Probing Microscale Structuring-Induced Phase Separation with Fluorescence Recovery Diffusion Dynamics in...

Area of Science:

• Materials Science
• Biomedical Engineering
• Polymer Chemistry

Background:

• Poly(ethylene glycol) (PEG)-based constructs need tunable mechanics and optimized microscale transport for controlled biomolecule release.
• Matrix inhomogeneities, such as aggregates and structuring, can significantly affect diffusion dynamics within PEG.
• Understanding these transport mechanisms is crucial for designing effective biomedical materials.

Purpose of the Study:

• To investigate the role of inhomogeneities and structuring in PEG matrices on microscale diffusion.
• To analyze the impact of polymer concentration and fillers (carboxymethyl cellulose and bentonite) on diffusion dynamics.
• To detect the onset of phase separation in PEG-based composites using diffusion measurements.

Main Methods:

• Fluorescence Recovery After Photobleaching (FRAP) was used to measure the diffusion coefficient (D) via diffusion half-time.
• Analysis of prebleach FRAP images provided structure factors to characterize matrix inhomogeneities.
• Phase contrast imaging, small-angle neutron scattering (SANS), and small-angle X-ray scattering (SAXS) were employed for structural characterization.

Main Results:

• Diffusion dynamics showed a concentration-dependent scaling (D ∼ φ⁻⁰.⁵⁴) in PEG solutions, consistent with Rouse theory.
• Bentonite addition above 0.1 wt% induced phase separation in the PEG matrix, evidenced by increased diffusion times and structure factors.
• PEG + bentonite systems formed a two-phase structure, unlike the one-phase PEG and PEG + CMC systems.

Conclusions:

• Microscale transport analysis, specifically diffusion half-time and prebleach FRAP imaging, sensitively detects phase separation onset in polymer matrices.
• The method provides a fast, high-throughput approach to investigate microscale mechanical responses and their correlation with polymer matrix structuring.
• This technique is valuable for optimizing the design of PEG-based biomedical constructs with controlled release kinetics.