Correlation of Enthesis Calcified Fibrocartilage 3D Microstructure with Full-Field Strain and Deformation

Enthesis calcified fibrocartilage (CFC) is a highly specialized structure that has an important role in anchoring the tendon or ligament to the bone and transmitting mechanical stresses associated with either joint motion or with muscle forces. The CFC 3D microstructure–mechanics relationship is invaluable for understanding the enthesis structure that impacts the mechanical behavior and how this is related to the failure and regeneration of the enthesis after injury. This can provide valuable information for developing biomaterials and for regenerative therapies. However, current approaches are unable to attain a non-invasive measurement of the localized mechanical behavior within this anisotropic and heterogenous insertion. In this research, full-field micromechanical structural analysis of the enthesis was investigated to understand the fundamental mechanics underlying its structural attributes using high-resolution in-situ micro-computed tomography combined with deep learning reconstruction and digital volume correlation. Our findings reveal that depending on the angle of the applied stress, the central region of the CFC lacunar morphology deforms more than other regions. Furthermore, we identified that the CFC microstructure organization and thickness have a strong positive correlation with the strain distribution at the interface. Regions with higher lacunar density were found to experience greater deformation, suggesting that the local microstructure plays a crucial role in modulating the mechanical response of the CFC. This study highlights the correlation between the structure and mechanical response of CFC at the microscopic level showing the anisotropic strain behavior in different regions of the enthesis calcified fibrocartilage.