Degradable polyelectrolyte multilayers that promote the release of siRNA.

We report an approach to the design of degradable polyelectrolyte-based films for the controlled release of siRNA from surfaces. Our approach is based on stepwise, layer-by-layer assembly of multilayered polyelectrolyte films (or "polyelectrolyte multilayers", PEMs) using siRNA and a hydrolytically degradable poly(β-amino ester) (polymer 1). Fabrication of films using siRNA sequences for green fluorescent protein (GFP) or firefly luciferase resulted in linear growth of ultrathin films (∼50 nm thick) that promoted the surface-mediated release of siRNA upon incubation in physiologically relevant media. Physicochemical characterization of these siRNA-containing films revealed large differences in film growth profiles, physical erosion profiles, and siRNA release profiles as compared to PEMs fabricated using polymer 1 and larger plasmid DNA constructs. For example, whereas films fabricated using plasmid DNA erode gradually and release DNA over a period of ∼48 h, films fabricated using siRNA released ∼65% of incorporated siRNA within the first hour of incubation, prior to the onset of any observed film erosion. This initial burst of release was followed by a second, slower phase of release (accompanied by gradual film erosion) over the next 23 h. These differences in release profiles and other behaviors likely result, at least in part, from large differences in the sizes of siRNA and plasmid DNA. Finally, we demonstrate that the siRNA in these films is released in a form that remains intact, functional, and able to silence targeted protein expression upon administration to mammalian cells in vitro. The results of this investigation provide a platform for the design of thin films and coatings that could be used to localize the release of siRNA from surfaces in a variety of fundamental and applied contexts (e.g., for development of new research tools or approaches to delivery from film-coated implants and other devices).