Synthesis and application of poly(ethylene glycol)–cholesterol (Chol–PEGm) conjugates in physicochemical characterization of nonionic surfactant vesicles

Vesicles possessing poly(ethylene glycol) (PEG) chains on their surface have been described as a blood-persistent drug delivery system with potential applications for intravenous drug administration. In this research with different molecular weights (400–10,000 g/mol) of PEG, a series of Chol–PEGm conjugates were generated by the DCC (N,N′-dicyclohexylcarbodiimide, DCC)/(4-dimethylaminopyridine, 4-DMAP) esterification method, and confirmed by FT-IR and 1H NMR spectrum. Then their properties in aqueous solution were studied by electron microscopy images, associative behavioral and systematic tensiometric studies over a wide concentration range. In order to elucidate the application of this Chol–PEGm in vesicles, conventional nonionic surfactant vesicles (niosomes) composed of span 60 and cholesterol were prepared and the influence of various hydrophilic chains of the Chol–PEGm conjugates was investigated. Results indicated that all the niosomes prepared, with or without Chol–PEGm composition were similar in micrograph with diameter between 120 nm and 180 nm. The fixed aqueous layer thickness (FALT) around niosomes increased as Chol–PEGm chain length increase, particularly in the Chol–PEG10,000 modified niosomes with 9.33 ± 0.67 nm. In vitro release experiments indicated that release rate of nimodipine from Chol–PEGm modified niosomes was enhanced. Chol–PEGm modified niosomes showed greater accumulative release than that of plain niosomes over a period of 24 h. These studies have shed some light on the suitability of Chol–PEGm containing niosome preparation.