On the fracture and fatigue of soft tissues

Soft biological tissues, such as skin, cartilage, and heart valves, are vital for fundamental physiological functions in living bodies. Through long-time evolution, soft tissues have acquired unparalleled fracture and fatigue properties. Understanding the toughening and fatigue-resistant mechanisms of soft tissues are critical for clinical applications and the development of bioinspired materials. In the past decades, significant progress has been achieved, but remains scattered in literatures. Thus, a comprehensive review is needed for further investigation. This review aims to summarize: (i) the structures and functions of soft tissues; (ii) the deformation and constitutive models of soft tissues; (iii) the toughening mechanism and numerical fracture modeling under monotonic loading; (iv) the fatigue damage mechanism and fatigue crack growth under cyclic loading; and (v) the deterioration of mechanical properties due to pathological processes such as calcification. This review may provide systematic knowledge for understanding the fracture and fatigue of soft tissues, and summarize the natural design principles. It is hoped to inspire further interdisciplinary research to design bioinspired soft materials with high toughness and durability, and facilitate their applications in biomedicine.