Viscoelastic evaluation of topical creams containing microcrystalline cellulose/sodium carboxymethyl cellulose as stabilizer
The purpose of this study was to examine the viscoelastic properties of topical creams containing various concentrations of microcrystalline cellulose and sodium carboxymethyl cellulose (Avicel® CL-611) as a stabilizer. Avicel CL-611 was used at 4 different levels (1%, 2%, 4%, and 6% dispersion) to prepare topical creams, and hydrocortisone acetate was used as a model drug. The viscoelastic properties such as loss modulus (G), storage modulus (G), and loss tangent (tan δ) of these creams were measured using a TA Instruments AR 1000 Rheometer and compared to a commercially available formulation. Continuous flow test to determine the yield stress and thixotropic behavior, and dynamic mechanical tests for determining the linear viscosity time sweep data, were performed. Drug release from the various formulations was studied using an Enhancer TM Cell assembly. Formulations containing 1% and 2% Avicel CL-611 had relative viscosity, yield stress, and thixotropic values that were similar to those of the commercial formulation. The elastic modulus (G) of the 1% and 2% formulation was relatively high and did not cross the loss modulus (G), indicating that the gels were strong. In the commercial formulation,G increased after preshearing and broke down after 600 seconds. The strain sweep tests showed that for all formulations containing Avicel CL-611, theG was aboveG with a good distance between them. The gel strength and the predominance ofG can be ranked 6%>4%>2%. The strain profiles for the 1% and 2% formulations were similar to those of the commercial formulation. The δ values for the 1% and 2% formulations were similar, and the formulations containing 4% Avicel CL-611 had lower δ values, indicating greater elasticity. Drug release from the commercial preparation was fastest compared to the formulations prepared using Avicel CL-611, a correlation with the viscoelastic properties. It was found that viscoelastic data, especially the strain sweep profiles of products containing Avicel CL-611 1% and 2%, correlated with the commercial formulation. Rheological tests that measure the viscosity, yield stress, thixotropic behavior, other oscillatory parameters such asG andG are necessary tools in predicting performance of semisolids.
probing the microstructure of liquid crystalline surfactant systems ; a physicochemical study using rheometry, DTA and 17O NMR
Abstract Mixtures of Brij 96 (decaethylene oxide oleyl ether) and water form liquid crystalline systems (creams) which have a potential as dosage forms for controlled dermal and transdermal drug delivery. By changing the water-surfactant mixing ratio in these systems, lamellar, viscous isotropic or hexagonal liquid crystalline phases can be obtained. First, a number of liquid crystalline creams were characterized using rheometry. Going from a lamellar cream (low water content) to a hexagonal (high water content) one, the macroscopic viscosity strongly increased. In Brij 96-water creams, the polyfethylene oxide) (PEO) chains of the surfactant molecules and the water form a continuous hydrophilic domain, the microstructure of which win be important for the diffusion of drugs through the creams. The hydrophilic domains in the liquid crystalline creams were investigated using 17 O nuclear magnetic relaxation and differential thermal analysis and compared with those of PEO-water solutions. From these studies the conclusions were drawn that (i) the hydrophilic domains may be regarded as PEO solutions in water, and that (ii) the cream structure has no detectable influence on the properties of the microstructure of the hydrophilic domains. In the most concentrated creams and PEO solutions studied, having a water-EO ratio of 1.5, an 8-fold retardation of the rotational mobility of the water molecules was observed using 17 O nuclear magnetic relaxation.
Silicones for cosmetics and toiletries : an environmental update
Although a variety of different silicone types may appear on product labels, we focuse on dimethicone and cyclomethicone, the Cosmetic, Toiletry, and Fragrance Association (CTFA) designations for those structures used most extensively in cosmetics and toiletries. The modes and extents of use, and the fates of these methyl silicones in the environment are discussed, presenting recent data that support the classification of methyl silicones as unique, environmentally friendly materials