Polyelectrolyte complexes of DNA and linear PEI: formation, composition and properties

Area of Science:

• Biomaterials Science
• Polymer Chemistry
• Gene Delivery Systems

Background:

• Poly(ethylene imine) (PEI) is a cationic polymer widely used for non-viral gene delivery.
• Understanding the complexation behavior of PEI with plasmid DNA is crucial for optimizing gene delivery efficiency and safety.

Purpose of the Study:

• To investigate the complexation dynamics between linear 13.4 kDa poly(ethylene imine) (LPEI) and plasmid DNA.
• To determine the optimal nitrogen to phosphate (N/P) ratios for forming stable and uniform PEI/DNA polyplexes.

Main Methods:

• Analytical ultracentrifugation (AUC) for size and molar mass determination.
• Scanning force microscopy (SFM) for morphological analysis.
• Preparative centrifugation and copper complex assay for quantifying free PEI.

Main Results:

• Incomplete DNA condensation and primary complex formation occurred below N/P ratio of 1.
• Polyplex merging and increased aggregation were observed around N/P ratio of 2.
• Stable, uniform polyplexes with an average size of 170 ± 65 nm formed at N/P ratios greater than 10.
• Virtually all PEI bound to DNA below N/P 2.5; excess PEI remained free in solution above this ratio.
• Individual PEI/DNA complexes contained 8–32 DNA plasmids and 70 ± 25 PEI molecules.

Conclusions:

• The N/P ratio significantly influences the size, morphology, and stability of PEI/DNA polyplexes.
• High N/P ratios (>10) are required for forming stable and uniform polyplexes suitable for gene delivery.
• The study provides critical insights into the fundamental complexation mechanisms governing PEI/DNA interactions.