Size-Dependent Suppression of Molecular Diffusivity in Expandable Hydrogels: A Single-Molecule Study

Area of Science:

• Biophysics
• Materials Science
• Nanotechnology

Background:

• Controlling hydrogel nanomatrix meshwork size is crucial for understanding molecular diffusion.
• Expansion microscopy offers a novel approach to tune hydrogel meshwork properties.

Purpose of the Study:

• To investigate the size-dependent suppression of molecular diffusivity in tuned hydrogel nanomatrices.
• To decouple meshwork-induced diffusion obstruction from viscosity effects.

Main Methods:

• Repurposing expansion microscopy to control hydrogel meshwork size.
• Employing single-molecule displacement/diffusivity mapping (SMdM) microscopy.
• Analyzing molecular diffusion across a range of polymer fractions (0.14-7 wt %).

Main Results:

• Larger molecules exhibit more impeded diffusion at a fixed meshwork size.
• Diffusion is progressively suppressed as meshwork size decreases, especially for larger molecules.
• Meshwork obstruction of diffusion is distinct from viscosity-induced suppression.

Conclusions:

• Molecular diffusivity in hydrogels is governed by both diffuser size and meshwork size.
• Two distinct mechanisms, diffuser-size-dependent and independent, contribute to diffusion slowdown in complex systems.
• This work provides insights into diffusion dynamics within cellular environments.