Formation and Characteristics of Lipid-Blended Block Copolymer Bilayers on a Solid Support Investigated by Quartz Crystal Microbalance and Atomic Force Microscopy

Liposomes
grafted with polymer have long been used in drug delivery
applications, and block copolymersomes have emerged as attractive
and more robust alternatives for both drug delivery and artificial
organelle applications. Hybrid membranes that could combine the respective
advantages of fluid lipid and robust polymer bilayers are an attractive
and enticing alternative. The properties of membranes in amphiphile
vesicles are challenging to study and many applications benefit from
surface-based access to the membrane. We therefore explore the self-assembly
and mechanical properties of supported hybrid bilayers (SHBs) composed
of polybutadiene-block-poly­(ethylene oxide) block
copolymers and zwitterionic phosphatidylcholine lipids on SiO2 supports. Quartz crystal microbalance with dissipation monitoring
(QCM-D) measurements show that formation of SHB on SiO2 by vesicle fusion depends on the mass fractions of lipids and block
copolymers. Atomic force microscopy was used to study the microscopic
mixing of lipids in the SHB to reveal that lipid-phase separation
is not observed in SHBs. Force spectroscopy was performed to extract
information about thickness and mechanical properties of the hybrid
membranes. SHBs are shown to combine the properties of lipid membranes
and polymer brushes, and the tip force required to rupture the membrane
decreases and the bilayer thickness increases as the block copolymer
fraction is increased.