Micromachines

36 pages, 2624 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Review of Design Considerations for Brain-on-a-Chip Models

by Tiffany Cameron, Tanya Bennet, Elyn M. Rowe, Mehwish Anwer, Cheryl L. Wellington and Karen C. Cheung

Micromachines 2021, 12(4), 441; https://doi.org/10.3390/mi12040441 - 15 Apr 2021

Cited by 37 | Viewed by 8476

Abstract

In recent years, the need for sophisticated human in vitro models for integrative biology has motivated the development of organ-on-a-chip platforms. Organ-on-a-chip devices are engineered to mimic the mechanical, biochemical and physiological properties of human organs; however, there are many important considerations when [...] Read more.

In recent years, the need for sophisticated human in vitro models for integrative biology has motivated the development of organ-on-a-chip platforms. Organ-on-a-chip devices are engineered to mimic the mechanical, biochemical and physiological properties of human organs; however, there are many important considerations when selecting or designing an appropriate device for investigating a specific scientific question. Building microfluidic Brain-on-a-Chip (BoC) models from the ground-up will allow for research questions to be answered more thoroughly in the brain research field, but the design of these devices requires several choices to be made throughout the design development phase. These considerations include the cell types, extracellular matrix (ECM) material(s), and perfusion/flow considerations. Choices made early in the design cycle will dictate the limitations of the device and influence the end-point results such as the permeability of the endothelial cell monolayer, and the expression of cell type-specific markers. To better understand why the engineering aspects of a microfluidic BoC need to be influenced by the desired biological environment, recent progress in microfluidic BoC technology is compared. This review focuses on perfusable blood–brain barrier (BBB) and neurovascular unit (NVU) models with discussions about the chip architecture, the ECM used, and how they relate to the in vivo human brain. With increased knowledge on how to make informed choices when selecting or designing BoC models, the scientific community will benefit from shorter development phases and platforms curated for their application. Full article

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

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15 pages, 2563 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Wearable Sensors and Systems for Wound Healing-Related pH and Temperature Detection

by Ning Tang, Youbin Zheng, Xue Jiang, Cheng Zhou, Han Jin, Ke Jin, Weiwei Wu and Hossam Haick

Micromachines 2021, 12(4), 430; https://doi.org/10.3390/mi12040430 - 14 Apr 2021

Cited by 76 | Viewed by 12027

Abstract

Wound healing is a complex tissue regeneration process involving many changes in multiple physiological parameters. The pH and temperature of a wound site have long been recognized as important biomarkers for assessing wound healing status. For effective wound management, wound dressings integrated with [...] Read more.

Wound healing is a complex tissue regeneration process involving many changes in multiple physiological parameters. The pH and temperature of a wound site have long been recognized as important biomarkers for assessing wound healing status. For effective wound management, wound dressings integrated with wearable sensors and systems used for continuous monitoring of pH and temperature have received much attention in recent years. Herein, recent advances in the development of wearable pH and temperature sensors and systems based on different sensing mechanisms for wound status monitoring and treatment are comprehensively summarized. Challenges in the areas of sensing performance, infection identification threshold, large-area 3-dimensional detection, and long-term reliable monitoring in current wearable sensors/systems and emerging solutions are emphasized, providing critical insights into the development of wearable sensors and systems for wound healing monitoring and management. Full article

(This article belongs to the Special Issue Flexible Sensors and Actuators for Biomedicine)

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9 pages, 4459 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Color-Tunable White LEDs with Single Chip Realized through Phosphor Pattern and Thermal-Modulating Optical Film

by Zhenpeng Su, Bo Zhao, Zheng Gong, Yang Peng, Fan Bai, Huai Zheng and Sang Woo Joo

Micromachines 2021, 12(4), 421; https://doi.org/10.3390/mi12040421 - 12 Apr 2021

Cited by 5 | Viewed by 2896

Abstract

In this paper, a new method to regulate the correlated color temperature (CCT) of white light-emitting diodes (LEDs) is proposed for the single-chip packaging structure, in which the blue light distribution emitted from the chip in the red/yellow phosphor layer was modulated through [...] Read more.

In this paper, a new method to regulate the correlated color temperature (CCT) of white light-emitting diodes (LEDs) is proposed for the single-chip packaging structure, in which the blue light distribution emitted from the chip in the red/yellow phosphor layer was modulated through changing the paraffin-polydimethylsiloxane (PDMS) film transparence and haze. The results show that the transmittance of the paraffin-PDMS film can be modulated from 49.76% to 97.64%, while the haze of that ranges from 88.19% to 63.10%. When the thickness of paraffin-PDMS film is 0.6 mm, and the paraffin-PDMS film concentration is 30 wt%, the CCT of white LED decreases from 15177 K to 3615 K with the increase of thermal load in the paraffin-PDMS film. The modulating range of its CCT reaches 11562 K. The maximum CCT variation at the same test condition is only 536 K in the repeated experiments within one week. Full article

(This article belongs to the Special Issue Microsystem for Electronic Devices)

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12 pages, 4650 KiB

Open AccessFeature PaperEditor’s ChoiceCommunication

Extremely High-Throughput Parallel Microfluidic Vortex-Actuated Cell Sorting

by Alex A. Zhukov, Robyn H. Pritchard, Mick J. Withers, Tony Hailes, Richard D. Gold, Calum Hayes, Mette F. la Cour, Fred Hussein and Salman Samson Rogers

Micromachines 2021, 12(4), 389; https://doi.org/10.3390/mi12040389 - 2 Apr 2021

Cited by 14 | Viewed by 5159

Abstract

We demonstrate extremely high-throughput microfluidic cell sorting by making a parallel version of the vortex-actuated cell sorter (VACS). The set-up includes a parallel microfluidic sorter chip and parallel cytometry instrumentation: optics, electronics and control software. The result is capable of sorting lymphocyte-sized particles [...] Read more.

We demonstrate extremely high-throughput microfluidic cell sorting by making a parallel version of the vortex-actuated cell sorter (VACS). The set-up includes a parallel microfluidic sorter chip and parallel cytometry instrumentation: optics, electronics and control software. The result is capable of sorting lymphocyte-sized particles at 16 times the rate of our single-stream VACS devices, and approximately 10 times the rate of commercial cell sorters for an equivalent procedure. We believe this opens the potential to scale cell sorting for applications requiring the processing of much greater cell numbers than currently possible with conventional cell sorting. Full article

(This article belongs to the Special Issue Microfluidics for Cell Detection and Sorting)

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19 pages, 1299 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Affinity Sensors for the Diagnosis of COVID-19

by Maryia Drobysh, Almira Ramanaviciene, Roman Viter and Arunas Ramanavicius

Micromachines 2021, 12(4), 390; https://doi.org/10.3390/mi12040390 - 2 Apr 2021

Cited by 64 | Viewed by 10755

Abstract

The coronavirus disease 2019 (COVID-19) outbreak caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) was proclaimed a global pandemic in March 2020. Reducing the dissemination rate, in particular by tracking the infected people and their contacts, is the main instrument against infection [...] Read more.

