In Vitro Magnetic Resonance Assessment of Tissue Engineered Bone and Cartilage

Magnetic Resonance Imaging (MRI), largely due to its noninvasive nature, is a powerful tool for the characterization of early structural and compositional changes in engineered tissues. For example, the development of extracellular matrix (ECM) is reflected in decreasing values of the MR derived relaxation times and diffusion coefficients. Hence, the regeneration and repair of any tissue, which requires a scaffold, appropriate cell types, and growth factors, can be monitored using MRI. This study identified early structural changes in two types of engineered tissues: engineered cartilage and engineered bone. The MRI measurements were performed using the Bruker 500 MHz (11.7 T) microimaging facility located in the Research Resources Center at UIC. The tissue-engineered cartilage constructs were prepared by seeding human marrow stromal cells (HMSCs) in commercially available collagen scaffolds under two different set of conditions: (a) hypoxia – constructs created under low oxygen conditions, and (b) normoxia – constructs created under normal oxygen conditions. Tissue engineered bone constructs were prepared using Leucine Zipper (LZ) based biomimetic scaffolds with low and high levels of osteogenic extracellular matrix (ECM). The T1 and T2 relaxation times fell as we move from low to high ECM in engineered bone and from normal to hypoxic conditions in engineered cartilage; both changes are consistent with higher amount of ECM generated in these constructs. Measurements of the average diffusion coefficient for these tissues was not statistically significant between the groups. These results show that MRI relaxation times are sensitive to small growth changes in tissue engineered cartilage and bone and hence could be used as biomarkers for tissue regeneration.