High throughput blood plasma separation using a passive PMMA microfluidic device

Since plasma is rich in many biomarkers used in clinical diagnostic experiments, microscale blood plasma separation is a primitive step in most of microfluidic analytical chips. In this paper, a passive microfluidic device for on-chip blood plasma separation based on Zweifach–Fung effect and plasma skimming was designed and fabricated by hot embossing of microchannels on a PMMA substrate and thermal bonding process. Human blood was diluted in various times and injected into the device. The main novelty of the proposed microfluidic device is the design of diffuser-shaped daughter channels. Our results demonstrated that this design exerted a considerable positive influence on the separation efficiency of the passive separator device, and the separation efficiency of 66.6 % was achieved. The optimum purity efficiency of 70 % was achieved for 1:100 dilution times.     

A comparison of different geometrical elements to model fluid wicking in paper-based microfluidic devices

Recently, microfluidic paper-based analytical devices (μPADs) have outstripped polymeric microfluidic devices in the ease of fabrication and simplicity. Surface tension-based fluid motion in the paper's porous structure has made the paper a suitable substrate for multiple biological assays by directing fluid into multiple assay zones. The widespread assumption in most works for modeling wicking in a paper is that the paper is a combination of capillaries with the same diameter equal to the effective pore diameter. Although assuming paper as a bundle of capillaries gives a good insight into pressure force that drives the fluid inside the paper, there are some difficulties using the effective pore radius. The effective pore radius is totally different from the average geometrical pore radius which makes it impossible to predict wicking in μPADs based on geometrical parameters. In this article, we introduce different analytical and numerical models to investigate the possibility of determining the permeability of the paper, based on geometrical parameters rather than effective parameters. The lattice Boltzmann method is used for numerical simulations. The permeability of each of the proposed models was compared with the experimental permeability. Results indicated that assuming paper as a combination of capillaries and annuluses leads to accurate results that totally depend on average geometrical values rather than effective values. This paves the way for prediction of the fluid wicking only by considering average geometrical pore and fiber diameters.     

Substance use and the paradox of good and bad attentional bias.

Habitual substance use is associated with attentional bias for stimuli related to the use. The current study tested whether individuals’ substance use can be predicted from their attentional bias for concern-related and substance-related stimuli. Participants (N = 71; 54% male) were selected among university students and the community. The study was conducted in Iran, in which alcohol consumption is illegal. Participants completed a substance use questionnaire and classic, substance-, and concern-related Stroop tests. The results show that after controlling for demographic variables and classic Stroop interference, increases in substance-related but decreases in concern-related reaction times predicted the amount of substances that had been consumed by the participants. Individuals’ attentional bias for both substance-related and substance-unrelated goals may be important in predicting substance use behavior. The implication of the findings for treatment prognosis has been discussed. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Control of austenitic transformation in ductile iron aided by calculation of Fe-C-Si-X phase boundaries

To control austenite transformation of ductile iron, thermodynamics procedures were used to calculate the Ae₃, the Gr/γ (A_cm), and the A₁ phase boundaries of high Mn and Ni-Cu-Mn alloyed iron as a function of austenitization temperature. The results of calculation show that segregation of Mn in the intergraphite regions reduces the carbon content of austenite at the Ae₃ phase boundary to the lowest value. If one ignores the effect of substitutional alloying elements on the nucleation of austenite, the austenite should first nucleate in the cell boundaries and then grow to the graphite nodules. In addition, the calculated results show that the A₁ temperature is the lowest in the intercellular region of a high Mn alloy. Therefore, if the austenitization temperature is not sufficiently high, only those parts of the matrix that have the A₁ phase boundary below the austenitization temperature transform to austenite, and dual formation of the α and γ phases will occur. By using the procedure introduced in this study, the volume fraction of each phase can be evaluated by calculating the A₁ phase boundary as a function of intergraphite distance. In the case of Ni-Cu-Mn alloy, Ni stabilizes austenite, which lowers the Ae₃ phase boundary. In this alloy, carbon content of austenite at the Ae₃ phase boundary is lower near the graphite nodule and higher in the intergraphite regions. However, the variation of carbon content of austenite at the Ae₃ phase boundary in the matrix of this alloy is much lower than in the high Mn alloy.     