The coronavirus disease 2019 (COVID-19) outbreak caused by severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) was proclaimed a global pandemic in March 2020. Reducing the dissemination rate, in particular by tracking the infected people and their contacts, is the main instrument against infection spreading. Therefore, the creation and implementation of fast, reliable and responsive methods suitable for the diagnosis of COVID-19 are required. These needs can be fulfilled using affinity sensors, which differ in applied detection methods and markers that are generating analytical signals. Recently, nucleic acid hybridization, antigen-antibody interaction, and change of reactive oxygen species (ROS) level are mostly used for the generation of analytical signals, which can be accurately measured by electrochemical, optical, surface plasmon resonance, field-effect transistors, and some other methods and transducers. Electrochemical biosensors are the most consistent with the general trend towards, acceleration, and simplification of the bioanalytical process. These biosensors mostly are based on the determination of antigen-antibody interaction and are robust, sensitive, accurate, and sometimes enable label-free detection of an analyte. Along with the specification of biosensors, we also provide a brief overview of generally used testing techniques, and the description of the structure, life cycle and immune host response to SARS-CoV-2, and some deeper details of analytical signal detection principles. Full article

(This article belongs to the Special Issue Micro/Nano Immunosensor Devices)

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12 pages, 4954 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Structural Reinforcement Effect of a Flexible Strain Sensor Integrated with Pneumatic Balloon Actuators for Soft Microrobot Fingers

by Satoshi Konishi, Fuminari Mori, Ayano Shimizu and Akiya Hirata

Micromachines 2021, 12(4), 395; https://doi.org/10.3390/mi12040395 - 2 Apr 2021

Cited by 15 | Viewed by 3876

Abstract

Motion capture of a robot and tactile sensing for a robot require sensors. Strain sensors are used to detect bending deformation of the robot finger and to sense the force from an object. It is important to introduce sensors in effective combination with [...] Read more.

Motion capture of a robot and tactile sensing for a robot require sensors. Strain sensors are used to detect bending deformation of the robot finger and to sense the force from an object. It is important to introduce sensors in effective combination with actuators without affecting the original performance of the robot. We are interested in the improvement of flexible strain sensors integrated into soft microrobot fingers using a pneumatic balloon actuator (PBA). A strain sensor using a microchannel filled with liquid metal was developed for soft PBAs by considering the compatibility of sensors and actuators. Inflatable deformation generated by PBAs, however, was found to affect sensor characteristics. This paper presents structural reinforcement of a liquid metal-based sensor to solve this problem. Parylene C film was deposited into a microchannel to reinforce its structure against the inflatable deformation caused by a PBA. Parylene C deposition into a microchannel suppressed the interference of inflatable deformation. The proposed method enables the effective combination of soft PBAs and a flexible liquid metal strain sensor for use in microrobot fingers. Full article

(This article belongs to the Special Issue MEMS Force Sensor)

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10 pages, 3067 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Development of Cultured Muscles with Tendon Structures for Modular Bio-Actuators

by Takuto Nomura, Masaru Takeuchi, Eunhye Kim, Qiang Huang, Yasuhisa Hasegawa and Toshio Fukuda

Micromachines 2021, 12(4), 379; https://doi.org/10.3390/mi12040379 - 1 Apr 2021

Cited by 16 | Viewed by 3743

Abstract

In this article, we propose a new actuator named the modular bio-actuator (MBA). The MBA has two tendon structures made of polydimethylsiloxane (PDMS) at both ends of the bio-actuator. The MBA can be easily handled and fixed on an artificial micro-robot body to [...] Read more.

In this article, we propose a new actuator named the modular bio-actuator (MBA). The MBA has two tendon structures made of polydimethylsiloxane (PDMS) at both ends of the bio-actuator. The MBA can be easily handled and fixed on an artificial micro-robot body to increase its design flexibility and output power. The tendon structures were connected to a bio-actuator in the form of a chain structure, and the connection between the tendon structures and the bio-actuator was maintained for more than three weeks. The contraction length of the MBA was linearly increased when the DC voltage applied to the MBA was increased. The MBA contracted over 200 µm when a DC voltage of 10 V and 1 Hz was applied to the bio-actuator. The output power of the MBA was measured using a PDMS cantilever, and the total output power of the MBA increased linearly when multiple MBAs were stacked on a PDMS cantilever. This study was aimed at improving the design flexibility and controllability of micro-robots and bionic systems. Full article

(This article belongs to the Special Issue Micro/Nano Robotics: A Theme Issue in Honor of Professor Toshio Fukuda)

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38 pages, 9793 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Recapitulating Cardiac Structure and Function In Vitro from Simple to Complex Engineering

by Ana Rita M. P. Santos, Yongjun Jang, Inwoo Son, Jongseong Kim and Yongdoo Park

Micromachines 2021, 12(4), 386; https://doi.org/10.3390/mi12040386 - 1 Apr 2021

Cited by 11 | Viewed by 6693

Abstract

Cardiac tissue engineering aims to generate in vivo-like functional tissue for the study of cardiac development, homeostasis, and regeneration. Since the heart is composed of various types of cells and extracellular matrix with a specific microenvironment, the fabrication of cardiac tissue in vitro [...] Read more.

Cardiac tissue engineering aims to generate in vivo-like functional tissue for the study of cardiac development, homeostasis, and regeneration. Since the heart is composed of various types of cells and extracellular matrix with a specific microenvironment, the fabrication of cardiac tissue in vitro requires integrating technologies of cardiac cells, biomaterials, fabrication, and computational modeling to model the complexity of heart tissue. Here, we review the recent progress of engineering techniques from simple to complex for fabricating matured cardiac tissue in vitro. Advancements in cardiomyocytes, extracellular matrix, geometry, and computational modeling will be discussed based on a technology perspective and their use for preparation of functional cardiac tissue. Since the heart is a very complex system at multiscale levels, an understanding of each technique and their interactions would be highly beneficial to the development of a fully functional heart in cardiac tissue engineering. Full article

(This article belongs to the Special Issue Bio-MEMS for Cell and Tissue Engineering)

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12 pages, 3828 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

A Label-Free Liquid Crystal Biosensor Based on Specific DNA Aptamer Probes for Sensitive Detection of Amoxicillin Antibiotic

by Duy Khiem Nguyen and Chang-Hyun Jang

Micromachines 2021, 12(4), 370; https://doi.org/10.3390/mi12040370 - 30 Mar 2021

Cited by 28 | Viewed by 4591

Abstract

We developed a liquid crystal (LC) aptamer biosensor for the sensitive detection of amoxicillin (AMX). The AMX aptamer was immobilized onto the surface of a glass slide modified with a mixed self-assembled layer of dimethyloctadecyl [3-(trimethoxysilyl) propyl] ammonium chloride (DMOAP) and (3-aminopropyl) triethoxysilane [...] Read more.

