Large and Giant Vesicles “Decorated” with Chitosan:  Effects of pH, Salt or Glucose Stress, and Surface Adhesion

Abstract

This paper describes the behavior of large and giant unilamellar vesicles (LUVs and GUVs, respectively) in the presence of chitosan, a positively charged polyelectrolyte. Variation of the zeta-potential of LUVs as a function of chitosan concentration is studied for two different molecular weights (MW) after a preliminary study devoted to pH and salt effects on zeta-potential in order to discriminate among the effects of protons, salt, and chitosan concentrations. The difference observed between pH and salt effects on the one hand and chitosan on the other allows us to conclude there is a strong LUV-chitosan interaction. In presence of chitosan, the zeta-potential of LUVs becomes positive and two distinct regimes of variation are suggested and interpreted as follows: a first step consists of chitosan adsorption flat on the membrane (independent of MW) followed by a possible reorganization of the polymer of higher molecular weight on the surface, giving rise to loops. Then a comparative observation of the effect of pH and salt by optical microscopy is made on naked and chitosan-decorated GUVs. Results further confirm a membrane-chitosan interaction and are interpreted in the light of the results obtained for LUVs in terms of both electrostatic and hydrophobic interaction. A large majority of decorated vesicles remain stable down to pH = 1 while in the absence of chitosan they burst quickly at pH between 2 and 3. Osmotic pressure and net charge change due to addition of HCl results in a decrease in the diameter of the decorated vesicles, which remain spherical while forming tubes of lipids. In presence of NaCl, a higher resistance of decorated vesicles is also evidenced (they are stable for NaCl concentrations up to 10-1 M while naked vesicles burst when [NaCl] is between 10-2 and 10-3 M). At higher salt concentration, aggregation of decorated vesicles occurs, which is attributed to the screening of electrostatic repulsions between vesicles covered by the positively charged chitosan. Finally, adhesion of vesicles on a positively charged surface is investigated. In absence of chitosan, the vesicles immediately burst when they come in contact with the surface. On the contrary, suspension of chitosan-vesicles remain stable down to pH = 1.5. Under gentle flow vesicles move: they do not adhere on the substrate, probably due to the repulsion between positively adsorbed charged chitosan and substrate; spherical deflation occurs, but in this case daughter vesicles are formed instead of lipid tubes.

Complexes of oppositely charged polyelectrolytes and surfactants – recent developments in the field of biologically derived polyelectrolytes

“…169,[175][176][177][178][179][180][181][182][183][184][185][186] Briey, chitosan adsorbs at onto the surface of negatively, neutrally and positively charged vesicles 183,185 and the adsorption does not seem to be inuenced by the vesicle size.…”

Caracterización estructural de vesículas modificadas con quitosano

“…Resultados similares han sido reportados por Quemeneur et al, al utilizar liposomas unilamelares a base de 1,2-dioleoil-snglicero-3-fosfatidilcolina (DOPC), modificados con un quitosano de un peso molecular de 225 kDa y un grado de desacetilación de 95%. Quemeneur et al sugieren que la incorporación del quitosano sobre la membrana de las vesículas se debe a una interacción eficiente de origen electrostático, producida entre los grupos amino cargados positivamente del polelectrolito y los fosfatos cargados negativamente en la superficie del liposoma (Quemeneur, Rammal, Rinuaudo, y Pépin-Donat, 2007). …”

Chitosan-coated microvesicles: Effect of polysaccharide-phospholipid affinity on decafluorobutane dissolution

“…For fluorescence microscopy experiments, chitosan was conjugated with fluorescein isothiocyanate (FITC) (Quemeneur, Rammal, Rinaudo, & Pepin-Donat, 2007). Briefly, 500 mg of purified chitosan was dissolved in 50 mL of HCl (0.1 mol-L −1 ).…”