Biodegradable branched poly(ethylenimine sulfide) for gene delivery.

We synthesized biodegradable b-PEIS (branched poly(ethylenimine sulfide)) by crosslinking linear PEIS. We controlled the degree of crosslinking and molecular weight by adjusting the amount of the crosslinker, bisepoxide. The b-PEIS was readily degradable under reductive conditions (5mm glutathione solution) and the degradation time was dependent on the degree of crosslinking. We controlled the molecular weights of the b-PEIS by regulating the amount of crosslinker and thus, the degree of crosslinking. Our titration data showed that there was almost no loss in buffering ability before or after bisepoxide crosslinking. We verified the degradation of this polymer by MALLS and gel electrophoresis, and confirmed that there was a high transfection efficiency and low cytotoxicity based on cellular data. Intracellular trafficking was observed by image restoration microscopy, demonstrating that b-PEIS does not accumulate in the cell interior.