Table 1.

Linking microstructure and composition to mechanical properties.

Highlights

•The fibrous nature of tendon is preserved across the interface, with tendon fibers splaying and unravelling to anchor to bone. This generates a spatial variation in fiber architecture and orientation, with the degree of alignment decreasing when approaching bone. •Collagen fibers are progressively reinforced by mineral crystals when crossing the interface between unmineralized and mineralized fibrocartilage. This reinforcement provides substantial stiffening to fibers only for mineral accumulation exceeding a percolation threshold. •The complex interplay between fiber orientation and degree of mineralization results in a non-monotonic variation of tissue stiffness along the insertion, with the appearance of a compliant region having stiffness lower than tendon and bone. •Interface roughness and interlocking between different sub-regions of the enthesis help to increase fracture toughness.

Limitations and outlooks

•The fibrous nature of the insertion suggests that discrete network models accounting for the individual collagen fibers could provide new insights into enthesis biomechanics, for example by elucidating the link between fiber architecture and local damage mechanisms at the sub-tissue scale. •In addition to tissue stiffness, the spatial variation of other material properties such as viscoelasticity and strength should be characterized and interpreted based on fiber architecture and degree of mineralization. •The role of internal interfaces and their complex interlocking patterns should be further investigated. A computational model comprising the interface between unmineralized and mineralized fibrocartilage and the one between mineralized fibrocartilage and bone could unravel new avenues to improve enthesis fracture toughness.