Transgene expression by substrate-mediated delivery. (A,B) Polyplexes and (C,D) lipoplexes with plasmid encoding for luciferase were incubated on substrates at low (0.5 μg; A, C) and high (2.0 μg; B, D) doses for 2 h. Bolus delivery used equivalent amounts of DNA that were immobilized to the substrate: (A) 0.2 μg/cm2, (B) 0.5 μg/cm2, (C) 0.25 μg/cm2, and (D) 0.1 μg/cm2. Activity was normalized to the number of cells seeded. Data are presented as average ± standard deviation of the mean. *P < 0.05 relative to other delivery methods for that condition; **P < 0.05 at different complex conditions.