Repetitive shear loading in fetal bovine cartilage causes depth-dependent alterations in shear mechanical properties...

During joint development, the collagen fiber network undergoes realignment and reorientation, forming the mature structure that is essential for cartilage mechanics. However, recreating this aligned collagen architecture and the shear mechanical properties in engineered cartilage remains challenging. Insights from immature cartilage development suggest that dynamic mechanical loading is necessary for normal joint formation, yet the role of shear loading, a common joint load, on collagen reorganization and changes in mechanical properties is unclear. Additionally, while proteoglycans are known to influence collagen fiber alignment in other tissues, the impact in immature cartilage, which has a unique collagen fiber structure and orientation, is not well understood. This study examines how repetitive shear loading of immature cartilage, with and without proteoglycans, impacts collagen fiber alignment and shear mechanical properties. Immature cartilage explants, either with intact or removed proteoglycans, were subjected to 8 h of 3% amplitude global cyclic shear loading. Both groups showed a decrease in shear stiffness in the superficial region. The largest shear mechanical changes occurred at low shear strains (toe modulus). Polarized light showed increased collagen fiber alignment and reorientation at all tissue depths induced by cyclic shear loading. These fiber alignment changes were larger in the proteoglycan-removed group than in the intact group. Together, these findings suggest that small-magnitude cyclic shear strain can cause permanent reorientation of collagen fibers and alter shear mechanics. The results offer insight into how shear loads and matrix composition interact to guide collagen organization in developing cartilage.