Women’s Special Issue Series: Micromachines

A special issue of Micromachines (ISSN 2072-666X).

Deadline for manuscript submissions: closed (8 March 2022) | Viewed by 39169

Special Issue Editors

College of Science and Engineering, James Cook University, Townsville, QLD 4811, Australia
Interests: electrochemical sensors; electrocatalysis; carbon nanomaterials; liquid/liquid interfaces
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Chair Neuro-Nanoscale Engineering, Microsystems Section, Department of Mechanical Engineering, Institute of Complex Molecular Systems (ICMS), Eindhoven University of Technology, 5600 MB Eindhoven, The Netherlands
Interests: micro- and nanoscale assisted neuroscience and technology; micro- and nanofabrication; microfluidic applications; 3D brain-on-a-chip; organ-on-a-chip platforms; systems engineering
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Dipartimento di Scienze Agroalimentari, Ambientali e Animali (DI4A), Università degli Studi di Udine, Via Sondrio 2/A, 33100 Udine, Italy
Interests: DNA probes; aptamers; electrochemical biosensors; SPR; qPCR; pathogens; antimicrobial activities of nanoparticles; food microbiology
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Departamento de Química Analítica, Química Física e Ingeniería Química, Universidad de Alcalá, Alcalá de Henares, Spain
Interests: micromotors; lab-on-a-chip; nanotechnology; sensors; environmental chemistry
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Bavarian Polymer Institute, Friedrich-Alexander University Erlangen-Nürnberg (FAU), Dr.-Mack-Straße 77, 90762 Fürth, Germany
Interests: drug delivery; gene delivery; liposomes; nanoparticles; functional materials; molecular diffusion; mass and heat transport simulation; cell signalling; cell death
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Institute of Communication and Computer Systems (ICCS), National Technical University of Athens, Heroon Polytehneiou 9, 15780 Athens, Greece
Interests: laser-induced forward transfer; dual-laser bioprinting; laser materials microprocessing
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Special Issue Information

Dear Colleagues,

We are delighted to present this special collection of articles highlighting the achievements of women scientists in micro/nanoscale structures, materials, devices, and systems from all around the world. This Special Issue is devoted to presenting research performed by early- and advanced-career female scientists.

Micromachines is a peer-reviewed open access journal concerning all aspects of micro/nanoscale structures, materials, devices, and systems, as well as related micro- and nanotechnology, from fundamentals to applications. Its Impact Factor has increased continuously in recent years, reaching 2.891 in 2020. Its primary areas of research interests include, but are not limited to, the following:

  • Micro/nanoscale structures, devices, systems, and applications;
  • Micro- and nanotechnologies for biological, chemical, medical, environmental, and energy applications;
  • Micro- and nanoscale fabrication and manufacturing technologies;
  • Theories and analyses of multiphysics phenomena in micro/nanoscale;
  • Material developments for micro- and nanostructures.

Communications, original research papers, and review articles are welcome. Biographies or articles celebrating outstanding women researchers are also welcome.

Articles where the lead authors are women, or that are completely authored by women, are encouraged. We welcome submissions from all authors, irrespective of gender.

Dr. Yang Liu
Prof. Dr. Regina Luttge
Prof. Dr. Marisa Manzano
Prof. Dr. Beatriz Jurado Sánchez
Prof. Dr. Anna Vikulina
Prof. Dr. Ioanna Zergioti
Guest Editors

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Micromachines is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

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Published Papers (16 papers)

