A comparison between the use of dynamic mechanical analysis and oscillatory shear rheometry for the characterisation of hydrogels.

In this study the use of dynamic mechanical analysis (DMA) for the mechanical characterisation of pharmaceutical hydrogels was evaluated. DMA was used in two different modes, the "controlled force" and the "multi-strain" (MS). The results obtained on dextran methacrylate hydrogels of various compositions were compared to those obtained using an oscillatory shear rheometer. The best agreement was found between the MS-DMA and the rheometer results. The moduli measured in MS-DMA were extrapolated towards zero compression to obtain the modulus of the hydrogels. This procedure resulted in good agreement with the data obtained with the rheometer. Hydrogels were analysed after swelling to equilibrium with both methods, DMA and rheology. A scaling between the elastic modulus (G') and the equilibrium swollen polymer volume fraction (v(2,s)) could be found, although the best correlation between G' and v(2,s) was obtained with the rheometer.