Encapsulating Vesicles and Colloids from Cochleate Cylinders

Encapsulating small vesicles or colloidal particles within a phospholipid bilayer affords multicompartment structures that are interesting for targeted drug delivery, imaging, or separations. Dioleoylphosphatidylserine (DOPS), an anionic lipid, forms cochleate cylinders, tightly wrapped tubes of concentric bilayers, on addition of millimolar Ca2+. Complexation of Ca2+ by the subsequent addition of ethylenediaminetetraacetic acid (EDTA) results in the unwrapping of the cochleate cylinders of DOPS sheets and reclosure to form micrometer-sized vesicles, which can entrap smaller vesicles in solution. Polystyrene spheres added to the cochleate cylinders before the EDTA unwrapping can also be enclosed.