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Research

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16 pages, 3829 KiB  
Article
Low-Viscosity Polydimethylsiloxane Resin for Facile 3D Printing of Elastomeric Microfluidics
by Elyse Fleck, Charlise Keck, Karolina Ryszka, Emma DeNatale and Joseph Potkay
Micromachines 2023, 14(4), 773; https://doi.org/10.3390/mi14040773 - 30 Mar 2023
Cited by 1 | Viewed by 2176
Abstract
Microfluidics is a rapidly advancing technology with expansive applications but has been restricted by slow, laborious fabrication techniques for polydimethylsiloxane (PDMS)-based devices. Currently, 3D printing promises to address this challenge with high-resolution commercial systems but is limited by a lack of material advances [...] Read more.
Microfluidics is a rapidly advancing technology with expansive applications but has been restricted by slow, laborious fabrication techniques for polydimethylsiloxane (PDMS)-based devices. Currently, 3D printing promises to address this challenge with high-resolution commercial systems but is limited by a lack of material advances in generating high-fidelity parts with micron-scale features. To overcome this limitation, a low-viscosity, photopolymerizable PDMS resin was formulated with a methacrylate-PDMS copolymer, methacrylate-PDMS telechelic polymer, photoabsorber, Sudan I, photosensitizer, 2-isopropylthioxanthone, and a photoinitiator, 2,4,6-trimethyl benzoyl diphenylphosphine oxide. The performance of this resin was validated on a digital light processing (DLP) 3D printer, an Asiga MAX X27 UV. Resin resolution, part fidelity, mechanical properties, gas permeability, optical transparency, and biocompatibility were investigated. This resin produced resolved, unobstructed channels as small as 38.4 (±5.0) µm tall and membranes as thin as 30.9 (±0.5) µm. The printed material had an elongation at break of 58.6% ± 18.8%, Young’s modulus of 0.30 ± 0.04 MPa, and was highly permeable to O2 (596 Barrers) and CO2 (3071 Barrers). Following the ethanol extraction of the unreacted components, this material demonstrated optical clarity and transparency (>80% transmission) and viability as a substrate for in vitro tissue culture. This paper presents a high-resolution, PDMS 3D-printing resin for the facile fabrication of microfluidic and biomedical devices. Full article
(This article belongs to the Special Issue Women’s Special Issue Series: Micromachines)
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12 pages, 1667 KiB  
Article
A Scalable, Modular Degasser for Passive In-Line Removal of Bubbles from Biomicrofluidic Devices
by Hannah B. Musgrove, Amirus Saleheen, Jonathan M. Zatorski, Abhinav Arneja, Chance John Luckey and Rebecca R. Pompano
Micromachines 2023, 14(2), 435; https://doi.org/10.3390/mi14020435 - 11 Feb 2023
Viewed by 2371
Abstract
Bubbles are a common cause of microfluidic malfunction, as they can perturb the fluid flow within the micro-sized features of a device. Since gas bubbles form easily within warm cell culture reagents, degassing is often necessary for biomicrofluidic systems. However, fabrication of a [...] Read more.
Bubbles are a common cause of microfluidic malfunction, as they can perturb the fluid flow within the micro-sized features of a device. Since gas bubbles form easily within warm cell culture reagents, degassing is often necessary for biomicrofluidic systems. However, fabrication of a microscale degasser that can be used modularly with pre-existing chips may be cumbersome or challenging, especially for labs not equipped for traditional microfabrication, and current commercial options can be expensive. Here, we address the need for an affordable, accessible bubble trap that can be used in-line for continuous perfusion of organs-on-chip and other microfluidic cultures. We converted a previously described, manually fabricated PDMS degasser to allow scaled up, reproducible manufacturing by commercial machining or fused deposition modeling (FDM) 3D printing. After optimization, the machined and 3D printed degassers were found to be stable for >2 weeks under constant perfusion, without leaks. With a ~140 µL chamber volume, trapping capacity was extrapolated to allow for ~5–20 weeks of degassing depending on the rate of bubble formation. The degassers were biocompatible for use with cell culture, and they successfully prevented bubbles from reaching a downstream microfluidic device. Both degasser materials showed little to no leaching. The machined degasser did not absorb reagents, while the FDM printed degasser absorbed a small amount, and both maintained fluidic integrity from 1 µL/min to >1 mL/min of pressure-driven flow. Thus, these degassers can be fabricated in bulk and allow for long-term, efficient bubble removal in a simple microfluidic perfusion set-up. Full article
(This article belongs to the Special Issue Women’s Special Issue Series: Micromachines)
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12 pages, 2152 KiB  
Article
Production of Lipid Constructs by Design via Three-Dimensional Nanoprinting
by Yuqi Huang, Arpad Karsai, Pallavi D. Sambre, Wan-Chih Su, Roland Faller, Atul N. Parikh and Gang-yu Liu
Micromachines 2023, 14(2), 372; https://doi.org/10.3390/mi14020372 - 02 Feb 2023
Viewed by 1481
Abstract