We developed a liquid crystal (LC) aptamer biosensor for the sensitive detection of amoxicillin (AMX). The AMX aptamer was immobilized onto the surface of a glass slide modified with a mixed self-assembled layer of dimethyloctadecyl [3-(trimethoxysilyl) propyl] ammonium chloride (DMOAP) and (3-aminopropyl) triethoxysilane (APTES). The long alkyl chains of DMOAP maintained the LC molecules in a homeotropic orientation and induced a dark optical appearance under a polarized light microscope (POM). In the presence of AMX, the specific binding of the aptamer and AMX molecules induced a conformational change in the aptamers, leading to the disruption of the homeotropic orientation of LCs, resulting in a bright optical appearance. The developed aptasensor showed high specificity and a low detection limit of 3.5 nM. Moreover, the potential application of the developed aptasensor for the detection of AMX in environmental samples was also demonstrated. Therefore, the proposed aptasensor is a promising platform for simple, rapid, and label-free monitoring of AMX in an actual water environment with high selectivity and sensitivity. Full article

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16 pages, 7134 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Optical Investigation of Individual Red Blood Cells for Determining Cell Count and Cellular Hemoglobin Concentration in a Microfluidic Channel

by Ann-Kathrin Reichenwallner, Esma Vurmaz, Kristina Battis, Laura Handl, Helin Üstün, Tivadar Mach, Gabriele Hörnig, Jan Lipfert and Lukas Richter

Micromachines 2021, 12(4), 358; https://doi.org/10.3390/mi12040358 - 26 Mar 2021

Cited by 6 | Viewed by 4973

Abstract

We demonstrate a blood analysis routine by observing red blood cells through light and digital holographic microscopy in a microfluidic channel. With this setup a determination of red blood cell (RBC) concentration, the mean corpuscular volume (MCV), and corpuscular hemoglobin concentration mean (CHCM) [...] Read more.

We demonstrate a blood analysis routine by observing red blood cells through light and digital holographic microscopy in a microfluidic channel. With this setup a determination of red blood cell (RBC) concentration, the mean corpuscular volume (MCV), and corpuscular hemoglobin concentration mean (CHCM) is feasible. Cell count variations in between measurements differed by 2.47% with a deviation of

- 0.26 \times 10^{6}

μL to the reference value obtained from the Siemens ADVIA 2120i. Measured MCV values varied by 2.25% and CHCM values by 3.78% compared to the reference ADVIA measurement. Our results suggest that the combination of optical analysis with microfluidics handling provides a promising new approach to red blood cell counts. Full article

(This article belongs to the Special Issue Microfluidics for Cell Detection and Sorting)

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10 pages, 2410 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Smart Wearable Sensors Based on Triboelectric Nanogenerator for Personal Healthcare Monitoring

by Ruonan Li, Xuelian Wei, Jiahui Xu, Junhuan Chen, Bin Li, Zhiyi Wu and Zhong Lin Wang

Micromachines 2021, 12(4), 352; https://doi.org/10.3390/mi12040352 - 25 Mar 2021

Cited by 88 | Viewed by 7658

Abstract

Accurate monitoring of motion and sleep states is critical for human health assessment, especially for a healthy life, early diagnosis of diseases, and medical care. In this work, a smart wearable sensor (SWS) based on a dual-channel triboelectric nanogenerator was presented for a [...] Read more.

Accurate monitoring of motion and sleep states is critical for human health assessment, especially for a healthy life, early diagnosis of diseases, and medical care. In this work, a smart wearable sensor (SWS) based on a dual-channel triboelectric nanogenerator was presented for a real-time health monitoring system. The SWS can be worn on wrists, ankles, shoes, or other parts of the body and cloth, converting mechanical triggers into electrical output. By analyzing these signals, the SWS can precisely and constantly monitor and distinguish various motion states, including stepping, walking, running, and jumping. Based on the SWS, a fall-down alarm system and a sleep quality assessment system were constructed to provide personal healthcare monitoring and alert family members or doctors via communication devices. It is important for the healthy growth of the young and special patient groups, as well as for the health monitoring and medical care of the elderly and recovered patients. This work aimed to broaden the paths for remote biological movement status analysis and provide diversified perspectives for true-time and long-term health monitoring, simultaneously. Full article

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

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23 pages, 4999 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Biofabrication in Congenital Cardiac Surgery: A Plea from the Operating Theatre, Promise from Science

by Laszlo Kiraly and Sanjairaj Vijayavenkataraman

Micromachines 2021, 12(3), 332; https://doi.org/10.3390/mi12030332 - 21 Mar 2021

Cited by 8 | Viewed by 4603

Abstract

Despite significant advances in numerous fields of biofabrication, clinical application of biomaterials combined with bioactive molecules and/or cells largely remains a promise in an individualized patient settings. Three-dimensional (3D) printing and bioprinting evolved as promising techniques used for tissue-engineering, so that several kinds [...] Read more.

Despite significant advances in numerous fields of biofabrication, clinical application of biomaterials combined with bioactive molecules and/or cells largely remains a promise in an individualized patient settings. Three-dimensional (3D) printing and bioprinting evolved as promising techniques used for tissue-engineering, so that several kinds of tissue can now be printed in layers or as defined structures for replacement and/or reconstruction in regenerative medicine and surgery. Besides technological, practical, ethical and legal challenges to solve, there is also a gap between the research labs and the patients’ bedside. Congenital and pediatric cardiac surgery mostly deal with reconstructive patient-scenarios when defects are closed, various segments of the heart are connected, valves are implanted. Currently available biomaterials lack the potential of growth and conduits, valves derange over time surrendering patients to reoperations. Availability of viable, growing biomaterials could cancel reoperations that could entail significant public health benefit and improved quality-of-life. Congenital cardiac surgery is uniquely suited for closing the gap in translational research, rapid application of new techniques, and collaboration between interdisciplinary teams. This article provides a succinct review of the state-of-the art clinical practice and biofabrication strategies used in congenital and pediatric cardiac surgery, and highlights the need and avenues for translational research and collaboration. Full article

(This article belongs to the Special Issue Three-Dimensional Polymeric Scaffolds for Tissue Engineering Applications)

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12 pages, 3853 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

A Magnetically Actuated Superhydrophobic Ratchet Surface for Droplet Manipulation

by ChangHee Son, BingQiang Ji, JunKyu Park, Jie Feng and Seok Kim

Micromachines 2021, 12(3), 325; https://doi.org/10.3390/mi12030325 - 19 Mar 2021

Cited by 16 | Viewed by 4341

Abstract

A water droplet dispensed on a superhydrophobic ratchet surface is formed into an asymmetric shape, which creates a Laplace pressure gradient due to the contact angle difference between two sides. This work presents a magnetically actuated superhydrophobic ratchet surface composed of nanostructured black [...] Read more.

