Direct measurement of the time-dependent mechanical response of HPMC and PEO compacts during swelling

Mechanical indentation is used to measure the time dependent mechanical properties of three model compact formulations during swelling in aqueous media. The formulations are based on polyethylene oxide (PEO), hydroxypropyl methylcellulose (HPMC) and a PEO/HPMC blend. The technique is sensitive to changes in compact thickness and mechanical response and is used to characterize changes in the mechanical properties of the model compacts during the swelling process. The gel thickness and the effective elastic modulus of the gel layer are obtained from the load/displacement relationship during initial indentation. The HPMC and hybrid compacts showed significantly more swelling (110%) than the PEO compact (67%). Viscoelastic properties of the gel layer are determined throughout the swelling process by an oscillatory indentation method. Results show the complex modulus of all three compacts decreasing by approximately an order of magnitude over the course of swelling for 6 h. The measurement techniques presented here can easily be extended to more complex systems.

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