Atomic force microscopy (AFM) in conjunction with microfluidic delivery was utilized to produce three-dimensional (3D) lipid structures following a custom design. While AFM is well-known for its spatial precision in imaging and 2D nanolithography, the development of AFM-based nanotechnology into 3D nanoprinting requires [...] Read more.
Atomic force microscopy (AFM) in conjunction with microfluidic delivery was utilized to produce three-dimensional (3D) lipid structures following a custom design. While AFM is well-known for its spatial precision in imaging and 2D nanolithography, the development of AFM-based nanotechnology into 3D nanoprinting requires overcoming the technical challenges of controlling material delivery and interlayer registry. This work demonstrates the concept of 3D nanoprinting of amphiphilic molecules such as 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC). Various formulations of POPC solutions were tested to achieve point, line, and layer-by-layer material delivery. The produced structures include nanometer-thick disks, long linear spherical caps, stacking grids, and organizational chiral architectures. The POPC molecules formed stacking bilayers in these constructions, as revealed by high-resolution structural characterizations. The 3D printing reached nanometer spatial precision over a range of 0.5 mm. The outcomes reveal the promising potential of our designed technology and methodology in the production of 3D structures from nanometer to continuum, opening opportunities in biomaterial sciences and engineering, such as in the production of 3D nanodevices, chiral nanosensors, and scaffolds for tissue engineering and regeneration. Full article
(This article belongs to the Special Issue Women’s Special Issue Series: Micromachines)
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18 pages, 2980 KiB  
Article
Production of Inhalable Ultra-Small Particles for Delivery of Anti-Inflammation Medicine via a Table-Top Microdevice
by Matthew J. Owen, Umit Celik, Subash K. Chaudhary, Jasper H. N. Yik, John S. Patton, Mei-chang Kuo, Dominik R. Haudenschild and Gang-yu Liu
Micromachines 2022, 13(9), 1382; https://doi.org/10.3390/mi13091382 - 25 Aug 2022
Viewed by 2191
Abstract
A table-top microdevice was introduced in this work to produce ultrasmall particles for drug delivery via inhalation. The design and operation are similar to that of spray-drying equipment used in industry, but the device itself is much smaller and more portable in size, [...] Read more.
A table-top microdevice was introduced in this work to produce ultrasmall particles for drug delivery via inhalation. The design and operation are similar to that of spray-drying equipment used in industry, but the device itself is much smaller and more portable in size, simpler to operate and more economical. More importantly, the device enables more accurate control over particle size. Using Flavopiridol, an anti-inflammation medication, formulations have been developed to produce inhalable particles for pulmonary delivery. A solution containing the desired components forms droplets by passing through an array of micro-apertures that vibrate via a piezo-electrical driver. High-purity nitrogen gas was introduced and flew through the designed path, which included the funnel collection and cyclone chamber, and finally was pumped away. The gas carried and dried the micronized liquid droplets along the pathway, leading to the precipitation of dry solid microparticles. The formation of the cyclone was essential to assure the sufficient travel path length of the liquid droplets to allow drying. Synthesis parameters were optimized to produce microparticles, whose morphology, size, physio-chemical properties, and release profiles met the criteria for inhalation. Bioactivity assays have revealed a high degree of anti-inflammation. The above-mentioned approach enabled the production of inhalable particles in research laboratories in general, using the simple table-top microdevice. The microparticles enable the inhalable delivery of anti-inflammation medicine to the lungs, thus providing treatment for diseases such as pulmonary fibrosis and COVID-19. Full article
(This article belongs to the Special Issue Women’s Special Issue Series: Micromachines)
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19 pages, 6924 KiB  
Article
Potentiometric pH Sensor Based on Flexible Screen-Printable Polyaniline Composite for Textile-Based Microfluidic Applications
by Yohan Laffitte and Bonnie L. Gray
Micromachines 2022, 13(9), 1376; https://doi.org/10.3390/mi13091376 - 23 Aug 2022
Cited by 4 | Viewed by 2080
Abstract
Skin pH can be used for monitoring infections in a healing wound, the onset of dermatitis, and hydration in sports medicine, but many challenges exist in integrating conventional sensing materials into wearable platforms. We present the development of a flexible, textile-based, screen-printed electrode [...] Read more.
