Relationship between red blood cell aggregation and dextran molecular mass

Abstract

The aim of this study was to investigate the aggregation of red blood cells (RBCs) suspended in dextran solution at various levels of molecular mass. Dextran solutions at molecular mass 40, 70, 100 and 500 kDa at concentration from 2 to 5 g/dL were used to suspend the RBCs. The radius and velocity of sedimenting RBC aggregates were investigated using image analysis. The radius and sedimentation velocity of aggregates increased initially, then decreased after achieving maxima. The maximal velocity of RBC aggregates showed a bell-shaped dependence on dextran molecular mass and concentration, whereas maximal radius showed monotonic increase with both factors. Difference between aggregate and solution density was estimated using aggregate radius and sedimentation velocity and dextran solution viscosity, and was consistent across most molecular mass and concentration levels. This allowed to calculate the porosity of aggregates and to show that it monotonically decreased with the increase in the solution density, caused by the increase in the dextran concentration. The results provide insight into the RBC aggregation process in solutions of proteins of different size, reflecting various pathological conditions. The currently reported data can be potentially applied to specific pathophysiological conditions giving an interpretation that is not yet fully discussed in the literature.

Figure 1

The procedure by which the image time sequence (bottom) was composed from the consecutive images of red blood cell (RBC) suspension (top) at hematocrit 10% in solution of dextran 70 kDa at concentration 3 g/dL.

Figure 2

The autocorrelation of time sequence as a function of sample height shift and time shift, averaged over 50 s time interval and whole imaged area of the sample of the red blood cell (RBC) suspension at hematocrit 10% in solution of dextran 70 kDa at concentration 3 g/dL. The slope of the linear fit is an estimation of the mean aggregate velocity.

Figure 3

The correlation of the images as a function of sample height shift, averaged over 50 s time interval and whole imaged area of the sample of the red blood cell (RBC) suspension at hematocrit 10% in solution of dextran 70 kDa at concentration 3 g/dL, which is the cross section of the autocorrelation function shown in Fig. 2 at Δt = 0. The parameter r_a of the exponential fit (solid line), was taken as a measure of the mean aggregate radius.

Figure 4

The mean of the solution viscosity (a) and density (b) as a function of dextran concentration.

Figure 5

The aggregate radius and velocity as a function of time at hematocrit 5% in solution of dextran 40 kDa at concentration 5 g/dL (a) and at hematocrit 10% in solution of dextran 70 kDa at concentration 3 g/dL (b). The solid lines represent an experimental function fitted to these data.

Figure 6

The mean and standard deviation of the peak aggregate radius (a, c) and velocity (b, d) as a function of dextran concentration at hematocrit 5% (a, b) and 10% (c, d). In this and next figures the standard deviations were calculated for the values over different experiments.

Figure 7

The mean and standard deviation of the time to reach peak aggregate radius and velocity as a function of dextran concentration at hematocrit 5% (a) and 10% (b).

Figure 8

The mean and standard deviation of the peak aggregate radius (a, c) and velocity (b,d) as a function of dextran molecular mass at hematocrit 5% (a, b) and 10% (c, d).

Figure 9

The mean and standard deviation of the time to reach peak aggregate radius and velocity as a function of dextran molecular mass at hematocrit 5% (a) and 10% (b).

Figure 10

The mean of the difference between aggregate and solution density at hematocrit 5% (a, c) and 10% (b, d) as a function of dextran concentration (a, b) and molecular mass (c, d).

Figure 11

The mean of the aggregate porosity at hematocrit 5% (a) and 10% (b) as a function of dextran concentration.