Micromachines

16 pages, 2929 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Optimisation of Design and Manufacturing Parameters of 3D Printed Solid Microneedles for Improved Strength, Sharpness, and Drug Delivery

by Sophia N. Economidou, Cristiane P. Pissinato Pere, Michael Okereke and Dennis Douroumis

Micromachines 2021, 12(2), 117; https://doi.org/10.3390/mi12020117 - 22 Jan 2021

Cited by 53 | Viewed by 5573

Abstract

3D printing has emerged as a powerful manufacturing technology and has attracted significant attention for the fabrication of microneedle (MN)-mediated transdermal systems. In this work, we describe an optimisation strategy for 3D-printed MNs, ranging from the design to the drug delivery stage. The [...] Read more.

3D printing has emerged as a powerful manufacturing technology and has attracted significant attention for the fabrication of microneedle (MN)-mediated transdermal systems. In this work, we describe an optimisation strategy for 3D-printed MNs, ranging from the design to the drug delivery stage. The key relationships between design and manufacturing parameters and quality and performance are systematically explored. The printing and post-printing set parameters were found to influence quality and material mechanical properties, respectively. It was demonstrated that the MN geometry affected piercing behaviour, fracture, and coating morphology. The delivery of insulin in porcine skin by inkjet-coated MNs was shown to be influenced by MN design. Full article

(This article belongs to the Special Issue Microneedles)

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13 pages, 4201 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Expanding 3D Nanoprinting Performance by Blurring the Electron Beam

by Lukas Matthias Seewald, Robert Winkler, Gerald Kothleitner and Harald Plank

Micromachines 2021, 12(2), 115; https://doi.org/10.3390/mi12020115 - 22 Jan 2021

Cited by 8 | Viewed by 2973

Abstract

Additive, direct-write manufacturing via a focused electron beam has evolved into a reliable 3D nanoprinting technology in recent years. Aside from low demands on substrate materials and surface morphologies, this technology allows the fabrication of freestanding, 3D architectures with feature sizes down to [...] Read more.

Additive, direct-write manufacturing via a focused electron beam has evolved into a reliable 3D nanoprinting technology in recent years. Aside from low demands on substrate materials and surface morphologies, this technology allows the fabrication of freestanding, 3D architectures with feature sizes down to the sub-20 nm range. While indispensably needed for some concepts (e.g., 3D nano-plasmonics), the final applications can also be limited due to low mechanical rigidity, and thermal- or electric conductivities. To optimize these properties, without changing the overall 3D architecture, a controlled method for tuning individual branch diameters is desirable. Following this motivation, here, we introduce on-purpose beam blurring for controlled upward scaling and study the behavior at different inclination angles. The study reveals a massive boost in growth efficiencies up to a factor of five and the strong delay of unwanted proximal growth. In doing so, this work expands the design flexibility of this technology. Full article

(This article belongs to the Special Issue Nanofabrication with Focused Electron/Ion Beam Induced Processing)

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8 pages, 6116 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

A Simple Route of Printing Explosive Crystalized Micro-Patterns by Using Direct Ink Writing

by Albertus Ivan Brilian, Veasna Soum, Sooyong Park, Soojin Lee, Jungwook Kim, Kuktae Kwon, Oh-Sun Kwon and Kwanwoo Shin

Micromachines 2021, 12(2), 105; https://doi.org/10.3390/mi12020105 - 21 Jan 2021

Cited by 5 | Viewed by 2998

Abstract

The production of energetic crystalized micro-patterns by using one-step printing has become a recent trend in energetic materials engineering. We report a direct ink writing (DIW) approach in which micro-scale energetic composites composed of 1,3,5-trinitro-1,3,5-triazinane (RDX) crystals in selected ink formulations of a [...] Read more.

The production of energetic crystalized micro-patterns by using one-step printing has become a recent trend in energetic materials engineering. We report a direct ink writing (DIW) approach in which micro-scale energetic composites composed of 1,3,5-trinitro-1,3,5-triazinane (RDX) crystals in selected ink formulations of a cellulose acetate butyrate (CAB) matrix are produced based on a direct phase transformation from organic, solvent-based, all-liquid ink. Using the formulated RDX ink and the DIW method, we printed crystalized RDX micro-patterns of various sizes and shapes on silicon wafers. The crystalized RDX micro-patterns contained single crystals on pristine Si wafers while the micro-patterns containing dendrite crystals were produced on UV-ozone (UVO)-treated Si wafers. The printing method and the formulated all-liquid ink make up a simple route for designing and printing energetic micro-patterns for micro-electromechanical systems. Full article

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

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19 pages, 16034 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

A Two-Scale Multi-Resolution Topologically Optimized Multi-Material Design of 3D Printed Craniofacial Bone Implants

by Jaejong Park, Tareq Zobaer and Alok Sutradhar

Micromachines 2021, 12(2), 101; https://doi.org/10.3390/mi12020101 - 20 Jan 2021

Cited by 14 | Viewed by 4421

Abstract

Bone replacement implants for craniofacial reconstruction require to provide an adequate structural foundation to withstand the physiological loading. With recent advances in 3D printing technology in place of bone grafts using autologous tissues, patient-specific additively manufactured implants are being established as suitable alternates. [...] Read more.

Bone replacement implants for craniofacial reconstruction require to provide an adequate structural foundation to withstand the physiological loading. With recent advances in 3D printing technology in place of bone grafts using autologous tissues, patient-specific additively manufactured implants are being established as suitable alternates. Since the stress distribution of these structures is complicated, efficient design techniques, such as topology optimization, can deliver optimized designs with enhanced functionality. In this work, a two-scale topology optimization approach is proposed that provides multi-material designs for both macrostructures and microstructures. In the first stage, a multi-resolution topology optimization approach is used to produce multi-material designs with maximum stiffness. Then, a microstructure with a desired property supplants the solid domain. This is beneficial for bone implant design since, in addition to imparting the desired functional property to the design, it also introduces porosity. To show the efficacy of the technique, four different large craniofacial defects due to maxillectomy are considered, and their respective implant designs with multi-materials are shown. These designs show good potential in developing patient-specific optimized designs suitable for additive manufacturing. Full article

(This article belongs to the Special Issue 3D Printed Implants for Biomedical Applications)

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18 pages, 3799 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Micropatterning of Substrates for the Culture of Cell Networks by Stencil-Assisted Additive Nanofabrication

by Anita Previdi, Claudio Piazzoni, Francesca Borghi, Carsten Schulte, Leandro Lorenzelli, Flavio Giacomozzi, Alessio Bucciarelli, Antonio Malgaroli, Jacopo Lamanna, Andrea Moro, Gabriella Racchetti, Alessandro Podestà, Cristina Lenardi and Paolo Milani

Micromachines 2021, 12(1), 94; https://doi.org/10.3390/mi12010094 - 18 Jan 2021

Cited by 3 | Viewed by 4092

Abstract

The fabrication of in vitro neuronal cell networks where cells are chemically or electrically connected to form functional circuits with useful properties is of great interest. Standard cell culture substrates provide ensembles of cells that scarcely reproduce physiological structures since their spatial organization [...] Read more.

The fabrication of in vitro neuronal cell networks where cells are chemically or electrically connected to form functional circuits with useful properties is of great interest. Standard cell culture substrates provide ensembles of cells that scarcely reproduce physiological structures since their spatial organization and connectivity cannot be controlled. Supersonic Cluster Beam Deposition (SCBD) has been used as an effective additive method for the large-scale fabrication of interfaces with extracellular matrix-mimicking surface nanotopography and reproducible morphological properties for cell culture. Due to the high collimation of SCBD, it is possible to exploit stencil masks for the fabrication of patterned films and reproduce features as small as tens of micrometers. Here, we present a protocol to fabricate micropatterned cell culture substrates based on the deposition of nanostructured cluster-assembled zirconia films by stencil-assisted SCBD. The effectiveness of this approach is demonstrated by the fabrication of micrometric patterns able to confine primary astrocytes. Calcium waves propagating in the astrocyte networks are shown. Full article

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16 pages, 8440 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

A Tunable-Gain Transimpedance Amplifier for CMOS-MEMS Resonators Characterization

by Rafel Perelló-Roig, Jaume Verd, Sebastià Bota and Jaume Segura

Micromachines 2021, 12(1), 82; https://doi.org/10.3390/mi12010082 - 15 Jan 2021

Cited by 10 | Viewed by 3087

Abstract

CMOS-MEMS resonators have become a promising solution thanks to their miniaturization and on-chip integration capabilities. However, using a CMOS technology to fabricate microelectromechanical system (MEMS) devices limits the electromechanical performance otherwise achieved by specific technologies, requiring a challenging readout circuitry. This paper presents [...] Read more.

CMOS-MEMS resonators have become a promising solution thanks to their miniaturization and on-chip integration capabilities. However, using a CMOS technology to fabricate microelectromechanical system (MEMS) devices limits the electromechanical performance otherwise achieved by specific technologies, requiring a challenging readout circuitry. This paper presents a transimpedance amplifier (TIA) fabricated using a commercial 0.35-µm CMOS technology specifically oriented to drive and sense monolithically integrated CMOS-MEMS resonators up to 50 MHz with a tunable transimpedance gain ranging from 112 dB to 121 dB. The output voltage noise is as low as 225 nV/Hz^1/2—input-referred current noise of 192 fA/Hz^1/2—at 10 MHz, and the power consumption is kept below 1-mW. In addition, the TIA amplifier exhibits an open-loop gain independent of the parasitic input capacitance—mostly associated with the MEMS layout—representing an advantage in MEMS testing compared to other alternatives such as Pierce oscillator schemes. The work presented includes the characterization of three types of MEMS resonators that have been fabricated and experimentally characterized both in open-loop and self-sustained configurations using the integrated TIA amplifier. The experimental characterization includes an accurate extraction of the electromechanical parameters for the three fabricated structures that enables an accurate MEMS-CMOS circuitry co-design. Full article

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

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36 pages, 3420 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Carbon Dots: An Emerging Smart Material for Analytical Applications

by Smita Das, Lightson Ngashangva and Pranab Goswami

Micromachines 2021, 12(1), 84; https://doi.org/10.3390/mi12010084 - 15 Jan 2021

Cited by 49 | Viewed by 8163

Abstract

Carbon dots (CDs) are optically active carbon-based nanomaterials. These nanomaterials can change their light emission properties in response to various external stimuli such as pH, temperature, pressure, and light. The CD’s remarkable stimuli-responsive smart material properties have recently stimulated massive research interest for [...] Read more.