Control of austenitic transformation in ductile iron aided by calculation of Fe-C-Si-X phase boundaries

To control austenite transformation of ductile iron, thermodynamics procedures were used to calculate the Ae₃, the Gr/γ (A_cm), and the A₁ phase boundaries of high Mn and Ni-Cu-Mn alloyed iron as a function of austenitization temperature. The results of calculation show that segregation of Mn in the intergraphite regions reduces the carbon content of austenite at the Ae₃ phase boundary to the lowest value. If one ignores the effect of substitutional alloying elements on the nucleation of austenite, the austenite should first nucleate in the cell boundaries and then grow to the graphite nodules. In addition, the calculated results show that the A₁ temperature is the lowest in the intercellular region of a high Mn alloy. Therefore, if the austenitization temperature is not sufficiently high, only those parts of the matrix that have the A₁ phase boundary below the austenitization temperature transform to austenite, and dual formation of the α and γ phases will occur. By using the procedure introduced in this study, the volume fraction of each phase can be evaluated by calculating the A₁ phase boundary as a function of intergraphite distance. In the case of Ni-Cu-Mn alloy, Ni stabilizes austenite, which lowers the Ae₃ phase boundary. In this alloy, carbon content of austenite at the Ae₃ phase boundary is lower near the graphite nodule and higher in the intergraphite regions. However, the variation of carbon content of austenite at the Ae₃ phase boundary in the matrix of this alloy is much lower than in the high Mn alloy.     

Design and simulation of a novel bipolar plate based on lung‐shaped bio‐inspired flow pattern for PEM fuel cell

Finding the optimal flow pattern in bipolar plates of a proton exchange membrane is a crucial step for enhancing the performance of the device. This design plays a critical role in fluid mass transport through microporous layers, charge transfer through conductive media, management of the liquid water produced in microchannels, and microporous layers and heat management in fuel cells. This article investigates different types of common flow patterns in bipolar plates while considering a uniform pressure and velocity distribution as well as a uniform distribution of reactants through all the surfaces of the catalyst layer as the design criteria so that there would be a consistent electron production by the catalyst layer. Then, by identifying the important parameters in achieving the best performance of a fuel cell, a microfluidic flow pattern is inspired from the lungs in the human body, and an innovative bipolar plate is suggested, which was not proposed before. Afterwards, numerical simulations were carried out using computational fluid dynamics methods, and the mentioned bipolar plate called lung‐shaped bipolar plate was modeled. Simulations in this research showed that the lung‐shaped microfluidic flow pattern is an appropriate flow pattern to gain maximum power and energy density. In other words, the best polarization curve and power density curve are obtained by using the lung‐shaped bipolar plate in a proton exchange membrane fuel cell compared with previously suggested patterns. Copyright © 2017 John Wiley & Sons, Ltd.     

Sublethal in vitro glucose-oxygen deprivation protects cultured hippocampal neurons against a subsequent severe insult

Rat and gerbil hippocampus exposed to a sublethal period of ischemia becomes resistant to a subsequent period of lethal ischemia induced several days later, a phenomenon referred to as ischemic preconditioning. Here we describe ischemic preconditioning induced in vitro in cultured hippocampal neurons. Mixed neuroglial hippocampal cell cultures of 14-17 DIV were exposed to a combined glucose and oxygen deprivation (GOD). Cultures subjected to 90 min, but not 60 min, of GOD showed extensive degeneration after a 1 day recovery period. An episode of 60 min of preconditioning GOD followed 1 and 2 days later by 90 min of GOD resulted in 40-60% protection. The data demonstrate that ischemic preconditioning can be mimicked in an in vitro hippocampal cell culture system.     

