of the Vroman effect. This maxima is, instead, rationalized by models based on kinetic equations. Some of these models include coupled mass transport equations [@Lu1994]. In all of them, to each kind of protein in solutions, there are associated different adsorptions/desorption rate constants. These processes are modeled as reversible by some authors [@CUYPERS1987]. Others, to fit better the experiments, assume that the adsorption can become irreversible with a “reaction” rate constant [@Lu1994]. Due to the difficulty for this approach to describe the variety of experimental results, some models include also a “displacement” rate constant of a reversibly adsorbed protein by a protein with a higher surface affinity [@Lundstrom1990; @Slack1995; @Dejardin1995]. However, these models are unable, in general, to describe solutions at low concentration, where the surface coverage is controlled by diffusion [@Dejardin1995], and cannot rationalize the different desorption behavior observed for sorbent-free with respect to sorbent-bearing washing solutions [@LeDuc1995].

The latter observation inspired LeDuc et al. to include also a “liberation” rate constant of semipermanently adsorbed protein by contact with a bulk protein [@LeDuc1995]. To simplify the model, the authors made strong approximations, likely to be incorrect, assuming that adsorbed proteins do not diffuse on the surface and that the 