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Our works focused on the development and application of polymeric gene carrier system.According to the difficulties of the gene carrier used in vivo, a variety of high efficiency and low toxicity of non-viral gene carrier systems were synthesized.PEI has good transfection efficiency in a variety of cell lines.However, the high molecular weight affect its metabolism in vivo and further applications in clinical.To overcome these difficulties, lots of efforts have been made.Firstly, hydrophobic poly (γ-benzyl L-glutamate) and polyphenylalanine unit were introduced to PEI to get cell membrane-like amphiphilic hyperbranched copolymers, resulting in high transfection efficiency.Secondly, We graft low molecular weight PEI to the biodegradable poly(amino acid)s, poly(β-amino ester)s and polycarbonate backbones, obtaining biodegradable polycationic gene carriers.Their transfection efficiency and cell biocompatibility are better than PEI-25K.This kind of material is expected for further application in vivo.Thirdly, Low molecular weight PEIs were conjugated on gold nanoparticles to build non-viral gene carriers with fluorescence properties.Results showed it gets higher transfection efficiency with red fluorescence of Au-PEI in HeLa cells, and it also showed good imaging properties in vivo.The stable fluorescence properties and mild preparation conditions of Au-PEI make it promising gene carrier with diagnosis and treatment functions in gene therapy.Furthermore, we grafted RGD to the hyaluronic acid as targeting shielding system to cover the polycationic gene carriers.The transfection efficiency of gene carrier with HA-RGD was 9.7 times higher than that with only HA and 8.4 times higher than that without shielding system.Based on these carriers, we developed commercial transfection agent with high stability and superexcellent transfection efficiency in many cell lines, compared with other market-existed transfection agents.Conclusion: Our work endowed polycationic gene carriers with superior transfection efficiency with versatile function and low cytotoxicity, making them promising materials for gene therapy in vivo.