Abstract
Nasoseptal cartilage has been assumed to be isotropic, unlike the well-defined zonal organization of articular cartilage attributed to postnatal biomechanical loading. We know from clinical experience that malrotation of surgical nasoseptal cartilage grafts can lead to increased graft absorption. Other studies have also suggested directionally dependent compressive stiffness suggesting anisotropy, but morphological investigations are lacking. This study characterizes immature and mature native bovine nasoseptal cartilage using a combination of immunohistochemistry, biomechanical testing and structural imaging. Our findings indicate that there is extensive postnatal synthesis and reorganization of the extracellular matrix in bovine nasoseptal cartilage, independent of joint loading forces responsible for articular cartilage anisotropy. Immature nasoseptal cartilage is more cellular and homogenous compared to the zonal organization of cells and extracellular matrix of mature cartilage. Mature samples also exhibited greater glycosaminoglycan content and type II collagen fibre alignment compared to immature cartilage and this correlates with greater compressive stiffness. Engineered neocartilage often consists of immature, isotropic, homogenous tissue that is unable to meet the functional and mechanical demands when implanted into the native environment. This study demonstrates the importance of anisotropy on biomechanical tissue strength to guide future cartilage tissue engineering strategies for surgical reconstruction.
Highlights
Nasoseptal cartilage has been assumed to be isotropic, unlike the well-defined zonal organization of articular cartilage attributed to postnatal biomechanical loading
This study demonstrates that significant cellular, molecular, morphological and biomechanical differences exist between immature and mature bovine nasoseptal cartilage, suggesting a role for postnatal functional adaptation, a phenomenon previously reported in articular cartilage[30]
This study demonstrated that mature anisotropic nasoseptal cartilage had a significantly greater compressive stiffness compared to the more homogenous immature nasoseptal cartilage (p = 00135)
Summary
Nasoseptal cartilage has been assumed to be isotropic, unlike the well-defined zonal organization of articular cartilage attributed to postnatal biomechanical loading. Immature nasoseptal cartilage is more cellular and homogenous compared to the zonal organization of cells and extracellular matrix of mature cartilage. Malrotation of surgical cartilage grafts has been reported to lead to graft absorption, using both articular as well as nasoseptal samples[18,19,20,21] These findings were attributed to collagen misalignment between graft and host, thereby suggesting that collagen orientation affected the strength of graft, raising the potential for anisotropy in nasoseptal cartilage[18,19,20]. Further work using microscopic magnetic resonance imaging and polarized light found a correlation between collagen orientation and compression stiffness, hinting at the importance of anisotropy for native tissue biomechanics[23]. There have been no further investigations elucidating the morphology of nasoseptal cartilage to explain these biomechanical findings
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