Skin pH can be used for monitoring infections in a healing wound, the onset of dermatitis, and hydration in sports medicine, but many challenges exist in integrating conventional sensing materials into wearable platforms. We present the development of a flexible, textile-based, screen-printed electrode system for biosensing applications, and demonstrate flexible polyaniline (PANI) composite-based potentiometric sensors on a textile substrate for real-time pH measurement. The pH response of the optimized PANI/dodecylbenzene sulfonic acid/screen-printing ink composite is compared to electropolymerized and drop-cast PANI sensors via open circuit potential measurements. High sensitivity was observed for all sensors between pH 3–10, with a composite based on PANI emeraldine base, demonstrating sufficient response time and a linear sensitivity of −27.9 mV/pH. This exceeded prior flexible screen-printed pH sensors in which all parts of the sensor, including the pH sensing material, are screen-printed. Even better sensitivity was observed for a PANI emeraldine salt composite (−42.6 mV/pH), although the response was less linear. Furthermore, the sensor was integrated into a screen-printed microfluidic channel demonstrating sample isolation during measurement for wearable, micro cloth-based analytical devices. This is the first fully screen-printed flexible PANI composite pH sensor demonstrated on a textile substrate that can additionally be integrated with textile-based microfluidic channels. Full article
(This article belongs to the Special Issue Women’s Special Issue Series: Micromachines)
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16 pages, 2960 KiB  
Article
A Portable ‘Plug-and-Play’ Fibre Optic Sensor for In-Situ Measurements of pH Values for Microfluidic Applications
by Rahul Kumar, Hien Nguyen, Bruno Rente, Christabel Tan, Tong Sun and Kenneth T. V. Grattan
Micromachines 2022, 13(8), 1224; https://doi.org/10.3390/mi13081224 - 30 Jul 2022
Cited by 3 | Viewed by 1769
Abstract
Microfluidics is used in many applications ranging from chemistry, medicine, biology and biomedical research, and the ability to measure pH values in-situ is an important parameter for creating and monitoring environments within a microfluidic chip for many such applications. We present a portable, [...] Read more.
Microfluidics is used in many applications ranging from chemistry, medicine, biology and biomedical research, and the ability to measure pH values in-situ is an important parameter for creating and monitoring environments within a microfluidic chip for many such applications. We present a portable, optical fibre-based sensor for monitoring the pH based on the fluorescent intensity change of an acrylamidofluorescein dye, immobilized on the tip of a multimode optical fibre, and its performance is evaluated in-situ in a microfluidic channel. The sensor showed a sigmoid response over the pH range of 6.0–8.5, with a maximum sensitivity of 0.2/pH in the mid-range at pH 7.5. Following its evaluation, the sensor developed was used in a single microfluidic PDMS channel and its response was monitored for various flow rates within the channel. The results thus obtained showed that the sensor is sufficiently robust and well-suited to be used for measuring the pH value of the flowing liquid in the microchannel, allowing it to be used for a number of practical applications in ‘lab-on-a-chip’ applications where microfluidics are used. A key feature of the sensor is its simplicity and the ease of integrating the sensor with the microfluidic channel being probed. Full article
(This article belongs to the Special Issue Women’s Special Issue Series: Micromachines)
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8 pages, 2610 KiB  
Communication
Nanoscale Detonation Carbon Demonstrates Biosafety in Human Cell Culture
by Anastasia A. Malakhova, Denis K. Rybin, Alexandr A. Shtertser and Dina V. Dudina
Micromachines 2022, 13(8), 1187; https://doi.org/10.3390/mi13081187 - 27 Jul 2022
Cited by 1 | Viewed by 1209
Abstract
The production method of nanoscale detonation carbon (NDC) has recently been developed at Lavrentyev Institute of Hydrodynamics SB RAS. This method uses the reaction of acetylene with oxygen conducted in the detonation mode in fuel-rich acetylene–oxygen mixtures. The morphology and structural features of [...] Read more.
The production method of nanoscale detonation carbon (NDC) has recently been developed at Lavrentyev Institute of Hydrodynamics SB RAS. This method uses the reaction of acetylene with oxygen conducted in the detonation mode in fuel-rich acetylene–oxygen mixtures. The morphology and structural features of the NDC particles can be varied by changing the concentration of oxygen in the gaseous mixtures. The particles of NDC can serve as reinforcements in metal matrix composites and additives imparting electrical conductivity to polymer matrix composites. Before NDC can be considered for industrial applications, it is necessary to address the related biological safety concerns. The present work was aimed at determining the cytotoxicity of NDC. The NDC powders with two morphologies (obtained using different acetylene/oxygen ratios) were tested on HEK293A human cells. The NDC powder was added to the culture medium in concentrations ranging from 10 ng/mL to 400 μg/mL. The cell viability was determined by a colorimetric EZ4U test and a real-time cell analyzer xCELLigence. None of the NDC samples showed a cytotoxic effect. The results of this study allow us to recommend NDC as a safe and useful product for the development of advanced carbon-based and composite materials. Full article
(This article belongs to the Special Issue Women’s Special Issue Series: Micromachines)
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11 pages, 1834 KiB  
Article
Fabrication of a Cell-Friendly Poly(dimethylsiloxane) Culture Surface via Polydopamine Coating
by Da Hyun Yang, Sangyong Jung, Jae Young Kim and Nae Yoon Lee
Micromachines 2022, 13(7), 1122; https://doi.org/10.3390/mi13071122 - 15 Jul 2022
