Influence of methyl-β-cyclodextrin and liposomes on rheological properties of Carbopol® 974P NF gels

The influence of positively-charged and sterically stabilized liposomes and/or methyl-β-cyclodextrin on rheological properties of Carbopol® 974P NF hydrogels was investigated. All formulations have displayed a shear-thinning behavior of Carbopol® gels, and the rate stress as a function of the shear rate was fitted using the Cross equation. An important loss of viscosity was observed when 1.5% Carbopol® gels were formed in Hepes/NaCl buffer or in a 5% aqueous solution of methyl-β-cyclodextrin. Nevertheless, when methyl-β-cyclodextrin was dissolved in buffer at 5% there was no additional effect on gel viscosity reduction. The incorporation of positively-charged and sterically stabilized liposomes at 2 mM of lipid concentration had no incidence on rheological properties of the Carbopol® gels, whereas gel viscosity was significantly increased in the presence of positively-charged liposomes at 10 mM of lipid concentration. Finally, the viscosity of hydrogels containing both liposomes and methyl-β-cyclodextrin tended to be close to control gels, remaining high and relevant for a topical delivery.