Advanced characterization of the 3D morphology and the mechanical properties of the enthesis: optimization study

Leyssens, Lisa [UCL] Ryelandt, Sophie [UCL] Favache, Audrey [UCL] Kerckhofs, Greet [UCL] et al.

Connective tissue injuries occurring at the interface between soft tissue and bone, also the enthesis, commonly result in disability and significant medical costs. The chances of failure of surgical reattachment are 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. The purpose of this study was to develop and optimize advanced techniques to characterize the 3D structure and mechanical properties of murine entheses. Achilles tendon-to-bone interfaces were extracted from different groups of mice. High-resolution X-ray microfocus computed tomography (HR microCT) and contrast-enhanced micro-CT (CE-CT) were used to determine the 3D structure and composition of the different tissues in the enthesis. Nanoindentation was used to study the mechanical properties at the enthesis. MicroCT revealed differences between the lean and the obese mice concerning the volume of the mineralized fibrocartilage layer and the surface of the connection between the mineralized and unmineralized fibrocartilage. Ageing did not influence these properties. CE-CT allowed observing the collagen fiber orientation within the unmineralized fibrocartilage and the connecting tendon. For the nanoindentation, we optimized the sample preparation protocol. With this preparation method, distinct mechanical properties could be detected for the different tissues within the enthesis. Further research will involve the analysis of a large set of samples.