A 3D printed multilayer biomimetic scaffold with a gradient-oriented structure for articular cartilage repair.

At present, most of the 3D printed cartilage scaffolds are homogeneous or isotropic, which is still quite different from the unique structure of natural articular cartilage. In this study, a multilayer cartilage scaffold with a gradient pore size and directional arrangement structure was constructed using 3D bio-printing and template-freezing orientation technology to achieve a high degree of mimicry of the natural cartilage structure at macroscopic and microscopic levels. Moreover, gelatin (Gt) and sodium alginate (Alg) were selected as the base materials for 3D printing bioinks to realize the mimicry of the main components of natural articular cartilage. For structural and performance comparison, we prepared three multilayer cartilage scaffolds: a uniform non-oriented group, a uniform oriented group and a gradient-oriented group, and evaluated their performances, respectively. The results showed that the gradient-oriented multilayer scaffolds had a more desirable microstructure, more suitable physicochemical properties, better biological properties and excellent mechanical properties than the other two groups. For example, the maximum strength is 432.75 kPa under 10 cycles of compression at 80% strain, and the creep deformation is 0.578 mm under 10 N load within 1 hour. Finally, the cartilage repair ability of the three scaffolds was investigated in a rabbit cartilage defect model, and the results further showed that the gradient-oriented multilayer scaffolds were more effective in promoting cartilage tissue repair and regeneration. In conclusion, these 3D printed multilayer gradient-oriented biomimetic cartilage scaffolds have good application potential in the repair and regeneration of articular cartilage tissue.