Dynamic change of extracellular matrix of knee articular cartilage during porcine development

Although extracellular matrix (ECM) maturation during articular cartilage development is well recognized, quantitative, temporally resolved characterizations in large-animal models remain scarce. Here, we systematically characterized porcine femoral condyle cartilage from embryonic day 45 (E45) to postnatal month 10 (P10M) using integrated morphological, biochemical, and ultrastructural approaches. Knee joint width increased from 2.5 mm at E45 and 11 mm at E100 and 46 mm at P10M, whereas chondrocyte density declined markedly after E75 (p < 0.05). The change was not statistically significant in collagen content until E75 (3.2 μg/mg), but rose significantly at E100 (6.7 μg/mg, p < 0.05). Glycosaminoglycan (GAG) content remained stable prenatally but increased markedly postnatally at P1M (163 μg/mg, p < 0.05), while water content decreased significantly at P10M (p < 0.05). Type II collagen gradually increased from E60 to P1M, whereas types III, XI, and IX accumulated from E60 onward. Collagen fibril diameter increased progressively from approximately 25 nm at E45 to approximately 80 nm at P10M (p < 0.05). Matrix metalloproteinase 1 (MMP-1) and cathepsin K exhibited elevated expression at both E45 and P1M, suggesting two distinct phases of ECM remodeling. Collectively, these findings demonstrate that cartilage ECM maturation follows a temporally ordered sequence, beginning with the establishment of a collagen framework, followed by GAG accumulation and fibril thickening. This high-resolution temporal map established in a large-animal model provides a critical reference for cartilage regeneration strategies.