to the Special Issue MEMS for Ultrasound)

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13 pages, 3323 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

In Vivo Microelectrode Arrays for Detecting Multi-Region Epileptic Activities in the Hippocampus in the Latent Period of Rat Model of Temporal Lobe Epilepsy

by Yuchuan Dai, Yilin Song, Jingyu Xie, Shengwei Xu, Xinrong Li, Enhui He, Huabing Yin and Xinxia Cai

Micromachines 2021, 12(6), 659; https://doi.org/10.3390/mi12060659 - 3 Jun 2021

Cited by 8 | Viewed by 3631

Abstract

Temporal lobe epilepsy (TLE) is a form of refractory focal epilepsy, which includes a latent period and a chronic period. Microelectrode arrays capable of multi-region detection of neural activities are important for accurately identifying the epileptic focus and pathogenesis mechanism in the latent [...] Read more.

Temporal lobe epilepsy (TLE) is a form of refractory focal epilepsy, which includes a latent period and a chronic period. Microelectrode arrays capable of multi-region detection of neural activities are important for accurately identifying the epileptic focus and pathogenesis mechanism in the latent period of TLE. Here, we fabricated multi-shank MEAs to detect neural activities in the DG, hilus, CA3, and CA1 in the TLE rat model. In the latent period in TLE rats, seizures were induced and changes in neural activities were detected. The results showed that induced seizures spread from the hilus and CA3 to other areas. Furthermore, interneurons in the hilus and CA3 were more excited than principal cells and exhibited rhythmic oscillations at approximately 15 Hz in grand mal seizures. In addition, the power spectral density (PSD) of neural spikes and local field potentials (LFPs) were synchronized in the frequency domain of the alpha band (9–15 Hz) after the induction of seizures. The results suggest that fabricated MEAs have the advantages of simultaneous and precise detection of neural activities in multiple subregions of the hippocampus. Our MEAs promote the study of cellular mechanisms of TLE during the latent period, which provides an important basis for the diagnosis of the lesion focus of TLE. Full article

(This article belongs to the Special Issue Miniaturised Medical Devices: Design, Manufacturing, Testing and Translation)

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27 pages, 3878 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Light-Emitting Textiles: Device Architectures, Working Principles, and Applications

by Marco Cinquino, Carmela Tania Prontera, Marco Pugliese, Roberto Giannuzzi, Daniela Taurino, Giuseppe Gigli and Vincenzo Maiorano

Micromachines 2021, 12(6), 652; https://doi.org/10.3390/mi12060652 - 2 Jun 2021

Cited by 37 | Viewed by 10608

Abstract

E-textiles represent an emerging technology aiming toward the development of fabric with augmented functionalities, enabling the integration of displays, sensors, and other electronic components into textiles. Healthcare, protective clothing, fashion, and sports are a few examples application areas of e-textiles. Light-emitting textiles can [...] Read more.

E-textiles represent an emerging technology aiming toward the development of fabric with augmented functionalities, enabling the integration of displays, sensors, and other electronic components into textiles. Healthcare, protective clothing, fashion, and sports are a few examples application areas of e-textiles. Light-emitting textiles can have different applications: sensing, fashion, visual communication, light therapy, etc. Light emission can be integrated with textiles in different ways: fabricating light-emitting fibers and planar light-emitting textiles or employing side-emitting polymer optical fibers (POFs) coupled with light-emitting diodes (LEDs). Different kinds of technology have been investigated: alternating current electroluminescent devices (ACELs), inorganic and organic LEDs, and light-emitting electrochemical cells (LECs). The different device working principles and architectures are discussed in this review, highlighting the most relevant aspects and the possible approaches for their integration with textiles. Regarding POFs, the methodology to obtain side emissions and the critical aspects for their integration into textiles are discussed in this review. The main applications of light-emitting fabrics are illustrated, demonstrating that LEDs, alone or coupled with POFs, represent the most robust technology. On the other hand, OLEDs (Organic LEDs) are very promising for the future of light-emitting fabrics, but some issues still need to be addressed. Full article

