The comparison of noninvasive assessments of shear modulus using quantitative T₂ magnetic resonance imaging and rheology of agarose hydrogel

Nondestructive and noninvasive assessments of the mechanical properties of biological tissues in vivo are essential in tissue engineering studies, for example, for designing scaffolds and monitoring tissue growth and degeneration. Agarose is widely used in biomaterial and tissue engineering studies to develop phantoms and tissue-mimicking materials because of its high biocompatibility, high stability, and low toxicity. This study aimed to provide an alternate method for nondestructive and noninvasive assessment of mechanical properties of agarose hydrogels by employing the more basic method without additional instruments compared to the standard method used in magnetic resonance imaging (MRI) measurements. In this study, the mechanical properties of agarose hydrogels of various concentrations were assessed noninvasively using quantitative T₂ MRI to obtain the relaxation rate r₂, and their results were compared to those from rheological measurements using the amplitude sweep method to obtain the shear modulus. The comparisons showed that the shear modulus and r₂ increased exponentially with agarose concentration; however, agarose with concentrations lower than 2% had a different exponential factor than those at higher concentrations, supporting the previous cascade model theory that suggested the concentration limit for forming percolating networks in agarose hydrogels and agarose–solvent interactions. The results of this study show that the shear modulus can be assessed noninvasively by quantitative T₂ MRI measurements; both methods characterize hydrogen bonding of the agarose. However, the factors related to agarose–water interactions and agarose network chains that contribute to the modulus must be considered, especially at agarose of low concentrations.