Mass Transport of Macromolecules in Solution to Surfaces

Abstract

Macromolecular mass transport to surfaces was measured in these studies. A method is described that was used to determine the effective diffusivity of macromolecules in sheared aqueous solutions. The adsorption of gamma globulin and albumin (γG and A, which had been covalently bound to fluorescein isothiocyanate (FITC)) onto glass planar surfaces was measured under diffusion-limited transport conditions using total internal reflection extrinsic fluorescence. The adsorbed concentration of tritium-labeled protein-FITC conjugate on the glass surface was determined by scintillation counting and compared to the fluorescence intensity measured to calibrate the experimental system. The rate of adsorption was found experimentally, and based on a Leveque type flow model a Brownian diffusivity for the adsorbing macromolecule was determined explicitly. Diffusivity was determined in isotonic phosphate-buffered saline solution (pH 7.4) for wall shear rates from 200 to 1,400 s-1. As expected, results obtained for the sheared homogeneous solutions did not appear to be a function of shear rate and were in good agreement with the literature values for Brownian diffusivity of γG and A. This approach was then extended as described in the accompanying paper to measurement of mass transport of macromolecules in sheared suspensions to surfaces.