1,723,051 research outputs found
Microfluidic-based speckle analysis for sensitive measurement of erythrocyte aggregation: A comparison of four methods for detection of elevated erythrocyte aggregation in diabetic rat blood
No full textBiochemical alterations in the plasma and red blood cell (RBC) membrane of diabetic blood lead to excessive erythrocyte aggregation (EA). EA would significantly impede the blood flow and increase the vascular flow resistance contributing to peripheral vascular diseases. In this study, a simple microfluidicbased method is proposed to achieve sensitive detection of hyperaggregation. When a blood sample is delivered into the device, images of blood flows are obtained with a short exposure time for a relatively long measuring time. A microparticle image velocimetry technique was employed to monitor variation of the flow rate of blood as a function of time. Given that EA formation in the channel creates clear speckle patterns, the EA extent can be estimated by calculating a speckle area (A(Speckle)) through a normalized autocovariance function. The hematocrit effect is assessed by comparing optical images transmitted through blood samples. EA variations caused by dextran treatment are quantitatively evaluated using characteristic time (lambda(Speckle)) obtained by fitting the variations of A(Speckle). Other indices including number of RBCs in an aggregate (N-RBC), characteristic time of erythrocyte sedimentation rate (lambda(ESR)), and aggregation index estimated from ultrasound signals (AI(Echo)) are determined under different EA conditions using conventional techniques. The four different methods are applied to diabetic blood samples to compare their indices under hyperaggregation conditions. It is found that the proposed method can detect variation of EA reasonably, compared with conventional measurement techniques. These experimental demonstrations support the notion that the proposed method is capable of effectively monitoring the biophysical properties of diabetic blood. (C) 2015 AIP Publishing LLC.11169sciescopu
Optimum periodicity of repeated contractile actions applied in mass transport
Full text linkDynamically repeated periodic patterns are abundant in natural and artificial systems, such as tides, heart beats, stock prices, and the like. The characteristic repeatability and periodicity are expected to be optimized in effective system-specific functions. In this study, such optimum periodicity is experimentally evaluated in terms of effective mass transport using one-valve and multi-valve systems working in contractile fluid flows. A set of nanoscale gating functions is utilized, operating in nanocomposite networks through which permeates selectively pass under characteristic contractile actions. Optimized contractile periodicity exists for effective energy impartment to flow in a one-valve system. In the sequential contractile actions for a multi-valve system, synchronization with the fluid flow is critical for effective mass transport. This study provides fundamental understanding on the various repeated periodic patterns and dynamic repeatability occurring in nature and mechanical systems, which are useful for broad applications.1110Ysciescopu
Stomata-Inspired membrane produced through photopolymerization patterning
No full textThe programmed movements of responsive functional hydrogels have received much attention because of their abundant functions and wide range of engineering applications. In this study, an innovative stomata-inspired membrane (SIM) is fabricated by using a temperature-responsive hydrogel through a simple, cost-effective, and high-throughput patterned photopolymerization. Polymerization-induced diffusion on the macroscale surface results in formation of a double-parted polymer membrane with fine pores after single illumination. After heating the SIM, the less deformable thick frame supports the whole structure and the highly deformable thin base regulates pore shape. Among various SIM types, the slit pores of monocot SIM, which are lined up in parallel, exhibit the largest radius deformation. The morphological configuration of the SIM can be easily controlled by changing the photomask for a given application. As the developed SIM features the sensing-to-activation functions of stimuli-responsive hydrogels and can be easily fabricated, this membrane can be potentially used for numerous practical applications, such as filter membranes with adjustable pores, membrane-based sensors, membrane-based actuators, and multifunctional membranes.11118sciescopu
Suppression of constant-light-induced blindness but not retinal degeneration by inhibition of the rhodopsin degradation pathway
