Superficial cartilage defect is an important factor that causes osteoarthritis. Therefore, it is very important to investigate the influence of superficial cartilage defects on its surface morphology and mechanical properties. In this study, the knee joint cartilage samples of adult pig were prepared, which were treated by enzymolysis with chymotrypsin and physical removal with electric friction pen, respectively. Normal cartilage and surface treated cartilage were divided into five groups: control group (normal cartilage group), chymotrypsin immersion group, chymotrypsin wiping group, removal 10% group with electric friction pen, and removal 20% group with electric friction pen. The surface morphology and structure of five groups of samples were characterized by laser spectrum confocal microscopy and environmental field scanning electron microscopy, and the mechanical properties of each group of samples were evaluated by tensile tests. The results show that the surface arithmetic mean height and fracture strength of the control group were the smallest, and the fracture strain was the largest. The surface arithmetic mean height and fracture strength of the removal 20% group with electric friction pen were the largest, and the fracture strain was the smallest. The surface arithmetic mean height, fracture strength and fracture strain values of the other three groups were all between the above two groups, but the surface arithmetic mean height and fracture strength of the removal 10% group with electric friction pen, the chymotrypsin wiping group and the chymotrypsin soaking group decreased successively, and the fracture strain increased successively. In addition, we carried out a study on the elastic modulus of different groups, and the results showed that the elastic modulus of the control group was the smallest, and the elastic modulus of the removal 20% group with electric friction pen was the largest. The above study revealed that the defect of the superficial area of cartilage changed its surface morphology and structure, and reduced its mechanical properties. The research results are of great significance for the prevention and repair of cartilage injury.
The superficial layer of articular cartilage acts as a critical physical barrier for joint homeostasis, and its damage is a hallmark of early osteoarthritis. To investigate the effect of superficial layer injury on solute permeation and retention in cartilage, two injury models were established using isolated porcine cartilage: chymotrypsin digestion (mucus layer injury) and physical abrasion (10% removal of the superficial layer). Rhodamine B (479 Da) and rhodamine-labeled dextrans (40 kDa, 150 kDa) were used as tracers. Combined with a custom-built permeation device and laser scanning confocal microscopy, solute transport behaviors under different injury degrees were analyzed. The results showed that superficial layer injury significantly impaired the barrier function, with retention concentrations increasing as injury severity rose. Solutes with lower molecular weights migrated more rapidly and exhibited higher retention levels. The peak solute concentration was localized in the superficial layer of normal cartilage but shifted toward the middle layer after injury. This study demonstrates that superficial layer integrity is essential for regulating cartilage solute transport, providing experimental evidence for understanding substance transport disorders in early cartilage degeneration of osteoarthritis.