Degeneration of articular cartilage is often triggered by a small tissue crack. As cartilage structure and composition change with age, the mechanics of cracked cartilage may depend on the tissue age, but this relationship is poorly understood. Here, we investigated cartilage mechanics and crack deformation in immature and mature cartilage exposed to a full-thickness tissue crack using indentation testing and histology, respectively. When a cut was introduced, tissue cracks opened wider in the mature than the immature cartilages. However, the opposite occurred upon mechanical indentation over the cracked region. Functionally, the immature cracked cartilages stress-relaxed faster, experienced increased tissue strain, and had reduced instantaneous stiffness, than the mature cracked cartilages. Taken together, mature cartilage appears to withstand surface cracks and maintain its mechanical properties better than immature cartilage and these superior properties can be explained by the structure of their collagen fibrous network.

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