Insights on the interactions of chitosan with phospholipid vesicles. Part II: Membrane stiffening and pore formation.

The interactions between the polysaccharide chitosan and phospholipids are studied using giant unilamellar vesicles (GUVs). We explore both bare GUVs incubated in chitosan solution post vesicle formation and GUVs prepared using a reverse-phase method where the polymer is adsorbed on both sides of the membrane leaflet. The fluctuations of the vesicle membrane are significantly reduced in the presence of chitosan as characterized by the bending rigidity, which increases with chitosan concentration denoting physical restrictions imposed to the bilayer as a consequence of the interaction with the polysaccharide. In the absence of chitosan, the rigidity of the bare phosphatidylcholine vesicles is also observed to increase (about 3-fold) upon the incorporation of a small fraction (10 mol %) of phosphatidylglycerol. Pore formation caused by chitosan is evidenced by loss of optical contrast of the giant vesicles denoting exchange between internal and external solutions through the pores. Our study provides evidence for the potential of chitosan to affect the bilayer permeability and to disrupt negatively charged membranes as well as to promote adhesiveness of vesicles on glass surfaces.