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.