2.2. RG NGELRG powder (5 g) was stirred in purified water (100 ml) containing 0.2 mmol/g of (2,2,6,6-tetramethylpiperidin-1-yl)oxyl (TEMPO; Alfa Aesar, USA), 2 mmol/g of NaBr (Ducksan, Korea), and 10 mmol/g of NaClO (Daejung, Korea) at pH 10 and room temperature for 24 h. The mixture was maintained at pH 10e11 with 0.5 M NaOH (Ducksan, Korea). After oxidation, 0.175 ml of ethanol (Ducksan, Korea) was added to quench the reaction, and the pH of the mixture was adjusted to 6 with 1 M HCl (Ducksan, Korea). The mixture was washed with ethanol and purified water, then it isfibrillated using a microfluidizer (Microfluidics corporation, USA) and concentrated, followed by dispersing it in water and vacuum evaporating (Buchi, Switzerland) at 70 C to form the gel.