PROBE MOLECULES LOADING INTO RED CELLS TROUGH HYDRODYNAMIC FOCUSING: A COMPUTATIONAL EVALUATION - Oral presentations - XLII Annual ESAO Congress, 2-5 September 2015, Leuven, Belgium

Introduction: This work aims at studying the fluid-dynamic conditions allowing the encapsulation of probing molecules (PM) into Red Blood Cells (RBCs) by applying shear stresses (τ) on their membrane. Indeed, it is well-known in the literature that this process enhances the opening of the pores, thus allowing the diffusion of solutes. In our microdevice τ were applied through a single passage in a sheath flow focuser, designed to drift the cells to a controlled τ solicitation zone. Material and methods: A computational model using Comsol Multiphysics was developed; the geometry is a cross-shaped microchannel (MC) with 50*50 μm cross-section and 87 mm length. Velocity (v), volume fraction of dispersed phase (rd) and τ for a suspension of RBCs and PM (FITC-Dextran) in a Phosphate Buffer were evaluated, varying the flow rate of RBCs suspension (Qb), sheath flow (Qf) and Ht. When the pair of τ values and time results subhaemolytic (according to Tillman Diagram (TD)), and the RBCs transit time is higher than the time required for PM diffusion into RBCs, encapsulation can be promoted. A dedicated efficiency index was used to evaluate the flow conditions (v, rd, τ) that are thought to increase the encapsulation rate. Results: Taking into account the efficiency index, the position on TD and the overall pressure drop, suitable fluid-dynamics conditions were: Qb = 40 μl/ min, Qf = 7 μl/min, PM 2 mM for Ht = 5% or Qb = 33 μl/min, Qf = 5,5 μl/min, PM 4 Mm, and Ht = 10%. In these conditions the area occupied by RBCs is the 75% of the channel section. The resistance of the MC and their connections to the pumping system to the high pressure evaluated through CFD (respectively of 4 and 3 atm) was verified. Discussion: The model allows the characterization of RBCs fluid-dynamic in simple microfluidic devices and to identify the optimal conditions to promote PM encapsulation. This model will be used to define appropriate test conditions.