The ability to control the rate of adsorption and desorption of proteins from surfaces is studied by using a molecular theory. We show how changing the chemical structure and charge of short linear and branched grafted polymers to an electrode surface can be used to promote fast adsorption of charged proteins on a time scale of seconds and control the desorption in a time scale ranging from milliseconds to hours. The optimal controlled release is found from the interplay of electrostatic attractions at short distances from the surface and the proper electrostatic and steric repulsive barrier at distances from the surfaces larger than the proteins' size. The implications of our results to the design of controlled-release devices is discussed.protein adsorption͞desorption ͉ surface modification ͉ grafted polymers ͉ kinetic theory C ontrol of protein adsorption is of primary importance in the design of biocompatible materials, biosensors, and bioactive surfaces (1-3). Furthermore, the process of protein adsorption is of great interest from a fundamental perspective because it encompasses very large, competing energy scales, and the process typically spans many time scales ranging from microseconds to hours (4, 5). Thus, a molecular understanding of the adsorption process and its control offers a great theoretical challenge in which energy, time, and length scales can be bridged. Furthermore, the ability to quantify how surface modifiers affect the adsorption͞desorption process will help in the molecular design of materials interacting with biological f luids. The aim of the work presented here is to demonstrate that by the proper choice of polymers grafted to the surface one can take advantage of the interplay between electrostatic and steric interactions to control the time scale for adsorption and desorption. This surface modification can serve as the basis for the design of controlled-release devices (6, 7).One of the most important, and still unresolved, problems in the design of biocompatible materials is the production of surfaces that can prevent nonspecific adsorption of blood proteins in vivo (8). There have been great advances in the understanding of how surface modification in vitro can reduce or prevent protein adsorption (9). There are two main ways of doing that. The first is by chemical modification of the surface exposed to the proteins (10). The second is by grafting polymer molecules on the surface exposed to the protein solution (11). The most commonly used polymer for this purpose is polyethylene glycol (PEG) (12); however, other polymers also have shown nonfouling capabilities (13). Grafted polymer layers have been shown to affect also the desorption of proteins. Experimental observations demonstrate that charged proteins may be trapped on poylelectrolyte grafted layers (14). Further, our recent theoretical predictions have shown that model PEG polymer layers can trap proteins adsorbed on hydrophobic surfaces, whenever the film thickness is larger than the protein size (15). Thus, the longer th...