Nonionic surfactant vesicles (niosomes) for ocular drug delivery: Development, evaluation and toxicological profiling

Niosomes are emerging drug delivery systems that maintain the drug targeting advantages of liposomes, while overcoming the problems of low drug encapsulation and instabilities usually associated with liposomes. The purpose of this study was to systematically develop and characterise the physicochemical and biological toxicological properties of prepared niosomes based on method of production, method of drug incorporation, construct composition and drug loading. Briefly, drug-free and model drug pilocarpine HCl-loaded niosomes were prepared using combinations of Tweens and Spans by either thin film hydration (TFH) or ether injection (EI) methods. The resulting niosomes were characterised based on vesicle size, polydispersity, zeta potential, structural microscopy and drug entrapment. Toxicity of optimised niosomes was tested on HCE-2 cell-line as a model of the corneal epithelium. Results indicated that EI method produced smaller niosomes than TFH method, although the latter method produces niosomes with better stability over time. Significant increase in drug entrapment was observed when pilocarpine HCl was incorporated into the organic phase during manufacture. No corneal cellular toxicity was observed with optimal Span-60 niosomes, with high drug encapsulation. This study provides a mechanistic insight to the design, evaluation and toxicological screening of niosomes with potential for ocular drug delivery to the elderly.