Adsorption and relaxation kinetics of albumin and fibrinogen on hydrophobic surfaces: Single-species and competitive behavior

We report the kinetic behavior of albumin and fibrinogen adsorption and rel axation from gentle shearing flow and phosphate buffer onto C16 self-assemb led monolayers. The adsorption kinetics were generally transport-limited; h owever, the ultimate coverages depended on the rates at which protein molec ules arrived at the surface, suggesting that interfacial relaxations determ ined the ultimate coverage. Of particular note was a dependence of the ulti mate coverage of both proteins on the wall shear rate, in addition to the i nfluence of the bulk solution concentration. Analysis of single protein exp eriments revealed interfacial protein relaxation rates of 0.12 and 0.15 nm( 2) molecule(-1) s(-1) for albumin and fibrinogen, respectively. These rates were constant over the range of experimental conditions and represent the initial relaxation rates after protein adhesion to the surface. The initial protein footprints were consistent with the free solution protein dimensio ns and, in the case of albumin, grew over a factor of 5 as the protein rela xed. For fibrinogen, relaxations were less extensive, increasing the footpr int by a factor of 3. The extents of relaxation and the sizes of the protei n footprints during the Linear regime of spreading suggest that interfacial denaturing contributes significantly to the relaxation process, in additio n to simple reorientations. The albumin relaxation behavior was shown, in a ddition to its influence on albumin coverage, to affect the coverage of fib rinogen in competitive situations. When the C16 layer was passivated with a lbumin prior to fibrinogen adsorption, short albumin exposures (still suffi cient to cover the C16 surface) were ineffective at preventing fibrinogen a dsorption. Prolonged incubation of albumin layers in albumin solution or bu ffer dramatically reduced subsequent fibrinogen adhesion.