Application of magnetic resonance microscopy to tissue engineering: A polylactide model

Abstract

Absorbable polymers are unique materials that find application as temporary scaffolds in tissue engineering. They are often extremely sensitive to histological processing and, for this reason, studying fragile, tissue-engineered constructs before implantation can be quite difficult. This research investigates the use of noninvasive imaging using magnetic resonance microscopy (MRM) as a tool to enhance the assessment of these cellular constructs. A series of cellular, polylactide constructs was developed and analyzed using a battery of tests, including MRM. Distribution of rat aortic smooth muscle cells within the scaffolds was compared as one example of a tissue engineering MRM application. Cells were loaded in varying amounts using static and dynamic methods. It was found that the cellular component was readily identified and the polymer microstructure readily assessed. Specifically, the MRM results showed a heterogeneous distribution of cells due to static loading and a homogenous distribution associated with dynamic loading, results that were not visible through biochemical tests, scanning electron microscopy, or histological evaluation independently. MRM also allowed differentiation between different levels of cellular loading. The current state of MRM is such that it is extremely useful in the refinement of polymer processing and cell seeding methods. This method has the potential, with technological advances, to be of future use in the characterization of cell-polymer interactions.

Label-free magnetic resonance imaging to locate live cells in three-dimensional porous scaffolds

“…Burg et al [54] previously reported a method to observe cellular distribution in a polymeric material (TR ¼ 600 ms, TE ¼ 11 ms, resolution 23 mm). Similar to our method, they observed that the signal intensity was higher in cells than in the liquid phase and scaffold.…”

Modeling of encapsulated cell systems

“…While NMR imaging allows the assessment of structural features of the construct, localized NMR spectroscopy enables the evaluation of the number of viable cells and of the cellular metabolic state in a volume of interest (VOI) contained within the construct (Constantinidis and Sambanis, 1998;Constantinidis et al, 2001Constantinidis et al, , 2002Burg et al, 2002;Stabler et al, 2005a, b). For instance, the resonance of total cellular choline, measured by water-suppressed 1 H NMR spectroscopy, correlates positively and linearly with the viable cell number, hence it is a reliable estimate of the latter (Long et al, 2000;Stabler et al, 2005a, b).…”

Nondestructive evaluation of osteogenic differentiation in tissue‐engineered constructs

“…[17][18][19][20][21][22] Information about cell distribution in tissue-engineered constructs and the characterization of cell-scaffold interactions provided by MR imaging indicates that MR imaging can be useful for examining polymer microstructure design and cell seeding. 23 The proton relaxation time of MR imaging is highly correlated to the glycosaminoglycan and collagen concentrations of cartilage matrix and engineered hyaline cartilage formation. 17,24,25 The change of the proton relaxation times also corresponds well with cartilage calcification and with mineralization level at the late stage of in vitro bone formation.…”