Kinetics of fibrinogen adsorption on hydrophilic substrates

Irreversible side-on adsorption of fibrinogen, modeled as a linear chain of touching beads of various size, was studied theoretically using the random sequential adsorption (RSA) model. Numerical simulation of the Monte Carlo type enabled one to determine the dependence of the surface blocking function (available surface function) on the protein coverage. These numerical results were interpolated using analytical functions based on a polynomial expansion. The dependence of the jamming coverage on the size of the simulation area was also determined. By an extrapolation of these results to the infinite area size, the maximum surface concentration of fibrinogen for the side-on adsorption was determined to be 2.26 x 10(3) microm(-2). This corresponds to a jamming coverage theta(infinity) of 0.29. It was shown that the blocking function can well be approximated in the limit of high coverage by the dependence C(theta(infinity) - theta)(4). Using this interpolating expression, the kinetics of fibrinogen adsorption under convection and diffusion transport conditions were evaluated for various bulk concentrations of the protein. These kinetic curves were derived by numerically solving the mass transport equation in the bulk with the blocking function used as a nonlinear boundary condition at the interface. It was shown that our theoretical results are in agreement with experimental kinetic data obtained by AFM, ellipsometry, and other techniques for hydrophilic surfaces in the limit of low bulk fibrinogen concentration.