Analysis of the Vesicular Structure of Nanoparticles in the Phospholipid-Based Drug Delivery System Using SAXS Data

Small-angle X-ray scattering (SAXS) is used to characterize the vesicular structure of the phospholipid transport nanosystem (PTNS) at PTNS concentrations in water of 25, 31.25, and 37.5% (w/w). The average vesicle radius, size polydispersity, bilayer thickness, and internal structure are determined from the experiment using two models for the photon scattering density distribution. Two independent methods are used to calculate the SAXS spectra: the form factor of a heterogeneous spherical shell and the method of separated form factors. The two methods for calculating the spectra and two models for description of the internal structure of the lipid bilayer provide identical results, which demonstrate a decrease in the vesicle radius, thickness of the bilayer, and thickness of the hydrocarbon-chain region upon an increase in the maltose concentration in water. It is shown that a decrease in the lipid bilayer thickness upon an increase in the maltose concentration is caused by interdigitation of the hydrocarbon chains. The hydrophobic volume of one vesicle suitable for water-insoluble drugs is shown to have a maximum value of 14.55 x 10(6) angstrom(3) at a PTNS concentration in water of 25%. Increasing the PTNS concentration in water up to 37.5% leads to a decrease in the hydrophobic volume to 6.16 x 10(6) angstrom(3).