confined compression test using a SMS (Stable Micro
Systems, Surrey UK) TA-xT2 texturometer equipped with
a 1 kg load cell at room temperature. The compression
limit was 500 g to protect the load cell and the speed test
was 0.2 mm/s. Cylinder-shaped samples sized 25 mm in
diameter and 10 mm in thickness were used. To minimize
the effect of water evaporation, hydrogel samples were
kept in sealed packs before measurement. The compressive
stress and strain were graphed and the average compression
modulus and standard deviation were determined.
The compression modulus was calculated by determining
the slope of the linear region in the 7.5–15% of strain in
the stress–strain curve. The data reported were the mean
of five samples.