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The in vivo mechanical function of biologic connective tissues is generally hypothesized to be a critical parameter influencing the presence and quantity of their constituent materials as well as their structural arrangement and consequent interactions. Or stated another way, the structure of a tissue likely contributes to its ability to perform its required mechanical function. To address this global hypothesis, it is the overall objective of this thesis project to quantitatively investigate relationships between the structure and mechanical function of soft tissues such as tendon. Specific structural and mechanical parameters were measured in tail tendon fascicles from adult control, adult Mov13 transgenic, and immature control mice. Data were fit to regression models, and correlations were obtained and investigated. Results demonstrated that fascicle structural parameters (from mechanical tests), stiffness and inflection point displacement, appear to be moderately- to well-correlated with structural parameters, mean fibril diameter, cell volume fraction, and CSDS GAG content $(\vert r\vert = 0.65{-}1.00).$ However, fascicle material parameters, modulus and strain at maximum stress, do not appear well-correlated with these structural parameters. The general structure-function trends observed were shown to be primarily due to having three very different experimental groups rather than significant correlations of parameters within groups. It is suggested that homotypical variation and/or experimental error in parameters from a given experimental group may preclude within-group correlations. Further, initial efforts toward development of a structurally-based mathematical model of the tendon fascicle involved analysis of a single fibril RVE model using both shear lag and finite element methods. Analysis of single fibril models demonstrates that the fibril aspect ratio plays a critical role in determining the predicted composite behavior. Current concepts for next level models which include multiple fibrils, incorporating an actual fibril size distribution, begin to address the geometric limitations of single fibril models. However, without knowledge of various experimental inputs such as 3D fibril geometry, fibril/matrix interface conditions, boundary conditions, or material definitions, mathematical models offer limited potential toward investigation of structure-function relationships at the present time. It is evident that modeling efforts should proceed in tandem with carefully designed experiments which begin to address and investigate unknown model parameters. |
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