Gene therapy has emerged as a promising treatment for various diseases including genetic disorders, infectious diseases, neurodegenerative disorders, and cancer. Recent advances in gene editing techniques, particularly CRISPR/Cas, have significantly enhanced site-specific gene editing and intensified interest in gene therapy. Although approximately 70% of gene therapy clinical trials worldwide have utilized recombinant viruses due to their efficient cell targeting and entry capabilities, the associated risks, such as immunogenicity, oncogenicity, and toxicity, as well as high production costs, necessitate the exploration of nonviral alternatives. Nonviral gene delivery agents such as cationic polymers, dendrimers, lipids, and peptides offer benefits over viral vectors, including reduced immunogenicity and carcinogenicity, and increased flexibility with respect to the size of the gene payload and cellular targets. In addition, the chemical versatility of nonviral gene vectors aids in understanding key bottlenecks in the transfection process, facilitating the creation of more efficient gene delivery agents. Cationic polymers are particularly attractive gene delivery vectors given their capacity to readily condense nucleic acids, production cost-effectiveness, stability, and amenability to chemical modification. Their high positive charge promotes the formation of polycation-nucleic acid complexes, termed polyplexes. These polyplexes are typically positively charged nanoparticles that shield nucleic acids from enzymatic degradation and facilitate gene transport across cell membranes. Polyethylenimine (PEI) is one of the most widely studied cationic polymers and remains a benchmark for polymeric nonviral gene delivery vectors due to its high in vitro transfection activities. Branched PEI (bPEI), unlike many other polycations, has a mixture of primary, secondary, and tertiary amines and a high charge density with titration studies suggesting ~10-30% of the PEI amine groups in bPEI are protonated at physiological pH. Despite PEI's demonstrated effectiveness for gene delivery, its associated cytotoxicity and potential to elicit adverse immune responses make further investigation into modified PEI derivatives a necessity. An additional concern for in vivo gene delivery is the aggregation of polyplexes with plasma proteins due to the overall positive charge of the polyplex nanoparticles.