Carbon dots (CDs) are optically active carbon-based nanomaterials. These nanomaterials can change their light emission properties in response to various external stimuli such as pH, temperature, pressure, and light. The CD’s remarkable stimuli-responsive smart material properties have recently stimulated massive research interest for their exploitation to develop various sensor platforms. Herein, an effort has been made to review the major advances made on CDs, focusing mainly on its smart material attributes and linked applications. Since the CD’s material properties are largely linked to their synthesis approaches, various synthesis methods, including surface passivation and functionalization of CDs and the mechanisms reported so far in their photophysical properties, are also delineated in this review. Finally, the challenges of using CDs and the scope for their further improvement as an optical signal transducer to expand their application horizon for developing analytical platforms have been discussed. Full article

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14 pages, 6162 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Design of a Kirigami Structure with a Large Uniform Deformation Region

by Hiroki Taniyama and Eiji Iwase

Micromachines 2021, 12(1), 76; https://doi.org/10.3390/mi12010076 - 12 Jan 2021

Cited by 8 | Viewed by 4605

Abstract

We designed a kirigami structure with a particular shape at both ends to provide a large uniform deformation region when stretched. When a kirigami structure is stretched, non-deformation regions, where the regions’ cuts do not open, and non-uniform deformation regions, where the regions’ [...] Read more.

We designed a kirigami structure with a particular shape at both ends to provide a large uniform deformation region when stretched. When a kirigami structure is stretched, non-deformation regions, where the regions’ cuts do not open, and non-uniform deformation regions, where the regions’ cuts are not uniformly deformed, are produced. The extent of the non-deformation and non-uniform deformation regions increases in proportion to the number of cut cycles in the width direction n_w this reduces the percentage of the uniform deformation region. We propose a method that increases the uniform deformation region in a kirigami structure by deforming the shape of the ends from a rectangle to a trapezoid when stretched. The proposed kirigami structure has separation lines at both ends that separate cuts in the width direction, and the position of contacts at both ends are moved to the center. The proposed kirigami structure has a large uniform deformation region, even when n_w is large, as evidenced by calculating the area of open cuts under stretching. The product of our study realizes a stretchable electro device with a large area, which maintains the position of evenly mounted functional elements when stretched. 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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15 pages, 4632 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Double-Deck Metal Solenoids 3D Integrated in Silicon Wafer for Kinetic Energy Harvester

by Nianying Wang, Ruofeng Han, Changnan Chen, Jiebin Gu and Xinxin Li

Micromachines 2021, 12(1), 74; https://doi.org/10.3390/mi12010074 - 12 Jan 2021

Cited by 5 | Viewed by 2972

Abstract

A silicon-chip based double-deck three-dimensional (3D) solenoidal electromagnetic (EM) kinetic energy harvester is developed to convert low-frequency (<100 Hz) vibrational energy into electricity with high efficiency. With wafer-level micro electro mechanical systems (MEMS) fabrication to form a metal casting mold and the following [...] Read more.

A silicon-chip based double-deck three-dimensional (3D) solenoidal electromagnetic (EM) kinetic energy harvester is developed to convert low-frequency (<100 Hz) vibrational energy into electricity with high efficiency. With wafer-level micro electro mechanical systems (MEMS) fabrication to form a metal casting mold and the following casting technique to rapidly (within minutes) fill molten ZnAl alloy into the pre-micromachined silicon mold, the 300-turn solenoid coils (150 turns for either inner solenoid or outer solenoid) are fabricated in silicon wafers for saw dicing into chips. A cylindrical permanent magnet is inserted into a pre-etched channel for sliding upon external vibration, which is surrounded by the solenoids. The size of the harvester chip is as small as 10.58 mm × 2.06 mm × 2.55 mm. The internal resistance of the solenoids is about 17.9 Ω. The maximum peak-to-peak voltage and average power output are measured as 120.4 mV and 43.7

μ W

. The EM energy harvester shows great improvement in power density, which is 786

μ W / {cm}^{3}

and the normalized power density is 98.3

μ W / {cm}^{3} / g

. The EM energy harvester is verified by experiment to be able to generate electricity through various human body movements of walking, running and jumping. The wafer-level fabricated chip-style solenoidal EM harvesters are advantageous in uniform performance, small size and volume applications. Full article

(This article belongs to the Section A：Physics)

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16 pages, 3790 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Capacitive Field-Effect Biosensor Studying Adsorption of Tobacco Mosaic Virus Particles

by Melanie Jablonski, Arshak Poghossian, Robin Severins, Michael Keusgen, Christina Wege and Michael J. Schöning

Micromachines 2021, 12(1), 57; https://doi.org/10.3390/mi12010057 - 6 Jan 2021

Cited by 20 | Viewed by 3704

Abstract

Plant virus-like particles, and in particular, tobacco mosaic virus (TMV) particles, are increasingly being used in nano- and biotechnology as well as for biochemical sensing purposes as nanoscaffolds for the high-density immobilization of receptor molecules. The sensitive parameters of TMV-assisted biosensors depend, among [...] Read more.

Plant virus-like particles, and in particular, tobacco mosaic virus (TMV) particles, are increasingly being used in nano- and biotechnology as well as for biochemical sensing purposes as nanoscaffolds for the high-density immobilization of receptor molecules. The sensitive parameters of TMV-assisted biosensors depend, among others, on the density of adsorbed TMV particles on the sensor surface, which is affected by both the adsorption conditions and surface properties of the sensor. In this work, Ta₂O₅-gate field-effect capacitive sensors have been applied for the label-free electrical detection of TMV adsorption. The impact of the TMV concentration on both the sensor signal and the density of TMV particles adsorbed onto the Ta₂O₅-gate surface has been studied systematically by means of field-effect and scanning electron microscopy methods. In addition, the surface density of TMV particles loaded under different incubation times has been investigated. Finally, the field-effect sensor also demonstrates the label-free detection of penicillinase immobilization as model bioreceptor on TMV particles. Full article

(This article belongs to the Special Issue FET and Field Effect-Based Sensors)

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10 pages, 3578 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Post-Moore Memory Technology: Sneak Path Current (SPC) Phenomena on RRAM Crossbar Array and Solutions

by Ying-Chen Chen, Chao-Cheng Lin and Yao-Feng Chang

Micromachines 2021, 12(1), 50; https://doi.org/10.3390/mi12010050 - 3 Jan 2021

Cited by 28 | Viewed by 5541

Abstract

The sneak path current (SPC) is the inevitable issue in crossbar memory array while implementing high-density storage configuration. The crosstalks are attracting much attention, and the read accuracy in the crossbar architecture is deteriorated by the SPC. In this work, the sneak path [...] Read more.

The sneak path current (SPC) is the inevitable issue in crossbar memory array while implementing high-density storage configuration. The crosstalks are attracting much attention, and the read accuracy in the crossbar architecture is deteriorated by the SPC. In this work, the sneak path current problem is observed and investigated by the electrical experimental measurements in the crossbar array structure with the half-read scheme. The read margin of the selected cell is improved by the bilayer stacked structure, and the sneak path current is reduced ~20% in the bilayer structure. The voltage-read stress-induced read margin degradation has also been investigated, and less voltage stress degradation is showed in bilayer structure due to the intrinsic nonlinearity. The oxide-based bilayer stacked resistive random access memory (RRAM) is presented to offer immunity toward sneak path currents in high-density memory integrations when implementing the future high-density storage and in-memory computing applications. Full article

(This article belongs to the Special Issue Progress of Emerging Hardware Development for Post-Moore’s Computing)

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22 pages, 4512 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Recent Advances in Single Crystal Diamond Device Fabrication for Photonics, Sensing and Nanomechanics

by Dipti Rani, Oliver Roman Opaluch and Elke Neu

Micromachines 2021, 12(1), 36; https://doi.org/10.3390/mi12010036 - 30 Dec 2020

Cited by 11 | Viewed by 5517

Abstract

In the last two decades, the use of diamond as a material for applications in nanophotonics, optomechanics, quantum information, and sensors tremendously increased due to its outstanding mechanical properties, wide optical transparency, and biocompatibility. This has been possible owing to advances in methods [...] Read more.

In the last two decades, the use of diamond as a material for applications in nanophotonics, optomechanics, quantum information, and sensors tremendously increased due to its outstanding mechanical properties, wide optical transparency, and biocompatibility. This has been possible owing to advances in methods for growth of high-quality single crystal diamond (SCD), nanofabrication methods and controlled incorporation of optically active point defects (e.g., nitrogen vacancy centers) in SCD. This paper reviews the recent advances in SCD nano-structuring methods for realization of micro- and nano-structures. Novel fabrication methods are discussed and the different nano-structures realized for a wide range of applications are summarized. Moreover, the methods for color center incorporation in SCD and surface treatment methods to enhance their properties are described. Challenges in the upscaling of SCD nano-structure fabrication, their commercial applications and future prospects are discussed. Full article

(This article belongs to the Special Issue Diamond: Materials, Devices and Applications)

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14 pages, 23914 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Cell Sorting Using Electrokinetic Deterministic Lateral Displacement

by Bao D. Ho, Jason P. Beech and Jonas O. Tegenfeldt

Micromachines 2021, 12(1), 30; https://doi.org/10.3390/mi12010030 - 30 Dec 2020

Cited by 18 | Viewed by 4014

Abstract

We show that by combining deterministic lateral displacement (DLD) with electrokinetics, it is possible to sort cells based on differences in their membrane and/or internal structures. Using heat to deactivate cells, which change their viability and structure, we then demonstrate sorting of a [...] Read more.

We show that by combining deterministic lateral displacement (DLD) with electrokinetics, it is possible to sort cells based on differences in their membrane and/or internal structures. Using heat to deactivate cells, which change their viability and structure, we then demonstrate sorting of a mixture of viable and non-viable cells for two different cell types. For Escherichia coli, the size change due to deactivation is insufficient to allow size-based DLD separation. Our method instead leverages the considerable change in zeta potential to achieve separation at low frequency. Conversely, for Saccharomyces cerevisiae (Baker’s yeast) the heat treatment does not result in any significant change of zeta potential. Instead, we perform the sorting at higher frequency and utilize what we believe is a change in dielectrophoretic mobility for the separation. We expect our work to form a basis for the development of simple, low-cost, continuous label-free methods that can separate cells and bioparticles based on their intrinsic properties. Full article

(This article belongs to the Special Issue Particles Separation in Microfluidic Devices, Volume II)

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11 pages, 13308 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Patterning Biological Gels for 3D Cell Culture inside Microfluidic Devices by Local Surface Modification through Laminar Flow Patterning

by Joshua Loessberg-Zahl, Jelle Beumer, Albert van den Berg, Jan C. T. Eijkel and Andries D. van der Meer

Micromachines 2020, 11(12), 1112; https://doi.org/10.3390/mi11121112 - 16 Dec 2020

Cited by 9 | Viewed by 5602

Abstract

Microfluidic devices are used extensively in the development of new in vitro cell culture models like organs-on-chips. A typical feature of such devices is the patterning of biological hydrogels to offer cultured cells and tissues a controlled three-dimensional microenvironment. A key challenge of [...] Read more.

