Controlled nucleic acid delivery systems

A nucleic acid delivery system comprising:

• a polymeric structure formed of a biocompatible polymer and
• a mixture comprising (i) one or more nucleic acid molecules that encode a protein or polypeptide or RNA product, and (ii) a first co-dispersant that is inert with respect to the one or more nucleic acid molecules and is selected from the group consisting of herring sperm DNA, a random or non-coding DNA having a molecular weight of about 100 kDa to about 2000 kDa, a DNase-free filler, a DNase-free bulk protein, Ficoll, dextran, diethylaminoethyl-dextran, dextran sulfate, ovalbumin, DNase free peptide, glycoproteins, peptide-nucleic acids, and combinations thereof, the mixture being contained within the polymeric structure, wherein the first co-dispersant is present in an amount effective to reduce the rate of diffusion of the one or more nucleic acid molecules from the polymeric structure.