Abstract
A key technical challenge in cartilage tissue engineering is the development of a noninvasive method for monitoring the composition, structure, and function of the tissue at different growth stages. Due to its noninvasive, three-dimensional imaging capabilities and the breadth of available contrast mechanisms, magnetic resonance imaging (MRI) techniques can be expected to play a leading role in assessing engineered cartilage. In this review, we describe the new MR-based tools (spectroscopy, imaging, and elastography) that can provide quantitative biomarkers for cartilage tissue development both in vitro and in vivo. Magnetic resonance spectroscopy can identify the changing molecular structure and alternations in the conformation of major macromolecules (collagen and proteoglycans) using parameters such as chemical shift, relaxation rates, and magnetic spin couplings. MRI provides high-resolution images whose contrast reflects developing tissue microstructure and porosity through changes in local relaxation times and the apparent diffusion coefficient. Magnetic resonance elastography uses low-frequency mechanical vibrations in conjunction with MRI to measure soft tissue mechanical properties (shear modulus and viscosity). When combined, these three techniques provide a noninvasive, multiscale window for characterizing cartilage tissue growth at all stages of tissue development, from the initial cell seeding of scaffolds to the development of the extracellular matrix during construct incubation, and finally, to the postimplantation assessment of tissue integration in animals and patients.
Highlights
Osteoarthritis is a major cause of articular cartilage damage; one that is evident in the aging population.[6]
Mature cartilage is an avascular tissue with a three-layered zonal structure and a few active chondrocytes, which results in a tissue with poor self-healing capabilities
In a 4-week study of chondrocytes grown in an agarose gel, Miyata et al.,[35] found that while the longitudinal relaxation times (T1) and apparent diffusion coefficient (ADC) decreased, the transverse relaxation time (T2) increased. These results demonstrate that magnetic resonance imaging (MRI) analysis is able to detect unexpected changes in the tissue microenvironment through measurements, in this case, of the T2 relaxation times
Summary
Musculoskeletal disorders impact nearly one in three Americans annually, with injuries to cartilage accounting for a large fraction of these afflictions.[1,2] In particular, damage to articular cartilage due to injuries in the knees, shoulders, and other joints comprises a major portion of these disorders.[3,4,5] Osteoarthritis is a major cause of articular cartilage damage; one that is evident in the aging population.[6].
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