Chitosan–DNA–rectorite nanocomposites: Effect of chitosan chain length and glycosylation

Two fully deacetylated chitosans with low- and high molecular weight (LMW and HMW) and their glycosylated derivatives substituted with the trimer GlcNAc–GlcNAc–Mannose (AAM) were intercalated into rectorite to prepare polymer/clay nanocomposites. The interlayer distance of rectorite depended on the amount of chitosan and the structure of intercalated chitosan. The largest interlayer distance of 3.35 nm was obtained when the mass ratio of LMW non-substituted chitosan to rectorite was 2:1. The four chitosan–rectorite nanocomposites were loaded with DNA and their dispersion stability and DNA retention capability were evaluated. Similarly as for DNA–chitosan polyplexes, the colloidal stability of the chitosan–DNA–rectorite nanocomposites increased with the increasing molecular weight of the intercalated chitosan and was improved by glycosylation. The nanocomposite of HMW and glycosylated chitosan did not aggregate in phosphate buffered saline (PBS) at pH 7.4 and retained a size of approximately 200 nm diameter. The DNA retention capability of the nanocomposites was also dependent on the structure of the intercalated chitosan. Nanocomposites based on the LMW and glycosylated chitosan required high amount of the polymer (corresponding to amino: phosphate ratio of 60) to retain the loaded DNA. The in vitro transfection study revealed that the chitosan/rectorite composites were able to deliver DNA to human cells, albeit with reduced efficacy compared to chitosan/DNA nanoparticles.