Pinched Segment Research Articles

Toxicity Test of Apricot and Cassava by Using Albino Rats as an Experimental Model

Toxicity tests of Apricot (Prunus armeniaca L.; Prunus persica (L.) Stokes) seed, and Cassava (Manihot esculenta Crantz.) root, were studied by using albino rats as an experimental model. The specimens of liver taken from the albino rats after 30 days diet on crude extract seeds of Apricot show slight enlargement, increase in weight and pallor with increased turgor as compared to the specimens from the albino rats on normal diet. Histological sections of the liver taken from 30 days diet, show small clear vacuoles within the cytoplasm representing distended and pinched off segment of endoplasmic reticulum. There were swelling and increased eosinophillic staining of the cells in a panlobular fashion. The features were of hydropic change or vacuolar degeneration. The results of the study shows the degenerative changes present in the liver persisted in focal areas in the mice fed on apricot seed and in the periportal and peribular areas in the mice fed on cassava root.

Separations of spherical and disc-shaped polystyrene particles and blood components (red blood cells and platelets) using pinched flow fractionation device with a tilted sidewall and vertical focusing channels (t-PFF-v)

Shape-based separation capabilities of a novel pinched flow fractionation device with a tilted sidewall and vertical focusing channels (t-PFF-v) were demonstrated for (1) spherical and disc-shaped polystyrene (PS) particles; (2) platelets (PLT) and red blood cells (RBC); and (3) singlet, doublet, and triplet clusters of disc-shaped PS particles. The tilted sidewalls and vertical focusing channels of the t-PFF-v device allowed us to perform enhanced separation of non-spherical particles. Using this t-PFF-v device with a Wp (pinched segment width) of 20μm and 15μm, not only spherical (diameter of 2μm) and disc-shaped (thickness of ∼2μm, diameter of ∼5.0μm) PS particles but also PLTs and RBCs from diluted blood were well separated with good separation resolutions (Rdisc,sphere=1.40 and RPLT,RBC=1.28). Additionally, time-lapse images of flowing particles indicated that both disc-shaped PS particles and RBCs are probably having type I orientation in the pinched segment (i.e., leaning against the tilted sidewalls at the pinched segment). Moreover, we observed streamlines of singlet, doublet, and triplet clustered disc-shaped PS particles, which suggested that these clustered particles could be well separated according to their aspect ratio. The doublet or triplet clustered PS particles are probably lay on the floor and rotated at the pinched segment (type II orientation). We believe that this shape-based separation capability achieved by the t-PFF-v device can be utilized for many application areas, such as medical, biological, material and colloidal sciences.

Redesigned t-PFF-v device fabricated with one-step anisotropic chemical wet etching process: enhanced separation efficiency for colloidal particles in continuous-mode

A pinched flow fractionation device with trapezoid-shaped pinched segment and cross-flow side channels (t-PFF-v) was redesigned and fabricated with a one-stop anisotropic chemical wet etching process and its enhanced separation capability was demonstrated for spherical polystyrene (PS) particles with diameter ranges of 2–8 µm. The tilted sidewalls and vertical focusing channels of the t-PFF-v device led to an improved separation resolution (Rm,n) via enhanced separation distance of PS particles at the pinched segment (Δxm,n) and reduced effluent particle distribution width (sn). Using this t-PFF-v device with Wp (pinched segment width) of 25 µm, PS particles with diameters of 4, 6, and 8 µm were simultaneously separated with good separation resolution (R4,6 = 3.2 and R6,8 = 3.4). Moreover, by adapting even smaller pinched segment width (Wp = 15 µm), PS particles with diameters of 2 and 4 µm, not well separated in the previous studies, were clearly separated with 9.5-fold improvement in R2,4 compared with the normal PFF device (n-PFF). The effects of inlet flow rate ratio (Q2/Q1) on the separation efficiency were also carefully investigated and provided additional insight on the separation processes within the pinched segment of t-PFF-v device. The drain flow through the cross-flow v-channels helps better alignment of particles at the sidewall of pinched segment and resulted in significantly reduced distribution of effluent particles, even under the operating conditions with low Q2/Q1 values.

Acoustic bubble enhanced pinched flow fractionation for microparticle separation

Pinched flow fractionation is a simple method for separating micron-sized particles by size, but has certain intrinsic limitations, e.g. requirement of a pinched segment similar to particle size and limited separation distance. In this paper, we developed an acoustic bubble enhanced pinched flow fractionation (PFF) method for microparticle separation. The proposed technique utilized microbubble streaming flows to overcome the limitations of conventional PFF. Our device has demonstrated separation of different sized microparticles (diameters 10 and 2 μm) with a larger pinched segment (60 μm) and at different buffer/particle solution flow rate ratios (5–25). The separation distances between particles are larger (as much as twice as large) than those achieved with conventional PFF. In addition, the separation position and distance can be adjusted by changing the driving voltage. The robust performance is due to the unique features of the flow field inside the pinched segment. We investigated several factors, including flow rate ratio, total flow rate and driving voltage, that affect the separation performance.

Bubble sorting in pinched microchannels for ultrasound contrast agent enrichment.

Ultrasound contrast agent (UCA) suspensions contain encapsulated microbubbles with a wide size distribution, with radii between 1 and 10 μm. Medical transducers generally operate at a narrow frequency bandwidth, severely limiting the fraction of bubbles that resonates to the driving ultrasound. Thus, the sensitivity of contrast enhanced ultrasound imaging, molecular imaging with targeted bubbles, and drug delivery with microbubbles can be improved by narrowing down the size distribution of the bubble suspension. Here, we use a low-cost lab-on-a-chip method for the sorting of microbubbles by their size without external actuation, based on a microfluidic separation technique known as pinched flow fractionation (PFF). We show by numerical investigation that the inclusion of particle rotation in the pinched segment is essential for an accurate description of the sorting behavior of particles with sizes close to the pinched segment width. Successful enrichment of a polydisperse contrast agent into a bubble suspension with a narrow size distribution (radius 1.56 ± 0.30 μm) was achieved with a PFF-based microdevice. This sorting technique can be readily parallelized, and may thus lead to an easy-to-use and robust device capable of enriching ultrasound contrast agents, leading to an improvement in the sensitivity of contrast ultrasound imaging.

