Routine Direct Quantification of Methacrylic Groups per Gelatin Unit in Gelatin Methacryloyl Using Ultraviolet Spectroscopy.

Gelatin methacryloyl (GelMA) is an essential biomaterial for 3D bioprinting due to its excellent biocompatibility and easily tunable physical properties. GelMA quality strongly depends on the number of methacrylic groups introduced during the synthesis. We present a direct UV assay for routine quantification of methacrylic groups in GelMA. The accuracy and precision of the method are comparable to those of NMR techniques. Moreover, the method is independent of sample concentration and adapted for gelatin from various sources. Additionally, we developed a UV-based method for determining methacrylic acid in GelMA and demonstrated how methacrylic acid contamination affects the quantification of methacrylic groups. Rather than reporting the degree of substitution alone, we define the methacrylic content as the quantity of methacrylic groups per 100 kDa gelatin unit, which makes the metric independent of the number of lysine residues in gelatin. This routine-ready approach lowers the barrier to reliable GelMA characterization and standardizes reporting across batches and laboratories.