Assembly of Bioreducible Layer-By-Layer Films for Sequential DNA Delivery

Layer-by-layer (LbL) films containing synthetic and bioactive molecules such as DNA are promising biomaterials for controlled and localized gene delivery for a number of biomedical applications including cancer DNA vaccine delivery. Gene delivery applications require that LbL films disassemble in physiological conditions. Our research focuses on the synthesis and engineering of bioreducible poly(amido amine)s containing the disulfide bond as gene delivery vectors. This talk describes a method to achieve sequential DNA release from LbL films containing strategically placed bioreducible and nonbioreducible polycations. In order to control DNA release sequence, the LbL film assembly and disassembly are studied by in situ atomic force microscopy, fluorescence spectroscopy, and dynamic light scattering. We found that the LbL film containing alternating layers of poly(amido amine) and DNA underwent fast degradation in reducing solution with micrometer particles released from the surface. This bulk degradation behavior was changed into a sequential DNA release pattern with nanometer products by periodic insertion of a nonbioreducible polycation poly(ethylenimine) into the film. The insertion also resulted in improved transfection of human embryonic kidney 293 cells. We will present results that directly link the LbL film structure with DNA release dynamics and cell transfection efficiency. Our work demonstrates a simple method for the designing of LbL films for sequential and sustained DNA release for biomedical applications.