Micromachines

15 pages, 1649 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

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

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

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

Cited by 6 | Viewed by 4022

Abstract

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

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

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

► Show Figures

Figure 1

12 pages, 2577 KiB

Open AccessFeature PaperEditor’s ChoiceCommunication

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

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

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

Cited by 9 | Viewed by 3338

Abstract

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

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

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

► Show Figures

Figure 1

19 pages, 5184 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Biocompatibility of SU-8 and Its Biomedical Device Applications

by Ziyu Chen and Jeong-Bong Lee

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

Cited by 33 | Viewed by 4957

Abstract

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

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

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

► Show Figures

Figure 1

16 pages, 12537 KiB

Open AccessFeature PaperEditor’s ChoiceReview

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

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

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

Cited by 22 | Viewed by 4475

Abstract

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

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

► Show Figures

Figure 1

19 pages, 3579 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Machine Assisted Experimentation of Extrusion-Based Bioprinting Systems

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

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

Cited by 26 | Viewed by 4422

Abstract

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

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

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

► Show Figures

Figure 1

13 pages, 2890 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Fabrication of Ultranarrow Nanochannels with Ultrasmall Nanocomponents in Glass Substrates

by Hiroki Kamai and Yan Xu

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

Cited by 13 | Viewed by 3844

Abstract

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

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

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

► Show Figures

Figure 1

9 pages, 2300 KiB

Open AccessFeature PaperEditor’s ChoiceCommunication

Large-Area and Ultrathin MEMS Mirror Using Silicon Micro Rim

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

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

Cited by 6 | Viewed by 3176

Abstract

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

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

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

► Show Figures

Graphical abstract

17 pages, 3541 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Functionalized Mesoporous Thin Films for Biotechnology

by Barbara Sartori, Heinz Amenitsch and Benedetta Marmiroli

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

Cited by 10 | Viewed by 3283

Abstract

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

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

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

► Show Figures

Graphical abstract

19 pages, 1190 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Geometric Methods for Efficient Planar Swimming of Copepod Nauplii

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

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

Cited by 1 | Viewed by 2071

Abstract

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

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

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

► Show Figures

Figure 1

14 pages, 7061 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

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

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

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

Cited by 5 | Viewed by 3172

Abstract

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

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

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

► Show Figures

Figure 1

12 pages, 2573 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

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

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

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

Cited by 28 | Viewed by 4827

Abstract

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

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

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

► Show Figures

Figure 1

16 pages, 54577 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

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

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

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

Cited by 10 | Viewed by 3939

Abstract

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

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

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

► Show Figures

Figure 1

13 pages, 3323 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

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

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

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

Cited by 6 | Viewed by 3212

Abstract

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

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

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

► Show Figures

Figure 1

19 pages, 5654 KiB

Open AccessFeature PaperEditor’s ChoiceReview

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

by Mohammad Javad Mirshojaeian Hosseini and Robert A. Nawrocki

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

Cited by 59 | Viewed by 9104

Abstract

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

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

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

► Show Figures

Graphical abstract

27 pages, 3878 KiB

Open AccessFeature PaperEditor’s ChoiceReview

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

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

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

Cited by 32 | Viewed by 8877

Abstract

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

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

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

► Show Figures

Figure 1

31 pages, 8928 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Lateral-Type Spin-Photonics Devices: Development and Applications

by Nozomi Nishizawa and Hiro Munekata

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

Cited by 18 | Viewed by 4603

Abstract

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

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

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

► Show Figures

Figure 1

45 pages, 13379 KiB

Open AccessFeature PaperEditor’s ChoiceReview

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

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

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

Cited by 18 | Viewed by 8018

Abstract

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

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

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

► Show Figures

Figure 1

36 pages, 8285 KiB

Open AccessFeature PaperEditor’s ChoiceReview

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

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

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

Cited by 15 | Viewed by 7249

Abstract

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

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

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

► Show Figures

Figure 1

17 pages, 4068 KiB

Open AccessFeature PaperEditor’s ChoiceReview

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

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

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

Cited by 18 | Viewed by 4734

Abstract

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

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

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

► Show Figures

Figure 1

9 pages, 1810 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

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

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

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

Cited by 9 | Viewed by 3092

Abstract

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

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

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

► Show Figures

Figure 1

20 pages, 5397 KiB

Open AccessFeature PaperEditor’s ChoiceReview

Plasmon Induced Photocatalysts for Light-Driven Nanomotors

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

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

Cited by 8 | Viewed by 3855

Abstract

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

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

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

► Show Figures

Graphical abstract

10 pages, 2569 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Printing a Pacinian Corpuscle: Modeling and Performance

