Hindered diffusion of spherical macromolecules through dilute fibrous media

Results are presented for the effect of solute–fiber hydrodynamic interactions on the hindered diffusion of a spherical macromolecule in random media comprised of cylindrical fibers. Hydrodynamic interactions are calculated by representing the sphere as a collection of point singularities and accounting for the fibers by using a numerical version of slender-body theory. Electrostatic and other nonhydrodynamic interactions are neglected. The calculations show that the hydrodynamic mobility of the solute decreases in an exponential-like fashion as the fiber volume fraction is increased. Also, at a given volume fraction, a medium of thinner fibers hinders solute transport more than a medium of thicker fibers. The results compare well with experimental data, both for protein diffusion in solutions of the polysaccharide Dextran and for protein diffusion in cross-linked agarose gels.