A soft and fatigue-resistant material that mimics heart valves

Bovine pericardium, a tissue commonly used to make artificial heart valves, fulfills two fundamental mechanical requirements: a low modulus to ensure opening and closing in cyclic pulsatile flow and a high fatigue threshold to prevent crack growth. The tissue consists of a soft matrix and crimped fibers. Inspired by this architecture, we develop a composite of a soft polymer matrix and a knitted fabric. When the stretch is small to modest, the knitted fabric is easily stretched, so that the composite is soft. When the stretch is large, the knitted fabric is stiff and strong, so that the composite resists fatigue crack growth. The mechanical behavior of the composite is comparable to that of bovine pericardium. The composite has an exceptionally long fatigue life, enduring 25 million cycles of pulsatile flow, two orders of magnitude longer than the polymer matrix. This soft and fatigue-resistant composite may find broad applications in biomedicine.