| Synthesized cationic lipids and the complexes formed with DNA constitute themost promising alternative to the use of viral vectors for the delivery of foreigngenes into cells for gene therapy applications. Morphology of DNA-lipid complexes(lipoplexes) have closely link with the mechanism of DNA interaction with cationicliposomes and DNA transfection efficiency.According to rheological theory of macromolecular in diluted solution, weestablished a novel method to study on morphology of lipoplexes on macroscopicalscope –rheological method in this paper. This method based on the exactmeasurement of viscosity in suspension system could conveniently studymorphology of lipoplexes by calculating the shape factor of particles in suspension.For determining the viscosity of lipoplex, mini-capillary viscometers weredesigned and manufactured by us. At the same time, the system at constanttemperature and automatic capillary viscometer were improved. The precision offlow time of suspension was up to 10-3 second, and coefficient of variation was lowerthan 0.3%. The results confirmed that the rheological method was suitable forresearch on morphology of lipoplexes. Hydration and presence of small amountwater in system affected the calculation of shape factor to a low degree, but thevariation was little. Compared to the observed result from TEM images, in generalthe shape factor from rheological method was mean value with average meaning.We employed two kinds of anionic polyelectrolytes, sodium polygalacturonate(PGU) and sodium dextran sulfate (DSS) of varying size, as models for DNA. Theprepared complexes were incubated under laminar flow conditions. The results showthe same quantitative relation between the shape parameter of lipoplexes and thelength of anionic polyelectrolytes, including DNA. The rheological behavior of PGUand DSS were similar to that of DNA.The analysis and characterization of varieties of lipoplexes show: the shapefactors of lipoplexes with different cationic lipid were not same, which related to themolecular structure of lipid. The morphology of lipoplexes were changed little withcholesterol used as helper lipid, while DOPE (1,2-dioleoyl-sn-glycero-3-phosphoethanolamine) was used as helper lipid and led to a increase of the axial ratioof lipoplexes because DOPE trended to form hexagonal structures and they wereeasy to separating from complexes.The idea and method of flow incubation of lipoplexes was introduced at first inthis paper, which aimed to regularize and improve the whole process of preparationand incubation. Using the rheological method, we could analyses the change of shapefactor of lipoplexes as a function of time. The results showed that flow incubationcould reduce the aggregation between complexes under turbulent flow condition, theaxial ratio of complexes have little relation to average molecular weight ofpolyanions and different cationic lipid. Futher, this paper made elementary discussion and interaction of generationmechanism of DNA with cationic liposomes.
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