Cited by 2 | Viewed by 1662
Abstract
In this study, we fabricated a poly(dimethylsiloxane) (PDMS) surface coated with polydopamine (PDA) to enhance cell adhesion. PDA is well known for improving surface adhesion on various surfaces due to the abundant reactions enabled by the phenyl, amine, and catechol groups contained within [...] Read more.
In this study, we fabricated a poly(dimethylsiloxane) (PDMS) surface coated with polydopamine (PDA) to enhance cell adhesion. PDA is well known for improving surface adhesion on various surfaces due to the abundant reactions enabled by the phenyl, amine, and catechol groups contained within it. To confirm the successful surface coating with PDA, the water contact angle and X-ray photoelectron spectroscopy were analyzed. Human umbilical vein endothelial cells (HUVECs) and human-bone-marrow-derived mesenchymal stem cells (MSCs) were cultured on the PDA-coated PDMS surface to evaluate potential improvements in cell adhesion and proliferation. HUVECs were also cultured inside a cylindrical PDMS microchannel, which was constructed to mimic a human blood vessel, and their growth and performance were compared to those of cells grown inside a rectangular microchannel. This study provides a helpful perspective for building a platform that mimics in vivo environments in a more realistic manner. Full article
(This article belongs to the Special Issue Women’s Special Issue Series: Micromachines)
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16 pages, 4566 KiB  
Article
A Parametric Analysis of Capillary Height in Single-Layer, Small-Scale Microfluidic Artificial Lungs
by Lindsay J. Ma, Emmanuel A. Akor, Alex J. Thompson and Joseph A. Potkay
Micromachines 2022, 13(6), 822; https://doi.org/10.3390/mi13060822 - 25 May 2022
Cited by 2 | Viewed by 1898
Abstract
Microfluidic artificial lungs (μALs) are being investigated for their ability to closely mimic the size scale and cellular environment of natural lungs. Researchers have developed μALs with small artificial capillary diameters (10–50 µm; to increase gas exchange efficiency) and with large capillary diameters [...] Read more.
Microfluidic artificial lungs (μALs) are being investigated for their ability to closely mimic the size scale and cellular environment of natural lungs. Researchers have developed μALs with small artificial capillary diameters (10–50 µm; to increase gas exchange efficiency) and with large capillary diameters (~100 µm; to simplify design and construction). However, no study has directly investigated the impact of capillary height on μAL properties. Here, we use Murray’s law and the Hagen-Poiseuille equation to design single-layer, small-scale μALs with capillary heights between 10 and 100 µm. Each µAL contained two blood channel types: capillaries for gas exchange; and distribution channels for delivering blood to/from capillaries. Three designs with capillary heights of 30, 60, and 100 µm were chosen for further modeling, implementation and testing with blood. Flow simulations were used to validate and ensure equal pressures. Designs were fabricated using soft lithography. Gas exchange and pressure drop were tested using whole bovine blood. All three designs exhibited similar pressure drops and gas exchange; however, the μAL with 60 µm tall capillaries had a significantly higher wall shear rate (although physiologic), smaller priming volume and smaller total blood contacting surface area than the 30 and 100 µm designs. Future μAL designs may need to consider the impact of capillary height when optimizing performance. Full article
(This article belongs to the Special Issue Women’s Special Issue Series: Micromachines)
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14 pages, 46510 KiB  
Article
Wireless Photometry Prototype for Tri-Color Excitation and Multi-Region Recording
by Aatreya Chakravarti, Amin Hazrati Marangalou, Ian Matthew Costanzo, Devdip Sen, Mirco Sciulli, Yusuke Tsuno and Ulkuhan Guler
Micromachines 2022, 13(5), 727; https://doi.org/10.3390/mi13050727 - 30 Apr 2022
Cited by 5 | Viewed by 2124
Abstract
Visualizing neuronal activation and neurotransmitter release by using fluorescent sensors is increasingly popular. The main drawback of contemporary multi-color or multi-region fiber photometry systems is the tethered structure that prevents the free movement of the animals. Although wireless photometry devices exist, a review [...] Read more.
Visualizing neuronal activation and neurotransmitter release by using fluorescent sensors is increasingly popular. The main drawback of contemporary multi-color or multi-region fiber photometry systems is the tethered structure that prevents the free movement of the animals. Although wireless photometry devices exist, a review of literature has shown that these devices can only optically stimulate or excite with a single wavelength simultaneously, and the lifetime of the battery is short. To tackle this limitation, we present a prototype for implementing a fully wireless photometry system with multi-color and multi-region functions. This paper introduces an integrated circuit (IC) prototype fabricated in TSMC 180 nm CMOS process technology. The prototype includes 3-channel optical excitation, 2-channel optical recording, wireless power transfer, and wireless data telemetry blocks. The recording front end has an average gain of 107 dB and consumes 620 μW of power. The light-emitting diode (LED) driver block provides a peak current of 20 mA for optical excitation. The rectifier, the core of the wireless power transmission, operates with 63% power conversion efficiency at 13.56 MHz and a maximum of 87% at 2 MHz. The system is validated in a laboratory bench test environment and compared with state-of-the-art technologies. The optical excitation and recording front end and the wireless power transfer circuit evaluated in this paper will form the basis for a future miniaturized final device with a shank that can be used in in vivo experiments. Full article
