Particle Diffusivity and Free-Energy Profiles in Hydrogels from Time-Resolved Penetration Data

Area of Science:

• Materials Science
• Physical Chemistry
• Biophysics

Background:

• Understanding particle transport in hydrogels is crucial for drug delivery and biomaterials.
• Existing methods often require complex inputs or specialized equipment.
• Hydrogel properties like mesh size and cross-linking influence particle diffusion and interactions.

Purpose of the Study:

• To develop a combined experimental and theoretical method for determining particle diffusivity and free-energy profiles in inhomogeneous hydrogels.
• To apply this method to dextran molecules of varying sizes penetrating polyethylene-glycol hydrogels.
• To establish scaling laws and a predictive model for particle-hydrogel interactions.

Main Methods:

• Utilized fluorescence intensity data of labeled tracer particles to obtain concentration profiles.
• Developed a computational approach to analyze these profiles for diffusivity and free-energy calculations.
• Employed fluorescence correlation spectroscopy for validating bulk diffusivities.

Main Results:

• The method accurately determined dextran diffusivities, consistent with independent measurements.
• Empirical scaling laws were identified for dextran diffusivity and free energy as a function of dextran mass.
• An elastic free-volume model quantitatively explained the steric repulsion and penetration behavior.

Conclusions:

• Particle penetration into hydrogels with steric interactions is governed by an elastic size-filtering mechanism.
• Hydrogel mesh-size distribution is broad, with penetration dominated by larger pores.
• The developed method offers a simplified yet powerful tool for characterizing particle-hydrogel systems.