Genipin-crosslinked type A gelatin hydrogels were prepared with different crosslinker concentrations before being tested in the presence of proteases. Crosslinking of the hydrogels induces a blue colour due to increased conjugation (see Figure ). The change of colour allows the crosslinking reaction to be followed by UV/Vis and fluorescence spectroscopies. In Figure , absorbance of hydrogels with different concentrations of genipin was measured at 590 nm over 18 h. In Figure , fluorescence experiments were carried out at λex=590 nm and λem=610 nm for 2 h on 7.5wt% G hydrogels with different concentrations of genipin.