No full textBackground: Continuous exposure to light, even at relatively low intensities, leads to retinal damage and blindness in wild-type animals. However, the molecular mechanisms underlying constant-light-induced blindness are poorly understood. It has been presumed that the visual impairment resulting from long-term, continuous exposure to ambient light is a secondary consequence of the effects of light on retinal morphology, but this has not been addressed. Results: To characterize the mechanism underlying light-induced blindness, we applied a molecular genetic approach using the fruit fly, Drosophila melanogaster. We found that the temporal loss of the photoresponse was paralleled by a gradual decline in the concentration of rhodopsin. The decline in rhodopsin and the visual response were suppressed by a C-terminal truncation of rhodopsin, by mutations in arrestin, and by elimination of a lysosomal protein, Sunglasses. Conversely, the visual impairment was greatly enhanced by mutation of the rhodopsin phosphatase, rdgC. Surprisingly, the mutations that suppressed light-induced blindness did not reduce the severity of the retinal degeneration resulting from constant light. Moreover, mutations known to suppress retinal degeneration did not ameliorate the light-induced blindness. Conclusions: These data demonstrate that the constant light-induced blindness and retinal degeneration result from defects in distinct molecular pathways. Our results support a model in which visual impairment caused by continuous illumination occurs through an arrestin-dependent pathway that promotes degradation of rhodopsin.1121sciescopu
Collective ordering of microscale matters in natural analogy
Full text linkCollective interaction occurs in many natural and artificial matters in broad scales. In a biological system, collective spatial organization of live individuals in a colony is important for their viability determination. Interactive motions between a single individual and an agglomerate are critical for whole procedure of the collective behaviors, but few has been clarified for these intermediate range behaviors. Here, collective interactions of microscale matters are investigated with human cells, plant seeds and artificial microspheres in terms of commonly occurring spatial arrangements. Human cancer cells are inherently attractive to form an agglomerate by cohesive motion, while plant chia seeds are repulsive by excreting mucilage. Microsphere model is employed to investigate the dynamic assembly equilibrated by an attraction and repulsion. There is a fundamental analogy in terms of an onset of regular pattern formation even without physical contact of individuals. The collective interactions are suggested to start before the individual components become physically agglomerated. This study contributes to fundamental understanding on the microscale particulate matters and natural pattern formation which are further useful for various applications both in academic and industrial areas.110Ysciescopu
Dehydration-mediated cluster formation of nanoparticles
Full text linkDrying procedure is a powerful method to modulate the bottom-up assembly of basic building component. The initially weak attraction between the components screened in a solution strengthens as the solvent evaporates, organizing the components into structures. Drying is process-dependent, irreversible, and nonequilibrated, thus the mechanism and the dynamics are influenced by many factors. Therefore, the interaction of the solvent and the elements during the drying procedure as well as the resulting pattern formations are strongly related. Nonetheless still many things are open in questions in terms of their dynamics. In this study, nanoscale dehydration procedure is experimentally investigated using a nanoparticle (NP) model system. The role of water is verified in a single NP scale and the patterns of collective NP clusters are determined. Stepwise drying procedures are proposed based on the location from which water is removed. Effective water exodus from a unit NP surface enhances the attractive interaction in nanoscale and induces heterogeneous distribution in microscale. This study provides fundamental proof of systematic relation between the dehydration process and the resultant cluster patterns in hierarchical multiscales.110Ysciescopu
Relationship between velocity profile and ultrasound echogenicity in pulsatile blood flows
No full textPulsatile blood flows are easily found in the vessels of living organisms. Under pulsatile flow conditions, red blood cells (RBCs) are aggregated and dispersed repetitively. The phenomenon of RBC aggregation is an influential factor in hemorheological and hemodynamic properties. This study aims to investigate the relationship between velocity profile and RBC aggregation in pulsatile blood flows. A rat extracorporeal bypass model was adopted to generate a real pulsatile flow without changing the rheological properties. To check the stability of the experimental model, variations of the hemodynamic parameters were measured consecutively for 2 h. Ultrasound speckle images of the blood flow in the extracorporeal bypass loop were acquired using a 35-MHz ultrasound scanner. The velocity fields were measured by the speckle image velocimetry (SIV) method, in which the cross-correlation algorithm is applied to the speckle images. In addition, the RBC aggregation was estimated by analyzing the echogenicity distribution of the speckle images. The shape of the velocity profile was cyclically varied according to the cardiac cycle. This variation may be closely related to the variation of the echogenicity distribution in pulsatile flows. The simultaneous measurement of velocity and RBC aggregation would be useful for understanding the effects of the hemorheological features on the hemodynamic characteristics of pulsatile blood flows.1122sciescopu
Detaching droplets in immiscible fluids from a solid substrate with the help of electrowetting
