COMPUTATIONAL MODEL OF RED CELL FLOW IN MICRO-CHANNELS FOR PROBING MOLECULES ENCAPSULATION

Aim: Preliminary experiments confirm the possibility to load Red Blood Cells (RBCs) with probing molecules (PM) by applying mechanical shear stresses (τ) on RBCs stroma. This work is aimed at studying the optimal fluid dynamic conditions allowing the encapsulation of PM into RBCs flowing in a microchannel (MC). Methods: A computational model was developed by using COMSOL Multiphysics 4.2a (Stockholm, Sweden). A 50 x 50 μm cross-section and 58.5 mm length MC was considered. The Mixture Model was used to evaluate velocity (v), volume fraction of dispersed phase (Id) and τ for a suspension of RBCs and PM (FITC-Dextran) in a Phosphate Buffer. When the pair of τ values and duration lays in the sub-haemolytic portion of the Tillman Diagram, and the RBCs transit time into the MC is higher than the diffusion characteristic time of PM into RBCs, encapsulation was promoted. The flow rate Q, and the haematocrit Ht and MC size were tuned to optimise fluid dynamic conditions and increase encapsulation. Results: Optimal conditions were Q = 40 μl/min and Ht <0.15 with the modelled MC. The resulting high pressure drop suggests to increase MC width (2000 μm) by keeping constant height and length. The new optimal conditions were Q = 1600 μl/min, 0.05<Ht<0.30. A normalized index (Ie) was defined as the product of v, τ and rd; encapsulation is higher in the round crown region of the MC section, where 0.8<Ie