DNA nanogels composed of chitosan and Pluronic with thermo-sensitive and photo-crosslinking properties.

Chitosan/Pluronic hydrogels were prepared to develop injectable depot systems for gene therapy to enhance local transgene expression at injection sites. Water-soluble chitosan and Pluronic were separately acrylated to prepare photo-crosslinkable polymers. A mixture of acrylated polymers was mixed with plasmid DNA and temperature was elevated to 37 degrees C to physically crosslink polymers to form hydrogels. Chitosan/Pluronic hydrogels were chemically crosslinked by photo-irradiated hydrogels at 37 degrees C. Mass erosion rates and release profiles of photo-crosslinked hydrogels were determined with varying photo-irradiation periods and chitosan contents of the hydrogels. The hydrogels with short photo-irradiation times degraded fast while high chitosan content in the hydrogels accelerated degradation rates. Release rates of plasmid DNA in the hydrogel were also controlled by changing chitosan content and photo-irradiation times. Released plasmid DNA was complexed with released Pluronic or chitosan and could be dissociated by adding sodium dodecyl sulfate. Scanning electron microscopy revealed that released plasmid DNA formed nanoparticles with released Pluronic or chitosan; released chitosan formed a condensed complex with plasmid DNA compared to released Pluronic. Transfection studies employing HEK293 cells showed that released fractions from chitosan/Pluronic hydrogels showed better transfection efficiency than those from Pluronic hydrogels. This result suggested that local transfection efficiencies of plasmid DNA in hydrogels were controlled by chitosan contents in chitosan/Pluronic hydrogels.