Long-term stability of chitosan-based polyplexes

Purpose. There is a lack of information about the long-term stability of chitosan-based polyplexes although a large amount is known as regards transfection efficiency and physicochemical characteristics. The aim of this work is to study the transfection efficiency and physicochemical properties of chitosan-based polyplexes over time when stored at different temperatures in an acetate-buffer at pH 5.5. Methods. Aqueous samples of chitosan-based polyplexes were aged at 4degreesC, 25degreesC, and 45degreesC for up to 1 year. Samples were taken at predetermined time-points and evaluated for in vitro transfection efficiency and physiochemical properties (particle size, zeta potential). Results. One year of storage at 4degreesC did not result in any major changes in the properties of the polyplexes. At 25degreesC there were minor changes in the physicochemical characteristics of the polyplexes, and the in vitro transfection efficiency was reduced at 1 year of storage. Storage at 45degreesC altered both the in vitro transfection efficiency and the physicochemical properties of the polyplexes after a short time. Conclusions. The biological and physicochemical stability of the chitosan-based polyplexes are maintained for 1 year of storage in acetate-buffer at 4degreesC. The changes in the polyplex characteristics at elevated temperatures may be explained by degradation of both plasmid and chitosan.