(This article belongs to the Special Issue Women’s Special Issue Series: Micromachines)
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16 pages, 21058 KiB  
Article
Mixing Improvement in a T-Shaped Micro-Junction through Small Rectangular Cavities
by Matteo Antognoli, Sara Tomasi Masoni, Alessandro Mariotti, Roberto Mauri, Maria Vittoria Salvetti, Elisabetta Brunazzi and Chiara Galletti
Micromachines 2022, 13(2), 159; https://doi.org/10.3390/mi13020159 - 21 Jan 2022
Cited by 6 | Viewed by 2330
Abstract
The T-shaped micro-junction is among the most used geometry in microfluidic applications, and many design modifications of the channel walls have been proposed to enhance mixing. In this work, we investigate through numerical simulations the introduction of one pair of small rectangular cavities [...] Read more.
The T-shaped micro-junction is among the most used geometry in microfluidic applications, and many design modifications of the channel walls have been proposed to enhance mixing. In this work, we investigate through numerical simulations the introduction of one pair of small rectangular cavities in the lateral walls of the mixing channel just downstream of the confluence region. The aim is to preserve the simple geometry that has contributed to spread the practical use of the T-shaped micro-junction while suggesting a modification that should, in principle, work jointly with the vortical structures present in the mixing channel, further enhancing their efficiency in mixing without significant additional pressure drops. The performance is analyzed in the different flow regimes occurring by increasing the Reynolds number. The cavities are effective in the two highly-mixed flow regimes, viz., the steady engulfment and the periodic asymmetric regimes. This presence does not interfere with the formation of the vortical structures that promote mixing by convection in these two regimes, but it further enhances the mixing of the inlet streams in the near-wall region of the mixing channel without any additional cost, leading to better performance than the classical configuration. Full article
(This article belongs to the Special Issue Women’s Special Issue Series: Micromachines)
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15 pages, 3822 KiB  
Article
Structural Design and Optimization of a Resonant Micro-Accelerometer Based on Electrostatic Stiffness by an Improved Differential Evolution Algorithm
by Libin Huang, Qike Li, Yan Qin, Xukai Ding, Meimei Zhang and Liye Zhao
Micromachines 2022, 13(1), 38; https://doi.org/10.3390/mi13010038 - 28 Dec 2021
Cited by 5 | Viewed by 1430
Abstract
This study designed an in-plane resonant micro-accelerometer based on electrostatic stiffness. The accelerometer adopts a one-piece proof mass structure; two double-folded beam resonators are symmetrically distributed inside the proof mass, and only one displacement is introduced under the action of acceleration, which reduces [...] Read more.
This study designed an in-plane resonant micro-accelerometer based on electrostatic stiffness. The accelerometer adopts a one-piece proof mass structure; two double-folded beam resonators are symmetrically distributed inside the proof mass, and only one displacement is introduced under the action of acceleration, which reduces the influence of processing errors on the performance of the accelerometer. The two resonators form a differential structure that can diminish the impact of common-mode errors. This accelerometer realizes the separation of the introduction of electrostatic stiffness and the detection of resonant frequency, which is conducive to the decoupling of accelerometer signals. An improved differential evolution algorithm was developed to optimize the scale factor of the accelerometer. Through the final elimination principle, excellent individuals are preserved, and the most suitable parameters are allocated to the surviving individuals to stimulate the offspring to find the globally optimal ability. The algorithm not only maintains the global optimality but also reduces the computational complexity of the algorithm and deterministically realizes the optimization of the accelerometer scale factor. The electrostatic stiffness resonant micro-accelerometer was fabricated by deep dry silicon-on-glass (DDSOG) technology. The unloaded resonant frequency of the accelerometer resonant beam was between 24 and 26 kHz, and the scale factor of the packaged accelerometer was between 54 and 59 Hz/g. The average error between the optimization result and the actual scale factor was 7.03%. The experimental results verified the rationality of the structural design. Full article
(This article belongs to the Special Issue Women’s Special Issue Series: Micromachines)
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Review