Microfluidic devices are used extensively in the development of new in vitro cell culture models like organs-on-chips. A typical feature of such devices is the patterning of biological hydrogels to offer cultured cells and tissues a controlled three-dimensional microenvironment. A key challenge of hydrogel patterning is ensuring geometrical confinement of the gel, which is generally solved by inclusion of micropillars or phaseguides in the channels. Both of these methods often require costly cleanroom fabrication, which needs to be repeated even when only small changes need be made to the gel geometry, and inadvertently expose cultured cells to non-physiological and mechanically stiff structures. Here, we present a technique for facile patterning of hydrogel geometries in microfluidic chips, but without the need for any confining geometry built into the channel. Core to the technique is the use of laminar flow patterning to create a hydrophilic path through an otherwise hydrophobic microfluidic channel. When a liquid hydrogel is injected into the hydrophilic region, it is confined to this path by the surrounding hydrophobic regions. The various surface patterns that are enabled by laminar flow patterning can thereby be rendered into three-dimensional hydrogel structures. We demonstrate that the technique can be used in many different channel geometries while still giving the user control of key geometric parameters of the final hydrogel. Moreover, we show that human umbilical vein endothelial cells can be cultured for multiple days inside the devices with the patterned hydrogels and that they can be stimulated to migrate into the gel under the influence of trans-gel flows. Finally, we demonstrate that the patterned gels can withstand trans-gel flow velocities in excess of physiological interstitial flow velocities without rupturing or detaching. This novel hydrogel-patterning technique addresses fundamental challenges of existing methods for hydrogel patterning inside microfluidic chips, and can therefore be applied to improve design time and the physiological realism of microfluidic cell culture assays and organs-on-chips. Full article

(This article belongs to the Special Issue Microfluidics: Tissue Chips and Microphysiological Systems)

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11 pages, 4728 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Femtosecond Laser Direct Writing of Integrated Photonic Quantum Chips for Generating Path-Encoded Bell States

by Meng Li, Qian Zhang, Yang Chen, Xifeng Ren, Qihuang Gong and Yan Li

Micromachines 2020, 11(12), 1111; https://doi.org/10.3390/mi11121111 - 15 Dec 2020

Cited by 16 | Viewed by 3957

Abstract

Integrated photonic quantum chip provides a promising platform to perform quantum computation, quantum simulation, quantum metrology and quantum communication. Femtosecond laser direct writing (FLDW) is a potential technique to fabricate various integrated photonic quantum chips in glass. Several quantum logic gates fabricated by [...] Read more.

Integrated photonic quantum chip provides a promising platform to perform quantum computation, quantum simulation, quantum metrology and quantum communication. Femtosecond laser direct writing (FLDW) is a potential technique to fabricate various integrated photonic quantum chips in glass. Several quantum logic gates fabricated by FLDW have been reported, such as polarization and path encoded quantum controlled-NOT (CNOT) gates. By combining several single qubit gates and two qubit gates, the quantum circuit can realize different functions, such as generating quantum entangled states and performing quantum computation algorithms. Here we demonstrate the FLDW of integrated photonic quantum chips composed of one Hadamard gate and one CNOT gate for generating all four path-encoded Bell states. The experimental results show that the average fidelity of the reconstructed truth table reaches as high as 98.8

\pm

0.3%. Our work is of great importance to be widely applied in many quantum circuits, therefore this technique would offer great potential to fabricate more complex circuits to realize more advanced functions. Full article

(This article belongs to the Special Issue New Trends and Applications in Femtosecond Laser Micromachining)

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13 pages, 4443 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Machine Learning-Based Pipeline for High Accuracy Bioparticle Sizing

by Shaobo Luo, Yi Zhang, Kim Truc Nguyen, Shilun Feng, Yuzhi Shi, Yang Liu, Paul Hutchinson, Giovanni Chierchia, Hugues Talbot, Tarik Bourouina, Xudong Jiang and Ai Qun Liu

Micromachines 2020, 11(12), 1084; https://doi.org/10.3390/mi11121084 - 7 Dec 2020

Cited by 5 | Viewed by 3157

Abstract

High accuracy measurement of size is essential in physical and biomedical sciences. Various sizing techniques have been widely used in sorting colloidal materials, analyzing bioparticles and monitoring the qualities of food and atmosphere. Most imaging-free methods such as light scattering measure the averaged [...] Read more.

High accuracy measurement of size is essential in physical and biomedical sciences. Various sizing techniques have been widely used in sorting colloidal materials, analyzing bioparticles and monitoring the qualities of food and atmosphere. Most imaging-free methods such as light scattering measure the averaged size of particles and have difficulties in determining non-spherical particles. Imaging acquisition using camera is capable of observing individual nanoparticles in real time, but the accuracy is compromised by the image defocusing and instrumental calibration. In this work, a machine learning-based pipeline is developed to facilitate a high accuracy imaging-based particle sizing. The pipeline consists of an image segmentation module for cell identification and a machine learning model for accurate pixel-to-size conversion. The results manifest a significantly improved accuracy, showing great potential for a wide range of applications in environmental sensing, biomedical diagnostical, and material characterization. Full article

(This article belongs to the Special Issue Advanced Machine Learning Techniques for Sensing and Imaging Applications)

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19 pages, 5622 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Fabrication of a 3D Multi-Depth Reservoir Micromodel in Borosilicate Glass Using Femtosecond Laser Material Processing

by Ebenezer Owusu-Ansah and Colin Dalton

Micromachines 2020, 11(12), 1082; https://doi.org/10.3390/mi11121082 - 6 Dec 2020

Cited by 8 | Viewed by 3854

Abstract

Micromodels are ideal candidates for microfluidic transport investigations, and they have been used for many applications, including oil recovery and carbon dioxide storage. Conventional fabrication methods (e.g., photolithography and chemical etching) are beset with many issues, such as multiple wet processing steps and [...] Read more.

Micromodels are ideal candidates for microfluidic transport investigations, and they have been used for many applications, including oil recovery and carbon dioxide storage. Conventional fabrication methods (e.g., photolithography and chemical etching) are beset with many issues, such as multiple wet processing steps and isotropic etching profiles, making them unsuitable to fabricate complex, multi-depth features. Here, we report a simpler approach, femtosecond laser material processing (FLMP), to fabricate a 3D reservoir micromodel featuring 4 different depths—35, 70, 140, and 280 µm, over a large surface area (20 mm × 15 mm) in a borosilicate glass substrate. The dependence of etch depth on major processing parameters of FLMP, i.e., average laser fluence (

{LF}_{av}

), and computer numerically controlled (CNC) processing speed (

{PS}_{CNC}

), was studied. A linear etch depth dependence on

{LF}_{av}

was determined while a three-phase exponential decay dependence was obtained for

{PS}_{CNC}

. The accuracy of the method was investigated by using the etch depth dependence on

{PS}_{CNC}

relation as a model to predict input parameters required to machine the micromodel. This study shows the capability and robustness of FLMP to machine 3D multi-depth features that will be essential for the development, control, and fabrication of complex microfluidic geometries. Full article

(This article belongs to the Special Issue New Trends and Applications in Femtosecond Laser Micromachining)

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15 pages, 3878 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

A Lipid Bilayer Formed on a Hydrogel Bead for Single Ion Channel Recordings

by Minako Hirano, Daiki Yamamoto, Mami Asakura, Tohru Hayakawa, Shintaro Mise, Akinobu Matsumoto and Toru Ide

Micromachines 2020, 11(12), 1070; https://doi.org/10.3390/mi11121070 - 1 Dec 2020

Cited by 5 | Viewed by 3863

Abstract

Ion channel proteins play important roles in various cell functions, making them attractive drug targets. Artificial lipid bilayer recording is a technique used to measure the ion transport activities of channel proteins with high sensitivity and accuracy. However, the measurement efficiency is low. [...] Read more.

Ion channel proteins play important roles in various cell functions, making them attractive drug targets. Artificial lipid bilayer recording is a technique used to measure the ion transport activities of channel proteins with high sensitivity and accuracy. However, the measurement efficiency is low. In order to improve the efficiency, we developed a method that allows us to form bilayers on a hydrogel bead and record channel currents promptly. We tested our system by measuring the activities of various types of channels, including gramicidin, alamethicin, α-hemolysin, a voltage-dependent anion channel 1 (VDAC1), a voltage- and calcium-activated large conductance potassium channel (BK channel), and a potassium channel from Streptomyces lividans (KcsA channel). We confirmed the ability for enhanced measurement efficiency and measurement system miniaturizion. Full article

(This article belongs to the Special Issue Lipid Bilayers on Chip)

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25 pages, 3388 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Recent Advances in the Fabrication and Application of Graphene Microfluidic Sensors

by Shigang Wu, Xin Wang, Zongwen Li, Shijie Zhang and Fei Xing

Micromachines 2020, 11(12), 1059; https://doi.org/10.3390/mi11121059 - 30 Nov 2020

Cited by 27 | Viewed by 4782

Abstract

This review reports the progress of the recent development of graphene-based microfluidic sensors. The introduction of microfluidics technology provides an important possibility for the advance of graphene biosensor devices for a broad series of applications including clinical diagnosis, biological detection, health, and environment [...] Read more.

This review reports the progress of the recent development of graphene-based microfluidic sensors. The introduction of microfluidics technology provides an important possibility for the advance of graphene biosensor devices for a broad series of applications including clinical diagnosis, biological detection, health, and environment monitoring. Compared with traditional (optical, electrochemical, and biological) sensing systems, the combination of graphene and microfluidics produces many advantages, such as achieving miniaturization, decreasing the response time and consumption of chemicals, improving the reproducibility and sensitivity of devices. This article reviews the latest research progress of graphene microfluidic sensors in the fields of electrochemistry, optics, and biology. Here, the latest development trends of graphene-based microfluidic sensors as a new generation of detection tools in material preparation, device assembly, and chip materials are summarized. Special emphasis is placed on the working principles and applications of graphene-based microfluidic biosensors, especially in the detection of nucleic acid molecules, protein molecules, and bacterial cells. This article also discusses the challenges and prospects of graphene microfluidic biosensors. Full article

(This article belongs to the Special Issue Microfluidic Machines)

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13 pages, 5620 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

PLGA Nanofiber/PDMS Microporous Composite Membrane-Sandwiched Microchip for Drug Testing

by Wei Li, Xindi Sun, Bing Ji, Xingyuan Yang, Bingpu Zhou, Zhanjun Lu and Xinghua Gao

Micromachines 2020, 11(12), 1054; https://doi.org/10.3390/mi11121054 - 28 Nov 2020

Cited by 13 | Viewed by 3789

Abstract

Lung-on-a-chip devices could provide new strategies for a biomimetic lung cell microenvironment and construction of lung disease models in vitro, and are expected to greatly promote the development of drug evaluation, toxicological detection, and disease model building. In this study, we developed a [...] Read more.

