Short answers, pulled from the story.
Cartilage is a resilient and smooth type of connective tissue that appears semi-transparent and non-porous in its natural state. A tough fibrous membrane called perichondrium usually covers this material.
Chondrification begins when condensed mesenchyme tissue differentiates into chondroblasts. These cells secrete molecules such as aggrecan and collagen type II to form the extracellular matrix.
The aggregate modulus for articular cartilage typically ranges from 0.5 to 0.9 MPa while Young's Modulus falls between 0.45 to 0.80 MPa. This substance is not as hard or rigid as bone yet remains stiffer than muscle or tendon.
Chondrocytes are bound in lacunae so they cannot migrate to damaged areas and hyaline cartilage lacks blood supply making new matrix deposition slow. Complete healing after injury is hindered by specific inflammation involving M1/M2 macrophages.
Cartilaginous fish like sharks, rays, and chimaeras possess skeletons composed entirely of cartilage. Other taxa like chondrichthyans rely on it for much of their skeleton.