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18 pages, 4748 KiB  
Review
Graphene-Based Polymer Composites for Flexible Electronic Applications
by Ana M. Díez-Pascual and Abbas Rahdar
Micromachines 2022, 13(7), 1123; https://doi.org/10.3390/mi13071123 - 16 Jul 2022
Cited by 20 | Viewed by 4373
Abstract
Graphene-based nanomaterials have gained a lot of interest over the last years in flexible electronics due to their exceptional electrical, mechanical, and optoelectronic properties, as well as their potential of surface modification. Their flexibility and processability make them suitable for electronic devices that [...] Read more.
Graphene-based nanomaterials have gained a lot of interest over the last years in flexible electronics due to their exceptional electrical, mechanical, and optoelectronic properties, as well as their potential of surface modification. Their flexibility and processability make them suitable for electronic devices that require bending, folding, and stretching, which cannot be fulfilled by conventional electronics. These nanomaterials can be assembled with various types of organic materials, including polymers, and biomolecules, to generate a variety of nanocomposites with greater stretchability and healability, higher stiffness, electrical conductivity, and exceptional thermal stability for flexible lighting and display technologies. This article summarizes the main characteristics and synthesis methods of graphene, its oxidized form graphene oxide (GO), and reduced GO derivative, as well as their corresponding polymeric composites, and provides a brief overview about some recent examples of these nanocomposites in flexible electronic applications, including electrodes for solar cells and supercapacitors, electronic textiles, and transistors. Full article
(This article belongs to the Special Issue Women’s Special Issue Series: Micromachines)
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21 pages, 3557 KiB  
Review
Progress on Optical Fiber Biochemical Sensors Based on Graphene
by Yani Zhang, Lei Zhou, Dun Qiao, Mengyin Liu, Hongyan Yang, Cheng Meng, Ting Miao, Jia Xue and Yiming Yao
Micromachines 2022, 13(3), 348; https://doi.org/10.3390/mi13030348 - 23 Feb 2022
Cited by 14 | Viewed by 3894
Abstract
Graphene, a novel form of the hexagonal honeycomb two-dimensional carbon-based structural material with a zero-band gap and ultra-high specific surface area, has unique optoelectronic capabilities, promising a suitable basis for its application in the field of optical fiber sensing. Graphene optical fiber sensing [...] Read more.
Graphene, a novel form of the hexagonal honeycomb two-dimensional carbon-based structural material with a zero-band gap and ultra-high specific surface area, has unique optoelectronic capabilities, promising a suitable basis for its application in the field of optical fiber sensing. Graphene optical fiber sensing has also been a hotspot in cross-research in biology, materials, medicine, and micro-nano devices in recent years, owing to prospective benefits, such as high sensitivity, small size, and strong anti-electromagnetic interference capability and so on. Here, the progress of optical fiber biochemical sensors based on graphene is reviewed. The fabrication of graphene materials and the sensing mechanism of the graphene-based optical fiber sensor are described. The typical research works of graphene-based optical fiber biochemical sensor, such as long-period fiber grating, Bragg fiber grating, no-core fiber and photonic crystal fiber are introduced, respectively. Finally, prospects for graphene-based optical fiber biochemical sensing technology will also be covered, which will provide an important reference for the development of graphene-based optical fiber biochemical sensors. Full article
(This article belongs to the Special Issue Women’s Special Issue Series: Micromachines)
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25 pages, 1001 KiB  
Review
Low Intensity Pulsed Ultrasound for Bone Tissue Engineering
by Colleen McCarthy and Gulden Camci-Unal
Micromachines 2021, 12(12), 1488; https://doi.org/10.3390/mi12121488 - 30 Nov 2021
Cited by 15 | Viewed by 4388
Abstract
