Tailor-made drug carrier: Comparison of formation-dependent physicochemical properties within self-assembled aggregates for an optimal drug carrier.

Self-assembled surfactant aggregates, such as micelles and vesicles, have been investigated for their application as drug carriers in the treatment of various diseases. However, the characteristics that decide which aggregate is the best drug carrier for each disease have not yet been clarified. In order to design an optimal drug carrier for each disease, various kinds of self-assembled aggregates, such as spherical micelles, lens-like vesicles, and tube-like vesicles, were evaluated by "multiple techniques" including dynamic light scattering, differential scanning calorimetry, nuclear magnetic resonance spectroscopy, and fluorescence measurement using the Laurdan probe. These studies led to the compilation of a database on the formation-dependent properties of self-assembled aggregates. As the relationship between physicochemical properties of self-assembled aggregates and their functions as drug carriers have been extensively reported, this database can be utilized for designing an optimal drug carrier, i.e., a tailor-made drug carrier.

Characterization of sorbitan surfactant-based vesicles at the molecular scale using NMR: Effect of acyl chain length vs. phospholipid composition.

We focused on the characterization of the hydrophobic-hydrophilic interface of the membrane of vesicles prepared with various sorbitan surfactants using two evaluation methods: Laurdan fluorescence intensity (GP(340) value) and NMR analysis (half linewidth). Laurdan fluorescence intensity analysis, used to evaluate the hydrophobicity of the interior of the vesicular membrane, indicated a similarity between Span vesicles and liposomes in terms of hydrophobicity, while NMR analysis, used to assess the mobility of lipid molecules, indicated a large difference between Span vesicles and liposomes in terms of molecular mobility at the interface. These results suggest that the physicochemical properties of Span vesicles and liposomes are roughly similar at the "meso-scale" but not completely similar at the "molecular scale."

Formation of lens-like vesicles induced via microphase separations on a sorbitan monoester membrane with different headgroups.

The microphase separation of lipid molecules on a vesicle membrane can be induced, depending on the difference in the geometric structures of their headgroups. Through cryo-transmission-electron-microscopy analysis, a lens-like vesicle was prepared by mixing 50 wt% Span 40 (sorbitan monopalmitate) and 50 wt% Tween 40 [polyoxyethylene (20) sorbitan monopalmitate]. Considering the molecular structures of Span 40 and Tween 40, the high-curvature region was mainly formed by Tween 40. As determined by Fourier-transform infrared spectroscopy, dielectric-dispersion analysis, and differential scanning calorimetry, a hydration layer was likely formed because polyoxyethylene conjugates with the headgroups of Tween 40. These investigations of the obtained self-assembled aggregates of nonionic surfactants with heterogeneous surfaces could contribute to the development of new types of biomaterials.