Repairable cascaded slide-lock system endows bird feathers with tear-resistance and superdurability

Significance Bird feathers have aroused tremendous attention for their contributions to the unique flight capability of birds against wind and even through bushes. Many studies have attempted to explore the mechanism underlying feathers’ superdurability. However, it is not yet clear why feathers are so superdurable. In this study, we discovered and characterized the sophisticated cascaded slide-lock system of bird feathers, which is composed of flexible hooklets, a slide rail, and spines at the end of the slide rail as terminating structures. This finding demonstrates that the superdurability of bird feathers against tears originates from their cascaded slide-lock system, not from the “hook–groove system” proposed centuries ago. Bird feathers have aroused tremendous attention for their superdurability against tears during long flights through wind and even bushes. Although feathers may inevitably be unzipped, the separated feather vanes can be repaired easily by bill stroking. However, the mechanism underlying bird feathers’ superdurability against tears remains unclear. Here, we reveal that the superdurability of bird feathers arises from their repairable cascaded slide-lock system, which is composed of hooklets, a slide rail, and spines at the end of the slide rail as terminating structures. Microscopy with a micronano manipulating system and 3D X-ray microscopy provided high-level visibility into the 3D fine structures and the entire unzipping process of feathers. The hooklets can slide along the slide rail reversibly when suffering external forces, and the sliding hooklet can be locked by the spine at the ends of barbules when larger pulling forces are applied and even slide farther away due to the unzipping of the interlocking structure with large deformation of the barbules. The elongation before separation of adjacent barbs can reach up to 270%, and the separation force can be maintained above 80% of the initial value even after 1,000 cycles of separating and repairing. These results prove that the cascaded slide-lock system ensures the superdurability of bird feathers against tears.