Lung-on-a-chip devices could provide new strategies for a biomimetic lung cell microenvironment and construction of lung disease models in vitro, and are expected to greatly promote the development of drug evaluation, toxicological detection, and disease model building. In this study, we developed a novel poly (lactic-co-glycolic acid) (PLGA) nanofiber/polydimethylsiloxane (PDMS) microporous composite membrane-sandwiched lung-on-a-chip to perform anti-tumor drug testing. The composite membrane was characterized, and the results showed that it was permeable to molecules and thus could be used to study small-molecule drug diffusion. In addition, the microchip could apply perfusion fluids to simulate blood flow under extremely low fluid shear stress, and could also simulate the spherical-like shape of the alveoli by deformation of the composite membrane. Using this chip, we evaluated the anti-tumor drug efficacy of gefitinib in two kinds of non-small cell lung cancer cells, the lung adenocarcinoma NCI-H1650 cell line and the large cell lung cancer NCI-H460 cell line. We further probed the resistance of NCI-H460 cells to gefitinib under normoxic and hypoxic conditions. The established composite membrane-sandwiched lung chip can simulate more biochemical and biophysical factors in the lung physiological and pathological microenvironment, and it has important applications in the personalized treatment of lung tumors. It is expected to play a potential role in clinical diagnosis and drug screening. Full article

(This article belongs to the Special Issue Microfluidics and Bioprinting Technologies for 3D Vascularized Tissue)

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24 pages, 5861 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Recent Advances in Microswimmers for Biomedical Applications

by Ada-Ioana Bunea and Rafael Taboryski

Micromachines 2020, 11(12), 1048; https://doi.org/10.3390/mi11121048 - 27 Nov 2020

Cited by 54 | Viewed by 7492

Abstract

Microswimmers are a rapidly developing research area attracting enormous attention because of their many potential applications with high societal value. A particularly promising target for cleverly engineered microswimmers is the field of biomedical applications, where many interesting examples have already been reported for [...] Read more.

Microswimmers are a rapidly developing research area attracting enormous attention because of their many potential applications with high societal value. A particularly promising target for cleverly engineered microswimmers is the field of biomedical applications, where many interesting examples have already been reported for e.g., cargo transport and drug delivery, artificial insemination, sensing, indirect manipulation of cells and other microscopic objects, imaging, and microsurgery. Pioneered only two decades ago, research studies on the use of microswimmers in biomedical applications are currently progressing at an incredibly fast pace. Given the recent nature of the research, there are currently no clinically approved microswimmer uses, and it is likely that several years will yet pass before any clinical uses can become a reality. Nevertheless, current research is laying the foundation for clinical translation, as more and more studies explore various strategies for developing biocompatible and biodegradable microswimmers fueled by in vivo-friendly means. The aim of this review is to provide a summary of the reported biomedical applications of microswimmers, with focus on the most recent advances. Finally, the main considerations and challenges for clinical translation and commercialization are discussed. Full article

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

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13 pages, 2638 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Microfluidic Device for the Analysis of Angiogenic Sprouting under Bidirectional Biochemical Gradients

by Keigo Nishimura, Minghao Nie, Shigenori Miura and Shoji Takeuchi

Micromachines 2020, 11(12), 1049; https://doi.org/10.3390/mi11121049 - 27 Nov 2020

Cited by 5 | Viewed by 3431

Abstract

In this paper, we developed a spheroid culture device that can trap a spheroid in the trapping site sandwiched by two extracellular matrix gels located at the upper and lower side of the spheroid. This device can form different biochemical gradients by applying [...] Read more.

In this paper, we developed a spheroid culture device that can trap a spheroid in the trapping site sandwiched by two extracellular matrix gels located at the upper and lower side of the spheroid. This device can form different biochemical gradients by applying target biochemicals separately in upper and lower channels, allowing us to study the angiogenic sprouting under various biochemical gradients in different directions. In the experiments, we confirmed the trapping of the spheroids and demonstrate the investigation on the direction and extent of angiogenic sprouts under unidirectional or bidirectional biochemical gradients. We believe our device can contribute to understanding the pathophysiological phenomena driven by chemical gradients, such as tissue development and tumor angiogenesis. Full article

(This article belongs to the Special Issue Microfluidic Machines, Volume II)

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12 pages, 3312 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Joule Heating Effects on Transport-Induced-Charge Phenomena in an Ultrathin Nanopore

by Zhixuan Wang, Wei-Lun Hsu, Shuntaro Tsuchiya, Soumyadeep Paul, Amer Alizadeh and Hirofumi Daiguji

Micromachines 2020, 11(12), 1041; https://doi.org/10.3390/mi11121041 - 26 Nov 2020

Cited by 10 | Viewed by 3646

Abstract

Transport-induced-charge (TIC) phenomena, in which the concentration imbalance between cations and anions occurs when more than two chemical potential gradients coexist within an ultrathin dimension, entail numerous nanofluidic systems. Evidence has indicated that the presence of TIC produces a nonlinear response of electroosmotic [...] Read more.

Transport-induced-charge (TIC) phenomena, in which the concentration imbalance between cations and anions occurs when more than two chemical potential gradients coexist within an ultrathin dimension, entail numerous nanofluidic systems. Evidence has indicated that the presence of TIC produces a nonlinear response of electroosmotic flow to the applied voltage, resulting in complex fluid behavior. In this study, we theoretically investigate thermal effects due to Joule heating on TIC phenomena in an ultrathin nanopore by computational fluid dynamics simulation. Our modeling results show that the rise of local temperature inside the nanopore significantly enhances TIC effects and thus has a significant influence on electroosmotic behavior. A local maximum of the solution conductivity occurs near the entrance of the nanopore at the high salt concentration end, resulting in a reversal of TIC across the nanopore. The Joule heating effects increase the reversal of TIC with the synergy of the negatively charged nanopore, and they also enhance the electroosmotic flow regardless of whether the nanopore is charged. These theoretical observations will improve our knowledge of nonclassical electrokinetic phenomena for flow control in nanopore systems. Full article

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

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9 pages, 8397 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Five-Dimensional Optical Data Storage Based on Ellipse Orientation and Fluorescence Intensity in a Silver-Sensitized Commercial Glass

by Chang-Hyun Park, Yannick Petit, Lionel Canioni and Seung-Han Park

Micromachines 2020, 11(12), 1026; https://doi.org/10.3390/mi11121026 - 24 Nov 2020

Cited by 4 | Viewed by 3130

Abstract

Five-dimensional (5D) recording and decoding is demonstrated by using femtosecond direct laser writing in a silver-containing commercial glass. In particular, laser intensities and ellipse orientations generated by anamorphic focusing are employed to produce 5D data storage unit (3D for XYZ, 1D for the [...] Read more.

Five-dimensional (5D) recording and decoding is demonstrated by using femtosecond direct laser writing in a silver-containing commercial glass. In particular, laser intensities and ellipse orientations generated by anamorphic focusing are employed to produce 5D data storage unit (3D for XYZ, 1D for the orientation of the elliptically-shaped data storage unit and 1D for its fluorescence intensity). In the recording process, two different images of a 4-bit bitmap format were simultaneously embedded in the medium by multiplexing the elliptical orientation of the laser focus and its intensity so as to access oriented elliptical patterns with independent fluorescence intensity. In the decoding process, two merged original images were successfully reconstructed by comparing each data storage unit with a fabricated calibration matrix of 16 × 16 levels for elliptic orientations and fluorescence intensities. We believe this technique can be applied to semi-permanent high-density data storage device. Full article

(This article belongs to the Special Issue Advanced Techniques for Ultrafast Laser Nano/Micro Patterning)

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22 pages, 5423 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Charge-Based Separation of Micro- and Nanoparticles

by Bao D. Ho, Jason P. Beech and Jonas O. Tegenfeldt

Micromachines 2020, 11(11), 1014; https://doi.org/10.3390/mi11111014 - 18 Nov 2020

Cited by 16 | Viewed by 5075

Abstract

Deterministic Lateral Displacement (DLD) is a label-free particle sorting method that separates by size continuously and with high resolution. By combining DLD with electric fields (eDLD), we show separation of a variety of nano and micro-sized particles primarily by their zeta potential. Zeta [...] Read more.

Deterministic Lateral Displacement (DLD) is a label-free particle sorting method that separates by size continuously and with high resolution. By combining DLD with electric fields (eDLD), we show separation of a variety of nano and micro-sized particles primarily by their zeta potential. Zeta potential is an indicator of electrokinetic charge—the charge corresponding to the electric field at the shear plane—an important property of micro- and nanoparticles in colloidal or separation science. We also demonstrate proof of principle of separation of nanoscale liposomes of different lipid compositions, with strong relevance for biomedicine. We perform careful characterization of relevant experimental conditions necessary to obtain adequate sorting of different particle types. By choosing a combination of frequency and amplitude, sorting can be made sensitive to the particle subgroup of interest. The enhanced displacement effect due to electrokinetics is found to be significant at low frequency and for particles with high zeta potential. The effect appears to scale with the square of the voltage, suggesting that it is associated with either non-linear electrokinetics or dielectrophoresis (DEP). However, since we observe large changes in separation behavior over the frequency range at which DEP forces are expected to remain constant, DEP can be ruled out. Full article

(This article belongs to the Special Issue Particles Separation in Microfluidic Devices, Volume II)

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15 pages, 1603 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

On-Chip Multiple Particle Velocity and Size Measurement Using Single-Shot Two-Wavelength Differential Image Analysis

by Shuya Sawa, Mitsuru Sentoku and Kenji Yasuda

Micromachines 2020, 11(11), 1011; https://doi.org/10.3390/mi11111011 - 17 Nov 2020

Cited by 1 | Viewed by 2587

Abstract

Precise and quick measurement of samples’ flow velocities is essential for cell sorting timing control and reconstruction of acquired image-analyzed data. We developed a simple technique for the single-shot measurement of flow velocities of particles simultaneously in a microfluidic pathway. The speed was [...] Read more.

