Material properties of hybrid lipid/polymer vesicles and incorporation of membrane proteins within these structures for robust applications in bionanotechnology

Vesicles have many applications from acting as microreactors and sensors to drug delivery vectors. While pure lipid and pure polymer vesicles have been used in the past for these applications, there are some disadvantages: although biocompatible, lipid membranes have poor long-term stability while the opposite is true of polymer membranes. A previous study showed that by blending POPC lipid with poly 1,2-butadiene-block-polyethyleneoxide (PBd-b-PEO) diblock copolymer to form a hybrid vesicle, the durability from the polymers can be combined with the biocompatibility of lipids (1). However, while the biocompatibility of PBd-b-PEO/POPC blend has been established, relatively little is known about membrane properties of this lipid-polymer mixture. A combination of techniques was used to probe the material properties and structure of hybrid membranes consisting of POPC lipid combined with PBd-b-PEO polymer of two different molecular weights. Hybrid vesicles of increasing polymer fraction were probed by fluorescence spectroscopy to determine proton permeability and contents release properties. Small angle x-ray scattering and cryogenic electron microscopy techniques were utilised to determine how hydrophobic thickness mismatch affects the structure and membrane properties of the hybrid vesicles. Confocal microscopy observed how increasing the polymer fraction affects membrane mixing, hydration and fluidity. Characterising the material properties of a hybrid vesicle could help design vesicles for bionanotechnology applications with controlled encapsulation and release. However, for many bionanotechnology applications it is also desirable for the system to incorporate biofunctional molecules for biomimetic membrane-based technologies. This hybrid lipid-polymer blend could be developed further to provide a stable, durable, homogenous environment for certain membrane proteins to create artificial cells.