Fibrinogen adsorption on hydrophilic and hydrophobic surfaces: Geometrical and energetic aspects of interfacial relaxations

This work examined the relationship between footprint growth and adsorption energetics for fibrinogen on model hydrophobic and hydrophilic surfaces. For adsorption runs at different free solution concentrations and flow rates in a slit-shear flow cell, single surface-dependent relaxation times were found on each of two model surfaces, By use of each relaxation time in an exponential growth model, predictions of the footprint size distributions were made for different adsorption histories. Then, from desorption rate measurements and a reversible binding model, the sizes of loosely and tightly bound populations were determined, in addition to the binding energy of the loosely bound population. These binding energies were then compared with the footprint size distributions to reveal markedly different behavior on the hydrophobic and hydrophilic surfaces. On the hydrophobic surface, a single footprint size correlated with a binding energy of 6kT, a feature that was independent of adsorption history and the footprint size distribution. On the hydrophilic surface, the footprint size associated with a similar binding energy for the loosely bound population depended on the adsorption history. These observations are discussed in the context of potentially different relaxation mechanisms on the two surfaces.