Precise and quick measurement of samples’ flow velocities is essential for cell sorting timing control and reconstruction of acquired image-analyzed data. We developed a simple technique for the single-shot measurement of flow velocities of particles simultaneously in a microfluidic pathway. The speed was calculated from the difference in the particles’ elongation in an acquired image that appeared when two wavelengths of light with different irradiation times were applied. We ran microparticles through an imaging flow cytometer and irradiated two wavelengths of light with different irradiation times simultaneously to those particles. The mixture of the two wavelength transmitted lights was divided into two wavelengths, and the images of the same microparticles for each wavelength were acquired in a single shot. We estimated the velocity from the difference of its elongation divided by the difference of irradiation time by comparing these two images. The distribution of polystyrene beads’ velocity was parabolic and highest at the center of the flow channel, consistent with the expected velocity distribution of the laminar flow. Applying the calculated velocity, we also restored the accurate shapes and cross-sectional areas of particles in the images, indicating this simple method for improving of imaging flow cytometry and cell sorter for diagnostic screening of circulating tumor cells. Full article

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

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14 pages, 5827 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Fundamental Study of Decellularization Method Using Cyclic Application of High Hydrostatic Pressure

by Daiki Zemmyo, Masashi Yamamoto and Shogo Miyata

Micromachines 2020, 11(11), 1008; https://doi.org/10.3390/mi11111008 - 15 Nov 2020

Cited by 8 | Viewed by 3458

Abstract

Decellularized tissues are promising materials that mainly consist of extracellular matrices (ECMs) obtained by removing all cells from organs and tissues. High hydrostatic pressure (HHP) has been used for decellularization to remove cells physically from organs or tissues rather than by chemical methods. [...] Read more.

Decellularized tissues are promising materials that mainly consist of extracellular matrices (ECMs) obtained by removing all cells from organs and tissues. High hydrostatic pressure (HHP) has been used for decellularization to remove cells physically from organs or tissues rather than by chemical methods. However, ultrahigh pressure induces denaturation of the ECM structure. In this study, we examined the effects of cyclic HHP at low and high pressures on the cell membrane structure to establish a novel decellularization method that enables decellularization without the denaturation of the ECM. A decellularization device using cyclic HHP (maximum pressure: 250 MPa, cycle number: 5) was developed. NB1RGB cell suspension was injected into a plastic bag to be subjected to cyclic HHP. After applying cyclic HHP, the amount of DNA inside the cells and the morphological changes of the cells were evaluated. As a result, the amount of DNA inside the cells decreased after the cyclic HHP compared to the static HHP. In addition, cyclic HHP was suggested to promote the destruction of the cell and nuclear membrane. In conclusion, it was revealed that the cell structure could be denatured and destroyed by cyclic HHP at a lower level than that of previous approaches. Full article

(This article belongs to the Section B：Biology and Biomedicine)

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35 pages, 5349 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Applications of CMOS Devices for the Diagnosis and Control of Infectious Diseases

by Saghi Forouhi and Ebrahim Ghafar-Zadeh

Micromachines 2020, 11(11), 1003; https://doi.org/10.3390/mi11111003 - 13 Nov 2020

Cited by 11 | Viewed by 5074

Abstract

Emerging infectious diseases such as coronavirus disease of 2019 (COVID-19), Ebola, influenza A, severe acute respiratory syndrome (SARS) and Middle East respiratory syndrome (MERS) in recent years have threatened the health and security of the global community as one of the greatest factors [...] Read more.

Emerging infectious diseases such as coronavirus disease of 2019 (COVID-19), Ebola, influenza A, severe acute respiratory syndrome (SARS) and Middle East respiratory syndrome (MERS) in recent years have threatened the health and security of the global community as one of the greatest factors of mortality in the world. Accurate and immediate diagnosis of infectious agents and symptoms is a key to control the outbreak of these diseases. Rapid advances in complementary metal-oxide-semiconductor (CMOS) technology offers great advantages like high accuracy, high throughput and rapid measurements in biomedical research and disease diagnosis. These features as well as low cost, low power and scalability of CMOS technology can pave the way for the development of powerful devices such as point-of-care (PoC) systems, lab-on-chip (LoC) platforms and symptom screening devices for accurate and timely diagnosis of infectious diseases. This paper is an overview of different CMOS-based devices such as optical, electrochemical, magnetic and mechanical sensors developed by researchers to mitigate the problems associated with these diseases. Full article

(This article belongs to the Special Issue Biologically Inspired Sensor and Actuator (BioSA) Platforms)

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10 pages, 2154 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Active Surface with Dynamic Microstructures and Hierarchical Gradient Enabled by in situ Pneumatic Control

by Jian-Nan Wang, Benfeng Bai, Qi-Dai Chen and Hong-Bo Sun

Micromachines 2020, 11(11), 992; https://doi.org/10.3390/mi11110992 - 4 Nov 2020

Cited by 2 | Viewed by 2440

Abstract

An active surface with an on-demand tunable topography holds great potential for various applications, such as reconfigurable metasurfaces, adaptive microlenses, soft robots and four-dimensional (4D) printing. Despite extensive progress, to achieve refined control of microscale surface structures with large-amplitude deformation remains a challenge. [...] Read more.

An active surface with an on-demand tunable topography holds great potential for various applications, such as reconfigurable metasurfaces, adaptive microlenses, soft robots and four-dimensional (4D) printing. Despite extensive progress, to achieve refined control of microscale surface structures with large-amplitude deformation remains a challenge. Moreover, driven by the demand of constructing a large area of microstructures with increased complexity—for instance, biomimetic functional textures bearing a three-dimensional (3D) gradient—novel strategies are highly desired. Here, we develop an active surface with a dynamic topography and three-tier height gradient via a strain-tunable mismatching-bonding process. Pneumatic actuation allows for rapid, reversible and uniform regulation of surface microstructures at the centimeter scale. The in-situ modulation facilitates large-amplitude deformation with a maximum tuning range of 185 μm. Moreover, the structural gradient can be modulated by programming the strain value of the bonding process. With our strategy, another two types of surfaces with a four-tier gradient and without gradient were also prepared. By providing active modulation and design flexibility of complicated microstructures, the proposed strategy would unlock more opportunities for a wealth of novel utilizations. Full article

(This article belongs to the Special Issue Additive Nano-Manufacturing)

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8 pages, 2928 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

DNA Ring Motif with Flexible Joints

by Shiyun Liu, Satoshi Murata and Ibuki Kawamata

Micromachines 2020, 11(11), 987; https://doi.org/10.3390/mi11110987 - 31 Oct 2020

Cited by 5 | Viewed by 4018

Abstract

The invention of DNA origami has expanded the geometric complexity and functionality of DNA nanostructures. Using DNA origami technology, we develop a flexible multi-joint ring motif as a novel self-assembling module. The motif can connect with each other through self-complementary sequences on its [...] Read more.

The invention of DNA origami has expanded the geometric complexity and functionality of DNA nanostructures. Using DNA origami technology, we develop a flexible multi-joint ring motif as a novel self-assembling module. The motif can connect with each other through self-complementary sequences on its segments. The flexible joints can be fixed in a straightened position as desired, thereby allowing the motif to take various shapes. We can adjust the number of flexible joints and the number of connectable segments, thereby enabling programmable self-assembly of the motif. We successfully produced the motif and evaluated several self-assembly patterns. The proposed multi-joint ring motif can provide a novel method for creating functional molecular devices. Full article

(This article belongs to the Special Issue Recent Advances of Molecular Machines and Molecular Robots)

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12 pages, 40331 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Electrical Characterization of a Double-Layered Conductive Pattern with Different Crack Configurations for Durable E-Textiles

by Tomoya Koshi, Ken-ichi Nomura and Manabu Yoshida

Micromachines 2020, 11(11), 977; https://doi.org/10.3390/mi11110977 - 30 Oct 2020

Cited by 5 | Viewed by 2610

Abstract

For the conductive patterns of electronic textiles (e-textiles), it is still challenging to maintain low electrical resistance, even under large or cyclic tensile deformation. This study investigated a double-layered pattern with different crack configurations as a possible solution. Patterns with single crack growth [...] Read more.

For the conductive patterns of electronic textiles (e-textiles), it is still challenging to maintain low electrical resistance, even under large or cyclic tensile deformation. This study investigated a double-layered pattern with different crack configurations as a possible solution. Patterns with single crack growth exhibit a low initial resistance and resistance change rate. In contrast, patterns with multiple crack growth maintain their conductivity under deformation, where electrical failure occurs in those with single crack growth. We considered that a double-layered structure could combine the electrical characteristics of patterns with single and multiple crack growths. In this study, each layer was theoretically designed to control the crack configuration. Then, meandering copper patterns, silver ink patterns, and their double layers were fabricated on textiles as patterns with single and multiple crack growths and double-layered patterns, respectively. Their resistance changes under the single (large) and cyclic tensile deformations were characterized. The results confirmed that the double-layered patterns maintained the lowest resistance at the high elongation rate and cycle. The resistance change rates of the meandering copper and silver ink patterns were constant, and changed monotonically against the elongation rate/cycle, respectively. In contrast, the change rate of the double-layered patterns varied considerably when electrical failure occurred in the copper layer. The change rate after the failure was much higher than that before the failure, and on the same order as that of the silver ink patterns. Full article

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

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14 pages, 4534 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Surface-Tension-Confined Channel with Biomimetic Microstructures for Unidirectional Liquid Spreading

by Yi Zhang, Yang Gan, Liwen Zhang, Deyuan Zhang and Huawei Chen

Micromachines 2020, 11(11), 978; https://doi.org/10.3390/mi11110978 - 30 Oct 2020

Cited by 5 | Viewed by 4181

Abstract

Unidirectional liquid spreading without energy input is of significant interest for the broad applications in diverse fields such as water harvesting, drop transfer, oil–water separation and microfluidic devices. However, the controllability of liquid motion and the simplification of manufacturing process remain challenges. Inspired [...] Read more.

