Production of melatonin-loaded liposomes optimized with hydrophilic excipients: Formulation strategy and thermodynamic insights

Melatonin is a multifunctional biological regulator; however, its clinical use remains constrained by unfavorable properties such as poor water solubility and high sensitivity to light and oxygen. In this work, liposomal formulation has been designed for oral administration to manage sleep disorders using Supercritical PArticle Formation (SPAF) technique, to enhance melatonin stability and enabling controlled release, while producing a product in powder form. A 1:1 w/w melatonin-phospholipid ratio and 60 min CO₂ contact time were optimal, yielding submicron vesicles with a mean size of 0.60 ± 0.29 µm and a number density of 2.56 × 10⁸ liposomes/g powder. To improve moisture control after freeze drying, maltodextrins were incorporated at a 1:1 w/w ratio with phospholipids, obtaining mean vesicle size of 2.51 ± 1.12 µm. Biological molecules were incorporated as nutraceutical excipients. The final dry powder was filled into hydroxypropyl methylcellulose (HPMC) capsules (0.40 ± 0.05 g average fill), providing a vesicle density of 1.21 × 10⁸ liposomes/g and approximately 6.03 × 10⁷ liposomes per capsule. Heavy metals (As = 0.0224 ± 0.0079 ppm, Pb = 0.0216 ± 0.005 ppm) and ethanol residues (1070 ± 390 ppm) were confirmed to be below regulatory thresholds. Microbial loads were < 10 CFU/g for Escherichia coli, while Listeria monocytogenes and Salmonella spp. were undetected, demonstrating that this melatonin-loaded formulation represents a safe and scalable liposomal nutraceutical delivery system.