Membrane composition of polymer-lipid hybrid vesicles

Hybrid vesicles (HVs) assembled from phospholipids and amphiphilic block copolymers (BCPs) are a more recent alternative to liposomes and polymersomes. We aim to change the properties of the HV membranes by varying the chemical composition of the hydrophobic block in the BCPs that have poly(carboxyethyl acrylate) (PCEA) as the hydrophilic part. To this end, statistical copolymers of cholesteryl methacrylate and either butyl methacrylate (BuMA) or 2-hydroxyethyl methacrylate (HEMA) as well as the corresponding homopolymers were synthesized and used as macroinitiator for the extension with PCEA. All the BCPs allowed for the assembly of small and giant HVs with soybean L-α-phosphatidylcholine. The extend of the co-extisting micellar populations varied as shown by transmission electron microscopy and small-angle X-ray spectroscopy. Although the membrane packings derived from spectra when using Laurdan as an environmentally sensitive fluorescent probe were comparable between the different HVs, their permeability towards 5(6)-carboxy-X-rhodamine or carboxyfluorescein depended on the membrane composition, i.e., HEMA-containing membranes had higher permeability than membranes containing the other tested BCPs for small and giant HVs. Further, membranes with BuMA offered the most suitable environment for the association with β-galactosidase illustrated by the efficient substrate conversion. Taken together, the hydrophobic block is a relevant mean to control the morphologies and membrane properties of HVs.