Correlations of Swine Internasal Suture Morphology and Mechanical Properties
Creators: Weerasinghe, Weerasinghe Mudiyanselage KS
Publisher: name: University of Alberta Library
Year: 2024

<p>Bones in the skull are connected by craniofacial sutures, which are joints made of collagen fibers, vasculature, and an extracellular matrix. Sutures are straight and flexible at an organism’s early ages and develop various morphological characteristics during growth. Patent (unfused) sutures respond to mechanical stimuli from activities such as mastication, locomotion, and intracranial pressure by changes to their morphology and material structure. The suture undergoes changes in morphology due to bone deposition and resorption at suture margins, as well as the formation of collagen fiber structure in the suture to resist stresses. The influence of morphological and material characteristics on the mechanical response of craniofacial sutures is crucial in understanding their growth and development.In previous literature, when craniofacial sutures were modeled using finite element (FE) software, their complex three-dimensional (3D) morphology was simplified by taking measurements from only one plane in two dimensions (2D), typically the ectocranial or endocranial planes that are easily accessible from the cranial surfaces. Previous works that conducted mechanical experiments on craniofacial sutures, often took average values of suture morphological measurements across their 3D structure when finding correlations between morphology and mechanical properties. When making these simplifications during modeling, experiments, or statistical analysis, little explanation was given for the degree of impact on the results. Thus, this study is a step towards discovering the effect of the simplifications that are commonly used in literature.This study can be divided into three stages. In the first stage, a mechanical experiment was conducted on fresh-frozen swine bone-suture-bone samples containing the internasal suture. Four to five samples were dissected from the maxilla of nine Duroc (female) juvenile swine. The test consisted of preloading and preconditioning followed by a quasi-static tensile test at a low strain regime. Low strain regimes were used to prevent any permanent deformation to the suture structure since the samples will be analyzed using micro-computed tomography (μCT) X-ray imaging to determine their morphological properties. In the mechanical experiment, the gradient of the load vs displacement data from the tensile loading stage was used as the mechanical property under investigation as a proxy for the suture stiffness.In the second stage of the study, the width and interdigitation of the suture samples were obtained in 3D using µCT X-ray imaging. The first and second stages provided mechanical and morphological data for statistical analysis in the third stage. A multiple regression model was used to predict the stiffness of the suture samples. Internasal suture morphological data as well as the position of the sample in the maxilla and the thickness of the sample (measured as the length between the outer and inner surfaces of the nasal bone near the internasal suture), were used as independent variables. Based on the mechanical test data, it was observed that the cranial sutures exhibit nonlinear behavior under loading. The nonlinear regions were likely caused by the materials that made up the suture such as the rearrangement of collagen fibers within the suture, which was observed at low loads. During tensile loading, the most significant factors affecting the gradient of load vs displacement data were found to be the mean suture width and the sample thickness. Further studies can investigate the effect of morphological factors, such as suture interdigitations, on mechanical response under different loading conditions like bending and compression. Therefore, the mechanical behavior of sutures can be better understood by considering the morphological adaptations of sutures and depending on the loading condition applied to the suture, some suture morphological features might have more significance on their mechanical properties. Findings from this thesis will have potential implications on suture morphological factors to consider when modeling and conducting experiments on cranial sutures. </p>