Characterization of human mesenchymal stem cell-engineered cartilage: analysis of its ultrastructure, cell density and chondrocyte phenotype compared to native adult and fetal cartilage.

The production of engineered cartilage from mesenchymal stem cells is a rapidly developing field. Potential applications include the treatment of degenerative joint disease as well as the treatment of traumatic and surgical bone injury. Prior to clinical application, however, further characterization of the morphology, ultrastructure, biocompatibility, and performance of the engineered tissue is warranted. To achieve this, human mesenchymal stem cells (hMSCs) were grown in vitro in pellet culture for 3 weeks in chondrogenic medium conditions. The resultant engineered cartilage was compared to native adult and fetal tissue. Routine histology, special stains, and ultrastructural and quantitative histomorphometric analyses were performed. The engineered tissue demonstrated a similar chondrocyte phenotype, collagen fibril appearance, and matrix distribution when compared to native cartilage. By histomorphometric analysis, the cell density of the engineered cartilage was between that of native fetal and adult cartilage. The cell-to-matrix ratio and cellular area fraction of engineered cartilage samples was significantly greater than in adult samples, but indistinguishable from fetal cartilage samples, supporting the hypothesis that hMSC-engineered cartilage regeneration may mimic fetal cartilage development.