(This article belongs to the Special Issue Emerging and Disruptive Next-Generation Technologies for POC: Sensors, Chemistry and Microfluidics for Diagnostics)

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19 pages, 5654 KiB

Open AccessFeature PaperEditor’s ChoiceReview

A Review of the Progress of Thin-Film Transistors and Their Technologies for Flexible Electronics

by Mohammad Javad Mirshojaeian Hosseini and Robert A. Nawrocki

Micromachines 2021, 12(6), 655; https://doi.org/10.3390/mi12060655 - 2 Jun 2021

Cited by 82 | Viewed by 11385

Abstract

Flexible electronics enable various technologies to be integrated into daily life and fuel the quests to develop revolutionary applications, such as artificial skins, intelligent textiles, e-skin patches, and on-skin displays. Mechanical characteristics, including the total thickness and the bending radius, are of paramount [...] Read more.

Flexible electronics enable various technologies to be integrated into daily life and fuel the quests to develop revolutionary applications, such as artificial skins, intelligent textiles, e-skin patches, and on-skin displays. Mechanical characteristics, including the total thickness and the bending radius, are of paramount importance for physically flexible electronics. However, the limitation regarding semiconductor fabrication challenges the mechanical flexibility of thin-film electronics. Thin-Film Transistors (TFTs) are a key component in thin-film electronics that restrict the flexibility of thin-film systems. Here, we provide a brief overview of the trends of the last three decades in the physical flexibility of various semiconducting technologies, including amorphous-silicon, polycrystalline silicon, oxides, carbon nanotubes, and organics. The study demonstrates the trends of the mechanical properties, including the total thickness and the bending radius, and provides a vision for the future of flexible TFTs. Full article

(This article belongs to the Special Issue Semiconducting-Nanomaterials-Based Electronic and Optoelectronic Devices)

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31 pages, 8928 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Lateral-Type Spin-Photonics Devices: Development and Applications

by Nozomi Nishizawa and Hiro Munekata

Micromachines 2021, 12(6), 644; https://doi.org/10.3390/mi12060644 - 31 May 2021

Cited by 18 | Viewed by 5266

Abstract

Spin-photonic devices, represented by spin-polarized light emitting diodes and spin-polarized photodiodes, have great potential for practical use in circularly polarized light (CPL) applications. Focusing on the lateral-type spin-photonic devices that can exchange CPL through their side facets, this review describes their functions in [...] Read more.

Spin-photonic devices, represented by spin-polarized light emitting diodes and spin-polarized photodiodes, have great potential for practical use in circularly polarized light (CPL) applications. Focusing on the lateral-type spin-photonic devices that can exchange CPL through their side facets, this review describes their functions in practical CPL applications in terms of: (1) Compactness and integrability, (2) stand-alone (monolithic) nature, (3) room temperature operation, (4) emission with high circular polarization, (5) polarization controllability, and (6) CPL detection. Furthermore, it introduces proposed CPL applications in a wide variety of fields and describes the application of these devices in biological diagnosis using CPL scattering. Finally, it discusses the current state of spin-photonic devices and their applications and future prospects. Full article

(This article belongs to the Special Issue Spin-Photonic Devices and Its Applications)

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45 pages, 13379 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Additive Manufacture of Small-Scale Metamaterial Structures for Acoustic and Ultrasonic Applications

by Alicia Gardiner, Paul Daly, Roger Domingo-Roca, James F. C. Windmill, Andrew Feeney and Joseph C. Jackson-Camargo

Micromachines 2021, 12(6), 634; https://doi.org/10.3390/mi12060634 - 29 May 2021

Cited by 26 | Viewed by 9203

Abstract

Acoustic metamaterials are large-scale materials with small-scale structures. These structures allow for unusual interaction with propagating sound and endow the large-scale material with exceptional acoustic properties not found in normal materials. However, their multi-scale nature means that the manufacture of these materials is [...] Read more.

