Rheological monitoring of long-term degrading polymer hydrogels

This paper reports on the rheological characterization of long-term degrading hydrogel slabs using a rotational rheometer. A rheological methodology was developed and validated using hydrogel slabs made of cross-linked methacrylated dextran. The method was based on the identification of the optimal amount of compression of the hydrogel slabs between the plates of the geometry, needed for reliable G' measurements. A G' plateau (G'(p)) could be identified for each hydrogel slab as a leveling off of G' upon further compression. This G'(p) was reproducible and of the same order of magnitude as G' of hydrogels prepared in situ between the plates of the geometry. The method allowed doing rheological measurements without prior knowledge of the exact dimensions of the hydrogels. Using this method, the enzymatic degradation of dextran methacrylate (dex-ma) hydrogel slabs with incorporated dextranase was characterized theologically. It was proven that the observed changes in the rheological behavior were enzyme linked. Being able to reproducibly measure the rheological properties of hydrogel slabs prepared outside the rheometer has as a great advantage that the influence of swelling, degradation, or any treatment can be theologically studied. (C) 1999 The Society of Rheology. [S0148-6055(99)01104-9].