Toward Cell Membrane Biomimetic Lipidic Cubic Phases: A High-Throughput Exploration of Lipid Compositional Space

The bicontinuous lipidic cubic phase (LCP), which is based on the fundamental structure of the lipid bilayer, is increasingly used in a range of applications including drug delivery, in meso crystallization of membrane proteins, biosensors, and biofuel cells. The majority of LCPs investigated to date have been formulated from a single lipid or a combination of two lipids in water. Such systems lack tunability, with only a narrow range of lattice parameters adopted. In addition, the lipid bilayer of these materials lacks the complexity of natural cell membranes, which are composed of hundreds of different lipids and which may be essential to retaining the functionality of proteins embedded within them. In this work, we investigate the phase behavior of quaternary lipid–water systems consisting of three different lipids (monoolein–cholesterol–phospholipid) and water using a combination of experimental and simulation techniques. This study provides a large library of lipidic materials with bilayer compositions, which more effectively mimic the native cell membrane and significantly increased tunability based on nanostructural parameters such as lattice parameter, aqueous channel size, and bilayer thickness. Importantly, the library contained several extremely swollen cubic phases with a maximum lattice parameter of up to 342.5 Å. Many of these cubic phases were successfully dispersed into highly swollen cubosomes. The swollen cubic phases described in this article contain only uncharged lipids and are therefore particularly useful for applications with a high salt concentration, including encapsulation of larger therapeutic proteins and peptides for in vivo delivery, or for the crystallization of large membrane proteins such as GPCRs