Reduction of water diffusion coefficient with increased engineered cartilage matrix growth observed using MRI

Non-destructive monitoring of tissue-engineered cartilage growth is needed to optimize growth conditions, but extracting quantitative biomarkers of extracellular matrix development remains a technical challenge. MRI provides a non-invasive way to obtain a three dimensional map of growing tissue where the image contrast is based on tissue water relaxation times and the apparent diffusion coefficient (ADC). In this study, bovine chondrocytes were seeded in alginate beads (0, 1, 2, and 4 million cells/ml) and the ADC was measured weekly using diffusion-weighted MRI at 14.1 T over a one-month incubation period. Two groups of tissue-engineering constructs were created: one with ascorbic acid (vitamin C) added as a vitamin cofactor to increase collagen synthesis, and another with no added ascorbic acid. When normalized to the control beads without chondrocytes, the ADC was found to monotonically fall with incubation time (decreasing by up to 40% at 4 weeks), and with the administration of vitamin C. These results reflect the expected development of the extracellular matrix in the tissue-engineered constructs. We conclude that the normalized ADC is a potential biomarker for characterizing engineered cartilage tissue growth.