Hindered diffusion in agarose gels: test of effective medium model

Area of Science:

• Biophysics
• Materials Science
• Physical Chemistry

Background:

• Diffusion of macromolecules in gels is reduced compared to free solutions.
• This reduction is attributed to hydrodynamic and steric interactions.
• Understanding these factors is crucial for various applications, including drug delivery and biomaterials.

Purpose of the Study:

• To quantify the diffusion of macromolecules in agarose gels.
• To investigate the influence of macromolecule size and gel concentration on diffusion.
• To evaluate the accuracy of an effective medium theory in predicting hindered diffusion.

Main Methods:

• Measured diffusion coefficients (D) and free solution diffusion coefficients (D infinity) using fluorescence recovery after photobleaching.
• Studied various proteins and Ficoll fractions in agarose gels with controlled volume fractions.
• Characterized gel properties by measuring hydraulic permeability and calculating Darcy permeability (kappa).

Main Results:

• Diffusivity ratio (D/D infinity) ranged from 0.20 to 0.63, decreasing with increasing macromolecule size (Stokes-Einstein radius, rs) and gel concentration (phi).
• Darcy permeability (kappa) decreased significantly with increasing agarose concentration.
• The effective medium theory provided accurate predictions of D/D infinity without adjustable parameters.

Conclusions:

• Hindered diffusion is more pronounced for larger macromolecules and in more concentrated gels.
• The effective medium theory is a valuable tool for predicting macromolecule diffusion in gels.
• This study provides insights into the fundamental principles governing transport in porous media.