Acoustic metamaterials are large-scale materials with small-scale structures. These structures allow for unusual interaction with propagating sound and endow the large-scale material with exceptional acoustic properties not found in normal materials. However, their multi-scale nature means that the manufacture of these materials is not trivial, often requiring micron-scale resolution over centimetre length scales. In this review, we bring together a variety of acoustic metamaterial designs and separately discuss ways to create them using the latest trends in additive manufacturing. We highlight the advantages and disadvantages of different techniques that act as barriers towards the development of realisable acoustic metamaterials for practical audio and ultrasonic applications and speculate on potential future developments. Full article

(This article belongs to the Special Issue 3D/4D Printing of Metamaterials and Multifunctional Structures)

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36 pages, 8285 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Microfluidic Based Physical Approaches towards Single-Cell Intracellular Delivery and Analysis

by Kiran Kaladharan, Ashish Kumar, Pallavi Gupta, Kavitha Illath, Tuhin Subhra Santra and Fan-Gang Tseng

Micromachines 2021, 12(6), 631; https://doi.org/10.3390/mi12060631 - 28 May 2021

Cited by 18 | Viewed by 8236

Abstract

The ability to deliver foreign molecules into a single living cell with high transfection efficiency and high cell viability is of great interest in cell biology for applications in therapeutic development, diagnostics, and drug delivery towards personalized medicine. Various physical delivery methods have [...] Read more.

The ability to deliver foreign molecules into a single living cell with high transfection efficiency and high cell viability is of great interest in cell biology for applications in therapeutic development, diagnostics, and drug delivery towards personalized medicine. Various physical delivery methods have long demonstrated the ability to deliver cargo molecules directly to the cytoplasm or nucleus and the mechanisms underlying most of the approaches have been extensively investigated. However, most of these techniques are bulk approaches that are cell-specific and have low throughput delivery. In comparison to bulk measurements, single-cell measurement technologies can provide a better understanding of the interactions among molecules, organelles, cells, and the microenvironment, which can aid in the development of therapeutics and diagnostic tools. To elucidate distinct responses during cell genetic modification, methods to achieve transfection at the single-cell level are of great interest. In recent years, single-cell technologies have become increasingly robust and accessible, although limitations exist. This review article aims to cover various microfluidic-based physical methods for single-cell intracellular delivery such as electroporation, mechanoporation, microinjection, sonoporation, optoporation, magnetoporation, and thermoporation and their analysis. The mechanisms of various physical methods, their applications, limitations, and prospects are also elaborated. Full article

(This article belongs to the Special Issue Micro/Nanofluidic Devices for Single Cell Analysis, Volume III)

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17 pages, 4068 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Recent Progress on Plant-Inspired Soft Robotics with Hydrogel Building Blocks: Fabrication, Actuation and Application

by Zhenyu Xu, Yongsen Zhou, Baoping Zhang, Chao Zhang, Jianfeng Wang and Zuankai Wang

Micromachines 2021, 12(6), 608; https://doi.org/10.3390/mi12060608 - 24 May 2021

Cited by 24 | Viewed by 5535

Abstract

Millions of years’ evolution has imparted life on earth with excellent environment adaptability. Of particular interest to scientists are some plants capable of macroscopically and reversibly altering their morphological and mechanical properties in response to external stimuli from the surrounding environment. These intriguing [...] Read more.

