Microparticles proposed for in vivo imaging or drug delivery applications may be either solid, porous, or hollow in construction. We investigate the contribution of extensional forces to the adhesion of both air-filled and solid microparticles in shear flow devices to surfaces coated with known inflammatory molecules ICAM and VCAM. The particles, coated with calibrated levels of antibodies to these human CAM molecules, are exposed to oriented coatings and quantified via microscopy. The difference in specific gravity for each particle type is related to the adhesion density of the particles. A binding density function is important for development of therapeutic encapsulated applications.