This study explores the preparation and characterization of soy lecithin vesicles modified with dipalmitoylphosphatidylcholine (DPPC), dioleoylphosphatidylcholine (DOPC), and cholesterol (CHO), focusing on how these compositional changes modulate bilayer fluidity and permeability. Large unilamellar vesicles (LUVs) with narrow size distribution were successfully obtained by the extrusion method, and unencapsulated ferricyanide was efficiently removed by gel chromatography on Sephadex. Remarkably, the incorporation of saturated DPPC enabled the formation of stable LUVs at room temperature, well below its gel-to-liquid crystalline phase transition temperature (~41 °C), a challenging task when using DPPC alone.
Bilayer fluidity was assessed using the fluorescent probe 6-propionyl-2-(N’,N’-dimethyl) aminonaphthalene (PRODAN), while permeability was evaluated through the encapsulation and release of K₄[Fe(CN)₆], a hydrophilic and electroactive molecule. Incorporation of the analyte did not affect vesicle assembly.
The highest bilayer fluidity was observed in Lec:Cho (1:1.6) and Lec:DPPC (1:2) systems, whereas Lec:DOPC mixtures were dominated by the ordering effect of DOPC.
Release studies revealed striking formulation-dependent differences. Complete release of K₄[Fe(CN)₆] occurred in Lec:Cho (1:1.6), Lec:DPPC (1:2), and Lec:DOPC (1:1), while lecithin, Lec:DOPC (1:2), and pure DOPC vesicles showed partial release of 63%, 59%, and 22%, respectively. Notably, release rates were not directly correlated with release percentages: lecithin vesicles exhibited the fastest release (0.79%/min), whereas Lec:DOPC (1:1) vesicles were the slowest (0.19%/min). Overall, these results establish a clear correlation between bilayer fluidity and the release rate of ionic hydrophilic molecules, while also demonstrating that compositional tuning, particularly with DPPC, allows the design of lecithin-based nanocarriers with tailored permeability. This approach opens new opportunities for the development of vesicle-based delivery systems in nanomedicine using ionic analytes.