Unidirectional liquid spreading without energy input is of significant interest for the broad applications in diverse fields such as water harvesting, drop transfer, oil–water separation and microfluidic devices. However, the controllability of liquid motion and the simplification of manufacturing process remain challenges. Inspired by the peristome of Nepenthes alata, a surface-tension-confined (STC) channel with biomimetic microcavities was fabricated facilely through UV exposure photolithography and partial plasma treatment. Perfect asymmetric liquid spreading was achieved by combination of microcavities and hydrophobic boundary, and the stability of pinning effect was demonstrated. The influences of structural features of microcavities on both liquid spreading and liquid pinning were investigated and the underlying mechanism was revealed. We also demonstrated the spontaneous unidirectional transport of liquid in 3D space and on tilting slope. In addition, through changing pits arrangement and wettability pattern, complex liquid motion paths and microreactors were realized. This work will open a new way for liquid manipulation and lab-on-chip applications. Full article

(This article belongs to the Special Issue Micro/Nano-surfaces: Fabrication and Applications)

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12 pages, 11278 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Method for Passive Droplet Sorting after Photo-Tagging

by Chandler Dobson, Claudia Zielke, Ching W. Pan, Cameron Feit and Paul Abbyad

Micromachines 2020, 11(11), 964; https://doi.org/10.3390/mi11110964 - 28 Oct 2020

Cited by 5 | Viewed by 3967

Abstract

We present a method to photo-tag individual microfluidic droplets for latter selection by passive sorting. The use of a specific surfactant leads to the interfacial tension to be very sensitive to droplet pH. The photoexcitation of droplets containing a photoacid, pyranine, leads to [...] Read more.

We present a method to photo-tag individual microfluidic droplets for latter selection by passive sorting. The use of a specific surfactant leads to the interfacial tension to be very sensitive to droplet pH. The photoexcitation of droplets containing a photoacid, pyranine, leads to a decrease in droplet pH. The concurrent increase in droplet interfacial tension enables the passive selection of irradiated droplets. The technique is used to select individual droplets within a droplet array as illuminated droplets remain in the wells while other droplets are eluted by the flow of the external oil. This method was used to select droplets in an array containing cells at a specific stage of apoptosis. The technique is also adaptable to continuous-flow sorting. By passing confined droplets over a microfabricated trench positioned diagonally in relation to the direction of flow, photo-tagged droplets were directed toward a different chip exit based on their lateral movement. The technique can be performed on a conventional fluorescence microscope and uncouples the observation and selection of droplets, thus enabling the selection on a large variety of signals, or based on qualitative user-defined features. Full article

(This article belongs to the Special Issue Droplet Microfluidics)

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17 pages, 16524 KiB

Open AccessFeature PaperEditor’s ChoiceReview

The Future Application of Organ-on-a-Chip Technologies as Proving Grounds for MicroBioRobots

by Haley C. Fuller, Ting-Yen Wei, Michael R. Behrens and Warren C. Ruder

Micromachines 2020, 11(10), 947; https://doi.org/10.3390/mi11100947 - 20 Oct 2020

Cited by 8 | Viewed by 4950

Abstract

An evolving understanding of disease pathogenesis has compelled the development of new drug delivery approaches. Recently, bioinspired microrobots have gained traction as drug delivery systems. By leveraging the microscale phenomena found in physiological systems, these microrobots can be designed with greater maneuverability, which [...] Read more.

An evolving understanding of disease pathogenesis has compelled the development of new drug delivery approaches. Recently, bioinspired microrobots have gained traction as drug delivery systems. By leveraging the microscale phenomena found in physiological systems, these microrobots can be designed with greater maneuverability, which enables more precise, controlled drug release. Their function could be further improved by testing their efficacy in physiologically relevant model systems as part of their development. In parallel with the emergence of microscale robots, organ-on-a-chip technologies have become important in drug discovery and physiological modeling. These systems reproduce organ-level functions in microfluidic devices, and can also incorporate specific biological, chemical, and physical aspects of a disease. This review highlights recent developments in both microrobotics and organ-on-a-chip technologies and envisions their combined use for developing future drug delivery systems. Full article

(This article belongs to the Special Issue Microengineered Physiological Systems for Disease Modeling and Drug Testing)

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18 pages, 10866 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Micro-Fabrication of Components for a High-Density Sub-Retinal Visual Prosthesis

by Douglas B. Shire, Marcus D. Gingerich, Patricia I. Wong, Michael Skvarla, Stuart F. Cogan, Jinghua Chen, Wei Wang and Joseph F. Rizzo

Micromachines 2020, 11(10), 944; https://doi.org/10.3390/mi11100944 - 19 Oct 2020

Cited by 6 | Viewed by 3917

Abstract

We present a retrospective of unique micro-fabrication problems and solutions that were encountered through over 10 years of retinal prosthesis product development, first for the Boston Retinal Implant Project initiated at the Massachusetts Institute of Technology and at Harvard Medical School’s teaching hospital, [...] Read more.

We present a retrospective of unique micro-fabrication problems and solutions that were encountered through over 10 years of retinal prosthesis product development, first for the Boston Retinal Implant Project initiated at the Massachusetts Institute of Technology and at Harvard Medical School’s teaching hospital, the Massachusetts Eye and Ear—and later at the startup company Bionic Eye Technologies, by some of the same personnel. These efforts culminated in the fabrication and assembly of 256+ channel visual prosthesis devices having flexible multi-electrode arrays that were successfully implanted sub-retinally in mini-pig animal models as part of our pre-clinical testing program. We report on the processing of the flexible multi-layered, planar and penetrating high-density electrode arrays, surgical tools for sub-retinal implantation, and other parts such as coil supports that facilitated the implantation of the peri-ocular device components. We begin with an overview of the implantable portion of our visual prosthesis system design, and describe in detail the micro-fabrication methods for creating the parts of our system that were assembled outside of our hermetically-sealed electronics package. We also note the unique surgical challenges that sub-retinal implantation of our micro-fabricated components presented, and how some of those issues were addressed through design, materials selection, and fabrication approaches. Full article

(This article belongs to the Special Issue Micro/Nanofabrication for Retinal Implants)

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30 pages, 5835 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Electro-Hydrodynamics of Emulsion Droplets: Physical Insights to Applications

by Muhammad Salman Abbasi, Ryungeun Song, Seongsu Cho and Jinkee Lee

Micromachines 2020, 11(10), 942; https://doi.org/10.3390/mi11100942 - 18 Oct 2020

Cited by 23 | Viewed by 5648

Abstract

The field of droplet electrohydrodynamics (EHD) emerged with a seminal work of G.I. Taylor in 1966, who presented the so-called leaky dielectric model (LDM) to predict the droplet shapes undergoing distortions under an electric field. Since then, the droplet EHD has evolved in [...] Read more.

The field of droplet electrohydrodynamics (EHD) emerged with a seminal work of G.I. Taylor in 1966, who presented the so-called leaky dielectric model (LDM) to predict the droplet shapes undergoing distortions under an electric field. Since then, the droplet EHD has evolved in many ways over the next 55 years with numerous intriguing phenomena reported, such as tip and equatorial streaming, Quincke rotation, double droplet breakup modes, particle assemblies at the emulsion interface, and many more. These phenomena have a potential of vast applications in different areas of science and technology. This paper presents a review of prominent droplet EHD studies pertaining to the essential physical insight of various EHD phenomena. Here, we discuss the dynamics of a single-phase emulsion droplet under weak and strong electric fields. Moreover, the effect of the presence of particles and surfactants at the emulsion interface is covered in detail. Furthermore, the EHD of multi-phase double emulsion droplet is included. We focus on features such as deformation, instabilities, and breakups under varying electrical and physical properties. At the end of the review, we also discuss the potential applications of droplet EHD and various challenges with their future perspectives. Full article

(This article belongs to the Special Issue Electrokinetics in Micro-/nanofluidic Devices)

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10 pages, 3373 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

A Flexible, Microfluidic, Dispensing System for Screening Drug Combinations

by Mark Davies, Mannthalah Abubaker and Lorraine Bible

Micromachines 2020, 11(10), 943; https://doi.org/10.3390/mi11100943 - 18 Oct 2020

Cited by 4 | Viewed by 2986

Abstract

It is known that in many cases a combination of drugs is more effective than single-drug treatments both for reducing toxicity and increasing efficacy. With the advent of organoid screens, personalised medicine has become possible for many diseases. Automated pipetting to well plates [...] Read more.

It is known that in many cases a combination of drugs is more effective than single-drug treatments both for reducing toxicity and increasing efficacy. With the advent of organoid screens, personalised medicine has become possible for many diseases. Automated pipetting to well plates is the pharmaceutical industry standard for drug screening, but this is relatively expensive and slow. Here, a rotary microfluidic system is presented that can test all possible drug combinations at speed with the use of droplets. For large numbers of combinations, it is shown how the experimental scale is reduced by considering drug dilutions and machine learning. As an example, two cases are considered; the first is a three-ring and three radii configuration and the second is a four ring and forty-eight radii configuration. Between these two, all other cases are shown to be possible. The proposed commercial instrument is shown to be flexible, the user choosing which wells to fill and which driver-computational sub-routine to select. The major issues addressed here are the programming theory of the instrument and the reduction of droplets to be generated by drug dilutions and machine learning. Full article

(This article belongs to the Special Issue Droplet Microfluidics)

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14 pages, 4731 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Micromachined Silicon Platform for Precise Assembly of 2D Multilayer Laue Lenses for High-Resolution X-ray Microscopy

by Wei Xu, Weihe Xu, Nathalie Bouet, Juan Zhou, Hanfei Yan, Xiaojing Huang, Ming Lu, Maxim Zalalutdinov, Yong S. Chu and Evgeny Nazaretski

Micromachines 2020, 11(10), 939; https://doi.org/10.3390/mi11100939 - 15 Oct 2020

Cited by 3 | Viewed by 2951

Abstract

We report on a developed micromachined silicon platform for the precise assembly of 2D multilayer Laue lenses (MLLs) for high-resolution X-ray microscopy. The platform is 10 × 10 mm² and is fabricated on ~500 µm thick silicon wafers through multiple steps of [...] Read more.

We report on a developed micromachined silicon platform for the precise assembly of 2D multilayer Laue lenses (MLLs) for high-resolution X-ray microscopy. The platform is 10 × 10 mm² and is fabricated on ~500 µm thick silicon wafers through multiple steps of photolithography and deep reactive-ion etching. The platform accommodates two linear MLLs in a pre-defined configuration with precise angular and lateral position control. In this work, we discuss the design and microfabrication of the platform, and characterization regarding MLLs assembly, position control, repeatability, and stability. The results demonstrate that a micromachined platform can be used for the assembly of a variety of MLLs with different dimensions and optical parameters. The angular misalignment of 2D MLLs is well controlled in the range of the designed accuracy, down to a few millidegrees. The separation distance between MLLs is adjustable from hundreds to more than one thousand micrometers. The use of the developed platform greatly simplifies the alignment procedure of the MLL optics and reduces the complexity of the X-ray microscope. It is a significant step forward for the development of monolithic 2D MLL nanofocusing optics for high-resolution X-ray microscopy. Full article

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12 pages, 3173 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Microfluidic Viscometer Using a Suspending Micromembrane for Measurement of Biosamples

by Lelin Liu, Dinglong Hu and Raymond H. W. Lam

Micromachines 2020, 11(10), 934; https://doi.org/10.3390/mi11100934 - 14 Oct 2020

Cited by 19 | Viewed by 3442

Abstract

The viscosity of biofluids such as blood and saliva can reflect an individual’s health conditions, and viscosity measurements are therefore considered in health monitoring and disease diagnosis. However, conventional viscometers can only handle a larger liquid volume beyond the quantity that can be [...] Read more.

