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The synergy between nanostructured lipid carriers (NLC) and chemical penetration enhancers provides the basis for a promising strategy to effectively deliver drugs through the skin. In the present work, focus is given to the study of the interaction of limonene, ethanol, and Carbopol Ultrez 10NF, as the gelling agent, with a co-encapsulating NLC dispersion, containing both olanzapine and simvastatin. The analysis is based on rheological, mechanical, and physicochemical properties. The nanoparticle size ranged from 130 to 400 nm, depending on the system considered. The inclusion of carbopol resulted in a considerable increase in the NLC particle size, which was attributed to carbomer bridging nanoparticles, resulting in some particle aggregation. Rheological measurements indicated that the viscosity of the neat carbopol hydrogel was reduced by the enhancers and to a higher extent by the presence of NLC. A more apolar medium can be pointed out as a general explanation, while a polymer/nanoparticle hydrophobic interaction coupled with surfactant/polymer H-bonding provides the rationale for the NLC effect. The inclusion of enhancers and a carbomer largely contributed to the physicochemical stability of the NLC formulation, as revealed by the low transmission profiles and more negative zeta potential values. [ABSTRACT FROM AUTHOR]

The rheological properties of agar hydrogels were investigated. The agar gels were prepared by mixing an aqueous solution of agar-agar with glycerin, sorbitol, citric acid, sodium citrate, and sodium chloride at various concentrations. Sodium citrate, citric acid, and also their mixture had the most significant effect on the viscosity of the agar gels. Adding citric acid to the agar-gel composition reduced the viscosity whereas addition of sodium citrate increased it. Hysteresis loops were constructed for various compositions. [ABSTRACT FROM AUTHOR]