Millions of years’ evolution has imparted life on earth with excellent environment adaptability. Of particular interest to scientists are some plants capable of macroscopically and reversibly altering their morphological and mechanical properties in response to external stimuli from the surrounding environment. These intriguing natural phenomena and underlying actuation mechanisms have provided important design guidance and principles for man-made soft robotic systems. Constructing bio-inspired soft robotic systems with effective actuation requires the efficient supply of mechanical energy generated from external inputs, such as temperature, light, and electricity. By combining bio-inspired designs with stimuli-responsive materials, various intelligent soft robotic systems that demonstrate promising and exciting results have been developed. As one of the building materials for soft robotics, hydrogels are gaining increasing attention owing to their advantageous properties, such as ultra-tunable modulus, high compliance, varying stimuli-responsiveness, good biocompatibility, and high transparency. In this review article, we summarize the recent progress on plant-inspired soft robotics assembled by stimuli-responsive hydrogels with a particular focus on their actuation mechanisms, fabrication, and application. Meanwhile, some critical challenges and problems associated with current hydrogel-based soft robotics are briefly introduced, and possible solutions are proposed. We expect that this review would provide elementary tutorial guidelines to audiences who are interested in the study on nature-inspired soft robotics, especially hydrogel-based intelligent soft robotic systems. Full article

(This article belongs to the Special Issue Emerging Liquid Alloy Intelligence: From Fundamental to Application Exploration)

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9 pages, 1810 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Modular and Self-Contained Microfluidic Analytical Platforms Enabled by Magnetorheological Elastomer Microactuators

by Yuxin Zhang, Tim Cole, Guolin Yun, Yuxing Li, Qianbin Zhao, Hongda Lu, Jiahao Zheng, Weihua Li and Shi-Yang Tang

Micromachines 2021, 12(6), 604; https://doi.org/10.3390/mi12060604 - 23 May 2021

Cited by 10 | Viewed by 3445

Abstract

Portability and low-cost analytic ability are desirable for point-of-care (POC) diagnostics; however, current POC testing platforms often require time-consuming multiple microfabrication steps and rely on bulky and costly equipment. This hinders the capability of microfluidics to prove its power outside of laboratories and [...] Read more.

Portability and low-cost analytic ability are desirable for point-of-care (POC) diagnostics; however, current POC testing platforms often require time-consuming multiple microfabrication steps and rely on bulky and costly equipment. This hinders the capability of microfluidics to prove its power outside of laboratories and narrows the range of applications. This paper details a self-contained microfluidic device, which does not require any external connection or tubing to deliver insert-and-use image-based analysis. Without any microfabrication, magnetorheological elastomer (MRE) microactuators including pumps, mixers and valves are integrated into one modular microfluidic chip based on novel manipulation principles. By inserting the chip into the driving and controlling platform, the system demonstrates sample preparation and sequential pumping processes. Furthermore, due to the straightforward fabrication process, chips can be rapidly reconfigured at a low cost, which validates the robustness and versatility of an MRE-enabled microfluidic platform as an option for developing an integrated lab-on-a-chip system. Full article

(This article belongs to the Section D：Materials and Processing)

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20 pages, 5397 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Plasmon Induced Photocatalysts for Light-Driven Nanomotors

by Enrique Contreras, Christian Palacios, I. Brian Becerril-Castro and José M. Romo-Herrera

Micromachines 2021, 12(5), 577; https://doi.org/10.3390/mi12050577 - 19 May 2021

Cited by 9 | Viewed by 4193

Abstract

Micro/nanomachines (MNMs) correspond to human-made devices with motion in aqueous solutions. There are different routes for powering these devices. Light-driven MNMs are gaining increasing attention as fuel-free devices. On the other hand, Plasmonic nanoparticles (NPs) and their photocatalytic activity have shown great potential [...] Read more.

Micro/nanomachines (MNMs) correspond to human-made devices with motion in aqueous solutions. There are different routes for powering these devices. Light-driven MNMs are gaining increasing attention as fuel-free devices. On the other hand, Plasmonic nanoparticles (NPs) and their photocatalytic activity have shown great potential for photochemistry reactions. Here we review several photocatalyst nanosystems, with a special emphasis in Plasmon induced photocatalytic reactions, as a novel proposal to be explored by the MNMs community in order to extend the light-driven motion of MNMs harnessing the visible and near-infrared (NIR) light spectrum. Full article

(This article belongs to the Special Issue Nano/Micromotors for Energy Applications)

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10 pages, 2569 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Printing a Pacinian Corpuscle: Modeling and Performance

by Kieran Barrett-Snyder, Susan Lane, Nathan Lazarus, W. C. Kirkpatrick Alberts and Brendan Hanrahan

Micromachines 2021, 12(5), 574; https://doi.org/10.3390/mi12050574 - 18 May 2021

Cited by 2 | Viewed by 3722

Abstract

The Pacinian corpuscle is a highly sensitive mammalian sensor cell that exhibits a unique band-pass sensitivity to vibrations. The cell achieves this band-pass response through the use of 20 to 70 elastic layers entrapping layers of viscous fluid. This paper develops and explores [...] Read more.

