Abstract
Adhesive hydrogels have been extensively studied for wet tissue adhesion and a broader range of biomedical applications. Yet, the mode-I and mixed-mode fracture mechanics of soft-soft (e.g. gel-gel and gel-tissue) interfaces has not been thoroughly explored. Here, an alternative approach was presented to studying gel-gel interfacial fracture mechanics, particularly stitch polymerinduced topohesion, using amylopectin-reinforced polyacrylamide (Amy/PAAm) as the model hydrogel with chitosan as the stitching polymer, and employing new T-shaped specimen configuration for mode-I and mixed-mode fracture studies. Amy/PAAm hydrogel precursors were photocured into adherends and bonded together with 200 mu L solutions of chitosan of varying molecular weights (MWs) to form T-shaped cross-section specimens for subsequent testing. The effect of different chitosan MWs (1.5, 15, 120, 250, and 343 kDa, and with no chitosan as control) and pHs of the chitosan solutions (ranging from 2.5 to 4.5) on the mode-I and mixed-mode fracture toughness was systematically studied. The mode-I and mixed-mode fracture initiation toughness was evaluated using nonlinear J-integral fracture mechanics. Chitosan with the highest MW and pH resulted in a 200 % increase in mode-I fracture toughness compared to the control, which is attributed to the robust interfacial chemistry and crack tip blunting phenomena. In the mixed-mode loading conditions, the fracture toughness is lower than that of mode-I for all configurations, and the highest MW and pH lead to about 65 % increase in the mixed-mode toughness. These results are supplemented and explained with strain fields around the fracture process zone at crack initiation using digital image correlation.