From mineralogy to functionality: Sicilian clays as structurally-driven suspensions for topical delivery of resveratrol

For the first time, four unexplored Sicilian clay deposits were investigated through a multidisciplinary approach as potential raw materials for clay-based topical suspensions in a pre-formulation context, to bridge a key gap between mineralogical characterization and functional screening. Particle-size distribution (PSD), chemical, mineralogical and structural characterization was performed using laser granulometry, XRF, ICP-MS, XRD, FT-IR, TGA on both bulk materials and the ≤ 2 µm fractions selected for suspension preparation. Varicoloured clays (CALT1 and CALT2) exhibited higher alumina and iron contents and were enriched in interlayered illite/smectite, with CALT1 also containing chlorite, whereas Plio-pleistocene clay (SIL) and grey clays of the Fm. Terravecchia (CEN) were relatively richer in smectite and kaolinite. The ≤ 2 µm fractions preserved the main phyllosilicate structures while minimizing coarse, non-clayey minerals (ranging 32–47 wt% in bulk samples), resulting in improved dispersion and more uniform rheological behaviour. Model clay-based dispersions containing resveratrol (0.6% w/w) were prepared in a hydro-alcoholic medium and used to compare technological performance and release behaviour. Preliminary release studies using Franz diffusion cells over 24 h revealed clay-dependent profiles. CALT1 and CALT2 showed the highest and most sustained resveratrol release (22.28 ± 0.003% and 17.32 ± 0.005%, respectively), while SIL and CEN exhibited lower release (16.34 ± 0.245% and 7.52 ± 0.032%). Overall, the results show that both mineralogical composition and PSD contribute to the rheological and release behaviour of the investigated suspensions. The study provides a mineralogy-based pre-formulation screening framework for selecting natural clay materials for future topical delivery applications.