Magnetic Resonance Characterization of Stem Cell Based Tissue - Engineered Cartilage and Bone
thesisposted on 20.06.2014, 00:00 authored by Padmabharathi Pothirajan
Magnetic resonance imaging (MRI) is a non-invasive technique that has been widely used in the assessment of musculoskeletal tissue engineering. Currently, there are many studies focusing on a single tissue type, for example, either tissue-engineered cartilage or tissue-engineered bone. There is a lack of adequate characterization techniques at the osteochondral interfaces, where there is a damage to both cartilage and its underlying subchondral bone. In the first part of my thesis, we established MRI characterization protocol for both the bone and the cartilage tissue constructs. We developed osteogenic and chondrogenic tissue constructs by seeding human marrow stromal cells (HMSCs, 2 million/ml) in collagen/chitosan gel with the ratio of 1:1 and grown in the culture medium with osteogenic and chondrogenic growth factors. We compared proton and sodium MRI properties of these tissue constructs in comparison with the control collagen/chitosan gel using the 11.7 T (1H freq. = 500 MHz) microimaging MRI system. This study shows that MRI can distinguish between early stage development of bone and cartilage. MRI characterization methods for engineered cartilage tissues are based on the correlation of water MR parameters, for example, the relaxation time T2, with extracellular matrix components, proteoglycans and collagen. These methods currently do not take into account the contribution of scaffold and cells in the MRI parameters. In the second part of the thesis, we developed a strategy to assess the contribution of scaffold, cells and extracellular matrix (ECM) in specially designed “polylactide-co-glycolid (PLGA)-puramatrix” gradient-porous structured scaffold seeded with BM-hMSCs. This scaffold system is uniquely designed to best support osteochondral defect repair and regeneration. We performed proton T1, T2 and diffusion MRI experiments on these chondrogenic scaffolds for scaffold only, scaffold with cells and ECM, and acellular scaffold with ECM using the 11.7 T microimaging MRI system. Though the contribution of scaffold in the water T2 is found to be dominating, we made an attempt to identify the true contribution of ECM and cells in T2. This thesis work has yielded evidence that above techniques may be especially useful for the assessment of engineered osteochondral constructs in preclinical and clinical studies.