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.
Low-temperature scanning electron microscopy of the phase inversion process in a cream formulation
Abstract The microstructure of a modified cetomacrogol cream B.P. has been studied using a cryo-SEM technique. Etching of the aqueous phase was used to determine the nature of the continuous phase. A phase inversion from w/o to o/w occurs during the cream manufacture. Additionally, the technique has been used to monitor the structure of a cream formulation during long-term storage. A link between microstructure and emulsion stability was observed.
Determination of the Rotational Correlation Time of Water by Proton NMR Relaxation in H217O and Some Related Results
Analysis of the 1H-17O dipolar contribution to the proton longitudinal relaxation rate in 17O-enriched water yields a correlation time for re-orientation of the O–H vector τrOH = (1.71 ± 0.07) ps in H2O at 25 °C. This result is insensitive to uncertainties in the calculated intermolecular relaxation contribution. From 1H, D, and 17O relaxation rates in H2O/D2O mixtures deuterium isotope effects on the correlation times were estimated. The quadrupole coupling constants of D and 17O in liquid water were determined.