No full textThe detachment (or removal) of droplets from a solid surface is an indispensable process in numerous practical applications which utilize digital microfluidics, including cell-based assay, chip cooling, and particle sampling. When a droplet that is fully stretched by impacting or electrowetting is released, the conversion of stored surface energy to kinetic energy can lead to the departure of the droplet from a solid surface. Here we firstly detach sessile droplets in immiscible fluids from a hydrophobic surface by electrowetting. The physical conditions for droplet detachment depend on droplet volume, viscosity of ambient fluid, and applied voltage. Their critical conditions are determined by exploring the retracting dynamics for a wide range of driving voltages and physical properties of fluids. The relationships between physical parameters and dynamic characteristics of retracting and jumping droplets, such as contact time and jumping height, are also established. The threshold voltage for droplet detachment in oil with high viscosity is largely reduced (similar to 70%) by electrowetting actuations with a square pulse. To examine the applicability of three-dimensional digital microfluidic (3D-DMF) platforms to biological applications such as cell culture and cell-based assays, we demonstrate the detachment of droplets containing a mixture of human umbilical vein endothelial cells (HUVECs) and collagen (concentration of 4 x 104 cells mL(-1)) in silicone oil with a viscosity of 0.65 cSt. Furthermore, to complement the technical limitations due to the use of a needle electrode and to demonstrate the applicability of the 3D-DMF platform with patterned electrodes to chemical analysis and synthesis, we examine the transport, merging, mixing, and detachment of droplets with different pH values on the platform. Finally, by using DC and AC electrowetting actuations, we demonstrate the detachment of oil droplets with a very low contact angle (<similar to 13 degrees) in water on a hydrophobic surface.1199sciescopu
Murray's law and the bifurcation angle in the arterial micro-circulation system and their application to the design of microfluidics
No full textMurray's law which is related to the bifurcations of vascular blood vessels states that the cube of a parent vessel's diameter equals the sum of the cubes of the daughter vessels' diameters D-0(3) - D-1(3) + D-2(3), alpha - D-0(3)/(D-1(3) + D-2(3)) - 1, where D-0, D-1, and D-2 are the diameters of the parent and two daughter vessels, respectively and a is the ratio). The structural characteristics of the vessels are crucial in the development of the cardiovascular system as well as for the proper functioning of an organism. In order to understand the vascular circulation system, it is essential to understand the design rules or scaling laws of the system under a homeostatic condition. In this study, Murray's law in the extraembryonic arterial bifurcations and its relationship with the bifurcation angle (theta) using 3-day-old chicken embryos in vivo has been investigated. Bifurcation is an important geometric factor in biological systems, having a significant influence on the circulation in the vascular system. Parameters such as diameter and bifurcation angle of all the 140 vessels tested were measured using image analysis softwares. The experimental results for alpha (= 1.053 +/- 0.188) showed a good agreement with the ratio of 1 for Murray's law. Furthermore, the diameter relation alpha approached the theoretical value of 1 as the diameter of parent vessel D-0 decreased below 100 mu m. The bifurcation angle theta decreased as D-0 increased and vice versa. For the arterial bifurcations of chicken embryos tested in this study, the bifurcation pattern appears to be symmetric (D-1 = D-2). The bifurcation angle exhibited a nearly constant value of 77 degrees, close to the theoretical value of 75 degrees for a symmetric bifurcation.X111112sciescopu
Regulation of the Longevity Response to Temperature by Thermosensory Neurons in Caenorhabditis elegans
No full textBackground: Many ectotherms, including C. elegans, have shorter life spans at high temperature than at low temperature. High temperature is generally thought to increase the "rate of living" simply by increasing chemical reaction rates. In this study, we questioned this view and asked whether the temperature dependence of life span is subject to active regulation. Results: We show that thermosensory neurons play a regulatory role in the temperature dependence of life span. Surprisingly, inhibiting the function of thermosensory neurons by mutation or laser ablation causes animals to have even shorter life spans at warm temperature. Thermosensory mutations shorten life span by decreasing expression of daf-9, a gene required for the synthesis of ligands that inhibit the DAF-12, a nuclear hormone receptor. The short life span of thermosensory mutants at warm temperature is completely suppressed by a daf-12(-) mutation. Conclusions: Our data suggest that thermosensory neurons affect life span at warm temperature by changing the activity of a steroid-signaling pathway that affects longevity. We propose that this thermosensory system allows C. elegans to reduce the effect that warm temperature would otherwise have on processes that affect aging, something that warm-blooded animals do by controlling temperature itself.X118277sciescopu
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