David Bento

Microbubble moving in blood flow in microchannels: effect on the cell-free layer and cell local concentration.

Gas embolisms can hinder blood flow and lead to occlusion of the vessels and ischemia. Bubbles in microvessels circulate as tubular bubbles (Taylor bubbles) and can be trapped, blocking the normal flow of blood. To understand how Taylor bubbles flow in microcirculation, in particular, how bubbles disturb the blood flow at the scale of blood cells, experiments were performed in microchannels at a low Capillary number. Bubbles moving with a stream of in vitro blood were filmed with the help of a high-speed camera. Cell-free layers (CFLs) were observed downstream of the bubble, near the microchannel walls and along the centerline, and their thicknesses were quantified. Upstream to the bubble, the cell concentration is higher and CFLs are less clear. While just upstream of the bubble the maximum RBC concentration happens at positions closest to the wall, downstream the maximum is in an intermediate region between the centerline and the wall. Bubbles within microchannels promote complex spatio-temporal variations of the CFL thickness along the microchannel with significant relevance for local rheology and transport processes. The phenomenon is explained by the flow pattern characteristic of low Capillary number flows. Spatio-temporal variations of blood rheology may have an important role in bubble trapping and dislodging.

An In Vitro Experimental Evaluation of the Displacement Field in an Intracranial Aneurysm Model

The purpose of this paper is to develop a system able to study experimentally the displacement field of an in vitro intracranial aneurysm. Origin and growth of aneurysms is the result of a complex interaction between biological processes in the arterial wall and the involved hemodynamic phenomena’s. Once the aneurysm forms, the repetitive pressure and shear stresses exerted by the blood flow on the debilitated arterial wall can cause a gradual expansion. One promising method to evaluate and measure this expansion is to use optical field experimental techniques, such as interferometry. In this work the Electronic Speckle Pattern Interferometry was used to evaluate the deformation occurred on an intracranial aneurysm model fabricated in polydimensiloxane (PDMS) by using a 3D printer combined with a soft lithography technique.

Genetic algorithm and particle swarm optimization combined with Powell method

In recent years, the population algorithms are becoming increasingly robust and easy to use, based on Darwins Theory of Evolution, perform a search for the best solution around a population that will progress according to several generations. This paper present variants of hybrid genetic algorithm - Genetic Algorithm and a bio-inspired hybrid algorithm - Particle Swarm Optimization, both combined with the local method - Powell Method. The developed methods were tested with twelve test functions from unconstrained optimization context.

Deformation of Red Blood Cells, Air Bubbles, and Droplets in Microfluidic Devices: Flow Visualizations and Measurements

Techniques, such as micropipette aspiration and optical tweezers, are widely used to measure cell mechanical properties, but are generally labor-intensive and time-consuming, typically involving a difficult process of manipulation. In the past two decades, a large number of microfluidic devices have been developed due to the advantages they offer over other techniques, including transparency for direct optical access, lower cost, reduced space and labor, precise control, and easy manipulation of a small volume of blood samples. This review presents recent advances in the development of microfluidic devices to evaluate the mechanical response of individual red blood cells (RBCs) and microbubbles flowing in constriction microchannels. Visualizations and measurements of the deformation of RBCs flowing through hyperbolic, smooth, and sudden-contraction microchannels were evaluated and compared. In particular, we show the potential of using hyperbolic-shaped microchannels to precisely control and assess small changes in RBC deformability in both physiological and pathological situations. Moreover, deformations of air microbubbles and droplets flowing through a microfluidic constriction were also compared with RBCs deformability.

