Horse and dog blood flows in PDMS rectangular microchannels: Experimental characterization of the plasma layer under different flow conditions

This work characterizes the plasma layer of horse and dog blood flows inside rectangular PDMS microchannels under different conditions (hematocrit of ca. 40% and 45%, respectively, flow rate varying between 1 and 30 μl/min, microchannel width and height varying from 100 to 350 μm and 30 to 40 μm, respectively), and relates it with the pressure drop. For that, images were acquired with a microscope/CMOS camera and digitally processed by a Matlab script. The results show that the cell-free layer thickness varies with the following parameters: it increases non-linearly with the increase of the blood flow rate (the average thickness growth observed with a 100% increase of the blood flow rate was ca. 55%); it increases with both microchannel width and height increase. Moreover, because plasma is a Newtonian fluid, the measured pressure drop varied linearly with the blood flow rate but with an apparent viscosity larger than that of plasma and smaller than that of the whole blood. This allowed inferring that plasma layers act as a lubricant making easier the blood flow. It was also observed a non-instantaneous response time, 3-4 s, of the erythrocytes to a squared-wave pulsatile flow, both when increasing and decreasing the flow rate.