HepG2 cells were seeded at a density of 10 4 cells per well (10 5 cells·mL -1 ) in a 96-well plate. After 24 h, cell culture medium was removed, and cells were treated with 0.5 wt% (individual solution) or 1 wt% (complexed state) of guanidinium and sulfonate functionalized bPEs. For the positive and negative controls, media was exchanged without the addition of any test compound. After incubation for 72 h (37 °C, 5% CO2), positive controls were treated with 5 µL Triton X-100 (20% v/v). Then, 15 µL of the yellow MTT reagent was added to each well, followed by incubation for 3 h. The reaction was stopped by the addition of 100 µL lysis buffer. The next day, absorption was measured at 595 nm with the SpectraMax ID5 microplate reader (Molecular Devices LLC, San José, USA). Cell viability for each test compound was determined, wherein viability of 0% and 100% were assigned to the positive and negative controls, respectively.