Migration and deformation of leukocytes in pressure driven flows

Direct numerical simulations (DNS) are used to study the motion and deformation of leukocytes in pressure driven flows in parallel plate channels. The influence of the adhesion force between the leukocytes and the channel wall on such motion and deformation is also investigated. Leukocytes are represented by two composite fluid models, consisting of a membrane, a cytoplasm and a nucleus. The adhesion force is computed using two adhesion force models. In the first model, the adhesion force is given by a potential, and in the second one it is given by Dembo's kinetic adhesion model. The numerical code is based on the finite element method and the level set technique is used to track the cell membrane position. In the absence of the adhesion force, the leukocyte moves away from the wall to an equilibrium location that depends on the ratio of the cell to plasma viscosities. In presence of the adhesion force, the leukocyte is attracted to the layer of endothelial cells and, as it gets closer, it flattens under the action of hydrodynamic forces. This deformation, in turn, further increases the adhesion force. The leukocyte, however, can be captured only when it is placed sufficiently close to the wall, which for the kinetic model is of the order of 30 nm. We also find that for the normal parameter values and flow rates the adhesive force given by the kinetic model is too small to capture the leukocyte.