Contact-line bending energy controls phospholipid vesicle adhesion

Abstract

Phospholipid bilayer bending energy is often discarded in the analysis of vesicle adhesion on the basis of a dimensionless parameter w = − Δ U R 0 2 / κ b ≫ 1 (interaction energy Δ U , spherical radius R 0 , bending rigidity κ b ), considered a regime of strong adhesion. In this study, we propose a model by which bending energy in a singular proximity of the contact line balances the adhesion energy. This is developed for a regime in which the membrane correlation length ξ is small compared with the vesicle radius R 0 , so a spherical cap with circular footprint presents an effective contact angle θ . Experiments are conducted in which the adhesion of 1-palmitoyl-2-oleoyl-glycero-3-phosphocholine (POPC) vesicles to hyaluronic acid hydrogel substrates is controlled by tuning the van der Waals attraction with systematic change in the hydrogel concentration. Theoretical interpretation of the data furnishes a dimensionless model parameter α ≈ 2 – 10 for contact angles θ ≈ 20 – 80 ∘ , beyond which vesicles collapse into discs. We show that the van der Waals interaction energy varies in the range − Δ U ≈ 0.14 – 0.68   μ J   m − 2 in response to varying the hydrogel concentration in a range c ha ≈ 2 – 10 %. The analysis provides a foundation for exploring vesicle–hydrogel interactions with electro-steric influences; these are poorly understood but pertinent in a wide variety of biological and technological applications.