Year

2024

Season

Spring

Paper Type

Master's Thesis

College

College of Arts and Sciences

Degree Name

Master of Science in Material Science & Engineering (MS)

Department

Biology

NACO controlled Corporate Body

University of North Florida. Department of Biology

First Advisor

Dr. Maria Laura Habegger

Second Advisor

Dr. Stephen Stagon

Third Advisor

Dr. Paul Eason

Abstract

Unlike mammals, shark endoskeletons are composed of cartilage, which is less stiff compared to bone. Despite this structural disadvantage, sharks have risen to become apex predators, with reported maximum posterior bite force estimates approximating 5914 N in bull sharks. Shark jaws are estimated to undergo high cycle loading within the organism’s lifecycle without evidence of failure. Fatigue resistance may relate to mineral distribution within a component of the endoskeletal system – tesserae. Tesserae are thin, roughly hexagonal tiles composed of calcium phosphate hydroxyapatite (HA) crystals and grow by accretion to eventually surround the hyaline cartilage core. Though tesserae dimensions are variable, they are reported to be on average 500 µm across and 250 µm thick. Ultrastructure characterization using backscatter electron imaging and micro-computed tomography (µ-CT) have revealed regions consist of oscillating layers of high and low calcium concentrations, referred to as spoke regions. Though mechanical behavior of the bulk material has been examined, an investigation into the mechanics of spoke regions has been limited due to the microscale of these structures. The objective of this research was to design and manufacture tesserae models mimicking material gradients in the spoke regions that could be optically resolved during mechanical testing to investigate regional variation in strain. Finite element analysis (FEA) of the models was utilized to further examine stress evolution within regions. It was hypothesized that the spoke structures may reduce long-range stress in the skeletal element, and under compressive loading would exhibit variable strain related to regional material composition. Mechanical testing and simulation indicated that the addition of neighboring tiles resulted in stress flow between adjacent tiles regardless of orientation to loading direction. Results further indicated that an ideal proportion of high- and low-modulus material exists in the spoke-like structures such that stress concentrations are mitigated, and strain in spoke-structures is minimized.

Download

Share

COinS