Protein-surface interactions graft density

The mechanism of action of the hydrophilic PEG chains can be explained in terms of steric interaction that is well known in the theory of steric stabilization. Before considering the steric interaction one must know the polymer configuration at the par-ticle/solution interface. The hydrophilic PEG chains can adopt a random coil (mushroom) or an extended (brush) configuration. This depends on the graft density of the PEG chains as will be discussed below. The conformation of the PEG chains on the nanoparticle surface determines the magnitude of steric interaction. This configuration determines the interaction of the plasma proteins with the nanoparticles. 

The simple Alexander—de Gennes theory, which assumed a steplike monomer density in the brush, captured the dependence of the interaction on the physical parameters (length of the polymer, density of grafting, quality of the solvent) and provided a satisfactory approximation for the calculation of the steric repulsion. However, new applications of grafted polymers on surfaces, such as the control of the catalytic selectivities of some chemical reactions by varying the thickness of a brush,4 the prevention of the adsorption of proteins on surfaces (a condition required for biocompatibility),5 or the control of... 

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