Taken together, we present a binding model for LPEI and BPEI polyplexes in Figure . Our model suggests that LPEI binds electrostatically to the phosphate backbone of DNA with a weaker binding to the nucleobases (Figure , step 1). This binding causes DNA structural rearrangements from Bform to Z-form and condensation (Figure , step 2). The addition of NaCl inhibits the binding of LPEI to the phosphate backbone, thereby making binding to the DNA nucleobases preferable (Figure10, step 3). In contrast, BPEI binds DNA primarily through hydrogen bonding and weak electrostatic interactions to the phosphate backbone, as well as hydrogen bonding interactions with the nucleobases (Figure , step a). This multi-modal binding causes efficient condensation of the DNA, which subsequently contributes to the disruption of Developing effective polymers that can deliver multiple types of cargo is essential for advancing polymer-based gene therapies. This can be achieved by designing polymers with multiple binding mechanisms while optimizing cargo release. PEI-based delivery systems are among these and can be optimized to efficiently deliver plasmid DNA, mRNA, and CRISPR-Cas9 technology . PEI is traditionally thought to interact with nucleic acids through electrostatic forces, but our findings show that multiple binding modes play a key role in DNA condensation. Recognizing and using these distinct binding mechanisms provides a foundation for engineering more versatile PEI formulations that improve DNA release, accommodation of other cargo types, and enhance gene delivery.