Modeling the making and breaking of bonds as an elastic microcapsule moves over a compliant substrate

By integrating the lattice Boltzmann model for hydrodynamics, the lattice spring model for micromechanics of elastic solids, and the Bell model for bond formation and rupture, we examine the fluid driven motion of elastic microcapsules on compliant surfaces. The capsules, modeled as threedimensional fluid-filled elastic shells, represent polymeric microcapsules or biological cells. We observed three regimes of capsule motion. Namely, the capsule rolls steadily along the substrate at a sufficiently high shear rate, it is stationary at a low shear rate, and exhibits an intermittent motion (saltation) at intermediate shear rates. At a given shear rate, the regime of capsule motion was found to depend on the substrate stiffness, and on the rate of rupture of the adhesive bonds. The capsule was observed to roll steadily on a sufficiently stiff substrate, and at a high rate of bond rupture. In the opposite limit of a soft substrate and low rate of bond rupture, the system was localized in the stationary regime. The findings provide guidelines for creating smart surfaces that could regulate the motion of the microcapsules.