Cholesteryl oleate (ChO)/γ-cyclodextrin (γ-CD) nanoparticles have been developed in which a crystalline ChO core is surrounded by multiple nanosheet shells composed of ChO/γ-CD inclusion complex crystals. This study revealed their structural responsiveness to thermal and bile stimuli, clarifying the underlying mechanism and emphasizing their potential as advanced drug delivery systems (DDS) carriers. Cryogenic transmission electron microscopy (cryo-TEM) revealed that heating above 55 °C disrupted the core-shell structure, yielding spherical nanoparticles (100-200 nm) and nanosheets. Differential scanning calorimetry (DSC), in situ synchrotron wide-angle X-ray diffraction (WAXD), and atomic force microscopy (AFM) force-distance curve analyses indicated that the spherical particles consisted of liquid-phase ChO, while the nanosheets retained the crystal structure of the ChO/γ-CD inclusion complex with a thickness of 7.8 nm, corresponding to two units of the ChO/γ-CD = 2:5 inclusion complex. Upon heating, the ChO crystal core melted to form spherical nanodroplets, while the nanosheet shells dissociated from the nanoparticle interface. Furthermore, cryo-TEM with tilt-angle imaging and WAXD analyses demonstrated that in a fed-state simulated intestinal fluid (FeSSIF), the nanosheets of the inclusion complex dissociated similarly. In contrast, the ChO core retained its cylindrical shape and crystalline structure. These changes are driven by a host-guest exchange mechanism, where bile acids form stable inclusion complexes with γ-CD, as well as by the solubilization of ChO molecules by bile acid/lecithin mixed micelles. These findings show that ChO/γ-CD nanoparticles possess dual responsiveness to exogenous stimulus (heat) and an endogenous stimulus (bile components), highlighting their potential as functional DDS carriers.
Omori et al. (Wed,) studied this question.