Characterizations of hydrogels. (A) FT-IR spectra of HA, OHA, chitosan, CMC, and representative hydrogel formed through the Schiff base reaction between OHA and CMC. (B) Rheological behavior of hydrogels. (C) ESR of hydrogels after immersing in PBS for 24 h. (D) Representative SEM images of hydrogels and drug-encapsulated hydrogels. Scale bar: 100 μm. (E) Pore size of hydrogels and drug-encapsulated hydrogels. (F, G) Degradation kinetics of hydrogels in PBS without (F) and with (G) 50 U/mL hyaluronidase.