Varga et al. [169] [170] [171] developed an "integrative systems" approach, combining quantitative experiments and computational modeling studies of vector uptake and trafficking kinetics, with the aim to take multiple potentially rate-limiting cellular and molecular processes into account. By applying their mathematical model to plasmid delivery with either Lipofectamine, several PEI-based vector formulations or an adenoviral vector, they could successfully predict experimentally observed effects and identify endosomal escape as the most important rate-limiting intracellular barrier for non-viral vectors. Recently, Zhou et al. [172] applied a similar strategy for the characterization of a novel lipopolymer (WLSP). This carrier shows an increased rate of endosomal escape compared to conventional PEI-based carriers.