CP and brain neoplasm: Therefore, besides branched poly(ethyleneimine) (b-PEI) polymers, this study utilized nylon-3 polymers with hydrophobic subunits derived from β-lactam cyclopentyl (CP) and cationic subunits derived from β-lactam without (“no”) methyl substitution (NM) with a subunit ratio of 1:4 (NM:CP), which have been previously investigated regarding efficacy of siRNA delivery into brain tumor cells [42].