Figure 4.

Hydrogel softening and stiffening by irradiation. (A) Schematic overview of experiment design showing treatments of photoresponsive hydrogels prior to mechanical characterization. Following preparation, fibronectin-coated gels were softened by exposure to UV (365 nm) irradiation for 30 min; 24 h later, (+) blue gels were exposed to blue (490 nm) light for 1 h, whereas (−) blue gels were unirradiated (left in the dark). Stiffness measurements were made after a further 24 h and compared to control gels (ctrl) that had not been exposed to UV or blue light. (B) Plot of hydrogel stiffnesses obtained by AFM. (−) Blue gels were significantly softer than controls, 5.9 ± 0.1 vs 9.7 ± 0.2 kPa. Stiffness was significantly increased to 7.6 ± 0.2 kPa in (+) blue gels (±SME; n > 97 measurements; p-values indicated from Kruskal–Wallis tests).