Co-culture of hWJMSCs and pACs in double biomimetic ACECM oriented scaffold enhances mechanical properties and accelerates articular cartilage regeneration in a caprine model

Background The dedifferentiation of chondrocytes and the unstable chondrogenic differentiation status of pluripotent mesenchymal stem cells (MSCs) are immense issues in cell-based articular cartilage repair and regenerative strategies. Here, to improve the cartilage characteristics of seed cells, a double biomimetic acellular cartilage extracellular matrix (ACECM)-oriented scaffold was used to mimic the cartilage microenvironment for human umbilical cord Wharton’s jelly-derived MSCs (hWJMSCs) and primary cartilage cells (pACs) to regenerate hyaline cartilage. Methods A double biomimetic ACECM-oriented scaffold was created from the cartilage extracellular matrix of pig articular cartilage using pulverization decellularization freeze-drying procedures. hWJMSCs and pACs were co-cultured at ratios of 50:50 (co-culture group, ACCC), 0:100 (ACAC group) and 100:0 (ACWJ group) in the ACECM-oriented scaffold, and the co-culture system was implanted in a caprine model for 6 months or 9 months to repair full-thickness articular cartilage defects. The control groups, which had no cells, comprised the blank control (BC) group and the ACECM-oriented scaffold (AC) group. Gross morphology and magnetic resonance imaging (MRI) as well as histological and biomechanical evaluations were used to characterize the cartilage of the repair area. Results Relative to the control groups, both the gross morphology and histological staining results demonstrated that the neotissue of the ACCC group was more similar to native cartilage and better integrated with the surrounding tissue. Measurements of glycosaminoglycan content and Young’s modulus showed that the repair areas had more abundant cartilage-specific content and significantly higher mechanical strength in the ACCC group than in the control groups, especially at 9 months. On MRI, the T2-weighted signal of the repair area was homogeneous, and the oedema signal disappeared almost completely in the ACCC group at 9 months. HLA-ABC immunofluorescence staining demonstrated that hWJMSCs participated in the repair and regeneration of articular cartilage and escaped surveillance and clearance by the caprine immune system. Conclusion The structure and components of double biomimetic ACECM-oriented scaffolds provided a cartilage-like microenvironment for co-cultured seed cells and enhanced the biomechanics and compositions of neotissue. This co-culture system has the potential to overcome the dedifferentiation of passage chondrocytes and the unstable chondrogenic differentiation status of MSCs.