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Characterizing the non-linear elastic properties of ex-vivo mouse tissues

Elastography imaging is a promising technique to non-invasively assess the mechanical properties of biological tissues. Characterization of the non-linear elastic behavior of soft tissues represents a promising challenge in this field. The strain hardening effect of tissues with the increase of the applied load is already known, but up to today, few quantitative data of this effect exist in literature. This study aimed at revealing the elastic properties of ex-vivo mouse tissues and at characterizing their non-linear elastic behavior. This was done using a dedicated indentation experimental system that measured the length of each sample under a controlled force. Three mouse tissue specimens were studied: a Tibialis Anterior (TA) muscle, an Extensor Digitorum Longus (EDL) muscle and an adipose tissue sample. The investigation of the stress-strain curve reconstructed from experimental data revealed that TA, EDL and fat tissues showed a linear elasticity for strains up to 3.05%, 8.2% and 9.2% respectively. The non-linear region of the curve was found to be exponential, showing that TA muscle exhibited a strain hardening effect higher than EDL muscle and adipose tissue. The present study provided biomechanical models allowing to estimate the Young's modulus of the specimens as a function of the strains at a specific stress profile. Our preliminary results suggest the validity of these models in describing the non-linear stress-strain relationship of tissues. This allows a proper interpretation of elastograms obtained through large compression and/or pre-compression and helps in preventing misdiagnosis. Further investigations are needed to confirm this preliminary evidence.