Bilayer-domain formation of thermoresponsive amphiphilic block copolymers in hybrid liposomes for synthetic molecular channels

Molecularly permeable vesicles have attracted interest as compartments for nanoreactors or artificial cells, as they can allow the transport of molecules from the exterior to the interior of the vesicles. One strategy to increase vesicle permeability is the incorporation of amphiphilic copolymers that contain thermoresponsive poly(propylene oxide) into phospholipid vesicles. However, the nanostructures of these polymers, which are directly related to the molecular permeability, remain to be elucidated. Here, we report on the nanostructures of polymers incorporated in such membranes and the permeability of the polymer/phospholipid hybrid vesicles against water-soluble molecules. Neutron-scattering experiments revealed that the polymers form disk-like bilayer domains on the membranes, whose thickness is almost equivalent to that of the bilayer membranes when the polymers alone are self-assembled into vesicles. These domains act as synthetic molecular channels for low-molecular-weight poly(ethylene glycol), and their permeability can be regulated by changing the molecular weight of the poly(propylene oxide). These findings provide valuable insight into the design of novel polymers for synthetic channels, the prediction of their permeability, and the preparation of permeable vesicles.