Tissue growth as a mechanism for collagen fiber alignment in articular cartilage

Articular cartilage is distinguished by the unique alignment of type II collagen, a feature crucial for its mechanical properties and function. This characteristic organization is established during postnatal development of the tissue, yet the underlying mechanisms remain poorly understood. In this study, a potential mechanism for type II collagen alignment by cartilage-specific growth from within the tissue was investigated. Bovine chondrocyte-derived cartilage organoids were cultured in a transwell system, subjecting the created tissue to transforming growth factor β1 stimulation from either the bottom (bottom-up) or the top (top-down) compartment to induce interstitial growth and appositional growth, respectively. The results demonstrate that interstitial growth within the tissue, stimulated from underneath, successfully produced aligned type II collagen parallel to the direction of this growth. In contrast, appositional growth did not yield such alignment. These findings underscore the critical role of the direction of growth in recreating the characteristic collagen organization of articular cartilage, offering valuable insights for the advancement of creating functional tissue in tissue engineering strategies.