Abstract
The tendon-to-bone interface, or enthesis, is a heterogeneous and anisotropic transitional zone that plays an important role in effective transfer of mechanical loads between soft and hard tissues within the musculoskeletal system. Despite its clinical significance in injury recovery and surgical repair, the local relationship between the structural and mechanical characteristics of the enthesis remains inadequately understood. This research aims to evaluate the full-field mechanical behaviour of the enthesis under physiological loading by using a combination of high-resolution in-situ micro-computed tomography (micro-CT) mechanical testing, digital volume correlation (DVC), and structural analysis.This thesis presents a novel investigation into the full-field correlation of the tendon-bone interface hierarchical structural organization and mechanical behaviour such as strain distribution under uniaxial tensile loading condition. Additionally, this research explores the optimization of imaging protocols for soft to hard interface mechanical analysis, the effects of contrast agents (CAs) in soft tissue micro-CT scanning, and their role in enhancing tissue visibility while considering their impact on the material and mechanical properties.
The research is structured around three primary themes: (1) characterization of enthesis calcified fibrocartilage (CFC) microstructure and its influence on local strain distribution; Findings from these studies reveal that, depending on the load angle, the CFC exhibits a non-uniform strain distribution, with regions of concentrated strain corresponding to lacunae that undergo specific morphological changes. Under uniaxial tensile testing, these lacunae tend to become more rounded in shape. This suggests that specific regions of the enthesis may be more susceptible to load accumulation, which could contribute to failure mechanisms in injuries and degenerative conditions. By correlating the microstructural characteristics with mechanical behaviour, this study provides insights into how alterations in tissue architecture may predispose the enthesis to damage or compromised function over time. (2) Development of in-situ imaging protocols for strain measurement in tendon and bone tissues using contrast agents such as Phosphotungstic acid in ethanol and distilled water solutions, mercury II Chloride, and Iodine. In this study the effects of the CAs on the mechanics of the enthesis and their capabilities to revealed bone, enthesis, and tendon structures enabled micro-CT with DVC to elucidate the effects of strain on morphometry of the lacunae. It was shown that CAs can penetrate deeper into the enthesis lacunae, impacting the number and volume of the lacunae in the fibrocartilage visualised in the enthesis. CAs have potential to alter tissue properties, such as soft tissues stiffness and enthesis lacunae morphology, potentially impacting DVC results. (3) Investigation of postnatal structural adaptation of the enthesis calcified fibrocartilage. Using high-resolution micro-CT imaging, this study analysed variations in CFC thickness, lacunar morphology, and tissue organization at different developmental stages (1, 3, and 6 months). Results showed a significant increase in CFC thickness with age, accompanied by changes in lacunae morphology, including increased lacunae count and shape alterations indicative of microstructural remodelling.
By integrating experimental data with computational models, this thesis provides a comprehensive framework for evaluating the mechanical environment of the enthesis, and the relationship between structure and deformations under various conditions. The outcomes of this research contribute to the broader understanding of the soft to hard tissues interfaces as well as establishing a methodological protocol for future studies investigating such interfaces and correlation of the musculoskeletal microstructure and micromechanics. This knowledge has the potential to the development of biomimetic materials and improved strategies for surgical reconstruction of tendon to bone attachments.
Keywords:
Tendon-to-bone interface, enthesis, digital volume correlation (DVC), micro-CT imaging, strain distribution, biomechanical characterization, full-field structural analysis, contrast agents.
| Date of Award | 23 Jun 2025 |
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| Original language | English |
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| Supervisor | Gordon Blunn (Supervisor) & Jovana Radulovic (Supervisor) |