Microfluidic Generation of Nanomaterials for Biomedical Applications

As nanomaterials (NMs) possess attractive physicochemical properties that are strongly related to their specific sizes and morphologies, they are becoming one of the most desirable components in the fields of drug delivery, biosensing, bioimaging, and tissue engineering. By choosing an appropriate methodology that allows for accurate control over the reaction conditions, not only can NMs with high quality and rapid production rate be generated, but also designing composite and efficient products for therapy and diagnosis in nanomedicine can be realized. Recent evidence implies that microfluidic technology offers a promising platform for the synthesis of NMs by easy manipulation of fluids in microscale channels. In this Review, a comprehensive set of developments in the field of microfluidics for generating two main classes of NMs, including nanoparticles and nanofibers, and their various potentials in biomedical applications are summarized. Furthermore, the major challenges in this area and opinions on its future developments are proposed.     

Cell Docking in Double Grooves in a Microfluidic Channel

Microstructures that generate shear‐protected regions in microchannels can rapidly immobilize cells for cell‐based biosensing and drug screening. Here, a two‐step fabrication method is used to generate double microgrooves with various depth ratios to achieve controlled double‐level cell patterning while still providing shear protection. Six microgroove geometries are fabricated with different groove widths and depth ratios. Two modes of cell docking are observed: cells docked upstream in sufficiently deep and narrow grooves, and downstream in shallow, wide grooves. Computational flow simulations link the groove geometry and bottom shear stress to the experimental cell docking patterns. Analysis of the experimental cell retention in the double grooves demonstrates its linear dependence on inlet flow speed, with slope inversely proportional to the sheltering provided by the groove geometry. Thus, double‐grooved microstructures in microfluidic channels provide shear‐protected regions for cell docking and immobilization and appear promising for cell‐based biosensing and drug discovery.     

On‐Chip Generation of Vortical Flows for Microfluidic Centrifugation

Microcentrifugation constitutes an important part of the microfluidic toolkit in a similar way that centrifugation is crucial to many macroscopic procedures, given that micromixing, sample preconcentration, particle separation, component fractionation, and cell agglomeration are essential operations in small scale processes. Yet, the dominance of capillary and viscous effects, which typically tend to retard flow, over inertial and gravitational forces, which are often useful for actuating flows and hence centrifugation, at microscopic scales makes it difficult to generate rotational flows at these dimensions, let alone with sufficient vorticity to support efficient mixing, separation, concentration, or aggregation. Herein, the various technologies—both passive and active—that have been developed to date for vortex generation in microfluidic devices are reviewed. Various advantages or limitations associated with each are outlined, in addition to highlighting the challenges that need to be overcome for their incorporation into integrated microfluidic devices.     

喷射式微流体滴化机理的研究及应用

喷射式流体滴化技术作为一种高效精确的微小体积流体分配方式,已应用于诸多科技领域．为实现一种高效稳定的晶片标示打点器,根据计算流体力学理论对流体喷射滴化的过程进行数学建模,通过有限体积法对喷嘴内径为0．1mm时液滴的生成和分离过程进行了数值模拟计算和理论分析．开发设计了由音圈电机驱动的喷射机构进行滴化实验,探讨了将其应用于晶片打点标示的可行性．数值仿真和实验数据都表明,非接触式喷射技术的引入,有效地提高了打点效率,改善了所得墨点的一致性,并减少了拖尾和卫星滴现象．     

A Polymer Microfluidic Chip With Interdigitated Electrodes Arrays for Simultaneous Dielectrophoretic Manipulation and Impedimetric Detection of Microparticles

This paper presents the design, fabrication, and characterization of a polymer microfluidic biochip with integrated interdigitated electrodes arrays (IDAs) used to simultaneously separate, manipulate, and detect microparticles using dielectrophoresis (DEP) and electrochemical impedance spectroscopy (EIS) methods. The DEP response of silica microspheres has been characterized, and microspheres of different sizes (1.8 and 3.5 in diameter) have been DEP flow separated and individually trapped in different microchambers by IDAs in a single run. Simultaneously, the impedance change caused by microspheres captured on IDAs has been analyzed for quantification. High-throughput polymer microfabrication techniques such as micro injection molding were used in this work, so that the polymer microfluidic chip can be produced in a low-cost, disposable platform. This low-cost microfluidic chip provides a generic platform for developing multifunctional lab-on-a-chip devices that require the ability to handle and sense microparticles.     

Sample Exposition System for Plasma Analysis of a Fusion Reactor

Plasma diagnosis of a fusion reactor can be performed by means of samples which first are exposed to the plasma and then investigated by surface analysis techniques. Construction and tests of such a diagnosis system are described. This system uses a demountable sample chamber in which the samples can be transported under UHV conditions to a distant laboratory for surface analysis.     

