Numerical analysis of the deformation of an adherent drop under shear flow

The adhesion of leukocytes to substrates is an important biomedical problem and has drawn extensive research. In this study, employing both single and compound drop models, we investigate how hydrodynamics interacts with an a dherent liquid drop in a shear flow. These liquid dr-op models have recentl y been used to describe the rheological behavior of leukocytes. Numerical s imulation confirms that the drop becomes more elongated when either capilla ry number ol initial contact angle increases. Our results short that there exists a thin region between the drop and the wall as the drop undergoes la rge stretching, which allows high pressure to build up and provides a lift force. In the literature, existing models regard the leukocyte as a rigid b ody to calculate the force and torque acting on the drop in order to charac terize the binding between cell receptors and endothelial ligands. The pres ent study indicates that such a rigid body! model is inadequate and the for ce magnitude obtained from it is less than half of that obtained using the deformable drop models. Furthermore, because of its much higher viscosity, the cell nucleus introduces a hydrodynamic time scale orders of magnitude s low er than the cytoplasm. Hence the single and compound drops experience d ifferent dynamics during stretching, but exhibit very comparable steady-sta te shapes. he present work offers a framework to facilitate the development of a comprehensive dynamic model for blood cells.