Magnetic resonance imaging characterization of hydrogel substrates for tissue engineering strategies after spinal cord injury
Shannahan, Kelsey Irene
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Spinal cord injury (SCI) often results in irreversible paralysis of the limbs. Ongoing cellular recovery immediately after SCI is limited by the influx of inhibitory molecules that prevent neurons from infiltrating the lesion, resulting in a loss of axonal connections . A range of studies have shown that a scaffold emiched in compounds that facilitate regeneration can lead to functional recovery. Therapeutic agents such as synthetic hydrogels have been shown to overcome the body's natural inhibitory response and promote permanent improvement in motor function. Hydrogel scaffolds with precise orientation have shown particular promise due to their proclivity for orienting lengthwise along the spinal cord, favoring axonal growth . Standard magnetic resonance imaging (MRI) techniques optimized for visualizing the spinal cord can measure this degree of diffusion along white matter tracts. However, there are no published studies reporting the MRI parameters of the hydrogel substrates, and an understanding of how the material behaves in vitro may help guide the selection of an ideal compound by matching relaxation parameters and anisotropy measurements to those of spinal cord tissue. This study sought to characterize three hydrogel substrates of varying concentration using MRI to measure relaxation and diffusion properties. Relaxation times for agarose decreased as the concentration increased; whereas PuraMatrixTM relaxation times increased with increasing concentration. The addition offibronectin (an extracellular matrix support protein) significantly prolonged the relaxation times for the PuraMatrixTM solutions. No differences in proton density or restricted diffusion were observed. The results were compared to known relaxation and diffusion values for the spinal cord at 3T, highlighting certain concentrations that may be a best fit for use in the spinal cord. MRI is capable of quantifying substrate properties in vitro and then assessing their integration into tissue in vivo.
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