Microfluidic Generation of All‐Aqueous Double and Triple Emulsions

Higher order emulsions are used in a variety of different applications in biomedicine, biological studies, cosmetics, and the food industry. Conventional droplet generation platforms for making higher order emulsions use organic solvents as the continuous phase, which is not biocompatible and as a result, further washing steps are required to remove the toxic continuous phase. Recently, droplet generation based on aqueous two‐phase systems (ATPS) has emerged in the field of droplet microfluidics due to their intrinsic biocompatibility. Here, a platform to generate all‐aqueous double and triple emulsions by introducing pressure‐driven flows inside a microfluidic hybrid device is presented. This system uses a conventional microfluidic flow‐focusing geometry coupled with a coaxial microneedle and a glass capillary embedded in flow‐focusing junctions. The configuration of the hybrid device enables the focusing of two coaxial two‐phase streams, which helps to avoid commonly observed channel‐wetting problems. It is shown that this approach achieves the fabrication of higher‐order emulsions in a poly(dimethylsiloxane)‐based microfluidic device, and controls the structure of the all‐aqueous emulsions. This hybrid microfluidic approach allows for facile higher‐order biocompatible emulsion formation, and it is anticipated that this platform will find utility for generating biocompatible materials for various biotechnological applications.     

Hierarchical CdS Nanorod@SnO2 Nanobowl Arrays for Efficient and Stable Photoelectrochemical Hydrogen Generation

An efficient photoanode based on CdS nanorod@SnO₂ nanobowl (CdS NR@SnO₂ NB) arrays is designed and fabricated by the preparation of SnO₂ nanobowl arrays via nanosphere lithography followed by hydrothermal growth of CdS nanorods on the inner surface of the SnO₂ nanobowls. A photoelectrochemical (PEC) device constructed by using this hierarchical CdS NR@SnO₂ NB photoanode presents significantly enhanced performance with a photocurrent density of 3.8 mA cm^?2 at 1.23 V versus a reversible hydrogen electrode (RHE) under AM1.5G solar light irradiation, which is about 2.5 times higher than that of CdS nanorod arrays. After coating with a thin layer of SiO₂, the photostability of the CdS NR@SnO₂ NB arrays is greatly enhanced, resulting in a stable photoanode with a photocurrent density of 3.0 mA cm^?2 retained at 1.23 V versus the RHE. The much improved performance of the CdS NR@SnO₂ NB arrays toward PEC hydrogen generation can be ascribed to enlarged surface area arising from the hierarchical nanostructures, improved light harvesting owing to the NR@NB architecture containing multiple scattering centers, and enhanced charge separation/collection efficiency due to the favorable CdS–SnO₂ heterojunction.     

Failure Analysis of a Reactor in Ethylbenzene Unit

In this study, failure of the cone of a reactor in an ethylbenzene unit of a petrochemical complex has been investigated. The material of the cone was found to be ASME A240 Type 304H which was severely corroded at elevated temperature. The study of the microstructure of the material showed the occurrence of carburization which led to sensitization and resulted in corrosion of the material. The result of the microhardness testing and double-loop electrochemical polarization investigation proved the diffusion of carbon through the material and occurrence of sensitization.     

A Genetic Algorithm Applied for Optimization of Antenna Arrays Used in Mobile Radio Channel Characterization Devices

This paper presents a proposed method for synthesizing scenario-dependent channel characterization system arrays that are adapted to the mobile radio environment where measurements take place. The criterion for synthesizing the array is the minimization of the angular CramÉr–Rao lower bound, which is the lower bound of the mean square estimation error (MSEE) for an unbiased estimator. The core of the process is a genetic algorithm (GA) that seeks for the most advantageous array topology for each scenario. Simulation results show that the method succeeds in synthesizing feasible antenna arrays that have increased direction of arrival (DoA) estimation accuracy and are superior to the arrays typically used during actual measurement campaigns.      

A Microfluidic Strategy for Controllable Generation of Water‐in‐Water Droplets as Biocompatible Microcarriers

Droplet microfluidics has been widely applied in functional microparticles fabricating, tissue engineering, and drug screening due to its high throughput and great controllability. However, most of the current droplet microfluidics are dependent on water‐in‐oil (W/O) systems, which involve organic reagents, thus limiting their broader biological applications. In this work, a new microfluidic strategy is described for controllable and high‐throughput generation of monodispersed water‐in‐water (W/W) droplets. Solutions of polyethylene glycol and dextran are used as continuous and dispersed phases, respectively, without any organic reagents or surfactants. The size of W/W droplets can be precisely adjusted by changing the flow rate of dispersed and continuous phases and the valve switch cycle. In addition, uniform cell‐laden microgels are fabricated by introducing the alginate component and rat pancreatic islet (β‐TC6) cell suspension to the dispersed phase. The encapsulated islet cells retain high viability and the function of insulin secretion after cultivation for 7 days. The high‐throughput droplet microfluidic system with high biocompatibility is stable, controllable, and flexible, which can boost various chemical and biological applications, such as bio‐oriented microparticles synthesizing, microcarriers fabricating, tissue engineering, etc.