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-beta-cyclodextrin on rheological properties of Carbopol(R) 974P NF hydrogels was investigated. All formulations have displayed a shear-thinning behavior of Carbopol(R) 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(R) gels were formed in Hepes/NaCl buffer or in a 5% aqueous solution of methyl-beta-cyclodextrin. Nevertheless, when methyl-beta-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(R) 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-beta-cyclodextrin tended to be close to control gels, remaining high and relevant for a topical delivery. (C) 2002 Elsevier Science B.V. All rights reserved.