As explained by Wolff’s law and the mechanostat hypothesis, mechanical stimulation can be used to promote bone formation. Low intensity pulsed ultrasound (LIPUS) is a source of mechanical stimulation that can activate the integrin/phosphatidylinositol 3-OH kinase/Akt pathway and upregulate osteogenic proteins through the [...] Read more.
As explained by Wolff’s law and the mechanostat hypothesis, mechanical stimulation can be used to promote bone formation. Low intensity pulsed ultrasound (LIPUS) is a source of mechanical stimulation that can activate the integrin/phosphatidylinositol 3-OH kinase/Akt pathway and upregulate osteogenic proteins through the production of cyclooxygenase-2 (COX-2) and prostaglandin E2 (PGE2). This paper analyzes the results of in vitro and in vivo studies that have evaluated the effects of LIPUS on cell behavior within three-dimensional (3D) titanium, ceramic, and hydrogel scaffolds. We focus specifically on cell morphology and attachment, cell proliferation and viability, osteogenic differentiation, mineralization, bone volume, and osseointegration. As shown by upregulated levels of alkaline phosphatase and osteocalcin, increased mineral deposition, improved cell ingrowth, greater scaffold pore occupancy by bone tissue, and superior vascularization, LIPUS generally has a positive effect and promotes bone formation within engineered scaffolds. Additionally, LIPUS can have synergistic effects by producing the piezoelectric effect and enhancing the benefits of 3D hydrogel encapsulation, growth factor delivery, and scaffold modification. Additional research should be conducted to optimize the ultrasound parameters and evaluate the effects of LIPUS with other types of scaffold materials and cell types. Full article
(This article belongs to the Special Issue Women’s Special Issue Series: Micromachines)
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10 pages, 1158 KiB  
Technical Note
Reconfigurable Electronic Platforms: A Top-Down Approach to Learn about Design and Integration of Electronic Systems
by Almudena Rivadeneyra, Francisco J. Romero, Michael Haider, Vijay D. Bhatt, Jose F. Salmeron, Noel Rodriguez, Diego P. Morales and Markus Becherer
Micromachines 2022, 13(3), 442; https://doi.org/10.3390/mi13030442 - 15 Mar 2022
Viewed by 2127
Abstract
This case report presents a real example of a study which introduces the use of reconfigurable platforms in the teaching of electronics engineering to establish a bridge between theory and practice. This gap is one of the major concerns of the electronics engineering [...] Read more.
This case report presents a real example of a study which introduces the use of reconfigurable platforms in the teaching of electronics engineering to establish a bridge between theory and practice. This gap is one of the major concerns of the electronics engineering students. Different strategies, such as simulation tools or breadboard implementations, have been followed so far to make it easier for students to practice what they study in lectures. However, many students still claim to have problems when they face real practical implementations. The use of reconfigurable platforms as a teaching tool is proposed to provide the students the possibility of fast experimentation, reducing both development time and the learning curve. In addition, reconfigurable platforms available on the market make this methodology suitable to be applied throughout the different courses of their curricula. The feasibility of this approach is demonstrated in a course at the M.Eng. level, where the objective is the study, design and development of electronic sensor nodes. We firmly consider, based on the students’ results and reflections collected during the course, that this methodology helps students to address the theoretical framework from a practical viewpoint, as well as to acquire some of the fundamental skills for their professional careers, such as the usage of communication protocols and embedded systems programming, in a more intuitive way when compared to traditional teaching methodologies. Full article
(This article belongs to the Special Issue Women’s Special Issue Series: Micromachines)
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