Abstract
The bovine hoof wall with an α-keratin structure protects the bovine foot from impact loads when the cattle are running. Reduced modulus, hardness and creep behavior of the bovine hoof wall have been investigated by a nanoindentation technique. The average reduced modulus of the Transverse Direction (TD) specimens from the outside to inside wall is 3.76 and 2.05 GPa, respectively, while the average reduced modulus of the Longitudinal Direction (LD) specimens from the outside to inside wall is 4.54 and 3.22 GPa, respectively. Obviously, the orientation and the position of the bovine hoof wall have a significant influence on its mechanical properties. The use of the generalized Voigt–Kelvin model can make a good prediction of creep stage. Mechanical properties of the LD specimens are stronger than those of the TD specimens. The bovine hoof wall has a layered structure, which can effectively absorb the energy released by the crack propagation and passivate the crack tip. Therefore, a kind of structural model was designed and fabricated by three-dimensional printing technology, which has a 55% performance improvement on fracture toughness. It is believed that the reported results can be useful in the design of new bionic structure materials which may be used in motorcycle helmets and athletes’ protective equipment to achieve light weight and improved strength at the same time.
Highlights
Biomaterials have created a variety of amazing functions through billions of years of evolution, such as: optimized multi-scale, hierarchical structures, excellent mechanical properties, adaptability and self-healing ability [1,2]
This is very interesting, because the keratin mainly contains organic proteins, rather than the other stronger biological materials compositing with high mineral content, e.g., teeth
It is necessary to study the relationship between the mechanical properties and the hierarchical structure because of the irreparability once it is keratinized [5,6]
Summary
Biomaterials have created a variety of amazing functions through billions of years of evolution, such as: optimized multi-scale, hierarchical structures, excellent mechanical properties, adaptability and self-healing ability [1,2]. Researchers have proved that the main constituents of the hoof wall are α-keratin and keratinized cells [4] This is very interesting, because the keratin mainly contains organic proteins, rather than the other stronger biological materials compositing with high mineral content, e.g., teeth. Nanoindentation technology is a set of test systems for micromechanical properties of materials, which is widely used for the characterization of surface properties of film materials, biomaterials and so on It can obtain various mechanical properties such as hardness, elastic modulus and strength [6]. Huang et al [7] carried out nanoindentation tests on the equine hoof wall and obtained the characterization of the hierarchical structure as well as the energy dissipation mechanisms under different water content and strain states. This work aims to study the microstructure and viscoelastic mechanical properties of the bovine hoof wall, investigate the creep process of the bovine hoof wall, propose a kind of bionic structure of the bovine hoof wall and fabricate the bionic structure through the 3D printing technique
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