The solutions were then transferred to 5 mm NMR tubes, and all NMR spectra were acquired at room temperature. The degree of methacrylation was determined by quantifying the percentage of ε-amino groups of gelatins (lysine, hydroxylysine) that were functionalized by the addition of methacrylic anhydride (MAA). The calculation of the degree of methacrylation for functionalized gelatin was performed using equation 1.