While flash nanoprecipitation (FNP) has proven to be an extremely rapid and highly efficient nanoparticle fabrication process for hydrophobic drugs, physical instability associated with nonequilibrium molecular orientation of amphiphilic stabilizers (ASs) in nanoparticles remains a major snag in the general application of this nanotechnology, particularly for a drug with ACDLog P in the range of ∼2-9. This study was aimed at elucidating the costabilizing role of cholesterol (CLT) in the FNP of AS-stabilized nanoparticles of itraconazole (ITZ), a model drug with an ACDLog P of 4.35 ± 1.22 and log P of 5.66. The presence of CLT was shown to reduce the initial particle size and markedly improve the short-term storage stability of ITZ nanoparticles. The stability-enhancement by CLT can be linked to its higher miscibility or stronger interaction with the AS hydrophobic moiety than with ITZ (as reflected by the absolute differences of their solubility parameter values). Surface analyses employing X-ray photoelectron spectroscopy (XPS) and atomic force microscopy (AFM) suggest that, through the coprecipitation of CLT with ITZ to form a mixed hydrophobic drug core, the CLT molecules that are exposed on the core surface serve to afford a stronger and more timely surface anchorage of the AS hydrophobic moieties, thereby facilitating the rearrangement of AS molecules toward the stable micelle-like structure. The present findings offer a mechanistic insight into the interplay between amphiphilic stabilizer and costabilizer in enhancing the physical stability of drug nanoparticles and may carry important implications for the development of more stable and efficacious nanoparticle therapeutics.
Keywords: amphiphilic stabilizers; cholesterol; flash nanoprecipitation; itraconazole nanoparticles; physical stability; solubility parameter.