Geometry effect in multi-step crossflow microfluidic devices for red blood cells separation and deformability assessment.

The efficient separation of blood components using microfluidic systems can help to improve the detection and diagnosis of several diseases, such as malaria and diabetes. Therefore, a novel multi-step microfluidic device, based on passive crossflow filters was developed. Three different designs were proposed, fabricated and tested in order to evaluate the most suitable geometry to perform, simultaneously, blood cells separation and cell deformability measurements. All the proposed geometries include a main channel and three sequential separation steps, all comprised of symmetrical crossflow filters, with multiple rows of pillars, to reduce the amount of red blood cells (RBCs) flowing to the outlets of the microfluidic device (MD). Sets of hyperbolic constrictions located at the outlets allow the assessment of cells deformability. Based on the proposed geometries, the three correspondent MD were evaluated and compared, by measuring the RBCs velocities, the cell-free layer (CFL) effect through the microchannels and by quantifying the amount of RBCs at the outlets. The results suggest that the proposed MD 3 configuration was the most effective one for the desired application, due to the formation of a wider CFL. As a result, a minor amount of RBCs flow through the hyperbolic contraction at the third separation level of the device. Nevertheless, for all the proposed geometries, the existence of three separation levels shows that it is possible to achieve a highly efficient cell separation. If needed, such microdevices have the potential for further improvements by increasing the number of separation levels, aiming the total separation of blood cells from plasma.