The Pacinian corpuscle is a highly sensitive mammalian sensor cell that exhibits a unique band-pass sensitivity to vibrations. The cell achieves this band-pass response through the use of 20 to 70 elastic layers entrapping layers of viscous fluid. This paper develops and explores a scalable mechanical model of the Pacinian corpuscle and uses the model to predict the response of synthetic corpuscles, which could be the basis for future vibration sensors. The −3dB point of the biological cell is accurately mimicked using the geometries and materials available with off-the-shelf 3D printers. The artificial corpuscles here are constructed using uncured photoresist within structures printed in a commercial stereolithography (SLA) 3D printer, allowing the creation of trapped fluid layers analogous to the biological cell. Multi-layer artificial Pacinian corpuscles are vibration tested over the range of 20–3000 Hz and the response is in good agreement with the model. Full article

(This article belongs to the Special Issue Biomaterials and Biomanufacturing)

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17 pages, 35517 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Three-Dimensional Arterial Pulse Signal Acquisition in Time Domain Using Flexible Pressure-Sensor Dense Arrays

by Jianzhong Chen, Ke Sun, Rong Zheng, Yi Sun, Heng Yang, Yifei Zhong and Xinxin Li

Micromachines 2021, 12(5), 569; https://doi.org/10.3390/mi12050569 - 17 May 2021

Cited by 23 | Viewed by 7095

Abstract

In this study, we developed a radial artery pulse acquisition system based on finger-worn dense pressure sensor arrays to enable three-dimensional pulse signals acquisition. The finger-worn dense pressure-sensor arrays were fabricated by packaging 18 ultra-small MEMS pressure sensors (0.4 mm × 0.4 mm [...] Read more.

In this study, we developed a radial artery pulse acquisition system based on finger-worn dense pressure sensor arrays to enable three-dimensional pulse signals acquisition. The finger-worn dense pressure-sensor arrays were fabricated by packaging 18 ultra-small MEMS pressure sensors (0.4 mm × 0.4 mm × 0.2 mm each) with a pitch of 0.65 mm on flexible printed circuit boards. Pulse signals are measured and recorded simultaneously when traditional Chinese medicine practitioners wear the arrays on the fingers while palpating the radial pulse. Given that the pitches are much smaller than the diameter of the human radial artery, three-dimensional pulse envelope images can be measured with the system, as can the width and the dynamic width of the pulse signals. Furthermore, the array has an effective span of 11.6 mm—3–5 times the diameter of the radial artery—which enables easy and accurate positioning of the sensor array on the radial artery. This study also outlines proposed methods for measuring the pulse width and dynamic pulse width. The dynamic pulse widths of three volunteers were measured, and the dynamic pulse width measurements were consistent with those obtained by color Doppler ultrasound. The pulse wave velocity can also be measured with the system by measuring the pulse transit time between the pulse signals at the brachial and radial arteries using the finger-worn sensor arrays. Full article

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

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14 pages, 3873 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

A Novel Approach for a Chip-Sized Scanning Optical Microscope

by Joan Canals, Nil Franch, Victor Moro, Sergio Moreno, Juan Daniel Prades, Albert Romano-Rodríguez, Steffen Bornemann, Daria D. Bezshlyakh, Andreas Waag, Florian Vogelbacher, Stefan Schrittwieser, Katarzyna Kluczyk-Korch, Matthias Auf der Maur, Aldo Di Carlo and Angel Diéguez

Micromachines 2021, 12(5), 527; https://doi.org/10.3390/mi12050527 - 6 May 2021

Cited by 2 | Viewed by 3656

Abstract

The recent advances in chip-size microscopy based on optical scanning with spatially resolved nano-illumination light sources are presented. This new straightforward technique takes advantage of the currently achieved miniaturization of LEDs in fully addressable arrays. These nano-LEDs are used to scan the sample [...] Read more.

