The effect of elevated haematocrit on human blood flow in microchannel

Blood is a non-Newtonian fluid and its viscosity can vary depending on several factors. However, in practical applications, at a high shear rate, blood can be considered as a Newtonian fluid with constant viscosity. In Newtonian fluids, the pressure gradient increases linearly when increasing the flow rate. This pressure gradient is highly dependent on the volume fraction of Red Blood Cells (RBC) along with some other channel parameters. When working with a Hydrodynamic Blood Plasma Separation (BPS) device, volume fraction of RBC increases after each constriction region, where the plasma is taken out through the side channel at the bifurcation. After a certain limit, this increasing pressure gradient due to high Haematocrit (HCT) may cause destruction of red blood cells. The main objective of this study is twofold: first is to find out the highest HCT value of blood that can flow through the main channel of our future BPS device and second is to determine the maximum achievable flow rate for blood with such high HCT ensuring that there is no cell damage. In order to obtain these information, straight microchannels with different lengths were manufactured in Poly (methyl methacrylate) (PMMA) while the width and height of the microchannels were kept constant, and tested with human blood samples at artificially high HCT. Our results are benchmarked against literature data.
This study provides design rules for the design of new blood plasma separation chips, and will also inform new blood flow modelling work with an external partner.