Fig. 2: Mechanical characterization of fatigue-resistant hydrogel adhesion.
a Schematic illustration of measuring nominal peeling force F versus displacement curve during a single cycle of loading within a water bath. b Representative curves of the peeling force per width of the hydrogel (F/W) versus displacement for the tough hydrogel adhesion (i.e., PAAm-alginate) and fatigue-resistant hydrogel adhesion (i.e., PVA) on a glass substrate. c Schematic illustration of measuring the interfacial crack extension c versus cycle number N during a cyclic peeling test at a peeling force of Fa. d Plot of crack extension rate (dc/dN) versus applied energy release rate G = Fa/W for the tough hydrogel adhesion and fatigue-resistant hydrogel adhesion on a glass substrate. The linear extrapolation to the G-axis gives the fatigue threshold Γ0. e Images of interfacial crack propagation during a cyclic peeling test for tough hydrogel adhesion with a thickness around 3 mm (swollen state) at an energy release rate of 200 J m−2, showing substantial interfacial crack propagation within 5000 cycles. f Images of interfacial crack propagation during a cyclic peeling test for fatigue-resistant hydrogel adhesion with a thickness around 100 μm (swollen state) at an energy release rate of 800 J m−2, showing no interfacial crack propagation within 30,000 cycles. g Summary of measured interfacial toughness and interfacial fatigue threshold for fatigue-resistant hydrogel adhesion on various substrates, including glass, ceramic, titanium (Ti), aluminum (Al), stainless steel, PU, and PDMS. Error bars = standard deviation (n = 3). Scale bars: 10 mm in (e, f).
