We discuss a novel method for capturing the dynamic coupling between a fluid and an elastic solid, the so-called fluid-structure interaction. This method integrates a lattice Boltzmann model to capture the fluid dynamics with a lattice spring model to capture the micromechanics of the solid phase. We then examine the fluid-driven motion of microcapsules, which are modeled as fluid-filled, elastic shells, along a corrugated substrate. We show that the ability of the capsules to navigate along the surface depends critically on capsule's elastic modulus. In particular, we illustrate how this substrate can be utilized to design a device for sorting microcapsules by their mechanical properties. These results apply not only to polymeric microcapsules, but also describe the interaction between the substrate and certain biological cells (e.g., leukocytes and other cells with cyoskeletons). Hence, by isolating species of a certain stiffness, the device could be highly useful for applications in biotechnology and tissue engineering or in the quality control of fabricated microcapsules. (c) 2006 Wiley Periodicals, Inc.