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.
Rheological Characterization of Petrolatum Using a Controlled Stress Rheometer
The current study focuses on characterizing the rheological characteristics of different petrolatum grades using a controlled stress rheometer. Both steady-state flow and dynamic oscillatory tests were conducted on the petrolatums. The thermorheological scans were found to be the most informative and reproducible for this study. Significant differences in the structure were observed between the petrolatum grades. The structural differences were found to be most significant in the temperature range 25–35°C. The findings from this study will help in identifying the critical parameters (for e.g., temperature, mixing) during the processing and handling of such materials, which can have a direct impact on the product rheology and performance.
The structure elucidation of semisolid w/o emulsion systems
Abstract In the course of investigating the effects of silicone surfactant (Abil WE 09®) on the microstructure of semisolid w/o emulsion systems with different water/oil ratios, only dispersed droplets of the internal water phase (1–15 μm size) were discovered in the gel network of white petrolatum. With increasing water content (from 40 to 90% w/w) the degree of dispersity was found to increase (microscopic analysis-polarized light microscopy and TEM). Experiments were also carried out using differential scanning calorimetry (DSC) and rheometry (rotational and oscillatory viscosimetry). The DSC results showed different behaviour of the investigated systems on controlled cooling. In semisolid emulsion systems with droplets small enough and of equal size, a homogeneous nucleation temperature was achieved. In emulsion systems containing a high percentage of water, the assumption that the behaviour of water was like that of the pure (bulk) water was acceptable. All semisolid emulsion systems exhibited pseudoplastic behaviour. Their viscoelastic properties determined using oscillation rheometry correlated well with rotational results.