Development of an In Vitro Release Assay for Low-Density Cannabidiol Nanoparticles Prepared by Flash NanoPrecipitation

Nanoparticle encapsulation is an attractive approach to improve the oral bioavailability of hydrophobic therapeutics. The high specific surface area of nanoparticle formulations, combined with the thermodynamically driven increased solubility of anamorphous drug core, promotes rapid drug dissolution. However, the physicochemical properties of the hydrophobic therapeuticcan present obstacles toin vitrocharacterization of nanoparticle formulations. Namely, drugs with low density and high membranebinding affinity frustrate traditional analytical methods to monitor release kinetics from nanoparticles. In this work, cannabidiol(CBD) was encapsulated into nanoparticles with low polydispersity and high drug loading via Flash NanoPrecipitation (FNP), ascalable self-assembly process. Hydroxypropyl methylcellulose acetate succinate (HPMCAS) and lecithin were employed asamphiphilic particle stabilizers during the FNP process. However, the low density and high membrane binding affinity of theamorphous CBD nanoparticle core prevented the characterization ofin vitrorelease kinetics by conventional methods. ReleasedCBD could not be separated from intact nanoparticles byfiltration or centrifugation. To address this challenge, an alternativeapproach is described to coencapsulate 6 nm hydrophobic Fe3O4colloids with CBD during FNP. The Fe3O4colloids were added at33% by mass (approximately 20% by volume) to increase the density of the nanoparticles, resulting in particles with an averagediameter of 160 nm (CBD-lecithin-Fe3O4) or 280 nm (CBD-HPMCAS-Fe3O4). This densification enabled the centrifugalseparation of dissolved (released) CBD from unreleased CBD during thein vitroassay while avoiding the losses associated with afiltration step. The resulting nanoparticle formulations provided more rapid and completein vitrodissolution kinetics than bulkCBD, representing a 6-fold improvement in dissolution compared to crystalline CBD. The coencapsulation of high-density Fe3O4colloids to enable the separation of nanoparticles from release media is a novel approach to measuringin vitrorelease kinetics of nanoencapsulated low-density, hydrophobic drug molecules.