Multilayered thin films that sustain the release of functional DNA under physiological conditions

The development of thin films and coatings that control the release of DNA from the surfaces of materials could have a significant impact on localized approaches to gene therapy. Here, we report multilayered polyelectrolyte assemblies that sustain the release of functional plasmid DNA from the surfaces of model substrates under physiological conditions. Multilayered assemblies consisting of alternating layers of plasmid DNA encoding for enhanced green fluorescent protein (EGFP) and a synthetic degradable polyamine were deposited on planar silicon and quartz substrates using a layer-by-layer fabrication process. Film growth was monitored by ellipsometry and UV spectrophotometry and correlated linearly with the number of polymer and plasmid layers deposited. In general, the thickness of deposited layers was found to be a function of both the pH and the ionic strength of the polyelectrolyte solutions used. Films up to 100 nm thick were investigated in this study. These assemblies erode gradually upon incubation in phosphate-buffered saline at 37 degreesC, as determined by ellipsometry and UV spectrophotometry, and sustain the release of incorporated plasmid into the incubation medium for a period of up to 30 h. Characterization of the released plasmid by agarose gel electrophoresis revealed that the DNA was released in a relaxed, open circular, rather than supercoiled, topology; subsequent cell transfection experiments demonstrated that the released plasmid is transcriptionally viable and promotes the expression of EGFP in the COS-7 cell line. These layered materials could represent an approach to the controlled administration of one or more functional DNA constructs from the surfaces of biomedical materials and devices.