The recent advances in chip-size microscopy based on optical scanning with spatially resolved nano-illumination light sources are presented. This new straightforward technique takes advantage of the currently achieved miniaturization of LEDs in fully addressable arrays. These nano-LEDs are used to scan the sample with a resolution comparable to the LED sizes, giving rise to chip-sized scanning optical microscopes without mechanical parts or optical accessories. The operation principle and the potential of this new kind of microscope are analyzed through three different implementations of decreasing LED dimensions from 20 µm down to 200 nm. Full article

(This article belongs to the Special Issue nano FIS 2020—Integrated Functional nano Systems)

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28 pages, 66273 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Study of Mosquito Aerodynamics for Imitation as a Small Robot and Flight in a Low-Density Environment

by Balbir Singh, Noorfaizal Yidris, Adi Azriff Basri, Raghuvir Pai and Kamarul Arifin Ahmad

Micromachines 2021, 12(5), 511; https://doi.org/10.3390/mi12050511 - 2 May 2021

Cited by 9 | Viewed by 6513

Abstract

In terms of their flight and unusual aerodynamic characteristics, mosquitoes have become a new insect of interest. Despite transmitting the most significant infectious diseases globally, mosquitoes are still among the great flyers. Depending on their size, they typically beat at a high flapping [...] Read more.

In terms of their flight and unusual aerodynamic characteristics, mosquitoes have become a new insect of interest. Despite transmitting the most significant infectious diseases globally, mosquitoes are still among the great flyers. Depending on their size, they typically beat at a high flapping frequency in the range of 600 to 800 Hz. Flapping also lets them conceal their presence, flirt, and help them remain aloft. Their long, slender wings navigate between the most anterior and posterior wing positions through a stroke amplitude about 40 to 45°, way different from their natural counterparts (>120°). Most insects use leading-edge vortex for lift, but mosquitoes have additional aerodynamic characteristics: rotational drag, wake capture reinforcement of the trailing-edge vortex, and added mass effect. A comprehensive look at the use of these three mechanisms needs to be undertaken—the pros and cons of high-frequency, low-stroke angles, operating far beyond the normal kinematic boundary compared to other insects, and the impact on the design improvements of miniature drones and for flight in low-density atmospheres such as Mars. This paper systematically reviews these unique unsteady aerodynamic characteristics of mosquito flight, responding to the potential questions from some of these discoveries as per the existing literature. This paper also reviews state-of-the-art insect-inspired robots that are close in design to mosquitoes. The findings suggest that mosquito-based small robots can be an excellent choice for flight in a low-density environment such as Mars. Full article

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22 pages, 14527 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Single-Molecular Förster Resonance Energy Transfer Measurement on Structures and Interactions of Biomolecules

by Yi Qiao, Yuhan Luo, Naiyun Long, Yi Xing and Jing Tu

Micromachines 2021, 12(5), 492; https://doi.org/10.3390/mi12050492 - 27 Apr 2021

Cited by 21 | Viewed by 7153

Abstract

Single-molecule Förster resonance energy transfer (smFRET) inherits the strategy of measurement from the effective “spectroscopic ruler” FRET and can be utilized to observe molecular behaviors with relatively high throughput at nanometer scale. The simplicity in principle and configuration of smFRET make it easy [...] Read more.

