Dynamics of interactions between human albumin and polyethylene surface

The adsorption of human albumin to polyethylene was studied using radioiodinated (125I or 131I) protein. Adsorption at 23°C under laminar flow conditions over a range of shear rates up to 2500 sec−1 and from 0.1 to 3.8 mg ml−1 was investigated. A steady-state surface concentration (SSSC) was reached within 2–3 hr under all conditions. The value of SSSC was independent of flow conditions. Concentration dependence followed a Langmuir-like isotherm. The existence of a dynamic equilibrium with equal rates of adsorption and desorption was established. Adsorption and desorption were measured simultaneously by the use of double labeling (125I-labeled albumin on the surface, exchanging with 131I-labeled albumin in solution). Two characteristics of the dynamic steady state were investigated: the extent and the rate of turnover. Both extent and rate were found to increase with increasing shear rate and protein concentration, with essentially zero turnover at zero concentration or flowrate. Turnover data were fitted to a first-order model to obtain estimates of the fractional extent of turnover and the fractional turnover rate. These parameters varied from 0 to 0.8 and from 0 to 0.045 hr−1, respectively. The results are discussed in relation to the problem of thrombus formation at surfaces in contact with blood.