Characterization of gel consistency: a new method for the measurement of the contractional flow

Classic viscosimetric methods are generally used for the characterization and Quality Control of semisolid pharmaceutical formulations. Although a diluted solution or a suspension can be characterized well by means of its rheologic behaviour, a gel system cannot be fully characterized in terms of classical viscosimetry. The fundamental properties of a gel preparation such as consistency, tackiness, stickiness, spreadability, should be analysed using more suitable methods, able to determine the mechanical properties of materials that show both viscous characteristics of liquid and elastic properties of solids. A new method is proposed for the determination of the extensional properties of gels. The Texture Analyser, an apparatus routinely employed for the determination of the consistency of semisolid materials in the food industry, is used here to study some carboxyvinyl gels prepared with different concentrations and at different pHs. The Texture Analyser is then equipped with a new purpose-built device that enables the characterization of the gel system when the sample is subjected to a shape deformation. This technique better simulates the processing conditions used in industrial production and the practical applications of the dosage forms (extrusion, tubing, and spreadability).