Aggregation Behavior of Pegylated Bile Acid Derivatives

Bile acids are amphiphilic endogenous steroids that act as anionic surfactants in the digestive tract and aggregate in aqueous solutions. Nonionic surfactants were synthesized by grafting poly(ethylene glycol) chains of various lengths (pegylation) to three bile acids (lithocholic, deoxycholic, and cholic acid) using anionic polymerization. The aggregation properties of the derivatives were studied with viscosity measurements and light scattering as well as with steady-state and time-resolved fluorescence techniques, and the aggregates were visualized by transmission electron microscopy to elucidate the effect of pegylation on the aggregation process. The fluorescence results showed a good correlation with the capacity of the bile acid derivatives to solubilize a hydrophobic drug molecule. The solubilization of ibuprofen depends on the length and the number of grafted PEG chains, and the solubilization efficiency increases with fewer PEG chains on the bile acid. The results indicate their potential for use in the design of new bile acid-based drug-delivery systems.