College of Science and Health Theses and Dissertations

Date of Award

Spring 6-14-2024

Degree Type

Thesis

Degree Name

Master of Science (MS)

Department

Physics

First Advisor

Eric Landahl, PhD

Second Advisor

Chris Goedde, PhD

Third Advisor

Gabriela B. Gonzalez Aviles, PhD

Abstract

The dorsal spine of the spiny dogfish, Squalus acanthias, has been used for age determination of individual specimens since the 1930s. Scientific literature regarding the dorsal spine has to date always referred to it as having an enamel exterior, with a dentin interior surrounding a central pulp cavity. This is similar to the structure observed in a human tooth.

The dorsal spine is composed of cartilage-based tissue that contains bioapatite. Bioapatite is a mixture of hydroxyapatite, Ca10(PO4)6(OH)2 (a calcium salt of phosphoric acid), and other biological material, e.g. calcium carbonate, CaCO3. Micro-computed tomographic (micro-CT) reconstruction using diffracted wide-angle X-ray scattering (WAXS) data and Rietveld refinement were used to study the 3D crystallography of the bioapatite within the dorsal spine of a closely related species, the Pacific spiny dogfish, Squalus suckleyi. Specifically, in light of prior claims made in the scientific literature regarding the composition of the dorsal spine, we are interested in the lattice parameter values, their distribution throughout the dorsal spine, and the corresponding crystallite size of the hydroxyapatite present therein.

Data collected from eight transverse layers of the dorsal spine sample were used to create 2D maps of the voxels (volume elements) within each layer. For each voxel, a 1D X-ray diffraction (XRD) pattern was obtained. The Rietveld refinement method was then applied to each 1D XRD pattern to obtain values for the crystal lattice parameters of the bioapatite therein. The Scherrer equation, along with the Williamson-Hall model, were then used to determine bioapatite crystallite sizes from both the full-width half maximum (FWHM) and Bragg angle data of the resulting peaks within the 1D XRD patterns.

Hydroxyapatite, the only crystalline phase present in the dorsal spine, has crystal lattice parameters of a = b = 9.432 Å, and c = 6.881 Å, as reported by Kay et al. Overall, with respect to all of the inspected voxels in all eight transverse layers of the dorsal spine, mean crystal lattice parameters and corresponding standard deviations of the bioapatite in the sample are a = b = 9.448 Å +/- 0.010 Å, and c = 6.900 Å +/- 0.002 Å, for out-of-plane scans (measurements made parallel to the spine’s axis); and a = b = 9.435 Å +/- 0.007 Å, and c = 6.900 Å +/- 0.004 Å, for in-plane scans (measurements made perpendicular to the spine’s axis). Hydroxyapatite crystallite sizes observed in biological specimens, as noted in peer-reviewed journal articles, were also observed throughout the dorsal spine.

Of note are two relevant observations. First, the lattice parameters are not the same everywhere. From the Rietveld refinement analysis, voxels in the lateral regions of the dorsal spine exhibit sharper 1D XRD peaks compared to voxels in the inner regions. Second, sharper diffraction peaks within a voxel imply that the bioapatite therein has larger crystallites. In-plane bioapatite crystallite sizes are markedly greater in the voxels in the lateral regions of the dorsal spine, and relatively much lower within the body of the dorsal spine.

Prior scientific literature referred to the dorsal spine of the closely related spiny dogfish, Squalus acanthias, as having an enamel exterior and a dentin interior. The results obtained in this analysis of the dorsal spine of the Pacific spiny dogfish, Squalus suckleyi, strongly suggest that the outer lateral regions are indeed made of bioapatite that is qualitatively more similar to tooth enamel than to dentin.

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