Novel pH-sensitive non-ionic surfactant vesicles: comparison between Tween 21 and Tween 20

Drug delivery systems using vesicular carriers such as liposomes or niosomes, have distinct advantages over conventional dosage forms because the vesicles can act as drug containing reservoirs and the modification of the vesicular compositions or surface properties can adjust the drug release rate and/or the affinity for the target site. In recent years, niosomes have been the object of growing scientific attention as an alternative potential drug delivery system to conventional liposomes. The aim of present work was firstly to determine the critical micelle concentration (CMC) and then to analyze the capability of polysorbate 21 (Tween 21) to form niosomal formulations. Non-ionic surfactant vesicles were prepared using Tween 21 and cholesterol (CHOL) at equimolar ratio (15 mM:15 mM) by employing the "film" technique. Cholesterol was used to complete the hydrophobic moiety of single alkyl chain non-ionic surfactant for vesicle formation. Dynamic light scattering was used to determine the size, zeta (ζ)-potential, polydispersity index and colloidal stability of the niosomal formulation. The vesicles were also characterized for their microviscosity and pH-sensitivity using fluorescent probes. The present work led to a simple, but positive result in pharmaceutical technology area. In particular, we have shown that the Tween 21:CHOL vesicles (i) are a homogenous and monodisperse vesicular population; (ii) are characterized by dimension compatible with the transport of drugs across biological barriers especially those whose diameter is about 100nm; (iii) shows a good stability at least 90 days at 4°C and (iv) are pH-sensitive systems. In conclusion, this niosomal formulation could be used as pH-sensitive nanodevices for delivery of drugs to pathological tissues, which exhibit an acidic environment as compared to normal tissues.