Preparation and Characterization of Glabridin-Loaded Poly(vinyl alcohol) Nanofiber Sheets: The Effects of PVA Grade on Release and Membrane Permeation

Glabridin is a hydrophobic isoflavonoid isolated from licorice that exhibits potent tyrosinase inhibitory activity and is therefore regarded as a promising skin-whitening agent. However, its pharmaceutical application is limited by its poor aqueous solubility and low skin permeability. To improve the dissolution and membrane permeation of glabridin, glabridin-loaded poly(vinyl alcohol) (PVA) nanofibers were prepared by electrospinning. Four PVA grades differing in their degrees of polymerization and hydrolysis were evaluated as nanofiber matrices. Bead-free nanofibers were successfully fabricated regardless of the PVA grade employed. Differential scanning calorimetry and powder X-ray diffraction analyses indicated that glabridin was predominantly present in an amorphous state within the nanofiber matrix, while ATR-FTIR spectroscopy suggested possible intermolecular interactions between glabridin and PVA. In vitro membrane permeation studies using Strat-M® membranes demonstrated that the nanofiber formulations enhanced the apparent membrane permeation of glabridin relative to the control formulation. In addition, the release and membrane permeation behavior of glabridin depended on the PVA grade, reflecting differences in the dissolution characteristics of the polymer matrix. Collectively, these findings suggest that electrospun PVA nanofibers provide a promising formulation platform for improving glabridin delivery while enabling control of its release and membrane permeation through appropriate selection of the PVA matrix.