Hyaline Characteristics of Mechanically Induced Cartilaginous Tissues

The mechanical properties of hyaline cartilage depend heavily on tissue structure and biochemical composition. Glycosaminoglycans (GAGs) and collagen fibrils are the key extracellular matrix components of hyaline cartilage that bestow compressive and tensile stiffness, respectively.[1–2] In articular cartilage, a decline in GAG content and collagen organization with injury or with diseases such as osteoarthritis is intimately linked with a decline in mechanical function.[3] In tissue-engineered cartilage and articular cartilage explants, mechanical loading in vitro results in increased aggrecan mRNA expression, GAG content, and increased stiffness.[4–6] These findings suggest that mechanical loading could be applied in vivo to promote cartilage repair via modulation of gene expression, tissue structure, and tissue composition. We have previously developed an in vivo model of skeletal repair in which application of a controlled bending motion to a healing osteotomy gap results in formation of cartilage within the gap.[6] Using this model, we sought to characterize the biochemical composition and collagen structure of the mechanically induced cartilaginous tissue. The objectives of this study were: 1) to quantify the total GAG content and aggrecan mRNA expression; and 2) to characterize the collagen fiber orientation.