The detailed experimental procedure has been described previously. In short, type A gelatin derived from porcine skin tissue was dissolved in CB (Carbonate-Bicarbonate) buffer (0.1 M buffer comprising 3.18 g sodium carbonate and 5.86 g sodium bicarbonate in 1 L distilled water), and the pH was adjusted with 5 M sodium hydroxide or 6 M hydrochloric acid. Subsequently, MAA (Methacrylic anhydride) was added to the gelatin solution under magnetic stirring at 500 rpm. The reaction proceeded for 1 h, and then the pH was readjusted to 7.4 to stop the reaction. After being filtered, dialyzed using Spectra Por S/P 2 Dialysis membrane (12 -14 kDa, 25 mm flat width) (Cole-Parmer, USA), and lyophilized, the samples were stored at -20°C until further use. The standard conditions of the synthesis were: CB buffer at 0.25 M, initial pH adjustment at pH 9, MAA amount at 0.01-0.1 mL per gram of gelatin concentration at 10 w/v%, reaction temperature at 50°C, and reaction time for 1 h.