Microfluidic devices for continuous production of pDNA/cationic liposome complexes for gene delivery and vaccine therapy.

To evaluate the process parameters for the production of plasmid DNA/cationic liposome (pDNA/CL) complexes in microfluidic systems, we studied two microfluidic devices: one with simple straight hydrodynamic flow focusing (SMD) and a second one with barriers in the mixing microchannel (patterned walls, PMD). A conventional bulk mixing method was used as a comparison to microfluidic mixing. The CL and the pDNA were combined at a molar positive/negative charge ratio of 6. The results showed that incorporating pDNA into the liposomal structures was different for the two microfluidic devices and that the temperature influenced the average size of complexes produced by the simple microfluidic device, while it did not influence the average complex size in the patterned wall device. Differences were also observed in pDNA probe accessibility in the complexes. The SMD yielded a similar quantity of non-electrostatic bound pDNA as that provided by the bulk mixing method. The complexes produced by the PMD had their pDNA probe accessibility decreased in 40% and achieved lower in vitro transfection levels in HeLa cells than the bulk mixing and simple microfluidic complexation methods. These differences are most likely due to different degrees of association between pDNA and CL, as controlled by the microfluidic devices. This study contributes to the development of rational strategies for controlling the formation of pDNA/CL complexes for further applications in gene and vaccine therapy.