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Author ORCID Identifier

https://orcid.org/0000-0002-1749-6861

AccessType

Open Access Dissertation

Document Type

dissertation

Degree Name

Doctor of Philosophy (PhD)

Degree Program

Biomedical Engineering

Year Degree Awarded

2023

Month Degree Awarded

February

First Advisor

Seth W. Donahue

Subject Categories

Biology and Biomimetic Materials

Abstract

Bighorn sheep rams do not show overt signs of traumatic brain injury from head impacts experienced during intraspecific combat. Rams’ cranial appendages bear the brunt of ramming impacts and are composed of a keratin-rich horn anchored to a bony horncore via a soft connective tissue interface. The horncore is filled with velar bone which has a unique porous architecture with a comparable bone volume fraction, but larger strut thickness and separation than typical mammalian trabecular bone. Velar bone absorbs more energy than the horn and substantially reduces post-impact brain cavity accelerations in computational models of bighorn sheep ramming. These findings have implications for brain injury mitigation, but are limited by assumed material properties of the horncore bone and horn-horncore interfacial tissue as these were previously unknown. Since bone adapts to mechanical stimuli, and the horncore is exposed to a high impact environment, horncore bone material and the velar bone architecture are expected to have superior energy absorption than other mammalian bone tissues. Furthermore, the horn-horncore interface is expected to have an interdigitated microstructure like other dermo-epidermal junctions (e.g., the equine hoof-bone interface) to facilitate load transfer between the impacted horn and energy absorbing horncore. This dissertation explored these possibilities by quantifying the composition, microstructure, and mechanical properties of horncore bone and the horn-horncore interface tissue. In addition, computational modeling was used to provide a preliminary comparison between velar and trabecular bone architectures under compressive loading. Horncore bone materials and the velar bone architecture were not shown to increase energy absorption compared to other mammalian bone tissues or trabecular bone architectures. Interestingly, velae had osteons which are rare in trabeculae. Velar osteons may provide crack arrest and deflection to increase microdamage accumulation (i.e., microcrack toughening) and increase the energy absorption of the entire horncore compared to a similar volume of trabecular bone. Furthermore, the horn-horncore interface displayed a 4-fold increase in microscopic contact area, but did so with a morphology unlike other dermo-epidermal junctions. Despite morphological differences, lap-shear properties were comparable to the equine hoof-bone interface and were positively correlated with the microscopic contact area.

DOI

https://doi.org/10.7275/33093940

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