2.7 Swelling Study
The standard test method for water absorption (ASTM D570-98) was tested through immersion of the samples in a container filled with water at room temperature (Liu & Kim, 2012). The hydrogels were excised into strips measuring 76.2 mm long and 25.4 mm wide with a thickness of 0.02 mm and were conditioned for 24 hr. Repeated immersion test was done which started with 24 hours of immersion in phosphate-buffered saline, pH7 (Sigma). At the end of the immersion period, the samples were removed from the water one by one and gently wiped with Whatman No 1 filter paper to remove the surface water. They were immediately weighed to the nearest 0.001 g. The swelling ratio was calculated using the equation below.
\begin{equation} \%\ Swelling\ ratio=\frac{\text{Weight\ of\ sample\ in\ swollen\ state\ }\times\text{Weight\ of\ sample\ in\ dry\ state\ }}{\text{Weight\ of\ sample\ in\ dry\ state}}\times 100\%\nonumber \\ \end{equation}