Adhesion of red blood cells to solid surfaces: Experimental results and modeling

Red blood cells (RBC), previously fixed with glutaraldehyde, adhere to glass slides coated with fibrinogen. The RBC solution is injected in a diffusion cell where the RBC's settle on the horizontal glass surface, which is observed with an inverted optical microscope. This experiment is repeated for a series of RBC concentrations in the solution. The relative surface covered by the RBC's, as well as the variance of this surface coverage, is obtained for each concentration by means of image processing. In order to model the process, the RBC's are approximated by disks or spheres. A simulation code was developed on the basis of the “Random Sequential Adsorption” (RSA) model. Usually, no overlap is allowed, and the particles, once adsorbed, stay permanently fixed in place. Here, the model is extended to account for possible overlap between the RBC's. The surface covered, estimated by simulation, as a function of the number of particles deposited on the surface, shows a clear deviation from a linear relation if overlaps are taken into account; this trend is supported by the experimental data. In the same way, the coverage fluctuation is best reproduced if overlaps are allowed. On the other hand, somewhat surprisingly, a model taking into account both the random diffusion of the RBC's and the gravitational force they experience, but assuming no overlaps, describes also quite reasonably the experimental coverage fluctuation.