3D characterization of the composition and mechanical properties of the bone-tendon interface

Connective tissue injuries occurring at the interface between soft tissue and bone, also called the bone-tendon interface, commonly result in pain, disability and significant medical costs. These injuries are commonly caused by sports activities or can be seen in elderly people, making them less mobile because of the inability to move without pain. The chances of failure of surgical reattachment are very high which makes the bone-tendon interface an important research topic. To address this clinical issue, it is necessary to regenerate a tissue that has the same properties as the original one. Before this is possible, it is important to understand the properties of the tissue that needs to be replaced. That is why the purpose of this thesis is to characterize the composition and mechanical properties of the Achilles tendon-to-bone interface. X-ray microfocus computed tomography and contrast-enhanced micro-computed tomography are used to determine the three-dimensional structure and composition of the interface while nanoindentation is used to study the mechanical properties. Age-related changes at the interface are investigated, as well as the influence of obesity-driven type 2 diabetes. The three aforementioned investigation methods are therefore applied to three different groups of mice: young mice, aged mice, and aged mice with diet-induced obesity. Results from X-ray microfocus computed tomography show differences in the dimensions of the interface, especially the diabetic group is different. Contrast-enhanced computed tomography allows to observe collagen fiber orientation at the interface. Nanoindentation has only quite recently emerged as a technique for analyzing biological samples and is still in an early stage of development, requiring optimization of a protocol for sample preparation, which is not necessarily the same for all groups. Finally, testing parameters for indenting biological tissue also need to be optimized.