In the human body, the most abundant simple molecule is water, and the most abundant complex molecule are proteins. It therefore stands to reason that protein-water interactions are both commonplace and important. The Stoichiometric Hydration Model (SHM) describes the interaction of water with collagen and its effects on collagen (and protein) structure. Micro Computed Tomography is used to expound on molecular hydration relationships for microscopic protein structures consistent with the SHM. Tendon samples are particularly suitable for study because it is composed of a symmetric and repetitive occurrence of collagen molecules, having nearly 100% collagen content, with the collagen molecules and fibrils aligned along the tendon long axis providing directional symmetry. This dissertation focuses on investigating collagen hydration with three-dimensional micro-CT (3D-micro-CT) dilatometry by addressing three specific aims. The first specific aim was to quantify the accuracy and precision of geometric measurements obtained from 3D-micro-CT to establish its use for dilatometry. The second specific aim was to use micro-CT imaging to relate changes in relative length, relative diameter, relative volume, density and differential density of bovine tendons to the molecular hydration properties of the collagen molecule. The third specific aim was to investigate the effect of glucose induced molecular changes—covalent crosslinking versus glucose bridges—resulting from glucose immersion in-vitro, as well as the combination of mechanical stress and glucose in-vivo. The following conclusions were obtained from the series of studies conducted: (1) The 3D-micro-CT dilatometry methodology used in this dissertation provided sufficiently precise and accurate measurements of tendon diameter, length, volume, density and differential density. (2) The unique approach using micro-CT dilatometry presented an independent method to support the presence of monolayer hydration coverage for collagen in its native state. (3) The measured dilatometric changes in native extensor tendons consistently supported the Stoichiometric Hydration Model. (4) The dominant source of dilatometric effects for glucose-immersed tendon samples in-vitro was the formation of hydrogen-bonds between glucose and collagen molecules that created glucose "spacers" in the collagen structure. Increased mechanical compression caused the formation of glucose bridges that replaced Ramachandran single water bridges. (5) Glucose-bridges also replaced single water bridges in-vivo due to the combined action of glucose and periodic mechanical stress on the tendon. Mechanical force caused the formation of a tightly bound, immobilized glucose-bridge such that concentration of free glucose is reduced in the tendon. (6) Glucose-bridge formation in-vivo is age-related, increasing up to a point determined by the maximum glucose bridge factor ( Sgb = 0.50) which was determined both empirically and theoretically. In summary, investigating collagen hydration with micro-CT provided robust supporting evidence for the Stoichiometric Hydration Model, and generated new insights on the effects of glucose on the collagen molecule consistent with the SHM.
|Advisor:||Fullerton, Gary D.|
|Commitee:||Cameron, Ivan L., Goins, Beth A., Iwata, Koji, McDavid, William P.|
|School:||The University of Texas Health Science Center at San Antonio|
|School Location:||United States -- Texas|
|Source:||DAI-B 69/08, Dissertation Abstracts International|
|Keywords:||Collagen, Hydration, Microcomputed tomography, Tomography|
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