Design complexity and fracture control in the equine hoof wall.

This research article explores the relationship between the structure and functionality of the equine hoof wall. It focuses on understanding how the wall’s design complexity prevents fracture and protects the internal tissues of the hoof from damage.

Morphological Study of the Equine Hoof Wall

• Researchers conducted detailed morphological analyses on samples of equine hoof walls. They observed that the shape, size and helical alignment of tubules and intermediate filaments within the hoof wall lamellae varied based on their position through the wall thickness.
• The orientation of intertubular intermediate filaments changes from being perpendicular to the tubule axis in the inner wall to parallel to the tubule axis in the outer wall.
• Data from the morphological study indicated three potential crack diversion mechanisms that help to prevent cracks from progressing to the sensitive, living tissues inside the hoof. These include a mid-wall diversion mechanism that inhibits inward and upward movement of cracks, as well as inner and outer wall mechanisms that prevent inward crack progression.

Mechanical Testing of the Equine Hoof Wall

• The researchers also conducted tensile and compact tension fracture tests on samples of fully hydrated hoof walls.
• These tests revealed a decrease in longitudinal stiffness from 0.56 to 0.30 GPa as moved from the outer to the inner wall. Interestingly, despite this decreasing stiffness, ultimate or maximum properties remained constant.
• The fracture toughness parameters, measured using the J-integral values, ranged from 5.5 to 7.8 kJ m-2 through the wall thickness. The highest toughness was seen in specimens where cracks initiated tangential to the wall surface (10.7 kJ m-2).
• The observed fracture paths were consistent with the morphological predictions, suggesting that the hoof wall is a structurally evolved entity capable of resisting and redirecting cracks initiated in varied orientations.

Conclusion

• The finding from this study provides insights into the exceptional qualities of the equine hoof wall. It suggests a sophisticated relationship between its complex design and its function of protecting sensitive internal hoof tissues from damage.
• The study emphasizes how the wall’s complexity – variations in tubule size, shape, filament alignment, and intertubular material orientation – alleviate risks of detrimental cracks while successfully maintaining its key biomechanical properties.
• It potentially paves the way for the development of more durable and efficient materials or structures drawing inspiration from nature’s engineering prowess reflected in the equine hoof wall structure.