Polymerizable vesicles based on a single-tailed fatty acid surfactant: a simple route to robust nanocontainers

Vesicles with polymerizable bilayers have attracted interest because of their increased robustness, which is advantageous for applications. However, to prepare such vesicles, lipids with polymerizable moieties usually need to be synthesized, and this often involves cumbersome, multistep reactions. Here, we present an alternative, simpler approach based on a commercially available, single-tailed surfactant, viz. 10-undecenoic acid (UDA), a fatty acid with a terminal double bond. Previously, the polymerization of UDA micelles in water has been studied. We show that UDA can also be induced to form vesicles by adjusting the pH: vesicles form at intermediate pH (6-8), whereas at higher pH (>11), the vesicles are transformed into micelles. The presence of UDA vesicles in the pH 6-8 range is confirmed using small-angle neutron scattering (SANS) and cryotransmission electron microscopy (cryo-TEM). Subsequent thermal polymerization of UDA bilayers is done using 2,2-dimethoxy-2-phenylacetophenone (DMPA) as initiator. A partial polymerization of the bilayers is achieved, and polymerized UDA vesicles resist disruption into micelles when the solution pH is increased. To make the bilayers more robust, the vesicles are copolymerized with divinylbenzene (DVB), a hydrophobic cross-linker that partitions into the bilayer. DVB-cross-linked UDA vesicles are very stable and cannot be disrupted by detergents like Triton X-100.