Figure 1.

Outward (a–g) and inward (h–q) budding of vesicles in contact with several aqueous solutions. (a–f) Side-view phase contrast images and (g) a cartoon of a vesicle sitting on a glass substrate and subjected to osmotic deflation. Initially, the vesicle contains a homogeneous polymer solution (a). After phase separation (b), the heavier and denser dextran-rich phase is located at the vesicle bottom. Further deflation causes the dextran-rich phase to wet the membrane (c), and then to bud out (d–f). The osmolarity ratio r from (a) to (f) is 1.0, 1.14, 1.32, 1.46, 1.65, and 1.76, respectively. The system was left to equilibrate for at least 2 h after each consecutive deflation step. (h–p) xz-confocal scans and (q) a cartoon of vesicles in contact with fluorescently labeled droplets of dextran-rich phase (green). The membrane is also fluorescently labeled (red). The confocal images in the rows (h–j), (k–m), and (n–p) show the mixed fluorescence signal, and the red and green channels separately. Inspection of (i,l) shows that the interface between the dextran-rich droplets and the PEG-rich background contains essentially no lipid.