Matrix fixed-charge density as determined by magnetic resonance microscopy of bioreactor-derived hyaline cartilage correlates with biochemical and biomechanical properties

Objective. To use noninvasive magnetic resonance imaging (MRI), biochemical analyses, and mechanical testing of engineered neocartilage grown in a hollow-fiber bioreactor (HFBR) to establish tissue properties, and to test the hypothesis that MRI can be used to monitor biochemical and biomechanical properties of neocartilage. Methods. Chondrocytes from day 16 embryonic chick sterna were inoculated into an HFBR and maintained for up to 4 weeks with and without exposure to chondroitinase ABC. The fixed-charge density (FCD) of the cartilage was determined using the MRI gadolinium exclusion method. The sulfated glycosaminoglycan (S-GAG), hydroxyproline, and DNA contents were determined using biochemical procedures, while dynamic and equilibrium moduli were determined from mechanical indentation tests. Results. S-GAG content, tissue cross-sectional area, and equilibrium modulus of the neocartilage increased with development time. There was a gradient of S-GAG content across the length of control neocartilage at the 4-week time point, with higher values being found toward the inflow region. Exposure to chondroitinase ABC resulted in a decrease in tissue area, negative FCD, proteoglycan content, and equilibrium and dynamic moduli. The treated bioreactors displayed a lengthwise variation in S-GAG content, with higher values toward the outflow end. Linear correlations were established among FCD, proteoglycan content, and biomechanical properties. Conclusion. HFBR-derived neocartilage showed regional variation in S-GAG content under control conditions, and in the decrease of S-GAG in response to enzyme treatment. In addition, the results support the hypothesis that tissue parameters derived from MRI can be used to noninvasively monitor focal neocartilage formation and biochemical and biomechanical properties.