Single-molecule Förster resonance energy transfer (smFRET) inherits the strategy of measurement from the effective “spectroscopic ruler” FRET and can be utilized to observe molecular behaviors with relatively high throughput at nanometer scale. The simplicity in principle and configuration of smFRET make it easy to apply and couple with other technologies to comprehensively understand single-molecule dynamics in various application scenarios. Despite its widespread application, smFRET is continuously developing and novel studies based on the advanced platforms have been done. Here, we summarize some representative examples of smFRET research of recent years to exhibit the versatility and note typical strategies to further improve the performance of smFRET measurement on different biomolecules. Full article

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

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10 pages, 4477 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Direct Writing of Cu Patterns on Polydimethylsiloxane Substrates Using Femtosecond Laser Pulse-Induced Reduction of Glyoxylic Acid Copper Complex

by Nam Phuong Ha, Tomoji Ohishi and Mizue Mizoshiri

Micromachines 2021, 12(5), 493; https://doi.org/10.3390/mi12050493 - 27 Apr 2021

Cited by 10 | Viewed by 3144

Abstract

We investigate the direct writing properties of copper (Cu) patterns on glass and polydimethylsiloxane (PDMS) substrates using femtosecond laser pulse-induced thermochemical reduction of glyoxylic acid copper (GACu) complex. The films of the GACu complex coated on the substrates were irradiated by focused femtosecond [...] Read more.

We investigate the direct writing properties of copper (Cu) patterns on glass and polydimethylsiloxane (PDMS) substrates using femtosecond laser pulse-induced thermochemical reduction of glyoxylic acid copper (GACu) complex. The films of the GACu complex coated on the substrates were irradiated by focused femtosecond laser pulses using a low numerical aperture of 0.45. Under the same conditions, such as laser scanning speed and pulse energy, the width of the line patterns fabricated on PDMS substrates was larger than that on glass substrates. X-ray diffraction peaks of the patterns on glass substrates corresponded to Cu without significant oxidation. By contrast, although Cu patterns were fabricated on PDMS substrates at a scanning speed of 10 mm/s and pulse energy of 0.49 nJ, Cu₂O was also generated under overheating conditions at a scanning speed of 1 mm/s and pulse energy of 0.37 nJ. All the patterns exhibited electrical conductivity. The minimum resistivity of the patterns on PDMS substrates is 1.4 × 10⁻⁵ Ωm, which is 10 times higher than that on glass substrates, indicating that microcracks formed by thermal shrinkage of the substrates during the laser irradiation increase the resistivity. This direct Cu writing technique on soft materials is useful for fabricating flexible microdevices. Full article

(This article belongs to the Special Issue Selected Papers from the 11th Symposium on Micro-Nano Science and Technology on Micromachines)

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18 pages, 2426 KiB

Open AccessFeature PaperEditor’s ChoicePerspective

Glioma-on-a-Chip Models

by Merve Ustun, Sajjad Rahmani Dabbagh, Irem Sultan Ilci, Tugba Bagci-Onder and Savas Tasoglu

Micromachines 2021, 12(5), 490; https://doi.org/10.3390/mi12050490 - 26 Apr 2021

Cited by 30 | Viewed by 6605

Abstract

Glioma, as an aggressive type of cancer, accounts for virtually 80% of malignant brain tumors. Despite advances in therapeutic approaches, the long-term survival of glioma patients is poor (it is usually fatal within 12–14 months). Glioma-on-chip platforms, with continuous perfusion, mimic in vivo [...] Read more.

Glioma, as an aggressive type of cancer, accounts for virtually 80% of malignant brain tumors. Despite advances in therapeutic approaches, the long-term survival of glioma patients is poor (it is usually fatal within 12–14 months). Glioma-on-chip platforms, with continuous perfusion, mimic in vivo metabolic functions of cancer cells for analytical purposes. This offers an unprecedented opportunity for understanding the underlying reasons that arise glioma, determining the most effective radiotherapy approach, testing different drug combinations, and screening conceivable side effects of drugs on other organs. Glioma-on-chip technologies can ultimately enhance the efficacy of treatments, promote the survival rate of patients, and pave a path for personalized medicine. In this perspective paper, we briefly review the latest developments of glioma-on-chip technologies, such as therapy applications, drug screening, and cell behavior studies, and discuss the current challenges as well as future research directions in this field. Full article

