A multi-gradient organoid of articular cartilage with bionic matrix microenvironment

Reconstructing the zonal organization of articular cartilage, including the heterogeneity in matrix distribution and chondrocyte status, remains a significant challenge. In this study, we developed a compression technique to engineer artificial cartilage architecture. By controlling the orientation of fibers within a collagen hydrogel, we obtained a gradient from parallel alignment in the surface layer to random distribution in deeper layers. Simultaneously, we established a diverse concentration gradient of chondroitin sulfate to mimic cartilage composition. Encapsulating chondrocytes within this construct yielded a "cartilage organoid." In vitro culture demonstrated that the plastic compression achieved an increased density, parallel alignment, and a flattened morphology of cells in the surface layer. Especially, type II collagen and superficial zone protein (SZP), which are crucial for the functional durability of articular cartilage, were specifically excreted by the regulated cells within the surface region. Subcutaneous implantation of the cartilage organoid confirmed the stable retention of these specific features of the organoid in vivo, accompanied by further tissue maturation. Following implantation into articular cartilage defects, successful regeneration of well-integrated cartilage tissue with region-specific characteristics was achieved. These findings suggest a biomimetic cartilage organoid fully mimicking the factors in the structure and composition of natural cartilages, which may be a promising candidate for cartilage reconstruction and functional regeneration.