Comparison of dynamic mechanical testing and MR elastography of biomaterials

Magnetic resonance elastography (MRE) is a novel experimental technique for estimating the dynamic shear modulus of biological tissue. MRE can be performed non-invasively, in living subjects. Soft biomaterials are notoriously difficult to characterize, since they are typically nonlinear, anisotropic, viscoelastic, and heterogeneous. The ability of MRE to capture the frequency-dependent response of tissue to small amplitude deformation over a range of frequencies was investigated by careful comparison to two different dynamic mechanical tests; direct shear and unconfined compression. The mechanical properties of a standardized gelatin biomaterial were probed over various loading rates. Results confirm direct correlation between estimates of shear modulus obtained by MRE, dynamic shear, and unconfined compression, but quantitative differences between values obtained by MRE compared to direct mechanical test. These results in gelatin are consistent with reports in agar from other groups [1,2]. Differences may be due to non-idealities inherent in loading of soft, wet, material (in mechanical testing), boundary effects (in MRE), or differences in strain amplitude and strain rate.