A water droplet dispensed on a superhydrophobic ratchet surface is formed into an asymmetric shape, which creates a Laplace pressure gradient due to the contact angle difference between two sides. This work presents a magnetically actuated superhydrophobic ratchet surface composed of nanostructured black silicon strips on elastomer ridges. Uniformly magnetized NdFeB layers sputtered under the black silicon strips enable an external magnetic field to tilt the black silicon strips and form a superhydrophobic ratchet surface. Due to the dynamically controllable Laplace pressure gradient, a water droplet on the reported ratchet surface experiences different forces on two sides, which are explored in this work. Here, the detailed fabrication procedure and the related magnetomechanical model are provided. In addition, the resultant asymmetric spreading of a water droplet is studied. Finally, droplet impact characteristics are investigated in three different behaviors of deposition, rebound, and penetration depending on the impact speed. The findings in this work are exploitable for further droplet manipulation studies based on a dynamically controllable superhydrophobic ratchet surface. Full article

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

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18 pages, 3884 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

A Microfluidic Device for Automated High Throughput Detection of Ice Nucleation of Snomax^®

by Priyatanu Roy, Margaret L. House and Cari S. Dutcher

Micromachines 2021, 12(3), 296; https://doi.org/10.3390/mi12030296 - 11 Mar 2021

Cited by 13 | Viewed by 4702

Abstract

Measurement of ice nucleation (IN) temperature of liquid solutions at sub-ambient temperatures has applications in atmospheric, water quality, food storage, protein crystallography and pharmaceutical sciences. Here we present details on the construction of a temperature-controlled microfluidic platform with multiple individually addressable temperature zones [...] Read more.

Measurement of ice nucleation (IN) temperature of liquid solutions at sub-ambient temperatures has applications in atmospheric, water quality, food storage, protein crystallography and pharmaceutical sciences. Here we present details on the construction of a temperature-controlled microfluidic platform with multiple individually addressable temperature zones and on-chip temperature sensors for high-throughput IN studies in droplets. We developed, for the first time, automated droplet freezing detection methods in a microfluidic device, using a deep neural network (DNN) and a polarized optical method based on intensity thresholding to classify droplets without manual counting. This platform has potential applications in continuous monitoring of liquid samples consisting of aerosols to quantify their IN behavior, or in checking for contaminants in pure water. A case study of the two detection methods was performed using Snomax^® (Snomax International, Englewood, CO, USA), an ideal ice nucleating particle (INP). Effects of aging and heat treatment of Snomax^® were studied with Fourier transform infrared (FTIR) spectroscopy and a microfluidic platform to correlate secondary structure change of the IN protein in Snomax^® to IN temperature. It was found that aging at room temperature had a mild impact on the ice nucleation ability but heat treatment at 95 °C had a more pronounced effect by reducing the ice nucleation onset temperature by more than 7 °C and flattening the overall frozen fraction curve. Results also demonstrated that our setup can generate droplets at a rate of about 1500/min and requires minimal human intervention for DNN classification. Full article

(This article belongs to the Special Issue Microfluidic Platforms for Ice Nucleation Studies)

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12 pages, 4238 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Capillary Forces between Concave Gripper and Spherical Particle for Micro-Objects Gripping

by Zenghua Fan, Zixiao Liu, Congcong Huang, Wei Zhang, Zhe Lv and Lefeng Wang

Micromachines 2021, 12(3), 285; https://doi.org/10.3390/mi12030285 - 8 Mar 2021

Cited by 8 | Viewed by 3151

Abstract

The capillary action between two solid surfaces has drawn significant attention in micro-objects manipulation. The axisymmetric capillary bridges and capillary forces between a spherical concave gripper and a spherical particle are investigated in the present study. A numerical procedure based on a shooting [...] Read more.

The capillary action between two solid surfaces has drawn significant attention in micro-objects manipulation. The axisymmetric capillary bridges and capillary forces between a spherical concave gripper and a spherical particle are investigated in the present study. A numerical procedure based on a shooting method, which consists of double iterative loops, was employed to obtain the capillary bridge profile and bring the capillary force subject to a constant volume condition. Capillary bridge rupture was characterized using the parameters of the neck radius, pressure difference, half-filling angle, and capillary force. The effects of various parameters, such as the contact angle of the spherical concave gripper, the radius ratio, and the liquid bridge volume on the dimensionless capillary force, are discussed. The results show that the radius ratio has a significant influence on the dimensionless capillary force for the dimensionless liquid bridge volumes of 0.01, 0.05, and 0.1 when the radius ratio value is smaller than 10. The effectiveness of the theorical approach was verified using simulation model and experiments. Full article

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16 pages, 5793 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

A Versatile Optoelectronic Tweezer System for Micro-Objects Manipulation: Transportation, Patterning, Sorting, Rotating and Storage

by Shuzhang Liang, Yuqing Cao, Yuguo Dai, Fenghui Wang, Xue Bai, Bin Song, Chaonan Zhang, Chunyuan Gan, Fumihito Arai and Lin Feng

Micromachines 2021, 12(3), 271; https://doi.org/10.3390/mi12030271 - 6 Mar 2021

Cited by 25 | Viewed by 4910

Abstract

Non-contact manipulation technology has a wide range of applications in the manipulation and fabrication of micro/nanomaterials. However, the manipulation devices are often complex, operated only by professionals, and limited by a single manipulation function. Here, we propose a simple versatile optoelectronic tweezer (OET) [...] Read more.

Non-contact manipulation technology has a wide range of applications in the manipulation and fabrication of micro/nanomaterials. However, the manipulation devices are often complex, operated only by professionals, and limited by a single manipulation function. Here, we propose a simple versatile optoelectronic tweezer (OET) system that can be easily controlled for manipulating microparticles with different sizes. In this work, we designed and established an optoelectronic tweezer manipulation system. The OET system could be used to manipulate particles with a wide range of sizes from 2 μm to 150 μm. The system could also manipulate micro-objects of different dimensions like 1D spherical polystyrene microspheres, 2D rod-shaped euglena gracilis, and 3D spiral microspirulina. Optical microscopic patterns for trapping, storing, parallel transporting, and patterning microparticles were designed for versatile manipulation. The sorting, rotation, and assembly of single particles in a given region were experimentally demonstrated. In addition, temperatures measured under different objective lenses indicate that the system does not generate excessive heat to damage bioparticles. The non-contact versatile manipulation reduces operating process and contamination. In future work, the simple optoelectronic tweezers system can be used to control non-contaminated cell interaction and micro-nano manipulation. Full article

(This article belongs to the Special Issue Micro/Nano Robotics: A Theme Issue in Honor of Professor Toshio Fukuda)

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25 pages, 12688 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Performance of Quad Mass Gyroscope in the Angular Rate Mode

by Sina Askari, Mohammad H. Asadian and Andrei M. Shkel

Micromachines 2021, 12(3), 266; https://doi.org/10.3390/mi12030266 - 4 Mar 2021

Cited by 24 | Viewed by 4219

Abstract

In this paper, the characterization and analysis of a silicon micromachined Quad Mass Gyroscope (QMG) in the rate mode of operation are presented. We report on trade-offs between full-scale, linearity, and noise characteristics of QMGs with different Q-factors. Allan Deviation (ADEV) and Power [...] Read more.