The viscosity of biofluids such as blood and saliva can reflect an individual’s health conditions, and viscosity measurements are therefore considered in health monitoring and disease diagnosis. However, conventional viscometers can only handle a larger liquid volume beyond the quantity that can be extracted from a person. Though very effective, micro-sensors based on electrokinetic, ultrasonic, or other principles often have strict requirements for the supporting equipment and complicated procedures and signal processing. Sample contamination is always an important issue. In this paper, we report a microfluidic viscometer requiring a small volume of biosamples (<50 µL) and straightforward operation procedures. It is fabricated with low-cost and biocompatible polymeric materials as one-time-use devices, such that contamination is no longer the concern. It contains a suspending micromembrane located along a microchannel. Under a steady driving pressure, the membrane displacement is a function of viscosity of the liquid sample being tested. We derived a simple analytical relation and perform a simulation for converting the membrane displacement to the sample viscosity. We conducted experiments with liquids (water and mineral oil) with defined properties to verify such a relation. We further applied the micro-viscometer to measure bovine blood samples with different hematocrit levels. It can be concluded that the microfluidic viscometer has a high compatibility with a broad range of biomedical applications. Full article

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

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42 pages, 14997 KiB

Open AccessFeature PaperEditor’s ChoiceReview

MEMS Ultrasound Transducers for Endoscopic Photoacoustic Imaging Applications

by Haoran Wang, Yifei Ma, Hao Yang, Huabei Jiang, Yingtao Ding and Huikai Xie

Micromachines 2020, 11(10), 928; https://doi.org/10.3390/mi11100928 - 12 Oct 2020

Cited by 32 | Viewed by 9628

Abstract

Photoacoustic imaging (PAI) is drawing extensive attention and gaining rapid development as an emerging biomedical imaging technology because of its high spatial resolution, large imaging depth, and rich optical contrast. PAI has great potential applications in endoscopy, but the progress of endoscopic PAI [...] Read more.

Photoacoustic imaging (PAI) is drawing extensive attention and gaining rapid development as an emerging biomedical imaging technology because of its high spatial resolution, large imaging depth, and rich optical contrast. PAI has great potential applications in endoscopy, but the progress of endoscopic PAI was hindered by the challenges of manufacturing and assembling miniature imaging components. Over the last decade, microelectromechanical systems (MEMS) technology has greatly facilitated the development of photoacoustic endoscopes and extended the realm of applicability of the PAI. As the key component of photoacoustic endoscopes, micromachined ultrasound transducers (MUTs), including piezoelectric MUTs (pMUTs) and capacitive MUTs (cMUTs), have been developed and explored for endoscopic PAI applications. In this article, the recent progress of pMUTs (thickness extension mode and flexural vibration mode) and cMUTs are reviewed and discussed with their applications in endoscopic PAI. Current PAI endoscopes based on pMUTs and cMUTs are also introduced and compared. Finally, the remaining challenges and future directions of MEMS ultrasound transducers for endoscopic PAI applications are given. Full article

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

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15 pages, 4573 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

A Scalable and Low Stress Post-CMOS Processing Technique for Implantable Microsensors

by Ah-Hyoung Lee, Jihun Lee, Farah Laiwalla, Vincent Leung, Jiannan Huang, Arto Nurmikko and Yoon-Kyu Song

Micromachines 2020, 11(10), 925; https://doi.org/10.3390/mi11100925 - 5 Oct 2020

Cited by 14 | Viewed by 5187

Abstract

Implantable active electronic microchips are being developed as multinode in-body sensors and actuators. There is a need to develop high throughput microfabrication techniques applicable to complementary metal–oxide–semiconductor (CMOS)-based silicon electronics in order to process bare dies from a foundry to physiologically compatible implant [...] Read more.

Implantable active electronic microchips are being developed as multinode in-body sensors and actuators. There is a need to develop high throughput microfabrication techniques applicable to complementary metal–oxide–semiconductor (CMOS)-based silicon electronics in order to process bare dies from a foundry to physiologically compatible implant ensembles. Post-processing of a miniature CMOS chip by usual methods is challenging as the typically sub-mm size small dies are hard to handle and not readily compatible with the standard microfabrication, e.g., photolithography. Here, we present a soft material-based, low chemical and mechanical stress, scalable microchip post-CMOS processing method that enables photolithography and electron-beam deposition on hundreds of micrometers scale dies. The technique builds on the use of a polydimethylsiloxane (PDMS) carrier substrate, in which the CMOS chips were embedded and precisely aligned, thereby enabling batch post-processing without complication from additional micromachining or chip treatments. We have demonstrated our technique with 650 μm × 650 μm and 280 μm × 280 μm chips, designed for electrophysiological neural recording and microstimulation implants by monolithic integration of patterned gold and PEDOT:PSS electrodes on the chips and assessed their electrical properties. The functionality of the post-processed chips was verified in saline, and ex vivo experiments using wireless power and data link, to demonstrate the recording and stimulation performance of the microscale electrode interfaces. Full article

(This article belongs to the Special Issue Implantable Neural Sensors for the Brain Machine Interface)

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10 pages, 4545 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Micropillar/Microwell Chip Assessment for Detoxification of Bisphenol A with Korean Pear (Pyrus pyrifolia)

by Dong Woo Lee, Moo-Yeal Lee, Sukkil Koh and Mihi Yang

Micromachines 2020, 11(10), 922; https://doi.org/10.3390/mi11100922 - 3 Oct 2020

Cited by 7 | Viewed by 3949

Abstract

A micropillar/microwell chip platform with 3D cultured liver cells has been used for HTP screening of hepatotoxicity of bisphenol A (BPA), an endocrine-disrupting chemical. We previously found the hepatotoxicity of BPA is alleviated by alcohol dehydrogenase (ADH) and aldehyde dehydrogenase 2 (ALDH2). In [...] Read more.

A micropillar/microwell chip platform with 3D cultured liver cells has been used for HTP screening of hepatotoxicity of bisphenol A (BPA), an endocrine-disrupting chemical. We previously found the hepatotoxicity of BPA is alleviated by alcohol dehydrogenase (ADH) and aldehyde dehydrogenase 2 (ALDH2). In this study, we have tested potential BPA detoxification with Korean pear (Pyrus pyrifolia) extract, stimulators of ADH and ALDH, as well as arbutin, a reference compound in the pears, on the micropillar/microwell chip platform with human liver cells. Surprisingly, the toxicity of BPA was reduced in the presence of Korean pear extract, indicated by significantly increased IC₅₀ values. The IC₅₀ value of BPA with Korean pear extract tested against HepG2 cells was shifted from 151 to 451 μM, whereas those tested against Hep3B cells was shifted from 110 to 204 μM. Among the tested various concentrations, 1.25, 2.5, and 5 mg/mL of the extract significantly reduced BPA toxicity (Ps < 0.05). However, there was no such detoxification effects with arbutin. This result was supported by changes in protein levels of ADH in the liver cells. Full article

(This article belongs to the Special Issue Lab-on-a-Chip Systems for Toxicology)

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21 pages, 5429 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Acoustic Microfluidic Separation Techniques and Bioapplications: A Review

by Yuan Gao, Mengren Wu, Yang Lin and Jie Xu

Micromachines 2020, 11(10), 921; https://doi.org/10.3390/mi11100921 - 2 Oct 2020

Cited by 75 | Viewed by 9059

Abstract

Microfluidic separation technology has garnered significant attention over the past decade where particles are being separated at a micro/nanoscale in a rapid, low-cost, and simple manner. Amongst a myriad of separation technologies that have emerged thus far, acoustic microfluidic separation techniques are extremely [...] Read more.

Microfluidic separation technology has garnered significant attention over the past decade where particles are being separated at a micro/nanoscale in a rapid, low-cost, and simple manner. Amongst a myriad of separation technologies that have emerged thus far, acoustic microfluidic separation techniques are extremely apt to applications involving biological samples attributed to various advantages, including high controllability, biocompatibility, and non-invasive, label-free features. With that being said, downsides such as low throughput and dependence on external equipment still impede successful commercialization from laboratory-based prototypes. Here, we present a comprehensive review of recent advances in acoustic microfluidic separation techniques, along with exemplary applications. Specifically, an inclusive overview of fundamental theory and background is presented, then two sets of mechanisms underlying acoustic separation, bulk acoustic wave and surface acoustic wave, are introduced and discussed. Upon these summaries, we present a variety of applications based on acoustic separation. The primary focus is given to those associated with biological samples such as blood cells, cancer cells, proteins, bacteria, viruses, and DNA/RNA. Finally, we highlight the benefits and challenges behind burgeoning developments in the field and discuss the future perspectives and an outlook towards robust, integrated, and commercialized devices based on acoustic microfluidic separation. Full article

(This article belongs to the Special Issue Microfluidic Sensors II)

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14 pages, 2188 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Graphene-Based Contacts for Optoelectronic Devices

by Susana Fernández, Antonio Molinero, David Sanz, José Pablo González, Marina de la Cruz, José Javier Gandía and Julio Cárabe

Micromachines 2020, 11(10), 919; https://doi.org/10.3390/mi11100919 - 1 Oct 2020

Cited by 12 | Viewed by 3517

Abstract

Hybrid transparent contacts based on combinations of a transparent conductive oxide and a few graphene monolayers were developed in order to evaluate their optical and electrical performance with the main aim to use them as front contacts in optoelectronic devices. The assessment of [...] Read more.

