Unilamellar

Unilamellar describes a structure consisting of a single lipid bilayer or lamella. In the context of vesicles, unilamellar vesicles are closed, spherical shells that enclose an aqueous interior and are bounded by one lipid bilayer, as opposed to multilamellar vesicles which have multiple concentric bilayers.

A unilamellar vesicle contains a single lipid bilayer separating the interior aqueous phase from the external milieu. The size of unilamellar vesicles varies widely: small unilamellar vesicles are typically less than 100 nanometers in diameter, while large unilamellar vesicles range from about 100 nanometers to the low micrometer scale. Unilamellar structures can be formed from natural or synthetic lipids as well as from polymeric components, yielding liposomes or polymersomes respectively.

Unilamellar vesicles are contrasted with multilamellar vesicles, which consist of multiple bilayers arranged like an onion, creating several aqueous compartments. The single-bilayer architecture of unilamellar vesicles generally offers higher encapsulation efficiency for aqueous cargo and more predictable release profiles, while multilamellar forms can provide greater stability and higher total cargo capacity per particle.

Preparation techniques for unilamellar vesicles include methods such as thin-film hydration followed by sizing (extrusion or sonication), detergent dialysis, and solvent injection approaches. Extrusion through polycarbonate membranes of defined pore size is commonly used to produce uniform, small unilamellar vesicles.

Applications span drug delivery, imaging, and gene therapy, where the single bilayer facilitates controlled release and predictable pharmacokinetics. In materials science, unilamellar polymeric vesicles, or polymersomes, extend these concepts to synthetic polymers.