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

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

Cited by 1 | Viewed by 3192

Abstract

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

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

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

► Show Figures

Figure 1

17 pages, 35517 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

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

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

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

Cited by 18 | Viewed by 6018

Abstract

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

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

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

► Show Figures

Figure 1

14 pages, 3873 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

A Novel Approach for a Chip-Sized Scanning Optical Microscope

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

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

Cited by 2 | Viewed by 3294

Abstract

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

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

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

► Show Figures

Figure 1

28 pages, 66273 KiB

Open AccessFeature PaperEditor’s ChoiceReview

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

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

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

Cited by 7 | Viewed by 5688

Abstract

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

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

► Show Figures

Figure 1

22 pages, 14527 KiB

Open AccessFeature PaperEditor’s ChoiceReview

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

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

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

Cited by 18 | Viewed by 6075

Abstract

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

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

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

► Show Figures

Figure 1

10 pages, 4477 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

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

by Nam Phuong Ha, Tomoji Ohishi and Mizue Mizoshiri

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

Cited by 10 | Viewed by 2755

Abstract

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

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

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

► Show Figures

Figure 1

18 pages, 2426 KiB

Open AccessFeature PaperEditor’s ChoicePerspective

Glioma-on-a-Chip Models

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

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

Cited by 25 | Viewed by 5642

Abstract

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

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

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

► Show Figures

Figure 1

28 pages, 5806 KiB

Open AccessFeature PaperEditor’s ChoiceReview

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

by Aimable Kalume, Chuji Wang and Yong-Le Pan

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

Cited by 13 | Viewed by 5215

Abstract

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

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

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

► Show Figures

Figure 1

13 pages, 3118 KiB

Open AccessFeature PaperEditor’s ChoiceArticle

Switchable Transducers in GaN MEMS Resonators: Performance Comparison and Analysis

by Imtiaz Ahmed and Dana Weinstein

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

Cited by 2 | Viewed by 3249

Abstract

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

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

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

► Show Figures

Figure 1

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 27 | Viewed by 7340

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)

► Show Figures

Figure 1

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 59 | Viewed by 9830

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)

► Show Figures

Figure 1

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 2549

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)

► Show Figures

Figure 1

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 9 | Viewed by 4496

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)

► Show Figures

Figure 1

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 60 | Viewed by 10036

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)

► Show Figures

Figure 1

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 11 | Viewed by 3529

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)

► Show Figures

Figure 1

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 9 | Viewed by 6040

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)

► Show Figures

Graphical abstract

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 13 | Viewed by 3343

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)

► Show Figures

Figure 1

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 26 | Viewed by 4067

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

► Show Figures

Figure 1

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 5 | Viewed by 4282

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)

► Show Figures

Figure 1

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 74 | Viewed by 6692

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)

► Show Figures

Figure 1

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 4139

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)

► Show Figures

Figure 1

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 14 | Viewed by 3904

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)

► Show Figures

Figure 1

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 12 | Viewed by 4182

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)

► Show Figures

Graphical abstract

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 6 | Viewed by 2695

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

► Show Figures

Figure 1

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 23 | Viewed by 4231

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)

► Show Figures

Figure 1

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 15 | Viewed by 3690

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)

► Show Figures

Graphical abstract

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 34 | Viewed by 4953

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)

► Show Figures

Figure 1

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 31 | Viewed by 6058

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)

► Show Figures

Figure 1

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 28 | Viewed by 4101

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

► Show Figures

Figure 1

Journal Menu

Journal Browser

Editor’s Choice Articles

Further Information

Guidelines

MDPI Initiatives

Follow MDPI