In this paper, the characterization and analysis of a silicon micromachined Quad Mass Gyroscope (QMG) in the rate mode of operation are presented. We report on trade-offs between full-scale, linearity, and noise characteristics of QMGs with different Q-factors. Allan Deviation (ADEV) and Power Spectral Density (PSD) analysis methods were used to evaluate the performance results. The devices in this study were instrumented for the rate mode of operation, with the Open-Loop (OL) and Force-to-Rebalance (FRB) configurations of the sense mode. For each method of instrumentation, we presented constraints on selection of control parameters with respect to the Q-factor of the devices. For the high Q-factor device of over 2 million, and uncompensated frequency asymmetry of 60

m

Hz

, we demonstrated bias instability of

0.095

^{\circ}

/

h

r and Angle Random Walk (ARW) of

0.0107

^{\circ}

/

\sqrt{hr}

in the OL mode of operation and bias instability of

0.065

^{\circ}

/

h

r and ARW of

0.0058

^{\circ}

/

\sqrt{hr}

in the FRB mode of operation. We concluded that in a realistic MEMS gyroscope with imperfections (nearly matched, but non-zero frequency asymmetry), a higher Q-factor would increase the frequency stability of the drive axis resulting in an improved noise performance, but has challenges in implementation of digital control loops. Full article

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

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20 pages, 4825 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Nanopatterning with Photonic Nanojets: Review and Perspectives in Biomedical Research

by Salvatore Surdo, Martí Duocastella and Alberto Diaspro

Micromachines 2021, 12(3), 256; https://doi.org/10.3390/mi12030256 - 3 Mar 2021

Cited by 44 | Viewed by 5866

Abstract

Nanostructured surfaces and devices offer astounding possibilities for biomedical research, including cellular and molecular biology, diagnostics, and therapeutics. However, the wide implementation of these systems is currently limited by the lack of cost-effective and easy-to-use nanopatterning tools. A promising solution is to use [...] Read more.

Nanostructured surfaces and devices offer astounding possibilities for biomedical research, including cellular and molecular biology, diagnostics, and therapeutics. However, the wide implementation of these systems is currently limited by the lack of cost-effective and easy-to-use nanopatterning tools. A promising solution is to use optical methods based on photonic nanojets, namely, needle-like beams featuring a nanometric width. In this review, we survey the physics, engineering strategies, and recent implementations of photonic nanojets for high-throughput generation of arbitrary nanopatterns, along with applications in optics, electronics, mechanics, and biosensing. An outlook of the potential impact of nanopatterning technologies based on photonic nanojets in several relevant biomedical areas is also provided. Full article

(This article belongs to the Special Issue Nanostructured Surfaces and Devices for Biomedical Applications)

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43 pages, 5180 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Inertial Microfluidics Enabling Clinical Research

by Srivathsan Kalyan, Corinna Torabi, Harrison Khoo, Hyun Woo Sung, Sung-Eun Choi, Wenzhao Wang, Benjamin Treutler, Dohyun Kim and Soojung Claire Hur

Micromachines 2021, 12(3), 257; https://doi.org/10.3390/mi12030257 - 3 Mar 2021

Cited by 35 | Viewed by 7159

Abstract

Fast and accurate interrogation of complex samples containing diseased cells or pathogens is important to make informed decisions on clinical and public health issues. Inertial microfluidics has been increasingly employed for such investigations to isolate target bioparticles from liquid samples with size and/or [...] Read more.

Fast and accurate interrogation of complex samples containing diseased cells or pathogens is important to make informed decisions on clinical and public health issues. Inertial microfluidics has been increasingly employed for such investigations to isolate target bioparticles from liquid samples with size and/or deformability-based manipulation. This phenomenon is especially useful for the clinic, owing to its rapid, label-free nature of target enrichment that enables further downstream assays. Inertial microfluidics leverages the principle of inertial focusing, which relies on the balance of inertial and viscous forces on particles to align them into size-dependent laminar streamlines. Several distinct microfluidic channel geometries (e.g., straight, curved, spiral, contraction-expansion array) have been optimized to achieve inertial focusing for a variety of purposes, including particle purification and enrichment, solution exchange, and particle alignment for on-chip assays. In this review, we will discuss how inertial microfluidics technology has contributed to improving accuracy of various assays to provide clinically relevant information. This comprehensive review expands upon studies examining both endogenous and exogenous targets from real-world samples, highlights notable hybrid devices with dual functions, and comments on the evolving outlook of the field. Full article

(This article belongs to the Special Issue Inertial Microfluidics)

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11 pages, 3849 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Stretchable MXene/Thermoplastic Polyurethanes based Strain Sensor Fabricated Using a Combined Electrospinning and Electrostatic Spray Deposition Technique

by Feiyu Fang, Han Wang, Huaquan Wang, Xiaofei Gu, Jun Zeng, Zixu Wang, Xindu Chen, Xin Chen and Meiyun Chen

Micromachines 2021, 12(3), 252; https://doi.org/10.3390/mi12030252 - 1 Mar 2021

Cited by 30 | Viewed by 4678

Abstract

In this work, a novel flexible electrically resistive-type MXene/Thermoplastic polyurethanes(TPU) based strain sensors was developed by a composite process of electrospinning (ES) and electrostatic spray deposition (ESD). Compared with other deposition processes, the sensing layer prepared by ESD has better adhesion to the [...] Read more.

In this work, a novel flexible electrically resistive-type MXene/Thermoplastic polyurethanes(TPU) based strain sensors was developed by a composite process of electrospinning (ES) and electrostatic spray deposition (ESD). Compared with other deposition processes, the sensing layer prepared by ESD has better adhesion to the ES TPU nanofiber membrane and is not easy to crack during the stretching process, thereby greatly improving the working range of the strain sensor. Furthermore, we obtained the sandwich structure easily by ES on the surface of the sensing layer again. This will help make the stress distribution more uniform during the stretching process and further increase the strain sensing range. The ESD-ES strain sensors were attached on skin to monitor various human motions. The results demonstrate that our ESD-ES strain sensors have wide application prospects in smart wearable device. Full article

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29 pages, 5721 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Liquid Crystal Devices for Beam Steering Applications

by Rowan Morris, Cliff Jones and Mamatha Nagaraj

Micromachines 2021, 12(3), 247; https://doi.org/10.3390/mi12030247 - 28 Feb 2021

Cited by 37 | Viewed by 6577

Abstract

Liquid crystals are valuable materials for applications in beam steering devices. In this paper, an overview of the use of liquid crystals in the field of adaptive optics specifically for beam steering and lensing devices is presented. The paper introduces the properties of [...] Read more.

Liquid crystals are valuable materials for applications in beam steering devices. In this paper, an overview of the use of liquid crystals in the field of adaptive optics specifically for beam steering and lensing devices is presented. The paper introduces the properties of liquid crystals that have made them useful in this field followed by a more detailed discussion of specific liquid crystal devices that act as switchable optical components of refractive and diffractive types. The relative advantages and disadvantages of the different devices and techniques are summarised. Full article

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

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18 pages, 2364 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Loading and Release of Charged and Neutral Fluorescent Dyes into and from Mesoporous Materials: A Key Role for Sensing Applications

by Estela Climent, Mandy Hecht and Knut Rurack

Micromachines 2021, 12(3), 249; https://doi.org/10.3390/mi12030249 - 28 Feb 2021

Cited by 6 | Viewed by 3122

Abstract

The aim of this study is to determine the efficiency of loading and release of several zwitterionic, neutral, anionic and cationic dyes into/from mesoporous nanoparticles to find the optimum loading and release conditions for their application in detection protocols. The loading is carried [...] Read more.

