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 numeric al simulations of soft tissue injury. Although many commercial systems exist for testing shear properties of viscoelastic materials with pro perties similar to soft biological tissue, none are capable of determi ning properties at high loading rates necessary for modeling soft tiss ue injury. Previous custom shear testing systems, though capable of hi gh-frequency loading, indirectly measure tissue properties by using an alytical corrections for inertial effects. To address these limitation s, a new custom designed oscillatory shear testing apparatus (STA) cap able of testing soft biological tissues in simple shear has been const ructed and validated. Through a proper selection of sample thickness, direct measurement of material properties at high frequencies is achie ved mechanically without analytical inertial adjustments. The complex shear modulus of three mixtures of silicone gel with viscoelastic prop erties in a range similar to soft biological tissue was characterized in the STA over a dynamic frequency range of 20-200 Hz and validated w ith a commercially available solids rheometer. The frequency-dependent complex shear modulus measurements of the STA were within 10% of the rheometer measurements for all mixtures over the entire frequency rang e tested. The STA represents substantive improvement over current shea r testing methods by providing direct measurement of the shear behavio r of soft viscoelastic materials at high frequencies. Mechanical prope rty data gained From this device will provide a more realistic basis f or numerical simulations of biological structures. (C) 1997 Elsevier S cience Ltd.