(197g) Encapsulation and Phase Behavior of Lipid/Copolymer/Protein Hybrid Biomembranes

Entrapment of biomembranes in mesoporous metal oxide gels has proven to be a challenge, as current and previous techniques utilize liposomes as biological membrane hosts. The instability of liposomes in mesoporous gels is attributed to their size and altered environment upon entrapment within the nanometer scale pores (5-50 nm). We have overcome these barriers by entrapping nanometer-scale lipid/protein/copolymer membrane assemblies such as styrene-maleic acid copolymer-stabilized lipid nanodiscs. We have investigated the phase behavior of the lipids in addition to the structure, localization, and environmental polarity of the involved proteins mainly by spectroscopy methods. We then compare the thermal stability of gel-entrapped bacteriorhodopsin in purple membrane or lipid nanodiscs and find differences related to oligomeric states of the protein. Next, will be discussed recent studies of hybrid biomembranes combining block copolymers and phospholipids. The chemical diversity afforded by inclusion of block copolymers is particularly relevant to the formation of stealth liposomes or stimuli-responsive membranes (e.g. pH- or thermo-responsive systems), which can aid in the control of drug retention and release. However, the phase behavior of these hybrid biomembranes has not been methodically explored. To this end, we have studied small (~100 nm) vesicles, copolymer-stabilized nanodiscs, and giant vesicles with membranes made of polybutadiene-block-polyethylene oxide (PBd-PEO) and dipalmitoylphosphatidylcholine (DPPC) using fluorescence spectroscopy and by fluorescence microscopy.