A Transparent, Skin-Inspired Composite Film with Outstanding Tear Resistance Based on Flat Silk Cocoon

Flexible and transparent substrates play a fundamental role as a mechanical support in advanced electronic devices. However, commonly used polymer films, such as polydimethylsiloxane, show low tear resistance because of their crack sensitivity. Herein, inspired by the excellent mechanical robustness of the skin and its fibrous structure, an epoxy-resin-based composite with a flat silk cocoon as a reinforcing fiber network is fabricated. With only 1 wt% of silk fiber, the tensile strength and modulus of the as-prepared composite film are considerably increased by 300% and 612% compared to those of pure resin, while still maintaining flexibility and transparency. More importantly, the composite shows remarkable tear resistance: without fracture after ≈30 000 tensile cycles. The potential application of such transparent composite films as mechanically robust substrates for flexible electronics is also demonstrated. In addition, this study represents a bioinspired strategy to construct high-performance functional composite materials.