Delivery of synthetic small interfering RNA(siRNA) remains the major obstacle to the therapeutic application of RNA interference.A novel nanogel that composed of hydrophilic polyethylene glycol and cationic polyethylenimine for siRNA delivery was synthesized and characterized.The nanogel was synthesized via inverse microemulsion polymerization of polyethylenimine with Mw=800 and poly(ethylene glycol) diacrylate (Mw=400).The successful synthesis of the nanogel was demonstrated by 1H-NMR

FTIR characterizations.Dynamic light scattering measurements show that the nanogels have an average size of 180 nm

while the nanogels are positively charged with a zeta potential of 37.9 mV.Such nanogel is suitable for siRNA loading by electrostatic interaction

which has been further demonstrated by gel retardation assay.The cytotoxicity of nanogel against MCF-7 cellswas evaluated using MTT method and it showed no significant cytotoxicity effect even at high concentration up to 1.0 mg/mL.The siRNA delivery efficiency of nanogel was evaluated by silencing green fluorescent protein (GFP) expression in MCF-7 KMRV cells that stably expressed GFP.The results indicated that the nanogel induced high gene silencing effect

which was comparable to that of Lipofectamine 2000TM.With proper particle size

strong siRNA binding ability and efficient gene silencing function

this nanogel/siRNA formulation is potential for efficient siRNA delivery in therapeutical application.