According to the rheological behavior data, comparing emulsions A and B, the first required a higher shear stress to be deformed than the second and when the forces acting on the emulsion ceased emulsion A recovered its structure faster. The droplets presented a smaller and nonhomogeneous size Figure 2. Nonetheless, in general, the reduction in droplet size results in an increase in the viscosity and storage modulus of the emulsions, which suggested an enhancement in emulsion stability. Conclusion In conclusion, the release assay confirmed the prediction of release profile suggested by the rheological data, showing the influence of the rheological features on the release of active substances from the vehicles. As it is possible to see also in Figure 3 , emulsion A needs a higher shear stress to flow than emulsion B, showing that emulsion A is more structured than emulsion B, since it needs more shear stress per unit of area to be disrupted and flow. Surface Activity in Drug Action. Giving her pussy to the dean for a favor.
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Thus, addition of a carbomer to the emulsion increases the interfacial tension of the multiphasic systems decreasing the wettability of active substance on the skin surface and a lower permeability of the drug, which is in accordance with in vitro release assay described below. The emulsions were also characterized as thixotropic, exhibiting a decrease in viscosity with increasing shear that is not completely recovered when the shear rate is ceased. The surface tension values for emulsion B are lower than those for emulsion A. A platinum plate was partially immersed into the surface layer of an aqueous phase and the monitored surface tension decreased with time, while the plate remained into position. Do a search to find mirrors if no download links or dead links.
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Table 6 Linear regression equations obtained in determining the reaction order of in vitro release of alpha-lipoic acid from formulations A and B. Little Cinderella and Max. Flow curves, stress and frequency sweeps, and creep and recovery assays were carried out to understand the rheological behavior of the emulsions. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. For a correct turbidity, about 0. The authors are grateful to Timothy J. Oxidants and Antioxidants in Cutaneous Biology.
This characteristic, the nonlinear relation between the shear stress and the shear rate, is typical of non-Newtonian behavior [ 27 ]. When the data were fitted to the zero-order, first-order, and Higuchi kinetic models by linear regression Table 6 , the regression coefficients R 2 were calculated Table 7. Relationships between surface free energy, surface texture parameters and controlled drug release in hydrophilic matrices. The flow curve data were fitted to the Herschel-Bulkley rheological model. The pharmacology of the antioxidant lipoic acid. Samples were examined after preparation and storage at room temperature.