Water promotes the formation of fibril bridging in antler bone illuminated by in situ AFM testing.

Water, as one of the main components of bone, has a significant impact on the mechanical properties of bone. However, the micro-/nanoscale toughening mechanism induced by water in bone remains at only the theoretical level with static observations, and further research is still needed. In this study, a new in situ mechanical test combined with atomic force microscopy (AFM) was used to track the micro-/nanocrack propagation of hydrated and dehydrated antler bones in situ to explore the influence of water on the micro-/nanomechanical behavior of bone. In hydrated bone, observations of the crack tip region revealed major uncracked ligament bridging, and the conversion of mineralized collagen fibrils (MCFs) from bridging to breaking is clearly seen in real time. In dehydrated bone, multiple uncracked ligament bridges can be observed, but they are quickly broken by cracks, and the MCFs tend to break directly instead of forming fibril bridges. These experimental results indicate that the hydrated interface promotes slippage between collagen and the mineral phase and slippage between MCFs, while the dehydrated interface causes MCFs to fracture directly under lower strain. The platform we built provides new insights for studying the mechanism of toughening of the components in bones.