(This article belongs to the Special Issue Microfluidic Brain-on-a-Chip)

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28 pages, 5806 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Optical-Trapping Laser Techniques for Characterizing Airborne Aerosol Particles and Its Application in Chemical Aerosol Study

by Aimable Kalume, Chuji Wang and Yong-Le Pan

Micromachines 2021, 12(4), 466; https://doi.org/10.3390/mi12040466 - 20 Apr 2021

Cited by 13 | Viewed by 6015

Abstract

We present a broad assessment on the studies of optically-trapped single airborne aerosol particles, particularly chemical aerosol particles, using laser technologies. To date, extensive works have been conducted on ensembles of aerosols as well as on their analogous bulk samples, and a decent [...] Read more.

We present a broad assessment on the studies of optically-trapped single airborne aerosol particles, particularly chemical aerosol particles, using laser technologies. To date, extensive works have been conducted on ensembles of aerosols as well as on their analogous bulk samples, and a decent general description of airborne particles has been drawn and accepted. However, substantial discrepancies between observed and expected aerosols behavior have been reported. To fill this gap, single-particle investigation has proved to be a unique intersection leading to a clear representation of microproperties and size-dependent comportment affecting the overall aerosol behavior, under various environmental conditions. In order to achieve this objective, optical-trapping technologies allow holding and manipulating a single aerosol particle, while offering significant advantages such as contactless handling, free from sample collection and preparation, prevention of contamination, versatility to any type of aerosol, and flexibility to accommodation of various analytical systems. We review spectroscopic methods that are based on the light-particle interaction, including elastic light scattering, light absorption (cavity ring-down and photoacoustic spectroscopies), inelastic light scattering and emission (Raman, laser-induced breakdown, and laser-induced fluorescence spectroscopies), and digital holography. Laser technologies offer several benefits such as high speed, high selectivity, high accuracy, and the ability to perform in real-time, in situ. This review, in particular, discusses each method, highlights the advantages and limitations, early breakthroughs, and recent progresses that have contributed to a better understanding of single particles and particle ensembles in general. Full article

(This article belongs to the Special Issue Optical Trapping and Manipulation: From Fundamentals to Applications, Volume II)

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13 pages, 3118 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Switchable Transducers in GaN MEMS Resonators: Performance Comparison and Analysis

by Imtiaz Ahmed and Dana Weinstein

Micromachines 2021, 12(4), 461; https://doi.org/10.3390/mi12040461 - 19 Apr 2021

Cited by 3 | Viewed by 3658

Abstract

This work presents a comprehensive comparison of switchable electromechanical transducers in an AlN/GaN heterostructure toward the goal of reconfigurable RF building blocks in next-generation ad hoc radios. The transducers’ inherent switching was achieved by depleting a 2D electron gas (2DEG) channel, allowing an [...] Read more.

This work presents a comprehensive comparison of switchable electromechanical transducers in an AlN/GaN heterostructure toward the goal of reconfigurable RF building blocks in next-generation ad hoc radios. The transducers’ inherent switching was achieved by depleting a 2D electron gas (2DEG) channel, allowing an RF signal launched by interdigital transducers (IDTs) to effectively excite the symmetric (S_o) Lamb mode of vibration in the piezoelectric membrane. Different configurations for applying DC bias to the channel for electromechanical actuation in the piezoelectric are discussed. Complete suppression of the mechanical mode was achieved with the transducers in the OFF state. Equivalent circuit models were developed to extract parameters from measurements by fitting in both ON and OFF states. This is the first time that an extensive comparative study of the performance of different switchable transducers in their ON/OFF state is presented along with frequency scaling of the resonant mode. The switchable transducer with Ohmic IDTs and a Schottky control gate showed superior performance among the designs under consideration. Full article

(This article belongs to the Special Issue Nitrides and Carbides MEMS/NEMS)

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