Gels formed from the interaction of lipid vesicles: Influence of charge in their structural and rheological properties

Abstract Research on colloidal dispersions has led to several reports of structured gels made of aggregated polymeric particles. In a previous work, we formed for the first time a gel from lipid vesicles with a high content of water; we hypothesized that electrostatic charge at the membranes promoted gelation. In the present work, we studied three gels formed from vesicles with different molar ratios of uncharged/charged lipids (3:1, 20:1, and 80:1) to correlate electrostatic balance with structure and rheology. X-ray scattering indicated that the structural unit of these gels is the lipid bilayer. Fluorescent confocal microscopy showed that the microstructure of the gels varied with charge. The sample with the highest amount of charge (3:1) presented a mesh-like lipid phase, made from small aggregates, while a decrease of charge formed bigger lipid flocs that packed tightly. As seen by oscillatory rheology, these structural differences altered the viscoelastic behavior of the gels: The sample with intermediate charge ratio (20:1) had the largest resistance to deformation, while deviations from this ratio decreased its rigidity. Knowledge of how electrostatic balance affects gel properties will help to adequate gel composition to specific applications.