The aim of this study is to determine the efficiency of loading and release of several zwitterionic, neutral, anionic and cationic dyes into/from mesoporous nanoparticles to find the optimum loading and release conditions for their application in detection protocols. The loading is carried out for MCM-41 type silica supports suspended in phosphate-buffered saline (PBS) buffer (pH 7.4) or in acetonitrile, involving the dyes (rhodamine B chloride, rhodamine 101 chloride, rhodamine 101 perchlorate, rhodamine 101 inner salt, meso-(4-hydroxyphenyl)-boron–dipyrromethene (BODIPY), sulforhodamine B sodium salt and fluorescein 27). As a general trend, rhodamine-based dyes are loaded with higher efficiency, when compared with BODIPY and fluorescein dyes. Between the rhodamine-based dyes, their charge and the solvent in which the loading process is carried out play important roles for the amount of cargo that can be loaded into the materials. The delivery experiments carried out in PBS buffer at pH 7.4 reveal for all the materials that anionic dyes are more efficiently released compared to their neutral or cationic counterparts. The overall best performance is achieved with the negatively charged sulforhodamine B dye in acetonitrile. This material also shows a high delivery degree in PBS buffer. Full article

(This article belongs to the Special Issue Hybrid Materials for Advanced Sensing and Controlled Release Applications)

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10 pages, 4441 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

A Self-Powered Vector Angle/Displacement Sensor Based on Triboelectric Nanogenerator

by Chengyu Li, Ziming Wang, Sheng Shu and Wei Tang

Micromachines 2021, 12(3), 231; https://doi.org/10.3390/mi12030231 - 25 Feb 2021

Cited by 18 | Viewed by 4830

Abstract

Recently, grating-structured triboelectric nanogenerators (TENG) operating in freestanding mode have been the subject of intensive research. However, standard TENGs based on interdigital electrode structures are unable to realize real-time sensing of the direction of the freestanding electrode movement. Here, a newly designed TENG, [...] Read more.

Recently, grating-structured triboelectric nanogenerators (TENG) operating in freestanding mode have been the subject of intensive research. However, standard TENGs based on interdigital electrode structures are unable to realize real-time sensing of the direction of the freestanding electrode movement. Here, a newly designed TENG, consisting of one group of grating freestanding electrodes and three groups of interdigitated induction electrodes with the identical period, has been demonstrated as a self-powered vector angle/displacement sensor (SPVS), capable of distinguishing the real-time direction of the freestanding electrode displacement. Thanks to the unique coupling effect between triboelectrification and electrostatic induction, periodic alternating voltage signals are generated in response to the rotation/sliding movement of the top freestanding electrodes on the bottom electrodes. The output peak-to-peak voltage of the SPVS can reach as high as 300 V at the rotation rate of 48 rpm and at the sliding velocity of 0.1 m/s, respectively. The resolution of the sensor reaches 8°/5 mm and can be further enhanced by decreasing the width of the electrodes. This present work not only demonstrates a novel method for angle/displacement detection but also greatly expands the applicability of TENG as self-powered vector sensors. Full article

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

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7 pages, 2506 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

An Ultra-High-Q Lithium Niobate Microresonator Integrated with a Silicon Nitride Waveguide in the Vertical Configuration for Evanescent Light Coupling

by Jianhao Zhang, Rongbo Wu, Min Wang, Youting Liang, Junxia Zhou, Miao Wu, Zhiwei Fang, Wei Chu and Ya Cheng

Micromachines 2021, 12(3), 235; https://doi.org/10.3390/mi12030235 - 25 Feb 2021

Cited by 8 | Viewed by 3753

Abstract

We demonstrate the hybrid integration of a lithium niobate microring resonator with a silicon nitride waveguide in the vertical configuration to achieve efficient light coupling. The microring resonator is fabricated on a lithium niobate on insulator (LNOI) substrate using photolithography assisted chemo-mechanical etching [...] Read more.

We demonstrate the hybrid integration of a lithium niobate microring resonator with a silicon nitride waveguide in the vertical configuration to achieve efficient light coupling. The microring resonator is fabricated on a lithium niobate on insulator (LNOI) substrate using photolithography assisted chemo-mechanical etching (PLACE). A fused silica cladding layer is deposited on the LNOI ring resonator. The silicon nitride waveguide is further produced on the fused silica cladding layer by first fabricating a trench in the fused silica while using focused ion beam (FIB) etching for facilitating the evanescent coupling, followed by the formation of the silicon nitride waveguide on the bottom of the trench. The FIB etching ensures the required high positioning accuracy between the waveguide and ring resonator. We achieve Q-factors as high as 1.4 × 10⁷ with the vertically integrated device. Full article

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

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21 pages, 5273 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Electrochemical Biosensors for the Detection of SARS-CoV-2 and Other Viruses

by Saim Imran, Soha Ahmadi and Kagan Kerman

Micromachines 2021, 12(2), 174; https://doi.org/10.3390/mi12020174 - 10 Feb 2021

Cited by 56 | Viewed by 7780

Abstract

The last few decades have been plagued by viral outbreaks that present some of the biggest challenges to public safety. The current coronavirus (COVID-19) disease pandemic has exponentiated these concerns. Increased research on diagnostic tools is currently being implemented in order to assist [...] Read more.

The last few decades have been plagued by viral outbreaks that present some of the biggest challenges to public safety. The current coronavirus (COVID-19) disease pandemic has exponentiated these concerns. Increased research on diagnostic tools is currently being implemented in order to assist with rapid identification of the virus, as mass diagnosis and containment is the best way to prevent the outbreak of the virus. Accordingly, there is a growing urgency to establish a point-of-care device for the rapid detection of coronavirus to prevent subsequent spread. This device needs to be sensitive, selective, and exhibit rapid diagnostic capabilities. Electrochemical biosensors have demonstrated these traits and, hence, serve as promising candidates for the detection of viruses. This review summarizes the designs and features of electrochemical biosensors developed for some past and current pandemic or epidemic viruses, including influenza, HIV, Ebola, and Zika. Alongside the design, this review also discusses the detection principles, fabrication techniques, and applications of the biosensors. Finally, research and perspective of biosensors as potential detection tools for the rapid identification of SARS-CoV-2 is discussed. Full article

(This article belongs to the Special Issue Recent Trends in Biosensors)

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14 pages, 2389 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Solvent-Free Polycaprolactone Dissolving Microneedles Generated via the Thermal Melting Method for the Sustained Release of Capsaicin

by Jaehong Eum, Youseong Kim, Daniel Junmin Um, Jiwoo Shin, Huisuk Yang and Hyungil Jung

Micromachines 2021, 12(2), 167; https://doi.org/10.3390/mi12020167 - 8 Feb 2021

Cited by 30 | Viewed by 5313

Abstract

(1) Background: Dissolving microneedles (DMNs), a transdermal drug delivery system, have been developed to treat various diseases in a minimally invasive, painless manner. However, the currently available DMNs are based on burst release systems due to their hydrophilic backbone polymer. Although hydrophobic biodegradable [...] Read more.

