Effects of temperature on the fracture and fatigue damage of temperature sensitive hydrogels

As an excellent model material for fundamental studies on temperature-sensitive hydrogels, poly(N-isopropylacrylamide) (NIPA) hydrogel has been applied in drug delivery, tissue engineering, and soft robotics. However, the lack of study on fracture and fatigue hinders further development of hydrogels for applications where cyclic loading-unloading is unavoidable. In this study, the fracture and fatigue damage of the NIPA hydrogel were studied for the first time by pure shear tests at different temperatures. Fracture behaviors were investigated under monotonic load from 31 °C to 39 °C. It is found that the fracture energy increases with the increase in temperature. The fracture energy is approximately 20 J m⁻² near the volume phase transition temperature. Temperature also significantly influences the fatigue life. By fitting the experimental data, the fatigue limit λ_f is determined. The results obtained from the experimental tests would be important for the engineering applications of the NIPA hydrogels.