Hi,

just for clarity, swelling causes volume expansion, not shrinkage. The shrinkage probably means the opposite process - you lose water from your hydrogels. The most obvious reason is water evaporation unless you keep the gel in water or a 100 % humid environment. You may easily compare the water content by measuring the dry weight. There might be other reasons, though, such as tighter packing caused by increased ionic strength, network density, or electrostatic force, etc.

Thanks for the enlightenment Petr Lepcio . We will be using the hydrogel for a specific biomedical application. Shall we consider swelling ratio for the characterization of hydrogels or is the calculation of water content enough for this matter?

The swelling ratio is calculated from the water content, so it is more or less the same thing expressed in two different ways. However, remember that many biomedical applications use a physiological solution rather than pure water, so the ionic exchange can alter the swelling ratio of your hydrogel. Therefore, all stability tests shall be done in relevant conditions.

Thanks for sharing Petr Lepcio . I highly appreciate your suggestions.