*2.6. In Vitro Gel Degradation*

The copolymer was dissolved in PBS at a concentration of 6 wt% and the solution was allowed to stir at 0 ◦C for 72 h. Then, 300 µL copolymer solution was placed into a glass vial of 11 mm in inner diameter and incubated at 37 ◦C for 10 min to obtain a hydrogel sample. Subsequently, 3 mL PBS with or without 5 U/mL proteinase K was added into the vials as the degradation medium and the hydrogels were incubated in an oscillating incubator (60 rpm) at 37 ◦C. At each preset time point, the solution was removed by gentle suction out from the vial with a pipette and the residual solution at the surface of the sample was further removed by a filter paper. The remaining mass of the hydrogel was weighed. Fresh medium was added to the vial. Three parallel samples were tested at each time point.
