Lipid Vesicle Preparation Using W/O/W Multiple Emulsions Via Solvent Evaporation: The Effect of Emulsifiers on the Entrapment Yield of Hydrophilic Materials

We studied the effects of emulsifiers on the entrapment yields of a hydrophilic material, calcein, in lipid vesicles formed using the multiple emulsion method. The primary emulsion (W₁/O) was prepared via sonication while the secondary emulsification that produced the W₁/O/W₂ multiple emulsions was achieved using the microchannel (MC) emulsification technique. The emulsifiers used in the continuous (W₂) phase were Tween® 80, Pluronic® F68, and bovine serum albumin (BSA). Lipid vesicles formed via solvent evaporation of the multiple emulsion droplets had an average diameter of about 180 nm, similar to the size of the water droplets in the primary W₁/O emulsions. The entrapment yields of calcein increased with decreasing concentrations of Tween® 80 but decreased with decreasing concentrations of Pluronic® F68 and BSA. The effects of type and concentration of emulsifier were considered in relation to three possible mechanisms: (i) destabilization/solubilization of lipid bilayers by emulsifiers, (ii) reversed-micellar transport of W₁ contents from internal to external water phases through the O phase, and (iii) release of inner water (W₁) contents into the continuous (W₂) phase via the instability of W₁/O/W₂ and leakage of W₁ contents. Using the food grade emulsifier Tween® 80 at a low concentration of about 0.1 or 0.05 wt%, calcein as a model hydrophilic material could be efficiently entrapped (ca. 80%) in homogenously dispersed lipid vesicles.