When exposed to an aqueous medium, certain tablets swell and rapidly form an interfacial rubbery or gelatinous layer. This layer allows some additional liquid to penetrate the tablet while also acting as a rate controlling layer for active diffusion.

As the outer tablet layer dissolves, a newly exposed layer of tablet medium retards diffusion and continues sustained, controlled drug release. Though dissolution testing is an established and necessary analysis for assessing efficacy and safety, texture analysis is emerging as a useful measurement technique for CR and ER dosages. The technique can be used to measure the swelling rate of gels and gel coatings, allowing scientists to determine the time before the gel dissipates and active ingredients become available and is a valuable tool to assist the formulation scientist in selecting the correct polymer for a particular application.

Numerous researchers have now used the TA.XTPlus Texture Analyzer to carry out tests to precisely detect the glassy core/rubbery gel interface. It has been confirmed that the TA.XTPlus Texture Analyzer is able to provide easy and accurate determination of dimensional changes associated with matrix hydration and swelling of complex formulations and results compare well to NMR imaging.

The project for this type of test is now available as an application study within the latest version of Exponent Help. Swollen compacts are removed at predetermined time intervals (usually over a period of hours) for external profiling and to determine water penetration and gel layer thickness as a function of residence time in the buffer medium. Samples are placed in the center of the testing platform, and a flat-tipped 2mm diameter cylinder probe is used to penetrate their surfaces to determine gel layer thickness, movement of the erosion and swelling fronts, and total work of probe penetration into the entire matrix. The resistance encountered by the probe is a function of the distance it penetrates into the swollen matrix (see above curves). By penetrating the swollen matrix, the glassy polymer can be differentiated from the polymer gel. This is a simple means of understanding the time-dependent polymer growth behaviour that can be used on a routine basis.

By Stable Micro Systems