Complexation of DNA with Polycationic Micelles

Abstract

Interpolyelectrolyte complexation is a ubiquitous phenomenon that plays vital roles in biological systems and in design of responsive materials. However, precise control of polyelectrolyte complexes (PEC) has been challenging, particular for DNA-polycation complexes designed for gene delivery applications. Incorporating polyionic micelles is a promising strategy to tune PEC properties, but has been under-utilized in designing polymeric gene delivery vehicles. Herein, cationic micelles self-assembled from amphiphilic block polymers are complexed with double stranded DNA. The structure, composition, and stability of the resulting "micelleplexes" are characterized to probe the fundamental physics that govern the formation and properties of micelleplexes. With cationic AB+ micelles, complexation of linear semiflexible DNA and flexible poly(styrenesulfonate) were compared and the influence of polyanion chain flexibility was extracted and discussed. DNA length was found to strongly influence the size, composition, and colloidal stability of micelleplexes, whereas DNA topology (linear or circular supercoiled) has minimal influence. To improve the colloidal stability and reduce the size of micelleplexes that are composed of multiple micelles connected by bridging DNA chains, AB+C micelles with hydrophilic nonionic outer coronas of varying length were designed. The addition of the outer nonionic corona dramatically improves the colloidal stability of micelleplexes over a much wider charge ratio, and the outer corona length closely correlates to micelleplex size, zeta potential, and the average number of micelles per micelleplex. In addition, AB+C micelleplexes adopt a beads-on-a-string structure that resembles the organization of DNA in chromatin. Lastly, structure, composition, and stability of micelleplexes were closely compared with those of another typically studied family of DNA complexes, "polyplexes", which form between DNA and cationic homopolymers or AB+ diblock copolymers with a hydrophilic nonionic A block. Compared to the polyplexes, micelleplexes showed more than a 4-fold increase in gene transfection efficiency, which was attributed to the high positive charge content of micelleplexes.