Cell-free layer measurements of in vitro blood flow in a microfluidic network: an automatic and manual approach

In microcirculation, the cell-free layer (CFL) is a well-known physiological phenomenon that plays an important role in reducing the flow resistance and in balancing nitric oxide (NO) production by endothelial cells and NO scavenging by red blood cells. To better understand this phenomenon, several blood flow studies have been performed in simple geometries at both in vivo and in vitro environments. However, to date little information is available regarding the effects imposed by a complex branching network on the CFL. The present study shows the CFL layer variation at a microchannel network. The images were captured using a high-speed video microscopy system and the thickness of the CFL was measured using both manual and automatic image analysis techniques. Using this methodology, it was possible to visualise the in vitro blood flowing through the network and to identify several flow phenomena that happen in microcirculation. Overall, the results have shown that the concentration of cells and the...

Computation of a Three-Dimensional Flow in a Square Microchannel: A Comparison Between a Particle Method and a Finite Volume Method

The authors acknowledge the financial support provided by PTDC/SAU-ENB/116929/2010 and EXPL/EMSSIS/2215/2013 from FCT (Science and Technology Foundation), COMPETE, QREN and European Union (FEDER). D. Bento acknowledge the financial support provided by SFRH/BD/91192/2012 from FCT (Science and Technology Foundation), COMPETE, QREN and European Union (FEDER). The authors are also very grateful to Dr. Alberto Gambaruto (Bristol University) for helpful explanations and suggestions regarding the MPS method.

Mathematical Model of Feet Temperature

In this work it is consider the problem of finding the best approximation to characterize the feet temperature distribution. For this study it was consider the nonlinear least squares technique, combined with penalty method, to identify the function that approximate better the data obtained through thermographic images. The preliminary results indicate that the best function approximation is based on trigonometric sums.

Cell-free layer (CFL) analysis in a glass capillary: Comparison between a manual and automatic method

In this study, in vitro blood flowing through a 100 μm glass capillary was studied. The images were captured using a confocal system and post-processed using Image J and MatLab. The aim of the present work, was to measure the trajectories of the cell-free layer (CFL) by using two different methods, i. e., a manual method (MM) and an automatic method (AM). For the MM we have used amanual tracking plugin (MTrackJ) from Image J to track labeled red blood cells (RBCs) flowing around the boundary of the RBCs core. For the AM we have used a MatLab scripts to measure automatically the CFL trajectories. The preliminary numerical results suggest that the CFL trajectories follow a polynomial function for both methods.

Cell-Free Layer Measurements in a Network with Bifurcating Microchannels Using a Global Approach

One of the most interesting hemodynamic phenomenon observed in microchannels is the existence of a marginal cell-free layer (CFL) at regions adjacent to the wall. This is a well known phenomenon that occurs in simple glass capillaries and in vivo microvessels, but has never been investigated in detail in biomedical microdevices containing complex geometries. In the present chapter, in vitro blood flowing through bifurcating microchannels was studied, with the aim of characterizing the cell-free layer (CFL). For that three different videos with different hematocrit and flow rates were considered. All images were obtained by means of a high-speed video microscopy system and then processed in MatLab using the Image Processing toolbox. The numerical data was obtained automatically and analyzed by optimization techniques using the genetic algorithm approach. The results suggest that the CFL were formed in a similar way at the upper and lower regions in all bifurcations.

Cell-Free Layer (CFL) Measurements in Complex Geometries: Contractions and Bifurcations

In this chapter we discuss the cell-free layer (CFL) developed adjacent to the wall of microgeometries containing complex features representative of the microcirculation, such as contractions, expansions, bifurcations and confluences. The microchannels with the different geometries were made of polydimethylsiloxane (PDMS) and we use optical techniques to evaluate the cell-free layer for red blood cells (RBCs) suspensions with different hematocrit (Hct). The images are captured using a high-speed video microscopy system and the thickness of the cell-free layer was measured using both manual and automatic image analysis techniques. The results show that in in vitro microcirculation, the hematocrit and the geometrical configuration have a major impact on the CFL thickness. In particular, the thickness of the cell-free layer increases as the fluid flows through a contraction–expansion sequence and that this increase is enhanced for lower hematocrit. In contrast, the flow rates tested in these studies did not show a clear influence on the CFL thickness.