Date of Award

12-2009

Document Type

Thesis

Degree Name

Master of Science (MS)

Legacy Department

Materials Science and Engineering

Advisor

Kennedy, M.

Committee Member

Dean , D.

Committee Member

Ellison , M.

Committee Member

Luzinov , I.

Abstract

A better understanding of the bioresponse of naturally occurring systems will help
to optimize the engineering of synthetic biomaterials. The aim of this thesis was to
characterize the mechanical and chemical behavior of two distinct biological composite
systems, human teeth and wool fibers. These mechanical and chemical properties were
also studied as a function of natural structure and environmental conditions.
Human teeth are composite systems consisting primarily of hydroxylapatite and
protein. This project investigated how the use of clinical dental treatments and
procedures, such as whitening and etching, affects mechanical properties. Analysis of
nanoindentation with the Oliver-Pharr model provided elastic modulus and hardness
across the DEJ. Mechanical properties of autoclaved and non-autoclaved teeth were
measured to ensure both comparability to published values and relevance to clinical
applications. Large increases were observed in the elastic modulus of enamel with
autoclaving (52.0GPa versus 113.4GPa), while smaller increases were observed in the
dentin (17.9GPa versus 27.9GPa). There was a similar trend in the increase in hardness of
enamel (2.0GPa versus 4.3GPa) and dentin (0.5GPa versus 0.7GPa) when subjected to
autoclaving. This work shows that the range of values previously reported in literature
may be due largely to the sterilization procedures. Treatment of the exterior of nonautoclaved
teeth with Crest Whitestrips, Opalescence or UltraEtch caused changes
in the mechanical properties of both the enamel and dentin. Those treated with Crest
Whitestrips showed a reduction in the elastic modulus of enamel (55.3GPa to 32.7GPa)
and increase in the elastic modulus of dentin (17.2GPa to 24.3GPa). Opalescence
treatments did not show a significant affect on the enamel properties, but did result in a
decrease in modulus of dentin (18.5GPa to 15.1GPa). Additionally, UltraEtch
treatment decreased the modulus and hardness of enamel (48.7GPa to 38.0GPa and
1.9GPa to 1.5GPa, respectively) and dentin (21.4GPa to 15.0GPa and 1.9GPa to 1.5GPa,
respectively). These changes were linked to the change in protein content, verified by
FTIR and fluorescence microscopy.
The second study characterized the amino acid distribution on the surface of
Merino wool fibers. Although previous research identified which amino acids compose
wool fibers, this was the first study to determine the amino acids distribution along the
surface. Specifically, which amino acids have high concentrations near topographical
surface features, such as the scale ridges. The distribution and types of amino acids along
the surface of wool fibers was analyzed using force spectroscopy techniques. Initial
measurements in phosphate buffer solution (PBS) showed carboxyl acid groups, aspartic
acids and glutamic acids, are randomly distributed over the surface of wool fibers.
Clusters of sulfur groups, cysteines, are uniformly distributed. In addition, the amine
groups, arginine and lysine, are concentrated near the edge of scales. SEM images of
wool fibers coated with functionalized nanoparticles were used to verify these results.
The SEM images showed the binding sites of various charged chemical groups. To
distinguish between positively charged surface groups, force spectroscopy was done
under elevated pH, indicating a high contribution of lysine just below the edge of the
scale.

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