where Ws and Wd are the weights of the samples swollen in buffers and in dry state, respectively. Swelling kinetics of the beads was studied by immersing of a certain amount of samples (∼0.20 g) in distilled water. At consecutive time intervals, the water absorbency of the hydrogels was measured according to the above mentioned method. The all swelling data were repeated 3 times and the mean values were shown in graphs