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Most small molecule chemotherapeutics must cross one or more cellular membrane barriers to reach their biochemical targets. Owing to the relatively low solubility of chemotherapeutics in the lipid membrane environment, high doses are often required to achieve a therapeutic effect. The resulting systemic toxicity has motivated efforts to improve the efficiency of chemotherapeutic delivery to the cellular interior. Toward this end, liposomes containing lipids with cationic head groups have been shown to permeabilize cellular membranes, resulting in the more efficient release of encapsulated drugs into the cytoplasm. However, the high concentrations of cationic lipids required to achieve efficient delivery remain a key limitation, frequently resulting in toxicity. Toward overcoming this limitation, here, we investigate the ability of ternary lipid mixtures to enhance liposomal delivery. Specifically, we investigate the delivery of the chemotherapeutic, doxorubicin, using ternary liposomes that are homogeneous at physiological temperature but have the potential to undergo membrane phase separation upon contact with the cell surface. This approach, which relies upon the ability of membrane phase boundaries to promote drug release, provides a novel method for reducing the overall concentration of cationic lipids required for efficient delivery. Our results show that this approach improves the performance of doxorubicin by up to 5-fold in comparison to the delivery of the same drug by conventional liposomes. These data demonstrate that ternary lipid compositions and cationic lipids can be combined synergistically to substantially improve the efficiency of chemotherapeutic delivery in vitro.

Conjugated polyelectrolytes (CPEs) are promising materials for generating optoelectronics devices under environmentally friendly processing conditions, but challenges remain to develop methods to define lateral features for improved junction interfaces and direct optoelectronic pathways. We describe here the potential to use a bottom-up approach that employs self-assembly in lipid membranes to form structures to template the selective adsorption of CPEs. Phase separation of gel phase anionic lipids and fluid phase phosphocholine lipids allowed the formation of negatively charged domain assemblies that selectively adsorb a cationic conjugated polyelectrolyte (P2). Spectroscopic studies found the adsorption of P2 to negatively charged membranes resulted in minimal structural change of the solution phase polymer but yielded an enhancement in fluorescence intensity (~50%) due to loss of quenching pathways. Fluorescence microscopy, dynamic light scattering, and AFM imaging were used to characterize the polymer-membrane interaction and the polymer-bound domain structures of the biphasic membranes. In addition to randomly formed circular gel phase domains, we also show that predefined features, such as straight lines, can be directed to form upon etched patterns on the substrate, thus providing potential routes toward the self-organization of optoelectronic architectures.

We demonstrate the construction of novel protein-lipid assemblies through the design of a lipid-like molecule, DPIDA, endowed with tail-driven affinity for specific lipid membrane phases and head-driven affinity for specific proteins. In studies performed on giant unilamellar vesicles (GUVs) with varying mole fractions of dipalymitoylphosphatidylcholine (DPPC), cholesterol, and diphytanoylphosphatidyl choline (DPhPC), DPIDA selectively partitioned into the more ordered phases, either solid or liquid-ordered (L(o)) depending on membrane composition. Fluorescence imaging established the phase behavior of the resulting quaternary lipid system. Fluorescence correlation spectroscopy confirmed the fluidity of the L(o) phase containing DPIDA. In the presence of CuCl(2), the iminodiacetic acid (IDA) headgroup of DPIDA forms the Cu(II)-IDA complex that exhibits a high affinity for histidine residues. His-tagged proteins were bound specifically to domains enriched in DPIDA, demonstrating the capacity to target protein binding selectively to both solid and L(o) phases. Steric pressure from the crowding of surface-bound proteins transformed the domains into tubules with persistence lengths that depended on the phase state of the lipid domains.

A novel transformation of giant lipid vesicles to produce nanotubular structures was observed upon the binding of streptavidin to biotinylated membranes. Unlike membrane budding and tubulation processes caused by proteins involved with endocytosis and vesicle fusion, streptavidin is known to crystallize at near the isoelectric point (pI 5 to 6) into planar sheets against biotinylated films. We have found, however, that at neutral pH membranes of low bending rigidity (10kT), such as 1-palmitoyl-2-oleoyl-sn-glycero-3-phosphocholine (POPC), spontaneously produce tubular structures with widths ranging from micrometers to below the diffraction limit (250 nm) and lengths spanning up to hundreds of micrometers. The nanotubes were typically held taut between surface-bound vesicles suggesting high membrane tension, yet the lipid nanotubes exhibited a fluidic nature that enabled the transport of entrained vesicles. Confocal microscopy confirmed the uniform coating of streptavidin over the vesicles and nanotubes. Giant vesicles composed of lipid membranes of higher bending energy exhibited only aggregation in the presence of streptavidin. Routes toward the development of these highly curved membrane structures are discussed in terms of general protein-membrane interactions.