Quantifying local characteristics of velocity, aggregation and hematocrit of human erythrocytes in a microchannel flow

Abstract

The effect of erythrocyte aggregation on blood viscosity and microcirculatory flow is a poorly understood area of haemodynamics, especially with relevance to serious pathological conditions. Advances in microfluidics have made it possible to study the details of blood flow in the microscale, however, important issues such as the relationship between the local microstructure and local flow characteristics have not been investigated extensively. In the present study an experimental system involving simple brightfield microscopy has been successfully developed for simultaneous, time-resolved quantification of velocity fields and local aggregation of human red blood cells (RBC) in microchannels. RBCs were suspended in Dextran and phosphate buffer saline solutions for the control of aggregation. Local aggregation characteristics were investigated at bulk and local levels using statistical and edge-detection image processing techniques. A special case of aggregating flow in a microchannel, in which hematocrit gradients were present, was studied as a function of flowrate and time. The level of aggregation was found to strongly correlate with local variations in velocity in both the bulk flow and wall regions. The edge detection based analysis showed that near the side wall large aggregates are associated with regions corresponding to high local velocities and low local shear. On the contrary, in the bulk flow region large aggregates occurred in regions of low velocity and high erythrocyte concentration suggesting a combined effect of haematocrit and velocity distributions on local aggregation characteristics. The results of this study showed that using multiple methods for aggregation quantification, albeit empirical, could help towards a robust characterisation of the structural properties of the fluid

Red blood cell aggregate flux in a bifurcating microchannel

“…Details for the experimental apparatus, sample preparation, flow measurement methodology and aggregate size characterization can be found elsewhere [11,12,14] and only a brief description is provided here.…”

“…Our previous work on red blood cell transport in straight and bifurcating microchannels (Sherwood et al [11][12][13] and Kaliviotis et al [14,15]) has investigated the cell depleted layer (CDL) formed near the walls, the spatial variation of RBC concentrations, the phenomenon of plasma skimming and the aggregate size distribution. A comprehensive literature review on these characteristics for in vivo and in vitro studies was also provided therein.…”

“…The aggregate size distribution in the flow was examined by the authors for flow in a straight rectangular microchannel (250x50 microns width and height respectively) through bulk and local aggregation indices [14]. A local aggregation index, A*, based on detecting the isointensity patterns formed by the aggregated cells was developed to characterise the aggregate size.…”

“…However, there are certain limitations in the use of image analysis for aggregate characterisation, with the main one been the RBC concentration, which affects the image quality due to high light absorption. Kaliviotis et al [14] addressed these imitations by developing advanced image processing techniques, taking advantage of the specific features of RBC aggregation mentioned earlier.…”

“…In this paper, we report on a study of RBC aggregate size fluxes in a T-junction for the first time, estimated through analysis of the bifurcating flows reported in Sherwood et al [11,12], using the aggregate detection methodology developed by Kaliviotis et al [14,15]. The paper is structured as follows: in the Methodology section the technique for flux calculation is described and information regarding sample preparation, the flow system, and flux calculation is provided; in the Results and discussion section the presentation and analysis of the RBC aggregate size flux is presented for 34 different flow splits (i.e.…”