| Bone and antler bone are composite materials with a multi-level layered structure composed of collagen,mineral,water and non-collagen,both of which are part of bone family materials.The difference is that antler bone has more collagen and water but less mineral,which makes the antler bone more flexible.Therefore,antler bone is an ideal bone material for exploring the toughening mechanism of bone.In the study of bone toughening mechanism,the relationship between the structure and mechanical properties of matching bones has always been a hot spot in the field of bone mechanics.Especially at the micro-/nanoscale,the study of the matching between structural units and mechanics of bone has far-reaching significance for revealing the excellent toughness of bone,in-depth understanding of the decline of bone mechanical properties caused by diseases,and the construction of biomimetic structural materials.At present,the research on the in-situ micro-/nanomechanical behavior of bone mainly includes combined X-ray diffraction with in-situ mechanical test and computer simulation,et.al.These methods enable us to have a profound understanding of the mechanism of bone toughening.However,there are few reports on the visual in situ characterization of bone micro-/nanomechanical behavior.In order to further understand the micro-/nanomechanical behavior of bone under stress state,a new in-situ mechanical platform was constructed by combining the miniature in-situ mechanical test system and atomic force microscopy to visually characterize the micro-/nanotoughening mechanism of bone and match the relationship between the macromechanics and the micro-/nanomechanical behavior of bone.The main research contents and results of this paper are as follows:Firstly,a new in-situ mechanical platform was built by combining a miniature in-situ mechanical test system with an atomic force microscopy.The maximum size of the platform can be used to observe the lamellar structure of bone,and the minimum can be used to observe the D-spacing structure of collagen fibrils.At the same time,the platform can conduct in situ imaging of the samples under different stress states,and obtain the micro-/nanomechanical behavior information of the bone matching with the macroscopic stress strain.Secondly,the platform was used to quantify the mechanical properties of antler bone samples under cyclic tension,and to conduct in situ imaging of tensile and demineralized specimens under different strain states.The reversible and irreversible changes of nanomorphology in bone were observed successfully and the relationship between the characteristic D-spacing of collagen fibrils and macroscopic strain was explored.Finally,the water content of bones decreases with age,and the mechanical properties of bones also decrease.In order to explore the effect of water on toughening mechanism of bone,the platform was used to track the micro-/nanocrack growth process of hydrated and dehydrated bone in situ.For the first time,it was observed in real-time that the process of mineralized collagen fibrils in hydrated bone from bridging to fracture.The experimental results show that in the hydrated bone,the hydrated interface between collagen phase and mineral phase and between the mineralized collagen fibrils can effectively promote the slippage between the two phases and between the mineralized collagen fibrils,and provide excellent toughness for bones.The dehydration interface in the dehydrated bone causes the mineralized collagen fibrils to break directly under lower strain,and the toughening mechanism of the mutual sliding between the mineralized collagen fibrils fails,and the toughness of the bone is significantly reduced.This study effectively explored the effect of water,the basic component of bone,on the toughening mechanism of bone,providing a reference for the study of disease and age-related bone toughness decline.It provides method guidance for exploring the mechanism of bone toughening played by the basic components of bone. |
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