Multiscale Characterization of Relaxation times of Tissue Surrogate Gels and Soft Tissues

The development of tissue surrogate materials that can replicate the mechanical response of biological soft tissues is of increasing interest. Such materials are required to enable robust experimental capabilities for evaluating next-generation armor systems that are critical to the survivability of the Soldier with regard to mechanical impact forces, including small caliber projectiles, fragments, and blast waves. Here, we characterize the viscoelastic stress relaxation response of heart tissue and candidate tissue surrogate gels, thermoplastic styrenic triblock/diblock copolymers. We explore the effects of gel composition and probe contact area on the relaxation modulus E(t) and characteristic relaxation times τ of these tissue surrogate gels, with comparisons to tissue response. We observe that E(t) varies only as a function of vol-% triblock, whereas τ varies as a function of volume of the material probed. The latter variation is explained by the coupling between viscoelastic material deformation and probe-material adhesion. Finally, we find that heart tissue is more compliant and relaxes more quickly than the candidate tissue surrogate gels studied here.