3.1 Synthesis and identification of GelMA
The amino groups on gelatin were partly replaced by methacrylic acid to
form GelMA with crosslinking ability (Bahcecioglu, Hasirci, Bilgen, &
Hasirci, 2019). The synthetic GelMA was identified by1H-NMR (Figure S1). The characteristic resonance peak
of the methacrylic acid group (5.5-6 ppm) appeared in GelMA, which is
missing in the control. The substitution degree of GelMA was assessed to
be 79.3 ± 2.7% by TNBS.