(1) Background: Dissolving microneedles (DMNs), a transdermal drug delivery system, have been developed to treat various diseases in a minimally invasive, painless manner. However, the currently available DMNs are based on burst release systems due to their hydrophilic backbone polymer. Although hydrophobic biodegradable polymers have been employed on DMNs for sustained release, dissolution in an organic solvent is required for fabrication of such DMNs. (2) Method: To overcome the aforementioned limitation, novel separable polycaprolactone (PCL) DMNs (SPCL-DMNs) were developed to implant a PCL-encapsulated drug into the skin. PCL is highly hydrophobic, degrades over a long time, and has a low melting point. Under thermal melting, PCL encapsulated capsaicin and could be fabricated into a DMN without the risk of toxicity from an organic solvent. (3) Results: Optimized SPCL-DMNs, containing PCL (height 498.3 ± 5.8 µm) encapsulating 86.66 ± 1.13 µg capsaicin with a 10% (w/v) polyvinyl alcohol and 20% (w/v) polyvinylpyrrolidone mixture as a base polymer, were generated. Assessment of the drug release profile revealed that this system could sustainably release capsaicin for 15 days from PCL being implanted in porcine skin. (4) Conclusion: The implantable SPCL-DMN developed here has the potential for future development of toxicity-free, sustained release DMNs. Full article

(This article belongs to the Special Issue Microneedles)

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11 pages, 2572 KiB

Open AccessFeature PaperEditor’s ChoicePerspective

Implanted Flexible Electronics: Set Device Lifetime with Smart Nanomaterials

by Hoang-Phuong Phan

Micromachines 2021, 12(2), 157; https://doi.org/10.3390/mi12020157 - 5 Feb 2021

Cited by 27 | Viewed by 4396

Abstract

Flexible electronics is one of the most attractive and anticipated markets in the internet-of-things era, covering a broad range of practical and industrial applications from displays and energy harvesting to health care devices. The mechanical flexibility, combined with high performance electronics, and integrated [...] Read more.

Flexible electronics is one of the most attractive and anticipated markets in the internet-of-things era, covering a broad range of practical and industrial applications from displays and energy harvesting to health care devices. The mechanical flexibility, combined with high performance electronics, and integrated on a soft substrate offer unprecedented functionality for biomedical applications. This paper presents a brief snapshot on the materials of choice for niche flexible bio-implanted devices that address the requirements for both biodegradable and long-term operational streams. The paper also discusses potential future research directions in this rapidly growing field. Full article

(This article belongs to the Special Issue Flexible Electronics for Wearable and Implantable Health Care Applications)

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21 pages, 7176 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Textile-Based Triboelectric Nanogenerators for Wearable Self-Powered Microsystems

by Peng Huang, Dan-Liang Wen, Yu Qiu, Ming-Hong Yang, Cheng Tu, Hong-Sheng Zhong and Xiao-Sheng Zhang

Micromachines 2021, 12(2), 158; https://doi.org/10.3390/mi12020158 - 5 Feb 2021

Cited by 40 | Viewed by 8050

Abstract

In recent years, wearable electronic devices have made considerable progress thanks to the rapid development of the Internet of Things. However, even though some of them have preliminarily achieved miniaturization and wearability, the drawbacks of frequent charging and physical rigidity of conventional lithium [...] Read more.

In recent years, wearable electronic devices have made considerable progress thanks to the rapid development of the Internet of Things. However, even though some of them have preliminarily achieved miniaturization and wearability, the drawbacks of frequent charging and physical rigidity of conventional lithium batteries, which are currently the most commonly used power source of wearable electronic devices, have become technical bottlenecks that need to be broken through urgently. In order to address the above challenges, the technology based on triboelectric effect, i.e., triboelectric nanogenerator (TENG), is proposed to harvest energy from ambient environment and considered as one of the most promising methods to integrate with functional electronic devices to form wearable self-powered microsystems. Benefited from excellent flexibility, high output performance, no materials limitation, and a quantitative relationship between environmental stimulation inputs and corresponding electrical outputs, TENGs present great advantages in wearable energy harvesting, active sensing, and driving actuators. Furthermore, combined with the superiorities of TENGs and fabrics, textile-based TENGs (T-TENGs) possess remarkable breathability and better non-planar surface adaptability, which are more conducive to the integrated wearable electronic devices and attract considerable attention. Herein, for the purpose of advancing the development of wearable electronic devices, this article reviews the recent development in materials for the construction of T-TENGs and methods for the enhancement of electrical output performance. More importantly, this article mainly focuses on the recent representative work, in which T-TENGs-based active sensors, T-TENGs-based self-driven actuators, and T-TENGs-based self-powered microsystems are studied. In addition, this paper summarizes the critical challenges and future opportunities of T-TENG-based wearable integrated microsystems. Full article

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

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16 pages, 5360 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Silicon Carbide and MRI: Towards Developing a MRI Safe Neural Interface

by Mohammad Beygi, William Dominguez-Viqueira, Chenyin Feng, Gokhan Mumcu, Christopher L. Frewin, Francesco La Via and Stephen E. Saddow

Micromachines 2021, 12(2), 126; https://doi.org/10.3390/mi12020126 - 26 Jan 2021

Cited by 12 | Viewed by 4553

Abstract

An essential method to investigate neuromodulation effects of an invasive neural interface (INI) is magnetic resonance imaging (MRI). Presently, MRI imaging of patients with neural implants is highly restricted in high field MRI (e.g., 3 T and higher) due to patient safety concerns. [...] Read more.

An essential method to investigate neuromodulation effects of an invasive neural interface (INI) is magnetic resonance imaging (MRI). Presently, MRI imaging of patients with neural implants is highly restricted in high field MRI (e.g., 3 T and higher) due to patient safety concerns. This results in lower resolution MRI images and, consequently, degrades the efficacy of MRI imaging for diagnostic purposes in these patients. Cubic silicon carbide (3C-SiC) is a biocompatible wide-band-gap semiconductor with a high thermal conductivity and magnetic susceptibility compatible with brain tissue. It also has modifiable electrical conductivity through doping level control. These properties can improve the MRI compliance of 3C-SiC INIs, specifically in high field MRI scanning. In this work, the MRI compliance of epitaxial SiC films grown on various Si wafers, used to implement a monolithic neural implant (all-SiC), was studied. Via finite element method (FEM) and Fourier-based simulations, the specific absorption rate (SAR), induced heating, and image artifacts caused by the portion of the implant within a brain tissue phantom located in a 7 T small animal MRI machine were estimated and measured. The specific goal was to compare implant materials; thus, the effect of leads outside the tissue was not considered. The results of the simulations were validated via phantom experiments in the same 7 T MRI system. The simulation and experimental results revealed that free-standing 3C-SiC films had little to no image artifacts compared to silicon and platinum reference materials inside the MRI at 7 T. In addition, FEM simulations predicted an ~30% SAR reduction for 3C-SiC compared to Pt. These initial simulations and experiments indicate an all-SiC INI may effectively reduce MRI induced heating and image artifacts in high field MRI. In order to evaluate the MRI safety of a closed-loop, fully functional all-SiC INI as per ISO/TS 10974:2018 standard, additional research and development is being conducted and will be reported at a later date. Full article

