Capsule-substrate adhesion, detachment, and mass transport under Stokes flows: Computation using the immersed interface method

Two-dimensional capsule-substrate adhesion under an imposed Stokes flow field is numerically simulated by using the immersed interface method (IIM) with the same viscosity for the fluid enclosed by the membrane and the surrounding fluid. The capsule membrane is considered to be either impermeable or permeable while the capsule membrane is assumed to be Neo-Hookean. The interaction between the capsule and the planar substrate is simply modeled by a potential function. The mass transfer across the capsule membrane is computed using the KedemKatchalsky transport equations. Comparison of our results with other numerical and analytical results for the capsulesubstrate adhesion in the absence of a flow field suggests that the present model is reasonably accurate in modeling capsule-substrate adhesion. Then adhesion of a malariainfected red blood cell (IRBC) onto the capillary wall is studied under various flow fields and adhesive forces. Our model can express the basic rolling behavior of IRBCs due to cytoadhesive interaction with endothelial cells on capillary wall. Furthermore, the numerical results show that the presence of an IRBC causes a higher flow resistance than a healthy RBC does, which may cause a microvascular blockage. Finally, the present model is used to study systematically a drug-loaded permeable capsule and the mass transfer between the capsule and the capillary wall for various parameters including flow velocity, membrane permeability, and adhesive forces.