(a) The swelling ratio of the SPS hydrogel sphere after immersed in the phosphate buffer solution for 1 h, 2 h, 3 h, 4 h, 5 h, 6 h and 18 h in the condition of pH 1.2, pH 6.8, pH 7.4 and pH 8.3, separately; (b) the degradation ratio of the SPS hydrogel sphere for 0.5 h, 1 h, 2 h, 4 h, 8 h, 16 h, 24 h, 48 h and 72 h in the condition of pH 1.2, pH 6.8, pH 7.4 and pH 8.3, separately; (c) the swelling ratio of the SA, SP and SPS hydrogel spheres after immersion in the PBS solution in the condition of pH 1.2 for 4 h, and then pH 7.4 for 8 h, and finally pH 8.3 for 60 h. (mean ± SD, n = 5).