Lipoplexes, the complexes of plasmid DNA with cationic lipids, are considered as an attractive alternative to viral delivery systems. However, synthesized lipoplexes showed several limitations including insufficient transfection, low reproducibility and low stability.
Here we attempt to delineate the relationships between the synthesis process, morphology (e.g., shape and liquid crystal structure), and the transfection efficiency of lipoplexes with rheological technology. Mini-capillary viscometers with automatic measurement and control components were designed and used to study the morphology of lipoplexes at a macroscopical scale. In such a dilute macromolecule suspension system, the shape factor of lipoplex was correlated with the viscosity measurement. The results showed that the shape factors of lipoplexes were different with various molecular structures of cationic lipid and helper lipid. A quantitative relation was set up between the shape factors and the length of DNA/polyelectrolytes, which may help better explain lipoplexes formation.
To improve the stability and reproducibility of lipoplexes, an incubation period was suggested before the use of lipoplex. A rheological method was introduced to fix the hydromechanical parameters so that the entire preparation and incubation process was carried out consistently. A laminar flow incubation environment was showed suitable for lipoplex preparation and helped improve lipoplex stability and minimize aggregation. Other flow incubations, such as turbulent flow or impinging flow, were more complicated and further study is necessary to fully understand them. In brief, the rheological methods can help reveal the mechanisms of lipoplex formation and advance the rational design of lipoplexes for pharmaceutical applications.