Confocal Micro-PIV/PTV Measurements of the Blood Flow in Micro-channels - Bioanalysis Advanced Materials Methods and Devices - page 141

Fig. 9.15 RBCs radial dispersion coefficient ( D yy )of75 m m PDMS circular micro-channel for

3 % Hct and 23 % Hct (adapted from [ 29 ])

where R y and t are the radial displacement and time interval respectively. Hence,
in vitro blood with several Hcts was used, the confocal micro-PTV system enabling
the paths of hundreds of labelled RBCs to be recorded in the centre plane of 100 and
50

m PDMS circular micro-channels. The results
demonstrated that for RBCs the D yy tends to increase with increasing Hct (as shown
in Figs. 9.15 and 9.16 ). For instance Fig. 9.15 shows clearly that RBCs D yy at Hct of
23% is almost one order magnitude bigger than D yy with 3% Hct.
These research findings are evidence that the RBCs flowing in a crowded
environment tend to undergo multi-body collisions which increase the amplitude
of the RBC's lateral motion and consequently RBC D yy . Hence, RBCs at high
concentrations tend to exhibit higher erratic radial displacement compared to dilute
suspensions of RBCs. Additionally, results given in Fig. 9.16 demonstrate that RBC
radial dispersion, at both moderate and high Hcts, tends to decrease with the
diameter. The main reasons for this are as follows: Hct reduction with diameter
(Faharaeus effect) and the constrictive effect of the geometry, the latter limiting the
amplitude of the radial displacements of the RBCs. Additional detailed results
relating to these data can be found elsewhere [ 26 , 28 , 29 ].
Very recently, in a study performed by Saadatmand et al. [ 37 ] fluid particle diffusion
was examined in concentrated suspensions of human RBCs (Hct up to 20%) through a

m m glass capillaries and 75 m