The equine hoof wall has been hailed as an efficient energy-absorbent natural polymer composite by researchers in the United States.
A study team at the University of California has thoroughly examined and described the hierarchical structure of the hoof wall, as well as correlations between its structure and mechanical behaviors.
They also explored its impressive energy dissipation mechanisms.
Wei Huang and his colleagues, writing in the journal Acta Biomaterialia, say their findings could provide inspirations for the design of impact-resistant and energy absorbent materials.
The equine hoof is considered an efficient energy absorption layer that protects the underlying skeletal elements from impact when galloping.
Examing fresh hoof walls at the microscale, the scientists found that tubules are embedded in the intertubular matrix which forms the hoof wall.
Both the tubules and intertubular areas consist of keratin cells, in which keratin crystalline intermediate filaments and amorphous keratin fill the cytoskeletons.
They report that cell sizes, shapes and intermediate filaments fractions are different between tubular and intertubular regions.
The structural differences between the tubular and intertubular areas in terms of their mechanical performance were assessed in hoof material that was dry, fresh and fully hydrated.
The stiffness and hardness in the tubule areas were found to be higher than in the intertubular areas in the dry and fresh samples when loaded along the hoof wall.
However, once the samples are fully hydrated, the intertubular areas become stiffer than the tubular areas due to higher water absorption in these regions.
They found that the tubules serve as a reinforcement, which acts to support the entire wall and prevent catastrophic failure under compression and impact loading.
Elastic buckling and cracking of the tubules was seen after compression along the hoof wall, but no shear-banding or severe cracks were found in the intertubular areas even after 60% compression.
This, they said, indicated the highly efficient energy absorption properties, without failure, of the hoof wall structure.
“The equine hoof wall is found to be an efficient energy absorbent natural polymer composite,” they concluded.
The study team comprised Huang, Nicholas Yaraghi, Wen Yang, Alexis Velazquez-Olivera, Zezhou Li, Robert Ritchie, David Kisailus, Susan Stover and Joanna McKittrick.
A natural energy absorbent polymer composite: The equine hoof wall
Wei Huang, Nicholas Yaraghi, Wen Yang, Alexis Velazquez-Olivera, Zezhou Li, Robert Ritchie, David Kisailus, Susan Stover and Joanna McKittrick
Acta Biomaterialia, Volume 90, May 2019, Pages 267-277, https://doi.org/10.1016/j.actbio.2019.04.003
The abstract of the study can be read here.