A High-Frequency Shear Device For Testing Soft Biological Tissues

Accurate mechanical property data obtained at large shear deformations and high frequencies are a fundamental component of realistic numerical simulations of soft tissue injury.  Although many commercial systems exist for testing shear properties of viscoelastic materials with properties similar to soft biological tissue, non are capable of determining properties of high loading rates necessary for modeling soft tissue injury.  Previous custom shear testing system, though capable of high-frequency loading, indirectly measure tissue properties by using analytical corrections for inertial effects. 

To address these limitations, an new custom designed oscillatory shear testing apparatus (STA) capable of testing soft biological tissues in simple shear has been constructed and validated.  Through a proper selection of sample thickness, direct measurement of material properties at high frequencies is achieved mechanically without analytical inertial adjustments.  The complex shear modules of three mixtures of silicone gel with viscoelastic properties in the range similar to soft biological tissue was characterized in the STA over a dynamic frequency range of 20-200 Hz and validated with a commercially available solids rheometer.  The frequency-dependent complex shear modules measurements of the STA were within 10% of the rheometer measurements for all mixtures over the entire frequency range tested. 

The STA represents substantive improvement over current shear testing methods by providing direct measurement of shear behavior of soft viscoelastic materials at high frequencies.  Mechanical property data gained from this device will provide a more realistic basis for numerical simulations of biological structures.