Polyelectrolyte Complex Micelle Formation by PEGylated DNA and Polylysine*

Nucleic acids are considered to be a special class of negatively charged polymers. They can interact with positively charged polymers to form polyelectrolyte complexes. A major limitation of the system is that the complexes formed may be unstable, particularly at charge ratios near the isoelectric point. The replacement of charged homopolymers with charged-neutral block copolymers can improve the stability of the complexes, leading to the observation of polyelectrolyte complex micelles (PCMs). In this study, we investigate the complexation behavior and morphology of PCMs formed by polylysine (PLys) as the cationic homopolymer and DNA-b-polyethylene glycol (DNA-b-PEG) as the anionic-neutral block copolymer. The PCMs consist of a pseudo-neutral PLys/DNA core and a neutral-hydrophilic PEG corona, and they remain stable over a wide range of charge ratios, including at the isoelectric condition. The binding strength of PLys to DNA-b-PEG is determined as a function of the charge ratio. The PCM morphology is also investigated as a function of PEG and PLys chain lengths.