Structural and mechanical characterization of the hoof in Mongolian equids

In this paper, the microstructure and mechanical properties (including nanoindentation, tensile test, and compression test) of Mongolian horse hooves were investigated. Many tubules and Intermediate Filaments (IF) were distributed longitudinally in the hoof of Mongolian horses, which could better help the hoof cushioning. The hardness and modulus of the hoof wall of Mongolian horses varied at different water contents. The hardness and modulus decreased with the increase in water content. The modulus of elasticity of the hoof wall decreased from 16.3% to 25.4%, and the hardness decreased from 17.8% to 29.3% from 10% to 20% water content. At 20-30% water content, the horseshoe wall modulus decreased by 3.5%-4.8%, and the hardness reduced by 4.1%-7.3%. The results of the tensile and compression experiments showed that the compression properties of Mongolian horse hooves were better than their tensile properties; their longitudinal compression energy absorption was better than their transverse compression properties; and Young's modulus and yield strength of the hoof wall increased as the compression rate increased. Finally, comparing the experiments belonging to this paper with hooves from other papers, it was found that the hardness of the tubular region and the intertubular region of Mongolian horse hooves was 17.7% and 39.4% higher than that of the hooves from the current study, respectively. The microstructural features of Mongolian horse-like hooves with superior mechanical properties provide a promising inspiration for the bionic design of lightweight and high-strength composites in engineering.