Adhesive interactions between vesicles in the strong adhesion limit

Area of Science:

• Colloidal physics
• Soft matter physics
• Biophysics

Background:

• Adhesive interactions between fluid bilayers are typically measured using supported bilayers, which cannot deform.
• Vesicles in suspension can deform via stretching, bending, and volume changes, unlike supported bilayers.
• This deformability can significantly alter adhesive interaction energies.

Purpose of the Study:

• To investigate the adhesive interaction energy between deformable vesicles in the strong adhesion limit.
• To quantify the enhancement of interaction energy due to vesicle deformability as a function of intervesicle separation.
• To explore the role of osmotic pressure and solute/ion equilibration in enhancing adhesion.

Main Methods:

• Theoretical modeling of vesicle deformability and its effect on interaction energy.
• Calculation of interaction energy based on vesicle properties: undeformed radius (R0), bending modulus (kb), area expansion modulus (ka).
• Incorporation of parameters from supported bilayer measurements: adhesive minimum (WP(0)) and separation (DP(0)).

Main Results:

• Weak adhesive potentials (e.g., |WP(0)| = 5 × 10−4 mJ/m2) lead to significantly deeper energy minima (>10×) in deformable vesicles due to increased area and flattening.
• Osmotic water expulsion enhances vesicle flattening and further increases adhesive interaction.
• Equilibration of ions and solutes due to osmotic water exchange further boosts adhesion energy.

Conclusions:

• Deformable vesicles exhibit substantially enhanced adhesion compared to rigid bilayers, even with weak intrinsic attractions.
• This progressive increase in adhesion energy can explain flocculation and instability in vesicle suspensions.
• Findings are critical for understanding and optimizing concentrated vesicle-based products (e.g., fabric softeners, drug delivery systems).