Performance optimization of microreactors by implementing geometrical and fluid flow control in the presence of electric field: a computational study

A two dimensional rectangular microchannel with circular micropillars was modeled in the presence of an electric field. Continuity and Navier–Stokes equations were solved along with convection–diffusion equation using finite element method. Reaction phenomenon was applied via a partial differential equation on the reaction surfaces and electric force was added as a source term to the transport equations. Velocity, concentration and electric potential distributions were obtained, with the aid of which, capture efficiency and average surface concentration of reaction surfaces were calculated. To ameliorate the reaction rate, different designs of reaction surfaces were investigated; the designs with four, five and six micropillars. The importance of flow specifications in the microreactor was inspected through varying a non-dimensionalized parameter, i.e. Peclet number. The electric field was implemented on the microchannel’s upper and lower walls and its effect on the performance of the device was studied. Different voltages were applied and the results were compared to the case without an electric field. The efficiency of the microreactors was observed to be dependent on the geometry of the reaction surfaces as well as the inlet velocity magnitude of the bulk flow and the electric field magnitude. It was observed that by increasing the inlet velocity, the flow regime became convection dominant. Therefore, the diffusion effect was minimized and the efficiency of the device lessened. It was also observed that in all cases, the presence of the electric field enhanced the reaction efficiency by pushing the flow towards the reaction surfaces. The six micropillar arrangement was shown to be the optimum design by analyzing both capture efficiency and average surface concentration.     

Exploring contraction–expansion inertial microfluidic-based particle separation devices integrated with curved channels

Separation of particles or cells has various applications in biotechnology, pharmaceutical and chemical industry. Inertial cell separation, in particular, has been gaining a great attention in the recent years since it has exhibited a label-free, high-throughput and efficient performance. In this work, first, an inertial contraction–expansion array microchannel device, capable of passively separating two particles with diameters of 4 and 10 μm, was numerically studied. Then, the validated model was combined with curved geometries in order to investigate the effect of curve features on the separation process. The overall purpose was to investigate the interaction between the two different separation methods (separation with curved channels and with contraction–expansion arrays) to find an ideal model that can enjoy the merits of both contraction–expansion and curved channel based methods. Moreover, the relation between separation strength and the aspect ratio in the contraction and expansion zones of the simulated model as well as its height were examined. Then, a new model that combines the curved and the contraction–expansion geometries was tested for its efficiency. This new geometry showed that separation could be achieved with shorter lengths compared with straight contraction–expansion geometries.     

Microfluidic‐Based Approaches in Targeted Cell/Particle Separation Based on Physical Properties: Fundamentals and Applications

Cell separation is a key step in many biomedical research areas including biotechnology, cancer research, regenerative medicine, and drug discovery. While conventional cell sorting approaches have led to high‐efficiency sorting by exploiting the cell's specific properties, microfluidics has shown great promise in cell separation by exploiting different physical principles and using different properties of the cells. In particular, label‐free cell separation techniques are highly recommended to minimize cell damage and avoid costly and labor‐intensive steps of labeling molecular signatures of cells. In general, microfluidic‐based cell sorting approaches can separate cells using “intrinsic” (e.g., fluid dynamic forces) versus “extrinsic” external forces (e.g., magnetic, electric field, etc.) and by using different properties of cells including size, density, deformability, shape, as well as electrical, magnetic, and compressibility/acoustic properties to select target cells from a heterogeneous cell population. In this work, principles and applications of the most commonly used label‐free microfluidic‐based cell separation methods are described. In particular, applications of microfluidic methods for the separation of circulating tumor cells, blood cells, immune cells, stem cells, and other biological cells are summarized. Computational approaches complementing such microfluidic methods are also explained. Finally, challenges and perspectives to further develop microfluidic‐based cell separation methods are discussed.