Figure 7. Cytotoxicity of CS-g-(PEI-b-mPEG) and 25 kDa PEI at various concentrations of pure polymers and complexes with siRNA at determined N/P ratios. Pure CS-g-(PEI-b-mPEG) copolymer did not exhibit significant cytotoxicity at any determined concentration, and after compacting with siRNAs, both CS-g-(PEI-b-mPEG)/siRNA and 25 kDa PEI/siRNA complexes showed much lower cytotoxicity. A: Cytotoxicity of various concentrations of pure CS-g-(PEI-b-mPEG) or 25 kDa PEI polymers; B: cytotoxicity of CS-g-(PEI-b-mPEG)/siRNA or 25 kDa PEI/siRNA complexes at determined N/P ratios. Data are presented as the percentage of viable cells compared with the untreated (control) cells (The asterisk indicates a p<0.05, mean ± SD, n=6).