Stretchable materials show high crack-initiation resistance that exceeds soft tissues

Mimicking soft tissues, various stretchable materials with fibrous structure have been developed for applications in artificial tissues and soft robotics. However, a fundamental issue in these stretchable composites has long been overlooked: the crack-initiation resistance is much lower than that of soft tissues. The crack can easily initiate and grow in the matrix of stretchable composites. This low crack-initiation resistance severely damages the integrity and function of stretchable composites. Here, we demonstrate a design principle to develop stretchable materials with high crack-initiation resistance. To illustrate the principle, we develop a stretchable composite of a knitted fabric and a highly entangled matrix. The matrix is tough to prevent damage caused by the large movement of fibers. The interface is strengthened to prevent fiber pullout from the matrix. Synergistically, the initiation toughness of this stretchable material is improved to 46.9 kJ/m², much higher than that of bovine pericardium. The principle of stretchable material for achieving high crack-initiation resistance may aid the applications in artificial tissues, soft robotics, and flexible electronics.