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(439d) Tunable Non-Viral Gene Delivery Via Lbl Thin Films

Authors: 
Wang, M. X., Massachusetts Institute of Technology
Samuel, R. E., Massachusetts Institute of Technology
Hammond, P. T., Massachusetts Institute of Technology


Multi-layered composite films fabricated of plasmid DNA and hydrolytically degradable polycation have considerable potential as a synthetic gene delivery system for localized non-viral transfection. Applications include various biomedical applications such as implant functionalization, specifically, as gene therapy in orthopedic implant-host bone integration. New bone formation can be promoted on the implant-bone interface if presented with appropriate growth factors. Bone formation and healing occurs through an extensive process of inflammation, reparation, formation, and remodeling. Development is controlled by various growth factors and can be promoted by transfection of wound sites with factors such as osteogenic BMPs. Since these factors play a role throughout the healing process, long-term gene delivery has great potential for promoting bone growth along different stages of reparation. We have developed polyelectrolyte multilayer (PEM) thin films whose initial and long-term release kinetics can be controlled via architecture modulation. These films consist of two distinct polymer sets. The first pair of polymers forms the baselayer of the film and is composed of cationic protamine sulfate and anionic sodium (4-polystyrene sulfonate) (SPS). Protamine sulfate is a natural polyamine that has been shown to support the adhesion, proliferation and differentiation of MC3T3-E1 pre-osteoblastic cells in vitro. These osteoconductive baselayers support the second polymer set fabricated from plasmid DNA and cationic Poly2, a poly-b-amino ester.  Poly-b-amino esters are hydrolytically degradable and have been shown to complex with and condense DNA, resulting in improved receptor-mediated endocytosis. It was found that DNA release profiles can be changed by varying PEM film architecture (changing upper-layer number). Release profiles were found to be dual phase, with an initial burst release in the first week followed by linear release up through four weeks. Initial release kinetics within the first seven days were highly dependent on architecture. The ensuing linear release from 7 through 28 days was slow and relatively unchanged between film architectures. This has great potential for long-term gene therapy wherein specific architectures can be used for timed transfection, maximizing the effect of the therapy by allowing release to coincide with specific bone healing phases.