Lattice Boltzmann simulations of pinched flow fractionation

Direct numerical simulations of microsphere motion through a microfluidic separation device (pinched flow fractionation, PFF, device) were performed using the lattice Boltzmann method. The results were compared with the original experimental work on PFF by Yamada et al. (2004) . The effects of the pinched segment width and the ratio between the particle solution and diluent flow rates were studied. Both analyses showed agreement with the experimental trends. Previous modelling of PFF has relied on the assumption that particles follow streamlines, and this assumption was evaluated. The simulations indicated that large particles experience a lift force due to a region of low pressure between the particle and the wall of the pinch. The lift force attracts the particles to the wall as they exit the pinched segment. Smaller particles experience a much weaker force. This force may provide an explanation for the experimental observation that a sharp expansion provides better separation performance than a gradual expansion, an effect that cannot be explained by streamline analyses. ► Microfluidic pinched flow fractionation was simulated. ► Computed particle trajectories were consistent with experimental work in the literature. ► Particles do not follow streamlines when they interact with walls. ► Deviation was caused by low pressure region between particle and wall.

Using a circular groove surrounded inlet to generate monodisperse droplets inside a microfluidic chip in a gravity-driven manner

A new approach to generate uniform-sized nanoliter droplets inside a simple microfluidic chip was developed by using a circular groove to break off the liquid infused from the surrounded inlet. We characterized the droplet formation by using circular grooves with different diameters ranging from 1.2 to 2.4 mm. Monodisperse droplets with a very narrow size distribution (RSD < 0.56%, n = 70 droplets) can be reliably produced and the volume of droplets varied between 74 and 576 nl by using different circular grooves. Influences of liquid properties on droplet formation were also investigated, including surface tension, viscosity and density. Moreover, the transport of droplets and reliable coalescing of two neighboring droplets were realized by using Y-shaped guiding lanes with two different designs. Controlling the velocities of each droplet based on their different physical properties or slowing down the first droplet relying on a pinched segment of the guiding lane has been developed. These methods have been used to control the contact conditions of two reagents coalescing in a ‘head-to-tail’ mode.

Continuous and Size-Dependent Sorting of Emulsion Droplets Using Hydrodynamics in Pinched Microchannels

In this report, a microfluidic system is presented for continuous and size-dependent separation of droplets utilizing microscale hydrodynamics. The separation scheme is based on laminar-flow focusing and spreading in a pinched microchannel, referred to as "pinched flow fractionation (PFF)", which was previously developed for the size-dependent separation of solid particles, such as polymer microparticles or cells. By simply introducing emulsion and the continuous phase into a microchannel, continuous separation could be achieved without using complicated operations or devices. We first examined whether this scheme could be applied for droplets, by using a pinched microchannel with one outlet, and observed the behaviors of monodisperse droplets generated at the upstream T-junction. Analysis via high-speed imaging revealed that the length of the pinched segment is critical for precise separation of droplets. Then, separation of a polydisperse oil-in-water emulsion that was prepared previously was demonstrated using a microfluidic device equipped with multiple outlets. These results showed the ability of the presented system to sort or select specific-sized droplets easily and accurately, which would be difficult to achieve using normal-scale schemes, such as centrifugation or filtration.

Continuous particle separation in a microchannel having asymmetrically arranged multiple branches

A new method for continuous size separation and collection of particles in microfabricated devices, asymmetric pinched flow fractionation (AsPFF), has been proposed and demonstrated. This method improves the separation scheme of pinched flow fractionation (PFF), which utilizes a laminar flow profile inside a microchannel. In this study, multiple branch channels with different channel dimensions were arranged at the end of the pinched segment, so that the flow rate distributions to each branch channel were varied, and a large part of the liquid was forced to go through one branch channel (drain channel). In the proposed channel system, the flow profile inside the microchannel was asymmetrically amplified, enabling the separation of one-order smaller particles compared with PFF. After introducing the method, we examined the effect of the asymmetric amplification by controlling the outlet of the drain channel. Also, a mixture of 1.0 approximately 5.0 microm particles was separated, and erythrocytes were successfully separated from blood. The results indicate that the AsPFF method could be applied to the separation of much smaller-size particles, since more precise separation can be achieved simply by changing the geometries of branch channels.

Pinched flow fractionation: continuous size separation of particles utilizing a laminar flow profile in a pinched microchannel.

A concept of "pinched flow fractionation" for the continuous size separation and analysis of particles in microfabricated devices has been proposed and demonstrated. In this method, particles suspended in liquid were continuously introduced into a microchannel having a pinched segment and were aligned to one sidewall in the pinched segment by another liquid flow without particles. The particles were then separated perpendicularly to the flow direction according to their sizes by the spreading flow profile inside the microchannel. Polymer microbeads were successfully separated, and the effects of the flow rate and channel shapes on the separation performance were examined. Also, separated particles were collected independently by making branches at the end of the pinched segment. Since this method utilizes only the laminar flow profile inside a microchannel, complicated outer field control could be eliminated, which is usually required for other kinds of particle separation methods such as field flow fractionation. Also, this method can be applied both for particle size analysis and for preparation of monodispersed particles, since separation can be rapidly and continuously performed.