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

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28 pages, 3995 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Next-Generation Diamond Electrodes for Neurochemical Sensing: Challenges and Opportunities

by Erin K. Purcell, Michael F. Becker, Yue Guo, Seth A. Hara, Kip A. Ludwig, Collin J. McKinney, Elizabeth M. Monroe, Robert Rechenberg, Cory A. Rusinek, Akash Saxena, James R. Siegenthaler, Caryl E. Sortwell, Cort H. Thompson, James K. Trevathan, Suzanne Witt and Wen Li

Micromachines 2021, 12(2), 128; https://doi.org/10.3390/mi12020128 - 26 Jan 2021

Cited by 24 | Viewed by 6821

Abstract

Carbon-based electrodes combined with fast-scan cyclic voltammetry (FSCV) enable neurochemical sensing with high spatiotemporal resolution and sensitivity. While their attractive electrochemical and conductive properties have established a long history of use in the detection of neurotransmitters both in vitro and in vivo, carbon [...] Read more.

Carbon-based electrodes combined with fast-scan cyclic voltammetry (FSCV) enable neurochemical sensing with high spatiotemporal resolution and sensitivity. While their attractive electrochemical and conductive properties have established a long history of use in the detection of neurotransmitters both in vitro and in vivo, carbon fiber microelectrodes (CFMEs) also have limitations in their fabrication, flexibility, and chronic stability. Diamond is a form of carbon with a more rigid bonding structure (sp³-hybridized) which can become conductive when boron-doped. Boron-doped diamond (BDD) is characterized by an extremely wide potential window, low background current, and good biocompatibility. Additionally, methods for processing and patterning diamond allow for high-throughput batch fabrication and customization of electrode arrays with unique architectures. While tradeoffs in sensitivity can undermine the advantages of BDD as a neurochemical sensor, there are numerous untapped opportunities to further improve performance, including anodic pretreatment, or optimization of the FSCV waveform, instrumentation, sp²/sp³ character, doping, surface characteristics, and signal processing. Here, we review the state-of-the-art in diamond electrodes for neurochemical sensing and discuss potential opportunities for future advancements of the technology. We highlight our team’s progress with the development of an all-diamond fiber ultramicroelectrode as a novel approach to advance the performance and applications of diamond-based neurochemical sensors. Full article

(This article belongs to the Special Issue Electrochemical Sensors for Neuroscience: Design, Fabrication and Performance)

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50 pages, 11413 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Electrophysiology Read-Out Tools for Brain-on-Chip Biotechnology

by Csaba Forro, Davide Caron, Gian Nicola Angotzi, Vincenzo Gallo, Luca Berdondini, Francesca Santoro, Gemma Palazzolo and Gabriella Panuccio

Micromachines 2021, 12(2), 124; https://doi.org/10.3390/mi12020124 - 24 Jan 2021

Cited by 38 | Viewed by 10950

Abstract

Brain-on-Chip (BoC) biotechnology is emerging as a promising tool for biomedical and pharmaceutical research applied to the neurosciences. At the convergence between lab-on-chip and cell biology, BoC couples in vitro three-dimensional brain-like systems to an engineered microfluidics platform designed to provide an in [...] Read more.

Brain-on-Chip (BoC) biotechnology is emerging as a promising tool for biomedical and pharmaceutical research applied to the neurosciences. At the convergence between lab-on-chip and cell biology, BoC couples in vitro three-dimensional brain-like systems to an engineered microfluidics platform designed to provide an in vivo-like extrinsic microenvironment with the aim of replicating tissue- or organ-level physiological functions. BoC therefore offers the advantage of an in vitro reproduction of brain structures that is more faithful to the native correlate than what is obtained with conventional cell culture techniques. As brain function ultimately results in the generation of electrical signals, electrophysiology techniques are paramount for studying brain activity in health and disease. However, as BoC is still in its infancy, the availability of combined BoC–electrophysiology platforms is still limited. Here, we summarize the available biological substrates for BoC, starting with a historical perspective. We then describe the available tools enabling BoC electrophysiology studies, detailing their fabrication process and technical features, along with their advantages and limitations. We discuss the current and future applications of BoC electrophysiology, also expanding to complementary approaches. We conclude with an evaluation of the potential translational applications and prospective technology developments. Full article

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

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10 pages, 2875 KiB

Open AccessFeature PaperEditor’s ChoiceCommunication

PyroMEMS as Future Technological Building Blocks for Advanced Microenergetic Systems

by Jean-Laurent Pouchairet and Carole Rossi

Micromachines 2021, 12(2), 118; https://doi.org/10.3390/mi12020118 - 23 Jan 2021

Cited by 14 | Viewed by 2987

Abstract

For the past two decades, many research groups have investigated new methods for reducing the size and cost of safe and arm-fire systems, while also improving their safety and reliability, through batch processing. Simultaneously, micro- and nanotechnology advancements regarding nanothermite materials have enabled [...] Read more.

For the past two decades, many research groups have investigated new methods for reducing the size and cost of safe and arm-fire systems, while also improving their safety and reliability, through batch processing. Simultaneously, micro- and nanotechnology advancements regarding nanothermite materials have enabled the production of a key technological building block: pyrotechnical microsystems (pyroMEMS). This building block simply consists of microscale electric initiators with a thin thermite layer as the ignition charge. This microscale to millimeter-scale addressable pyroMEMS enables the integration of intelligence into centimeter-scale pyrotechnical systems. To illustrate this technological evolution, we hereby present the development of a smart infrared (IR) electronically controllable flare consisting of three distinct components: (1) a controllable pyrotechnical ejection block comprising three independently addressable small-scale propellers, all integrated into a one-piece molded and interconnected device, (2) a terminal function block comprising a structured IR pyrotechnical loaf coupled with a microinitiation stage integrating low-energy addressable pyroMEMS, and (3) a connected, autonomous, STANAG 4187 compliant, electronic sensor arming and firing block. Full article

(This article belongs to the Special Issue Miniaturized Pyro Devices)

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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 3347

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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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 68 | Viewed by 6496

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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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 10 | Viewed by 3517

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 15 | Viewed by 5092

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 4 | Viewed by 4607

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 3585

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 65 | Viewed by 9535

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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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 7 | Viewed by 3355

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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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 11 | Viewed by 5181

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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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 22 | Viewed by 4199

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 30 | Viewed by 6429

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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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 22 | Viewed by 4454

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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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 14 | Viewed by 6551

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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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 12 | Viewed by 6357

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 21 | Viewed by 4735

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 6 | Viewed by 3678

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 4288

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 7 | Viewed by 4461

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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