Preparation and Characterization of Silymarin-Loaded Nanostructured Lipid Carriers for UV-Protection

Background: Silymarin is a polyphenol-rich plant extract with antioxidant and UV-absorbing properties. However, its limited solubility and stability present challenges, necessitating further formulation research. Objectives: This study aimed to develop a novel silymarin-loaded nanostructured lipid carrier (NLC) and evaluate its in vitro photoprotective potential. Methods: NLCs were prepared by melt emulsification followed by high-shear homogenization using cetyl palmitate (CP) or beeswax (BW) as the solid lipids, oleic acid as the liquid lipid, and Tween 80 as the surfactant. The NLCs were characterized in terms of particle size, polydispersity index, zeta potential, drug loading, and entrapment efficiency. Their infrared spectra, thermal behavior, crystallinity, in vitro drug release, rheological properties, and in vitro sun protection effects were also evaluated. In addition, a stability study was conducted on the BW-containing NLCs. Results: Formulations containing CP showed mean particle sizes ranging from 102.9 to 140.0 nm and a polydispersity index (PDI) of 0.25 - 0.48, whereas those incorporating BW showed a broader size range (108.8 - 898.8 nm; PDI: 0.28 - 0.88). The developed silymarin-loaded NLCs exhibited high encapsulation efficiency, as confirmed by DSC, XRD, and FTIR analyses. Although silymarin-loaded NLCs, particularly BW-based formulations, exhibited relatively higher UV protection, the achieved SPF values (3.76 - 6.01) indicate that silymarin alone is insufficient for effective clinical photoprotection. Finally, stability assessments revealed notable challenges, with high silymarin loading and elevated surfactant concentrations leading to marked particle aggregation and loss of colloidal stability (PDI reaching 1.0) after three months of storage. Conclusions: This study developed silymarin-loaded NLCs with high loading capacity and biocompatible natural ingredients. However, the formulations showed long-term stability challenges and inadequate sun protection, necessitating the inclusion of UV filters in future research. Their practical application is also limited by the need for comprehensive biocompatibility and safety assessments. Therefore, these formulations should be considered proof-of-concept systems rather than finalized delivery systems.