Hybrid transparent contacts based on combinations of a transparent conductive oxide and a few graphene monolayers were developed in order to evaluate their optical and electrical performance with the main aim to use them as front contacts in optoelectronic devices. The assessment of the most suitable strategies for their fabrication was performed by testing different protocols addressing such issues as the protection of the device structure underneath, the limitation of sample temperature during the graphene-monolayer transfer process and the determination of the most suitable stacking structure. Suitable metal ohmic electrodes were also evaluated. Among a number of options tested, the metal contact based on Ti + Ag showed the highest reproducibility and the lowest contact resistivity. Finally, with the objective of extracting the current generated from optoelectronic devices to the output pins of an external package, focusing on a near future commercial application, the electrical properties of the connections made with an ultrasonic bonding machine (sonic welding) between the optimized Ti + Ag metal contacts and Al or Au micro-wires were also evaluated. All these results have an enormous potential as hybrid electrodes based on graphene to be used in novel designs of a future generation of optoelectronic devices, such as solar cells. Full article

(This article belongs to the Special Issue Graphene based Electronic Devices)

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13 pages, 3601 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Toward Vasculature in Skeletal Muscle-on-a-Chip through Thermo-Responsive Sacrificial Templates

by Li Wan, James Flegle, Burak Ozdoganlar and Philip R. LeDuc

Micromachines 2020, 11(10), 907; https://doi.org/10.3390/mi11100907 - 30 Sep 2020

Cited by 16 | Viewed by 4656

Abstract

Developing new approaches for vascularizing synthetic tissue systems will have a tremendous impact in diverse areas. One area where this is particularly important is developing new skeletal muscle tissue systems, which could be utilized in physiological model studies and tissue regeneration. To develop [...] Read more.

Developing new approaches for vascularizing synthetic tissue systems will have a tremendous impact in diverse areas. One area where this is particularly important is developing new skeletal muscle tissue systems, which could be utilized in physiological model studies and tissue regeneration. To develop vascularized approaches a microfluidic on-chip design for creating channels in polymer systems can be pursued. Current microfluidic tissue engineering methods include soft lithography, rapid prototyping, and cell printing; however, these have limitations such as having their scaffolding being inorganic, less desirable planar vasculature geometry, low fabrication efficiency, and limited resolution. Here we successfully developed a circular microfluidic channel embedded in a 3D extracellular matrix scaffolding with 3D myogenesis. We used a thermo-responsive polymer approach with micromilling-molding and designed a mixture of polyester wax and paraffin wax to fabricate the sacrificial template for microfluidic channel generation in the scaffolding. These findings will impact a number of fields including biomaterials, biomimetic structures, and personalized medicine in the future. Full article

(This article belongs to the Special Issue Microengineered Physiological Systems for Disease Modeling and Drug Testing)

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15 pages, 12024 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

A Capacitive Pressure Sensor Interface IC with Wireless Power and Data Transfer

by Chaoping Zhang, Robert Gallichan, David M. Budgett and Daniel McCormick

Micromachines 2020, 11(10), 897; https://doi.org/10.3390/mi11100897 - 27 Sep 2020

Cited by 12 | Viewed by 4093

Abstract

This paper presents a capacitive pressure sensor interface circuit design in 180 nm XH018 CMOS technology for an implantable capacitive pressure sensor, which has a wireless power supply and wireless data transfer function. It integrates full-bridge rectifiers, shorting control switches, low-dropout regulators, bandgap [...] Read more.

This paper presents a capacitive pressure sensor interface circuit design in 180 nm XH018 CMOS technology for an implantable capacitive pressure sensor, which has a wireless power supply and wireless data transfer function. It integrates full-bridge rectifiers, shorting control switches, low-dropout regulators, bandgap references, analog front end, single slope analog to digital converter (ADC), I2C, and an RC oscillator. The low-dropout regulators regulate the wireless power supply coming from the rectifier and provide a stable and accurate 1.8 V DC voltage to other blocks. The capacitance of the pressure sensor is sampled to a discrete voltage by the analog front end. The single slope ADC converts the discrete voltage into 11 bits of digital data, which is then converted into 1 kbps serial data out by the I2C block. The “1” of serial data is modulated to a 500 kHz digital signal that is used to control the shorting switch for wireless data transfer via inductive back scatter. This capacitive pressure sensor interface IC has a resolution of 0.98 mmHg (1.4 fF), average total power consumption of 7.8 mW, and ±3.2% accuracy at the worst case under a −20 to 80 °C temperature range, which improves to ±0.86% when operated between 20 and 60 °C. Full article

(This article belongs to the Special Issue Power Electronics and Sensors)

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41 pages, 4549 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Recent Advances of Wearable Antennas in Materials, Fabrication Methods, Designs, and Their Applications: State-of-the-Art

by Shahid M. Ali, Cheab Sovuthy, Muhammad A. Imran, Soeung Socheatra, Qammer H. Abbasi and Zuhairiah Zainal Abidin

Micromachines 2020, 11(10), 888; https://doi.org/10.3390/mi11100888 - 24 Sep 2020

Cited by 76 | Viewed by 8509

Abstract

The demand for wearable technologies has grown tremendously in recent years. Wearable antennas are used for various applications, in many cases within the context of wireless body area networks (WBAN). In WBAN, the presence of the human body poses a significant challenge to [...] Read more.

The demand for wearable technologies has grown tremendously in recent years. Wearable antennas are used for various applications, in many cases within the context of wireless body area networks (WBAN). In WBAN, the presence of the human body poses a significant challenge to the wearable antennas. Specifically, such requirements are required to be considered on a priority basis in the wearable antennas, such as structural deformation, precision, and accuracy in fabrication methods and their size. Various researchers are active in this field and, accordingly, some significant progress has been achieved recently. This article attempts to critically review the wearable antennas especially in light of new materials and fabrication methods, and novel designs, such as miniaturized button antennas and miniaturized single and multi-band antennas, and their unique smart applications in WBAN. Finally, the conclusion has been drawn with respect to some future directions. Full article

(This article belongs to the Special Issue Future Wearable and Implants)

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21 pages, 3226 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Advances in Label-Free Detections for Nanofluidic Analytical Devices

by Thu Hac Huong Le, Hisashi Shimizu and Kyojiro Morikawa

Micromachines 2020, 11(10), 885; https://doi.org/10.3390/mi11100885 - 23 Sep 2020

Cited by 19 | Viewed by 4175

Abstract

Nanofluidics, a discipline of science and engineering of fluids confined to structures at the 1–1000 nm scale, has experienced significant growth over the past decade. Nanofluidics have offered fascinating platforms for chemical and biological analyses by exploiting the unique characteristics of liquids and [...] Read more.

Nanofluidics, a discipline of science and engineering of fluids confined to structures at the 1–1000 nm scale, has experienced significant growth over the past decade. Nanofluidics have offered fascinating platforms for chemical and biological analyses by exploiting the unique characteristics of liquids and molecules confined in nanospaces; however, the difficulty to detect molecules in extremely small spaces hampers the practical applications of nanofluidic devices. Laser-induced fluorescence microscopy with single-molecule sensitivity has been so far a major detection method in nanofluidics, but issues arising from labeling and photobleaching limit its application. Recently, numerous label-free detection methods have been developed to identify and determine the number of molecules, as well as provide chemical, conformational, and kinetic information of molecules. This review focuses on label-free detection techniques designed for nanofluidics; these techniques are divided into two groups: optical and electrical/electrochemical detection methods. In this review, we discuss on the developed nanofluidic device architectures, elucidate the mechanisms by which the utilization of nanofluidics in manipulating molecules and controlling light–matter interactions enhances the capabilities of biological and chemical analyses, and highlight new research directions in the field of detections in nanofluidics. Full article

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

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13 pages, 1848 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Single-Cell Elasticity Measurement with an Optically Actuated Microrobot

by István Grexa, Tamás Fekete, Judit Molnár, Kinga Molnár, Gaszton Vizsnyiczai, Pál Ormos and Lóránd Kelemen

Micromachines 2020, 11(9), 882; https://doi.org/10.3390/mi11090882 - 22 Sep 2020

Cited by 18 | Viewed by 3497

Abstract

A cell elasticity measurement method is introduced that uses polymer microtools actuated by holographic optical tweezers. The microtools were prepared with two-photon polymerization. Their shape enables the approach of the cells in any lateral direction. In the presented case, endothelial cells grown on [...] Read more.

A cell elasticity measurement method is introduced that uses polymer microtools actuated by holographic optical tweezers. The microtools were prepared with two-photon polymerization. Their shape enables the approach of the cells in any lateral direction. In the presented case, endothelial cells grown on vertical polymer walls were probed by the tools in a lateral direction. The use of specially shaped microtools prevents the target cells from photodamage that may arise during optical trapping. The position of the tools was recorded simply with video microscopy and analyzed with image processing methods. We critically compare the resulting Young’s modulus values to those in the literature obtained by other methods. The application of optical tweezers extends the force range available for cell indentations measurements down to the fN regime. Our approach demonstrates a feasible alternative to the usual vertical indentation experiments. Full article

(This article belongs to the Special Issue New Trends and Applications in Femtosecond Laser Micromachining)

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12 pages, 3021 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Fused Deposition Modeling of Microfluidic Chips in Polymethylmethacrylate

by Frederik Kotz, Markus Mader, Nils Dellen, Patrick Risch, Andrea Kick, Dorothea Helmer and Bastian E. Rapp

Micromachines 2020, 11(9), 873; https://doi.org/10.3390/mi11090873 - 19 Sep 2020

Cited by 62 | Viewed by 6966

Abstract

Polymethylmethacrylate (PMMA) is one of the most important thermoplastic materials and is a widely used material in microfluidics. However, PMMA is usually structured using industrial scale replication processes, such as hot embossing or injection molding, not compatible with rapid prototyping. In this work, [...] Read more.

Polymethylmethacrylate (PMMA) is one of the most important thermoplastic materials and is a widely used material in microfluidics. However, PMMA is usually structured using industrial scale replication processes, such as hot embossing or injection molding, not compatible with rapid prototyping. In this work, we demonstrate that microfluidic chips made from PMMA can be 3D printed using fused deposition modeling (FDM). We demonstrate that using FDM microfluidic chips with a minimum channel cross-section of ~300 µm can be printed and a variety of different channel geometries and mixer structures are shown. The optical transparency of the chips is shown to be significantly enhanced by printing onto commercial PMMA substrates. The use of such commercial PMMA substrates also enables the integration of PMMA microstructures into the printed chips, by first generating a microstructure on the PMMA substrates, and subsequently printing the PMMA chip around the microstructure. We further demonstrate that protein patterns can be generated within previously printed microfluidic chips by employing a method of photobleaching. The FDM printing of microfluidic chips in PMMA allows the use of one of microfluidics’ most used industrial materials on the laboratory scale and thus significantly simplifies the transfer from results gained in the lab to an industrial product. Full article

(This article belongs to the Special Issue 3D Printing of MEMS Technology)

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