The contribution of nanostructures of bone to the macroscale mechanical properties has received much attention, but most of nano-toughening mechanisms have remained in the theoretical stage or at static experimental observation. Our study shows that the medullary surface of the bovine femur provides a smooth natural surface ideal for observing nanostructures in bone. Mechanical loading is applied using an in situ mechanical device and the nanomechanical behaviours of the specimens are in situ recorded and imaged using an atomic force microscope (AFM). By the in situ observation of nanomechanical behaviours under stress, the existing nano-toughening mechanisms, such as fibril slippage and fibril bridging, are confirmed. Before the micro failure stage, mineralized collagen fibrils are strained with the increase of stress, followed by pre-separation (or slippage) due to stress concentration, resulting in cracked nanoscale interfaces. When micro-failure occurs (i.e. crack initiation), the nano-bridging mechanism contributes to resisting the formation of nanometre crack interface, the propagation of crack tip and the failure of crack bridging. Our study provides direct evidence for the connection between bridging-type mechanisms at different scale, which are composed of the corresponding bone structures at each level. Through the in situ observation of the microscopic failure in bone, some visual information are offered on the interaction between nanomechanical behaviours and nanostructures.

骨骼的纳米结构对宏观力学性能的贡献已引起广泛关注，但大多数纳米增韧机理仍处于理论阶段或静态实验观察。我们的研究表明，牛股骨的髓质表面提供了光滑的自然表面，非常适合观察骨骼中的纳米结构。使用原位机械装置施加机械载荷，并使用原子力显微镜（AFM）原位记录样品的纳米力学行为并对其成像。通过在应力作用下的纳米力学行为的原位观察，证实了现有的纳米增韧机理，例如原纤维滑移和原纤维桥接。在微失效阶段之前，矿化的胶原纤维随着应力的增加而拉紧，然后由于应力集中而进行预分离（或打滑），从而导致纳米级界面破裂。当发生微故障（即裂纹萌生）时，纳米桥接机制有助于抵抗纳米裂纹界面的形成，裂纹尖端的传播以及裂纹桥接的失败。我们的研究为不同规模的桥接型机制之间的联系提供了直接证据，这些机制由各个级别的相应骨骼结构组成。通过原位观察骨骼的微观破坏，可以提供有关纳米力学行为和纳米结构之间相互作用的一些视觉信息。纳米桥联机制有助于抵抗纳米裂纹界面的形成，裂纹尖端的扩展以及裂纹桥接的失败。我们的研究为不同规模的桥接型机制之间的联系提供了直接证据，这些机制由各个级别的相应骨骼结构组成。通过原位观察骨骼的微观破坏，可以提供有关纳米力学行为和纳米结构之间相互作用的一些视觉信息。纳米桥联机制有助于抵抗纳米裂纹界面的形成，裂纹尖端的扩展以及裂纹桥接的失败。我们的研究为不同规模的桥接型机制之间的联系提供了直接证据，这些机制由各个级别的相应骨骼结构组成。通过原位观察骨骼的微观破坏，可以提供有关纳米力学行为和纳米结构之间相互作用的一些视觉信息。