Sphingomyelin-based liposomes with different cholesterol contents and polydopamine coating as a controlled delivery system

Sphingomyelin (SM)-based liposomes (SMLs) exhibited different loading and release behaviors of encapsulated drugs, depending on cholesterol contents and polydopamine (PDA) coating layer. Herein, three SMLs with different compositions were formulated by intercalating the cholesterol contents (40%, 50%, and 60%) in the lipid bilayer. Then, the SMLs were further coated with a PDA layer, hereafter referred to as SMLs@PDA. In-vitro release test was carried out by loading ibuprofen (Ibu) and acetaminophen (Acet) into the SMLs. When increasing the cholesterol contents in the SMLs, the loading amount of hydrophobic ibuprofen was increased, due to the increased hydrophobic interactions between ibuprofen and cholesterol. On the other hand, the loading amount of hydrophilic acetaminophen was decreased at higher cholesterol content in the SMLs. The release rate of Ibu-loaded SMLs (SMLs-Ibu) was significantly decreased at the highest cholesterol content (60%), whereas the release rate of Acet-loaded SMLs (SMLs-Acet) was not significantly decreased at the highest cholesterol content. After coating the SMLs-Acet with the PDA layer (SMLs-Acet@PDA), the release rate of SMLs-Acet@PDA was significantly reduced, probably due to the strong π–π stacking interactions between the resonance structure of acetaminophen and aromatic π system of PDA layer, as well as the effective diffusion barrier by the thick PDA layer. The fast release kinetics of SML-drug system was predicted using the Fickian diffusion model, and the slow release kinetics was predicted by the Higuchi model. Our work can contribute a significant advance for preclinical development of lipid-based nanocarriers by demonstrating the release and loading relationships between encapsulated drugs and lipid compositions.