Ethosomal Nanocarriers for Trans-Resveratrol Delivery: Formulation, Physicochemical Characterization, Stability, and In Vitro Release Performance

Background: Trans-resveratrol (3,5,4′-trihydroxystilbene) is a natural polyphenolic antioxidant widely used in anti-aging dermocosmetics for its strong radical-scavenging capacity and its activation of cell-protective pathways such as sirtuin 1 (SIRT1). However, its poor aqueous solubility, photochemical lability, and low bioavailability limit its incorporation into topical formulations and its delivery into the skin. Objective: In this study, ethosomal nanocarriers were designed as a phospholipid–ethanol vesicular system to solubilize, stabilize, and control the release of trans-resveratrol for dermocosmetic applications. Microfluidization is not a commonly used method; however, circulating the formulation through the interaction chamber under optimized pressure can produce ethosomes with desirable colloidal stability by this simple process. Methods: Resveratrol-loaded ethosomes were prepared with synthetic phosphatidylcholine (Lipoid P75), ethanol, and vitamin E. Microfluidization was optimized by varying the number of high-pressure homogenization cycles and the applied pressure. Vesicle size, size distribution and distribution uniformity, zeta potential, pH, conductivity, density, and long-term stability were monitored for up to 180 days; morphology was examined by cryogenic scanning electron microscopy (cryo-SEM) and molecular compatibility by Fourier-transform infrared (FTIR) spectroscopy. A trans-resveratrol high-performance liquid chromatography (HPLC) assay was developed and validated according to International Council for Harmonisation (ICH) Q2 guidelines for quantitative analysis. Encapsulation efficiency was determined by HPLC after ultracentrifugation, cytotoxicity was assessed in human keratinocytes (HaCaT), and in vitro release was evaluated using Franz diffusion cells with two different membranes. Results: All ethosome formulations yielded a nanoscale size distribution (median diameter around 190 nm for loaded and around 90 nm for unloaded) and good colloidal stability, with absolute zeta potentials above the 30 mV threshold at early time points and a skin-compatible pH (around 6.5). The optimized formulation (T16; 1.5% w/w trans-resveratrol, 5% w/w phosphatidylcholine (Lipoid P75), 0.3% w/w vitamin E and 30% w/w ethanol, processed with seven microfluidization cycles) achieved a high encapsulation efficiency (EE) of 95.5% on day 1. 84.2% EE was retained after 180 days, consistent with strong partitioning of the lipophilic active into the ethanol–phospholipid bilayer. FTIR confirmed preservation of the phospholipid bilayer and indicated non-covalent loading, with the resveratrol bands largely masked by the dominant lipid signals. Cryogenic Scanning Electron Microscopy (Cryo-SEM) confirmed near-spherical vesicles with narrow size distribution. In vitro release showed a sustained, controlled release profile relative to a 1.5% w/w resveratrol solution. Slower diffusion across the skin-mimicking Strat-M membrane was observed compared to cellulose acetate membrane. Conclusions: Optimized trans-resveratrol-loaded ethosomes represent a stable, efficient vesicular system enabling formulation stability and controlled topical release. The antioxidant and photoprotective efficacy of the loaded system was not assessed in this study and is identified as a topic for future work.