**Neutral and non-condensing polymer-based gene delivery systems**

Although, cationic polymers, which electrostatically interact with DNA to neutralize its negative charge and condense DNA into nanosized particles, are generally considered as gene carriers, neutral polymers such as polyvinyl alcohol (PVA) and polyvinyl-pyrolidone (PVP) can also be used for gene transfer. They can protect DNA from enzymatic degradation and facilitate cellular uptake of DNA. These polymers may interact with DNA via hydrogen bonding and/or van der Waals interactions; van der Waals interaction of the hydrophobic vinyl backbones may cover around DNA to make its surface more hydrophobic. In a study, intramuscularly administered PVP/plasmid DNA formulation resulted in a significant increase in the number and distribution of the reporter-gene expressing cells in rat tibialis, compared to naked plasmid [Park et al., 2006].
