Characterization of scaffolds for tissue engineering by benchtop-magnetic resonance imaging

Several publications have shown approaches for the optimization of tissue engineering constructs by magnetic resonance imaging (MRI). However, the technology is still scarcely used, probably because of the poor spatial resolution of clinical scanners and their temporally limited availability for many researchers. The new benchtop- MRI (BT-MRI) equipment used in the present study is much more affordable, for example, because of the low static magnetic field strength of 0.5 T and the absence of a helium cooling system. In this study, the method of BT-MRI was evaluated for the characterization of a tissue engineering scaffold. Hollow cylinder scaffolds were made of hydroxyapatite (HA), collagen, and chitosan and wrapped in a polyglycolic acid mesh. Mass transport between construct and surrounding medium was investigated by dynamic contrast agent-enhanced MRI with gadolinium(III)-diethylaminepentaacetic acid. The results demonstrate that BT-MRI permits detailed, space-resolved insights into diffusion processes within the three-dimensional matrices, enabling a comparison of the mass transport inside different scaffold types. Inhomogeneities of the HA distribution in scaffolds caused by the fabrication were also visible in MR images. The fate of cells, labeled with superparamagnetic iron oxide nanoparticles and seeded on the scaffold surface, was monitored. For the first time, it was shown that mass transport, inhomogeneities of the HA distribution, and localization of superparamagnetic iron oxide nanoparticle-labeled cells are accessible in a tissue engineering scaffold by BT-MRI. Hence, it is demonstrated that BT-MRI is a powerful analytic method for the noninvasive evaluation of tissue engineering constructs.