Nonlinear Fracture Mechanics of Hydrogel-Like Soft Materials

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Hydrogel-like soft materials are abundant in nature including soft tissues such as cartilage, tendons and ligaments. With similar mechanical properties and biocompatibility, synthetic polymer-based hydrogels have been used extensively for a wide range of biomedical applications such as artificial tissues and drug delivery. More recently, hydrogel-like materials have been explored as a class of soft active materials in the development of soft machines and soft robotics. For many of these applications, mechanical properties of the hydrogel-like soft materials are important, governing how they deform and fail under various conditions. In particular, fracture of hydrogel-like soft materials has not been well understood, and it remains a challenge to predict if and when such materials would fracture. This project aims to establish a knowledge base necessary for failure analysis and prediction of hydrogel-like soft materials. The results will enable engineering of such materials with reliable fracture properties for a range of applications including tissue engineering and soft robotics. The three PIs, jointly with expertise in fracture mechanics/dynamics, soft materials, experiments, modeling and simulations, will collaborate to bring different perspectives onto this project. Education and outreach activities will be integrated within the project to enhance its broader societal impacts, which include research experience for undergraduates, engaging minorities and underrepresented groups, and outreach to high school students and general public.The fracture processes of hydrogel-like soft materials are highly nonlinear in general, coupling large deformation with particular kinetic processes due to solvent diffusion and polymer viscoelasticity. This project is to establish a nonlinear, transient theoretical framework that defines the fracture driving force and a fracture criterion for crack growth in hydrogel-like soft materials, with explicit recognition of the associated kinetic processes. The theoretical framework will enable implementation of numerical simulations that would predict particular fracture behaviors relevant to hydrogel-like materials such as delayed fracture and rate dependence. The results will be compared to experimental measurements for validation. The developed methodology with modeling and experiments will then be used for measuring fracture properties of hydrogel-like soft materials. The distinct effects of solvent diffusion and viscoelasticity on fracture will be elucidated through numerical simulations and a set of experiments from quasistatic to dynamic regimes.