Properties of various phospholipid mixtures as emulsifiers or dispersing agents in nanoparticle drug carrier preparations

The characteristics of mixed phospholipids were examined when used as dispersing agents and emulsifiers. Synthesized phospholipids were mixed to investigate the potential effects of different hydrophilic or lipophilic groups on emulsification and dispersion. To examine the effects of the hydrophilic polar head group on the dispersing or emulsifying potency of phospholipids, l--phosphatidylcholine dimyristoyl (DMPC) and l--phosphatidylethanolamine dimyristoyl (DMPE) were mixed in various ratios. Moreover, all combinations of two kinds of phosphatidylcholines (PCs) out of l--phosphatidylcholine dilauroyl (DLPC), DMPC, l--phosphatidylcholine dipalmitoyl (DPPC) and l--phosphatidylcholine distearoyl (DSPC) were tested (50:50, w/w) to examine the effects of the hydrophobic carbon chains on the dispersing or emulsifying potency of phospholipids. Mean diameters of vesicles and O/W emulsions prepared by sonication were measured. Vesicles prepared with DMPC–DMPE mixtures gave larger particle sizes than those of DMPC alone. Particle sizes of vesicles prepared with a mixture of two kinds of PCs increased when adding a PC with a longer carbon chain, while particle sizes in a mixture with a PC having a shorter carbon chain was comparable to those in pure PC. In vesicles that were generated by hydration of phospholipids and had a bilayer form, the physical form of the phospholipids consisting of bilayers was thought to be an important factor influencing particle sizes. Among the emulsions, DMPC–DMPE mixtures gave a similar droplet size to DMPC alone. Droplet size in emulsions prepared with a mixture of two kinds of PCs had a strong positive correlation with the total number of carbons, which corresponds to hydrophilic–lipophilic balance (HLB). In O/W emulsions, in which phospholipids were absorbed at water–oil interfaces and which have a single layer form, HLB was thought to be a major factor in the determination of particle size; likewise with non-ionic emulsifiers.