Spreading of giant vesicles on moderately adhesive substrates by fingering: A reflection interference contrast microscopy study

The spreading of giant vesicles of neutral phospholipids on avidin-covered solid substrates is studied by reflection interference contrast microscopy. Contact formation, bilayer-substrate separation distances, and edge profiles are evaluated. The spreading occurs in two steps: advancement of lobes of average thickness {}70 nm by fingering, sometimes followed by thinning to {}30±{}10 nm, determined by interfacial forces, and resulting in a pancakelike shape. The average advancement speed of the fingers appears constant at early times ({}0.2 {μ}m/s) and slows down at a later stage. Locally, the bilayer advances stepwise owing to discontinuous water expulsion. The spreading is impeded by pinning centers resulting in fjord formation. The vesicle spreading is tentatively interpreted in terms of the classical theory of viscous fingering.